Patent Publication Number: US-2005130099-A1

Title: Instrument for distributing restorative material on a tooth surface

Description:
FIELD OF THE INVENTION  
      This invention relates to a dental instrument for homogeneously applying and shaping tooth restorative material, and specifically, a dental instrument with interchangeable roller tips for distributing the restorative material.  
     BACKGROUND OF THE INVENTION  
      Composite materials, i.e., tooth restorative materials containing binders in the form of hardenable, generally organic substances, have become the standard filling materials in dentistry. A disadvantage of these composite materials, however, is their tendency to adhere more or less to the instrument that is used to apply or shape them. As a result, and by way of example, the composite material has a tendency to be drawn off from the edges of the cavity, to be distributed inhomogeneously on the tooth surface, and to form air bubbles during the distribution. The instruments used for distributing the restorative material typically comprise a steel instrument with an uncoated working tip portion or a tip portion coated with TiNi, for example, or a plastic material with or without a coated or treated working tip portion. As a further example, the adhesion of the composite material to the instrument has been adjusted by coating the working ends of the instrument with Teflon™, but these instruments have limited shapes and are not always satisfactory in practice. Another solution is proposed in U.S. Pat. No. 6,071,122, wherein the working tip of the plastic instrument has a discontinuous surface that includes an array of micropits. While that instrument achieves reduced adhesion of the composite material, homogeneous distribution free of air bubbles has not yet been fully achieved. There is thus a need to develop a dental instrument that is effective in distributing homogeneously a composite restorative material to a tooth surface, and which avoids the integration of air bubbles in the restorative.  
     SUMMARY OF THE INVENTION  
      The present invention provides a dental instrument with interchangeable roller tips for distributing restorative materials on a tooth surface, which roller tips distribute the restorative material quickly, precisely and homogeneously with little adherence of the restorative material to the roller tip due, in part, to the short contact time between the roller tip and the composite material. To this end, a dental instrument is provided having an elongate body with a handle portion and a working end extending therefrom. A roller tip is rotatably mounted on the working end so as to rotate about a center axis of the end of the instrument, and is sized to distribute the restorative material on a tooth surface, including a cavity surface. The roller tip is removable from the working end, such that differently shaped tips may be placed on the working end during the restoration of the tooth, as necessary, to ensure complete and even coverage to an uneven surface. In an exemplary embodiment, a bushing or rolling element bearing is rotatably mounted on the working end between the working end and the roller tip, such that the roller tip is rotatable on the working end by means of the rotatable bushing or bearing. In another exemplary embodiment, the dental instrument includes two working ends extending in opposing directions from the handle portion to provide different angles for the working ends or to provide differently shaped roller tips on the working ends. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention.  
       FIG. 1  is a perspective view of a dental instrument of the present invention;  
       FIG. 2  is a cross-sectional view of a first working end of the instrument of  FIG. 1 , as taken along line  2 - 2 ;  
       FIG. 2A  is a cross-sectional view of an alternative embodiment of the first working end of the instrument of  FIG. 1 , also taken along line  2 - 2 ;  
       FIG. 3  depicts a side elevational view of an alternative embodiment of a dental instrument of the present invention with the working end in partial cross-section;  
       FIGS. 4A-4C  depict various embodiments for the roller tips of the instrument of the present invention; and  
       FIGS. 5A-5B  depict uses of an instrument of the present invention in applying and shaping restorative materials on tooth surfaces. 
    
    
     DETAILED DESCRIPTION  
      Reference will be made to  FIGS. 1-5B  in which like reference numerals are used to refer to like parts. An exemplary dental instrument  10  of the present invention is depicted in perspective view in  FIG. 1 . Instrument  10  is uniquely designed for distributing tooth restorative materials on a tooth surface within the oral cavity of a patient, i.e. within the patient&#39;s mouth, without the adherence problems of the prior art. Instrument  10  is also designed for distributing tooth restorative materials on an artificial tooth surface to form a prosthetic tooth. Instrument  10  has an elongate body  12  with a first working end  14  and a second working end  16  that extend from opposite ends  18   a ,  18   b  of a handle portion  18 . As shown in  FIG. 1 , the first working end  14  extends from end  18   a  of the handle portion  18  such that its center axis is substantially coaxial with the center axis of the handle portion  18 . This construction may be referred to as an axial working end. As further shown in  FIG. 1 , the second working end  16  extends from end  18   b  of the handle portion  18  in a direction such that its center axis is perpendicular (90°) to the center axis of the handle portion  18 . This construction may be referred to as a right angle working end. Depending on the tooth to be restored, differently angled working ends allow the dentist to choose the appropriate angle for most effectively distributing the restorative material on the tooth surface, particularly where the tooth surface is located in the oral cavity. While the second working end  16  is shown at a 90° angle from the center axis of the handle portion  18 , it may be appreciated that angles in the range of 5-90° may be useful and angles in the range of 45-90° may be even more useful. In addition, both working ends  14 ,  16  may be coaxial with the center axis of the handle portion  18  or both ends  14 ,  16  may be angled relative to the center axis of the handle portion  18 . Thus, the particular angles for the first and second working ends  14 ,  16  depicted in  FIG. 1  are not intended to limit the configuration of the instrument  10  of the present invention.  
      Each of the first and second working ends  14 ,  16  are depicted with a roller tip  20 ,  20   a , respectively, sized to distribute restorative material on a tooth surface, wherein tips  20 ,  20   a  are removable from the first and second working ends  14 ,  16  and interchangeable with each other or with other roller tips  20 . An exemplary embodiment of the roller tip  20  is more clearly depicted in cross-sectional view in  FIG. 2 , as taken along line  2 - 2  of  FIG. 1 . The first working end  14  is shown having a reduced diameter as compared to the diameter of the remaining portion of the elongate body  12 , including handle portion  18 , but the invention is not so limited. In this embodiment, mounted on the first working end  14  is a bushing  30 , which is rotatable on the first working end  14  about the center axis of the first working end  14 . The roller tip  20  is mounted on, and rotatable with, the bushing  30  so as to be rotatable about the first working end  14  by means of the rotation of the rotatable bushing  30 , which rotates relative to working end  14 . Because the center of the roller tip  20  is coaxial with the center of the working end  14  of the instrument  10  in this exemplary embodiment, torque is avoided during rotation of the roller tip  20  to distribute the restorative material. While the roller tip  20  is depicted as a closed cylinder at distal end  15 , it may be appreciated that the roller tip  20  may be an open cylinder at distal end  15  thereby exposing the bushing  30 . However, the exemplary embodiment shown in  FIG. 2  is advantageous in that it prevents restorative material from entering into the bushing area and interfering with operation of the rotatable tip  20  and bushing  30 . Roller tip  20  is further shown having a substantially uniformly cylindrical surface  22  for distributing restorative material on a tooth surface. It may be appreciated, however, as will be discussed in more detail below, that roller tip  20  may be shaped to have a non-uniform outer surface  22 .  
      In an exemplary embodiment, bushing  30  includes a clip portion  32  for engaging a ridge portion  13  of first working end  14 . Clip portion  32  prevents restorative material from getting between the bushing  30  and the first working end  14 . Clip portion  32  further assists in the retention and easy removal of the roller tip  20  such that the roller tip  20  is interchangeable with other roller tips. A bulbous shape for top portion  31  of bushing  30  is also advantageous in that it also assists in the interchangeability of roller tip  20  without the risk of axial disassembling. A similar construction for bushing  30  may be used at second working end  16 .  
      Advantageously, the elongate body  12 , including first and second working ends  14 ,  16  and/or bushing  30 , comprise a plastic material containing a friction-reducing additive to facilitate rotation of the bushings  30  around the first and second working ends  14 ,  16 . Friction is the force that retards, that is partially brakes, the movement of two surfaces against each other, and the kinetic coefficient of friction, μ, is a measurement of the extent of friction present during rotation. The kinetic coefficient of friction is measured by dividing the frictional resistance force, f, by the normal force, N, that presses the two surfaces together when they move relative to each other. Advantageously, the amount of friction-reducing material in one or both of the elongate body  12  and bushings  30  is sufficient to provide a kinetic coefficient of friction of less than 0.2 between the first working end  14  and the bushing  30  on which the roller tip  20  is mounted, and between the second working end  16  and the bushing  30  on which roller tip  20   a  is mounted.  
      In an exemplary embodiment, the elongate body  12  comprises a plastic material containing 2-30 wt. % of a friction-reducing additive. In another exemplary embodiment, the bushings  30  comprise a plastic material containing 2-30 wt. % of a friction-reducing additive. In yet another exemplary embodiment, each of the elongate body  12  and the bushings  30  comprise a plastic material containing 2-30 wt. % of a friction-reducing additive. In each of these exemplary embodiments, the friction-reducing additive is advantageously polytetrafluoroethylene present in an amount of 2-20 wt. %, and more advantageously, the polytetrafluoroethylene is present in an amount of 5-15 wt. %. In addition to or in place of polytetrafluoroethylene as a friction-reducing additive, and by way of example only, fluorinated ethylene propylene, perfluoroalkoxy copolymers, carbon fibers and molybdenum disulfide may be also be effective to provide a low coefficient of friction. Similar to the polytetrafluoroethylene additive, the fluorinated ethylene propylene and perfluoroalkoxy copolymers are advantageously present in an amount of 2-20 wt. % of the plastic material, while carbon fibers are advantageously present in an amount of 5-30 wt. % of the plastic material and molybdenum disulfide is advantageously present in an amount of 3-6 wt. % of the plastic material. It may be understood, however, that other now known or hereafter developed friction-reducing materials may be used as an additive in accordance with the present invention in an appropriate and/or similar amount to achieve a low-frictional resistance between the rotating components.  
      The plastic material for the elongate body  12  is advantageously one or a combination of polyetherimide, polybutylene terephthalate, polyphenylsulfone, polyethersulfone, polyphthalamid (PA6T/6I), and polyetheretherketone. To increase the stiffness of the elongate body  12 , the plastic material may be reinforced with glass fibers or carbon fibers. The friction-reducing additive may be compounded within the plastic matrix to form a plastic material charged with the friction-reducing additive to reduce the friction with the rotating bushing  30 . Alternatively, the first and second working ends  14 ,  16  of the elongate body  12  may be coated with the friction-reducing additive. Thus, the plastic material containing the friction-reducing additive encompasses both a plastic matrix with a friction-reducing additive dispersed therein or a plastic body with the surface thereof coated with a friction-reducing additive.  
      The plastic material for the bushing is advantageously an acetyl resin, but the invention is not so limited. Advantageously, the friction-reducing additive is compounded within the plastic matrix to provide the low friction resistance. While coating an inside surface of the bushing  30  with the friction-reducing additive is not precluded from the present invention, it may be appreciated that the small size of the bushings  30  limit the practicality of this approach.  
      The roller tips  20 ,  20   a  advantageously comprise a resilient material that has the ability to return to its original shape after a mechanical compression, with no plastic deformation occurring when subjected to mechanical stress under normal circumstances. Roller tips  20 ,  20   a  also advantageously comprise a material having low surface energy, for example, less than 25 mN/m, which also contributes to low adhesion with the restorative composite materials. Examples of such resilient materials include silicones, polyurethanes, and thermoplastic elastomers. Advantageously, roller tips  20 ,  20   a  comprise a fluorine-charged thermoplastic vulcanizate, such as the Viton® fluoroelastomers from DuPont Dow Elastomers, Wilmington, Del. and Fluoroprene® from Freudenberg-NOK, Plymouth, Mich., which each contain 40-70 wt. % fluorine. These fluorine charged materials have low surface tension, on the order of 18-20 mN/m, and thus, have low adhesion to the restorative composite materials. In an exemplary embodiment, the roller tip material has a Shore A hardness of 20-60, and more advantageously, the roller tip has a Shore A hardness on the order of 30. The roller tip material may be a solid material or a microporous material. Because the roller tips  20 ,  20   a  are interchangeable on the working ends  14 ,  16  of instrument  10 , various roller tips  20  may be provided having different hardnesses, different shapes and different colors, as desired.  
      The bushings  30  may be pre-mounted inside the roller tips  20 ,  20   a  to provide units that are then mounted on the working ends  14  and  16  of the elongate body  12  to form the instrument  10 , and the units are interchangeable. Alternatively, the bushings  30  may be pre-mounted on the working ends  14  and  16 , and the roller tips  20 ,  20   a  are interchangeably mounted on the pre-mounted bushings  30 . In either embodiment, the roller tips  20 ,  20   a  may be pre-molded and flexible enough to be mounted on the bushings  30  without difficulty. Alternatively, when the roller tips  20 ,  20   a  and bushings  30  are pre-mounted to form units, the roller tips  20 ,  20   a  may be over-molded onto the bushings  30 , such as where the material of the roller tips is not flexible enough to be easily mounted on the bushings  30 . Advantageously, as depicted in  FIG. 2 , the roller tip  20  is shorter than the bushing  30  to provide clearance between roller tip  20  and elongate body  12  to avoid friction between the two.  
       FIG. 2  depicts in cross-sectional view an alternative embodiment of the instrument of the present invention in which a rolling element bearing  34  is mounted on working end  14  instead of bushing  30 . Rolling element bearing  34  includes rolling elements  36 , such as ball bearings, cylindrical rollers or taper rollers, positioned and rotatable between an outer ring  38  and an inner ring  39 . The rolling element bearing  34  may also be used on working end  16  in place of bushing  30 . The description above regarding the materials, construction, and mounting of bushing  30  apply equally to rolling element bearing  34 .  
       FIG. 3  depicts in partial cross-section another exemplary embodiment of a dental instrument  10 ′ of the present invention having an elongate body  12  with a handle portion  18  and a single working end  14  extending therefrom. Thus, dental instruments in accordance with the present invention may have one or two working ends. In  FIG. 3 , there is also depicted an embodiment in which the bushing  30  (or rolling element bearing  34 ) is eliminated, such that the roller tip  20  is directly rotatable about the working end  14 . To achieve low friction resistance between the roller tip  20  and the working end  14  of the elongate body  12 , the elongate body  12  comprises a plastic material containing a friction-reducing additive, as discussed above in reference to instrument  10 . If additional friction reduction is desired, the roller tip  20  can be gas-phase fluorinated. Thus, in this embodiment, rather than the roller tip  20  rotating via rotation of a bushing  30  (or rolling element bearing  34 ), the roller tip  20  itself rotates directly relative to the working end  14 . Thus, an instrument of the present invention may be provided with one or two working ends  14  and/or  16 , and may be provided with or without bushings  30  (or rolling element bearings  34 ). While the greatest friction reduction may occur with a plastic elongate body  12  charged with a friction-reducing additive upon which is mounted a bushing(s) or bearing(s) charged with a friction-reducing additive, it may be understood that the materials of these components may be altered and/or the bushing(s)/bearing(s) eliminated as long as the kinetic coefficient of friction is less than 0.2 between the working ends  14 ,  16  and the rotating component (roller tip  20 , bushing  30 , or rolling element bearing  34 ).  
       FIGS. 4A-4C  depict various shapes for the roller tips  20 . While the roller tip  20  on first working end  14  of  FIGS. 1-3  was depicted as being substantially uniformly cylindrical along its outer surface  22 ,  FIG. 4A  depicts a drop-shaped or pear-shaped roller tip  20   a , also shown on second working end  16  in  FIG. 1 , where the outer surface  22   a  has a maximum circumference  24   a  adjacent the handle portion  18 , and then sharply tapers inward to an intermediate circumference  26   a  from which it then tapers less drastically to a distal tip  28   a  furthest from the handle portion  18 , thereby forming a very small circumference distal tip  28   a  that is adapted to fit within small cavities in a tooth surface (not shown). The drop-shaped roller tip  20   a  in  FIG. 4A  provides the benefit of the large maximum circumference surface  24   a  for applying and shaping the composite material generally to the tooth surface, while the small distal tip portion  28   a  ensures homogeneous distribution into small irregularities in the tooth surface not reachable by the larger rolling surface  24   a .  FIG. 4B  depicts a tapered roller tip  20   b  with a relatively small uniform taper angle such that the outer surface  22   b  has a maximum circumference  24   b  adjacent the handle portion  18  and then slightly tapers inward to a minimum circumference  28   b  furthest from the handle portion  18  to provide a larger distal tip portion  28   b  that is adapted to engage larger irregularities in the tooth surface.  FIG. 4C  is similar to  FIG. 4B  but depicting a larger uniform taper angle from the maximum circumference  24   c  such that the distal tip  28   c  is smaller in diameter. All statements made herein regarding roller tip  20  are equally applicable to roller tips  20   a ,  20   b  and  20   c , for example, statements regarding the material of construction or method of mounting.  
      The dentist may interchange these roller tips  20 ,  20   a ,  20   b ,  20   c , as desired, to provide the working ends  14 ,  16  with shapes most suitable for the particular tooth surface being restored. For example, instrument  10  of  FIG. 1  may be provided with additional roller tips  20   b ,  20   c  that are removably mountable on working ends  14 ,  16  upon removal of roller tips  20 ,  20   a  such that all roller tips  20 ,  20   a ,  20   b ,  20   c  are fully interchangeable. The additional roller tips  20   b ,  20   c  may be pre-mounted on bushings  30  or bearings (not shown) for embodiments in which the roller tips  20 ,  20   a  are substantially permanently mounted on bushings  30  (or roller element bearings  34 ), and the bushings  30  (bearings  34 ) are removably mounted on the working ends  14 ,  16 . Alternatively, additional roller tips  20   b ,  20   c  may be removably mountable directly on the working ends  14 ,  16  for those embodiments where no bushings or bearings are used, or removably mountable on bushings  30  (or roller element bearings  34 ) that are pre-mounted on the working ends  14 ,  16 . It may be appreciated that other roller tip shapes may be utilized for the instrument  10  (or  10 ′) of the present invention other than those depicted in  FIGS. 1-4B .  
      As a result of the interchangeable roller tips  20 ,  20   a ,  20   b ,  20   c , the dental instrument of the present invention is particularly suitable for use with both anterior and posterior teeth. By way of example, a substantially uniformly cylindrical-shaped roller tip  20  depicted in  FIGS. 1-3  may be ideal for distributing restorative material on the front surface of an anterior tooth, while the drop-shaped and pear-shaped roller tips  20   a ,  20   b ,  20   c  depicted in  FIGS. 4A-4C  may be particularly suitable for anterior proximal surfaces and for the surfaces of proximal teeth, in particular on the marginal area and the cavity walls of a posterior tooth.  
       FIGS. 5A and 5B  depict the benefit of the instrument  10  (or  10 ′) of the present invention in distributing restorative material onto a tooth surface in the oral cavity. In  FIG. 5A , a roller tip  20  with a substantially uniformly cylindrical outer surface  22  is mounted on an axial working end  14 , i.e., the working end  14  has a center axis coaxial with the center axis of the handle portion  18 , as shown in  FIG. 1 . A restorative material  40  is distributed on a front tooth surface  50  by manipulating the instrument  10  to roll the roller tip  20  across the tooth surface  50 , back and forth as necessary, to provide a homogeneous and relatively flat layer of restorative material that is free of bubbles. The homogeneity and bubble-free nature are due to the quick distribution achievable by means of the rotating roller tip  20  whereby adherence of the restorative material  40  to the surface  22  of the roller tip  20  is reduced or avoided. “Distribution” as referred to herein may include the initial application of the restorative material  40  to the tooth surface  50 , as well as the spreading, shaping, adapting and/or smoothing of the material  40  into a uniform layer. Alternatively, the restorative material  40  may be first introduced onto the tooth surface  50  by other means, and distribution with the instrument  10  (or  10 ′) of the present invention may include the spreading, shaping, adapting and/or smoothing of the material  40  into a uniform layer. Thus, the terms “distributing” and “distribution” are intended to be broad in scope, referring to any application and/or manipulation of the restorative material relative to the tooth surface. Likewise, “tooth surface” broadly refers to any external surface of the tooth or any internal surface, such as the walls of a tooth cavity. By virtue of the roller tips  20  ( 20   a ,  20   b ,  20   c ), instrument  10  (or  10 ′) of the present invention is also particularly useful in creating a defined layer thickness of restorative material on a tooth surface.  
       FIG. 5B  depicts use of an instrument  10  (or  10 ′) of the present invention for distributing restorative material  40  on a posterior tooth surface  60 , both on the marginal area and on the cavity walls. The drop-shaped roller tip  20   a  depicted in  FIG. 4A  is mounted on a right angle working end  16  of the elongate body  12 , i.e., the center axis of the working end  16  is angled 90° relative to the center axis of the handle portion  18 , as shown in  FIG. 1 . The distal tip  28   a  of the roller tip  20   a  is capable of distributing the restorative material  40  into the cavity  62  and forming a uniform or homogeneous layer on the cavity walls, and the outer surface  22   a  including the maximum circumference  24   a  to the intermediate circumference  26   a  is effective to distribute the restorative material  40  on the marginal area. The restorative material  40  does not stick to the instrument  10  because it does not have time to adhere completely to the tip surface  22   a  due to the quick and efficient distribution achieved by the roller tip  20   a . The quick and efficient distribution also avoids the integration of air bubbles during the distribution process.  
      The easy interchangeability of the roller tips  20 ,  20   a ,  20   b ,  20   c , as well as a double-ended instrument  10  having differently shaped tips  20  and  20   a  ( 20   b  or  20   c ) provides the dentist with flexibility during the distribution process. The control of friction between the roller tips  20  ( 20   a ,  20   b ,  20   c ) and the elongate body  12 , or between the bushings  30  and the body  12 , enable the quick, smooth and efficient distribution. There is thus provided a dental instrument for distributing restorative material on a tooth surface that is far superior to the dental instruments of the prior art. Also, as stated previously, while the dental instrument  10  (or  10 ′) is particularly useful for distributing restorative material on a tooth surface that resides in the oral cavity, the invention is not so limited. Dental instrument  10  (or  10 ′) may also be used to shape a prosthetic tooth. Thus, the roller tips  20  ( 20   a ,  20   b ,  20   c ) are sized for use with a tooth surface, including those of natural and artificial teeth residing in the oral cavity as well as artificial prosthetic teeth intended to later reside in the oral cavity.  
      While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, while the dental instrument of the present invention addresses shortcomings experienced in the distribution of composite-type restorative materials, the instrument may well find applicability with other dental materials. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept.