This invention relates to dental restoration systems, and more particularly to a method and apparatus for providing on a tooth root a level surface of a contour corresponding to the shape of the mouth of the root canal for thereby facilitating the installation of a post and core during the fabrication of a superstructure on the tooth root. 
In the restoratin of devitalized dentition, a post and core is generally utilized for retaining a crown onto a tooth root.  Typically, the tooth root is initially prepared by drilling a desired depth and diameter into the apical canal to provide an enlarged central bore for receiving a dental post.  The dental post is then inserted and cemented in the bore.  An appropriate core is built up on an upper portion of the dental post, and finally dental restorative material is used to fabricate the superstructure in the form of a crown on the core. 
Since the actual canal in the tooth root tends to flare outwardly at its occlusal surface, the mouth of the canal at that surface of the tooth root tends to approach an oval shape.  The enlarged central bore drilled into the tooth root, on the other hand, is generally circular in shape, and likewise the dental post is also circular in shape.  Consequently, at the upper end, the dental post will not be securely retained in the tooth and will tend to laterally shift.  While it would be possible to drill the central bore large enough to encompass the entire oval shape at the flared upper mouth, this would tend to destroy healthy dentition in the lower tooth and weaken the existing tooth root. 
As a solution to this problem, U.S. Pat.  No.  4,600,292, entitled "Contoured Dental Post" by the same inventor of the present application, describes a dental post which includes an elongated cylindrical pin provided with at least one radially projecting rib extending longitudinally along at least a portion of the length of the pin.  Preferably, a pair of opposing ribs are utilized.  The central cylindrical pin with the pair of diametrically opposed projecting ribs, approximates the oval shape of the mouth of the canal in the tooth root into which a correspondingly shaped bore can be formed for receiving the post.  The side ribs project only partway down the length of the center pin to avoid the necessity of excessive drilling and destruction of healthy dentition.  In order to provide an oriented insertion of the post, one rib is shorter than the other.  To facilitate formation of an appropriate bore for receiving the contoured dental post, the aforementioned U.S. Patent also describes a dental drill jig for contouring the central bore in the tooth root into an approximate oval shape at the upper end of the bore in order to accommodate the contoured dental post.  The dental jig includes a head having a stepped configuration.  An elongated shaft depends from the center of the head block for insertion into the pre-drilled central bore formed into the tooth root.  A pair of offset apertures are provided through the head block of the jig which extend into the shaft along opposing sides thereof.  The distance from the top portion of each section of the stepped head to the lower distal end of the offset apertures in the shaft are substantially equal so that a single drill bit can be utilized to drill two ancillary bores into the tooth root.  In this manner, the pair of ancillary bores are formed on either side of the central bore, contiguous with the central bore.  One of the ancillary bores penetrates further into the depth of the tooth root than the other.  The shape of the resulting aperture in the tooth root correspondingly receives the contoured dental post. 
The aforementioned dental post and jig have been commerically incorporated into a dental post system referred to as the Triax. TM.,  which is marketed by the Whaleadent International Division of IPCO Corporation. 
While such system has been most successful, it is appropriate to have a level surface on the tooth root on which the dental jig can be positioned.  In order to achieve such level surface, the tooth root is intially prepared by cutting it down below the damaged portion to provide the flat surface needed.  In many instances, however, by cutting the tooth down to such level surface on which the dental jig can be placed, healthy dentition is destroyed which could otherwise be retained. 
Likewise, in order to provide a suitable base upon which the dental core will sit, there is likewise needed a level portion at the occlusal surface of the tooth root.  This is also achieved by leveling off the tooth root to provide a suitable planar surface.  However, again, healthy dentition could be destroyed which could otherwise be retained and incorporated within the dental restoration built upon the tooth root.