Patent Publication Number: US-6902400-B1

Title: Dental bur

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a novel and useful dental bur which is particularly useful in removing composite dental posts. 
   Dental core and post reconstitution of non-vital teeth requires the use of a root canal post. In the past, metallic posts have been used with some success. However, it has been found that metal posts are difficult to remove when a failure or fracture of the post occurs. Removal techniques have often damaged dentin material located laterally relative to the metal posts. 
   Recently, carbon and quartz fiber-based composite posts have been available to dental practitioners as a substitute for the traditional metallic posts. Such composite posts offer certain advantages in that they are more flexible and dissipate stress to a greater degree than metallic posts. However, despite these advantages, composite posts also break requiring removal of the same from the tooth canal. 
   In the past, ultrasonic diamond coated files, normally used to remove a metallic post have been used to remove composite posts. It has been found that the ultrasonic file is very difficult to control and often drifts into the surrounding dentin tooth structure causing damage thereto. Likewise, a hollow end cutting drill, much like a hole saw, used to remove metal posts adequately functions to remove metal posts, but tends to drift laterally when used to remove composite posts, again causing damage to the surrounding dentin material. 
   A dental bur which successfully and accurately removes dental composite posts would be a notable advance in the dental field. 
   BRIEF SUMMARY OF THE INVENTION 
   In accordance with the present invention a novel and useful dental bur structure is herein provided. 
   The dental bur structure of the present invention connects to means of rotation normally found in a dental practitioner&#39;s office. For example, a dental drill motor turning at about 40,000 RPMs would suffice in this regard. 
   The bur of the present invention includes as one of its elements a rotatable shaft having a proximal portion and a distal portion, relative to the means of rotation. The rotatable shaft may be composed of a rigid or semi rigid material such as carbon steel. 
   The bur of the present invention is also constructed with a tip located at the end of the distal portion of the rotatable shaft. The tip possesses a smooth, non-cutting surface. Such tip generates heat upon the rotation of the rotatable shaft to melt a portion of the matrix of a dental composite post. Such action serves as a guide for the dental bur along the canal of the tooth. Also, the smooth surface of the tip prevents any damage to the dentin surrounding the composite posts. The tip may include an end which is sharp or rounded as long as the surface of the tip remains smooth. 
   Means is also provided for removing composite material from the damaged composite posts. Such means may take the form of a fluted surface having a very unagressive or low rake angle. Of course, the rotatable shaft of the bur of the present invention is positioned in the post canal by the heat generating tip previously described which then allows the fluted surface to efficiently remove composite material as the bur travels down the tooth canal. 
   Also located at the proximal end of the rotatable shaft is a dentin-abrading surface. Such abrading surface may take the form of a rasp formed from diamond particles. In this embodiment, the dentin-abrading surface generates a minimum amount of heat and easily dissipates the same at the upper part of the tooth canal. Such dentin removal permits the bur of the present invention to provide excellent surface for adhesion of a new composite post following removal of the broken composite post. 
   It may be apparent that a novel and useful dental bur structure has been hereinabove described. 
   It is therefore an object of the present invention to provide a dental bur structure which accurately and simply removes composite material forming a broken composite post in order to extract the same from a tooth canal. 
   Another object of the present invention is to provide a dental bur structure which includes a heat-generating tip that serves as a guide for the dental bur as it travels down the tooth canal to allow accurate removal of the dental post. 
   A further object of the present invention is to provide a dental bur structure which is capable of removing a broken composite post without damaging adjacent dentin material. 
   Yet another object of the present invention is to provide a dental bur structure which is adaptable to use in a dental practitioner&#39;s existing equipment. 
   The invention possesses other objects and advantages especially as concerns particular characteristics and features thereof which will become apparent as the specification continues. 

   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
       FIG. 1  is a fragmented elevational view of the bur of the present invention. 
       FIG. 2  is an enlarged partial front elevational view of the tip portion of the bur depicted in  FIG. 1 . 
       FIG. 3  is an enlarged broken front elevational view of the tip portion of the dental bur depicted in  FIG. 1  showing another embodiment thereof. 
       FIG. 4  is a sectional view of a tooth with a broken composite post therewithin. 
       FIG. 5  is a sectional view showing the bur of the present invention in use, removing the broken post depicted in  FIG. 4 . 
     For a better understanding of the invention reference is made to the following detailed description of the preferred embodiments thereof which should be referenced to the prior described drawings. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
   Various aspects of the present invention will evolve from the following detailed description of the preferred embodiments thereof which should be taken in conjunction with the prior described drawings. 
   The invention as a whole is shown in the drawings by reference character  10 ,  FIG. 1 . Dental bur  10  includes as one of its elements a rotatable shaft  12  which is connected to a conventional hand piece (not shown) and rotated by a motor  14 . Typically, motor  14  rotates shaft  12  at about 40,000 RPMs. Shaft  12  includes recesses  16  which are of a conventional configuration to lock into existing sources of rotation found in a dental practitioner&#39;s facility. Rotatable shaft  12  may be formed of any suitable material such as carbon steel. Rotatable shaft  12  includes a proximal portion  18  and a distal portion  20  relative to engagement end  22  which eventually links to motor  14 . 
   Bur  10  includes as one of its elements a tip  22  located at the distal end  20  of rotatable shaft  12 . Tip  22  is rounded and includes a smooth surface  24  which lacks a cutting structure. End  26  may take the form of a sharp terminus,  FIG. 2 , or may be formed into an end  28  which is rounded to a certain degree,  FIG. 3 . Also, surface  29  may be slightly concave. In any case, end  22  is intended to generate heat through friction upon the rotation of shaft  12  when in contact with composite material, which will discussed in detail hereinafter. 
   Means  30  is also found in the present invention for removing composite material from a broken composite dental post. Means  30  may take the form of a fluted surface  32  having a plurality of flutes or ridges  34  which extend outwardly to a certain degree. Flutes  34  are formed on rotatable shaft  12  with a very low rake angle  36 , typically ranging between 5 and 25 degrees. 
   Proximal portion  18  also includes dentin-abrading means  36  which is shown in the form of an abrading surface  38 . Abrading surface  38  may be composed of a plurality of diamond particles  40  adhered to rotatable shaft  12 . In this format, abrading surface  38  generates a minimum of heat and dissipates such generated heat easily, as will be described as the specification continues. Thus, abrading surface  38  is essentially in the form of a rasp. 
   In operation,  FIGS. 4 and 5 , depict the circumstances and use of the present invention  10 . Specifically,  FIG. 4  depicts a tooth  42  having a dentin structure  44 . A canal  46  contains a broken composite post  48  and canal filling material  50 , which may be gutta percha. Edge portion  52  of post  48  indicates the broken interface between post  48  and a crown portion which has been removed. Composite posts  48  may be formed of side-by-side carbon fiber strands  54  which are placed in a matrix  56  of a binder such as an epoxy material. The dental practitioner operates bur  10  by first drilling a pilot hole at the top portion of composite post  48  near edge  52  in order to center bur  10 . Bur  10  is then rotated by motor  14  according to directional arrow  58 . Such rotation may take place at a rate of about 40,000 RPM. Tip  22  contacts composite post  48  and generates a great deal of heat to melt the composite material in its vicinity. Such melting is due to the smooth surface  24  of tip  22 . Bur  10  is then guided through broken post  48  via such melting process as being the path of least resistance downwardly through canal  46 . If per chance, tip  28  were to touch dentin material  44 , tip  22  would not damage the same since there is no cutting structure. As bur  10  travels down canal  48 , means  30  removes composite material  60 . Bur  10  continues its travel until it reaches gutta purcha section  50  of canal  48 . At this point, dentin abrading means  36  contacts the upper wall  62  of canal  48  and removes a small degree of dentin to provide an unencumbered surface. Following retrieval of bur  10  from canal  46 , a new dental post is inserted within canal  46  and cemented to wall  62 . A new crown portion (not shown) is then attached to the new post to complete to restoration process. 
   While in the foregoing, embodiments of the present invention have been set forth in considerable detail for the purposes of making a complete disclosure of the invention, it may be apparent to those of skill in the art that numerous changes may be made in such detail without departing from the spirit and principles of the invention.