U.S. patent application number 10/822548 was filed with the patent office on 2005-01-20 for hand-held microwave polymerization system for dentistry.
Invention is credited to Durand, Jean-Pierre, Seghatol, Marc.
Application Number | 20050011885 10/822548 |
Document ID | / |
Family ID | 25680467 |
Filed Date | 2005-01-20 |
United States Patent
Application |
20050011885 |
Kind Code |
A1 |
Seghatol, Marc ; et
al. |
January 20, 2005 |
Hand-held microwave polymerization system for dentistry
Abstract
A hand-held microwave system for intra-oral dentistry utilizes
microwave energy to cure polymer materials intra-orally so as to
produce dental composites having improved physical characteristics,
and also utilizes microwave energy to detect the presence of and to
preferentially heat caries or cavities, thereby disinfecting and
therapeutically treating the caries in a potentially non-invasive
manner. The intra-oral polymerization process can be accomplished
with less overall energy and with composite-matrices that maximally
absorb the microwave energy so as to reduce heating of adjacent
tissue. The antenna of a hand-held version of the intra-oral
microwave system is also advantageously designed to detect the
presence of and to preferentially heat caries or cavities, thereby
disinfecting and therapeutically treating the caries in a
potentially non-invasive manner. A method and product by process
for the system are also disclosed.
Inventors: |
Seghatol, Marc; (St.
Laurent, CA) ; Durand, Jean-Pierre; (St. Catherine,
CA) |
Correspondence
Address: |
Brad Pedersen
Patterson, Thuente, Skaar & Christensen, P.A.
4800 IDS Center
80 South 8th Street
Minneapolis
MN
55402-2100
US
|
Family ID: |
25680467 |
Appl. No.: |
10/822548 |
Filed: |
April 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10822548 |
Apr 12, 2004 |
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10166569 |
Jun 10, 2002 |
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6737619 |
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10166569 |
Jun 10, 2002 |
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09399997 |
Sep 20, 1999 |
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6441354 |
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10822548 |
Apr 12, 2004 |
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09897317 |
Jul 2, 2001 |
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09897317 |
Jul 2, 2001 |
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09399580 |
Sep 20, 1999 |
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6254389 |
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Current U.S.
Class: |
219/679 |
Current CPC
Class: |
A61L 2/12 20130101; A61C
13/16 20130101; A61C 13/20 20130101; H05B 6/80 20130101; A61C
13/206 20130101; H05B 2206/045 20130101; A61C 13/203 20130101; A61C
5/77 20170201; A61C 5/00 20130101 |
Class at
Publication: |
219/679 |
International
Class: |
H05B 006/64 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 18, 1998 |
CA |
2,246,663 |
Claims
What is claimed:
1. A method for constructing a part of a tooth using a hardened
object, said method comprising: (i) forming a hardenable object
into a shape suited for reconstructing part of a tooth from a
microwave curable composition comprising: (a) multi-functional
polymers and monomers at least one member selected from the group
consisting of mono-functional methacrylate polymer, di-functional
methacrylate polymer, tri-functional methacrylate polymer,
mono-functional methacrylate monomer, di-functional methacrylate
monomer, and tri-functional methacrylate monomer; filler; coupling
agent; initiator; plasticizer; and optionally additional additives
for pigmenting; or (b) a polymer matrix including a polymerizable
resin adapted for use in an oral environment which contains at
least one ester of unsaturated compounds; coupling agent; filler;
initiator; and; optionally, additional additives for pigmenting;
and (ii) using a hand held microwave source to apply microwave
energy to harden said hardenable object.
2. A method according to claim 1, wherein said composition is
(a).
3. A method according to claim 1, wherein said filler comprises
inorganic filler or organic filler.
4. A method according to claim 1, wherein (b) comprises a polymer
matrix including a polymerizable resin adapted for use in an oral
environment; filler; initiator; coupling agent; and, optionally,
additional additives for pigmenting.
5. A method according to claim 4, wherein the polymerizable resin
comprises at least one of
2,2-bis[4-(2-hydroxy-3-methacrylyloxypropoxy)ph- enyl]propane,
triethyleneglycol dimethacrylate, or an urethane dimethacrylate
resin.
6. A method according to claim 1, wherein said composition
comprises (b).
7. A method according to claim 6, wherein said initiator comprises
at least one microwave sensitive compound.
8. A method according to claim 7, wherein said initiator is a
peroxide.
9. A method according to claim 8, wherein the initiator is selected
from the group comprising benzoyl peroxide and dilauroyl
peroxide.
10. A method according to claim 7, wherein said composition
contains up to 2.5% by weight of said initiator.
11. A method according to claim 1, wherein (a) further comprises an
amine accelerator.
12. A method for forming a hardened reline material for a dental
prosthesis comprising: (i) forming a hardenable object configured
for relining a dental prosthesis from a microwave curable
composition comprising a polymer matrix including a polymerizable
resin adapted for use in an oral environment; filler; initiator;
coupling agent; and optionally, additional additives for
pigmenting; and (ii) using a hand held microwave source to apply
microwave energy to harden said hardenable object.
13. A method according to claim 12, wherein the polymerizable resin
contains at least one of
2,2-bis[4-(2-hydroxy-3-methacrylyloxypropoxy)phe- nyl]propane,
triethyleneglycol dimethacrylate, or an urethane dimethacrylate
resin.
14. The method of claim 12, wherein said filler comprises inorganic
filler or organic filler.
15. The method and materials to make polymer-based objects,
including: (a) the process, which is the combination of injection,
measurable pressure and microwave energy; (b) the composition used
in this process and systems.
16. The use of said process and system of claim 15, to give high
accuracy shape and hardening of polymers and polymer-containing
composites.
17. The use of a hand-held microwave applicator to harden polymers
and polymer containing composites at the site of application (i.e.,
intra-oral, orthopedic).
18. The composition of claim 15, wherein said polymer-based
materials, which are suitable for denture base, include one and two
component denture bases, said denture base comprising of mono-,
di-, tri-, or multifunctional methacrylate polymers or monomers;
cross-linking agent; organic pigments or metal oxides; plasticizers
and initiators.
19. The composition of claim 18, wherein said mono-, di-, tri-, or
multifunctional methacrylate polymers are within the scope of the
general formula: 6The R.sub.1 is hydrogen, alkyl, substituted alkyl
group, cyclic hydrocarbon, benzyl, ether, hydroxalkyl; R.sub.2 is
hydrogen, halogen, alkyl, substituted alkyl group; and n is an
integer at least equal to 2.
20. The composition of claim 15, wherein said polymer-based objects
are made from polymer based material that is suitable for use as
composite resins, said polymer based material further comprised of
a polymer matrix; fillers; initiator; and coupling agent.
21. The composition in claim 20, wherein said polymer matrix is a
polymerizable resin suitable for use in an oral environment.
22. The composition of claim 21, wherein the polymerizable resin
includes
2,2-bis[4-(2-hydroxy-3-methacrylyloxpropoxy)phenyl]propane,
triethyleneglycol dimethacrylate, urethane dimethacrylate resins,
and spiro orthocarbonates.
23. The composition of claim 20, wherein said initiator comprises
microwave sensitive compounds.
24. The composition of claim 23, wherein said initiator comprises a
peroxide.
25. The composition of claim 24, wherein said initiator is selected
from the group comprised of benzoyl peroxide and dilauroyl
peroxide.
26. The composition of claim 20, wherein the initiator comprises up
to 2.5% by weight of the composition.
27. The composition of claim 15, wherein said polymer-based
materials, which are suitable for soft dentures, consist of
organopolysiloxanes or phosphonitrile fluoroelastomers.
28. The composition of claim 27, wherein said organopolysiloxanes
are within the scope of the general formula:
[R.sub.nSiO.sub.4-n/2].sub.m, wherein n=1-3 and m>1. R is
methyl, longer alkyl, fluoroalkyl, phenyl, vinyl, alkoxy or
alkylamino.
29. The composition of claim 27, wherein said phosphonitrilic
fluoroelastomers are within the scope of the general formula:
7wherein X is H or F, and n is usually form 1 to 11.
30. A method for forming a hardened reline material for a dental
prosthesis comprising: (i) forming a hardenable object configured
for relining a dental prosthesis from a microwave curable
composition comprising a polymer matrix including a polymerizable
resin adapted for use in an oral environment; filler; initiator;
coupling agent; and optionally, additional additives for
pigmenting; and (ii) using a hand held microwave source to apply
microwave energy to harden said hardenable object.
31. A method according to claim 30, wherein the polymerizable resin
contains at least one of
2,2-bis[4-(2-hydroxy-3-methacrylyloxpropoxy)phen- yl]propane,
triethyleneglycol dimethacrylate, or an urethane dimethacrylate
resin.
32. The method of claim 30, wherein said filler comprises inorganic
filler or organic filler.
33. A method for forming a hardened object comprising: (i) forming
a hardenable object from a microwave curable composition
comprising: (a) at least one polymer including repeating monomer
units represented by the formula 8wherein R.sub.1 represents a
hydrogen atom, an alkyl group, a substituted alkyl group, a benzyl
group, a hydroxy alkyl group, a cyclic hydrocarbon, or an ether
group, R.sub.2 represents a hydrogen atom, a halogen atom, an alkyl
group, or a substituted alkyl group, and n is an integer of 2 or
more; a curing agent; a filler; an initiator; a plasticizer; and,
optionally, additional additives for pigmenting; (b) at least one
member selected from the group consisting of an organopolysiloxane
and a phosphonitrile fluoroelastomer; filler; crosslinking agent;
and, optionally, additional additives for pigmenting; or (c) a
polymer matrix including a polymerizable resin adapted for use in
an oral environment; filler; initiator; coupling agent and,
optionally, additional additives for pigmenting; and (ii) using a
hand-held microwave source to apply microwave energy to harden said
hardenable object.
34. A method according to claim 33, wherein the polymerizable resin
contains at least one of
2,2-bis[4-(2-hydroxy-3-methacrylyloxypropoxy)phe- nyl]propane,
triethyleneglycol dimethacrylate, or an urethane dimethacrylate
resin.
35. A method according to claim 33, wherein said at least one
phosphonitrile fluoropolymer is obtained by polymerizing monomers
comprising: 9wherein X represents a hydrogen atom or fluorine atom,
n is a value of 1 to 11.
36. A method according to claim 33, wherein said organopolysiloxane
is represented by the formula [R.sub.nSiO.sub.4-n/2].sub.m, wherein
n=1-3 and m>1. R is methyl, longer alkyl, fluoroalkyl, phenyl,
vinyl, alkoxy or alkylamino.
37. A method for forming a hardened object comprising: (i) forming
a hardenable object from a microwave curable composition, said
object when cured comprising a dental prosthesis or an orthodontic
element, said microwave curable composition comprising: (a) at
least one member selected from the group consisting of
mono-functional methacrylate polymer, di-functional methacrylate
polymer, tri-functional methacrylate polymer, mono-functional
methacrylate monomer, di-functional methacrylate monomer, and
tri-functional methacrylate monomer; curing agent, filler,
initiator; plasticizer; and optionally, additional additives for
pigmenting; (b) at least one member selected form the group
consisting of an organopolysiloxane and a phosphonitrile
fluoroelastomer; filler; crosslinking agent; and optionally,
additional additives for pigmenting; or (c) a polymer matrix
including a polymerizable resin adapted for use in an oral
environment; filler; initiator; coupling agent; and; optionally,
additional additives for pigmenting; and (ii) using a hand-held
microwave source to apply microwave energy to harden said
hardenable object.
38. A method according to claim 37, wherein the polymerizable resin
comprises at least one of
2,2-bis[4-(2-hydroxy-3-methacrylyloxypropoxy)ph- enyl]propane,
triethyleneglycol dimethacrylate or an urethane dimethacrylate
resin.
39. A method according to claim 37, wherein said hardened object
comprises a dental prosthesis.
40. A method according to claim 39, wherein said dental prosthesis
comprises a composite resin filling, inlay, overlay, facing, veneer
or orthodontic appliance.
41. A method according to claim 37, wherein said filler comprises
organic filler or inorganic filler.
Description
RELATED APPLICATIONS
[0001] The present invention is a continuation of two co-pending
applications, the first of which is U.S. patent application Ser.
No. 10/166,569 entitled, "MICROWAVE POLYMERIZATION SYSTEM FOR
DENTISTRY," filed Jun. 10, 2002, which is a continuation of U.S.
patent application Ser. No. 09/399,997, also entitled, "MICROWAVE
POLYMERIZATION SYSTEM FOR DENTISTRY," filed Sep. 20, 1999, and now
issued as U.S. Pat. No. 6,441,354, which claims priority to PCT
Application No. PCT/US99/20960, filed Sep. 17, 1999, which claims
priority to Canadian Patent No. 2,246,663, filed Sep. 18, 1998, the
second of which is U.S. patent application Ser. No. 09/897,317
entitled, "HAND-HELD MICROWAVE INTRA-ORAL DENTAL SYSTEM," filed
Jul. 2, 2001, which is a continuation of U.S. patent application
Ser. No. 09/399,580, also entitled, "HAND-HELD MICROWAVE INTRA-ORAL
DENTAL SYSTEM," filed Sep. 20, 1999, and now issued as U.S. Pat.
No. 6,254,389, the contents of all of which are hereby incorporated
by reference.
FIELD OF THE INVENTION
[0002] The present invention relates generally to the field of
dentistry. More specifically, the present invention relates to a
hand-held microwave system for intra-oral dentistry that utilizes
microwave energy to cure polymer materials intra-orally so as to
produce dental composites having improved physical characteristics,
and also utilizes microwave energy to detect the presence of and to
preferentially heat caries or cavities, thereby disinfecting and
therapeutically treating the caries in a potentially non-invasive
manner.
BACKGROUND OF THE INVENTION
[0003] The use of polymer materials in the dental arts for the
restoration of lost or damaged teeth is well known. Such uses fall
into two general categories: (i) the use of polymer materials to
produce dental prosthetics, such as dentures, bridges and crowns,
that are either permanent or removable articles, and (ii) the use
of polymer materials to create dental composites for fillings to
repair teeth instead of using conventional amalgam fillings or as
veneers to refinish tooth enamel surfaces. The first category of
dental articles, dental prosthetics, are created outside of the
patient (i.e., extra-oral), typically by making an impression of
what the desired article should look like and then molding the
article to match the impression. The second category of dental
articles, dental composites, are created directly in the patient's
mouth (i.e., intra-oral) as fillings or veneers to repair or
resurface teeth. Regardless of which category is being considered,
dental articles made of polymer materials must have adequate
strength, durability, and dimensional stability and must also be
biocompatible and chemically inert. It is also important to be able
to process each type of dental article rapidly, conveniently,
safely and economically.
[0004] An example of a dental prosthetic in the first category of
dental articles that is created using polymer materials is a
removable denture. Most commercial dentures are created using a
paste or resin matrix formed of various polymers, co-polymers and
monomers (typically methyl methacrylate), as well as certain
cross-linking agents, initiators, accelerators and other additives.
This resin matrix is formed into a plaster mold and is then
hardened or cured by applying energy in the form of heat.
Typically, the plaster mold containing the uncured denture is
prepared in a dental laboratory based on an impression taken by the
dentist. To cure the resin matrix, the plaster mold is placed into
a flask that is then put in a thermal water-bath for up to 8 hours.
This conventional process of curing a denture takes such a long
time because both the plaster molds and the polymers in the resin
matrix are relatively poor thermal conductors and are heated only
from the outside via the thermal water-bath. The conventional
process can also result in large numbers of voids and significant
shrinkage during curing due to uneven thermal conduction and
non-uniform polymerization of the resin matrix. These problems are
discussed in Feilzer A. J. et al., "Curing contraction of
composites and glass-ionomer cements," Journal of Prosthetic
Dentistry, Vol. 59, pp. 297-300 (1988); and Ferracane J. L. et al.,
"Wear and marginal breakdown of composite with various degrees of
cure," J Dent. Res., Vol. 76, No. 8, pp. 1508-16 (1997). The lack
of completely uniform polymerization of the denture also leaves
residual monomers that are toxic and can act as irritants to oral
tissues and compromise the physical characteristics of the
denture.
[0005] In an effort to overcome the long cure times associated with
the conventional thermal water-bath technique, a technique of using
commercial microwave ovens to heat and cure polymer resins to form
dental prosthetics has been developed. In the conventional thermal
curing method for polymer dental articles, a temperature
differential is required to force heat by conduction from the
surface of the flask and mold to the center of the article. Because
the heat penetrates from the outside to the internal portions of
the material by thermal conduction, overheating and degrading
polymers can occur at the outer surface of the article. When
microwaves are used to initiate the thermal curing processing, it
is possible for the article to be heated uniformly as the
electromagnetic radiation instantaneously penetrates deeply and
heating occurs throughout all three dimensions of the irradiated
article. The main advantages provided by microwave energy include a
rapid internal heating independent of the heat flow through the
surface, as well as minimal thermal lag and thermal gradients
throughout the interior of the article, which results in a more
homogeneous curing of the article with a higher degree of
conversion of monomers into polymer chains.
[0006] Comparisons of these two techniques can be found in Hayden
W. J., "Flexure strength of microwave-cured denture baseplates,"
General Dentistry, Vol. 343, pp. 367 (1986); Al Doori D et al., "A
comparison of denture base acrylic resins polymerized by microwave
irradiation and by conventional water bath curing systems," Dental
Materials, Vol. 4, pp. 25-32 (1988); and Geerts G. et al., "A
comparison of the bond strengths of microwave and water bath-cured
denture materials," The Journal of Prosthetic Dentistry, Vol. 66,
No. 3, pp. 403-07 (September 1991). Various types of flasks and
molding equipment that can be used in conjunction with a commercial
microwave oven for processing and curing dental articles made of
polymers have been developed as described, for example, in U.S.
Pat. Nos. 4,971,735, 5,151,279, 5,324,186 and 5,510,411, European
Patent No. 0 687 451 A2, and Japanese Patent No. JP7031632A. The
repair of dentures and related articles using microwave processing
is also described in Turck M. D. et al., "Microwave processing for
dentures, relines, repairs and rebases," The Journal of Prosthetic
Dentistry, Vol. 69, No. 3, pp. 340-43 (1993). Generally, dentures
cured by commercial microwave ovens have improved mechanical
properties, and often have better adaptation than those cured by
the water-bath method. The primary advantage of microwave curing,
however, is the reduced processing times which can be shortened
from 8 hours or more to as little as a few minutes.
[0007] While the use of commercial microwave ovens to cure dental
prosthetics solves some of the problems of conventional thermal
water-bath cured prosthetics, dental prosthetics processed in this
manner can be less than satisfactory in terms of their physical and
biocompatibility characteristics because varying degrees of cure,
micro-shrinkage and porosities are still present. Any large degree
of micro-shrinkage or porosities in the polymers of dental
prosthetics cured using conventional microwave ovens will lead to
fitting inaccuracy and unreliability. These problems are discussed
in Wallace P. W. et al., "Dimensional accuracy of denture resin
cured by microwave energy," The Journal of Prosthetic Dentistry,
Vol. 68, pp. 634-40 (1992); and Salim S. et al., "The dimensional
accuracy of rectangular acrylic resin specimens cured by three
denture base processing methods," The Journal of Prosthetic
Dentistry, Vol. 67, pp. 879-85 (1992).
[0008] It understood in the dental arts that micro-shrinkage is
primarily due to the resin matrix. The physical and mechanical
properties of a polymer material, such as hardness, stiffness and
abrasion resistance and strength, are highly influenced by the
arrangement of the resin matrix when the fillers and coupling
agents are fixed during the curing process. Micro-shrinkage results
from the shorter distance between atoms in the resin matrix after
polymerization than before polymerization. The monomers in the
resin matrix are located at Van der Waals distance, which change to
a covalent bond distance once the resin matrix is polymerized. If
all of the monomers in the resin matrix are not converted into
polymer chains during the polymerization curing process, then this
change in distance can induce mechanical stresses in the form of
micro-shrinkage in those areas where there was not complete
conversion of the monomers into polymers. Commercial resin matrices
are found to undergo volume shrinkage of as much as 7% with most
resin matrices shrinking 2-3%. This kind of micro-shrinkage causes
volumetric dimensional change that can result in poor fitting of
the dental prosthetic to oral tissues and can build up mechanical
stress in the dental prosthetic that can lead to premature
mechanical failure. A discussion of some of these issues can be
found in D. Bogdal, "Application of Diol Dimethacrylates in Dental
Composites and Their Influence on Polymerization Shrinkage," J.
Appl. Polym. Sci., Vol. 66, pp. 2333-2337 (1997), and D. Bogdal et
al., "The Determination of Polymerization Shrinkage of Materials
for Conservative Dentistry," Polimery, Vol. 41, pp. 469 (1996).
[0009] Another problem caused by the residual monomers not being
converted into polymer chains during the polymerization curing
process is the leaching of any unbound monomers or additives out of
the article. The leaching has an impact on both the structural
stability and biocompatibility. The residual monomers can leach
into salivary fluids which then irritates any mouth tissues in
contact with these contaminated fluids; or the residual monomers
can diffuse directly into the dentin and pulp of teeth adjacent to
the dental prosthetic. These problems are described in Ferracane J.
L., "Elution of leachable components from composites," Journal of
Oral Rehabilitation, Vol. 21, pp. 441-52 (1994); and Hume W. R. et
al., "Bioavailability of components of resin-based materials which
are applied to teeth," Crit. Rev. Oral Biol. Med., Vol. 7, No. 2,
pp. 172-79 (1996).
[0010] The primary solutions to these problems have focused on
increasing the degree of polymerization and cross-linking of all of
the monomers in the resin matrix by changing the formulation of the
resin matrix. Improvements in resin formulation involve, for
example, the introduction of spiro orthocarbonates and
stereoisomers. U.S. Pat. No. 5,502,087 describes various
polymer-based resins that are designed to improve the physical
characteristics of thermal water-bath cured resin matrices or
light-activated resin matrices. U.S. Pat. No. 5,147,903 describes
polymer materials that exhibit desired degrees of swelling and
cross-linking for light-activated resin matrices. Examples of
polymer resin matrices that are specifically formulated to utilize
microwave energy supplied by a commercial microwave oven for the
thermal polymerization of the polymers into dental articles are
shown in U.S. Pat. Nos. 4,873,269, and 5,218,070, and Canadian
Patent No. 2,148,436. The impact of the role played by the polymer
initiator in a microwave cured resin matrix has been evaluated by
Urabe H. et al. in "Influence of polymerization initiator for base
monomer on microwave curing of composite resin inlays," Journal of
Oral Rehabilitation, Vol. 26, pp. 442-46 (1999).
[0011] Another solution to these problems is also described in
Canadian Patent No. 2,148,436 in which the resin matrix in the mold
is compressed by a mechanical ram that injects additional uncured
polymer components into the mold while the mold and flask are being
cured inside a commercial microwave oven. The mechanical ram slowly
forces some of the uncured polymer material contained in an
injection cartridge through a passageway or sprue into the mold.
The addition of polymer material applied under mechanical
compression while it is still fluid is another way of reducing
problems related to the polymerization shrinkage and porosity. U.S.
Pat. Nos. 5,175,008 and 5,302,104 and Canadian Patent No. 2,120,880
describe various solutions for providing similar types of
mechanical compression in the context of molding dental prosthetics
without using microwave energy to cure the resin matrix.
[0012] There had been relatively little research, however, into the
potential impact of the microwave energy itself on the
polymerization process. The most common use of microwave energy to
cure dental prosthetics actually involves a two-stage process
where, as described in U.S. Pat. No. 4,971,735, the microwave
energy first quickly heats water in or around the flask or humidity
in a moist mold, with the superheated water vapor then thermally
conducting the generated heat to the resin matrix. Due to the
superheated nature of this process, cure times can be dramatically
reduced. Moreover, because the microwave energy is primarily being
absorbed by water as the intermediary thermal agent, this process
lends itself very well to the use of commercial microwave ovens
operating at full power settings where the primary objective is to
heat the water, and not necessarily the resin matrix. This is
advantageous because commercial microwave ovens are controlled by
cycling the microwave generator, known as a magnetron, on and off
to provide an average output power that corresponds to the
percentage of the duty cycle. For example, a 50% duty cycle
operates the magnetron on 50% of the time and produces a power
output in terms of watts of energy produced by the oven that would
be one-half of the maximum power output of the oven.
[0013] The other mechanism by which microwave energy can be used to
cure dental prosthetics involves a single stage process where the
microwave energy is directly absorbed by the molecules of the resin
matrix without any substantial assistance of an intermediary
thermal transfer agent, such as water vapor. In this case, the
microwave energy essentially vibrates the resin molecules in a
complicated process that is dependent upon the specific nature of
the chemical composition of the resin matrix. It has been found
that where water vapor in the form of humidity is present in the
process, the actual polymerization of the resin matrix will occur
as a result of a combination of thermal conduction from water vapor
and internal microwave energy transfer.
[0014] Unfortunately, the high temperatures generated in the
targeted article by microwave heating with available commercial
microwave ovens set to manufacturers' recommendations (e.g., 3
minutes at 550 W at 100% duty cycle for a G.C. Acron dental
microwave oven) tend to result in the thermal degradation of, and
porosity formation in, many thermosetting polymer materials since
high temperatures (above 150.degree. C.) are often produced during
these curing processes. In addition, hot and cold spots are often
found within commercial microwave ovens that tend to create thermal
gradients corresponding to these variations in microwave energy
internal to the article being cured. The problems caused by these
hot and cold spots can be compounded by the superheated nature of
the water vapor, which effectively amplifies any uneven
distribution of the thermal energy to the resin matrix.
[0015] What little research has been done on the effect of
microwave energy on the polymerization process has generally
focused on the duty cycle used for the microwave curing process.
The impact on porosity of denture material cured using lower
wattage, longer duration microwave cure times (i.e., a lower duty
cycle for a longer time) versus higher wattage, shorter duration
microwave cure times (i.e., a higher duty cycle for a shorter time)
is compared in Alkhatib M. B., et al., "Comparison of
microwave-polymerized denture base resins," The International
Journal of Prothodontics, Vol. 3, No. 2, pp. 249-55 (1990).
European Patent No. 0 193 514 B1 describes a microwave processing
system for dental prosthetics that has a magnetron, a waveguide, a
surface radiating antenna, a flask, and a temperature sensor that
is inserted in the flask and connected to a regulating processor.
The regulating processor limits the temperature in the flask as
measured by the temperature sensor by turning on and off the
magnetron based on frequency modulation of the duty cycle. Although
not used for polymerization of dental articles, U.S. Pat. No.
5,645,748 does describe a microwave system for sterilization that
controls duty cycle of a microwave oven for the purpose of
minimizing arcing caused by metallic surgical or dental
instruments.
[0016] Any increase in the degree of conversion of monomers into
polymer chains in the polymerization process will result in
improved mechanical properties and biocompatibility of microwave
cured dental prosthetics. While existing solutions utilizing
improved resin compositions and mechanical compression during the
curing process with a commercial microwave oven have resulted in
many improvements over the conventional thermal water-bath method
of producing dental prosthetics, it would be desirable to further
improve the uniformity and the degree of conversion of monomers
into polymer chains in the polymerization process and further
compensate for volumetric shrinkage during the polymerization
process in order to produce even better dental prosthetics.
[0017] With respect to the second category of dental articles
created using polymer materials, dental composites formed of
polymer matrix-composites are increasingly being used as an
alternative to mercury-containing dental amalgam for aesthetic and
restorative dental materials. These kinds of polymer
matrix-composites are usually photo polymerizable in that they are
cured using some kind of light instead of heat. Generally, the
polymer matrix-composite is based on a photo polymerizable
polyfunctional methacrylate compound that can be used alone or as
mixture with monomethacrylates, light sensitive cure initiators
pigments and fillers in a mixture with various comonomers such as
triethyleneglycol dimethacrylate. Although the half-life of these
polymer matrix-composites cured by light is on the order of 5-8
years and, therefore, they tend to wear out earlier than
conventional dental amalgams, the enhanced biofunctionality and
more pleasing aesthetic qualities of these polymer
matrix-composites have gained favor over conventional dental
amalgams.
[0018] The main deficiencies of polymer composite resins used as
dental composites are surface degradation that leads to inadequate
wear resistance, polymerization shrinkage and a lack of density. In
addition to the problems previously described for dental
prosthetics, micro-shrinkage of polymer dental composites produces
interfacial gaps on the surface of the composites, which can
results in microleakage through the dental composite. The long-term
consequence of such microleakage can be bacterial penetration into
the tooth that can cause a variety of adverse reactions in the
tooth such as pulp damage, tooth sensitivity, possible pulpal death
and loss of adhesion of the dental composite.
[0019] Just as with polymer dental prosthetics, improving the
degree of polymerization of polymer matrix-composites is generally
considered to be one way of improving their physical and
biofunctionality characteristics of polymer dental composites as
this would lead to stronger dental composites that are less
susceptible to degradation, wear and fracture. It would also lead
to improved biocompatibility, since there would be reduced amounts
of uncured monomer that could act as a biohazard.
[0020] Unlike polymer dental prosthetics, however, the curing of
polymer matrix-composites by application of thermal energy
generally has not been used to date. Obviously, in the case of the
conventional thermal water-bath process, it would be impractical to
require a patient to remain at the dentist's office for up to 8
hours with their mouth open and with a tooth immersed in a hot
water bath in order to set a thermally polymerizable
matrix-composite. It is also not possible to place a patient's
mouth into a commercial microwave oven to set a thermally
polymerizable matrix-composite.
[0021] While there are numerous hand-held medical catheter devices
that utilize radio frequency and microwave energy to perform
ablations and similar heating operations, for example, in the
vascular system of a patient, there have been relatively few uses
of thermal or electrical energy applied to hand-held dental tools
for intra-oral applications. There have been a few hand-held dental
probes that utilize an electrically resistive heated tip for
diagnosis of dental decay or for melting a sealing material in an
intra-oral context as described, for example, in U.S. Pat. Nos.
4,527,560 and 5,893,713. U.S. Pat. No. 5,421,727 describes the use
of radio frequency/microwave energy as part of a hand-held
endodontic root canal device to raise the temperature of the
adjacent tooth, thereby tending to disinfect the tooth during the
root canal procedure as a result of the increased temperature.
[0022] The extra-oral use of microwave energy for the purpose of
characterizing dental decay in extracted teeth has been described
by N. Hoshi et al., in "Application of Microwaves and Millimeter
Waves for the Characterization of Teeth for Dental Diagnosis and
Treatment," IEEE Transactions on Microwave Theory and Techniques,
June 1998, Vol. 46, No. 6, pp. 834-38. This study confirmed the
higher absorbency behavior of carious lesions in extracted teeth
when irradiated by microwave energy as compared to the lower
absorbency of such microwave energy by healthy enamel and
dentin.
[0023] While existing photo polymerizable dental composites have
enjoyed success as compared to conventional dental amalgams for
dental fillings and veneers, it would be desirable to further
improve the uniformity and degree of conversion of monomers into
polymer chains in the polymerization process in order to produce
even better dental composites. It would also be desirable to
provide a dental tool that could take advantage of the use of
microwave energy for purposes other than the polymerization of
dental composites.
SUMMARY OF THE INVENTION
[0024] The present invention is a hand-held microwave system for
intra-oral dentistry that utilizes microwave energy to cure polymer
materials intra-orally so as to produce dental composites having
improved physical characteristics, and also utilizes microwave
energy to detect the presence of and to preferentially heat caries
or cavities, thereby disinfecting and therapeutically treating the
caries in a potentially non-invasive manner. The intra-oral
polymerization process can be accomplished with less overall energy
and with composite-matrices that maximally absorb the microwave
energy so as to reduce heating of adjacent tissue. The antenna of a
hand-held version of the intra-oral microwave system is also
advantageously designed to detect the presence of and to
preferentially heat caries or cavities, thereby disinfecting and
therapeutically treating the caries in a potentially non-invasive
manner.
[0025] The hand-held dental tool is designed to apply continuous
microwave energy in accordance for use in creating dental
composites directly in a patient's mouth. Microwave energy having a
frequency of between 1 GHz to 50 GHz, and preferably between 14 GHz
to 24 GHz, is applied by an antenna at the distal end of the
hand-held tool which is connected via a conductor or wave guide to
a microwave generator that supplies low power microwave energy in
response to precisely controlled voltages. Preferably, the
microwave energy power is less than about 10 W and ideally between
3 W and 5 W and the control voltages operate between 12 V and 65 V,
depending upon the desired curing time and the particular
composition of the resin matrix to be cured. Preferably, the
antenna and distal end of the hand-held tool are structured to
enable the operator to exert some degree of pressure on the
composite resin-matrix in the mouth while it is being cured by the
application of microwave energy. The low power microwave energy
provided by the hand-held tool of this embodiment is safe for
intermittent human exposure as the power and frequency ranges
emitted by the antenna are similar to that emitted by cellular
telephones.
[0026] One of the advantages of the hand-held dental tool is that
it can also serve as a tool for non-invasively detecting and/or
treating caries or cavities. Carious tooth tissue consists of
demineralized and softened and moist tooth enamel or dentin, and
contains micro-organisms. If the carious tooth tissue has not
degraded to the point where the physical properties of the tooth
are compromised, it is possible for the carious tooth tissue to
recalcify and reharden if the micro-organisms causing the carious
tooth tissue can be killed and the tooth can be kept under aseptic
conditions. Infected tooth tissue which is not removed or not kept
under aseptic conditions will remain as an active carious lesion,
and will continue to cause progressive and destructive loss of
tooth tissue. The use of the continuous microwave energy supplied
by the hand-held dental tool embodiment of the present invention
can eliminate or reduce the infection caused by the micro-organisms
as the type of microwave energy is selected to preferentially heat
and destroy the micro-organisms in the carious tooth tissue. In
some cases, the hand-held dental tool can be used to kill the
micro-organisms internal to the tooth tissue by the use of
microwave energy and then a sealant can be applied to the exterior
of the tooth which will be sufficient to keep an aseptic
environment and promote the recalcification of the underlying tooth
tissue. In other cases, portions of the carious tooth tissue may
need to be removed and the hand-held tool can be used to kill the
micro-organisms both internal to the tooth tissue and on the
surface of the cavity. Once the micro-organisms have been
destroyed, a polymer dental composite can be applied to the cavity.
The polymer dental composite is preferably microwave cured using
the hand-held dental tool to seal the treated tooth tissue and
provide additional physical and structural support for the
cavity.
[0027] The present invention is a microwave polymerization system
for dentistry that utilizes specifically controlled microwave
energy to cure polymer materials so as to produce dental
prosthetics and dental composites. Unlike the microwave energy
delivered by commercial microwave ovens which is controlled by
pulsing a maximum output power on and off at a given duty cycle,
the present invention utilizes metered and controlled microwave
energy that is preferably continuous and voltage controlled, and
regulates the application of this microwave energy by use of
various feedback mechanisms. The metered and controlled microwave
energy enables a higher degree of conversion and cross-linking of
monomers into polymer chains in the polymerization process, thereby
enhancing the physical and biocompatibility characteristics of both
dental prosthetics and dental composites made in accordance with
the present invention. In an extra-oral embodiment, gaseous
pressure is applied to the resin matrix during the polymerization
process to further enhance the polymerization process. In an
intra-oral embodiment, the polymerization process can be
accomplished with less overall energy and with composite-matrices
that maximally absorb the microwave energy so as to reduce heating
of adjacent tissue.
[0028] In one embodiment, a microwave oven is designed to apply
continuous microwave energy in accordance with the extra-oral
embodiment of the present invention for use in producing dental
prosthetics at either a dental laboratory or a dental office.
Microwave energy of between 1 GHz to 100 GHz, and preferably about
2.45 GHz, is continuously generated in the microwave oven in
response to precisely controlled voltages of between 25 V and 110
V, depending upon the desired curing time and the particular
composition of the resin matrix to be cured. A flask for use in the
microwave oven is preferably provided with a mechanism to rotate
the flask and with quick disconnect rotatable couplers for both
liquid polymer insertion and gas pressurization while the article
is rotating and undergoing the microwave curing process. The
insertion of additional polymer and the gas pressurization system
are utilized to maintain controlled gaseous pressure on the polymer
material during the curing process to increase the density of the
cured dental prosthetic and to compensate for micro-shrinkage that
may occur during polymerization. Pressurization rates depend upon
the strength characteristics of the polymer composition being used
and preferably range between 10 psi to 125 psi with optimal ranges
of between 12-35 psi. The flask may be equipped with an internal
membrane to compress and adapt the pasty curable resin matrix onto
the mold and with a vacuum forming system to draw the curable resin
matrix into the mold and assist in maintaining the resin matrix in
the mold during the curing process. In one embodiment, a cartridge
is provided with quick disconnect couplers between the gas
pressurization system and a sprue connected to the flask to permit
filling of the mold with the curable resin matrix stored in the
cartridge. Optionally, the microwave oven may be provided with
features that also allow it to be used to sterilize dental
prosthetics and other objects in a dental office or dental
laboratory.
[0029] In another embodiment, a hand-held dental tool is designed
to apply continuous microwave energy in accordance with the
intra-oral embodiment of the present invention for use in creating
dental composites directly in a patient's mouth. Microwave energy
having a frequency of between 1 GHz to 50 GHz, and preferably
between 14 GHz to 24 GHz, is applied by an antenna at the distal
end of the hand-held tool which is connected via a conductor or
wave guide to a microwave generator that supplies low power
microwave energy in response to precisely controlled voltages.
Preferably, the microwave energy power is less than about 10 W and
ideally, between 3 W and 5 W, and the control voltages operate
between 12 V and 65 V, depending upon the desired curing time and
the particular composition of the resin matrix to be cured.
Preferably, the antenna and distal end of the hand-held tool are
structured to enable the operator to exert some degree of pressure
on the composite resin-matrix in the mouth while it is being cured
by the application of microwave energy. The low power microwave
energy provided by the hand-held tool of this embodiment is safe
for intermittent human exposure as the power and frequency ranges
emitted by the antenna are similar to that emitted by cellular
telephones.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is an isometric view of a microwave oven embodiment
of the present invention.
[0031] FIG. 2 is an electrical schematic of the control circuitry
for generating the microwave energy in the microwave oven
embodiment shown in FIG. 1.
[0032] FIG. 3 is an exploded isometric view of a flask for use in
the microwave oven embodiment shown in FIG. 1.
[0033] FIG. 4 is a cross-sectional side view of the flask shown in
FIG. 3.
[0034] FIG. 5 is a top cut-away view of the flask shown in FIG. 3
showing a mold in position within the flask.
[0035] FIG. 6 is a partial cross-sectional side view of the flask
of FIG. 3 in position in the microwave oven embodiment of FIG.
1.
[0036] FIG. 7 is a partial cross-sectional side view of the flask
similar to FIG. 6 showing the details of a preferred embodiment of
the air pressurization system.
[0037] FIG. 8 is a partial cross-sectional side view showing the
details of a preferred embodiment of the polymer material injector
system of the microwave oven embodiment of FIG. 1.
[0038] FIG. 9 is an isometric view of a hand-held dental tool
embodiment of the present invention.
[0039] FIGS. 10-13 are various embodiments of antennas for the
distal end of the hand-held dental tool embodiment of FIG. 9.
[0040] FIG. 14 is an electrical schematic of the control circuitry
for generating the microwave energy in the hand-held dental tool
embodiment shown in FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] Referring now to the various figures, a detailed description
of the preferred embodiment of the present invention will be
presented. Various complex dielectric permittivity, temperature and
distribution pattern studies of microwave heated teeth and
simulations of specific absorption rate distribution have been
conducted as part of the research into the present invention. The
complex permittivity was measured on different types of dental
tissues, using extracted teeth, including enamel, dentin and
caries. Reflective coefficients have been obtained using a network
analyzer. The characteristics of enamel caries and dentin are
different. The dielectric loss factor of caries is fairly higher
than that of normal healthy parts particularly in the millimetric
wave in the frequency between 12 GHz to 25 GHz. When the tooth is
exposed to millimetric microwaves in this range, caries are
preferentially heated. Temperature rise can kill the microorganisms
in caries. Control and/or extinction of microorganism slows or
stops the progress of caries, permitting previously carious tissue
to recalcify by biological latent support of the pulp. Temperature
distribution measurement with microwave heating reveals that the
temperature of caries is higher than that of normal tooth tissue.
These properties are used with the provisions of this invention for
the diagnostic and treatment of teeth having caries and subsequent
internal heat conditioning and/or curing of provided dental
restorative materials. When dielectric loss factor is higher, the
absorption of microwave is better and local temperature is higher.
Microwave energy heats by radiation and is able to penetrate
through various substances including desiccated tissue and thus can
create an addressed effect.
[0042] To understand the details on which the preferred embodiment
is based, it is helpful to understand how microwave energy is
generated and absorbed. The microwave energy absorbed by a given
dental material is governed by the following equation:
P=2.pi. fE.sup.2 .epsilon.' tan .delta.
[0043] where:
[0044] P=Power density (w/m.sup.3)
[0045] f=frequency
[0046] E=electrical field strength (rms)
[0047] .epsilon.'=dielectric constant of the dental material
[0048] tan .delta.=dielectric loss factor.
[0049] This equation shows that in order to determine the microwave
energy in terms of the incident microwave power level absorbed by a
dental article, both the applied electric field strength and the
dielectric material characteristics must be known. One of the
difficulties in properly evaluating this equation is that when a
curable dielectric resinous material is polymerized, its microwave
absorption is drastically reduced because the dielectric constant
of the material changes as a result of the polymerization process.
Similarly, when microwave energy is directed to a tooth containing
a carious lesion, the absorption of the microwave energy changes.
The present invention utilizes this difference in absorption as a
mechanism for identifying carious lesions with the same hand-held
dental tool that can be used to non-invasively treat those
caries.
[0050] In one embodiment as shown in FIG. 14, a system of caries
control in a non-invasive atraumatic way, without surgical burs
entry and with a reduced risk and necessity of exposing the dental
pulp organ comprise, a hand-held microwave applicator with a
sufficient microwave power delivery capability is provided to heat
the dental tissues or restorative materials. The electronic circuit
diagram of FIG. 14 is designed to suit small microwave generators
such as an oscillation source coupled with a RF power amplifier or
impatt diodes or similar solid state or transistorized microwave
emitters with an output power of about 2 to 5 watts which requires
usually an electrical voltage of about 60 DC. The bias voltage is
applied through a high impedance line (56) in order to limit the
perturbation of electromagnetic signals. A power supply module is
provided with a current and voltage limiting means to permit the
polarization of the impatt diode in the specific limits with a
resonant circuit (57), such as a 50 ohms line, having a length
preferably equal to the half of the length of the selected
frequency. The length of the line may be calculated with the
following equation: L=3.times.10.sup.8/2f
.epsilon..sub.cff.sup.1/2. One end of the "resonator" is connected
to the impatt diode (58) and the other end of it is coupled (59) to
a transmission line including an isolator (60) to provide isolation
of the microwave source from the rest of the circuit in order to
avoid frequency variations, caused by a mismatch of the output
(61). A coupler (62) having a coupling of about -15 dB permit a
sampling of the signal emitted by the microwave generator in order
to measure the incident and reflected power levels. The couplers
should be perfectly matched at both extremities to permit precise
measurements. Matching circuit (63) at the input and the output as
well as load resistors permit achievement of an adaptation at each
end, equal or better than -15 dB. Detecting diodes (64) rectify the
radio frequencies signal in order to convert the power to a dc
voltage which can advantageously be subsequently transmitted to a
micro controller or a "ADC" analog digital converter which converts
this voltage to a digital signal for an appropriate processing of
the acquired information and the precise monitoring and the control
of the microwave's energy delivered to the dental target. The
controller is a means of setting the power level, exposure cycles,
processing modes, and may also be used in the selection of the
frequency of microwave generation. As shown in FIG. 9, the control
of the microwave source is preferably made by a selector (65),
located on the device, allowing the operator to set different power
levels and modes. Between the tip antenna and the microwave source
or amplifier, a shielded cable (66) or wave guide, as short as
possible is used to operatively transmit the microwave power to the
head antenna.
[0051] A suitable connector preferably permits the interchange of
different provided head antennas to match different applications
and enhance energy transmission and deposition on the dental
target. A means of electrical supply (67), such as a shielded
cable, connects the mobile applicator to the power supply. The
hand-held applicator may be equipped with a water cooling system
(68) and a digital display (69).
[0052] One head antenna (70), as shown in FIG. 11, is provided for
therapeutic purposes to target teeth and treat, heat or detect
dental caries, and is made of a highly conductive metal such as
copper, platinum or gold, plated or not, having the format of a
rectangular or a loop-shaped band, of which one end is connected to
the inner and the outer conductors of the transmission line.
[0053] One provided monopole head antenna has the form of an I as
shown in FIG. 12. This applicator is made for example by stripping
the outer jacket and the outer conductor of a coaxial shielded
cable, the inner conductor and dielectric (Teflon.RTM.) constitute
the applicator. To increase the directivity of the radiating
microwave energy, a loaded I-applicator (71) having an increased
forwarding effect may be made by placing a platinum ring over the
outer conductor of the coaxial cable and soldering a platinum rod
on the inner conductor of the antenna.
[0054] Another provided head antenna (72), as shown in FIG. 13, is
made of a microstrip, which may be made of miscible polymeric or
other conductive materials, having the format, for example, of a
square metal skin is positioned on a dielectric substrate with a
ground plane on its back.
[0055] An electrically shielded temperature probe may be embedded
in the head of the hand-held applicator antenna to provide a means
of monitoring the temperature of the heated target for judging the
efficiency of tissue heating and to avoid sudden temperature
rises.
[0056] The provided head antenna designs help in achieving good
impedance matching and effective delivery of microwave for internal
heat conditioning of dental targets. As shown in FIG. 10, a means
of safely containing any leakage of microwave energy close to the
irradiation space can be used such as the disclosed head antenna
choke (73), made of microwave absorbing materials.
[0057] Preferably, the antennas are made with a portion that is
strong and flexible enough to be used as a positioning and
compression tool for the pasty resin matrix for the dental
composite. The loop and patch antenna may preferably carry negative
dental molds to aid in the formation of the dental composite.
Alternatively, a miniaturized version of a manual resin injector,
such as previously described in connection with FIG. 8, may be
provided to deliver the pasty resin matrix for the dental composite
as part of the hand-held tool. While the hand-held tool is
preferably used in an intra-oral application with dental
composites, it will be recognized that the hand-held tool can also
be used in the dental office, for example, to accomplish repairs or
welds of dental prosthetics devices as well.
[0058] In one embodiment as shown in FIG. 8, an economic manual
fluid resin pressurization and injection device (46) is provided to
remove the need of being connected to an external pressurized fluid
source. A mechanical force accumulator such as a spring (47) is
compressed by turning the internally threaded cylinder (48) while
holding the device handle (49). A force boosting piston (50) is
especially useful for molding and filling of composite curable
dental materials. The injection nozzle and the piston acts as
previously described. This embodiment can be miniaturized and
employed with the hand-held intra-oral microwave applicator.
[0059] In general, various polymer based material compositions are
useful for the construction of dental devices. These compositions
may be used in the filling of teeth and the construction of
appliances used for replacing teeth and other oral structures.
[0060] One preferred composition for dental composites suited to be
formed and hardened in accordance with the providing of this
invention consists of a polymerizable mixture including one or a
selection from the large family of polyfunctional methacrylate
esters, and oligomers including the compound prepared from one
molecule of bisphenol A and two molecules of glycidyl methacrylate
called 2,2bis[4(2-hydroxy-3 methacryloyloxy-propylo-
xy)-phenyl]propane, known as Bis-GMA for its lower degree of
shrinkage and/or 2,2-bis[4-methacryloxyethoxy)Phenyl]propane for
its good water resistance properties. Other monomers, such as
triethyleneglycol dimethacrylate for viscosity reduction, urethane
dimethacrylates, spiro orthocarbontes, etc., are advantageously
employed in admixture with silanized inorganic fillers and organic
fillers, coupling agents, microwave sensitive cure initiation
system including organic peroxides and amines and color pigments
are advantageously added. The weight of the fillers as an overall
weight of the composite is preferably in the range of 30 to 90% and
include silanized silicon dioxide particles.
[0061] In one embodiment, compositions specially suitable for
making dental removable appliances such as dentures is provided
which comprise a liquid and a powdery component. The liquid
component in accordance with the invention contains preferably from
40% to 90% of mono-, di-, tri-, or multifunctional acrylic monomer,
a cross-linking agent, a plasticizer, a stabilizer. an accelerator
and color pigments. The mono-, di, tri-, or multifunctional acrylic
monomer in accordance with the invention are within the scope of
the formula: 1
[0062] where R1 in accordance with the invention is hydrogen,
alkyl, substituted alkyl group, cyclic hydrocarbon, benzyl, ether,
hydroxyalkyl and R2 is hydrogen, halogen, alkyl, substituted alkyl
or cyclic hydrocarbon group.
[0063] Monomers within the scope of the following formula are also
particularly suitable to the invention: 2
[0064] wherein R is an acrylic-free organic moiety, R.sub.1 is
hydrogen, hologen, halogen, alkyl, substituted alkyl or cyano
radical and n is an integer from 1 to 20 and m is an integer from 1
to 1000. These monomers may be used alone or in admixture.
[0065] The microwave sensitive initiators in accordance with the
invention include benzoyl and peroxide, dilauroyl peroxide up to
2.5%. The polymerization accelerator in accordance with the
invention is a quaternary ammonium chloride, which is easily
soluble in the methacrylate monomers and reacts with barbituric
acid derivatives. A preferred compound is the quaternary ammonium
with an alkyl of 1 to 20 carbons, such as,
dodecyltrimethylammonium. These quaternary ammonium chlorides may
be added in alone or in admixture from 0.09 to 1.5%. The
cross-linking agent, in accordance with the provided microwave
hardening material compositions, is a polyfunctional monomer
wherein at least two carbon-carbon double bonds, such as
1,3-butanediol dimethacrylate, 1,4-butanediol dimethacrylate,
1,4-butanediol divinyl ether, di(ethylene glycol) dimethacrylate,
di(ethylene glycol) divinyl ether, pentaerythritol diacrylate
monostearate, ethylene glycol dimethacrylate, trimetylolpropane
trimethacrylate, pentaerythritol triacrylate, pentaerythritol
tetraacrylate, trimetylolpropane triacrylate. The cross-linking
agents may be used alone or in admixture.
[0066] Polymerization promoters for the monomers of the provided
curable material compositions for the present invention are useful
because they rapidly react with the quaternary ammonium chloride to
produce radicals, which promotes a rapid and uniform polymerization
in the composition and a higher degree of conversion. The
barbituric acid derivative in accordance with the invention include
1,3,5-trimethylbarbituric acid, 1,3-dimethyl-5-isobutylbarbituric
acid, 1,3-dimethyl-5-phenylbarbituric acid, 5-n-butylbarbituric
acid, 5-ethylbarbituric acid, 1-cyclohexyl-5-ethylbarbituric acid
and 1-benzyl-5-phenylbarbituric acid. These acid derivatives may be
used alone or in admixture in very small amounts. The
polymerization stabilizers comprise hydroquinone, hydroquinone
monomethyl ether or 4-ethoxyphenol which are usually added to the
liquid component of dental compositions (up to 4%). The plasticizer
in accordance with the invention is generally a low molecular
weight ester, such as dibutyl phthalate or phosphates.
[0067] The composition for a one component microwavable curable
material system in accordance with this invention is approximately
the same as the one for the two component materials with some
variations mainly in the initiation system. Preferred initiators,
for a one component dental composition for denture or such, need to
be thermally stable at room or higher temperatures such as
50.sub.iC. and initiate polymerization at higher temperatures such
as benzopinacole, tert-butyleperbenzoate, and
2,2'dichlorobenzopinacol.
[0068] The powder component in accordance with the invention
includes from 20% to 80% of mono-di-tri, or multifunctional acrylic
or acrylate ester polymer. The powder may advantageously include
from 5% to 40% of a copolymer. The powder component in accordance
with the invention may advantageously include from 0.1% to 3% of an
initiator for radical polymerization including organic peroxides
such as benzoyl peroxide and dilauroyl peroxide. The powder
component in accordance with the invention can include up to 1% of
a barbituric acid derivative to promote chemical reaction. The
mono-, di-, tri-, or multifunctional acrylic polymer used in
denture base in accordance with the invention are: 3
[0069] where the R1 in accordance with the invention is hydrogen,
alkyl, substituted alkyl group, cyclic hydrocarbon, benzyl, ether,
hydroxyalkyl, R2 is hydrogen, halogen, alkyl, substituted alkyl
group and n is an integer at least equal to 2. The copolymer in
accordance with this invention are mainly composed of methyl
methacrylate polymer or a mixture of methyl methacrylate polymer
and an methacrylate polymer other than methyl methacrylate
polymer.
[0070] Inorganic and organic fillers may be added into the
compositions of one or two components' denture base. Useful
inorganic fillers include glass, metal ceramics, silicon dioxide in
powdery or fiber format, which are preferably silanized with a
coupling agent, such as 3-methacryloxyloxypropyltrimethoxy. Organic
fillers include splinter or bead polymers of high molecular weight,
or fibers such as aramide fibers, polyacrylate fibers, polyamide
fibers and polyacrylonitrile fibers. Organic fillers may be used
alone or mixed with inorganic fillers.
[0071] Thermoplastic compounds such as poly functional
methacrylate, polycarbonate, polysulfone, fluoropolymers,
elastomers, polyurethanes, impression compound, wax, gutta percha,
polycaprolactone and mixtures of thermoset and thermoplastics are
advantageously heat processed with the provided method and permit
dental rehabilitation.
[0072] Microwave absorbing substances can advantageously be
incorporated into disclosed thermoplastic and thermohardening
material compositions to decrease internal heat generation of
compositions which does not have sufficient dielectrical loss when
microwaved nor do they have sufficient heatability for a desired
speed of heating. These microwave absorbents are also useful when
the employed polymeric material has only a low microwave absorption
behavior at low temperatures such as many thermoplastic polymers
including polycarbonate and also for substantially increasing the
speed and the addressability such as in welding and joining
functions. These absorbers may be powdery, hollowed, coated and
comprise ferromagnetics, metallic oxides or specialty ceramics.
Microwave absorbent materials and/or sterilants can be
advantageously utilized with the intra-oral embodiment of the
present invention to increase the speed and addressability of
heating the dental composite and to increase the effectiveness of
the sterilization of the targeted caries. The following tables set
forth several examples in accordance with the various aspects of
the present invention. All ratio for materials are expressed in
weight.
Experiment of Decay Control in the Cavity Microwave Applicator
[0073]
1 Microwave Preparation irradiation Incubation Results Section of
decayous Surface 1.5 W/cm.sup.2 Culture of Microwave freshly
extracted desinection, 15 energy density irradiated &
irradiation human teeth prepared, seconds of irradiation non
irradiated destroy 80% 2 mm.sup.3 deeping in (200 W in the witness
carious zone cloramine T cavity decayous teeth microorganisms-
solution applicatior) sections in a Witness teeth 60 sec. medium at
cultures cloudy 37.sub.iC 24 h.
[0074] In commercial microwave ovens, microwave power reduction and
control is accomplished by pulsing the full power generated by the
microwave generator on and off over some duty cycle or time base,
wherein a duty cycle or time base is defined to be the amount of
time from beginning the pulsing of power to the time pulsing is
completed. For example, in an 800 watt oven, it is possible to
achieve a relative average output of 400 watts, or 50% power, by
pulsing the full 800 watts on and off, assuming the pulse width is
equal to half the pulse period. Even though an average output of
400 watts can be accomplished in this manner, for each on-time of
the duty cycle, the full 800 watts is actually on and applied
inside the oven.
[0075] The high electromagnetic field strength associated with
applying the full energy of the microwave oven, even for only a
portion of a duty cycle, can cause lighting, standing waves, and
hot spot problems when using microwave energy to polymerize dental
articles such as dental prosthetics. When microwave energy is used
to heat water or articles of food, for example, using the average
power delivered to the target article is adequate to evaluate the
energy absorption because the thermal and dielectric
characteristics of the article are constant and relatively uniform.
In contrast, when microwave energy is used to cure polymer dental
articles the changing characteristics of the targeted article, both
in terms of changes in the dielectric constant of the material that
changes microwave energy absorption and in terms of changes in
thermal conductivity that changes the manner in which thermal
energy is translated throughout the article, make the use of
average power delivered to the targeted article more complicated
and less meaningful. The present invention recognizes this
limitation of conventional commercial microwave ovens and solves
these problems by creating a microwave polymerization system for
dental articles utilizing metered and controlled microwave energy
that is preferably continuous and voltage controlled, and regulates
the application of this microwave energy by use of various feedback
mechanisms.
[0076] Referring now to FIG. 1, one apparatus, provided in
accordance with an extra-oral embodiment of this invention,
comprises a microwave applicator having a three-dimensionally
defined irradiation space having the format of a cavity (1), which
is open at least on one side and includes a means of preventing the
escape of microwave through the opening such as a door (2). The
door has a means of being guided to a precise closing position such
as hinges (3), and is able to be locked. The opening dimensions are
preferably less than those of the walls of the cavity. The door is
made of materials similar to those used for the cavity, being of
good conductivity and dissipation for the electrical, thermal and
microwave energy, including conductive metals or metal-plated
materials. The dimensions of the cavity applicator and walls should
preferably be set to minimize electromagnetic resonance or standing
waves situations which may occur in some internal zones of the
cavity applicator, thus causing hot or cold spots. Therefore, the
dimensions of the cavity should not be a multiple of the wavelength
.lambda. g of the transmitted microwave energy or pair fractions of
the wavelength such as 1/4, 1/2. For example, for the frequency of
2.45 Ghz, the wavelength is: .lambda. g=n/f=4.82 inch; 9.64 is a
multiple of .lambda. g; 11.24 is a multiple .lambda. g/3 and is not
"resonant" and is preferred as a cavity wall dimension. A flat
flange (4) made of said conductive materials is fixed to the
opening of the cavity applicator, and extends outwardly from the
walls, and comes into close contact with a wave trap (5),
preferably mounted on the door, and which should have a dimension
of .lambda. g/4 of the emitted wave length. Leaky microwaves will
be 90.degree. out of phase when going outward as well as when
returning, obliging the leaky waves to travel a total of
180.degree.. The returning waves will be in counter phase with the
leaking waves thus producing an energy cancellation. Each corner of
the door is provided with a curved band (6) to maintain the said
.lambda. g/4 distance of the emitted wavelength, and the wave
trap's efficiency. To minimize wave leakage, microwave-absorbing
materials may also be installed in the wave trap. A means for
efficiently locking the closed door is provided such as a
T-screwing handle (7). Safety microswitches (8) are installed in a
serial manner to electrically disconnect the microwave generator
electrical supply when the door is open. A rectangular wave guide
(9) or a cable, connects operatively the cavity applicator to the
microwave source. The wave guide includes a means of being tuned
(10), and in one preferred embodiment, comprise a directional
coupler (11). An aperture (12) is made both in the wave guide and
in a wall of the cavity, such that they are juxtaposed. This
creates a passage for electromagnetic waves to enter the cavity.
The aperture preferably has a length corresponding to .lambda. g/2
of the employed wave length and a width equivalent to the wave
guide width. A deflecting plate (13) is fixed at one end of the
wave guide at an angle of about 45.degree., and causes the incident
microwave beam to deviate into the cavity. The means of tuning the
wave guide and system is advantageously provided on the wave guide.
For example, three holes can be drilled into one wall of the wave
guide, and three tuning screws are placed into the threaded holes
across the said wave guide wall, the space between the holes is
preferably at a distance equivalent to .lambda. g/4. This provides
an efficient means to control and reduce the standing waves in the
wave guide and the microwaves that are returning to the microwave
source (14).
[0077] In one embodiment of the microwave applicator, a probe
consisting of a directional coupler is mounted close to the output
of the microwave source on the wave guide. This coupler senses the
transmitted and reflected microwave magnitude and permit the
monitoring and control of irradiation parameters. The directional
coupler includes high frequency detecting diodes that are mounted
on a printed circuit, which is mounted on the wave guide. The
output of detecting diode optionally is connected to an electronic
display to permit the irradiation monitoring and control of the
transmitted and reflected microwave levels through the process in
real time by an operator. Preferably, the microwave probe is
connected to a central process micro controller to follow a preset
or real time self-adjusted thermal processing program including
irradiation modes and intensities based on desired curing times and
the particular composition of the resin matrix to be cured. It will
be seen that the measurement of the transmitted and reflected
microwave energy allows for calculation of the actual microwave
energy absorbed by the article being irradiated which can be
monitored and adjusted as desired during the polymerization curing
process.
[0078] In one embodiment, as shown in FIG. 2, the control of the
microwave generation is accomplished at the source by changing
adequately the base voltage at the transistor, such as disclosed in
diagram 1, for a precise control of the wave generator output
power. For a microwave generator of 2.45 Ghz, such a magnetron,
usually about -3500 DC volts are required to function. A high
voltage transformer (15) raises the electrical voltage to about
1750 AC volts; then, a doubling circuit (16) composed of a high
voltage condenser and a high voltage rectifying diode brings the
voltage to about -3500 DC volts. A secondary low voltage coil of 3
AC volts supplies the heating filament of the mode of the microwave
generator. The base of the transistor (17) is connected to a micro
controller (18). This power transistor can be used as a variable
resistor, to permit monitoring and automated management of the
different irradiation and timing functions during the process. This
providing permits the control of the microwave output power in two
ways. First, by changing the duty cycles at the transformer by
applying pulses to the base connection of the transistor. The
second way of controlling of power is to reduce conveniently the
applied voltage of the primary circuit of the transformer by
changing adequately the base voltage of the transistor. This
embodiment permits a soft management of microwave power by avoiding
overheating of the microwave source, providing adequate heating of
sensitive small sized or high absorbency materials, and avoiding
the occurrence of corona discharges, particularly when metallic
objects are used.
[0079] Referring again to FIG. 1, the generated microwave energy
travels through the wave guide, is introduced and radiate into the
defined exposure space from the wave guide aperture. To further
reduce the standing wave patterns presence in the cavity
application system, one or more microwave stirrers (19) are made
with microwave deflecting blades and installed on an axle through a
bushing on one or more of the cavity inside walls. The stirrer
rotates by means such as a belt, pulleys, and electrical motor
(20). The overall surface of the stirrer can be about 3/4 of
dimension of the cavity's wall. Each blade has a different
configuration and passes close to the aperture causing the
microwave beam to be oriented and delivered to different areas of
the cavity. The materials used for the fabrication of the stirrer
should have good electrical conductivity. The stirrer shaft is
preferably made of a non-conductive material to minimize microwave
conduction and leakage through the bushing. To improve the
homogeneity of the established electromagnetic fields in the cavity
microwave applicator, flat or curved reflectors made of conductive,
specialty materials or active electromagnetic components may be
fitted in appropriate locations such as at the lower corners useful
to enhance energy distribution uniformity. The apparatus is
provided with a stand (21) made of microwave transparent material
to support suited dental compositions or objects that are to be
microwave irradiated.
[0080] In one embodiment, as shown in FIGS. 3, 4, 5, and 6, in
order to produce a dental polymer based object with high flexural
strength and high modulus of elasticity and very low levels of
post-cure leachables, being preformed or not, is irradiated and
internally heated while compressed by a fluid such as air or
nitrogen, resting on perforated tray (22) in a flask (23) made of
heat and pressure resistant microwave partially transparent
materials which may be filled and reinforced such as polyester,
polyethylene, polypropylene and polysulfone, and having at least
two body members and a means of clamping such as screws and,
preferably, as the disclosed bracket (24) and a pressure limiting
valve (25). When used in conjunction with the provided cavity
applicator, the flask is introduced in the cavity and is connected
to a mechanical gas coupling means (26) being positioned on a wall
and or the bottom of the cavity applicator. This permits the
introduction or removal of gas as needed before, while and after
the irradiation of the processed target. A gas such as air or
nitrogen is introduced through one of the flask pneumatic
connections such as the ring opening (27) provided with each body
member of the flask and allows easy and fast processing and making
of objects having highly desirable properties. Preferably, a means
of rotary mechanical gas coupling which employs an electrical motor
(28), permit more uniform microwave exposure of the substance or
object by entertaining the flask and targeted object in a rotary
movement in the cavity while under pressure a constant. Microwave
absorbing substances such as water can be introduced into the flask
recess to increase heat or steam generation and the control and
metering of the microwave can be adjusted to accommodate such a
two-stage thermal transfer process.
[0081] In one embodiment, a means for a vacuum forming method is
characterized by the use of the ring opening of the lower body
member of the flask and a mechanical gas coupler which is
positioned at the bottom of the cavity wall, in connection with a
vacuum source to allow the thermal conditioning of thermoplastic
softening compositions as well as the cure of thermosetting dental
material compositions with highly desirable qualities useful in
many dental applications, such as fabrication of dentures, trays or
base plates, by attracting with suction the polymer-based material
before and/or during the irradiation towards the mold, positioned
on a dental model and a perforated tray to condition thermoplastic
or thermohardening dental materials.
[0082] In one embodiment, the lower half of the flask is connected
by providing coupling means to a vacuum source. A pasty
polymer-based material (29) is set on or in a mold or pattern and
positioned on a perforated tray in the flask. A flexible membrane
(30), made of a material partially transparent to microwaves, such
as silicone rubber, is firmly retained by a means such as a recess
between the two body members of the flask, permitting the forming
of a dental material by applying hydrostatic forces while microwave
irradiated. Additional pressure can be exerted on the dental
material by the introduction of pressurized gas from the upper ring
opening of the flask. The embodiment is useful in the fabrication
of dental devices such as tray, base plate, fiber reinforced
composite crown and bridge, and molding of thermoplastic based
objects such as vinyl esther oral protectors, permitting to reduce
substantially the size and the number of the voids.
[0083] In one embodiment, a dental model (31) made of materials
such as wax or elastomer, which can bear components such as
artificial teeth, having the forms of the object to be produced is
vested in a coating material (32) such as plaster in a flask having
at least two body members and a clamping means. First, the
cup-shaped recess of the lower member of the flask is filled with
the coating material, then the model which may include a plaster
cast is positioned in the coating material to a depth that is about
half of its total height or to its largest contour. Once the
coating material is set, a separating medium such as alginate based
isolation solution for plaster is applied to its exposed surface.
The two parts of the flask are then joined by a retaining and
alignment setup such as screws and nuts and preferably clamping
bracket means. The jointly clamped body members of the flask are
then filled with more fluid coating material through its upper ring
opening. Each ring opening (33) can be secured to the flask by
means of threading or a shoulder. Once the added coating or mold
making material is set, for dental patterns made of wax or the
like, the complete flask is heated in the apparatus or in a hot
water bath a few minutes to soften and melt the wax. Subsequently,
the flask is split opened after removal of the clamping means, thus
exposing the internal forms of the mold and defining the shape of
the object to be produced as well as holding in position, objects
such as artificial teeth. All of the parts are then washed with hot
water. When using thermosetting material, an isolation medium is
applied to all exposed surfaces of the mold to prevent the adhesion
of the polymer material when in close contact with the mold at the
processing stage. The fabrication method of the mold resembles to
the known technique of lost wax casting. A drying treatment of the
plaster molds can be done by its irradiation and heating in the
cavity applicator or an oven. Once the dental mold is made, it is
packed and may also be painted or sprayed by a dental material
composition. The flask members are then clamped, introduced and
mechanically connected in the cavity applicator to a fluid under
pressure such as air and the process of microwave curing is
initiated.
[0084] In one embodiment, as shown in FIGS. 5 and 6, the flask is
provided with an opening (34) preferably with the disclosed means
of quick connection permitting the positioning and removal of the
injection nozzle (35) while flask body members are joined. The mold
space within the flask is operatively connected to the flask
opening through vested runners made of material such as wax,
preferably set on the model before the second filling of the flask
of the coating material. Physical changes, including the
progressive mold filling densification and the volumetric shrinkage
of many thermally conditioned polymer-based materials, is
substantially compensated in this invention with the pressurization
and, when needed, introduction of the fluid polymer-based dental
materials into the flask. The material injection means includes the
use of a fluid conduct (36) with a male mechanical hydraulic
coupler which allows the introduction of a fluid into the fluid
conduct (37) through the mechanical coupler into the cavity
applicator, which results in the compression filling of the
materials contained in fluid dental material reservoir (38) into
the mold. When under a hydraulic pressure, the piston (39) forces
the material from its compartment through the injector (40) and the
opening of the flask and to fill the mold. The cover (41) of the
capsule is made to be removable by a means such as threads and is
connected to one or more injectors in connection with the flask.
The capsule can be advantageously trained into a rotary motion
transmission by means such as a key path (42), on a rotary platform
pin (43) in the cavity to enhance irradiation uniformity of the
mold and dental composition while submitted to hydraulic forces.
The piston and the capsule are advantageously equipped with sealing
joints (44). For the processing of some materials such as
thermohardening polymers, the capsule, conduct, and nozzle are
preferably shielded by being made of microwave impervious materials
such as steel, and conserve the unprocessed material compositions
in its original temperature and fluidity condition, under pressure
and while being continuously available and able to be introduced as
needed in the mold to compensate for the volumetric shrinkage and
to fill voids and/or compensate for progressively occurring
deformations of the object in thermal process. This continual
pressurized injection allows a substantial increase of the
dimensional precision of the produced dental objects. The presence
of porosity is significantly reduced and produced objects are more
suited for dental uses in terms of biofunctionality, fit and
durability when compared to objects such as prosthetics produced by
the conventional methods and materials. Preferably, a bleeder (45)
made of microwave transparent materials is employed in an
appropriate housing made on at least one of the flask members
closing surface, and provides a means of hydraulically connecting
the mold to the exterior of the flask, useful in reducing the
energy and time required to appropriately fill the mold and also
minimize porosity occurrence. Said bleeder accelerates the emptying
of the existing air in the mold space when introducing resinous
materials into it while preventing the leakage of resinous fluid
dental materials under pressure by moving outwardly and blocking
the external orifice of the housing.
[0085] In one embodiment, low microwave absorbing materials
including thermoplastic resins are indirectly heated with the use
of a compression-injection capsule coated or layered with microwave
absorbing substances such as metal oxides including zinc oxide,
carbon black and specialty ceramics.
[0086] In one embodiment, a shielded temperature probe made, for
example, of a thermocouple with a temperature dependent resistor, a
fluoro-optic, or an infrared temperature magnitude detecting means
is advantageously used with a pivoting electrical connector to
permit the sensing of the thermal conditions of the microwave
irradiated target. This embodiment permits a precise setting of the
pace of thermal conditioning as well as the indication of the reach
of a specific temperature magnitude useful for the thermal
processing of delicate materials such as some thermoplastics or low
temperature boiling monomers, as well as to increase safety in the
dental prosthesis sterilization functions and is preferably used in
connection with the central micro-programmable controller to
optimize the feedback and control of the microwave generator.
[0087] In one embodiment, as shown in FIG. 7, to permit a safe and
quick sterilization of dental objects without fear of corrosion or
arc occurrence, a cylindrical column (51) made of microwave
transparent materials is closed at one end and externally threaded
at the neck, is made of sufficiently thick glass or polymer to
resist heat and pressure, and is used in conjunction with the
provided flask and cavity applicator. The cylindrical column
permits heating of a liquid and hot steam generation and,
optionally, the production of a microwave shielding atmosphere is
screwed into the lower flask half member through its ring opening
with its sealing joints (52). A liquid such as distilled water is
introduced to fill the column up to a pre-determined level. A
specially shielded flask operatively connected or not with the
steam generation column is introduced in the said cavity through
the door, or only its column introduced from the provided top
circular opening (53) into the cavity applicator, which is provided
with a disk form closing door. To sterilize, the steam, having
reached the evaporation temperature under microwave irradiation,
fills the flask with the vapor rise up. The upper flask half is
preferably made of a heat conduction and exchanging material (54)
such as stainless steel and comprises a heat sink to cool by
conduction the internally contacting warm vapor. The condensed and
liquefied sterilizing solution returns by gravity to the base of
the column where it is repeatedly heated and evaporated, providing
a constant steam flow and contact with treated dental objects
contained in the flask. To detect the temperature magnitude with
high accuracy, the temperature probe for a microwave environment
can be placed within the flask. The flask can be sealed immediately
following removal of the probe after sterilization with the use of
an annular elastic sealing coupler positioned on one of the flask
inlets, such as the injection opening or the pressure limiting
valve manifold. The means of microwave and temperature magnitude
detection permit a precise control and delivery of microwave to a
dental target, useful in avoiding arcing occurrence by generating
adequate microwave power levels and/or creating a shielding vapor
pressure atmosphere inside the flask. The temperature and microwave
sensing and control are preferably done in an automated manner with
the programmable micro-controller. Once the predetermined
temperature is reached, a signal is sent to the micro-controller,
which then reduces the power of emission so as to maintain a
sufficient amount of time to sterilize (6 min). Equilibrium
temperature is reached quickly since there are no great swings in
the temperature and optimal control of the microwave delivery is
achieved.
[0088] In one embodiment, the temperature is safely and
economically controlled for sterilization function through a gas
pressure sensor which is connected to the flask for example through
the pressure limiter manifold (55) or vent to control the
sterilization temperature inside the flask, specially when used
with the shielded flask, positioned externally with only its steam
column introduced in the cavity applicator. This pressure sensor is
operatively connected to a micro-controller to maintain the right
warm steam pressure temperature magnitude and permit monitoring.
The temperature sensor for microwave environment can also, alone or
jointly with the pressure sensor, be used with the disclosed
device. Any increase of temperature of a gas having a given volume
conduct to an increase of its pressure. By limiting and/or
controlling the pressure of the gas, an effective control of flask
internal temperature is achieved. The micro-controller controls the
flask internal temperature via the microwave generator, using the
provided microwave power control.
[0089] We have conducted complex dielectric permittivity,
temperature and distribution pattern studies of microwave heated
teeth and simulations of specific absorption rate distribution. The
complex permittivity was measured on different types of dental
tissues, using extracted teeth, including enamel, dentin and
caries. Reflective coefficients have been obtained using a network
analyzer. The characteristics of enamel caries and dentin are
different. The dielectric loss factor of caries is fairly higher
than that of normal healthy parts particularly in the millimetric
wave in the frequency between 12 GHz to 25 GHz. When the tooth is
exposed to millimetric microwaves in this range, caries are
preferentially heated. Temperature rise can kill the microorganisms
in caries. Control and/or extinction of microorganisms slow or stop
the progress of caries, permitting previously carious tissue to
recalcify by biological latent support of the pulp. Temperature
distribution measurement with microwave heating reveals that the
temperature of caries is higher than that of normal tooth tissue.
These properties are used with the provisions of this invention for
the diagnostic and treatment of teeth having caries and subsequent
internal heat conditioning and/or curing of provided dental
restorative materials. When dielectric loss factor is higher, the
absorption of microwave is better and local temperature is higher.
Microwave energy heats by radiation and is able to penetrate
through various substances including desiccated tissue and thus,
can create an addressed effect.
[0090] In general, various polymer-based material compositions are
useful for the construction of dental devices. These compositions
may be used in the filling of teeth and the construction of
appliances used for replacing teeth and other oral structures. One
utility of these compositions is in the construction and repair of
removable dental devices such as dentures and dental anchored
restorations such as crowns, bridges, inlays, and veneers. Also,
utility is found in the making of mouth guards, oral border
molding, impression trays, base plates, and orthodontic dental
appliances. Various thermoplastic containing dental compounds are
also advantageously thermally conditioned and softened while
treated with the provided method and apparatus and formed
subsequently by various methods.
[0091] Another example of polymers used in the dental arts is soft
liners. A permanent soft liner is placed on the interface between
the interior surfaces of the denture and the denture-bearing mucosa
of the patients. This soft liner should be permanently resilient,
highly stable in dimension, adhering to the denture-base polymer,
biocompatible, easy to clean and not capable of sustaining
microbial growth. Several kinds of soft liners including
polysiloxane, polyurethanes, plasticized polymethacrylates,
polyvinyl chlorides and polyphosphazene fluoroelastromers are
currently employed. Most soft liners do not fulfill the above
requirements due to inherent disadvantages. These include the
leaching of potentially harmful bonding agents, such as epoxy and
urethane adhesives, sulfuric, perfluoroacetic acid, poor adhesion
to the polymethylmethacrylate (PMMA) denture base material,
porosity in denture base and the liner resulting from vaporization
of the incorporated monomers and solvents, dimensional changes
caused by micro-shrinkage and dehydration and rehydration steps.
The improvements of denture soft liners may be based on the use of
novel materials, such as methacryloxy polydimethylsiloxanes or
methacryloxyalkyl-terminated polydialkylsiloxanes.
[0092] Microwave curing resilient compounds for making devices such
as denture liners are molded and cured with the provided novel
method and apparatus including organopolysiloxanes and
phosphonitrilic fluoroelastomers [poly(fluroalkoxy)phosphazene]
with a cross-linking agent, a filler and an initiator. Silicones
are containing a repeating silicone-oxygen backbone with organic
side groups attached via carbon silicone bonds. One composition for
soft denture liners, in accordance with this invention, contain
silicones within the scope of the structural formula:
[R.sub.nSiO.sub.(4-n/2)].sub.m
[0093] Wherein n=1-3 and m>1. R groups are usually methyl,
longer alkyl, fluoroalkyl, phenyl, vinyl, alkoxy or alkylamino. One
preferred silicone compound is polydimethylsiloxane (PDMS) of the
following structure: 4
[0094] Methacryloxy-terminated polydimethylsiloxanes are
particularly useful since they bond well to PMMA made dentures due
to the chemical similarity.
[0095] The cross-linking agents for soft liners are normal
multi-functional monomers wherein there are at least two
carbon-carbon double bonds. Preferred cross-linking monomers are
acryloxy or methacryloxyalkyl-terminated siloxane monomers, such as
1,3-bis[(p-acryloxymethy)phenethyl]tetramethyldisiloxane,
1,3-bis(3-methacryloxypropyl)tetramethyldisiloxane, due to chemical
similarity.
[0096] The normal initiators in the soft denture liners in
accordance with the invention are general peroxides, such as
benzoyl peroxide, lauroyl peroxide, which are usually added to the
powdery component of resilient compositions in small amounts.
[0097] The phosphonitrilic fluoroelastomers
(poly(fluoroalkoxy)phosphazene- s) in accordance with this
invention are polymerized by monomers within the following formula:
5
[0098] where X is H or F, and n is usually from 1 to 11, 30 to 60%
of total ingredients for a firmer liner and up to 90% for a softer
one.
[0099] The cross-linking agent suitable for the fluoroelastomers
are monomers with at least two functional groups, such as
tetraethylene glycol dimethacrylate, ethylene glycol
dimethacrylate, 1,6-hexamethylene glycol dimethacrylate,
trimethylopropane trimethacrylate, pentaerythritol triacrylate,
pentaerythritol triallyl ether, pentaerythritol tetraacrylate.
[0100] The fillers, which are preferably mainly hydrophobic,
improve hardness and the ability to grind and polish the cured
resilient materials and the bond durability between the liner and
base. Particles of fillers may be beads or fibers, pigments and
other additives can be added to the soft material system (fillers
7% for soft, 30% for firm liners).
[0101] Thermoplastic compounds such as polyfunctional methacrylate,
polycarbonate, polysulfone, fluoropolymers, elastomers,
polyurethanes, impression compound, wax, polycaprolactone and
mixture of thermoset and thermoplastics are advantageously heat
processed with the provided method and permit dental
rehabilitation.
[0102] Microwave absorbing substances can advantageously be
incorporated into disclosed thermoplastic and thermohardening
material compositions to decrease internal heat generation of
compositions which does not have sufficient dielectrical loss when
microwaved, nor do they have sufficient heatability for a desired
speed of heating. These microwave absorbents are also useful when
the employed polymeric material has only a low microwave absorption
behavior at low temperatures such as many thermoplastic polymers
including polycarbonate and also for substantially increasing the
speed and the addressability, such as in welding and joining
functions. These absorbers may be powdery, hollowed, coated and
comprise ferromagnetics, metallic oxides, or specialty ceramics.
Microwave absorbent materials and/or sterilants can be
advantageously utilized with the intra-oral embodiment of the
present invention to increase the speed and addressability of
heating the dental composite and to increase the effectiveness of
the sterilization of the targeted caries.
[0103] The following tables set forth several examples in
accordance with the various aspects of the present invention. All
ratio for materials are expressed in weight.
2 Cavity applicator dimensions Cavity: 32 cm .times. 32 cm .times.
28 cm made of steel Wave guide: 3.8 cm .times. 7.6 cm .times. 45.7
cm such as WR 284 made of copper Steerer: 20 cm made of steel Flask
(made of polypropylene) diameter 8 cm - bleeder 2 mm diameter: 3.5
mm long interior: diameter 13 cm - membrane thickness: 3 mm
exterior: recess depth: 1.5 cm - ring: 3.5 cm
[0104]
3 Injection capsule dimensions (made of stainless steel/wall
thickness 6 mm) Diameter Stroke Piston height Dentures: 10 cm 5 cm
2 cm Manual: 5 cm 6 cm 2 cm Composite boosting piston: 3.5 cm 2.5
cm 1.5 cm
[0105]
4 Process programmable micro-controller Micro-controller Pic of
Microship inc. or Parallax
[0106]
5 Microwave frequency Magnetron frequency: 2.45 GHz Output power
600 W Impatt diode frequency: 24 GHz Output power 5 W
[0107]
6 Vacuum source such as a 600 W cleaning aspirator for dental
Vacuum forming of resinous or microwave softened dental materials
The steam generation column is made of polycarbonate with walls
having a thickness of 1 cm 6 cm inside diameter and a height of 12
cm
[0108]
7 Pressure limiting valve Aperture: 4 mm.sup.2 Weight: 80 g
Pressure: 24 PSI
Experiment of Decay Control in the Cavity Microwave Applicator
[0109]
8 Microwave Preparation irradiation Incubation Results Section of
decayous Surface 1.5 W/cm.sup.2 Culture of Microwave freshly
extracted disinfection, 15 energy density irradiated &
irradiation human teeth prepared, seconds of irradiation non
irradiated destroy 80% 2 mm.sup.3 steeping in (200 W in the witness
carious zone cloramine T cavity decayous teeth microorganisms-
solution applicator) sections in a Witness teeth 60 sec. medium at
cultures cloudy 37.degree. C. 24 h.
[0110]
9 Steps of the procedure in order Examples of microwave processing
Compression, Microwave of polymer based material forming
irradiation Bench cooling Aesthetic composite A 100 de 3 M inc,
color ivory, 0.15% 1 min 3 min, 450 W 3 min of benzoide peroxide
for initiation. 1 cc Example 1 * Example 2 2 min 5 min, 250 W 3 min
* Mechanical test (3 points bend, Size: 25 .times. 2 .times. 1.75
mm Load at max Displacement failure) of specimens of example 2 at
max Testing specifications, crosshead 25 PSI membrane 45 N 0.42 mm
speed compression, flask 2 mmm/min, Instron device & plaster
mold Mold injection Microwave filling irradiation Bench cooling GC
Acron resine for dentures, 40 cc 100 psi, 3 min 7 min,. 225 W + 1
min, 6 min Flask with bleeder plaster mold 400 W Large capsule
Example 1 Example 2 100 psi, 3 min 4 min, 450 W 6 min Soft
materials 80 psi, 5 min 12 min, 225 W + 1.5 min, 6 min Molloplast
B, Regnesi & co GER, 400 W 40 cc
Examples of Some Polymer Based Dental Materials Processed with the
Providing of this Invention
[0111]
10 Step 1 Step 2 Compression Microwave Composite resin matrix
forming irradiation BisGMA - TEDGMA - Ratio 6/4 15 PSI 20 PSI 0.5%
of benzoide peroxide for 2 min 5 min 350 W initiation
EXAMPLE
[0112] Disq size 6 mm diam..times.3 mm., plaster & Teflon mold:
diametral compression strength 100 MPa, 80 degree of conversion
[0113] ADA specification no. 27
11 Filling a denture plaster mold Microwave within the flask
irradiation GC Acron resine for dentures, 55 Kgf/cm.sup.2 30
Kgf/cm.sup.2 40 cc Flask with bleeder plaster mold 3 min 6 min,.
300 W Large injection capsula Example Soft materials for denture
base mold filling 5 min, 375 W, lining 45 Kgf/cm.sup.2, 5 min 20
Kgf/cm.sup.2 Molloplast B, Regnesi & co GER, 40 cc Large
injection capsula
[0114]
12 Repair, soldering of denture resin G-C ACRON, denture repair
.about.25 psi, air pressure - 80 g pressure material powder &
fluid limiting valve weight on a regular dental index made of
plaster 2 min, 200 W + 1 min, 350 W Repair of denture resin G-C
ACRON, denture repair 18 psi, air pressure - on a regular dental
material powder & fluid index made of plaster 5 min, 325 W
[0115]
13 Microwave softening of thermoplastic Microwave dental material
irradiation Adaptation time Border molding compound in a 5 cc 4
min, 200 W 2 min syringe Dental custom tray, polycapratone 2 min,
300 W 1.5 min sheet thermosoftening Thickness: 3 mm Microwave
softening of thermoplastic Microwave dental polymers irradiation
Border molding compound 5 cm.sup.3 plastic 4 min, 200 W cylinder
Dental custom tray 3 mm, 2 min, 300 W polycaprolactone sheet
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