Provided are assemblies and related methods for abrading applications. More particularly, these assemblies and methods are directed to shaping, grinding and polishing applications for dental materials.

Background

Dental abrasives are commonly used in the dental industry for shaping, grinding and polishing a variety of dental materials, such as natural teeth, dentures and restorative resins. These dental procedures are useful in optimizing bite function and providing a natural and aesthetic appearance for the patient.

Dental abrasive assemblies can assume many different configurations, depending on the desired application. For example, some assemblies use abrasive particles coated on a rotating disc. The disc typically has a circular or non-circular hole located at the center of rotation. The hole in the disc engages to a suitable rotary power tool configured to spin the disc at high speeds during use.

Other assemblies use an integral polymeric composite embedded with abrasive particles. The composite can be molded into a suitable shape to facilitate polishing of the dental substrate. Again these molded composites are generally coupled to a rotary power tool to bring the abrasive particles to bear on the substrate to be polished. These moldable composites have the advantage of providing great freedom to optimize the shape of the abrasive member to suit the particular application at hand.

Both coated abrasive discs and composites naturally wear out rapidly during an abrading operation. To facilitate the replacement of these discs and composites, abrasive assemblies often include a disposable "head" component along with a non-disposable "drive" component. The head component includes the dental abrasive and is configured to allow a dental practitioner to conveniently engage and disengage it from the drive component.

Summary

While the use of a removable head component does provide a convenient way to replace the coated abrasive articles during or between abrading operations, several technical issues remain. For example, both the engagement and disengagement forces should be relatively low to allow easy user replacement of the head component. Yet, at the same time, these forces should be sufficiently high to prevent the abrasive member from wobbling or unintentionally dislodging from the power tool. Further, the mechanical coupling between the head and the drive components should also be sufficient to efficiently drive the head portion at high rotational speeds without slippage. Provided are abrasive assemblies that combine a head portion including an integral abrasive member and a drive portion including a cylindrical mandrel. The abrasive member has a receptacle adapted to receive a working end of the mandrel. As the abrasive member engages to, or disengages from, the mandrel, the receptacle resiliently expands and the working end of the mandrel resiliently compresses, each in cooperation with the other. In some embodiments, the receptacle and working end of the mandrel are shaped to provide contact over an extended area between the two components.

Optionally, the abrasive member is compressed in both directions parallel and directions perpendicular to the longitudinal axis of the mandrel.

In one aspect, a rotary dental abrasive assembly is provided. The rotary dental abrasive assembly comprises: a unitary abrasive member having a generally circular receptacle with a minimum inner diameter when the abrasive member is relaxed, the member comprising a resilient polymer composite comprising abrasive particles; and a generally cylindrical mandrel having an outer surface, a longitudinal axis and a bulbous working end received in the receptacle, the working end being divided into a plurality of sections by elongated slots extending from the outer surface of the mandrel toward the longitudinal axis, wherein the working end has an maximum outer diameter when relaxed and the plurality of sections and the abrasive member cooperatively deflect as the abrasive member is engaged to, and disengaged from, the mandrel.

In another aspect, a rotary dental abrasive assembly comprising: a unitary abrasive member having a generally circular receptacle with a concave inner surface, the member comprising a resilient polymer composite with abrasive particles distributed therein; and a generally cylindrical mandrel having an outer surface, a longitudinal axis and a bulbous working end received in the receptacle, the working end being divided into a plurality of sections by elongated slots radially extending from the outer surface of the mandrel toward the longitudinal axis, wherein the inner surface is complemental with the working end of the mandrel and the plurality of sections and the abrasive member cooperatively deflect as the abrasive member is engaged to, and disengaged from, the mandrel.

In still another aspect, a method of assembling a rotary dental polishing assembly is provided comprising: providing a mandrel having an outer surface, a longitudinal axis and a bulbous working end divided into a plurality of sections, the sections separated from each other by elongated slots extending from the outer surface toward the longitudinal axis; urging the working end toward a receptacle located on an abrasive member thereby inducing the plurality of sections to deflect resiliently toward each other as portions of the abrasive member around the receptacle resiliently expand; and retaining the working end against the receptacle such that the abrasive member contacts the mandrel along both concave and convex surfaces of the working end.

Advantageously, these abrasive assemblies and methods allow for increased manufacturing tolerances in both the abrasive member and mandrel. This benefit is achieved because the resilience of one member compensates for the manufacturing variability in the other member, and vice versa. Moreover, the resiliency of the mandrel provides freedom to use abrasive members with higher abrasive loadings, while still maintaining the same degree of retention and frictional engagement. The resilience of the mandrel also allows the walls of the abrasive member to be made thicker while maintaining the same retention and frictional engagement. Finally, the assembly as a whole can tolerate a much greater degree of mandrel wear while retaining adequate coupling between the abrasive member and mandrel. This increases reliability of the coupling and extends the operational lifetime of the mandrel.

Brief Description of the Drawings FIG. 1 is a perspective view of a dental abrasive assembly according to one embodiment;

FIG. 2 is a plan view of the assembly in FIG. 1 ;

FIG. 3 is a side cross-sectional view of the assembly in FIGS. 1-2 according to section "3-3" identified in FIG. 2;

FIG. 4 is a magnified side cross-sectional view of the assembly in FIGS. 1-3 presenting the circled region of FIG. 3 in greater detail;

FIG. 5a is a head-on view of a first component of the assembly in FIGS. 1-4;

FIG. 5b is a fragmentary elevational view of the component in FIG. 5a;

FIG. 6 is a cross-sectional view of a second component of the assembly in FIGS. 1-4;

FIG. 7 is a plan view of a dental abrasive assembly according to another embodiment;

FIG. 8 is a side cross-sectional view of the assembly in FIG. 5 according to section "5-5" identified in FIG. 5;

FIG. 9 is a magnified side cross-sectional view of the assembly in FIGS. 5-6 presenting the circled region of FIG. 6 in greater detail;

FIGS. 10a and 10b are perspective and cross-sectional views, respectively, of an abrasive member according to still another embodiment; and

FIGS. 1 1a and 1 lb are perspective and cross-sectional views, respectively, of an abrasive member according to yet another embodiment.

Detailed Description

An abrasive assembly according to one embodiment is shown in FIGS. 1-4 and broadly designated by the numeral 100. The assembly 100 includes an abrasive member 102 and a mandrel 104 (visible in FIGS. 1, 3 and 4) that is coupled to the abrasive member 102.

As shown in the FIGS. 1-2, the abrasive member 102 is a molded brush having a unitary construction, with a central annular hub 106 and a plurality of fingers 108 extending outwardly from the hub 106 in generally radial directions. In the embodiment shown here, the abrasive member 102 has thirty fingers 108. However, the number of fingers used could easily be made greater or smaller depending on the desired application. The hub 106 is symmetrically disposed about a longitudinal axis 122 that is perpendicular to the plane of the page in FIG. 2. Also symmetric about the longitudinal axis 122 and located on the opposite side of the hub 106 (visible in FIGS. 3 and 4) is a generally circular receptacle 1 10.

The abrasive member 102 is made from a composite abrasive, preferably a resilient polymeric composite abrasive. In some embodiments, the composite abrasive includes a thermoplastic material and abrasive particles distributed in the thermoplastic material.

In some embodiments, the abrasive member 102 comprises one or more thermoplastic elastomers. Thermoplastic elastomers include segmented polyester thermoplastic elastomers, segmented polyurethane thermoplastic elastomers, segmented polyamide thermoplastic elastomers, blends of thermoplastic elastomers and thermoplastic polymers, and ionomeric thermoplastic elastomers. Such segmented thermoplastic elastomers are further described in U.S. Pat. No. 5,903,951. Preferred thermoplastic elastomer polymers are segmented polyester thermoplastic elastomers, including those commercially available as HYTREL, available from E.I. duPont de Nemours, Wilmington, Delaware.

The abrasive member 102 need not be made from a thermoplastic elastomer. Instead, the abrasive member 102 may be comprised of a polymeric composite prepared from a conventional rubber or elastomeric material. These elastomeric materials include, for example, silicones, polyurethanes, and fluoropolymer elastomers.

In some embodiments, the abrasive particles are uniformly distributed in the abrasive member 102. The abrasive particles may be organic, inorganic, or a composite of either organic, inorganic, or both. The abrasive particle composition, concentration, and size can be tailored according to the nature of the intended workpiece surface and the desired effect of the molded brush on the workpiece surface.

Suitable inorganic particles can include those of silicon carbide, talc, garnet, glass bubbles, glass beads, cubic boron nitride, diamond, and aluminum oxide, including ceramic aluminum oxide such as that available as CUBITRON from 3M Company, St. Paul, Minnesota. Suitable organic abrasive particles include particles of comminuted thermoplastic or thermoset polymeric materials.

In some embodiments, the molded brush includes composite abrasive particles. Composite abrasive particles include agglomerates comprising inorganic particles adhered in an organic polymeric binder. Precisely shaped abrasive particles may also be employed. Sizes of abrasive particles may vary from mean particle diameters of less than 1 micrometer to particle mean diameters of up to about half the thickness of the molded brush bristle tip. The concentration of abrasive particles in the molded brushes may vary from zero to more than 50%.

As another option, the molded brushes may contain additives such as lubricants, colorants, coupling agents, compatibilizers, mold release agents, nucleating agents, and the like, as is known in the art. Abrasive particles and additives may be incorporated into the moldable organic polymer at the time of molding, or alternatively, abrasive particles and/or additives may be compounded with the moldable organic polymer prior to molding. Subsequently, a masterbatch can be molded, or mixed with additional moldable organic polymer, or other masterbatches, and then molded.

The preferred dimensions and materials described herein are selected so as to allow molding the brush while maintaining the thermoplastic material at a sufficiently high temperature to fill the mold. With the benefit of the teachings found herein, one of skill in the art could select thicknesses, materials, and temperatures to mold brushes not necessarily falling within the particularly preferred dimensions set forth herein. Moreover, the location of the mold gates and thickness of the hub could be optimized by one of ordinary skill in the art. Further details on configurations of integrally molded brushes and methods of making the same are found in U.S. Patent No. 5,903,951 (Ionta et al.).

As shown in FIGS. 3 and 4, the assembly 100 further includes a mandrel 104 that is

complementary to the abrasive member 102 and has a generally cylindrical shape. The mandrel 104 is generally symmetrical about its longitudinal axis 122, but need not have a uniform diameter or cross- sectional shape along its longitudinal axis 122. For example, as shown by the cross-sectional view of FIG. 3, the mandrel 104 includes sections having different diameters. Preferably, the mandrel 104 is made from a metal such as a 300- or 400- series stainless steel that permits autoclaving without issues of corrosion. Alternatively, the mandrel could be made from metals such as bronze or titanium, or even non- metallic materials, such as filled polymeric composites.

The mandrel 104 has a barrel section 1 12 and a bulbous working end 1 14 extending outwardly from the barrel section 1 12. The working end 114 has a maximum diameter that is somewhat smaller than that of the barrel section 1 12. Additionally, the working end 1 14 has a local diameter that varies with respect to its longitudinal axis 122, and further includes a neck 1 16 immediately adjacent the barrel section 1 14. By virtue of having a neck 1 16 with reduced diameter next to the barrel section 1 12, the working end 114 has an undercut that assists in retaining the abrasive member 102 on the mandrel 104 upon engagement. Optionally and as shown, there is a small gap between the bottom surface of the receptacle 110 and the outermost tip of the working end 1 14.

FIGS. 5a, 5b and 6 show additional features of the mandrel 104 and the abrasive member 102 in their relaxed configurations.

FIG. 5a is a head-on view of the working end 1 14 of the mandrel 104. As shown, the working end 1 14 is split into four discrete sections 124 by a pair of elongated slots 120 extending along radial directions from an outer surface 1 18 of the mandrel 104 toward the longitudinal axis 122 of the mandrel 104. The pair of elongated slots 120 intersect each other at the longitudinal axis 122, thereby dividing the working end 1 14 into sections 124 that are similar in size and shape. As further shown from the side view in FIG. 5b, the pair of elongated slots 120 not only traverse the working end 1 14 but also traverse a substantial length of the barrel 1 12. While the particular number and orientation of the slots 120 shown were found to be especially suitable, these should not be deemed to be limiting. For example, if a reduced degree of deflection is desired, just a single slot may be used to divide the working end 1 14 into two sections. On the other hand, if a greater degree of deflection is desired, additional slots may be used to divide the working end 1 14 into more than four sections. In these alternative embodiments, the cross-sectional area of the sections decreases with the increasing number of divisions, thereby providing increased flexibility. If desired, the degree of deflection for a given compressive force can also be tailored by controlling the length of the slots 120 along the longitudinal axis of the barrel 1 12.

The mandrel 102 also includes a shoulder 144, located where the relatively large barrel 1 12 joins the relatively small working end 1 14. The shoulder 144 extends around the circumference of the mandrel 104 and provides a hard stop when seating the abrasive member 102 on the working end 1 14 of the mandrel 104, as shown in FIGS. 3 and 4. In some embodiments, the shoulder 144 has an overall diameter ranging from 60 to 90 percent of the maximum outer diameter 126 of the working end 1 14.

As shown in FIG. 3, the mandrel 104 also includes a drive end 1 15 located remote from the working end 1 14. As shown, the drive end 1 15 has features such as notches or undercuts that are asymmetric about the longitudinal axis 122 to facilitate mechanical coupling between the mandrel 104 and a power tool. A suitable power tool is capable of rotating the abrasive member 102 at high speeds during an abrading operation.

The complemental abrasive member 102 is shown in its relaxed configuration in FIG. 6, which reveals further aspects of the receptacle 110 and the hub 106. In particular, the receptacle 1 10 has an inner surface including concave side surfaces 132 and a generally flat bottom surface 134. The receptacle 1 10 has an overall shape generally complemental to that of the working end 1 14 when the mandrel 104 is relaxed. As shown, for example, the concave side surfaces 132 of the receptacle 1 10 substantially match the corresponding convex surfaces on the side surfaces of the working end 1 14. Additionally, the flat bottom surface 134 complements the tip of the working end 1 14, which is also flat.

Optionally and as shown, at least a portion of the side surfaces 132 or the bottom surface 134 complemental with the working end 1 14 faces in a direction with a component toward the direction of disengagement of the working end 1 14 from the receptacle 1 10. In other words, at least a portion of the inner surface complemental with the working end 1 14 has a normal vector with an axial component parallel to the longitudinal axis 122, where the axial component defines the direction of disengagement of the working end 1 14 from the receptacle 1 10.

As further defined in FIG. 6, the receptacle 110 has a passageway 138 with a minimum inner diameter 128 that provides a pre-determined level of resistance when the working end 1 14 of the mandrel is both engaged to, and disengaged from, the receptacle 1 10. The receptacle 110 also has a certain maximum inner diameter 130 located between the passageway 138 and the bottom surface 134. The hub 106 surrounds, and is concentric with, the receptacle 1 10. As shown in FIG. 6, the hub 106 has a first hub diameter 140 when the abrasive member 102 is relaxed. Optionally, however, the hub 106 could assume other shapes, including shapes with variable diameter. In such cases, the first hub diameter 140 represents the largest diametric dimension of the hub 106 along the longitudinal axis 122.

Using gentle finger pressure, a dental practitioner snaps the abrasive member 102 onto the mandrel 104 to provide the configuration illustrated in FIG. 3. As shown in this figure, the working end 1 14 of the mandrel 104 is received in the receptacle 1 10 when the abrasive member 102 and the mandrel 104 are mutually engaged. As previously noted in FIGS. 5a and 5b, the working end 1 14 displays a maximum outer diameter 126 when relaxed. By virtue of the working end 1 14 being divided into four discrete sections 124 separated by the grooves 120, the working end 1 14 is resiliently compressed to a certain diameter somewhat smaller than the outer diameter 126 when the mandrel 104 is engaged to the abrasive member 102.

In more detail, as the dental practitioner urges the working end 1 14 toward the receptacle 1 10, the four sections 124 of the mandrel 104 and the hub 106 of the abrasive member 102 cooperatively deflect to allow the bulbous working end 1 14 to slide past the passageway 138. In other words, the sections 124 resiliently deflect inwardly toward each other as the receptacle 1 10 resiliently expands in diameter. The sections 124 have a tendency to spring back, or expand back, to their relaxed configurations.

Advantageously, this exerts outward pressure on the inner surfaces of the receptacle 1 10 to assist in securing the abrasive member 102 on the mandrel 104.

As the working end 1 14 is fully seated in the receptacle 1 10, the sections 124 relax toward their original configuration and the receptacle 1 10 shrinks back toward its original diameter to create an interference fit. Advantageously, the abrasive member 102 contacts the mandrel 104 along both concave and convex surfaces of the working end 1 14 to assist in retaining the abrasive member 102 on the mandrel 104. As a further advantage, residual compressive forces acting between the abrasive member 102 and the mandrel 104 help prevent slippage, or relative rotation between the abrasive member 102 on the mandrel 104 during an abrading operation. The use of a unitary abrasive member 102 is also

advantageous because abrasive particles directly contact the working end 1 14 of the mandrel 104, thereby enhancing the frictional coupling between the two components.

Advantageously, the minimum inner diameter 128 of the receptacle 1 10 and the maximum outer diameter 126 of the working end 1 14 are sized to provide both an interference fit and mechanical retention between the abrasive member 102 and mandrel 104. Preferably, the degree of interference between the abrasive member 102 and mandrel 104 exceeds 100 micrometers along the diameter of at least a portion the assembly 100. More preferably, the degree of interference exceeds 250 micrometers along the diameter of at least a portion of the assembly 100. When the working end 1 14 is received in the receptacle 1 10, the hub 106 expands to assume a second hub diameter 142 that is greater than the first hub diameter 140. The second hub diameter 142 is measured at the same position along the hub as the first hub diameter 140. Preferably, the difference between the second hub diameter 142 and the first hub diameter 140 ranges from 1 to 50 percent of the difference between the maximum outer diameter 126 of the working end 1 14 and the minimum inner diameter 128 of the passageway 138 of the receptacle 1 10. More preferably, the difference between the second hub diameter 142 and the first hub diameter 140 ranges from 10 to 40 percent of the difference between the maximum outer diameter 126 and the minimum inner diameter 128. Most preferably, the difference between the second hub diameter 142 and the first hub diameter 140 ranges from 15 to 30 percent of the difference between the maximum outer diameter 126 and the minimum inner diameter 128.

The compressibility of the mandrel 104 also reduces the required degree of expansion of the abrasive member 102. Preferably, the abrasive member has a diameter (e.g. hub diameter or other radial dimension) that increases when the abrasive member 102 engages the mandrel 104 and the inward deflection of the sections 124 reduces the increase of the diameter by an amount ranging from 10 to 90 percent of the increase that would have been observed had the sections 124 been rigid (see Examples). More preferably, the inward deflection of the sections 124 reduces the increase of the diameter by an amount ranging from 30 to 70 percent of the increase that would have been observed had the sections 124 been rigid. Most preferably, the inward deflection of the sections 124 reduces the increase of the diameter by an amount ranging from 40 to 60 percent of the increase that would have been observed had the sections 124 been rigid.

In some embodiments, at least some portion of the abrasive member 102 is urged into one or more of the grooves 120 when the abrasive member 102 and the mandrel 104 are engaged to each other. This has a particular advantage of providing additional mechanical retention at the interface between the mandrel 104 and abrasive member 102 that restricts rotational slippage between these two components during an abrading operation.

The distribution, or sharing, of significant structural deflection between the abrasive member 102 and the mandrel 104 is advantageous in providing increased manufacturing tolerances for both of these components. As a further advantage, the composite material used to make the abrasive member 102 can be made substantially stiffer because the mandrel 104 is compressible. This in turn permits higher abrasive particle loadings and/or higher glass transition temperature (T _g ) thermoplastic to be used than previously possible, thus facilitating the optimization of the abrasive member 102. If the stiffness of the abrasive member 102 is fixed, this configuration is still beneficial because it provides greater latitude to adjust the dimensions of the abrasive member 102 according to the application at hand.

As a further unique advantage, the assembly 100 not only induces compression of the abrasive member 102 along radial directions, but also along axial directions. For example, portions of the abrasive member 102 adjacent the neck 1 16 are compressed along directions parallel to the longitudinal axis 122 by opposing forces acting on the abrasive member 102 by the working end 1 14 and the shoulder 144. By compressing the abrasive member 102 along directions parallel and directions perpendicular to the longitudinal axis 122, the assembly 100 creates an interference fit over an extended area along the interface the abrasive member 102 and the mandrel 104, further enhancing the frictional coupling between the two components.

The combination of an expandable abrasive member 102 with a compressible mandrel 104 also presents practical advantages to the dental practitioner. Using two compliant, complemental members creates an interference fit that is evenly distributed over an extended interfacial area. This reduces slippage between the abrasive member 102 and the mandrel 104, and provides a high degree of control in the abrading operation. Spreading the interference fit over a comparatively large area also helps avoid "wobbling" of the abrasive member 102 at high rotational speeds. The use of two compliant members allows for higher filler loading in the abrasive member 102 while preserving low engagement and disengagement forces. Finally, the complemental configuration minimizes the effects of wear in the mandrel 104, extending its operational lifetime.

FIGS. 7-9 show an abrasive assembly 200 according to an alternative embodiment. As shown in these figures, the assembly 200 includes an abrasive member 202 having a receptacle 210 and a mandrel 204 having a working end 214. Like the assembly 100, the working end 214 is received in the receptacle 210. Unlike the assembly 100, however, the receptacle 210 is an aperture in communication with opposing sides of the abrasive member 202. When fully engaged, the outer tip of the working end 214 is recessed within the receptacle 210 such that inadvertent contact cannot occur between the metallic working end 214 of the mandrel 204 and the patient's tooth or gingival tissue during an abrading operation.

Other aspects of the assembly 200 are similar to those of assembly 100 and shall not be repeated here.

FIGS. 10a, 10b, 1 1a, and 1 lb show abrasive members 302 and 402 according to two additional embodiments. The abrasive member 302 has a pointed tip to allow a practitioner to access recessed areas of a patient's dental structure. In this embodiment, the abrasive member 402 has a ridged "cup" shape to allow a practitioner to access, for example, interproximal areas. Both of abrasive members 302,402 have receptacles adapted for use with the mandrel 104. Other aspects of the abrasive members 302,402 have been substantially described in the context of previous embodiments and will not be repeated here.

EXAMPLES

Abrasive disc preparation

Abrasive discs with a configuration similar to that shown in FIGS. 1-4, and 6 were designed to particular dimensions, and steel injection molds were fabricated according to those dimensions, which are shown in Table 1. Three different hub minimum inner diameters were made for testing purposes. For reference, the hub minimum inner diameter corresponds to 128 in Fig. 6, and the disc outer diameter is measured from bristle tip to bristle tip through the center of the hub, e.g. 3-3 in Fig. 2. The comparative abrasive disc having a metal eyelet hub had the minimum inner diameter measured across the center of the eyelet opening.

Table 1

Plastic pellets having the composition shown in Table 2 were compounded according to conventional methods.

Table 2

The plastic pellets were loaded into an extruder at 450 deg. F (232 deg. C) and injected into the injection mold, the mold was cooled and the finished part was removed, thus producing a finished abrasive disc.

The mandrel used for all examples was of monolithic construction and made from stainless steel. The mandrel was commercially available as an RA Mandrel, available with SOF-LEX brand Finishing and Polishing System, 3M ESPE, St. Paul, MN. Abrasive discs of the comparative example having a metal hub were also available with the SOF-LEX brand System.

Measurement of removal force

The abrasive disc was inserted into the fixed jaw of an Instron (Norwood, MA) and a mandrel was inserted into the hub of the disc. The mandrel was then connected to the movable jaw which pulled the mandrel out of the hub. This removal force was measured in kilograms (kg). The sample size was five for each hub size. The results shown in Table 3 show the three sizes have slightly less removal force than the comparative example, but all three sizes had acceptable function in actual use.

Table 3

Measurement of rotational force of disc on mandrel

The abrasive disc was fixed in position and a mandrel was inserted into the hub. The mandrel was then connected to a torque tester which measures the rotational force required to cause the mandrel to slip in the hub. The sample size was 5 for each hub size. The data is shown in Table 4 and show that the rotational forces are less than the comparative example but adequate to function well under load when polishing a tooth.

Table 4

Measurements with abrasive disc and hub disengaged (relaxed)

Measurements were made with pin gauges for the abrasive disc minimum inner diameters, and an optical comparator for the mandrel outer diameters. The maximum inner diameter of the hub was less accessible to measuring devices, so was based on the designed dimension. The results are shown in Table 5. For reference, hub minimum inner diameter and mandrel minimum outer diameter correspond to 128 in Fig. 6, and hub maximum inner diameter and mandrel maximum outer diameter correspond to 130 in Fig. 6. Table 5

Measurements with abrasive disc and hub engaged

To measure the extent of mandrel compression during engagement with the abrasive disc, measurements of the outer diameter of the disc's hub were made using an optical comparator. The measurements were taken on the outside of the hub at a point corresponding to the minimum inner diameter of the inside of the hub, refer to 140 in Fig. 6. A first measurement (relaxed) was made without a mandrel inserted into the hub. A second measurement (slotted mandrel) was made with a slotted mandrel inserted into the hub of Example 2. A third measurement (solid mandrel) was made with a modified mandrel inserted into the hub of Example 2. To simulate a solid mandrel without slots, the slots of a slotted mandrel were filled with epoxy cement to prevent flexing of the segments. The results are shown in Table 6.

Table 6

Performance during actual use

The abrasive discs and mandrels were assembled into a low speed air-driven handpiece (Model No. PD-58, Patterson Dental, St. Paul, Minnesota), operated at 0-17,000 rpm. This handpiece was outfitted to a conventional airmotor (Model No. PD-20 BC/RM, Patterson Dental, St. Paul, Minnesota) and dental unit (Model #5200, Forest Dental Products, Hillsboro, Oregon) and used to shape and polish a simulated restoration of Filtek Supreme composite (3M ESPE) with satisfactory results. All of the patents and patent applications mentioned above are hereby expressly incorporated by reference. The embodiments described above are illustrative of the present invention and other constructions are also possible. Accordingly, the present invention should not be deemed limited to the embodiments described in detail above and shown in the accompanying drawings, but instead only by a fair scope of the claims that follow along with their equivalents.