Teeth that have been weakened by decay and require endodontic therapy to maintain their functionality intraorally may present with minimal coronal structure remaining. This can hamper isolation and risk further coronal damage when a dam clamp is affixed to the tooth. Ability to seal teeth that are severely broken down and prevent coronal leakage can be additionally compromised. Building up the coronal tooth structure following decay removal and identification of the canal orifices can facilitate the endodontic process, providing a strong core and coronal seal.
Dr. C. John Munce, in an attempt to circumvent these issues, developed a plastic cone that could be used to extend the orifice, which he termed “projection” and reinforce the missing coronal tooth structure. These canal projectors are made from a tapered black colored plastic cone with a central channel to allow placement on a standard endodontic hand file. A resin core can then be built up around the projectors, reinforcing the tooth. Upon curing of the resin the projectors are withdrawn leaving straight-line access into each individual canal.
METHODS AND MATERIALS
Isolation of the tooth to be treated is accomplished with a rubber dam and clamp. When fracture of the tooth due to pressure from the clamp is possible or there is insufficient coronal tooth structure to secure the clamp, it is recommended to use a split dam technique with clamps on adjacent teeth.
Decay is removed and all canal orifices are identified and explored with a stainless steel hand file. Canals should be taken to a size 20 (minimum) and the orifice enlarged with a size 2 round bur in a slow speed handpeice. The widening of the orifice will facilitate placement of the canal projector and prevent flow of adhesive into the canal causing possible blockage. A matrix band or other method of shaping the coronal may be employed at this stage.
Phosphoric acid gel is applied to the exposed dentin and enamel. Rinsing and drying is accomplished after 30 seconds. A canal projector is placed onto a hand file that fits each canal and slide up the file so that 5-8mm of file protrudes beyond the tip of the projector (Fig. 1). The hand file is then reintroduced into the canal and using cotton pliers the projector is pushed down the file till it fits snuggly into the orifice (Fig. 2).
A dual cure dentin adhesive such as Nanabond (Pentron, Wallingford, CT) or Prime & Bond NT (Caulk, Milford, DE) is applied deep into the coronal with a jiffy tube, flooding the pulpal floor. Air thinning will then assure complete coverage of all exposed tooth within the preparation. A light curing tip is applied to the buccal tooth structure for 30 seconds allowing the light to transmit thru the enamel and initially set the adhesive.
A self-cure activator may be added to the adhesive ensuring complete cure of the bonding agent. With an intraoral tip placed on the automix syringe, a dual cure core material (ie. Buildit FR, Pentron, Wallingford, CT) is injected into the tooth, backfilling from the pulpal floor in and around the canal projectors (Fig. 3). The curing light is again applied to the tooth to set the core material.
The hand files are turned counterclockwise to disengage them from the projector and are withdrawn from the canal, leaving the projector in the tooth (Fig. 4). The projector is left in each canal so that debris during coronal adjustment of the height does not enter the orifice and lead to canal blockage. Any matrix that had been placed is removed at this time and using a coarse wide diamond in a high-speed handpeice, the occlusal height is reduced (Fig. 5). The projector being fabricated of plastic is easily trimmed level with the occlusal surface. A hand file larger then the one originally placed in the projector is threaded clockwise into each projector and a gentle tug removes the projector from the tooth (Fig. 6).
The result is a solid coronal structure with straight line access into each canal with maximum structural reinforcement (Fig. 7). The individual canals are isolated from each other allowing each to be treated independent of the others. The original hand file is introduced into the projected orifice and taken to working length. Rotary files can now be used to shape and disinfection of the canals performed chemically.
When endodontic treatment is not to be completed at the initial appointment, temporization is simplified with the used projectors. Two to three millimeters of the coronal end of the projector is cut with a scissor or diamond. The shortened projector is reinserted into the canal and covered by Cavit (3M ESPE, MN). At the next appointment the Cavit can be removed quickly and the projector retrieved with a hand file.
CONCLUSION
Coronal leakage is a major contributor to endodontic failure. A bonded core placed prior to disinfection and obturation of the canal system of the tooth can greatly diminish the leakage potential both during and after endodontic therapy.
Isolation can be a challenging task when minimal coronal structure remains and endodontic therapy is required as part of the oral rehabilitation (Fig. 8). Coronal reinforcement has traditionally been addressed following the endodontic phase. But a coronal bonded buildup can simplify the endodontic phase and strengthen the tooth, decreasing the possibility of further damage to the tooth due to the dam clamp or mastication before a full coverage restoration can be placed. The canal projector core allows isolation of the individual canals surrounded by a resin buildup (Fig. 9).
Visualization of the orifice is elevated to the occlusal plane instead of deep within the tooth. Should the restoring dentist wish to place posts in to the tooth, post space preparation is simplified and misdirection of the post preparation is minimized.
Product information
Canal projectors are available through CJM Engineering (www. cjmengineering.com).
Dr. Kurtzman is in private practice in Silver Spring, MD and is an Assistant Clinical Professor at the University of Maryland School of Dentistry, Department of Endodontics, Prosthetics and Operative Dentistry. Dr. Kurtzman has earned Diplomat status in the International Congress of Oral Implantologists.
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