U.S. patent application number 10/285303 was filed with the patent office on 2003-08-21 for dental mill blanks.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Carufel, Roger J., Cummings, Kevin M., Rusin, Richard P..
Application Number | 20030157357 10/285303 |
Document ID | / |
Family ID | 22852295 |
Filed Date | 2003-08-21 |
United States Patent
Application |
20030157357 |
Kind Code |
A1 |
Rusin, Richard P. ; et
al. |
August 21, 2003 |
Dental mill blanks
Abstract
A dental mill blank comprising a resin and a filler, wherein the
blank is fabricated such that it passes a Thermal Shock Test. The
mill blank is substantially free of cracks and discontinuities.
Further, the blank may have superior cuttability and hardness.
Inventors: |
Rusin, Richard P.;
(Woodbury, MN) ; Cummings, Kevin M.; (Little
Canada, MN) ; Carufel, Roger J.; (Marine on St.
Croix, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
22852295 |
Appl. No.: |
10/285303 |
Filed: |
October 31, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10285303 |
Oct 31, 2002 |
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10027278 |
Dec 21, 2001 |
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10027278 |
Dec 21, 2001 |
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09227230 |
Jan 8, 1999 |
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Current U.S.
Class: |
428/542.8 ;
433/202.1 |
Current CPC
Class: |
A61C 13/0022 20130101;
A61K 6/893 20200101; A61K 6/887 20200101; A61K 6/893 20200101; A61K
6/887 20200101; C08L 75/16 20130101; C08L 75/16 20130101; C08L
33/00 20130101; C08L 33/00 20130101; C08L 63/00 20130101; A61K
6/891 20200101; C08L 63/00 20130101; A61K 6/891 20200101; A61K
6/893 20200101; A61K 6/891 20200101; A61K 6/887 20200101 |
Class at
Publication: |
428/542.8 ;
433/202.1 |
International
Class: |
B29B 007/00; A61C
013/08 |
Claims
We claim:
1. A carvable mill blank for making a dental prosthetic comprising
a) a polymeric resin and b) a filler, wherein the blank is
substantially free of cracks and fabricated such that the blank
passes a Thermal Shock Test.
2. The blank of claim 1 wherein the blank is substantially free of
discontinuities in the material that are larger than about 1
millimeter.
3. The blank of claim 1 wherein the blank is substantially free of
discontinuities in the material that are larger than about 0.1
millimeter.
4. The blank of claim 1 wherein the blank is substantially free of
discontinuities in the material that are larger than about 0.01
millimeter.
5. The blank of claim 1 wherein the blank further comprises a
fluoride releasing material.
6. The blank of claim 1 wherein the polymeric resin is made from a
material comprising a free radically curable monomer, oligomer or
polymer.
7. The blank of claim 1 wherein the polymeric resin is made from a
material comprising a cationically curable monomer, oligomer or
polymer.
8. The blank of claim 1 wherein the polymeric resin is made from a
material comprising a free radically curable monomer, oligomer or
polymer and cationically curable monomer, oligomer or polymer.
9. The blank of claim 6 wherein the material is selected from the
group consisting of
2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propan- e
(bisGMA), triethyleneglycol dimethacrylate (TEGDMA),
2,2-bis[4-(2-methacryloyloxyethoxy)-phenyl]propane (bisEMA),
2-hydroxy ethyl methacrylate (HEMA), urethane dimethacrylate (UDMA)
and any combinations thereof.
10. The blank of claim 7 wherein the material is selected from the
group consisting of diglycidyl ether of bisphenol A,
3,4-epoxycyclohexylmethyl-- 3-4-epoxy cyclohexene carboxylate,
bisphenol F epoxides, and polytetrahydrofuran.
11. The blank of claim 1 wherein the resin is made from a material
comprising a monomer, oligomer or polymer comprising both a free
radically curable functionality and a cationically curable
functionality.
12. The blank of claim 1 wherein the filler is selected from the
group consisting of barium glass, quartz and zirconia silica.
13. The blank of claim 1 wherein the filler is derived from a
sol-gel process.
14. The blank of claim 1 wherein the blank is capable of being
further hardened after or during milling by a curing process.
15. A carvable mill blank for making a dental prosthetic comprising
a) a resin component and b) a fluoride releasing component.
16. A method of making the dental mill blank of claim 1 comprising
the steps of a) mixing a paste comprising a resin and a filler, b)
shaping the paste into a desired configuration, c) minimizing
material discontinuities from the paste d) curing the paste into a
blank, and e) relieving internal stresses in the blank.
17. The method in claim 16 wherein shaping the paste is performed
using a mold and further comprising the steps of f) trimming excess
paste material from the mold, and g) removing the cured paste from
the mold.
18. The method in claim 16 further comprising the step of f)
mounting a handle to the cured paste.
19. The method in claim 16 wherein the curing system is selected
from the group consisting of heat, light, microwave, e-beam and
chemical cure.
20. The method in claim 16 wherein the stress relieving step
comprises slowly heating the cured paste in an oven temperature of
at or above Tg of the resin.
21. A method of making the dental mill blank of claim 1 comprising
the steps of a) mixing a paste comprising a resin and a filler, b)
shaping the paste into a desired configuration, c) minimizing
material discontinuities from the paste d) slow curing the paste on
a light box for a sufficient time to effectuate low stress cure,
such that the cured paste passes a Thermal Shock Test.
22. A method of making a dental prosthetic comprising the steps of
a) mixing a paste comprising a resin and a filler, b) shaping the
paste into a desired blank configuration, c) minimizing material
discontinuities from the paste, d) curing the paste into a blank,
e) carving the blank into a desired shape and morphology, wherein
the blank is substantially free of cracks and fabricated such that
the blank passes a Thermal Shock Test.
23. The method of claim 22 further comprising the step of: f)
adding additional material to the carved blank.
24. The method of claim 22 further comprising the step of: f)
attaching the carved blank to tooth or bone structure.
25. The method of claim 22 further comprising the steps of: f)
manually changing the morphology of the carved blank and g)
finishing the outer surface of the carved blank.
26. The method of claim 22 wherein an intermediate step between
curing and carving the paste comprises attaching a handle to the
cured paste and wherein the carving is performed by a milling
machine.
27. The method of claim 22 wherein the carving step is performed by
a hand-held instrument.
28. The mill blank in claim 1 wherein the wherein the mill blank
has a Barcol Hardness value greater than about 0% of the Barcol
Hardness of a Standard Fumed Silica Mill Blank, and a Cuttability
value greater than about 30% of the Cuttability value of a Standard
Fumed Silica Mill Blank.
29. The mill blank in claim 1 wherein the mill blank has a Barcol
Hardness value greater than about 5% of the Barcol Hardness of a
Standard Fumed Silica Mill Blank.
30. The mill blank in claim 1 wherein the mill blank a Barcol
Hardness value greater than about 15% of the Barcol Hardness of a
Standard Fumed Silica Mill Blank.
31. The mill blank in claim 1 wherein the mill blank has a
Cuttability value greater than about 50% of the Cuttability of a
Standard Fumed Silica Mill Blank.
32. The mill blank in claim 1 wherein the mill blank has a
Cuttability value greater than about 100% of the Cuttability of a
Standard Fumed Silica Mill Blank.
33. The mill blank in claim 1 wherein the filler is at least about
50% by weight of the total weight of the mill blank.
34. The mill blank in claim 1 wherein the filler is at least about
65% by weight of the total weight of the mill blank.
35. The mill blank in claim 1 wherein the filler is at least about
80% by weight of the total weight of the mill blank.
Description
FIELD OF THE INVENTION
[0001] This invention is related to polymeric based mill blanks
that are substantially free of cracks and are suitable for use in
fabricating dental and medical prostheses by CAD/CAM
(computer-aided design/computer-aided machining) procedures.
BACKGROUND OF THE INVENTION
[0002] The art of fabricating custom-fit prosthetics in the medical
and dental fields is well-known. Prosthetics are replacements for
tooth or bone structure; examples include restoratives,
replacements, inlays, onlays, veneers, full and partial crowns,
bridges, implants, posts, etc. Currently, most prostheses in
dentistry are either made by hand by a dental practitioner while
the patient is in the dental chair, or by an independent laboratory
who is capable of such fabrication.
[0003] Materials used to make the prostheses typically include
gold, ceramics, amalgam, porcelain and composites. For dental
restorative work such as fillings, amalgam is a popular choice for
its long life and low cost. Amalgam also provides a dental
practitioner the capability of fitting and fabricating a dental
filling during a single session with a patient. The aesthetic value
of amalgam, however, is quite low, as its color drastically
contrasts to that of natural teeth. For large inlays and fillings,
gold is often used. However, similar to amalgam, gold fillings
contrast to natural teeth hues. Thus, dental practitioners are
increasingly turning to ceramic or polymer-ceramic composite
materials whose color can be matched with that of the tooth.
[0004] The conventional procedure for producing dental prosthetics
typically requires the patient to have at least two sessions with
the dentist. First, an impression is taken of the dentition using
an elastomeric material from which a cast model is made to
replicate the dentition. The prosthetic is then produced from the
model using metal, ceramic or a composite material. A series of
steps for proper fit and comfort then follows. Thus, fabrication of
custom prostheses involves intensive labor, a high degree of skill
and craftsmanship, and lengthy times (1-2 days). Alternatively, a
practitioner may opt for a sintered metal system that may be
faster. However, those procedures are still labor intensive and
complicated.
[0005] In recent years, technological advances have provided
computer automated machinery capable of fabricating prostheses
using minimal human labor and drastically lower work time. This is
frequently referred to as "digital dentistry," where computer
automation is combined with optics, digitizing equipment, CAD/CAM
(computer-aided design/computer aided machining) and mechanical
milling tools. Examples of such a computer-aided milling machine
include the CEREC 2.TM. machine supplied by Siemens (available from
Sirona Dental Systems; Bensheim, Germany) VITA CELAY.TM.,
(available from Vita Zahn Fabrik; Bad Sackingen, Germany)
PRO-CAM.TM. (Intra-Tech Dental Products, Dallas, Tex.) and PROCERA
ALLCERAM.TM. (available from Nobel Biocare USA, Inc.; Westmont,
Ill). U.S. Pat. Nos. 4,837,732, 4,575,805 and 4,776,704 also
disclose the technology of computer-aided milling machines for
making dental prostheses. These machines produce dental prostheses
by cutting, milling, and grinding the near-exact shape and
morphology of a required restorative with greater speed and lower
labor requirements than conventional hand-made procedures.
[0006] Fabrication of a prostheses using a CAD/CAM device requires
a "mill blank," a solid block of material from which the prosthetic
is cut or carved. The mill blank is typically made of ceramic
material. U.S. Pat. No. 4,615,678 discloses a blank adapted for use
in machine fabrication of dental restorations comprising a ceramic
silica material. There exist various mill blanks available
commercially, including VITA CELAY.TM. porcelain blanks Vita Mark
II Vitablocks.TM. and VITA IN-CERAM.TM. ceramic blanks (both
available from Vita Zahn Fabrik; Bad Sckingen, Germany). Machinable
micaceous ceramic blanks (e.g. Corning MACOR.TM. blanks and
Dentsply DICOR.TM.) are also known in the art.
SUMMARY OF THE INVENTION
[0007] The invention provides mill blanks for making dental
prosthetics comprising a polymeric resin and a filler, wherein the
mill blank is substantially free of cracks, or fissures, and able
to withstand a Thermal Shock Test, a test that exposes the
existence of internal stresses in the mill blank, which can lead to
cracking of the material before or during the milling operation or
during clinical use of the ultimate prosthesis. Preferably, the
mill blank of the present invention is also substantially free of
material discontinuities larger than about 1 millimeter. The mill
blank's surprising ability to pass a Thermal Shock Test is a result
of the relief of stress created during the curing process or proper
low stress curing wherein little or no stress is actually created
in the blank. Preferably low stress cure is performed by slow light
curing methods. Heat treatment following a fast cure has also been
surprisingly found to minimize internal stresses and provide the
mill blank the same ability to pass the Thermal Shock Test.
[0008] By careful selection of the resin and filler, additional
desirable material properties may be achieved, including superior
cuttability and hardness over commercially available blanks.
Preferred resins arc free radically curable, cationically curable,
or a combination thereof. Preferred fillers for the invention are
those that have been derived by sol-gel process.
DESCRIPTION OF THE INVENTION
[0009] Physical properties such as hardness and brittleness of
ceramics limit the usefulness as dental prosthetics. Metals also
have their shortcomings, as they are not aesthetic and may cause
concern regarding allergic reactions and the like. Thus, it would
be advantageous to have a prosthetic made from a strong and durable
material, where the material would be suitable for use in simple
and economical devices such as existing CAD/CAM manufacturing
equipment.
[0010] The present invention focuses on mill blanks made of highly
filled composite material, suitable for use in fabricating dental
prostheses, preferably using precision manufacturing equipment,
such as CAD/CAM milling devices.
[0011] The blanks of the present invention display excellent
performance in many characteristics important for dental or medical
use, including compressive strength, diametral tensile strength,
flexural strength, fracture toughness, hardness, resistance to
wear, wear on opposing dentition, durability, polishability, polish
retention, esthetics, thermal expansion, visual opacity, x-ray
opacity, impact strength, chemical durability, biocompatibility,
modulus, shelf life, patient comfort, ease-of-use, and structural
integrity.
[0012] A "composite" material refers to a hardenable (or hardened)
composition containing at least in part, a polymerizable (or
polymerized) resin(s), filler particles of one or more types, a
polymerization initiator, and any desired adjuvants. Composites of
the present invention can be multiple- or one-part compositions
where polymerization may be initiated by a variety of means
including heat, light, radiation, e-beam, microwave, or chemical
reaction.
[0013] It has been surprisingly found that a mill blank made of
composite material provides certain advantages and appealing
features over ceramic and porcelain blanks. Careful selection of
the combination of the components provides improved cuttability
performance. "Cuttability", as used herein, is a property of a mill
blank of the present invention, characterized by how well a blank
responds to contact from a cutting tool. For example, a measurement
may be performed by measuring the depth of a cut made by a cutting
tool when the tool is applied with a constant force for a fixed
period of time. Preferably, the cuttability value of a mill blank
is established by a standard test described herein, where the
Cuttability Value is determined by comparison to a standard
material.
[0014] It has also been surprisingly found that careful selection
of the resin, filler and adjuvants provides an advantageous
capability of the composite to be loaded with substantially high
amounts of filler. This filler loading translates into improved
durability, wear, and hardness of the composite mill blank. The
addition of filler to a composition provides desirable levels of
viscosity for material processing and strength for durability of
the finished product. "Wear", as used herein, is also a property of
a mill blank of the present invention that can be characterized by
compressive strength and diametral tensile strength. Hardness can
be characterized by a Barcol Hardness measurement. It is desirable
for a dental prosthetic to have a high resistance to wear and a
high degree of hardness in order for it to maintain its intended
shape and integrity as well as be useful in the oral environment.
However, it is also desireable that the prosthetic material not
unduly wear opposing or surrounding dentition.
[0015] A further advantage the present invention has over ceramic
mill blanks is the ease of finishing. A practitioner would have the
ability, if necessary, to repair or modify a prosthetic made from
the present invention's composite composition much more easily than
if the repair had to be made on a ceramic or porcelain prosthetic.
Ideally, like materials would be used to repair a prosthetic in the
oral environment, materials appropriate for repairing the instant
prosthetic may be cured by radiant energy within the oral
environment. In contrast, ceramics require firing and sintering at
extremely high temperatures (typically greater than 700.degree. C.)
and therefore a repair material made of ceramic is not useful in
the mouth.
[0016] The polymeric resin and filler of the present invention are
preferably selected such that the resulting mill blank has a Barcol
Hardness that is greater than or equal to the Barcol Hardness of a
Fumed Silica Mill Blank Standard. More preferably, the mill blank
has a Barcol Hardness that is about 5% greater than the Barcol
Hardness of a Fumed Silica Mill Blank Standard, and most preferably
about 15% greater. Preferably, the polymeric resin and filler of
the present invention are selected such that the Cuttability Value
is about 30% greater than the Cuttability Value of a Fumed Silica
Mill Blank Standard, more preferably 50% greater, and most
preferably 100% greater. The Fumed Silica Mill Blank Standard is a
mill blank made from bis-GMA TEGDMA resin loaded with silane
treated fumed silica filler, such as the filler available under the
trade name AEROSIL OX50 (Degussa Corporation, Pigments Division,
Teterboro, N.J.). The fumed silica filler has an average primary
particle size of 40 nanometers (nm), a surface area of 50.+-.15
m.sup.2/g as measured by DIN 66131, pH value of 3.7-4.7 via ASTM
D1208, purity of greater than 99.8% SiO.sub.2 and has a tap density
of approximately 130 g/l per ISO 787/.times.1 synthesized via
continuous flame hydrolysis of SiCl.sub.4.
[0017] As used herein, "curable" and "polymerizable" are used
interchangeably.
[0018] Polymerizable resins suitable for use in the dental
composite mill blank of the present invention are hardenable
organic resins having sufficient strength, hydrolytic stability,
and non-toxicity to render them suitable for use in the oral
environment. Preferably, the resin is made from a material
comprising a free radically curable monomer, oligomer, or polymer,
or a cationically curable monomer, oligomer, or polymer, or both.
Alternatively, the resin may be made from a material comprising a
monomer, oligomer or polymer comprising both a free radically
curable functionality and a cationically curable functionality.
[0019] A particularly preferred polymerizable resin for use in the
present invention is a mixture of two free radically curable
monomers, namely, diglycidylmethacrylate of Bisphenol A (frequently
referred to as "Bis-GMA") and triethyleneglycol dimethacrylate
(frequently referred to as "TEGDMA"). Such a material is available
commercially under the trade name 3M Restorative.TM. Z100 (3M Co.,
St. Paul, Minn.). This particular resin creates unexpectedly
preferred cutting and milling characteristics during the production
of a dental prosthetic.
[0020] Other preferred polymerizable resins containing free
radically curable functionalities include acrylates and
methacrylates commonly used in contemporary dental composites e.g.
2,2-bis[4-(2-hydroxy-3-methacryloy- loxypropoxy)phenyl]propane
(bisGMA); triethyleneglycol dimethacrylate (TEGDMA);
2,2-bis[4-(2-methacryloyloxyethoxy)-phenyl]propane (bisEMA);
2-hydroxy ethyl methacrylate (HEMA); urethane dimethacrylate (UDMA)
and combinations thereof.
[0021] Resins made from cationically curable material suitable for
use in the present invention include epoxy resins. Epoxy resins
impart high toughness to composites, a desirable feature for
composite mill blanks. Epoxy resins may optionally be blended with
various combinations of polyols, methacrylates, acrylates, or vinyl
ethers. Preferred epoxy resins include diglycidyl ether of
bisphenol A (e.g. EPON 828, EPON 825; Shell Chemical Co.),
3,4-epoxycyclohexylmethyl-3-4-epoxy cyclohexene carboxylate (e.g.
UVR-6105, Union Carbide), bisphenol F epoxides (e.g. GY-281;
Ciba-Geigy), and polytetrahydrofuran.
[0022] As used herein, "cationically active functional groups" is a
chemical moiety that is activated in the presence of an initiator
capable of initiating cationic polymerization such that it is
available for reaction with other compounds bearing cationically
active functional groups. Materials having cationically active
functional groups include cationically polymerizable epoxy resins.
Such materials are organic compounds having an oxirane ring, i.e.,
a group of the formula 1
[0023] which is polymerizable by ring opening. These materials
include monomeric epoxy compounds and epoxides of the polymeric
type and can be aliphatic, cycloaliphatic, aromatic or
heterocyclic. These materials generally have, on the average, at
least 1 polymerizable epoxy group per molecule, preferably at least
about 1.5 and more preferably at least about 2 polymerizable epoxy
groups per molecule. The polymeric epoxides include linear polymers
having terminal epoxy groups (e.g., a diglycidyl ether of a
polyoxyalkylene glycol), polymers having skeletal oxirane units
(e.g., polybutadiene polyepoxide), and polymers having pendent
epoxy groups (e.g., a glycidyl methacrylate polymer or copolymer).
The epoxides may be pure compounds or may be mixtures of compounds
containing one, two, or more epoxy groups per molecule. The
"average" number of epoxy groups per molecule is determined by
dividing the total number of epoxy groups in the epoxy-containing
material by the total number of epoxy-containing molecules
present.
[0024] These epoxy-containing materials may vary from low molecular
weight monomeric materials to high molecular weight polymers and
may vary greatly in the nature of their backbone and substituent
groups. Illustrative of permissible substituent groups include
halogens, ester groups, ethers, sulfonate groups, siloxane groups,
nitro groups, phosphate groups and the like. The molecular weight
of the epoxy-containing materials may vary from about 58 to about
100,000 or more.
[0025] Useful epoxy-containing materials include those which
contain cyclohexane oxide groups such as
epoxycyclohexanecarboxylates, typified by
3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,
3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexane
carboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate.
For a more detailed list of useful epoxides of this nature,
reference is made to the U.S. Pat. No. 3,117,099, which is
incorporated herein by reference.
[0026] Blends of various epoxy-containing materials are also
contemplated. Examples of such blends include two or more weight
average molecular weight distributions of epoxy-containing
compounds, such as low molecular weight (below 200), intermediate
molecular weight (about 200 to 10,000) and higher molecular weight
(above about 10,000). Alternatively or additionally, the epoxy
resin may contain a blend of epoxy-containing materials having
different chemical natures, such as aliphatic and aromatic, or
functionalities, such as polar and non-polar. Other types of useful
materials having cationically active functional groups include
vinyl ethers, oxetanes, spiro-orthocarbonates, spiro-orthoesters,
and the like.
[0027] The resin may be chosen from acrylate-based compositions
that contain a free radically active functional group. Materials
having free radically active functional groups include monomers,
oligomers, and polymers having one or more ethylenically
unsaturated groups. As used herein, "free radically active
functional group" is a chemical moiety that is activated in the
presence of an initiator capable of initiating free radical
polymerization such that it is available for reaction with other
compounds bearing free radically active functional groups. Suitable
materials contain at least one ethylenically unsaturated bond, and
are capable of undergoing addition polymerization. Such free
radically polymerizable materials include mono-, di- or poly-
acrylates and methacrylates such as methyl acrylate, methyl
methacrylate, ethyl acrylate, isopropyl methacrylate, n-hexyl
acrylate, stearyl acrylate, allyl acrylate, glycerol diacrylate,
glycerol triacrylate, ethyleneglycol diacrylate, diethyleneglycol
diacrylate. triethyleneglycol dimethacrylate, 1,3-propanediol
diacrylate, 1,3-propanediol dimethacrylate, trimethylolpropane
triacrylate, 1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol
diacrylate, pentaerythritol triacrylate, pentaerythritol
tetraacrylate, pentaerythritol tetramethacrylate, sorbitol
hexacrylate, bis[1-(2-acryloxy)]-p-ethoxyphen- yldimethylmethane,
bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylme- thane, and
trihydroxyethyl-isocyanurate trimethacrylate; the bis-acrylates and
bis-methacrylates of polyethylene glycols of molecular weight
200-500, copolymerizable mixtures of acrylated monomers such as
those in U.S. Pat. No. 4,652,274, and acrylated oligomers such as
those of U.S. Pat. No. 4,642,126; and vinyl compounds such as
styrene, diallyl phthalate, divinyl succinate, divinyl adipate and
divinylphthalate. Mixtures of two or more of these free radically
polymerizable materials can be used if desired.
[0028] If desired, both cationically active and free radically
active functional groups may be contained in a single molecule.
Such molecules may be obtained, for example, by reacting a di- or
poly-epoxide with one or more equivalents of an ethylenically
unsaturated carboxylic acid. An example of such a material is the
reaction product of UVR-6105 (available from Union Carbide) with
one equivalent of methacrylic acid. Commercially available
materials having epoxy and free-radically active functionalities
include the "Cyclomer" series, such as Cyclomer M-100, M-101, or
A-200 available from Daicel Chemical, Japan, and Ebecryl-3605
available from Radcure Specialties.
[0029] The resin can also include an acid functionality, such as
carboxylic acid, phosphoric and phosphonic acids. Examples of such
compounds include the aliphatic carboxy compounds, such as acrylic
acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid,
crotonic acid, aconitic acid, glutaconic acid, mesaconic,
citraconic acid, acid, tiglicinic acid, 2-chloroacrylic acid,
3-chloroacrylic acid, 2-bromoacrylic acid, 1-methacryloyl malonic
acid, 1-acryloyl malic acid, N-methacryloyl and N-acryloyl
derivatives of amino acids, and acids such as tartaric acid, citric
acid, malic acid that have been further functionalized with an
ethylenic functionality. For example, citric acid may be
ethylenically functionalized by substituting with an acryloyl or
methacryloyl functionality. These polymerizable groups may be
attached directly to the acid containing compound, or may be
optionally attached through a linking group. Preferred linking
groups include substituted or unsubstituted alkyl, alkoxyalkyl,
aryl, aryloxyalkyl, alkoxyaryl, aralkyl or alkaryl groups.
Particularly preferred linking groups comprise an ester
functionality and most particularly preferred linking groups
comprise an amide functionality.
[0030] Polymeric initiator systems for the above resins would no
longer be limited to systems which are compatible with the oral
environment as the bulk of the polymerization of the resin
constituents would occur outside of the patient's mouth, such as in
a manufacturing facility where the mill blanks may be produced.
Thus, many of the commonly known polymerization systems may be
employed, such as curing systems involving 2-part resins, heat,
radiation, redox reactions or combinations thereof. By having the
capability of employing various polymerization systems, waiting
time for the patient is drastically reduced, as those particular
steps would be completed in the manufacturing site or laboratory.
However, since a composite mill blank provides a practitioner the
opportunity to finish a prosthetic at chairside (i.e while the
patient waits), it is preferred that polymeric initiator systems
that are compatible with the oral environment are employed.
[0031] One class of useful initiators includes sources of species
capable of initiating both free radical and cationic
polymerization.
[0032] Preferred free radical polymerization systems contain three
components: an onium salt, a sensitizer, and a free radical donor.
Suitable salts include mixed ligand arene cyclopentadienyl metal
salts with complex metal halide ions, as described in "CRC Handbook
of Organic Photochemistry", vol II, ed. J. C. Scaiano, pp. 335-339
(1989). Preferably, the source is an onium salt such as a sulfonium
or iodonium salt. Of the onium salts, iodonium salts (e.g., aryl
iodonium salts) are particularly useful. The iodonium salt should
be soluble in the composition and preferably is shelf-stable,
meaning it does not spontaneously promote polymerization when
dissolved therein in the presence of the cationic polymerization
modifier and photosensitizer (if included). Accordingly, selection
of a particular iodonium salt may depend to some extent upon the
particular polymerizable reactants, cationic polymerization
modifiers, and sensitizers (if included).
[0033] Suitable iodonium salts are described in U.S. Pat. Nos.
3,729,313; 3,741,769; 4,250,053; 4,394,403; and 5,545,676, the
disclosures of which are incorporated herein by reference. The
iodonium salt can be a simple salt, containing an anion such as
Cl.sup.-, Br.sup.-, I.sup.-, C.sub.4H.sub.5SO.sub.3.sup.-, or
C(SO.sub.2CF.sub.3).sub.3.sup.-; or a metal complex salt containing
an antimonate, arsenate, phosphate, or borate such as
SbF.sub.5OH.sup.-, AsF.sub.6.sup.-, or
B(C.sub.6F.sub.5).sub.4.sup.-. Mixtures of iodonium salts can be
used if desired.
[0034] The initiation system may also include a sensitizer such as
a visible light sensitizer that is soluble in the polymerizable
composition. The sensitizer preferably is capable of absorbing
light having wavelengths in the range from about 300 to about 1000
nanometers.
[0035] Examples of suitable sensitizers include ketones, coumarin
dyes (e.g., ketocoumarins), xanthene dyes, acridine dyes, thiazole
dyes, thiazine dyes, oxazine dyes, azine dyes, aminoketone dyes,
porphyrins, aromatic polycyclic hydrocarbons, p-substituted
aminostyryl ketone compounds, aminotriaryl methanes, merocyanines,
squarylium dyes, and pyridinium dyes. Ketones (e.g., monoketones or
alpha-diketones), ketocoumarins, aminoarylketones, and
p-substituted aminostyryl ketone compounds are preferred
sensitizers. For applications requiring deep cure of
epoxy-containing materials (e.g., cure of highly filled
composites), it is preferred to employ sensitizers having an
extinction coefficient below about 100 lmole.sup.-1cm.sup.-1, more
preferably about or below 100 lmole.sup.-1cm.sup.-1, at the desired
wavelength of irradiation for photopolymerization. The
alpha-diketones are an example of a class of sensitizers having
this property, and are particularly preferred for dental
applications.
[0036] Examples of particularly preferred visible light sensitizers
include camphorquinione; glyoxal; biacetyl,
3,3,6,6-tetramethylcyclohexan- edione;
3,3,7,7-tetramethyl-1,2-cycloheptanedione; 3,3,8,8-tetramethyl-1,2-
-cyclooctanedione; 3,3,18,18-tetramethyl-1,2-cyclooctadecanedione;
dipivaloyl; benzil; furil; hydroxybenzil; 2,3-butanedione;
2,3-pentanedioone; 2,3-hexanedione; 3,4-hexanedione;
2,3-heptanedione; 3,4-heptanedione; 2,3-octanedione;
4,5-octanedione; and 1,2-cyclohexanedione; Of these, camphorquinone
is the most preferred sensitizer.
[0037] The third component in the free radical polymerization
system is the electron donor. A wide variety of donors can be
employed. The donor is soluble in the resin component of the mill
blank processor and should meet the oxidation potential (E.sub.ox)
limitation discussed in more detail below. Preferably, the donor
also is selected based in part upon shelf stability considerations.
Accordingly, a selection of a particular donor may depend in part
on the resin component, iodonium salt and sensitizer chosen.
Suitable donors are capable of increasing the speed of cure or
depth of cure of a composition of the invention upon exposure to
light of the desired wavelength. Also, the donor has an E.sub.ox
greater than zero and less than or equal to E.sub.ox
(p-dimethoxybenzene). Preferably E.sub.ox (donor) is between about
0.5 and 1 volts against a saturated calomel electrode. E.sub.ox
(donor) values can be measured experimentally, or obtained from
references such as N. L. Weinburg, Ed., Technique of Electroorganic
Synthesis Part II Techniques of Chemistry, Vol. V (1975), and C. K.
Mann and K. K. Barnes, Electrochemical Reactions in Nonaqueous
Systems (1970).
[0038] In the cases where cationic polymerization occurs, it may be
desirable to delay the onset of polymerization. For example, in the
case of a hybrid composition that includes both free radically
active functional groups and cationically active functional groups,
it may be desirable to use an initiation system suitable for
initiating both free radical and cationic polymerization which is
designed such that for a given reaction temperature,
photoinitiation of free radical polymerization occurs after a
finite induction period T.sub.1 and photoinitiation of cationic
polymerization occurs after a finite induction period T.sub.3,
where T.sub.3 is greater than T.sub.1. T.sub.1 and T.sub.3 are
measured relative to administration of the first dose of actinic
radiation which occurs at T.sub.0. Such initiation systems are
described in Oxman et al., "Compositions Featuring Cationically
Active and Free Radically Active Functional Groups, and Methods for
Polymerizing Such Compositions," filed Jun. 5, 1998 and bearing
U.S. Ser. No. 09/092,550, which is assigned to the same assignee as
the present application and hereby incorporated by reference. As
described therein, the photoinitiation system includes: (i) a
source of species capable of initiating free radical polymerization
of the free radically active functional group and cationic
polymerization of the cationically active functional group; and
(ii) a cationic polymerization modifier. The amount and type of
modifier are selected such that in the absence of the modifier,
initiation of cationic polymerization under the same irradiation
conditions occurs at the end of a finite induction period T.sub.2
(also measured relative to T.sub.0), where T.sub.2 is less than
T.sub.3.
[0039] The induction periods (T.sub.1, T.sub.2, and T.sub.3) can be
measured using differential scanning calorimetry. Following the
first irradiation event at T.sub.0, the enthalpy of the reaction is
measured as a function of time. Both initiation of free radical
polymerization and initiation of cationic polymerization result in
an increase in enthalpy, observed as a pair of separate peaks when
data is charted on a graph. The time at which initiation occurs is
taken to be the time at which the enthalpy begins to rise.
[0040] The cationic polymerization modifier preferably has a
photoinduced potential less than that of 3-dimethylaminobenzoic
acid in a standard solution of 2.9.times.10.sup.-5 moles/g
diphenyliodonium hexafluoroantimonate and 1.5.times.10.sup.-5
moles/g camphorquinone in 2-butanone, measured according to the
procedure described in the aforementioned Oxman et al. application.
In general, useful cationic polymerization modifiers are typically
bases having pK.sub.b values, measured in aqueous solution, of less
than 10. Examples of classes of suitable cationic polymerization
modifiers include aromatic amines, aliphatic amines, aliphatic
amides, aliphatic ureas; aliphatic and aromatic phosphines, and
salts of organic or inorganic acids (e.g.., salts of sulfinic
acid). Specific examples include 4-(dimethylamino)phenylacetic
acid, dimethylaminophenethanol, dihydroxy p-toluidine,
N-(3,5-dimethylphenyl)-N,N-dimethanolamine,
2,4,6-pentamethylaniline, dimethylbenzylamine,
N,N-dimethylacetamide, tetramethylurea, N-methyldiethanolamine,
triethylamine, 2-(methylamino)ethanol, dibutylamine,
diethanolamine, N-ethylmorpholine, trimethyl-1,3-propanediamine,
3-quinuclidinol, triphenylphosphine, sodium toluene sulfinate,
tricyclohexylphosphine, N-methylpyrollidone, and
t-butyldimethylaniline. These modifiers may be used alone or in
combination with each other, or with a material having photoinduced
potential greater than that of 3-dimethylaminobenzoic acid in a
standard solution of 2.9.times.10.sup.-5 moles/g diphenyliodonium
hexafluoroantimonate and 1.5.times.10.sup.-5 moles/g camphorquinone
in 2-butanone; an example of such a material is ethyl
4-(dimethylamino)benzoate ("EDMAB").
[0041] In other cases, it may be desirable to accelerate initiation
of cationic polymerization. For example, in certain hybrid
compositions it may be desirable to achieve near-simultaneous
initiation of the free radically active functional groups and the
cationically active functional groups. Examples of suitable
initiation systems for accomplishing this objective are described
in Oxman et al., U.S. Ser. No. 08/838,835 filed Apr. 11, 1997
entitled "Ternary Photoinitiator System for Curing of Epoxy/Polyol
Resin Compositions" and Oxman et al., U.S. Ser. No. 08/840,093
filed Apr. 11, 1997 entitled "Ternary Photoinitiator System for
Curing of Epoxy Resins," both of which are assigned to the same
assignee as the present application and hereby incorporated by
reference. As described therein, the photoinitiator system includes
an iodonium salt (e.g., an aryliodonium salt), a visible light
sensitizer (e.g., camphorquinone), and an electron donor. The
systems have a photoinduced potential greater than or equal to that
of 3-dimethylaminobenzoic acid in a standard solution of
2.9.times.10.sup.-5 moles/g diphenyliodonium hexafluoroantimonate
and 1.5.times.10.sup.-5 moles/g camphorquinone in 2-butanone,
measured according to the procedure described in the aforementioned
Oxman et al. applications. An example of a suitable electron donor
is ethyl 4-(dimethylamino)benzoate ("EDMAB").
[0042] In the case of hybrid compositions that include both free
radically active functional groups and cationically active
functional groups, it may be desirable to use one initiation system
for free radical polymerization and a separate initiation system
for cationic polymerization. The free radical polymerization
initiation system is selected such that upon activation, only free
radical polymerization is initiated.
[0043] One class of initiators capable of initiating polymerization
of free radically active functional groups, but not cationically
active functional groups, includes conventional chemical initiator
systems such as a combination of a peroxide and an amine. These
initiators, which rely upon a thermal redox reaction, are often
referred to as "auto-cure catalysts." They are typically supplied
as two-part systems in which the reactants are stored apart from
each other and then combined immediately prior to use.
[0044] A second class of initiators capable of initiating
polymerization of free radically active functional groups, but not
cationically active functional groups, includes free
radical-generating photoinitiators, optionally combined with a
photosensitizer or accelerator. Such initiators typically are
capable of generating free radicals for addition polymerization at
some wavelength between 200 and 800 nm. Examples include
alpha-diketones, monoketals of alpha-diketones or ketoaldehydes,
acyloins and their corresponding ethers, chromophore-substituted
halomethyl-s-triazines, and chromophore-substituted
halomethyl-oxadiazoles.
[0045] A third class of initiators capable of initiating
polymerization of free radically active functional groups, but not
cationically active functional groups, includes free
radical-generating thermal initiators. Examples include peroxides
and azo compounds such as azobisisobutyronitrile (AIBN). A
preferred thermal initiator is benzoyl peroxide.
[0046] Dual initiation systems include a separate photoinitiation
system for initiating polymerization of the cationically active
functional groups. The cationic initiation system is selected such
that activation of the free radical initiation system does not
activate the cationic initiation system. Examples of suitable
cationic photoinitiation systems for a dual initiation system
composition include the onium salts and mixed ligand arene
cyclopentadienyl metal salts with complex metal halide ions
described above. Also suitable are cationic initiators that are
activated by heat, or part cationic initiators. Such systems are
described in "Chemistry and Technology of Epoxy Resins," ed. by B.
Ellis, Chapman & Hall, 1993.
[0047] A filler for the present invention is preferably a finely
divided material that may optionally have an organic coating.
Suitable coatings include silane or encapsulation in a polymeric
matrix.
[0048] Fillers may be selected from one or more of any material
suitable for incorporation in compositions used for medical
applications, such as fillers currently used in dental restorative
compositions and the like. The filler is finely divided and
preferably has a maximum particle diameter less than about 50
micrometers and an average particle diameter less than about 10
micrometers. The filler can have a unimodal or polymodal (e.g.,
bimodal) particle size distribution. The filler can be an inorganic
material. It can also be a crosslinked organic material that is
insoluble in the polymerizable resin, and is optionally filled with
inorganic filler. The filler should in any event be non-toxic and
suitable for use in the mouth. The filler can be radiopaque,
radiolucent or non-radiopaque.
[0049] Examples of suitable inorganic fillers are
naturally-occurring or synthetic materials such as quartz, nitrides
(e.g., silicon nitride); glasses containing, for example Ce, Sb,
Sn, Zr, Sr, Ba, An, La, Y and Al; colloidal silica; feldspar;
borosilicate glass; kaolin; talc; titania; and zinc glass; low Mohs
hardness fillers such as those described in U.S. Pat. No.
4,695,251; and submicron silica particles (e.g., pyrogenic silicas
such as the "Aerosil" Series "OX 50", "130", "150" and "200"
silicas sold by Degussa and "Cab-O-Sil M5" silica sold by Cabot
Corp.). Examples of suitable organic filler particles include
filled or unfilled pulverized polycarbonates, polyepoxides,
polyaramid, and the like. Preferred filler particles are quartz,
barium glass, and non-vitreous microparticles of the type described
in U.S. Pat. No. 4,503,169. Metallic fillers may also be
incorporated, such as particulate metal filler made from a pure
metal such as those of Groups IVA, VA, VIA, VIIA, VIII, IB, or IIB,
aluminum, indium, and thallium of Group IIIB, and tin and lead of
Group IVB, or alloys thereof. Conventional dental amalgam alloy
powders, typically mixtures of silver, tin, copper, and zinc, may
also optionally be incorporated. The particulate metallic filler
preferably has an average particle size of about 1 micron to about
100 microns, more preferably 1 micron to about 50 microns. Mixtures
of these fillers are also contemplated, as well as combination
fillers made from organic and inorganic materials.
Fluoroaluminiosilicate glass fillers, either untreated or silanol
treated, are particularly preferred. These glasses have the added
benefit of releasing fluoride at the site of dental work when
placed in the oral environment.
[0050] Optionally, the surface of the filler particles may be
treated with a surface treatment such as a coupling agent in order
to enhance the bond between the filler and the polymerizable resin.
The coupling agent may be functionalized with reactive curing
groups, such as acrylates, methacrylates, epoxies, and the like.
Examples of coupling agents include
gamma-methacryloxypropyltrimethloxysilane,
gamma-mercaptopropyltriethoxys- ilane,
gamma-aminopropyltrimethoxysilane,
beta-(3,4-epoxycyclohexyl)ethyl-- trimethoxysilane,
gamma-glycidoxypropyltrimethoxysilane, and the like.
[0051] Preferable fillers are those that have been derived through
sol-gel processes. It has been surprisingly found that sol-gel
derived fillers impart superior machining characteristics to
composites used for dental mill blanks. Moreover, it was
surprisingly found that sol-gel derived fillers may be incorporated
into resins at higher levels than conventional milled glass
fillers. Sol-gel processes for making fillers are described, for
example, in U.S. Pat. No. 4,503,169 (Randklev) and by Noritake et
al. in GB Patent 2291053 B. As used herein, "sol-gel" refers to any
method of synthesizing inorganic particles that comprises a step
wherein at least one of the precursors is an aqueous or organic
dispersion, sol, or solution.
[0052] A preferred method for preparing the sol-gel derived
microparticles or fillers for the present invention involves the
combining of (1) an aqueous or organic dispersion or sol of
amorphous silica with (2) an aqueous or organic dispersion, sol, or
solution of the desired radiopacifying ceramic metal oxide or a
precursor organic or inorganic compound which is calcinable to the
desired radiopacifying ceramic metal oxide. For brevity, the
aforementioned dispersion or sol of silica will be sometimes
referred to hereafter as the "silica starting material", and the
aforementioned dispersion, sol, or solution of the radiopacifying
ceramic metal oxide or precursor compound will sometimes be
referred to hereafter as the "ceramic metal oxide starting
material". The mixture of silica starting material and ceramic
metal oxide starting material is dried to a solid and fired to form
microparticles. Comminution may optionally be done at any stage.
The microparticles can then be combined with an appropriate resin
to form a composite of the invention.
[0053] Although either aqueous or organic silica starting materials
can be employed in the sol-gel method just described, aqueous
silica starting materials are preferred for reasons of economy.
Suitable aqueous silica starting materials preferably contain
colloidal silica at concentrations of about 1 to 50 weight percent,
more preferably 15 to 35 weight percent. Suitable organic silica
starting materials include organo-sols containing colloidal
dispersions of silica in organic solvents (preferably
water-miscible polar organic solvents) such as ethanol, normal or
isopropyl alcohol, ethylene glycol, dimethylformamide and the
various "Cellosolve" glycol ethers. The size of the colloidal
silica particles in the silica starting material can vary, e.g.,
from 0.001 to 0.1 micrometers, preferably about 0.002 to 0.05
micrometers. Preferred sol-gel filters are those comprising
zirconia and silica.
[0054] Another class of useful fillers are bioactive glasses and
ceramics. Examples include Bioglass.TM. (U.S. Biomaterials;
Alachua, Fla.); Bio-Gran.TM. (Orthovita; Malvern, Pa.); Cerabone
A-W (Nippon Electric Glass: Japan); glasses comprising calcium
oxide, silicon oxide, and phosphorous oxide; and the various phases
of calcium phosphate including hydroxyapatite, monetite, brushite,
and whitlockite.
[0055] Optionally, dental mill blanks may contain
fluoride-releasing agents. The benefits of fluoride in reducing the
incidence of caries are well established. Thus fluoride released
from dental prostheses would be advantageous. Fillers that impart
fluoride release include ZnF.sub.2, YbF.sub.2, rare-earth
fluorides, SnF.sub.2, SnF.sub.4, ZrF.sub.4, NaF, CaF.sub.2,
YF.sub.3, and fluoroaluminosilicate glasses. Rare earths are the
elements of atomic weights 57-71, inclusive.
[0056] The fluoride-releasing material of the present invention may
be naturally occuring or synthetic fluoride minerals, fluoride
glass such as fluoroaluminosilicate glass, simple and complex
inorganic fluoride salts, simple and complex organic fluoride salts
or combinations thereof. Optionally these fluoride sources can be
treated with surface treatment agents.
[0057] Examples of the fluoride-releasing material are
fluoroaluminosilicate glasses described in U.S. Pat. No.
4,3814,717, which may be optionally treated as described in U.S.
Pat. No. 5,332,429, the disclosures of which are both incorporated
by reference herein.
[0058] The fluoride releasing material may optionally be a metal
complex described by formula
M(G).sub.g(F).sub.n or M(G).sub.g(ZF.sub.m).sub.n
[0059] where M represents an element capable of forming a cationic
species and having a valency of 2 or more,
[0060] G is an organic chelating moiety capable of complexing with
the element M,
[0061] Z is hydrogen, boron, nitrogen, phosphorus, sulfur,
antimony, arsenic,
[0062] F is a fluoride atom, and
[0063] g, m and n are at least 1.
[0064] Examples of preferred M elements are the metals of groups
IIA, IIIA, IVA, and transition and inner transition metal elements
of the periodic table. Specific examples include Ca.sup.+2,
Mg.sup.+2, Sr.sup.+2, Zn.sup.+2, Al.sup.+3, Zr.sup.+4, Sn.sup.+2,
Yb.sup.+3, Y.sup.+3, Sn.sup.+. Most preferably, M is Zn.sup.+2.
[0065] Compositions of the present invention may optionally
comprise at least two sources of fluoride. The first source is the
fluoride-containing metal complex as described above. The second
source is a fluoride-releasing fluoroaluminosilicate glass. With
the use of both materials, excellent fluoride release is provided
both in the initial period and over the long term use of the
composition.
[0066] The mill blanks of the present invention may optionally
comprise additional adjuvants suitable for use in the oral
environment, including colorants, flavorants, anti-microbials,
fragrance, stabilizers, and viscosity modifiers. Other suitable
adjuvants include agents that impart fluorescence and/or
opalescence.
[0067] As the polymer resin is initially a paste, any of the
standard methods for compounding paste may be used to form the
composite material. Preferably, methods which optimize mixing and
minimize the incidence of material discontinuities such as voids
and cracks should be instituted. For example, application of vacuum
or pressure can be beneficial during any stage of compounding,
forming or curing the paste. Pressure can be applied by various
means, including isostatic, uniaxial, centrifugal, impact, or
pressurized gas. Heat may optionally be applied at any stage.
However, during curing, a uniform temperature in the sample is
preferably maintained to minimize internal stresses.
[0068] During compounding and extrusion, methods that minimize and
preferably eliminate material discontinuities such as voids or
bubbles are preferred. Preferably the blanks of the present
invention are substantially free of discontinuities in the material
that are larger than about 1 millimeter. More preferably,
fabrication techniques are employed such that the material is
substantially free of discontinuities in the material that are
larger than about 0.1 millimeter. Most preferably, blanks of the
present invention are substantially free of discontinuities in the
material that are larger than about 0.01 millimeter.
[0069] Blanks of composite may be made in any desired shape or
size, including cylinders, bars, cubes, polyhedra, ovoids, and
plates. Molds may be made of a variety of materials, including
stainless steel, cobalt alloys, nickel alloys, aluminum alloys,
plastic, glass, ceramic, or combinations thereof. Alternatively, a
variety of methods for forming and shaping the blanks into any
desired configuration can be employed, such as injection molding,
centrifugal casting and extrusion. During polymerization and
curing, compression from springs or other means may optionally be
used to reduce internal stresses. Preferably, the outer surface of
the blank is smooth and non-tacky.
[0070] Curing may be performed in one or multiple stage methods. In
a two-stage process, it is preferred that initial curing provide a
material sufficient to sustain the forces of milling or carving.
The second curing stage, therefore, can be performed on the
composite after a prosthetic is milled from a blank.
[0071] Cured blocks may be attached to mounting stubs to facilitate
affixation of the blank in a milling machine. Mounting stubs
function as handles from which a blank is held by as it is milled
by a machine.
[0072] Various means of milling the mill blanks of the present
invention may be employed to create custom-fit dental prosthetics
having a desired shape and morphology. The term "milling" as used
herein means abrading, polishing, controlled vaporization,
electronic discharge milling (EDM), cutting by water jet or laser
or any other method of cutting, removing, shaping or carving
material. While milling the blank by hand using a hand-held tool or
instrument is possible, preferably the prosthetic is milled by
machine, including computer controlled milling equipment. However,
a preferred device to create a prosthetic and achieve the full
benefits of the composite material of the present invention is to
use a CAD/CAM device capable of milling a blank, such as the Sirona
Cerec 2 machine. By using a CAD/CAM milling device, the prosthetic
can be fabricated efficiently and with precision. During milling,
the contact area may be dry, or it may be flushed with a lubricant.
Alternatively, it may be flushed with an air or gas stream.
Suitable lubricants are well known in the art, and include water,
oils, glycerine, ethylene glycols, and silicones. After machine
milling, some degree of finishing, polishing and adjustment may be
necessary to obtain a custom fit in to the mouth and/or aesthetic
appearance.
[0073] A milled dental prosthetic can be attached to the tooth or
bone structure with conventional cements or adhesives or other
appropriate means such as glass ionomer, resin cement, zinc
phosphate, zinc polycarboxylate, compomer, or resin-modified glass.
In addition, material can optionally be added to the milled
prosthetic for various purposes including repair, correction, or
enhancing esthetics. The additional material may be of one or more
different shades or colors. The added material may be composite,
ceramic, or metal. A light-cured composite is preferred.
[0074] To fabricate blanks of the present invention, the following
steps are preferably performed: Compound the paste; extrude the
paste into a mold; cure the paste via heat, light, microwave,
e-beam or chemical cure; remove the blank from its mold and trim
excess if necessary; and optionally, mount on a holder stub if
necessary. A preferred method of making the dental mill blank of
the present invention comprises the steps of a) mixing a paste
comprising a resin and a filler, b) shaping the paste into a
desired configuration, c) minimizing material discontinuities from
the paste, d) curing the paste into a blank, and e) relieving
internal stresses in the blank.
[0075] Optionally, where a mold is used to shape the paste, excess
paste material can be trimmed from the mold. The cured past is then
removed from the mold. Another optional step that can be performed
in making a mill blank is to mount a handle onto the cured paste.
Preferably, the handle is a holder stub.
[0076] Mill blanks of the present invention may be cured in a
manner such that the material contains minimal internal stresses.
This may be accomplished, for example, by application of pressure
on the composite material during the curing process. In the
alternative, the avoidance of internal stress imparted by shrinkage
may be obtained by selection of mill blank components such that the
overall composition exhibits little or no shrinkage during cure. A
preferred curing method entails the use of light to fast cure the
composite. During this fast cure, the temperature may optionally be
adjusted and controlled. The fast cure technique requires a
subsequent heat treatment to effectuate stress relief. Heat
treatment of a cured blank requires the blank be heated for a
sufficient time and at a sufficient temperature to effectively
eliminate internal stresses such that the blank passes a Thermal
Shock Test. Preferably, the blank is raised to a temperature of at
or above Tg (glass transition temperature) of the resin component
of the blank. More preferably, the blank is heated to above Tg and
is maintained at that temperature for at least about one-half
hour.
[0077] A preferred method of heat treatment for a cured blank is to
place the blank in an oven and raise the oven temperature to about
the Tg of the resin component of the blank at a rate of about, for
example, 3-5.degree. C. minute. Upon completing heat treatment, the
blank is allowed to equilibrate to room temperature either by
immersion into room temperature water or by slowly cooling via
ambient temperature. Alternatively, the heat treatment may be
accomplished by placing the blank in a preheated oven and
maintaining the oven temperature at or above Tg for a sufficient
time to eliminate internal stresses in the composite blank.
[0078] Another method of curing the blanks of the present invention
is through a slow cure using low intensity light. In this
technique, cure is accomplished over a long period of time to
minimize internal stresses, such that the resulting cured blank
will pass a Thermal Shock Test. Preferably, the cure takes place
over a time period of about 24 hours, however it is envisioned that
with proper equipment and procedure, curing times may be shorter.
Progress of this cure may be evaluated by ascertaining a sample of
the material at predetermined times over the cure time and
evaluating progress of cure by Barcol Hardness measurement.
[0079] Other techniques may be used to relieve the stress of mill
blanks of the present invention, including application of energy in
a form other than heat, such as sonic or microwave energy.
[0080] A preferred method for testing the existence of residual
internal stress of a composite mill blank is the Thermal Shock Test
involving the use of liquid Nitrogen. Residual internal stress is
undesirable because it adversely affects the structural integrity
of the blank and increases the likelihood of later catastrophic
failure of the blank or the ultimate prosthetic. To conduct such a
test, commercially available liquid nitrogen is poured into a 250
milliliter (mL) Dewar flask. A fully cured mill blank is immersed
in the liquid nitrogen until excessive bubbling subsides. If the
blank explodes or experiences a large crack while immersed in the
liquid nitrogen, the blank fails the Test. If the blank does not
explode or did not appear to have a substantial crack, the mill
blank must then be inspected for internal stress fractures
(cracks). As used herein, a "crack" is defined as fissure where
material has separated or broken away.
[0081] To inspect for cracks from internal stresses, the mill blank
should be removed from the flask and brought to room temperature.
This may be done slowly by immersing the blank in room temperature
water. The blank can then be dried off and inspected for cracking.
If, after up to about one hour upon the blank returning to room
temperature, the blank cracks, this result also indicates a failing
score for the Test.
[0082] It is essential for proper test results that the test
material be free of any gross interphase between two or more
materials. Thus, if a mill blank is attached to a stub, the
mounting stub must be removed prior to immersing the blank in the
liquid nitrogen-filled flask. Similarly, if a mill blank comprises
more than one piece of material, whether it is of the same or
different composition as the test material, then the material that
will not ultimately be milled into a prosthetic must be removed
prior to thermal shock testing.
[0083] Inspection may first be done with an unaided human eye,
looking specifically for cracks that may have propagated to the
blank's surface. However, while visual inspection is useful for
observing cracks and discontinuities at or near the surface, it is
desirable to have a nondestructive method for detecting these
defects throughout the entire sample. Thus, further inspection is
preferably conducted using an x-ray device that can reveal internal
cracks and discontinuities. Inspection may be alternatively
performed by other methods known in the art, such as ultrasonic
imaging, CAT scans, NMR imaging, or eddy current measurements.
[0084] X-ray radiography is preferably used to detect cracks and
discontinuities less than about 1 mm in size. This method can be
used to measure the incidence of cracks and discontinuities in a
blank or a batch of blanks, and furthermore as a tool for
optimizing the fabrication process to minimize the incidence of
cracks and discontinuities. This method is particularly useful as a
quality test, wherein blanks that have detectable cracks or
discontinuities are disqualified for use.
[0085] X-ray radiography comprises exposing the block to x-rays
while simultaneously recording them opposite the source. Methods,
materials, and equipment for such radiography are well known in the
medical art. The x-ray energy and exposure times are appropriately
adjusted to the material and geometries of the blanks to be
inspected.
[0086] The following examples are meant to be illustrative of the
invention and should not meant to limit the scope or range of the
invention. Unless otherwise indicated, all parts and percentages
are by weight, and all molecular weights are weight average
molecular weights.
[0087] TEST METHODS
[0088] The following methods were used to evaluate the examples and
samples.
[0089] Thermal Shock Test: Liquid Nitrogen Dip Test
[0090] A 250 mL Dewar flask (Pope Scientific, .TM.8600) was filled
with 200 mL, of industrial grade liquid nitrogen. Samples
(composite mill blanks) were immersed in the liquid nitrogen until
excessive bubbling subsided (approximately two minutes). The blanks
were removed from the liquid nitrogen and allowed to equilibrate to
room temperature by immersing the blanks in room temperature water.
The samples were dried off and visually inspected for cracks.
[0091] In the case of certain materials that are peculiarly
sensitive to the Thermal Shock Test, special sample handling
procedures may be required to assure appropriate evaluation of
internal stress as compared to other factors. For example, some
mill blank materials may by hydrophilic to the point of taking up
atmospheric water during the cooling process of the heat treatment.
The presence of such atmospheric water, particularly in a
non-uniform concentration throughout the mill blank, may result in
test failure even though the sample does not possess internal
stress imparted by polymerization shrinkage. Maintenance of such
samples in a desiccated environment (e.g. during the cooling step
of the heat treatment) before the Thermal Shock Test will assure
that an otherwise acceptable mill blank does not show a false
failure of the Thermal Shock test. Alternative evaluation
techniques may be required to show that certain materials are
sufficiently free of internal stress so that they would pass the
Thermal Shock Test absent the peculiarity of the materials that
makes such passage impossible.
[0092] Barcol Hardness
[0093] Hardness of a cured sample was measured using a "Barber
Coleman Impressor" Model GYZJ 934-1 (Barber Coleman; Rockford,
Ill.).
[0094] Cuttability Value (used for evaluating Samples 1-10)
[0095] A Unitek.TM. electrical handpiece (model No.738-151, 3M
Unitek, Monrovia, Calif.) was clamped at its base such that it was
level and pivoted freely about its base. Guides were placed to
prevent sideways motion of the handpiece. A 151.8 g weight was
suspended from the neck of the handpiece 10 centimeters (cm) from
the base. The diamond rested on a mill blank secured to a platform;
the cutting tool was 17.5 cm from the handpiece base.
[0096] A CEREC.TM. cylinder diamond 1.6 millimeters (mm) in
diameter (Sirona Dental Systems; Bensheim, Germany) was secured in
the handpiece. The length of contact between the diamond and the
sample was 5 mm. This 5 mm diamond segment was allowed to rest on
the block. The handpiece was operated at its top speed
(approximately 20,000 rpm) for 60 seconds .+-.1 second. The diamond
and work area was flushed continuously with deionized water. At
least three cuts were made on each block. A STARRETT 721 Electronic
Digital Caliper (L. S. Starrett Co.; Athol, Mass.) was used to
measure the height of the block adjacent to each cut and the
distance from the botttom of the cut to the opposite edge of the
block. The depth of the cut was calculated from the difference of
these two measurements. A new diamond was used to test each
block.
[0097] X-Ray Inspection
[0098] X-ray radiography was performed on a Profexray(TM) Rocket
300 X-ray unit (Litton Industries, Des Plaines, Ill.). 3M
Diagnostic Imaging Film, Ultra Detail Plus, Rare Earth Veterinary
X-ray type (3M, St. Paul, Minn.) was used to record the x-ray
image; the film was developed with a 3M XT 2000 Film Processor (3M,
St. Paul, Minn.). The samples were set directly on the film
container, resulting in a 1:1 magnification. Settings of 300 mA, 80
kV were used; images were taken at various exposure times.
[0099] The resulting radiographs were viewed on a x-ray illuminator
unit, and examined for the presence of any cracks or
discontinuities, e.g. voids, pores, or knit lines.
EXAMPLES
[0100] Preparatory Example 1
[0101] A light curable resin was compounded by dissolving and
mixing the following constituents:
[0102] 0.01 pbw Ethyl 4-dimethylaminobenzoate (EDMAB)
[0103] 0.0017 pbw camphorquinonie (CPQ)
[0104] 0.01 pbw 2-(2'-Hydroxy-5'-methylphenyl)Benzotriazole
("Tinuvin-P"; Ciba-Geigy Corp.; Hawthorne, N.Y.)
[0105] 0.006 pbw Diphenyl Iodonium Hexafluorophosphate
[0106] 0.4862 pbw
2,2-bis[4-(2-Hydroxy-3-methacryloyloxy-propoxy)phenyl]pr- opane
(Bis-GMA)
[0107] 0.4862 pbw triethyleneglycol dimethacrylate (TEGDMA)
Preparatory Example 2
[0108] A sol-gel derived filler was prepared as follows: 25.5 parts
silica sol ("Ludox" LS:E.I duPont de Nemours & Co.) were
acidified by the rapid addition of 0.255 parts concentrated nitric
acid. In a separate vessel, 12.9 parts ion-exchanged zirconyl
acetate (Magnesium Elektron, Inc.) were diluted with 20 parts
deionized water and the resultant solution acidified with 0.255
parts concentrated nitric acid. The silica sol was pumped into the
stirred zirconyl acetate solution and mixed for one hour. The
stirred mixture was filtered through a 3 micrometer filter followed
by a 1 micrometer filter. The filtrate was poured into trays to a
depth of about 25 mm and dried at 65.degree. C. in a forced air
oven for about 35 hours (hrs). The resultant dried material was
removed from the oven and tumbled through a rotary tube furnace
(Harper Furnace Corp.), which was preheated to 950.degree. C. The
calcined material was comminuted in a tumbling ball mill with 1/4"
alumina media until an average particle size of 0.5-1.2 micrometers
(as measured on a Micromeritics 5100 sedigraph) was achieved. The
mill charge included 75 parts calcined material, 3 parts methanol,
1.9 parts benzoic acid, and 1.1 parts deionized water. The filler
was then loaded into ceramic saggers and fired in an electric
furnace (L&L Furnace Corp.) in air at 880-900.degree. C. for
approximately 8 hrs. The fired filler was then ball-milled for 4-5
hrs. The mill charge included 32 parts fired filler, 1.25 parts
ethanol, and 0.3 parts deionized water. Next, the filler was passed
through a 74 micrometer nylon screen in a vibratory screener
(Vortisiv V/S 10010). The filler was then blended in a V-blender
(Patterson-Kelly Corp.) for about 15 min.
[0109] Silane treatment was as follows: 32 parts by weight (pbw) of
the filler was added to 48.94 pbw of deionized water under vigorous
stirring. Trifluoroacetic acid (TFAA), 0.104 pbw, was added slowly.
The pH was then adjusted to 3.0-3.3. by adding further 5 pbw
increments of TFAA. Then, 3.56 pbw of silane A-174 (Union Carbide;
Stamford, Conn.) was added. After stirring vigorously for 2 hrs a
solution of 0.0957 pbw of calcium hydroxide and 0.30 pbw of
deionized water was added and stirred an additional 5 minutes. The
slurry was poured into a tray lined with a plastic sheet, and then
dried in an oven set at 90.degree. C. for 13 hours. The cakes of
dried filler were crushed and passed through a 74 .mu.m screen.
Preparatory Example 3
[0110] A commerical barium glass with a nominal average particle
size of 0.7 .mu.m (type 8235, grade UF-0.7 (Schott Glaswerke;
Landshut Germany) was silane treated as follows: 2000 pbw of the
glass was added to 3242 pbw of deionized water under vigorous
stirring. 6.5 pbw of Trifluoroacetic acid (TFAA) was added slowly
and the pH was then adjusted to 3.0-3.3. by adding further 5 pbw
increments of TFAA. Then, 40.0 pbw of silane A-174 (Witco;
Greenwich, Conn.) was added. After stirring vigorously for 2 hours,
a solution of 5.98 pbw of calcium hydroxide and 200 g of deionized
water was added and stirred an additional 5 minutes. The slurry was
poured into a tray lined with a plastic sheet, and then dried in an
oven set at 90.degree. C. for 13 hours. The cakes of dried filler
were crushed and passed through a 74 .mu.m screen. The vendor
literature shows a coefficient of thermal expansion (CTE) of
4.7.times.10.sup.-6/.degree. C., refractive index of 155.1, density
of 3.04 g/cc, and a nominal composition of 30% BaO, 10%
B.sub.2O.sub.3, 10% Al.sub.2O.sub.3, and 50% SiO.sub.2 by
weight.
Preparatory Example 4
[0111] Fumed silica, Aerosil OX50 (Degussa AG; Frankfurt, Germany),
was silane treated as follows: A-174 (3.7 g) was added with
stirring to 50 g of deionized water acidified to pH 3-3.3 by
dropwise addition of trifluoroacetic acid. The resultant mixture
was stirred at about 25.degree. C. for 1 hour at which time 95 g of
OX-50 were added to the mixture with continued stirring for 4
hours. The slurry was poured into a plastic-lined tray and dried at
35.degree. C. for 36 hours. The silanol treated dried powder was
sieved through a 74 micrometer mesh screen.
Preparatory Example 5
[0112] Silane treated quartz was prepared as follows. Quartz rock
was heated to about 660.degree. C., quenched in water, drained,
then dried in a forced air oven for 16 hours at about 200.degree.
F. The quenched quartz was combined with quartz media into a mill
and tumbled for about 70 hours. The charge included 99 pbw quenched
quartz and 1 part methanol. The resulting particles were blended
with 0.1 wt. % carbon black in a V-blender for 1 hour, then fired
in an electric furnace at about 950.degree. C. for 4 hours. The
resulting particles were then passed through a 100 micrometer nylon
screen, and blended in a V-blender for 30 minutes. 34.68 pbw of
deionized water was adjusted to ph of 3.00-3.30 with about 0.1 pbw
of TFAA. A-174 silane, 1.74 pbw, was added and then vigorously
stirred for 1 hour. The quartz powder and Aerosil R972 fumed
SiO.sub.2 (Degussa), 62.43 and 1.01 pbw, respectively, were slowly
charged to the vessel. After 90 minutes of stirring, the slurry was
dried in tray at 60.degree. C. for 18 hours and then sieved through
a 70 .mu.m screen.
[0113] Curing and Heat Treatment Samples
[0114] Paste Samples A-I
[0115] A cartridge of composite material containing 500 g of Sample
9 was placed in an air oven ("Stabil-Therm"; Blue-M Electric Co.)
at 60.degree. C. for 2 hours. Clean glass tubes, marked to fill
height and plugged at the bottom end with silicone plugs, were
placed in the oven at 60.degree. C. for 1 hour.
[0116] The glass tubes were filled with the composite to the fill
line and returned to the air oven for 30 minutes. The filled tubes
were centrifuged (International Eqpt. Co.) at 2850 rpm for 60
minutes.
[0117] Fast Cure
[0118] Centrifuged paste contained in glass tubes were placed in an
800 mL beaker containing about 400 mL of room temperature water.
The tubes were placed in the beaker evenly spaced apart, with the
silicone plug at the bottom. The beaker was then placed in a
Suntest Box (Suntest Accelerated Exposure Table Unit #7011,
Germany) for 10 minutes. After curing, the tubes were removed from
the beaker and the silicone plugs were removed. The tubes were then
inverted from their original curing position and replaced in the
beaker for an additional 10 minutes of curing inside the Suntest
Box. The tubes were then removed from the Suntest Box and the glass
tubes were separated from the cured composite blank. One blank was
cut in half and inspected for discontinuties and cracks.
[0119] Slow Cure
[0120] The glass tubes containing centrifuged paste were set on a
Glow-Box (Model 12.12D, 22 Watts power consumption--available from
12R Co., Cheltenham, Pa.) for 24 hours with the silicone plugs at
the top. The Glow Box provided approximately 300 foot candles of
light output (measured by GE Light Meter Type 213; Cleveland,
Ohio). The silicone plugs were then removed. The tubes were
inverted from their original curing position and replaced on the
Glow Box for an additional 24 hours of curing. The tubes were then
removed from the Glow Box and the glass tubes were separated from
the cured composite blank. One blank was cut in half and inspected
for discontinuities and cracks. Barcol hardness measurements were
taken.
[0121] Post Cure
[0122] Blanks cured by both the slow and fast light cure methods
above were then post-cured in a Suntest Box for 10 minutes.
[0123] Heat Treatment
[0124] Fast light cured blanks were placed in a forced air oven
("Stabil-Therm," Blue-M Electric Co.). The oven was ramped up to
100.degree. C. at 4.degree. C./minute. The oven temperature was
maintained for 30 minutes. The oven was then shut off and the
blanks were permitted to equilibrate to ambient temperature before
they were tested.
[0125] Samples A through D were cured on the Glow-Box for the times
shown in Table 1. Approximately 3 mm were cut off from each end.
The samples were sectioned with a diamond saw into equidistant
sections of approximately 10 mm thickness to produce 5 interfaces.
The final dimension of each section was 14 mm.times.10 mm. Barcol
hardness measurements with a GYZJ 934-1 hardness meter were taken
in the center of each section on the obverse side of the section to
the Glow-Box. An average of over three measurements were
recorded.
[0126] A similar procedure for the samples made using the fast cure
method (Samples E-I) was followed. Data is shown in Table 2.
1TABLE 1 Slow Cure Process Barcol Hardness Sample Cure Time (hrs.)
1 2 3 4 5 A 24 40 20 0 0 0 B 48 82 80 73 63 0 C 72 87 84 81 80 77 D
96 88 88 87 86 84
[0127]
2TABLE 2 Fast Cure Process Barcol Hardness Sample Cure Time (min.)
1 2 3 4 5 E 5 0 0 0 0 0 F 10 0 0 0 0 0 G 15 48 51 50 52 55 H 20 84
85 81 84 84 I 25 88 90 91 89 91
[0128] Forty-one samples were made using the same procedure
described above for making Samples A-I. Eight samples were slow
cured, twelve were fast cured, and the remaining twenty-one samples
were fast cured and heat-treated. All forty-one samples tested
using the Thermal Shock Test.
3 TABLE 3 Results of Thermal Shock Test Cure Mode Heat Treat Pass
Fail Slow No 8 0 Fast No 0 12 Fast Yes 21 0
[0129] Sample Preparation
[0130] Composite Paste Samples 1-8 were prepared by charging
fillers and resin to a plastic beaker and then stirring and
kneading these constituents into a paste with a flattened glass
rod.
4TABLE 4 Sample Amount of Preparatory Type and Amount of Filler No.
Example 1 Resin (pbw) (pbw) 1 30 70, Preparatory Example 2 2 30 70,
Preparatory Example 3 3 30 70, Preparatory Example 5 4 40 60,
Preparatory Example 4 5 20 80, Preparatory Example 2 6 20 80,
Preparatory Example 5 7 40 60, Preparatory Example 3 8 50 50,
Preparatory Example 4 9* 14.7 85.3 Preparatory Example 2
[0131] * Sample No. 9 was compounded in a double planetary
mixer.
[0132] A Comparative Sample 10 was made from commerically available
Vita Mark II A3C/I12 Restorative (Vita Zahnfabrik, Bad Sackingen,
Germany). When possible, pastes were compounded in a range
containing filler from 70 to 80 weight percent. With the
Preparatory Example 3 filler, Schott 8235 Glass, the paste became
dry and crumbly at about 73-76% by weight of filler. With the
Preparatory Example 4 fillers Aerosil OX50, the paste became far
too thick to mix by hand when the filler content was greater than
about 60% by weight.
[0133] Loading Curing and Heat Treatment of Samples 1-9
[0134] The paste was filled into plastic cuvets and then compressed
manually with a stainless steel plunger. The filled cuvets were
then placed in a Kulzer.TM. Dentacolor.TM. XS Curing Unit.TM.
(Heraueus Kulzer; Irvine, Calif.) and cured for 90 seconds on each
long side. Total curing time was 360 seconds. The plastic cuvet was
then broken off to produce a cured mill block of approximately
10.times.10 mm cross section by 3-4 cm long. Blocks were heat
treated in an oven by placing them in a cool oven. The oven was
then heated to 100 C and maintained at that temperature for one
hour. The oven was then turned off and the samples were allowed to
cool in the oven to room temperature.
[0135] Each sample was evaluated for cuttability and Barcol
Hardness. Barcol Hardness of the composite blanks was tested with a
Barber Coleman Impressor Model GYZJ 934-1 (Barber Coleman;
Rockford, Ill.). An average of the three readings was recorded.
[0136] Cuttability is calculated by the following equation, percent
increase compared to Sample 8 equals [(Cuttability--Cuttability of
Sample 8)/Cuttability of Sample 8] multiplied by 100.
5TABLE 5 % Increase Cuttability: of Cuttability Filler or Filler
Avg Compared to Sample No. Product wt % Depth (mm) Sample 8
Barcol-avg 1 Sol-gel 70 0.93 70 79.3 2 Glass 70 0.71 29 86.0 3
Quartz 70 0.72 32 77.3 4 Fumed 60 0.56 2 78.3 Silica 5 Sol-gel 80
1.24 127 85.0 6 Quartz 80 1.45 166 80.3 7 Glass 60 1.05 93 75.5 8
Fumed 50 0.55 0 75.0 Silica 9 Sol-Gel 85.3 2.01 268 89.5
Comparative Vita Mark II 0.83 44 -- 10 A3C/I12 (no heat
treatment)
[0137] Sample 11
[0138] 3M F2000 shade A2 (3M Co.; St. Paul, Minn.),
fluoride-releasing material, was extruded into a cuvet to about 3/4
full. The filled cuvet was placed standing vertically in a Hanau
Sun-Test box with a xenon lamp and exposed to light for 30 min. The
cuvet was rotated lengthwise and exposed to light another 30 min.
The cured block was heat treated in a Despatch oven at 100.degree.
C./60 min., then allowed to cool in the oven.
[0139] X-Ray Analysis of Samples
[0140] Examples X1-X8 were fabricated in the same way as Samples
E-I except that they were centrifuged at 2700 RPM, and light cured
for 30 minutes immersed in water; and not heat-treated.
[0141] Examples X9-X12 were fabricated in the same way as Sample
E-I except that they were centrifuged at 2700 RPM, and light cured
for 41 minutes immersed in water; and heat-treated in the same way
as samples 1-9.
[0142] Examples X13-X22 were fabricated in the same way as Samples
E-I except that they were centrifuged at 2700 RPM, and light cured
for 30 minutes immersed in water; and heat-treated in the same way
as samples 1-9.
[0143] Example X23 was fabricated in the same way as Samples E-I
except that it was centrifuged at 2400 RPM, and light cured for 30
minutes immersed in water; and heat-treated in the same way as
samples 1-9.
[0144] Examples X24-28 are commercial Vita Mark II Vitablocs.
[0145] Examples X29-X32 were fabricated in the same way as Samples
A-D except that the paste was heated to 45.degree. C. for
filling.
6TABLE 6 Exposure Sample # time (sec) Observation X1 1/30 many
pores, .about.0.5-2 mm X2 1/30 no cracks or other discontinuities
visible X3 1/30 no cracks or other discontinuities visible X4 1/30
no cracks or other discontinuities visible X5 1/30 several pores
1-4 mm X6 1/30 no cracks or other discontinuities visible X7 1/30
no cracks or other discontinuities visible X8 1/30 no cracks or
other discontinuities visible X9 1/30 no cracks or other
discontinuities visible X10 1/30 no cracks or other discontinuities
visible X11 1/30 large pit at end open to surface X12 1/30 large
pit at end open to surface X13 1/30 flat pores, about 0.1 mm thick
.times. 3 mm long X14 1/30 flat pores, about 0.1 mm thick .times. 3
mm long X15 1/30 flat pores, about 0.1 mm thick .times. 3 mm long
X16 1/30 flat pores, about 0.1 mm thick .times. 3 mm long X17 1/30
no cracks or other discontinuities visible X18 1/30 no cracks or
other discontinuities visible X19 1/30 no cracks or other
discontinuities visible X20 1/30 no cracks or other discontinuities
visible X21 1/30 flat pores, about 0.1 mm thick .times. 3 mm long
X22 1/30 flat pores, about 0.1 mm thick .times. 3 mm long X23 1/30
one pore .about.3 mm; one crack .about.5 mm long X24 1/30 no cracks
or other discontinuities visible X25 1/30 no cracks or other
discontinuities visible X26 1/30 no cracks or other discontinuities
visible X27 1/30 no cracks or other discontinuities visible X28
1/30 no cracks or other discontinuities visible X29 1/30 no cracks
or other discontinuities visible X30 1/30 narrow longitudinal crack
0.1 mm wide top to bottom X31 1/30 small crack .about.0.1 mm wide
X32 1/30 small crack <0.1 mm wide
* * * * *