Dental instruments having a handle formed by two-shot molding

A dental instrument having a two-shot molded handle and methods for making the same. The dental instrument includes a dental instrument shank of metal with a handle formed near the proximal end of the shank. The handle includes a first polymer formed over a portion of the shank, and a second polymer formed over at least a portion of the first polymer. The first polymer may be rigid so as to more firmly attach to the shank and better resist torsional and/or tensional slippage between the shank and handle during use, while the second polymer may be flexible so as to increase gripability and comfort during manual use of the instrument. The first and second polymers may be of different colors to provide contrast (e.g., to highlight characters formed in the first rigid polymer).

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The invention is in the field of dental instruments and processes for overmolding one or more polymers onto dental instruments (e.g., endodontic files).

2. The Relevant Technology

Dental instruments are often designed to be manually manipulated or to be fitted within a collet of a powered hand piece that provides rotation of an instrument during use. A dental instrument (e.g., an endodontic file) that is intended for hand use is typically provided with an enlarged diameter plastic handle attached to the proximal end of the instrument, configured for manipulation between the thumb and forefinger of the dental practitioner. An instrument intended for use with a powered hand piece has a stem at the instrument proximal end configured to be removably received within a collet of the powered hand piece, by which the instrument may then be rotated as desired by a dental practitioner.

It may be desirable for the enlarged plastic handle of a dental instrument intended for hand use to have a gripable surface. At the same time, dental instruments intended for use with a powered hand piece must include a rigid handle that can be received within a collet.

It would be an improvement in the art to provide dental instruments and methods for manufacturing dental instruments having a two-shot molded handle, at least some of which may include an overmolded handle suitable for manipulation by hand and by a powered hand piece.

BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS

In one aspect, the present invention provides a method for overmolding a plurality of polymers having different properties onto a dental instrument. The method involves providing a dental instrument substrate made of metal, overmolding a first polymer onto a portion of the dental instrument substrate, and then applying a second polymer over a portion of the first polymer. The first polymer is overmolded so that an exposed outer surface of the first polymer corresponds to a portion of the dental instrument to be gripped within a collet of a dental hand piece for powered use. The second polymer is applied so that an exposed outer surface of the second polymer corresponds to a portion of the dental instrument to be gripped by a dental practitioner for manual use.

According to one embodiment, the first polymer may comprise a rigid polymer material. A rigid polymer material provides strength and durability, which is important for portions of the dental instrument that will be subjected to stresses and forces associated with gripping the instrument within the collet of a dental hand piece. Strength and durability will prevent these portions of the dental instrument from cracking or being deformed under stress. According to one embodiment, the rigid polymer material may comprise either a rigid thermoplastic or a rigid chemical cure or thermocure polymer material.

According to one embodiment, the second polymer may comprise an elastomeric material. An elastomeric material provides increased comfort and grippability to portions of the dental instrument that are gripped by a dental practitioner when using the dental instrument manually. According to one embodiment, the elastomeric polymer material may comprise either a thermoplastic elastomer or an elastomeric chemical cure or thermocure polymer material.

The resulting dental instrument includes portions having characteristics of rigidity, strength, and durability, and other portions having characteristics of elasticity, comfort, and grippability. These characteristics allow the dental instrument manufactured according to the inventive method to be used advantageously with a powered hand piece or manually, as desired.

According to one embodiment, the first polymer and second polymer are overmolded and applied respectively so as to form a handle having a trilobular cross sectional configuration. A handle having a trilobular cross sectional configuration is advantageous when manipulating the instrument by hand as it allows the dental practitioner to more easily apply the needed torque. In addition, a trilobular cross sectional configuration also provides improved gripability. A trilobular cross section may also be suitable for use within a powered hand piece.

According to one embodiment, the dental instrument manufactured according to the inventive method may be autoclavable. This may be accomplished according to one embodiment by selecting first and second polymers that are chemically or thermally curable and that have melting and decomposition temperatures that are significantly greater than autoclaving temperatures, which are typically 143° C.

In another aspect, the invention provides a dental instrument having a two-shot molded handle. Such an instrument includes a dental instrument shank formed of metal, and a handle formed near a proximal end of the shank. The handle includes a rigid first polymer formed over a portion of the shank, and a flexible second polymer formed over at least a portion of the first polymer. The rigid first polymer helps attach the handle more firmly to the shank so as to better resist torsional and/or tensional slippage between the shank and the handle during use.

Forming the handle such that it includes a rigid first polymer formed over a portion of the shank provides increased resistance to torsional and/or tensional slippage as compared to a dental instrument including a handle that only includes a flexible polymer formed over the shank. This is because the rigid first polymer has increased strength and durability as compared to flexible polymers. This allows the rigid first polymer to more firmly bond to the shank and to provide better resistance to torsion and/or tension. Resistance to torsion prevents the handle from breaking away and turning independently of the shank during rotation of the instrument, while resistance to tension prevents the handle from pulling off the shank during longitudinal (e.g., vertical) manipulation of the instrument.

Providing the handle with a flexible second polymer formed over at least a portion of the rigid first polymer provides the handle with improved grippability (particularly beneficial for manual use) as compared to a handle that only includes a rigid polymer formed over the shank. Such a dental instrument includes properties of strength and durability (i.e., resistance to torsional and/or tensional slippage) while also being easily grippable and comfortable for manual use.

In one such example of an instrument intended for manual use, the handle may be enlarged so as to facilitate better manual gripping and manual manipulation or instrumentation of the instrument during use. The handle may be enlarged to such a degree so as to not be insertable within a powered handpiece.

In another example (which may or may not include an enlarged handle) the rigid first polymer may be completely encased by the flexible second polymer. Encasing the rigid polymer with a flexible polymer increases the gripping surface area available to the dental practitioner during use.

The dental instruments may include a handle of any desired shape. Exemplary handles may have a substantially triangular cross section (i.e., trilobular), a substantially circular cross section, a substantially square or rectangular cross section, or other cross sectional configuration.

In order to increase and/or provide mechanical interlock between the different portions of the handle, a portion of the proximal end of the dental instrument shank may include a roughened, stamped, or knurled surface so as to form a mechanical interlock between the shank and the rigid first polymer so as to further resist torsional and/or tensional slippage between the shank and the handle during use. In another example, the shank may be bent or twisted (e.g., into a U-, S-, or spiral curve) in order to form such a mechanical interlock between the shank and the rigid first polymer.

In a similar manner, a portion of the rigid first polymer may include a roughened surface so as to form a mechanical interlock between the rigid first polymer and the flexible second polymer so as to increase resistance to torsional and/or tensional slippage between the rigid first polymer portion of the handle and the flexible second polymer portion of the handle.

In one embodiment, a portion of the first polymer may be molded to form an identifying character (e.g., numbers, letters, or other marks identifying the diameter, taper, length, or other characteristics of the instrument) of a first color. The second flexible polymer may be of a second, different color, such that the difference in colors enhances the visual contrast between the identifying character formed of the first polymer and the surrounding or adjacent flexible polymer. The increased visual contrast aids the dental practitioner in identifying the character, particularly when dealing with very small dental instruments (e.g., endodontic files).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of the inventive method and exemplary inventive dental instruments will now be provided, with specific reference toFIGS. 1-7illustrating preferred embodiments of the invention. It will be appreciated that like structures will be provided with like reference designations.

II. Exemplary Methods of Overmolding Polymers Onto Dental Instruments

FIGS. 1A-1Cillustrate an exemplary method of overmolding a plurality of polymers having different properties onto a dental instrument100. The inventive method involves providing a dental instrument substrate102made of metal, as seen inFIG. 1A. A first polymer104is overmolded onto a portion of the dental instrument substrate102, as seen inFIG. 1B. A second polymer106is then applied over a portion of the first polymer104, as seen inFIG. 1C.

The first polymer104is overmolded over the dental instrument substrate102such that an exposed outer surface108of the first polymer104corresponds to a portion of the dental instrument100to be gripped within a collet of a dental hand piece for powered use. The second polymer106is applied over the first polymer104such that an exposed outer surface110of the second polymer106corresponds to a portion of the dental instrument to be gripped by a dental practitioner for manual use. According to one embodiment, the steps of overmolding a first polymer and applying a second polymer may be performed by injection molding, e.g., by a two-color injection molding process.

According to one embodiment, and as illustrated inFIG. 1C, the second polymer106may be applied so as to have an exposed outer surface110with a concave configuration. The concave configuration may provide increased gripability, while also preventing contact of the surface110with the collet of a powered handpiece, which may otherwise rip or tear the exposed outer surface110.

FIG. 2illustrates a perspective view of the dental instrument100ofFIG. 1C. The instrument100includes a metallic dental instrument substrate102. A handle112is provided at the proximal end of the metallic dental instrument substrate102in order to facilitate manual gripping of the dental instrument100by the dental practitioner or mechanical gripping by a dental hand piece (e.g., a reciprocating hand piece).

The handle112includes an overmolded first polymer and an applied second polymer. The first polymer includes an exposed outer surface108corresponding to a portion of the instrument100to be gripped within a collet of a dental hand piece. The second polymer includes an exposed outer surface110corresponding to a portion of the instrument100to be gripped by a dental practitioner during manual use.

The dental instrument ofFIG. 2includes a handle112having a trilobular cross section. A handle112having a trilobular cross sectional configuration is advantageous when manipulating the instrument by hand as it allows the dental practitioner to more easily apply the needed torque. In addition, a trilobular configuration provides improved gripability.

FIG. 3is a perspective view of an alternative embodiment of a dental instrument200that includes a dental instrument substrate202and a handle212, which includes an overmolded first polymer and an applied second polymer. The first polymer includes an exposed outer surface208corresponding to a portion of the instrument200to be gripped within a collet of a dental hand piece. The second polymer includes an exposed outer surface210corresponding to a portion of the instrument200to be gripped by a dental practitioner during manual use. The handle212of dental instrument200has a circular cross section. As illustrated, the outer surface210may be characterized by a concave curvature.

The outer surfaces208and210are configured to have specific properties. According to one embodiment, the first polymer comprising outer surface208may be a rigid polymer material. A rigid polymer material provides strength and durability, which is important for portions of the dental instrument that will be subjected to stresses and forces associated with gripping the instrument within the collet of a dental hand piece. Strength and durability will prevent these portions of the dental instrument from cracking or being deformed under stress.

According to one embodiment, the rigid polymer material may comprise any rigid thermoplastic material. Suitable rigid thermoplastics include polycarbonates, acrylonitrile butadiene styrene, polyamides, acetals and polysulfones. According to another embodiment, the rigid polymer material may comprise a rigid chemical cure or thermocure polymer material. Besides providing rigidity, strength, and durability, a chemical cure or thermocure polymer material also provides the advantageous characteristic of being autoclavable. Exemplary rigid chemical cure or thermocure polymers include epoxies, phenolics, acrylates, urethanes and polyesters.

According to one embodiment, the second polymer comprising outer surface210may be an elastomeric material. An elastomeric material provides increased comfort and grippability to portions of the dental instrument that are gripped by a dental practitioner when using the dental instrument manually. According to one embodiment, the elastomeric polymer material may comprise a thermoplastic elastomer. Alternatively, the elastomeric polymer material may comprise an elastomeric chemical cure or thermocure polymer material for the added advantage of autoclavability.

Examples of suitable thermoplastic elastomers include SARLINK (which comprises EPDM (i.e., ethylene-propylene rubber) particles embedded in a polypropylene matrix), ENGAGE (a polyolefin elastomer), SANTOPRENE (a synthetic rubber), and J-VON (a synthetic rubber). Examples of suitable elastomeric chemical cure or thermocure polymers include silicone rubber, natural rubber, synthetic rubber, and lower durometer urethanes.

The resulting dental instrument includes portions having characteristics of rigidity, strength, and durability, and other portions having characteristics of elasticity, comfort, and grippability. These characteristics allow the dental instrument manufactured according to the inventive method to be used advantageously with a powered hand piece or manually, as desired.

FIG. 4Aillustrates dental instrument100being gripped manually by a dental practitioner's hand430. The trilobular configuration of handle112allows the dental practitioner to more easily apply the needed torque during use.

Referring toFIGS. 4B and 4C, a trilobular handle configuration is also suitable for use within a powered hand piece.FIG. 4Billustrates dental instrument100having a trilobular handle112received within a collet450of a powered hand piece400. As best seen inFIG. 4C, the lobes of the handle112are received within and securely held by the (e.g., round) collet450of the hand piece400. The exposed outer surface110of the relatively soft second polymer is not in gripping contact with the collet450of the handpiece400, which might otherwise tear, rip, or deform the relatively soft second polymer.

According to one embodiment, the dental instruments manufactured according to the inventive method may be autoclavable. This may be accomplished according to one embodiment by selecting first and second polymers that are chemically or thermally curable and that have melting and decomposition temperatures that are significantly greater than autoclaving temperatures (e.g., typically about 143° C.).

III. Additional Exemplary Dental Instruments

FIGS. 5A and 5Billustrate an alternative dental instrument500having a two-shot molded handle512and a metallic dental instrument shank502including a proximal end514and a distal end516. Handle512is formed near proximal end514of shank502. Handle512includes a rigid first polymer504formed over a portion of shank502, and a flexible second polymer506formed over at least a portion of first polymer504. As described above, rigid first polymer504has good strength and durability (particularly as compared to flexible polymers). This allows the rigid first polymer to more firmly attach to shank502so as to better resist torsional and/or tensional slippage between shank502and handle512, particularly as compared to a handle that only includes a grip enhancing flexible polymer formed over shank502.

Dental instrument500is illustrated as including an enlarged handle512, which facilitates better manual gripping and manipulation of the instrument during use. In some embodiments, the handle may be so large as to not be insertable within a collet of a powered handpiece.

As illustrated inFIGS. 5A and 5B, handle512of dental instrument500may be formed such that second polymer506completely encases rigid first polymer504. Such an embodiment may be particularly suited for manual use, having an increased surface area covered by flexible second polymer506, while also having increased resistance to torsional and/or tensional slippage between shank502and handle512.

Although illustrated as having a substantially square cross section, it is to be understood that handle512(as well as any of the handles disclosed) may be of any desired shape. Alternative handles may be have a substantially triangular cross section (i.e., trilobular), a substantially circular cross section, a substantially rectangular cross section, or other cross sectional configuration.

FIG. 6Aillustrates another dental instrument600having a two-shot molded handle612and a metallic dental instrument shank602including a proximal end614and a distal end616. Handle612includes a rigid first polymer604formed over proximal end614of shank602, and a flexible second polymer606formed over a portion of rigid first polymer604. A portion of rigid first polymer604is molded so as to form an identifying character618(e.g., numbers, letters, or other marks). The identifying character618may identify the diameter, taper, length, or any other desired characteristics of instrument600. Flexible second polymer606is formed over much of first polymer604. Rigid first polymer604may be of a first color, while flexible second polymer606is of a different, second color. In such an embodiment, the difference in color between rigid first polymer604and flexible second polymer606increases or enhances the visual contrast between identifying character618and the surrounding or adjacent second color of second polymer606. This increased visual contrast (as compared to if the identifying character and surrounding/adjacent areas were all of the same color) aids the dental practitioner in identifying the character618, particularly if dental instrument600is very small.

In addition, the ability to form an identifying character618having enhanced contrast during the molding of handle612reduces the cost and steps required as compared to a process in which an identifying character of a different color is added (e.g., by ink) after the handle has been formed.

FIG. 6Billustrates another dental instrument600′ having a two-shot molded handle612′ and a metallic dental instrument shank602′. Handle612′ includes a rigid first polymer604′ formed over a portion of shank602′, and a flexible second polymer606′ formed over a portion of rigid first polymer604′. A portion of rigid first polymer604′ is molded so as to form an identifying character618′. Character618′ is located on the proximal end of handle612′, and is quite large (relative to the character618ofFIG. 6A). Such placement and sizing may be particularly advantageous when a plurality of differently sized instruments are arranged together in a vertical orientation, allowing the dental practitioner to easily identify the character at the proximal end of each handle.

In the illustrated embodiment, flexible second polymer606′ is formed over all of first polymer604′ except that portion forming character618′. Rigid first polymer604′ may be of a first color (e.g., a dark color), while flexible second polymer606′ is of a different, second color (e.g., a light color). In such an embodiment, the difference in color between rigid first polymer604′ and flexible second polymer606′ increases or enhances the visual contrast between identifying character618′ and the surrounding or adjacent second color of second polymer606′, particularly because the second color surrounds the first color of the identifying character618′.

FIG. 7illustrates a cross sectional view of the proximal portion of a dental instrument700including a metallic shank702and a handle712. The shank702is illustrated as including a roughened surface720so as to form a mechanical interlock between shank702and rigid first polymer704. Roughened surface720provides increased mechanical bonding between shank702and rigid first polymer704in addition to any chemical bonding present. Although illustrated as having a roughened surface, it is to be understood that proximal end714of shank702may be roughened, stamped, knurled, or even bent or twisted (e.g., into a U or S-curve) in order to provide increased mechanical interlock between shank702and rigid first polymer704. Roughening, stamping, knurling, bending or twisting shank702are all examples of means for increasing mechanical interlock between the shank and the rigid first polymer.

Rigid first polymer704of handle712is illustrated as also including a roughened surface722at the interface between rigid first polymer704and flexible second polymer706. Such a roughened surface provides increased mechanical interlock between rigid first polymer704and flexible second polymer706so as to further increase the ability of dental instrument700to resist torsional and/or tensional slippage that might otherwise occur.