2. Description of the Related Art A variety of dental procedures are known for replacing or repairing damaged, weakened or missing tooth structures. For example, a dental prosthesis commonly known as a filling is often used to fill cavities in teeth caused by tooth decay or caries. Somewhat larger prosthetics also used to fill cavities are known as inlays and onlays. Fillings, inlays and onlays may also be utilized to restore the shape of teeth that have been chipped or broken.

Other types of dental prosthetics include bridges, full crowns and partial crowns.

Typically, these prosthetics are much larger than fillings and as a result are often more visible in the oral cavity. Full and partial crowns may be supported by remaining portions of the original tooth structure and/or by a post extending toward the bony region of the jaw.

Bridges, on the other hand, are structures that connect to adjacent tooth structure and provide an artificial tooth or tooth crown to replace corresponding, missing structure.

In the past, fillings and some inlays and onlays were often made of a silver-colored metal alloy known as amalgam due to its relatively long life and relatively low cost.

Another advantage offered by amalgam is that it allows a dental practitioner to fit and fabricate the restoration during a single session with a patient. Unfortunately, amalgam is

not considered aesthetic since its silver color sharply contrasts to the appearance of natural teeth in the oral cavity.

Another material used for dental prosthetics, and particularly for larger inlays and fillings, is gold. However, like amalgam, the color of gold sharply contrasts with the appearance of natural teeth and is highly visible in the oral cavity. In addition, gold is relatively expensive in comparison to other dental materials.

As a consequence, many dental practitioners are increasingly turning to ceramic or polymer-ceramic composite materials for use to make dental prosthetics. Dental ceramic materials and dental polymer-ceramic composite materials can provide an appearance that closely matches the appearance of natural teeth. Such materials are also available in various color shades so that the practitioner can select a color that closely matches the color of adjacent tooth structure.

Dental polymer-ceramic composite materials for use as restoratives are available from various manufacturers in paste-type form. Such materials are often supplied in capsules that are releasably received in a receptacle of a hand-held dispenser. The dispenser typically includes a lever that, when depressed, extrudes a quantity of the material from the capsule and directly onto the tooth structure. The material includes a polymerization initiator that serves to harden the material once it has been placed on the tooth structure and shaped by the practitioner to resemble natural tooth structure.

A variety of techniques may be employed to help shape the unhardened restorative paste to a desired configuration once dispensed onto the patient's tooth structure. For example, if the material is used to fill a relatively small cavity, the material can be dispensed directly into the cavity and then shaped by hand. A hand instrument such as a dental pick is used to help pack the material in the cavity and to blend the external surface of the paste with adjacent, external portions of the patient's tooth. As another example, if a portion of one or more sides of a tooth is to be restored, the practitioner may elect to use a matrix band or sectional matrix band next to the tooth structure to help hold the material in place while it hardens. The matrix band or sectional matrix band serves as a formwork, similar to formwork used in concrete, to help hold the material in place and also to help define an outer surface of the composite material while it hardens.

However, larger prosthetics are often fabricated outside of the oral cavity and then placed in the patient's oral cavity once completed. For these types of prosthetics, an impression is often taken of the patient's tooth structure of interest along with adjacent regions of the gingiva, using an elastomeric impression material that provides a negative physical image of the tooth structure and gingival region. Next, a cast positive model is made by pouring a quantity of plaster of Paris into the impression and allowing the plaster of Paris to harden. The resulting plaster of Paris or"stone"model is then used in the laboratory to make a prosthetic that is ultimately transferred to the patient's oral cavity.

The laboratory procedure for making the prosthetic may be somewhat involved, depending on the type of prosthetic that is needed. In one method, for example, a wax replica of the desired crown is built on the stone model. The wax replica is then embedded in a refractory investment material and fired to create another negative physical image of the oral structure of interest. Porcelain is then forced into the investment material under pressure and heat in order to make the crown.

However, a number of disadvantages arise when the foregoing procedure is followed to make a crown. In such a procedure, the patient typically travels to the practitioner's office two times: a first time to enable an impression to be taken, and a second time a few days later after the stone model has been made and the crown has been fabricated in the dental laboratory. Moreover, if the completed crown must be returned to the laboratory because its shape, fit or appearance is not satisfactory, the patient is often then required to return to the dental office for a third visit. In many dental practices, the crown is not made in a laboratory that is part of the office but is instead sent to a central laboratory in another area of the town or region.

Furthermore, the fabrication of custom dental crowns and other prosthetics by hand from stone models is an art that involves a high degree of skill and craftsmanship, as well as intensive labor. Moreover, prosthetics that are placed in the anterior regions of the patient's oral cavity are often highly visible. It is widely considered difficult to make a porcelain prosthetic that exactly matches the translucency and color of natural teeth.

Recently, increased interest has been directed toward the use of computer automated machinery for fabricating dental prosthetics, using far less labor than prior methods such as the method for making a crown described above. For example, several

systems are known for collecting a set of electronic data that is representative of the patient's tooth structure of interest. The data is then used by an automated mechanical milling machine (such as computer-aided milling machine) to fabricate a prosthetic that, when completed, closely matches the shape of natural tooth structure.

Examples of computer-aided milling machines used in the field of dentistry include the CEREC 2TM machine available from Sirona Dental Systems of Bensheim, Germany, the VITA CELAYTM machine from Vita Zahn Fabrik of Bad Säckingen, Germany, PRO- CAMTM from Intra-Tech Dental Products, of Dallas, Texas and PROCERA ALL CERAMTM from Nobel Biocare USA of Westmont, Illinois. U. S. Patent Nos. 4,837,732, 4,776,704 and 4,575,805, as well as PCT Patent Application No. WO 96/37163 also disclose systems for making dental prosthetics using computer-aided milling machines.

The fabrication of a dental prosthesis using a computer-aided machining system typically involves the use of a"mill blank", a block of material from which the prosthetic is cut. Dental mill blocks are often made of a ceramic material. Commercially available dental mill blanks include VITA CELAYTM porcelain blanks from Vita Zahn Fabrik, VITA NCERAMTM ceramic blanks from Vita Zahn Fabrik, MACORTM micaceous ceramic blanks from Corning, and DICORTM micaceous ceramic blanks from Dentsply. A dental mill blank made of a ceramic silica material as described in U. S. Patent No. 4,615,678. An improved ceramic dental mill blank is described in applicant's co-pending application entitled"CERAMIC DENTAL MILL BLANKS", U. S. Serial No. 09/383,560, filed August 26,1999.

Dental mill blanks may also be made of resinous materials. An example of a dental mill blank made of a polymeric resin and a filler is described in applicant's co- pending U. S. patent application entitled"DENTAL MILL BLANKS", U. S. Serial No.

09/227,230, filed January 8,1999. Dental mill blanks made of such material exhibit superior milling characteristics such as hardness and cutting properties relative to previously known dental mill blanks.

Many commercially available dental mill blanks are made of a two-piece construction comprising a stub portion and a milling portion. The stub portion is cylindrical and adapted to fit into a collet or Jacobs chuck of a milling machine. The milling portion is typically made of a different material than the stub portion, and is secured

to the stub portion by adhesive or other means. An example of such construction is described in U. S. Patent No. 4,615,678.

The milling portion of two-piece mill blanks is typically made of one of the ceramic materials described above so that the resulting prosthetic provides an aesthetic appearance. By contrast, the stub portion of such mill blanks is often made of metal, since the metal stub portion is ultimately detached from the milling portion and does not form part of the finished prosthetic. The stub portion is typically made of a metal such as an aluminum alloy that is relatively easy to machine to precise tolerances.

Often, the stub portion of dental mill blanks made of two-piece construction has an enlarged collar that is located directly adjacent the milling portion. The collar extends outwardly from the stub portion in lateral directions and presents one or more reference surfaces that can be utilized by the computer-aided milling machine to determine the amount of wear on the milling tool. The collar also may have a notch or gap that is adapted to receive an indexing pin of the milling machine.

While the two-piece dental mill blanks described above have provided satisfactory results in the past, there is a continuing need in the art to improve mill blanks and the processes for making mill blanks. There is particularly a need for a mill blank that is relatively inexpensive and easy to manufacture, and yet provides all of the advantages of the mill blanks currently known.

Summary of the Invention The present invention is directed toward a dental mill blank that can be used to make a dental prosthesis, as well as a method of milling a mill blank to make a dental prosthesis. The mill blank of the invention is inexpensive, and yet can be made of a number of materials so that a practitioner can select the best material for the restoration at hand. The method of milling a mill blank according to the invention is simplified in comparison to past practice, and enables the use of relatively inexpensive mill blanks such as the mill blanks of the present invention.

In more detail, the present invention in one aspect is directed toward a mill blank for a dental prosthesis. The mill blank includes a stub portion for releasably mounting the

mill blank in a milling machine. The stub portion has a central axis. The mill blank also includes a shoulder portion located next to the stub portion. The shoulder portion extends outwardly from the stub portion in directions along the central axis as well as in directions perpendicular to the central axis. The mill blank further includes a milling portion for making a dental prosthesis. The milling portion is located next to the shoulder portion and extends outwardly from the shoulder portion in a direction along the central axis. The stub portion, the shoulder portion and the milling portion are integrally connected to each other and made as a unitary body from the same material. The shoulder portion includes a notch for receiving an indexing pin of the milling machine.

Another aspect of the present invention is directed toward a method of milling a mill blank to make a dental prosthesis. The method includes the act of providing a mill blank having a stub portion for mounting the mill blank in a milling machine, and a milling portion for making a dental prosthesis. The milling portion and the stub portion are integrally connected to each other and made as a unitary body from the same material.

The method also includes the act of calibrating wear of a tool of the milling machine by contacting the tool against the milling portion in an area next to the stub portion.

Further aspects of the invention are defined in the features of the claims.

Brief Description of the Drawings Fig. 1 is a side elevational view of a dental mill blank that is constructed in accordance with one embodiment of the present invention; Fig. 2 is a fragmentary, front elevational view of a portion of the mill blank illustrated in Fig. 1; Fig. 3 is a bottom view of the mill blank shown in Figs. 1 and 2; Fig. 4 is a bottom view of a dental mill blank that is constructed in accordance with another embodiment of the invention; Fig. 5 is a side elevational view of a dental mill blank that is constructed in accordance with yet another embodiment of the invention; Fig. 6 is a side cross-sectional view of a dental mill blank that is constructed according to still another embodiment of the invention; and

Fig. 7 is a side elevational view of a dental mill blank that is constructed according to an additional embodiment of the invention.

Detailed Description of the Preferred Embodiments A dental mill blank according to one embodiment of the invention is illustrated in Figs. 1-3 and is designated by the numeral 10. The mill blank 10 broadly includes a stub portion 12, a milling portion 14 and a shoulder portion 16 that is located between the stub portion 12 and the milling portion 14.

The stub portion 12 is elongated and extends along a central reference axis that is designated 18 in Fig. 1. The stub portion 12 preferably has an overall cylindrical shape, although other shapes are also possible. For example, the stub portion 12 could have a hexagonal shape or octagonal shape in reference planes perpendicular to the central axis 18. Preferably, the stub portion 12 has an outer end section 20 that is chamfered to facilitate insertion of the mill blank 10 into a collet or chuck of a milling machine.

The shoulder portion 16 is located directly next to the stub portion 12. The shoulder portion 16 extends outwardly from the stub portion 12 in directions along the central axis 18 as well as in directions perpendicular to the central axis 18. Preferably, the shoulder portion 16 presents an outermost, external cylindrical surface that is coaxial with the central axis 18. As an alternative, however, the outermost surface of the shoulder portion 16 may have a shape other than cylindrical such as square, hexagonal, octagonal and other polygons or non-polygons (including oval), and need not be centrally aligned with respect to the central axis 18.

The milling portion 14 is located directly adjacent the shoulder portion 16 and extends outwardly from the shoulder portion 16 in a direction along the central axis 18.

The milling portion 14 in the illustrated embodiment has an overall cylindrical shape that is coaxial with respect to the central axis 18, although other constructions are also possible. For example, the milling portion 14 may have a shape in reference planes perpendicular to the central axis 18 that is rectangular, square, hexagonal or other types of polygons or non-polygons including oval. Moreover, the milling portion 14 may or may not be centrally aligned with respect to the central axis 18.

Optionally, but not necessarily, the cross-sectional configuration of the milling portion 14 is identical to the cross-sectional configuration of the shoulder portion 16 when considered in reference planes perpendicular to the central axis 18. In the illustrated embodiment, the milling portion 14 and the shoulder portion 16 have matching cross- sectional configurations that together present a single cylindrical shape which is coaxial with respect to the central axis 18.

Various means of milling the mill blank 10 of the present invention may be employed to create a custom-fit dental prosthetic or dental prosthetic component 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.

The shoulder portion 16 includes a notch 22 for receiving an indexing pin of a milling machine. As shown in the drawings, the notch 22 extends along a cylindrical surface section of the shoulder portion 16 as well as along a flat end section of the shoulder portion 16 that faces the stub portion 12. Optionally, but not necessarily, the notch 22 has a curved upper wall that can be observed in Fig. 2 such that the notch 22 presents an overall, generally inverted"U"-shaped configuration in the front view.

Optionally, the shoulder portion 16 presents a calibration surface, such as the calibration surface 24, for use during the milling process to establish tool wear. The calibration surface 24 in this embodiment has the shape of a partial cylinder, although other shapes are also possible. The calibration surface 24 may be located next to the notch 22 or alternatively may be located on the shoulder portion 16 in an area opposite the notch 22 relative to the central axis 18.

The calibration surface 24 is manufactured to be located a precise distance, within very precise dimensional tolerances, from the central axis 18. An example of a suitable dimensional tolerance is plus or minus 0.2 mm. The dimensional tolerance is preferably plus or minus 0.1 mm, more preferably is plus or minus 0.05 mm and most preferably is plus or minus 0.01 mm.

The calibration surface 24 is used by the milling machine, typically before the milling process begins, as a reference surface to accurately determine the overall dimension (such as the length) of the milling tool. As an example, the milling machine

may rotate the milling tool while slowly moving the tool toward the calibration surface 24.

The milling machine has a speed sensor for detecting rotational speed of the tool and a positional sensor for tracking the axial position of the tool. The rotational speed of the tool slightly decreases as soon as the tool contacts the calibration surface 24. The machine is programmed to determine the overall length of the tool and compensate for tool wear by determining the axial position of the tool (i. e., the distance from the reference axis 18) in relation to the calibration surface 24 as soon as a decrease in the rotational speed is detected. Other methods to use the calibration surface 24 as a reference surface are also possible, such as methods that employ laser sighting techniques.

The stub portion 12, the milling portion 14 and the shoulder portion 16 are integrally connected to each other and made as a unitary body from the same material. The selected material should be suitable for use in the oral cavity as a dental prosthetic and also capable of being milled in the intended milling machine without undue hindrance.

Examples of suitable materials include ceramics, polymers, polymer-ceramic materials and metals.

Examples of suitable metals include stainless steel, alloys of gold or titanium, nickel-based alloys, cobalt-based alloys or any other alloy suitable for use in the oral environment. Examples of suitable alloys, palladium-based alloys, include those marketed under the tradenames RexilliumTMIII, Jeneric/Pentron, Inc., Wallingford, Connecticut; DegudentTMH, Degussa Corporation, South Plainfield, New Jersey; PaladentTMB, Jeneric/Pentron Inc., Wallingford, Connecticut; Rexillium NBF, Jeneric/Pentron, Inc., Wallingford, Connecticut and AllvacTM-6-4, Teledyne Allvac, Monroe, North Carolina.

Examples of suitable ceramic materials include glasses, monocrystalline and polycrystalline ceramics, and glasses with crystalline phases. Polycrystalline ceramics include nanocrystalline materials and may be single phase or multiphase. Preferred crystalline ceramic materials include aluminum oxide, magnesium-aluminum spinel (MgA1204), zirconium oxide, yttrium aluminum garnet, zirconium silicate, yttrium oxide and mullite. Preferred glass containing materials include feld-pathic porcelains; glasses containing crystalline; phases such as mica, leucite, canasite, alumina, zirconia, spinel, hydroxyapatite; and amorphous glasses such as Pyrex, VycorTM, (both from Corning, Inc., Corning, New York). Preferred ceramics include those marketed under the

tradenames In-Ceram, (Vita Zahnfabnik, Bad Säckingen, Germany), Mark IITM, (Vita Zahnfabnik, Bad Säckingen, Germany), ProCADTM, (Ivoclar AG, Schaan, Lichtenstein), Empress (Ivoclar AG, Schaan, Lichtenstein), Empress 2TM (Ivoclar AG, Schaan, Lichtenstein), MACORTM, (Corning Inc., Corning, New York), DICORTM, (Dentsply International, York, PA), DenzirTM, (Dentronic AB, Shelleftea, Sweden), Prozyr, (Norton Desmarquest, Vincennes Cedex, France), LucaloxTM, (General Electric, Richmond Heights, OH), Bioglass TM, (U. S. Biomaterials Corp., Hachua, FL), Cerabone A/W, (Nippon Electric Glass, Shiga, Japan), Transtar TPA (Ceradyne, Inc., Costa Mesa, California), AD-998 (Coors Ceramics, Golden, Colorado), and 998 (Vesuvius McDanel, Pennsylvania).

The ceramic mill blanks may be provided either in a fully dense form, with little or no porosity, or in a porous, partially fired form. If the ceramic mill blank is porous, it may be fired to a fully dense state after milling. Alternatively, the porous ceramic mill blank may be infiltrated with, for example, a molten glass or a resin that is then hardened after infiltration.

Preferably, the ceramic material transmits light in the visible wavelengths in order to provide an aesthetically pleasing appearance once milled into a prosthetic and placed in the oral cavity. Preferably, the ceramic material is essentially colorless; i. e., it neither adds nor subtracts color to the light passing through the material to any appreciable extent.

Optionally, however, colorants may be added to achieve desired shades that mimic the color of natural teeth that may be observed in certain patients.

Preferably, the ceramic mill blanks according to the invention and the resulting prosthetics have a Contrast Ratio value less than about 0.7, preferably less than about 0.6, and more preferably less than about 0.5. The Contrast Ratio value can be determined by following the technique described in Section 3.2.1 of ASTM-D2805-95, modified for samples of about 1 mm thick. The Contrast Ratio value is an indication of the level of light transmissivity possessed by the mill blank 10 and the resulting prosthesis.

Further details regarding preferred ceramic dental mill blank materials and manufacturing methods for those materials, including information concerning modification of the Contrast Ratio described above, are set out in applicant's co-pending U. S. patent application entitled"CERAMIC DENTAL MILL BLANKS", U. S. Serial No. 09/383,560.

Preferred polymer-ceramic composite materials for the mill blank 10 include polymerizable resins having sufficient strength, hydrolytic stability, and non-toxicity to render it 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, polymer or both. Alternatively, the resin may be made from a material comprising a monomer, oligomer or polymer comprising a free radically curable functionality and a cationically curable functionality. Suitable resins include epoxies, methacrylates, acrylates and vinyl ethers.

Polymers for the polymer-ceramic composite mill blank 10 include thermoplastic and thermosetting polymers. Suitable thermoplastic polymers include polycarbonates, nylon, polyetheretherkitone, polyurethanes, polyimids and polyamides. The polymer material may be filled with one or more types of ceramic filler as described below.

The polymer-ceramic composite material also includes an initiator for initiating polymerization of the material. For example, one class of useful initiators includes sources of species capable of initiating both free radical and cationic polymerization. Preferred free radical polymerization systems contain three components: an onium salt, a sensitizer and a free radical donor. Optionally, the sensitizer may be a visible light sensitizer that is capable of absorbing light having wavelengths in the range from about 3 nanometers to about 1000 nanometers. If the resin in the polymer-ceramic composite is not sufficiently hardened before milling, further hardening can be carried out after milling and before use in the oral cavity.

Preferably, the polymer-ceramic composite material also includes a filler. The filler is preferably a finely divided material that may optionally have an organic coating.

Suitable coatings include silane or encapsulation in a polymeric matrix. The filler may be selected from one or more of many materials suitable for incorporation in compositions used for medical or dental applications, such as fillers currently used in dental restorative compositions and the like.

Suitable fillers include zirconiz-silica, baria-silica glass, silica, quartz, colloidal- silica, fumed silica, ceramic fibers, ceramic whiskers, calcium phosphate, fluoroaluminosilicate glass and rare-earth fluorides. Suitable fillers also include nanosize heavy metal oxide particles such as described in applicant's co-pending patent application

entitled"RADIOPAQUE DENTAL MATERIALS WITH NANO-SIZED PARTICLES" ; U. S. Serial No. 09/429,185 filed October 28,1999. Other suitable fillers are described in applicant's co-pending patent applications entitled"CLUSTERED PARTICLE DENTAL FILLERS" (U. S. Serial No. 09/428.830 filed October 28,1999) and"DENTAL MATERIALS WITH NANO-SIZED SILICA PARTICLES" (U. S. Serial No. 09/428,937 filed October 28,1999). Additional suitable fillers are described in U. S. Patent No.

4,503,169, and applicant's co-pending patent application entitled"RADIOPAQUE CATIONICALLY POLYMERIZABLE COMPOSITINS COMPRISING A RADIOPAQUE FILLER, AND METHOD FOR POLYMERIZING SAME" (U. S. Serial No. 09/168,051 filed October 7,1998). The fillers may be in any morphology, including spheres, platelets, whiskers, needles, fibers, ovoids, etc. or any combination of the foregoing.

Further information regarding preferred polymer-ceramic composite materials, including details of suitable compositions and method of manufacturing those materials, are set out in applicant's co-pending U. S. patent application entitled"DENTAL MILL BLANKS", U. S. Serial No. 09/227,230.

The mill blanks of the invention are suitable for fabricating into a variety of restorations, including inlays, onlays, crowns, veneers, bridges, implant abutments, copings and bridge frameworks. Various means of milling the mill blank of the present invention may be employed to create custom-fit dental prosthesiss having a desired shape.

It is preferable that the prosthesis be milled quickly without imparting undue damage.

Preferably, the prosthesis is milled by computer controlled milling equipment, such as machines sold under the tradenames Sirona CEREC 2, Dentronics DECIM or CadCam Ventures PROCAM.

By using a CAD/CAM milling device, the prosthesis can be fabricated efficiently and with precision. During milling, the contact area may be dry, or it may be flushed with or immersed in a lubricant. Alternatively, it may be flushed with an air or gas stream.

Suitable liquid lubricants are well known, and include water, oils, glycerine, ethylene glycols, and silicones. After milling, some degree of finishing, polishing and adjustment may be necessary to obtain a custom fit in to the mouth and/or aesthetic appearance.

A dental mill blank 10a according to another embodiment of the invention is illustrated in Fig. 4 in bottom view. The dental mill blank 10a is essentially the same as the mill blank 10 described above, except for the differences as noted below.

The mill blank 10a has a shoulder portion 16a with a notch 22a. The notch 22a is somewhat similar to the notch 22, in that the notch 22a extends along both a side section as well as an end section of the shoulder portion 16a. However, and as can be observed by comparing Fig. 4 to Fig. 3, the notch 22a has a somewhat different configuration than the notch 22.

More particularly, the notch 22a has a"V"-shaped configuration in bottom view.

Such a shape may be easier to manufacture in certain circumstances than the notch 22.

The"V"shape as shown is radially aligned with a central longitudinal axis of the mill blank 10a, although other orientations are also possible. Like the notch 22, the notch 22a is adapted to receive an indexing pin of a milling machine in order to index the mill blank 10a to a collet or chuck of the milling machine.

In other respects, the mill blank 10a is identical to the mill blank 10. As such, a detailed description of such identical features need not be repeated.

A dental mill blank 10b according to another embodiment of the invention is shown in side elevational view in Fig. 5. The dental mill blank 10b is essentially the same as the mill blank 10 except for the differences that are described below.

The dental mill blank 10b has a milling portion 14b with an outermost end that is remote from a stub portion 12b. Additionally, the mill blank 10b includes a calibration portion 26b that is directly adjacent the outermost end of the milling portion 14b. In the illustrated embodiment, the calibration portion has a cylindrical shape, although other shapes are also possible.

The calibration portion 26b is provided for use with certain milling machines that calibrate using an upper portion of the mill blank. For example, milling machines known as Cerac 2 from Sirona are adapted to calibrate and determine tool wear by use of a calibration surface remote from the stub. The calibration portion 26b eliminates the need for a calibration surface next to a stub portion, such as the calibration surface 24 that is located next to the stub portion 12 in the dental mill blank 10 described above.

A dental mill blank 10c according to another embodiment of the invention is shown in side elevational view in Fig. 6. The dental mill blank 10c is identical to the dental mill blank 10 except for the differences described below.

The dental mill blank 10c has a stub portion 12c, a milling portion 14c and a shoulder portion 16c. In this embodiment, however, the shoulder portion 16c extends outwardly past the milling portion 14c in a radial direction relative to a central reference axis and has a cross-sectional shape that is different than the cross-sectional shape of the milling portion 14c. The shoulder portion 16c is provided with a notch 22c that functions similarly to the notch 22 described above.

As illustrated in Fig. 6, the shoulder portion 16c and the milling portion 14c have cylindrical shapes that are each coaxial with a central longitudinal axis of the mill blank lOc. However, and as described above with reference to the mill blank 10, the shoulder portion 16c and the milling portion 14c may have other cross-sectional configurations as well, including configurations that are polygonal or non-polygonal. Additionally, the shoulder portion 16c and the milling portion 14c need not be centrally aligned with the central axis of the mill blank 10c. Moreover, the shoulder portion 16c may have a shape smaller than the milling portion 14c when viewed along the longitudinal axis of the mill blank 10c, such that the milling portion 14c extends outwardly past the shoulder 16c is a radial direction.

A dental mill blank 10d that is constructed in accordance with a further embodiment of the invention is shown in side elevational view in Fig. 7. The dental mill blank 10d is identical to the dental mill blank 10 except for the differences described below.

The dental mill blank l Od has a stub portion 12d, a milling portion 14d and a shoulder portion 16d. In this embodiment, however, the milling portion 14d extends outwardly past the shoulder portion 16d in a radial direction relative to a central reference axis 18d and has a cross-sectional shape that is different than the cross-sectional shape of the shoulder portion 16d. A calibration surface 24d in the illustrated embodiment is located on the shoulder portion 16d, although other constructions are possible. For example, the calibration surface 24d may be located on an upper section of the milling portion 14d remote from the stub portion 12d, or may be located on a portion that is

directly adjacent the outermost end of the milling portion 14d, similar to the location of the calibration portion 26b shown in Fig. 5. As another option, the shoulder portion 16d may be the same diameter as the stub portion 12d, and the indexing pin contacts the underside of the milling portion 14d when the mill blank 10d is placed in the collet or chuck.

Preferably, the shoulder portion 16d extends radially outwardly from the reference axis 18d a distance that is sufficiently small in order to avoid contact with an indexing pin once the stub portion 12d is inserted in a milling machine. Consequently, the reduced- sized shoulder portion 16d provides clearance for the indexing pin when the mill blank 10d is placed in the chuck or collet. Preferably, the cross-sectional shape of the shoulder portion 16d in reference planes perpendicular to the reference axis 18d is sufficiently small so that the indexing pin does not contact the mill blank 10d regardless of the rotational orientation of the mill blank 10d in the milling machine with respect to the central reference axis 18d. Such construction is an advantage, in that the user need not take the time to align a notch (such as the notch 22) with the indexing pin. Moreover, omission of the notch simplifies manufacture.

As one example, the shoulder portion 16d may have a circular configuration in reference planes perpendicular to the reference axis 18d, and may be oriented in coaxial relationship with the reference axis 18d as well as with the stub portion 12d and the milling portion 14d. However, the shoulder portion 16d may have any one of a number of other configurations, including the configurations described above with respect to the shoulder portion 16 of the mill blank 10.

A variety of other constructions are also possible and may be apparent to those skilled in the art. For example, the stub portion of the mill blank, such as the stub portion 12, may have a slot extending along its length to provide additional indexing as may be required. Optionally, such a slot may be radially aligned with the notch 22, and as an additional option the notch 22 may be formed using a cutting disk or wheel that also cuts the slot in the stub portion 12.

Alternative constructions include mill blanks having a calibration surface located on a shoulder portion near a stub portion, but lacking a notch to receive an indexing pin.

For example, such mill blanks could have shapes similar to the mill blank 10 illustrated in

Figs. 1-3 or the mill blank 10c shown in Fig. 6 except that the notch 22,22c respectively is omitted.

As other options, any of the mill blanks described above may be included as a kit that includes other items for use during the milling process or for use in the practitioner's office. For example, the mill blank may be provided in a kit that also includes a milling lubricant, a milling tool and/or instructions for using the mill blank. Alternatively, the mill blanks may be included in a kit that also includes a bonding agent, impression material, finishing or polishing materials, temporary prosthetic devices or any other item that may be useful in the practitioner's office for installation of the finished restoration or restoration component in the patient's oral cavity. Optionally, multiple shades, sizes, or geometrics may be provided in a kit.

Other constructions and options are also possible. As such, the scope of the invention should not be deemed limited to the presently preferred embodiments that are described in detail above, but instead only by a fair scope of the claims that follow along with their equivalents.