Patent Publication Number: US-2006003286-A1

Title: Tools and methods for measuring tooth reduction

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is a continuation in part application and claims the benefit of copending U.S. application Ser. No. 10/116,174, filed Apr. 3, 2002, the complete disclosure of which is herein incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION  
      This invention relates generally to the field of dentistry, and in particular to the reduction of teeth to facilitate placement of a dental prosthetic device, such as a crown. Or specifically, the invention is related to a dental tool and methods for measuring the amount of tooth reduction.  
      Artificial dental crowns are used as a restoration for teeth, and are particularly useful when teeth have been broken, have been weakened by decay, or have one or more large fillings. Dental crowns are constructed to fit over the remaining portion of the tooth to make the tooth stronger and provide the tooth with the shape and contour of the natural tooth. As such, crowns are often referred to as caps.  
      Dental crowns are typically fabricated outside the patient&#39;s mouth and then installed in the mouth. The manner of installation may vary depending on the nature of the crown. For example, full crowns are employed to cover the entire surface of a tooth as well as the sides of the tooth. Partial crowns are inlays which cover the top surface and portions of the sides. Inlays are employed to cover central portions of the top surface and may also extend partially onto the sides. Finally, veneers are used to cover a side surface of a tooth. A detailed discussion of how such dental crowns may be placed onto a tooth is set forth in U.S. Pat. No. 5,525,059, the complete disclosure of which is herein incorporated by reference.  
      Dental crowns may be employed to treat a variety of conditions. For example, as previously mentioned, the tooth may have been previously weakened by decay or may have a very large filling. Another reason for using a crown is if the individual has discolored fillings and would like to improve the appearance of the tooth. As a further example, the patient may have had an endodontic treatment of the root requiring protection of the remaining tooth.  
      Dental crowns may be constructed of a variety of materials. For example, the crown may be constructed of a porcelain that is bonded to a precious metal. In such cases, the precious metal is used to form the base and the porcelain is applied in layers over the metal base. As another example, the crown may be constructed entirely of porcelain. Because these look very natural, they may often be used for the front teeth. Other examples include porcelain and composite resin materials, glass, and precious metals, such as gold, platinum and palladium. A further description of materials used for dental crowns and how they may be bonded to the underlying tooth is set forth in U.S. Pat. No. 6,183,256, the complete disclosure of which is herein incorporated by reference.  
      In order to receive a crown, the dentist must first alter the shape of the tooth to a size and shape most conducive for receiving a crown. To do so, the dentist will typically remove most of the outer surface of the tooth, leaving a strong inner core. Ideally, the amount of tooth removed will be about the same as the thickness of the crown to be fitted. After the tooth has been formed to the proper shape, an impression of the prepared tooth along with the opposing jaw is used to determine the manner in which the teeth are brought together when the patient bites down. The impressions are then used by a dental technician to fabricate the crown to the shape of the reduced tooth.  
      Determining the appropriate size and shape of the tooth to be fitted with a crown is a difficult process, especially when the tooth is near the back of the patient&#39;s mouth. In such cases, it is nearly impossible to determine the amount of tooth that has been removed. However, determination of the amount of reduction is critical in order to ensure that the crown will properly fit. For example, if the tooth is reduced too much, the crown may not fit properly. On the other hand, if the occlusal surface is not sufficiently reduced, the crown will be too large and will interfere with the patient&#39;s bite.  
      In order to determine the amount of tooth reduction, some have proposed the use of a thin rubber strip upon which the patient is instructed to bite. If the dentist is unable to pull the rubber strip from the patient&#39;s mouth, the dentist assumes that the tooth has not been sufficiently reduced in size. However, for teeth near the back of the patient&#39;s mouth, it is nearly impossible to appropriately position such a rubber strip in the patient&#39;s mouth.  
      Hence, this invention relates to a tooth reduction measuring tool along with methods for its use to facilitate proper tooth reduction when preparing for a crown.  
     BRIEF SUMMARY OF THE INVENTION  
      In one embodiment, the invention provides a tooth reduction measuring system that comprises a holding tool having a proximal end and a distal end. A connector is provided at the distal end. The system also includes a flexible loop that may be coupled to the holding tool by the connector. For example, the connector may comprise a grasping mechanism, such as a pair of jaws, that are used to grasp the connector. The loop may have a thickness in the range from about 1 mm to about 2 mm and have an opening that is sized large enough to be placed around a tooth. In use, the loop may be positioned relative to a pair of opposing teeth, one of which has been reduced, such that the pair of opposing teeth are within the opening. The loop may be pulled by the holding tool into a gap between the opposing teeth to permit evaluation of the size of the gap based on the thickness of the loop.  
      To operate the grasping mechanism, the tool may include a pair of handles. Examples of tools that may operate in this way include hemostats, clamps, forceps and the like.  
      In another embodiment, the invention provides a tooth reduction measuring tool that comprises a shaft having a proximal end and a distal end, with the proximal end defining a handle. A flexible loop extends from the distal end and has a thickness in the range from about 1 mm to about 2 mm. The loop defines an opening that is sufficiently large to be placed around a tooth. In this way, the loop may be positioned relative to a pair of opposing teeth, one of which has been reduced, such that the pair of opposing teeth are within the opening. After instructing the patient to bite down, the shaft may be pulled to move the loop into a gap between the opposing teeth to permit the dentist to evaluate the size of the gap based on the thickness of the loop. For example, if the dentist is unable to pull the loop through the gap, the dentist may determine that the tooth needs to be further reduced, at least on the back side of the tooth. Alternatively, the dentist may choose another measuring tool with a loop having a smaller thickness and repeat the process to determine approximately how much more of the tooth needs to be reduced.  
      Optionally, the loop may include a marking material that produces a mark when engaging the tooth. In this way, when the dentist pulls on the loop and it engages the tooth, a mark will be produced on a loop or the tooth. The dentist may then evaluate the position of the mark to determine the location where additional tooth reduction needs to occur.  
      In another aspect, the loop may be constructed of a polymer so that the tool may be constructed in a relatively inexpensive manner. Further, the shaft may also be constructed of a polymer and integrally formed with the loop. In this way, the measuring tool may be disposed of after use. Further, the measuring tool may be placed into a sterile package so that the measuring tool will remain sterile until use.  
      To place a crown on a tooth, an initial amount of tooth structure is removed from the target tooth. The amount of removed tooth structure is then measured by grasping the measuring tool and placing the loop around or adjacent to the target tooth. The patient is then instructed to bite down to move an opposing tooth into position generally adjacent to the target tooth. The tool may then been retracted to pull the loop into a gap between the target tooth and the opposing tooth. The size of the gap may then be evaluated based on the thickness of the tooth relative to the gap as previously described. If needed, additional tooth structure may be removed from the target tooth or the opposing tooth if the loop is unable to move through the gap. Once the target tooth is appropriately sized and shaped, an impression may be taken and a crown formed. Following fabrication of the crown, it may be bonded to the target tooth.  
      In some cases, the loop may extend from the shaft at an acute angle to facilitate manipulation of the loop when measuring the back teeth. Alternatively, the loop may extend axially from the handle.  
      In some cases, the loop may be sold as a package, with the loops being connected to a frame or other packaging material. In this way, a loop may be separated from the frame and coupled to the tool prior to use. Following use, the loop may be discarded and the tool may be sterilized. Another loop may then be used with the tool. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a top view of one embodiment of a tooth reduction measuring tool according to the invention.  
       FIG. 2  illustrates another embodiment of a tooth reduction tool having an angled flexible loop according to the invention.  
       FIG. 3  is a side view of a portion of a patient&#39;s jaw showing a middle tooth that has been reduced in preparation for receiving a crown.  
       FIG. 4  is a top view of the teeth illustrated in  FIG. 3 .  
       FIG. 5  illustrates a method for using the tooth reduction measuring tool of  FIG. 1  to determine the amount of tooth reduction of the middle tooth of  FIG. 3  according to the invention.  
       FIG. 6  is a top view of the middle tooth showing how the flexible loop of the tooth reduction measuring tool is positioned to measure the amount of reduction according to the invention.  
       FIG. 7  illustrates the middle tooth of  FIG. 3  after receiving a crown.  
       FIG. 8  illustrates a set of flexible loops that may be used to measure the amount of tooth reduction according to the invention.  
       FIG. 9  illustrates an alternative method for measuring the amount of tooth reduction using a flexible loop that is removably held by a holding device according to the invention.  
       FIG. 10  illustrates the method of  FIG. 9  from a top view. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The invention provides various tools and techniques for determining the amount of tooth reduction when preparing a tooth to receive an artificial dental crown. Once the tooth is appropriately prepared, the tooth may be fitted with a wide variety of dental crowns that are constructed of a wide variety of materials, such as those previously described in the background section of this application. Hence, the invention is not intended to be limited for use with only a specific type of dental crown. Further, the invention may also be used with a wide variety of techniques and tools that are employed to alter the shape of the tooth during preparation of the tooth. Hence, the invention is also not intended to be limited to a specific method for altering the shape and/or size of the tooth.  
      To measure the amount of tooth reduction, the invention utilizes a flexible loop that is positioned over the reduced tooth while the patient&#39;s mouth is open. The patient is then instructed to bite down and the loop is manipulated in an attempt to slide the loop between a gap defined by the reduced tooth and the opposing tooth. The thickness of the flexible loop may be selected such that if it cleanly passes through this gap, an appropriate amount of material has been removed. Conveniently, loops of different sizes may be used in an iterative process to prevent the over-reduction of a tooth. For example, a loop with a smaller thickness may initially be used. Once this cleanly passes through the gap, a loop with a larger thickness may be attempted to see if it will pass through the gap. The second loop may be of the desired thickness so that if the second loop fails to be pulled through the gap, the dentist may remove additional material until the second loop passes between the gap.  
      To help determine where additional material needs to be removed, the loop may include a marking material that produces a mark where it comes into contact with the tooth. Examples of marking materials include occlusal marking paper, such as that sold by G.E. Rudichhauser.  
      The loop may be held by essentially any type of tool or device that permits the loop to be inserted into the mouth and manipulated between the teeth. The loop may be integrally coupled to a tool or a handle or may be removably coupled to such a tool or device. This may be an off the shelf tool or one that is specifically manufactured for this application. For example, a tool such as a hemostat, pliers, clamps, forceps and the like may be used to grasp and hold the loop. Following use, the loop may be discarded and the tool reused. Loops may be sold separately or in packages so that following sterilization the tool may be reused with another loop.  
      Once the tooth has been appropriately prepared, the crown may be fabricated and coupled to the tooth using techniques known in the art. As such, the invention is not intended to be limited to a specific technique for forming and attaching a crown, but may use any of the techniques known to those skilled in the art.  
      Referring now to  FIG. 1 , one embodiment of a tooth reduction measuring tool  10  will be described. Measuring tool  10  comprises a shaft or handle  12  having a distal end  14  and a proximal end  16 . Coupled to distal end  14  is a flexible loop  18 . Loop  18  defines an opening  19  that is configured to be large enough to receive a patient&#39;s tooth. For instance, the cross sectional area of opening  19  may be in the range from about 25 mm 2  to about 175 mm 2 , and more preferably from about 50 mm 2  to about 95 mm 2 .  
      Shaft  12  is preferably rigid or semi-rigid to provide a convenient way to grasp measuring tool  10  and to manipulate loop  18  as described hereinafter. Conveniently, a roughened or serrated portion  20  may be provided on shaft  12  to facilitate grasping of shaft  12  when performing a procedure. A wide variety of materials may be used to construct shaft  12 , such as stainless steel, plastics, composites, and the like. In some cases, it may be advantageous to construct shaft  12  of a polymer to reduce the overall cost of measuring tool  10  and to permit it to be disposed of after a single use. Shaft  12  may have a variety of external shapes, such as round, oval, triangular, and the like. Typically, the thickness of shaft  12  will be large enough to facilitate easy grasping while also being small enough to be easily manipulated within the patient&#39;s mouth. For example, for a circular shaft, the diameter may be in the range from about 2 mm to about 10 mm, and more preferably from about 3 mm to about 5 mm. Further, the length of shaft  12  is preferably long enough so that it can be used manipulate loop  18  to the reduced tooth without interfering with the dentist&#39;s movements. For instance, shaft  12  may have a length in the range from about 5 cm to about 15 cm.  
      Loop  18  is preferably constructed of a flexible material having a specified thickness. Examples of materials that may be used include polymers, flexible wires, braided materials, and the like. One advantage of constructing loop  18  and shaft  12  of the same material is that they may be integrally formed together during the manufacturing process. For example, if both are made of a polymer, a molding process may be used as known in the art to fabricate both shaft  12  and the loop  18 . However, other techniques may be used to couple loop  18  to shaft  12  as is known in the art.  
      Loop  18  may be provided with a variety of thicknesses to facilitate the measurement of a wide range of gaps between a patient&#39;s reduced tooth and the opposing tooth. For example, the flexible loop may have a thickness in the range from about 1 mm to about 2 mm. Further, measuring tool  10  may be fabricated in a variety of sizes, such as, for example, a measuring tool having a 1 mm loop, a measuring tool having a 1.5 mm loop, and a measuring tool having a 2 mm loop. In this way, the dentist may select the measuring tool with the appropriately sized flexible loop when measuring the size of the gap. Further, multiple measuring tools with different sized loops may be used in an iterative process when reducing the size and/or shape of the tooth as previously described.  
      In some embodiments, flexible loop  18  may also be provided with a marking material that produces a visible mark on loop  18  and the tooth when sufficient force is applied to loop  18 . For example, if loop  18  is passed over a reduced tooth and shaft  12  is pulled, the locations where loop  18  contacts the reduced tooth and/or the opposing tooth is marked on loop  18 . In this way, the dentist is provided with additional information about where additional tooth reduction is needed. An example of such a marking material is articulating paper.  
       FIG. 2  illustrates an alternative embodiment of a tooth reduction measuring tool  22 . Measuring tool  22  may employ the use of a shaft  12  that may be constructed in a manner similar to that previously described in connection with  FIG. 1 . Hence, the same reference numerals will be used to describe the same components of shaft  12 . Extending from shaft  12  is a flexible loop  24  that may be constructed of the same types of materials used to construct loop  18  as previously described. In the embodiment of  FIG. 2 , loop  24  extends at an angle relative to the longitudinal axis extending through shaft  12 . As shown, the angle between the axis and loop  24  is about 45 degrees. However, other angles may be used including angles from about 1 to about 90 degrees. Such an angling of loop  24  relative to shaft  12  may in certain circumstances permit easier introduction of loop  24  about a reduced tooth when performing a measurement.  
      Referring now to  FIGS. 3-6 , one method for measuring the amount of tooth reduction using measuring tool  10  will be described. Shown in  FIG. 3  is a portion of a jaw  26  having teeth  28 ,  30  and  32 . In describing the method, it will be appreciated that only a minimal number of teeth are shown to facilitate description of the inventive method. As such, it will be appreciated that the method may be employed with essentially any tooth in a patient&#39;s mouth that is being reduced. As best shown in  FIGS. 3 and 4 , tooth  30  has already experienced a procedure where a certain portion of the tooth has been reduced to form a reduced portion  34 . Once reduced portion  34  is formed using any of the techniques known within the art, measuring tool  10  may be employed to measure the amount of reduction. This is accomplished by grasping shaft  12 , typically between the thumb and first two fingers, and manipulating shaft  12  until loop  18  passes over tooth  30  as best shown in  FIG. 5 . Because of the spacing between teeth  28  and  30  and between teeth  30  and  32 , as well as because of the amount of tooth reduction, loop  18  should fit around reduced portion  34  as best shown in  FIG. 6 . The patient is then instructed to bite down so that a gap  36  between tooth  30  and an opposing tooth  38  is formed. It is this gap that needs to be measured in order to properly fabricate the desired crown. While the patient remains biting, shaft  12  is manipulated in an attempt to pull loop  18  over tooth  30 , with loop  18  passing through gap  36 . If loop  18  is unable to pass through gap  36 , the dentist may evaluate where loop  18  is engaging tooth  30  to determine where on tooth  30  additional material needs to be removed. To facilitate this evaluation, loop  18  may be provided with a marking material as previously described.  
      If loop  18  freely passes through gap  36 , then sufficient material has been removed and no further tooth reduction is required. As such, a crown  50  may be placed upon tooth  30  as illustrated in  FIG. 7  as is known in the art.  
      To avoid overly reducing tooth  30 , the dentist may initially remove only a small portion of the tooth. Tool  10  may then be used to determine whether loop  18  will pass through gap  36 . If not, additional material may be removed and the process repeated as many times as necessary in order to permit loop  18  to pass through gap  36 . Further, in an alternative embodiment the dentist may initially use a tool that has a loop with a size that is smaller than the intended gap. Once this loop passes through the gap, the dentist knows that he or she is close to removing the appropriate amount of material. Additional material then may be removed and the measuring process repeated with a tool having a loop with the desired thickness of gap  36 . Once this passes through the gap, an appropriate amount of material has been removed and the crown may be fabricated and applied.  
      As previously mentioned, the measuring tools may be constructed of disposable material so that they may simply be discarded after use. Conveniently, the measuring tools may be provided within sterile packaging so that they remain sterile until use. In some cases, it will be appreciated that sterilizable materials may be used to construct the measuring tools so that they may be reused after appropriate sterilization.  
      Shown in  FIG. 8  is a kit  60  containing a set of disposable flexible loops  62  that are held together by a frame  64 . Flexible loops  62  may be constructed of any of the materials described herein. In one specific application, loops  62  may be constructed of an occlusal marking paper so that when loop  62  comes into contact with a tooth, a mark will appear at the point of contact. In such cases, frame  64  may include tabs  66  that are also constructed of an occlusal marking paper having score lines  68  adjacent to loops  62 . In this way, loops  62  may easily be removed from frame  64  by tearing the paper along score lines  68 .  
      Loops  62  may be used with essentially any type of tool capable of holding the loop and positioning it within a patient&#39;s mouth. Examples of suitable tools include those with jaws, clips, retractable hooks or the like that may grasp loop  62 .  
      One example of a procedure where one of the loops  62  is used to measure the amount of tooth reduction is illustrated in  FIGS. 9 and 10 . Loop  62  is held by a hemostat  70  having a pair of jaws  72 . Hemostat  70  may be used to grasp loop  62  either before or after being removed from frame  64 . Hemostat  70  includes a pair of handles as is known in the art to operate jaws  72 . Another example of a suitable hemostat is described in, for example, U.S. Pat. No. 5,931,843, the complete disclosure of which is herein incorporated by reference.  
      Once held by hemostat  70 , loop  62  may be used with any of the procedures and techniques described herein. For example, as shown in  FIGS. 9 and 10 , loop  62  may be positioned over a reduced portion  74  of a tooth  76  to measure the amount of tooth reduction in a manner to that previously described. Because loop  62  is constructed of a marking material, marks will be left on the areas of loop  62  that come into contact with a tooth when pulling loop  62  between the opposing teeth.  
      Following use, jaws  72  may be separated and loop  62  removed. Loop  62  may then be discarded. Following sterilization, hemostat  70  may be reused with another loop  62 .  
      The invention has now been described in detail for purposes of clarity and understanding. However, it will be appreciated that certain changes and modifications may be practiced within the scope of the appending claims.