Endodontic Cavity Preparation

Chapter 10 ENDODONTIC CAVITY PREPARATION
John I. Ingle, Van T. Himel, Carl E. Hawrish, Gerald N. Glickman, Thomas Serene, Paul A. Rosenberg, L. Stephen Buchanan, John D. West, Clifford J. Ruddle, Joe H. Camp, James B. Roane, and Silvia C. M. Cecchini

The chapter on success and failure (chapter 13) substantiates the endodontic dogma of careful cavity preparation and canal obturation as thekeystones to successful root canal therapy. Apical moisture-proof seal, the first essential for success, is not possible unless the space to be filled is carefully prepared and débrided to receive the restoration. As in restorative dentistry, the final restoration is rarely better than the initial cavity preparation. Endodontic cavity preparation begins the instant the involved tooth is approachedwith a cutting instrument, and the final obturation of the canal space will depend in great measure on the care and accuracy exercised in this initial preparation. DIVISIONS OF CAVITY PREPARATION For descriptive convenience, endodontic cavity preparation may be separated into two anatomic divisions: (a) coronal preparation and (b) radicular preparation. Actually, coronal preparation is merely a meansto an end, but to accurately prepare and properly fill the radicular pulp space, intracoronal preparation must be correct in size, shape, and inclination. If one thinks of an endodontic preparation as a continuum from enamel surface to apex, Black’s principles of cavity preparation—Outline, Convenience, Retention, and Resistance Forms—may be applied (Figure 10-1).1 The entire length of thepreparation is the full outline form. In turn, this outline may have to be modified for the sake of convenience to accommodate canal anatomy or curvature and/or instruments. In some techniques, the canal may be prepared for slight retention of a primary gutta-percha point. But most important, resistance must be developed at the apical terminus of the preparation, the so-called “apical stop,” the barrieragainst which virtually every canal filling must be compacted.

CORONAL CAVITY PREPARATION Basic Coronal Instruments Preparations on and within the crown are completed with power-driven rotary instruments. For optimal operating efficiency, separate ranges of bur speed are needed. Although two handpieces are usually required, developments in electric handpiece engineering allow one motor toprovide both low- and high-speed ranges of rpm. Handpieces are also being developed that automatically reverse on lockage of the file.2 The correct burs are mounted by the dental assistant prior to their use. Rarely should a bur have to be placed or changed during the operation. For initial entrance through the enamel surface or through a restoration, the ideal cutting instrument is the round-endcarbide fissure bur such as the Maillefer Transmetal bur or Endo Access diamond stone (Dentsply/Maillefer, Tulsa, Okla.), mounted in a contra-angle handpiece operating at accelerated speed. With this instrument, enamel, resin, ceramic, or metal perforation is easily accomplished, and surface extensions may be rapidly completed. Porcelain-fused-to-metal restorations, however, are something else. Stokesand Tidmarsh have shown the effectiveness of various bur types in cutting through different types of crowns3 (Figure 10-2). Precious metal alloys are relatively easy to penetrate, whereas nonprecious metals present considerable difficulty. Although nonprecious alloys can be cut with tungsten carbide burs, they “chatter” severely. This vibration results in patient discomfort and tends to loosenthe crown from the luting cement. “The extra coarse, dome-ended cylinder…was the only bur type that cut smoothly and remained clinically effective during the cutting of five successive access cavities in the nonprecious metal” found frequently under metal-ceramic crowns.3 Teplitsky and Sutherland also found diamond instrumentation perfect for access

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Endodontics mm from the nose of the...