Patent Application
20130302751
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.
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.
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.
a is a head-on view of a first component of the assembly in
b is a fragmentary elevational view of the component in
a and 10b are perspective and cross-sectional views, respectively, of an abrasive member according to still another embodiment; and
a and 11b are perspective and cross-sectional views, respectively, of an abrasive member according to yet another embodiment.
An abrasive assembly according to one embodiment is shown in
As shown in the
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, Del.
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, Minn. 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. Pat. No. 5,903,951 (Ionta et al.).
As shown in
The mandrel 104 has a barrel section 112 and a bulbous working end 114 extending outwardly from the barrel section 112. The working end 114 has a maximum diameter that is somewhat smaller than that of the barrel section 112. Additionally, the working end 114 has a local diameter that varies with respect to its longitudinal axis 122, and further includes a neck 116 immediately adjacent the barrel section 114. By virtue of having a neck 116 with reduced diameter next to the barrel section 112, 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 114.
a,
5
b and 6 show additional features of the mandrel 104 and the abrasive member 102 in their relaxed configurations.
a is a head-on view of the working end 114 of the mandrel 104. As shown, the working end 114 is split into four discrete sections 124 by a pair of elongated slots 120 extending along radial directions from an outer surface 118 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 114 into sections 124 that are similar in size and shape. As further shown from the side view in
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 114 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 114 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 112.
The mandrel 102 also includes a shoulder 144, located where the relatively large barrel 112 joins the relatively small working end 114. 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 114 of the mandrel 104, as shown in
As shown in
The complemental abrasive member 102 is shown in its relaxed configuration in
Optionally and as shown, at least a portion of the side surfaces 132 or the bottom surface 134 complemental with the working end 114 faces in a direction with a component toward the direction of disengagement of the working end 114 from the receptacle 110. In other words, at least a portion of the inner surface complemental with the working end 114 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 114 from the receptacle 110.
As further defined in
The hub 106 surrounds, and is concentric with, the receptacle 110. As shown in
Using gentle finger pressure, a dental practitioner snaps the abrasive member 102 onto the mandrel 104 to provide the configuration illustrated in
In more detail, as the dental practitioner urges the working end 114 toward the receptacle 110, 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 114 to slide past the passageway 138. In other words, the sections 124 resiliently deflect inwardly toward each other as the receptacle 110 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 110 to assist in securing the abrasive member 102 on the mandrel 104.
As the working end 114 is fully seated in the receptacle 110, the sections 124 relax toward their original configuration and the receptacle 110 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 114 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 114 of the mandrel 104, thereby enhancing the frictional coupling between the two components.
Advantageously, the minimum inner diameter 128 of the receptacle 110 and the maximum outer diameter 126 of the working end 114 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 114 is received in the receptacle 110, 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 114 and the minimum inner diameter 128 of the passageway 138 of the receptacle 110. 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 (Tg) 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 116 are compressed along directions parallel to the longitudinal axis 122 by opposing forces acting on the abrasive member 102 by the working end 114 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.
Other aspects of the assembly 200 are similar to those of assembly 100 and shall not be repeated here.
a,
10
b,
11
a, and 11b 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.
Abrasive discs with a configuration similar to that shown in
Plastic pellets having the composition shown in Table 2 were compounded according to conventional methods.
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, Minn. Abrasive discs of the comparative example having a metal hub were also available with the SOF-LEX brand System.
The abrasive disc was inserted into the fixed jaw of an Instron (Norwood, Mass.) 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.
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.
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
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
The abrasive discs and mandrels were assembled into a low speed air-driven handpiece (Model No. PD-58, Patterson Dental, St. Paul, Minn.), operated at 0-17,000 rpm. This handpiece was outfitted to a conventional airmotor (Model No. PD-20 BC/RM, Patterson Dental, St. Paul, Minn.) and dental unit (Model #5200, Forest Dental Products, Hillsboro, Oreg.) 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.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US11/60283 | 11/11/2011 | WO | 00 | 3/29/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61415130 | Nov 2010 | US |
