U.S. patent application number 12/783091 was filed with the patent office on 2010-09-16 for addressable matrices/cluster blanks for dental cad/cam systems and optimization thereof.
This patent application is currently assigned to IVOCLAR VIVADENT AG. Invention is credited to Dmitri G. Brodkin, Robert A. Ganley.
Application Number | 20100233658 12/783091 |
Document ID | / |
Family ID | 41728255 |
Filed Date | 2010-09-16 |
United States Patent
Application |
20100233658 |
Kind Code |
A1 |
Ganley; Robert A. ; et
al. |
September 16, 2010 |
ADDRESSABLE MATRICES/CLUSTER BLANKS FOR DENTAL CAD/CAM SYSTEMS AND
OPTIMIZATION THEREOF
Abstract
A cluster mill blank includes a framework constructed to
cooperate with a blank holder of an existing CAD/CAM system, and a
plurality of sub-blanks attached to the framework forming an
addressable matrix or cluster blank. CAD/CAM systems including such
a framework, as well as associated methods are described.
Inventors: |
Ganley; Robert A.;
(Williamsville, NY) ; Brodkin; Dmitri G.;
(Livingston, NJ) |
Correspondence
Address: |
BOND, SCHOENECK & KING, PLLC
ONE LINCOLN CENTER
SYRACUSE
NY
13202-1355
US
|
Assignee: |
IVOCLAR VIVADENT AG
Schaan
LI
|
Family ID: |
41728255 |
Appl. No.: |
12/783091 |
Filed: |
May 19, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12329200 |
Dec 5, 2008 |
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12783091 |
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12118981 |
May 12, 2008 |
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12329200 |
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61024935 |
Jan 31, 2008 |
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60935006 |
Jul 20, 2007 |
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Current U.S.
Class: |
433/201.1 |
Current CPC
Class: |
Y10T 409/305544
20150115; Y10T 409/309016 20150115; A61C 13/0022 20130101; A61C
13/08 20130101 |
Class at
Publication: |
433/201.1 |
International
Class: |
A61C 13/08 20060101
A61C013/08 |
Claims
1. A system for milling dental prostheses in a CNC milling machine,
comprising: a) a primary fixture of a milling machine for receiving
a large millable dental blank; b) a plurality of smaller millable
dental blanks each capable of being machined to form a dental
prosthesis; and c) lateral affixing means for affixing a lateral
side of the plurality of smaller millable dental blanks in a space
defined by the large millable dental blank in the primary
fixture.
2. The system of claim 1, wherein the millable dental blanks
comprise ceramic, metal or plastic blanks.
3. The system of claim 1, wherein the lateral affixing means
comprises an interchangeable jig sized and shaped as the large
millable dental blank and interchangeable with the large millable
dental blank in a receptacle of the primary fixture, and having a
lateral wall against which the lateral side of the plurality of
smaller millable dental blanks is affixed.
4. The system of claim 3, wherein the jig comprises a plastic tray
having a plurality of alignment indentations for receiving the
plurality of smaller millable dental blanks.
5. The system of claim 4, wherein the plastic tray is made from the
large millable blank using the same CNC milling machine.
6. The system of claim 5 wherein the large millable blank is a PMMA
disk.
7. A system for milling dental prostheses in a CNC milling machine,
comprising: a) primary fixture of a milling machine for receiving a
large millable blank; b) an interchangeable jig sized and shaped as
the large millable dental blank and interchangeable with the large
millable dental blank with respect to the primary fixture of the
milling machine, and having a lateral wall; and c) a plurality of
smaller millable dental blanks each with a lateral side affixed to
the lateral wall of the jig.
8. The system of claim 7, wherein the interchangeable jig comprises
a variety of jigs interchangeable with the primary fixture or
fixtures to mill a variety of commercially available plastic, metal
and ceramic dental blanks.
9. The system of claim 8, wherein the jig comprises a plastic tray
having a plurality of alignment indentations for receiving the
plurality of smaller millable dental blanks.
10. The system of claim 9, wherein the plastic tray is made from
the large millable blank using the same CNC milling machine.
11. The system of claim 10, wherein the large millable blank is a
PMMA disk.
12. A method for milling dental prostheses in a CNC milling
machine, comprising: providing a primary fixture for receiving a
large millable blank; affixing a lateral side of one or more
smaller millable dental blanks in the same space provided for the
large millable dental blank; milling one or more dental prostheses
in the smaller millable dental blanks; and removing the one or more
dental prostheses from the smaller millable dental blanks.
13. A method for milling dental prosthesis in a CNC milling
machine, comprising: providing a primary fixture for receiving a
large millable blank; affixing a lateral side of one or more
smaller millable dental blanks to a lateral wall of a jig sized and
shaped as the large millable dental blank; placing the jig in the
primary fixture held in the milling machine; milling one or more
dental prostheses in the smaller millable dental blanks; removing
the jig from the primary fixture; and removing the smaller millable
dental blanks from the jig.
14. The method of claim 13, wherein the jig comprises a variety of
jigs interchangeable with the primary fixture or fixtures to mill a
variety of commercially available plastic, metal and ceramic
blanks.
15. A method for machining dental prostheses in a CNC milling
machine, wherein the milling machine comprises at least one type of
a blank holding fixture cooperating with a chuck of the milling
machine, the method comprising: affixing a lateral side of each of
a plurality of ceramic millable dental blanks to a lateral wall of
the fixture; securing the fixture to the chuck of the milling
machine; machining a single dental prosthesis in each of the
plurality of ceramic millable dental blanks by a machining process
with machining tools; and removing the plurality of ceramic
millable dental blanks from the fixture.
16. The method of claim 15, wherein the machining tools comprise
diamond burrs or fluted cutters.
17. The method of claim 15, wherein the machining process comprises
wet or dry machining.
18. A method for milling dental prostheses in a CNC milling
machine, comprising: affixing a lateral side of each of a plurality
of ceramic millable dental blanks to internal lateral walls of an
internal periphery and/or internal holders of a fixture by
disposing a post of each of the plurality of ceramic millable
dental blanks in a different one of a plurality of holes in the
fixture, with the plurality of ceramic millable dental blanks
disposed in a flat layer with a top and a bottom of each of the
plurality of ceramic millable dental blanks unblocked by another of
the plurality of ceramic millable dental blanks, each of the
plurality of ceramic millable dental blanks having a different
characteristic with respect to one another; securing the fixture to
a chuck of the milling machine; milling a single dental prosthesis
in each of the plurality of ceramic millable dental blanks with a
diamond burr by first milling a top side of each of the plurality
of ceramic millable dental blanks, turning the fixture over, and
then milling an opposite bottom side of each of the plurality of
ceramic millable dental blanks; and removing the plurality of
ceramic millable dental blanks from the fixture.
19. A system for milling dental prostheses, comprising: a) a CNC
milling machine capable of a wet-milling process with a chuck, a
diamond bun, and a liquid delivery system; b) a fixture securable
in the chuck of the milling machine; c) a plurality of ceramic
millable dental blanks each capable of being machined to form a
dental prosthesis; and d) a lateral side of each of the plurality
of ceramic millable dental blanks securable to a lateral wall(s) of
the fixture.
20. A method of making a jig for a CNC milling machine for milling
dental prostheses comprising: inserting a large blank into a
fixture of the CNC milling machine; milling openings in the large
blank, wherein the openings are used to receive smaller millable
dental blanks.
21. The method of claim 20, wherein the large blank is
disk-shaped.
22. The method of claim 20, wherein the large blank is fabricated
of plastic, metal or ceramic.
23. The method of claim 22, wherein the plastic comprises PMMA.
24. The method of claim 20, wherein the openings milled in the
large blank are modified by addition of adapters, gaskets, liners
or castable materials to assure tight secure fit of the smaller
millable dental blanks.
25. A method of milling dental prostheses in a CNC milling machine,
comprising: inserting a large blank into a fixture of the CNC
milling machine; milling openings in the large blank, wherein the
openings are used to receive smaller millable dental blanks;
inserting smaller millable dental blanks into the openings in the
large blank; and milling the dental blanks into dental
prostheses.
26. The method of claim 25, wherein the large blank is
disk-shaped.
27. The method of claim 25, wherein the openings milled in the
large blank are modified by addition of adapters, gaskets, liners
or castable materials to assure tight secure fit of the smaller
millable dental blanks.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
application Ser. No. 12/329,200, filed Dec. 5, 2008, which is a
continuation-in-part of U.S. application Ser. No. 12/118,981, filed
May 12, 2008, which claims priority to U.S. Patent Application No.
60/935,006, filed Jul. 20, 2007 and U.S. Patent Application No.
61/024,935, filed Jan. 31, 2008, all of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention is directed to computer-aided systems
for designing and manufacturing dental prostheses and restorations.
The invention also relates to cluster mill blanks and their use in
dental CAD/CAM systems to expand a range of systems compatible with
a given blank; enable mill blank interchangeability with other
systems; provide access to an increased variety of mill blanks for
a given system; and maximize the system's versatility, selection of
materials and efficiency of operation. According to certain
aspects, the present invention is also directed to techniques and
methods associated with the abovementioned cluster blanks.
BACKGROUND OF THE INVENTION
[0003] In the discussion that follows, reference is made to certain
structures and/or methods. However, the following references should
not be construed as an admission that these structures and/or
methods constitute prior art. Applicant expressly reserves the
right to demonstrate that such structures and/or methods do not
qualify as prior art.
[0004] Today, there is a progressively increasing trend in
dentistry toward the use of automated technologies for treatment
planning, virtual procedures, orthodontics, design and
manufacturing of dental restorations both in dental offices (chair
side) and dental laboratories (lab side). This trend, sometimes
called "digital revolution," is most evident in lab side explosion
of CAD/CAM technologies. A number of CAD/CAM systems available to
dental laboratories has increased nearly ten-fold in the last
decade. Currently, there are over 25 dental CAD/CAM systems and
quite a few copy-milling systems using mill blanks in a variety of
shapes and sizes. Blank shapes vary from simple geometries such as
rectangular, cylindrical or hexagonal to more complex such as smart
blanks described in U.S. Pat. No. 6,979,496 which is incorporated
by reference herein in its entirety. Their sizes range from about
0.5'' to about 4'' in length or diameter. Mill blanks are available
in all 4 types of materials--metals, polymers (resins, plastics),
ceramics and composites. Ceramic mill blanks can be divided into
three major categories: feldspathic (leucite-based and sanidine or
feldspar-based), glass-ceramic (lithium silicate, micaceous, etc.),
and crystalline ceramic based such as alumina and/or zirconia
(soft-sintered or fully dense). All three ceramic categories as
well as composite blanks are already available or soon will be
available in a variety of shades. Stocking the necessary inventory
of shades for each given type of blank adds to economic pressures
on the facility operating a CAD/CAM system.
[0005] A conventional 4 inch diameter disk-shaped zirconia blank
100 is illustrated in FIGS. 1-2. As illustrated therein a plurality
of milled shapes 110 are formed in the zirconia blank 100. The
blank 100 is formed entirely from zirconia, and therefore is quite
costly. As illustrated in FIG. 2, use of such blanks 100 to form a
plurality of milled shapes 110 results in a significant amount of
wasted intervening block area 120 defined between the milling
envelopes 112.
[0006] While CAD/CAM technology provides dental laboratories with
opportunities for improved quality, reproducibility and elimination
of human error, most CAD/CAM systems are geared to milling
soft-sintered zirconia and thus lacking material selection to be
competitive in a supersaturated and fast-paced market. Since the
price for a CAD/CAM system, depending on manufacturer and
configuration, runs from $50,000 to $500,000 only the largest labs
and outsource centers can afford to operate multiple systems to
expand their material selection. Most CAD/CAM systems manufacturers
do not make their own blocks, rather they purchase them from
suppliers such as Ivoclar, Vita or Metoxit, with an established
core competency in dental or advanced materials development and
manufacturing. Understandably, CAD/CAM materials are fairly
expensive adding substantially to CAD/CAM system operating costs.
For example, the price of ceramic milling blanks range from about
$0.60 to $4.50 per gram of material. Yield per blank as defined in
U.S. Pat. No. 6,979,496 is fairly low and most of it goes to
waste.
[0007] The first CAD/CAM systems comprising milling units for chair
side or lab side use such as Cerec (Sirona) and Lava (3M/ESPE) were
closed systems wherein mill blanks are attached to a stub retainer,
projection, mandrel, holder or carrier body, which have a unique
patented geometry as described in U.S. Pat. Nos. 6,485,305 and
6,769,912 and can be also protected by a bar-code, thereby
preventing interchangeability with other (CAD/CAM) systems.
Variations of a work piece (millable part) on a stub assembly are
also described in U.S. Pat. Nos. 7,214,435, 6,669,875, 6,627,327,
6,482,284, 6,224,371, 6,991,853 and 6,660,400. With advent of the
open architecture systems, blank interchangeability between systems
has become not only possible but extremely desirable. While the
market is currently dominated by closed systems, the market
penetration of open systems is steadily increasing. From 25
commercial CAD/CAM systems at least 5 or 6 are utilizing the same
D-250 dental 3D scanner and DentalDesigner.TM. dental CAD software
(3Shape A/S, Copenhagen, Denmark). In an open architecture system,
the blanks are not bar-code protected and any blank can be used as
long as it fits the existing housing (blank holder, chuck, collect,
support) of the milling unit.
[0008] Not all types of blanks can be economically produced in any
shape and size. For example, zirconia and alumina blocks can be
formed in any given shape and size to meet the demand for larger
cases that can be milled from larger blanks. On the other hand,
large feldspathic and glass-ceramic blanks are not so desirable due
to a number of mechanical and economic constraints.
[0009] U.S. Patent Application 2006/0115794 appears to teach a
system for continuous production of prosthodontic pieces such as
crown cores, crowns or the like. The system utilizes turning and
milling on a live center computer numerical control CNC machine of
a zirconia rod stock that is automatically fed into the machine.
Multiple pieces are cut one after another from the continuous rod
stock. This patent application further appears to teach utilization
of multiple machines wherein each machine is fed a rod stock of a
different shape and/or size. A central control unit obtains
specifications for a piece that is to be cut and selects the
machine on which the piece is to be made by determining the rod
stock that will require the least amount of cutting. In addition to
the above mentioned economical and processing difficulties of
fabricating and milling long rod stock from materials other than
fully dense zirconia, considering the cost of the CNC machine, it
is far more advantageous to enable one machine to mill all cases
than to have many machines, each dedicated to a certain type of
case.
[0010] U.S. Pat. No. 7,234,938 appears to disclose the multi-blank
holder or workpiece receiver constructed as an elongated strip with
multiples bores in it for embedding a plurality of identical blanks
or workpieces. The invention relates to a milling/grinding machine,
wherein, the workpiece receiver or mill blank holder has a
plurality of bores arranged along its longitudinal axis, for
receiving the workpieces or blanks. This invention also comprises a
moldable embedding material disposed within the through-bore for
retaining the workpiece within the through-bore. It further teaches
a milling/grinding machine, comprising an embedding device for the
automatic embedding of the workpiece in the workpiece receiver.
[0011] U.S. Patent Application 2006/0106485 describes the use of a
virtual blank corresponding to a physical blank being processed to
form a plurality of manufacturing features. This application
further teaches virtual machining of each manufacturing feature of
the plurality of manufacturing features into the virtual blank
wherein each manufacturing feature exhibits an associative
relationship with the coordinate system. Manufacturing instructions
are generated to create the actual part by machining the plurality
of manufacturing features into the blank. Such methods were
pioneered in the automotive industry and described in U.S. Pat.
Nos. 6,775,581; 7,024,272; 7,110,849 and U.S. Patent Application
2006/0106485, incorporated by reference herein in their entirety.
It is also described in the white paper: Horizontal Modeling &
Digital Process Design. The approach of electronically designing an
article comprising an assembly of components is described in US
Application 2007/0136031 incorporated by reference herein in its
entirety. Again, this disclosure is not related to dentistry.
[0012] Thus, a need exists in the art for enabling blank
interchangeability, maximizing yield per blank, and reducing
material waste, to maximize the system's versatility, selection of
materials and efficiency of operation. There is also a desire to
reduce inventory of blanks thus reducing operating costs associated
with commercial CAD/CAM systems.
SUMMARY OF THE INVENTION
[0013] The present invention provides techniques and arrangements
that can optionally address one or more of the abovementioned
shortcomings associated with the existing CAD/CAM systems.
According to certain aspects, the present invention provides mill
blanks by way of providing cluster blanks and software for
efficient utilization thereof.
[0014] "Cluster blank" as used herein, is defined as a multiple
blank assembly comprising at least two and preferably four or more
individual blanks fixed to a framework (carrier body, housing,
gripping yoke) compatible with the existing housing (blank holder,
chuck, collect, support) of a milling unit, with minimal or no
modification. The cluster blank thus forms a sort of addressable
matrix of blanks that the milling unit or CAD/CAM system can access
to efficiently mill shaped bodies into the blanks, with minimal
waste and material removal, and with maximum interchangeability and
flexibility. Accordingly, the terms "cluster blank" and
"addressable matrix" may be used interchangeably herein.
[0015] Various cluster blanks can be formed from individual blanks
using prefabricated or custom-made frameworks to enable use of said
individual blanks in the maximum possible number of systems. A
cluster blank can comprise the same individual blanks of identical
size and shade, or different shades of the same size and type
blank. Cluster blanks can also comprise various sizes and shades of
the same blank type (material) and also a variety of different
types of blanks from one or different manufacturers can be
assembled on the same framework to make a "hybrid" cluster blank.
To maximize the impact of cluster blanks on system efficiency, the
present invention also provides for use of nesting software and
system optimization software based on digital process design (DPD)
methodologies using a virtual blank approach.
[0016] Accordingly, the present invention provides a cluster mill
blank comprising a framework constructed to cooperate with a blank
holder of an existing CAD/CAM system; and a plurality of sub-blanks
attached to the framework.
[0017] According to further aspects the present invention provides
a CAD/CAM system comprising a milling machine, a blank holder, a
cluster milling blank comprising a framework constructed to
cooperate with the blank holder, and a plurality of sub-blanks
attached to the framework; and nesting software having at least a
first order level of functionality.
[0018] According to yet another aspect, the present invention
provides a method of milling objects using the CAD/CAM system
described above, the method comprising analyzing historic actual
milling data, or analyzing data corresponding to milled objects,
with the nesting software thereby obtaining a size and shape
distribution for milling envelopes and their correlation with
specific types of dental articles, selecting a batch of cases
corresponding to objects to be milled by selecting their
corresponding electronic data, optimizing the number, type, size,
arrangement, dimensions and/or shades of sub-blanks selected for
milling the batch of cases, assembling the selected sub-blanks on
to one or more frameworks utilizing one or more templates to
produce one or more cluster blanks; and milling the objects into
respective sub-blanks.
[0019] While the present invention is described herein mainly with
reference to machining dental prostheses, it should be understood
that the present invention is not so limited. For example, the
principles of the present inventions can be applied to medical
devices in general (e.g., implants, replacement joint parts,
skeletal replacements, etc.) According to its broader aspects, the
present invention can apply to the milling or shaping of
essentially any three-dimensional object. Examples of
three-dimensional objects include, but are not limited to, dental
articles, such as, a coping, pontic, framework, denture teeth,
space maintainer, tooth replacement appliance, orthodontic
retainer, denture, post, facet, splint, cylinder, pin, connector,
crown, partial crown, veneer, onlay, inlay, bridge, fixed partial
denture, implant or abutment.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0020] FIG. 1 is a conventional disk-shaped blank.
[0021] FIG. 2 is illustrative of the waste from milling the blank
of FIG. 1.
[0022] FIG. 3 is a cluster blank formed according to a first
embodiment of the present invention.
[0023] FIG. 4 is a cluster blank formed according to a second
embodiment of the present invention.
[0024] FIG. 5 is a cluster blank formed according to a further
embodiment of the present invention.
[0025] FIG. 6 is a cluster blank formed according to yet another
embodiment of the present invention.
[0026] FIG. 7 is a cluster blank for according to yet an additional
embodiment of the present invention.
[0027] FIG. 8a illustrates a conventional CAD/CAM milling machine
comprising a two disk milling blank holder in open position.
[0028] FIG. 8b illustrates a conventional CAD/CAM milling machine
comprising a two disk milling blank holder in closed position.
[0029] FIG. 9 is a schematic illustration of a cluster blank master
template formed according to the principles of the present
invention.
[0030] FIG. 10 is a modification of the master template of FIG. 9,
constructed according to one embodiment of the present
invention.
[0031] FIG. 11 is a modification of the master template of FIG. 9,
constructed according to another embodiment of the present
invention.
[0032] FIG. 12 is a graphical representation of the size
distribution of milling envelopes.
[0033] FIG. 13 is a top perspective view of sub-blanks mounted onto
a framework in accordance with an embodiment of the present
invention.
[0034] FIG. 14 is a top perspective view of sub-blanks mounted onto
a framework in accordance with an embodiment of the present
invention.
[0035] FIG. 15 is a fragmentary perspective view of a sub-blank
mounted in a framework in accordance with an embodiment of the
present invention.
[0036] FIG. 16 is fragmentary perspective view of a sub-blank
mounted in a framework in accordance with an embodiment of the
present invention.
[0037] FIG. 17 is a fragmentary perspective view of sub-blanks
mounted in a framework in accordance with an embodiment of the
present invention.
[0038] FIG. 18 is a fragmentary perspective view of sub-blanks
mounted in a framework in accordance with an embodiment of the
present invention.
[0039] FIG. 19 is a cross-sectional view of sub-blanks mounted in a
framework taken at line 19-19 of FIG. 18.
[0040] FIG. 20 is top perspective view of sub-blanks mounted onto a
framework in accordance with an embodiment of the present
invention.
[0041] FIG. 21 is side top perspective view of sub-blanks mounted
onto a framework in accordance with an embodiment of the present
invention.
[0042] FIG. 22 is a side view of the framework in FIG. 21.
[0043] FIG. 23 is front plan view of the framework of FIG. 21, with
a partial cross-sectional view at line 23-23 of FIG. 22.
[0044] FIG. 24 is top perspective view of the framework of FIG. 21,
with a partial cross-sectional view at line 24-24 of FIG. 22.
[0045] FIG. 25 is a fragmentary perspective view of a cluster blank
in accordance with an embodiment of the present invention.
[0046] FIG. 26 is a top plan view of a cluster blank in accordance
with an embodiment of the present invention.
[0047] FIG. 27 is an exploded view of the cluster blank assembly of
FIG. 26.
[0048] FIG. 28 is a cross-sectional view of the cluster blank of
FIG. 26 taken at line 28-28 of FIG. 26.
[0049] FIG. 29 is a cross-sectional view of the cluster blank of
FIG. 26 taken at line 29-29 of FIG. 26.
[0050] FIG. 30 is an enlarged view of a sub-blank fitting in FIG.
29.
[0051] FIG. 31 is a cross-sectional view of the cluster blank of
FIG. 26 taken at line 31-31 of FIG. 26.
[0052] FIG. 32 is a perspective view of a sub-blank in a receptacle
in accordance with the present invention.
[0053] FIG. 33 is a fragmented view of the sub-blank of FIG.
32.
[0054] FIG. 34 is a top plan view of a cluster blank in accordance
with an embodiment of the present invention.
[0055] FIG. 35 us a perspective view of the cluster blank of FIG.
34.
[0056] FIG. 36 is a cross-sectional view of the cluster blank of
FIG. 34 taken at line 36-36.
[0057] FIG. 37 is a cross-sectional view of the cluster blank of
FIG. 34 taken at line 37-37.
[0058] FIG. 38 is a cross-sectional view of the cluster blank of
FIG. 34 taken at line 38-38.
[0059] FIG. 39 is a perspective view of the cluster blank of FIG.
34 with the sub-blanks removed.
[0060] FIG. 40 is a perspective view of the cluster blank of FIG.
34 with the holder being mechanically fastened to the
framework.
[0061] FIG. 41 is a perspective view of the cluster blank of FIG.
34 with sub-blanks therein.
[0062] FIG. 42 is a perspective view of the cluster blank of FIG.
34 sub-blanks therein.
[0063] FIG. 43 is a perspective view of the cluster blank of FIG.
34 a sub-blanks being mechanically fastened to the holder.
[0064] FIG. 44 is a perspective view of the cluster blank of FIG.
34 with a holder being mechanically fastened to the framework.
DETAILED DESCRIPTION OF THE INVENTION
[0065] According to one optional aspect of the present invention,
various cluster blanks are formed from individual blanks using
prefabricated or custom-made frameworks to enable the use of
individual blanks in the maximum possible number of systems.
Hereafter individual blanks being assembled into a cluster blank
will be termed sub-blanks. A cluster blank can comprise sub-blanks
of identical size and shade, or different shades, sizes and/or
types of sub-blanks. For example, a cluster blank can comprise
various sizes and shades of the same sub-blank type and also a
variety of different types of sub-blanks from one or different
manufacturers can be assembled on the same framework to make a
"hybrid" cluster blank. For example, e.max CAD MO and/or LT blanks
(Ivoclar) also known as "blue blocks" can potentially be processed
by any robust CAD/CAM system utilizing wet-milling process and
having software capable of designing full-contour restorations. An
example of such a system capable of, but not yet milling "blue
blocks" are Zeno.RTM.Tec system (Wieland), specifically ZENO.RTM.
4820 and ZENO.RTM. 3020 milling units interfaced with
DentalDesigner.TM. Software from 3Shape mentioned above. Examples
of cluster blanks formed according to the present invention are
shown in FIGS. 3-6.
[0066] Sub-blanks may be arranged in an addressable matrix, whereby
the addressable matrix is designed from parameters received from a
history of prior milling operations or prior business operations.
The sub-blanks have properties associated with parameters received
from a history of prior milling operations or prior business
operations. These properties can include type of material, material
characteristics, size of the sub-blank, shape of the sub-blank,
and/or shade of the sub-blank. The parameters received from a
history of prior milling operations can include type of case,
material selection parameters, size of the dental article, shape of
the dental article, shade of the dental article, optimal tool path,
milling parameters, and statistics of milling envelops used in the
fabrication of dental articles. Examples of statistics of milling
envelops include shape and dimensions of the milling envelops and
the correlation of the milling envelops with specific types of
dental articles. Examples of milling parameters include type of
tooling, depth of cut, feed rate, rotations per minute (rpm) and/or
linear speed. Examples of type of tooling include a cutting,
grinding or abrasive surface. The tooling can vary by material,
shape, and/or size of tooling. Examples of cutting, grinding or
abrasive surface include diamond, carbides, hardened steel, or
ceramic. Examples of tooling shape include, but are not limited to
cylindrical, conical, disc-shaped, ball-shaped, or fluted. The size
of the tool may be dependent on diameter and length. Diamond
tooling may include diamond grit. The depth of cut of the tooling
may range in size form microns to millimeters. Further examples of
milling parameters include post-milling parameters such as coating,
glazing, or heat treatment parameters. Examples of parameters
related to history of prior business operations include inventory
used, inventory remaining, and case histories.
[0067] A first cluster blank 10 formed according to certain
embodiments of the present invention is illustrated in FIG. 3. As
illustrated therein, the cluster blank 10 comprises a plurality of
sub-blanks 12. According to the illustrated embodiment, two
different types of sub-blanks 12 are included in the cluster blank
10. Namely, according to the illustrated embodiment, a plurality of
first cluster blanks 14 are generally located in the central area
of the cluster blank 10, and a second plurality of sub-blanks 16
are provided around the periphery of the cluster blank 10 according
to a non-binding illustrative example, the first plurality of
cluster blanks comprise C14 blue blocks and the second plurality of
sub-blanks comprise B32 blue blocks. Each of the sub-blanks 12 are
attached, or may be otherwise integrated with, a common 18. The
framework 18 can be formed from any suitable material. For example,
the framework 18 can be constructed from a metal such as steel or
an aluminum alloy, a plastic or polymer such as PMMA, or composite
material such as Paradigm.RTM. MZ100 manufactured by 3M. The
framework may comprise stationary or moving parts.
[0068] The cluster blanks 10, 20 as described in the illustrative
embodiments above, may optionally be composed from a plurality of
blue blocks and customized for use in the above-mentioned Zeno.RTM.
Tec System.
[0069] A modification of the embodiment depicted in FIG. 3 is
illustrated in FIG. 4. This embodiment is similar to the embodiment
illustrated in FIG. 3, except for the arrangement and type of
sub-blanks 12 associated with the framework 18. According to the
embodiment illustrated in FIG. 4, the sub-blanks 14 each have the
same construction, for example, each have the same size, shade,
and/or are formed from the same material. According to one optional
embodiment, each of the sub-blanks 14 are essentially identical to
one another.
[0070] Frameworks can be in any shape or form including 2D and 3D.
The frameworks can be mass-produced (pre-fabricated) or custom made
for each desired pairing of system and mill blank. Sub-blanks can
be mechanically attached (locked in) to a framework or
alternatively adhesively bonded (glued) thereto or formed as an
integral part of the framework. Sub-blanks can be also mounted into
openings in the framework using castable mounting materials,
modeling materials, polymer composites and other hardenable
materials. Frameworks for cluster blanks can be designed for
multiple uses, and/or as disposable implements. Furthermore,
frameworks of cluster blanks can comprise a monolithic single part,
or can comprise an assembly of a plurality parts or components. In
the latter case parts or components of the framework assembly can
be permanently affixed to each other or be detachable. The
framework assembly can also comprise moving parts. For example,
moving parts can be used to rotate or otherwise change the position
of a sub-blank in a cluster blank before, during or after milling.
This movement can be manual or automated and controlled by the same
means as a CNC milling unit.
[0071] Cluster blanks 30, 40 and 50 formed according to further
embodiments of the present invention are illustrated in FIGS. 5-7,
respectively.
[0072] As illustrated in FIG. 5, cluster blank 30 includes a
plurality of sub-blanks 32 arranged on a polygonal framework 34.
According to the non-limiting, illustrative embodiment, the
sub-blanks comprise 9 round blocks arranged in three rows of three
blocks each, and the framework 34 is substantially square. The
block 32 and the framework 34 can be formed from any of the
materials previously described herein.
[0073] As illustrated in FIG. 6, a cluster blank 40 formed
according to an alternative embodiment of the present invention
includes at least one sub-blank having a first characteristic and a
plurality of second sub-blanks 44 having a second characteristic
which differs from that of the at least one first sub-blank 42.
According to the non-limiting, illustrative example, the first
sub-blank 42 comprises a substantially round block, and the
plurality of second sub-blanks 44 comprise polygonal or
substantially square blanks symmetrically arranged around the first
sub-blank 42. The first and second sub-blanks 42, 44 are attached
to a polygonal framework 46. According to the non-limiting
illustrative embodiment, the framework 46 is substantially square.
Both the sub-blanks 42, 44 and the framework 46 can be formed from
any of the previously described materials.
[0074] FIG. 7 illustrates a cluster blank 50 forming an addressable
4.times.4 matrix (SBij) comprising 16 sub-blanks 52 having various
dental shades set in framework 54. According to one illustrative
embodiment, if each sub-blank 52 represents one Vita Classic shade,
this 4.times.4 addressable matrix can cover the entire Vita Classic
shade range. In general each and all individual sub-blank positions
in a given cluster blank/addressable matrix are assigned indices
(numbers) based on specific ways and algorithms of how they are
addressed by a software of a CAD/CAM system or operational software
of a central processing facility such as nesting software types
described below. For example, each sub-blank is assigned at least
one number corresponding to its individual position/slot in a given
cluster-blank in which the sub-blank is placed and at least the
second number corresponding to the host cluster blank
identification number or its place in a job queue, i.e. batch of
cases to be milled. In this case cluster blank/addressable matrix
of FIG. 7 is represented by a vector SB.sub.km, where k corresponds
to a place of a cluster blank in a job queue and m varies from 1 to
16 for the total number of 16 sub blank positions in a given
cluster blank. Operating software adds other vectors to the
addressable matrix such as the ones associated with specific
sub-blank material, size, shape, shade and also milling parameters
and case specifics. Therefore, each physical cluster
blank/addressable matrix is represented by in at least the same
size or larger "virtual" matrix in CPU and operating memory of a
CAD/CAM system. The CAD/CAM system or milling center addresses the
addressable matrix via its operational software or other means to
automate the operations, saving time and money and minimizing
waste. Thus the required optimization can be conducted by well
known methods used in operations research and image processing such
as factor analysis based on eigenvectors and eigenvalues.
[0075] As nearly all dental CAD/CAM systems are capable of milling
plastic (e.g. PMMA) or composite material, frameworks formed from
such materials can be milled, modified or optimized using the same
milling unit and nesting software used to mill the blanks.
Furthermore, the frameworks can be re-used, making their
fabrication in the same milling unit even more economical. Compared
to attachment onto a stub or mandrel, like in the Sirona system,
attachment along the entire perimeter of a blank lowers stresses
during milling and thus lowers strength and stiffness requirements
for the framework material, thus making PMMA or polymer composite
materials a feasible choice for cluster blank frameworks.
[0076] Furthermore open architecture systems are not limited to CNC
milling machines specifically designed for dental use, practically
any robust 3-axis or higher CNC machine can be utilized. More and
more off-the-shelf CNC machines are being modified for dental use,
i.e. fitted with a blank holder and interfaced with an open
architecture scanner such as 3Shape's D-250, and used in large labs
and milling centers for commercial production of dental articles
primarily such as zirconia frameworks and custom implant abutments.
For a custom made system the cluster blank approach is most
advantageous in that it allows one to "many" the existing range of
blocks to a given milling unit without serious modification of the
machine hardware.
[0077] According to another aspect, the present invention provides
for nesting software to be used in conjunction with cluster blanks.
Nesting software can convert physical m-unit addressable matrix
(comprising m sub blanks) into a multidimensional matrix by adding
dimensions related to the type and other characteristics of
sub-blanks, assignment of milling subroutines and/or algorithms
optimizing tool path, tool selection, depth of cut, feed rate, RPM,
linear speed and other milling parameters. One of the added
dimensions for computer representation of an addressable matrix can
be assembly instructions if the addressable matrix is assembled
automatically. If necessary, sub-blanks and/or frameworks of
cluster blanks are marked with indices or alphanumeric codes,
barcodes, or other form of identification in any computer-readable
format. Alternatively, frameworks of cluster blanks comprise
magnetic strips, microelectronic chips or other re-writable data
storage microdevices that carry identification and any other
information relevant to milling and processing of a given cluster
blank. This is especially useful when the CAD/CAM system is not
equipped with nesting software.
[0078] An example of nesting software of the first order (as
defined below) is given in U.S. Pat. No. 5,662,566, incorporated by
reference herein in its entirety. Currently, nesting software is
hardly being utilized in dental CAD/CAM systems and its use is
limited to mapping parts to be milled into individual large-size
blanks (mill jobs) to maximize an average yield per blank, wherein
the average yield per blank is calculated as the weight of a
finished restoration divided by a weight of a blank prior to being
shaped by material removal. Cluster blanks of the invention allow
for a much broader use of nesting software in conjunction with
actual cluster blanks, and in certain embodiments nesting software
also enables the use of virtual blanks.
[0079] Nesting software is becoming a necessity for systems capable
of milling large blanks. It is more imperative for milling cluster
blanks. To illustrate the embodiments of this invention related to
applications of nesting software in conjunction with cluster
blanks, a 4'' diameter disk-shaped blank as a typical example of a
large single blank can be beneficially converted into a cluster
blank. Hereafter the former is called a precursor blank and the
latter is referred to as an equivalent cluster blank. These blanks
made of soft-sintered zirconia can accommodate up to 10-15 mill
jobs or 20-40 units varying from single units up to a 14-unit round
house (see FIG. 5A). FIGS. 1-2 are illustrative of how such a blank
looks after milling wherein the arrangement of mill jobs were not
optimized leading to the actual yield of much less than 50% of the
blank material. The holes left after milling individual cases
define milling envelopes for these cases. The term milling envelope
is used to explain various aspects of the present invention related
to use of nesting software. A milling envelope is defined by its
maximum length (MEL) and maximum width (MEW) provided that its
depth is equal to the thickness of the blank.
[0080] It is important to note that although 4'' round zirconia
blanks are used in the illustrative examples of large blanks
(precursor blanks) converted into equivalent cluster blanks,
zirconia is not the only dental material that can be produced in a
plurality of small and large shapes millable into single or
multi-unit frameworks according to the present invention. For
example, lithium silicate-based glass ceramics, which can be easily
processed by machining into dental articles without undue wear of
the milling tools and which subsequently can be converted into
lithium disilicate restorations showing high strength of up to
about 800 MPa are useful for single units as well as multi-unit
dental restorations. Glass ceramics are shaped while in the glass
state thus any glass-forming, glass-shaping technique can be
potentially used for these materials. Other examples of strong
dental materials formable into any shape and form, and further
amenable for milling into multi-unit dental articles are dental
alloys. Zirconia, glass-ceramics and alloys can be produced as
simple shapes (rectangular, cylindrical, disk or polygon) or
complex shapes ("smart" or near-net shapes) of any size. The
driving force of reducing waste is equally strong for all these
materials. If nesting software were to be used, the material waste
would be much less that that shown in FIGS. 1-2. Alternatively
sub-blanks can be assembled into a cluster blank, which will
further reduce the waste perhaps even ten-fold compared to
application of the first order nesting software to one or few large
blanks. The further reduction of waste achieved according to the
present invention comes from synergetic use of cluster blanks in
combination with higher order nesting software, as described in the
embodiments below.
[0081] The nesting software estimates the size and shape of milling
envelopes corresponding to mill jobs in a job queue based on prior
statistics or case electronic data, computes the required number of
sub-blanks and frameworks, orders assembly of the sub-blanks and
frameworks into the required number of cluster blanks, and
optimally distributes mill jobs between the sub-blanks and the
cluster blanks to minimize material waste and shade inventory.
[0082] In relation to the present invention, existing and future
nesting software modules can be classified based on the level of
intelligence and number of cases they can handle concurrently,
i.e., using an "N/n" ratio wherein "N" is the number of cases
"optimized" concurrently (Characteristic Batch Size) and "n" is the
average number of individual units per blank. The function of
nesting software is to maximize an average yield per blank and
therefore to optimize "n" (not necessarily maximize), i.e. to
optimize (and not necessarily minimize) number of blanks used for
milling the characteristic number of cases, "N", relevant to
operations of the given CAD/CAM facility. In terms of its use in
the embodiments of the present invention, nesting software is
classified as first, second and the third order based on its
ability to simultaneously handle smaller or larger batches (queue)
of cases, i.e., the N/n ratio. Examples of "n" are 7 or greater, 10
or greater and 30 or greater.
[0083] The first order nesting software, wherein N/n<10 is
capable of maximizing yield from a given blank, i.e. it can
position consecutive mill jobs within the blank being milled to
minimize waste. The related procedure amounts to distributing mill
jobs accumulated in a queue allocated for one or a set of new
blank(s) installed in a fixture or a cartridge of the milling unit.
In other words the first order nesting software fits a limited
number of individual cases into a volume of a blank. As the queue
of mill jobs is small and different each time, the result is also
different each time and no patterns can be elucidated. That is
about where the industry is now. Currently, the holders capable of
housing large multi-case blanks are limited to carrying a maximum
of two blanks at a time (for example, see FIG. 8). For example, N/n
is 0.55 and 0.35 for blanks of FIGS. 1 and 2, respectively. If both
blanks were milled in a system using nesting software in
combination with a milling unit equipped with a two-blank holder
the resulting average number of units per blank would be 26.5 and
the associated N/n ratio would be 0.87 (see Table 1 below). From
the analysis of the data in a Table 1, it was concluded that about
30 is a good estimate of the "optimized" average number of milled
units per 4'' round blank.
TABLE-US-00001 TABLE 1 Examples of N/n calculation Number of Number
(or average number) Blank cases, N of units per blank, n N/n first
4'' disk 12 22 0.55 second 4'' disk 11 31 0.35 Combination 23 26.5
0.87
[0084] The first order nesting software is used for directing mill
jobs into known positions within a cluster blank where the
corresponding sub-blanks are located, i.e. correctly positioning
milling envelopes corresponding to each mill job within the
appropriate sub-blanks of a cluster blank. This function will be
referred to as placement function. Waste is thus limited to two
components: 1) material removed during milling of a sub-blank; and
2) material thrown out, i.e. volume difference between the actual
milling envelope and the corresponding sub-blank of a cluster
blank. Most of the waste is now avoided by the use of a framework
or template of the cluster blank. The second component of waste is
subject to minimization through use of higher order nesting
software as shown below.
[0085] The second order nesting software, wherein N/n=10-100, is
capable of maximizing yield from a relatively large batch of
blanks, wherein the size of the batch N, is operations-relevant,
i.e., related to a characteristic time sufficient to acquire
statistically significant data depending on the size and logistics
of a given CAD/CAM facility. Hereinafter N is called Characteristic
Batch Size if it is operations-relevant, namely if it is defined by
the logistics of operations of a given milling center and market
requirements. For example, under steady state operations each
business day the number of cases received (daily input) is equal to
the number of cases shipped to the customers (daily output). An
average residence time of a case in a milling center, or time
passed from a case entering milling center to a case leaving it, is
limited by the market situation. Currently, for a milling center to
be successful the turn-around time should be less than a week,
i.e., customers should receive their cases back in less than a
week, therefore the residence time of the case in a milling center
should be 3-5 business days, regardless of the complexity of the
case. Therefore, each day the number of cases in the pipeline of a
given milling center is 3-5 times the daily input/output. Therefore
Characteristic Batch Size is at least equal to the number of cases
in a daily job queue for a high productivity CNC milling machine
and can be as large or larger than total daily case load, i.e., all
the cases, in all stages, in the pipeline of a given milling center
or the daily job queue for the whole milling center. Examples of
high productivity CNC milling machines especially suited for large
milling centers are ZENO.RTM. 6400 L milling machine with four
material holders and Etkon's HSC (High Speed Cutting) machines.
[0086] Small to mid-size milling centers process from 100 to 500
cases a day or 500-3000 cases a week. If only 4'' round blanks are
used in such a milling center, assuming an "optimized" n value of
30, the resulting N/n ratio is in the range of 17-100. The nesting
software of the second order is not just fitting a limited number
of individual cases in a volume of a large blank as does the first
order nesting software. Second order nesting software also
optimizes the arrangement and assortment of sub-blanks assembled
into a range of cluster blank templates for a given master type,
thus minimizing waste and shade inventory for much larger batches
of cases.
[0087] A possible master template 60 master type framework or
simply master for a cluster blank equivalent to a 4'' round
precursor blank is shown in FIG. 9. The template 60 for this master
type comprises an outer ring 62 and an inner core 64 wherein outer
ring 62 can hold larger size sub-blanks such as either 66 or 68,
and inner core holds smaller size sub-blanks 70, 72. While the
overall dimensions of these templates are the same and specific to
a given master type, there may be a difference in a number and size
of openings (as represented in the illustrative embodiment in
broken lines) in each template. For example, the template shown in
FIG. 9 can house the largest sub-blanks 66 for 4 to 6-unit
frameworks in the outer ring according to one configuration, or
medium sub-blanks 68 for 2 to 3-unit frameworks in the outer ring
according to an alternative configuration. The inner core can
likewise have different arrangements of relatively smaller
sub-blanks. For example, as illustrated in FIG. 10, the inner core
64' may comprise an arrangement of first polygonal sub-blanks 70'
and second round or oval sub-blank 72'. According to the
illustrated example, the inner core 64' comprises an arrangement of
2 relatively large polygonal blanks 70' and four relatively smaller
round or oval blanks 72'. A further alternatively constructed inner
core 64'' is illustrated in FIG. 11. As illustrated therein, the
inner core 64'' arrangement may comprise an arrangement of first
polygonal sub-blanks 70'' and second round or oval sub-blanks 72''.
According to the illustrated example, the inner core 64'' comprises
an arrangement of 2 relatively large polygonal blanks 70'' and two
relatively smaller round or oval blanks 72''. Any type of
arrangement of sub-blanks may be used, such as for example, large
sub-blanks for the manufacture of two- to three-unit articles and
small sub-blanks for the manufacture of single-unit dental
articles.
[0088] The maximum number of sub-blanks depends on the construction
and diameter of the template, and also on the arrangement, shape
and size of the constituent sub-blanks. Based on feed-back from the
nesting software of the second order, some and not necessarily all
the available positions on the template are filled, or are
necessarily filled with sub-blanks of the same shade.
[0089] In one aspect of the invention, the method is provided
wherein a CAD/CAM system equipped with nesting software collects
data to determine the types of sub-blanks that will be required for
future operations. At the beginning of the process, for a
sufficient time period, the 4'' round zirconia precursor blanks are
milled rather than the cluster blanks and the nesting software
operates as 1.sup.st order simultaneously collecting statistics on
the size distribution of milling envelopes. Based on actual milling
of precursor blanks, the size distribution diagrams, histograms,
curves or surfaces are generated for milling envelopes
corresponding to posterior and anterior single dental units and
multi-unit dental frameworks. FIG. 12 shows 2D "Frequency vs. MEL"
section of one such curve wherein milling envelopes are
characterized in the most simplistic way by their maximum length
(MEL) and maximum width (MEW). Even in this simple representation
the resulting size distribution is a complex surface in an
orthogonal 3D system of coordinates also shown schematically in
FIG. 12. The size distribution curve exhibits peaks and valleys the
physical meaning of which is shown in the Table 2 below.
TABLE-US-00002 TABLE 2 Positions and physical meaning of peaks and
valleys on milling envelope size distribution curve Positions of
peaks and valleys on milling envelope size distribution Peak* MEL,
Corresponding Valley** Corresponding curve mm MEW, mm MEL, mm MEW,
mm 1.sup.st (Anterior single units) 15 13 18 15 2.sup.nd (Posterior
single units) 22 16 28 19 3.sup.rd (3-unit frameworks) 35 21 40 22
4.sup.th (4-unit frameworks) 45 23 55 23 *The most frequent value
of MEL for certain type of cases, e.g. the most frequent milling
envelope length (MEL) for a three unit bridge framework is about 35
mm. **In-between values correspond to rarely occurring, the largest
n-unit cases and rarely occurring, the smallest (n + 1)-unit cases.
For example the holes (milling envelopes) left after milling of
nearly all 3-unit frameworks are shorter than 40 mm, however the
holes for 4-unit frameworks are mostly longer than 40 mm. Therefore
40 mm .times. 22 mm sub-blank will fit most of 3-unit
frameworks.
[0090] The milling envelope size distribution presented in FIG. 12
leads to logical selection of cylindrical sub-blanks of about 15-18
mm in diameter or rectangular sub-blanks of 15.times.18 mm.sup.2 in
cross-section for anterior single units, 19.times.28 mm.sup.2
sub-blanks for posterior single units, 22.times.40 mm.sup.2
sub-blanks for 3-unit frameworks, and 23.times.55 mm.sup.2
sub-blank for 4-unit frameworks. With more accurate statistics
corresponding to a larger volume of cases these dimensions could be
further refined into subcategories related to anterior and
posterior multi-unit frameworks. These sub-blanks are also required
in at least two different thicknesses, therefore to minimize
zirconia waste, specifically the second component of waste, the
nesting software should manipulate with at least 8 different
sub-blank sizes arranging them in outer ring/inner core templates
shown, for example, in FIG. 9.
[0091] Statistical analysis of size and shape distribution for
milling envelopes yields the optimal sub-blank dimensions. It is
found that if 1) the variety of sub-blank shapes and sizes is
consistent with the number of characteristic features (e.g. MEL and
MEW peaks or valleys) of the milling envelope size distribution
curves; and 2) the number of available modifications of the
utilized master template allows for the arrangement of these
characteristic shapes and sizes to match the given
operations--relevant batch of cases in the most optimal way, it
will lead to reduction of the second component of waste and also to
reduction of shade inventory. The optimal number of shapes and
sizes for sub-blanks can be elucidated logically by analysis of
data provided by the nesting software of the second order. The
nesting software of the second order is also capable of
recommending on its own the minimum number of sub-blank sizes to
achieve the required minimization of waste and shade inventory.
However it is not capable of designing or re-designing a master
template and developing the required number of its modifications.
The latter task will require nesting software of the third order
which can also use a virtual blank approach in lieu of actual
statistics acquired during milling.
[0092] The third and highest order nesting software, N/n>100 can
be deployed in the large central processing facilities and milling
centers processing more than a thousand cases a day. The potential
economy of scale in such facilities justifies the customized
sub-blanks variety and custom cluster blank designs. The designs
should be changed periodically to respond to changing demands of
the market. These facilities are large enough to dictate their
parameters to the manufacturers of sub-blanks, CAD/CAM units and/or
software. The nesting software appropriate for such facilities has
design capabilities integrated into a process feed-back loop that
allows for modification of the range of sizes and shapes for
constituent sub-blanks and the corresponding template design based
on the actual feed-back data. For example nesting software of the
third order is capable of modifying template dimensions, number,
size, shape and arrangement of sub-blanks in a template, as well as
to select the optimal shade distribution if the cluster blank
template and cluster blank housing/holder dimensions were designed
parametrically within the design envelope given by CNC machine
support dimensions.
[0093] Since prior to milling, all mill jobs exist as CAD files,
STL files or any other standard digital representations of complex
3D objects, the optimization functions described above can be
implemented prior to actual milling or concurrently with milling.
For example the size and shape distribution for milling envelopes
can be forecasted, i.e., derived or extrapolated from the plurality
of the CAD files to be milled. This data can be further used to
assemble, design and fabricate sub-blanks and templates/frameworks
for cluster blanks. This and other capabilities and functions of
different order nesting software are compared in a table below.
TABLE-US-00003 TABLE 3 Nesting Software Capabilities and Functions
1.sup.st Order 2.sup.nd Order 3.sup.rd Order Nesting Nesting
Nesting Nesting Software Capabilities/Functions Software Software
Software Characteristic N/n ratio: <10 10-100 >100 where "N"
- number of cases "optimized" concurrently and "n" - average number
of individual units per blank. Ranges for Characteristic Batch
Size, N, for n = 7 <70 70-700 >700 corresponding to the
optimized average number of units milled from a cluster blank
(e.g., FIGS. 25-27) Ranges for Characteristic Batch Size, N, for n
= 30 <300 300-3000 >3000 corresponding to the optimized
average number of units milled from a cluster blank Single blank
optimization function: minimizes X X X waste/maximize yield from a
single large blank Placement function: positions mill jobs onto
sub-blanks X X X of equivalent cluster blank Statistical function:
gives actual statistics on size and X X shape distribution for
milling envelopes Sub-blank optimization function: yields the
optimal sub- X X blank dimensions and optimal number of sub-blanks
Planning function: optimizes arrangement and X X assortment of
sub-blanks to be assembled into a range of cluster blank templates
to minimize waste and shade inventory for a large batch of cases
Virtual statistics: uses CAD files for future mill jobs to X
forecast size and shape distribution for milling envelopes Cluster
blank template optimization function: yields the X optimal template
design and optimal number of master template modifications Robotic
function: automated template fabrication and X assembly of cluster
blanks optionally based on virtual blank method
[0094] According to nesting software functions summarized in the
table above, there is provided a method of employing nesting
software for effective utilization, design and assembly of cluster
blanks to optimize placement of sub-blanks in a cluster blank
assembly, minimize waste and inventory of shades. The method can
optionally comprise system optimization software based on digital
process design (DPD) methodologies, specifically horizontally
structured CAD/CAM manufacturing using a virtual blank approach.
Said method comprises one or more of the following operations in
any combination and in any order:
[0095] 1) Analyze historic milling data provided by nesting
software related to placement of units on precursor blanks to gain
size and shape distribution for milling envelopes.
[0096] 2) Select an operations-relevant batch of cases to be milled
represented by their corresponding CAD, STL or equivalent files and
a range (of designs) of cluster blank templates to be fitted with
an optimal arrangement of sub-blanks.
[0097] 3) Alternatively to 1) use higher order nesting software to
provide "virtual statistics" extrapolating milling envelope size
and shape distribution from CAD files or any equivalent digital
representations of cases to be milled.
[0098] 4) Based on actual or virtual statistical analysis of the
operations-relevant plurality of milling envelopes establish the
optimal number of sub-blanks, their shapes and dimensions.
[0099] 5) Assemble the selected sub-blanks in the selected
templates to produce cluster blanks and mill the cases as directed
by nesting software.
[0100] 6) Re-acquire actual or virtual statistics on milling
envelopes and yields.
[0101] 7) Modify or redesign templates based on maximum average
yield, minimum waste per sub-blank and minimum sub-blank shade
inventory criteria.
[0102] 8) Mill modified or redesigned templates from plastic
precursor blanks using the same CAD/CAM system.
[0103] 9) Alternatively, mass production of templates can be
carried out using specialized equipment or can be outsourced.
[0104] 10) Assemble cluster blanks for milling the next
operations-relevant batch of cases as directed by nesting
software.
[0105] 11) Alternatively, at least some of operations 5) through
10) can be automated by the nesting software of the third order and
carried out robotically.
[0106] It should be noted that if the operations 5) through 10) are
automated by the nesting software of the third order, it is de
facto functioning as the manufacturing platform, specifically a
digital manufacturing platform. Currently, perhaps there is an
advantage to a milling center in operating CAD/CAM systems of
different types but with increasing demand for standardization and
raising market penetration of open architecture systems the driving
force to operate a one type, one platform system capable of milling
all types of materials will increase progressively. The need in
such a manufacturing platform for large central processing
facilities and milling centers will increase greatly with further
progress of digital revolution in dentistry, advent of
impression-less dentistry and web-based processing centers.
[0107] FIGS. 13 through 24 illustrate sub-blanks mounted in
frameworks by various means of attachment. FIGS. 13 and 14
illustrate different embodiments of the invention having round
frameworks 80 and 82. Framework 80 is a round configuration having
sub-blanks disposed along the periphery of framework 80. Framework
82 has a set of sub-blanks disposed in two rows at opposite sides
of the framework. Each sub-blank 84 is attached to a support 86
having a flange 88 attached to shaft 90 having a longitudinal axis
that is attached to framework 80. Sub-blank 84 may be glued or
otherwise adhered to flange 88. Shaft 90 may have any
cross-sectional shape such as hexagonal or octagonal, although it
is preferable that it has a round cross-section. Shaft 90 may be
snapped into frameworks 80 and 82. Alternatively, shaft 90 may
contain a groove that extends about its circumference to receive a
set screw or other structure.
[0108] FIGS. 15 and 16 show sub-blanks 92 and 94, respectively
attached to a framework 96 and 98, respectively. In FIG. 15,
sub-blank 92 is nested in framework 96 by support 100. FIG. 16
shows sub-blank 94 having a notch 102 thereon for attachment to
framework 98.
[0109] FIGS. 17 through 19 show a rectangular-shaped framework 104
having sub-blanks 106 aligned in two rows, attached at opposite
sides of framework 104. Sub-blanks 106 are shown attached to a
support 108, which is attached to framework 104. Support 108
includes a flange 110 and a shaft 112 for attachment to framework
104.
[0110] FIGS. 20 through 24 show yet another embodiment of a cluster
blank 120 having a rectangular-shaped framework 122 with a series
of sub-blanks 124 attached along both sides of framework 122.
Sub-blanks 124 are attached to a support 126, which fits into
framework 122. Support 126 includes a flange section 128 and a
shaft 130, which extends into framework 122. In this example, the
portion of the sub-blank to be milled is disposed completely
outside the framework.
[0111] FIGS. 25 through 27 illustrate a cluster blank 140 having
sub-blanks 142 inserted and attached to a round framework 144. The
cut-away view in FIG. 25 illustrates the sub-blank in position and
attached or fitted snugly into a receptacle 146 which fits into
framework 144.
[0112] FIG. 27 illustrates an exploded view of cluster blank 140
showing a top section 148 and a bottom section 150 of framework
144. Sub-blanks 142 are placed in bottom section 150 and top
section 148 is positioned over sub-blanks 142 and bottom section
150 to hold sub-blanks 142 in place during milling. A bolt 152 or
similar fastening means is inserted into a series of openings in
the top and bottom sections to fasten and hold the sections
together.
[0113] FIGS. 28 through 33 show cross-sectional views of sub-blanks
142 positioned in framework 144. Each sub-blank is shown attached
to holder 146 which is positioned on bottom section 150. Top
section 148 is fitted onto bottom section 150 and bolts 152 or
similar means hold top and bottom sections together. As clearly
shown in FIG. 30, the sharp edge of the holder 146 squeezes into
the framework unit 148. FIGS. 32 and 33 more clearly show the sharp
edge of holder 146 that fits within framework 148. Sub-blanks 142
may be glued or similarly attached to 146 or the latter can snugly
contain the sub-blanks and serve as compression fittings, i.e.,
being squeezed by top and/or bottom sections. It should be
mentioned that the layout of the sub-blanks in framework 148 may be
any configuration including those shown in FIGS. 3 through 7 and 9
through 11. Holder 146 may be fabricated of a flexible, elastic or
rubber material. Moreover, the holder may be fitted to the cluster
blank by a snap connection or a compression fit. In all
embodiments, the sub-blanks may be attached directly to the
framework, or attached to an intermediate piece, which is attached
to the framework.
[0114] FIGS. 34 through 44 show yet another embodiment of a cluster
blank 170 having a framework 171 with sub-blanks 172 disposed
therein. Framework 171 includes an internal periphery 174 and
external periphery 176. Sub-blanks 172 may be attached directly to
framework 171 as shown in FIGS. 13-24 or may be attached to holders
178, as shown in FIGS. 34-40. Sub-blanks 172 may be aligned annular
along the inner periphery of framework 171 as shown in FIG. 13, or
may be aligned in rows as shown in FIG. 34.
[0115] Holders 178 are detachable/attachable to the internal
periphery 174 of framework 171. Framework 171 may be of any shape
such as circular, oval or polygonal and may include stationary
and/or moving parts. It is preferable that the framework is a
single, solid piece although multi-unit frameworks may also be
used. The framework, holder and sub-blanks may be fabricated of
plastic, composite, metallic or ceramic material.
[0116] FIG. 36 shows a cross-sectional view of framework 171 at
line 36-36 of FIG. 34. Sub-blanks 172 are attached to a support,
mandrel or stem including a shaft 180 and a platform or flange 182.
Shaft 180 is mechanically fastened to holder 178 with a hexagonal
socket screw 184 and hexagonal socket screw 186. FIG. 37 shows a
cross-sectional view of framework 171 at line 37-27 of FIG. 34.
Holder 178 is mechanically fastened to framework 171 with shoulder
screws 188. FIG. 38 shows a cross-sectional view of framework 171
at line 38-28 of FIG. 34 with a dowel pin 190 through prong 192 of
framework 171. The fastening means discussed includes any
mechanical means and is not limited to those shown.
[0117] FIGS. 39 through 44 shows various perspective views of
framework 171. FIG. 39 shows framework 171 having a series of
prongs or projections 194 disposed in internal periphery 174 of
framework 171. The mechanism to attach holder 178 to framework 171
is not limited to projections or prongs, and any type of mechanism
or design may be used. Prongs 194 are shown disposed at opposite
sides of internal periphery 174. Holders 178 can be mechanically
fastened onto prongs 194 of framework 171 with components such as a
hexagonal screw using hexagonal wrench 196. Likewise, sub-blanks
172 can be mechanically fastened to holders 178 with hexagonal
screws using a hexagonal wrench 198, as shown in FIG. 43.
[0118] FIG. 44 shows a series of four sub-blanks 172 disposed in
rows opposite to one another. It should be mentioned that the
sub-blanks 172 are in no way limited to the size, shape or color
shown. The sub-blanks can be of identical size, shade and/or
material or can be of different sizes, shades, and/or materials.
Moreover, if larger or smaller sub-blanks are used, the number of
sub-blanks will vary depending on the size. For example, if longer
sub-blanks are used, a single row of sub-blanks could be used as
opposed to the two rows shown in FIGS. 34 and 44. The sub-blanks
can be used to manufacture dental articles of all sizes including,
but not limited to, single-unit dental articles, two-unit dental
articles, three-unit dental articles, four-unit dental articles,
five-unit dental articles and six-unit dental articles. As shown in
the Figures, the sub-blanks have a base, a top and a plurality of
sides The base is mechanically fastened to, adhesively secured to,
or integrally attached to supports, mandrels or stems, which
include platforms or flanges 182 and shafts 180. The top and sides
are unenclosed for facile machining.
[0119] The following example illustrates the increased yield, and
reduced material waste, that can result from replacing a one-piece
disk or blank with a cluster blank formed according to the present
invention.
[0120] Individual ZirCAD blocks of two sizes--C14 and B40 (from
e.max CAD) are used as sub-blanks. A Charly4dental CNC milling
machine 56 (see, e.g., FIG. 8) for serial production of dental
prostheses (available from Charlyrobot, Cruseilless, France) is
used. Charly4dental is equipped with a disk fixing system capable
of housing two 100 mm (.about.4'') or smaller disks 58. It is
primarily designed for dry-milling of soft-sintered zirconia and
resin disks (like PMMA). A first 100 mm PMMA disk is used to
fabricate the framework (template) for a cluster blank using the
same milling machine. Four symmetrically arranged rectangular
openings with the dimensions of 25.times.20 mm.sup.2 and
45.times.20 mm.sup.2 are milled in PMMA disk, then 2 ZirCAD C15,
and 2 of C40 zirconia blanks are placed in the openings and the
resulting even gaps filled with LECOSET 100 castable mounting
material (available from LECO, product#812-125). Two 3-unit bridges
and 2 molars are milled into the sub-blanks. If a one-piece 100 mm
zirconia disk is used, the remaining zirconia will have to be
disposed of, as shown in FIG. 2. In case of a cluster blank, the
remnants of sub-blanks are removed and PPMA framework can be reused
to assemble the next cluster blank.
[0121] All numbers expressing quantities or parameters used in the
specification are to be understood as additionally being modified
in all instances by the term "about". Notwithstanding that the
numerical ranges and parameters set forth, the broad scope of the
subject matter presented herein are approximations, the numerical
values set forth are indicated as precisely as possible. For
example, any numerical value may inherently contains certain
errors, evidenced by the standard deviation associated with their
respective measurement techniques, or round-off errors and
inaccuracies.
[0122] Although the present invention has been described in
connection with preferred embodiments thereof, it will be
appreciated by those skilled in the art that additions, deletions,
modifications, and substitutions not specifically described may be
made without department from the spirit and scope of the invention
as defined in the appended claims.
* * * * *