Accessing Root Canal Systems
James C. Kulild, DDS, MS
Endodontic access can be the most challenging part of nonsurgical endodontics if the root canal system (RCS) is calcified or hidden, the tooth is restored with a full-coverage restoration, malaligned in the arch, or the mouth opening is limited. Four essential components to achieving predictable success in endodontic therapy are quality diagnostic radiographs, understanding of external and internal tooth morphology, use of correct armamentarium, and most importantly, proper technique. Using these components results in access openings which allow the operator a greater opportunity to locate and obturate all RCSs (Figure 1).
A straight-on parallel and a shift-shot periapical radiograph are absolutely necessary to evaluate the size, numbers, and position of RCSs. They also help identify root curvatures and additional roots. A bitewing radiograph may also be extremely valuable in identifying the location and depth of the root canal chamber. Digital radiographic technology also provides a substantive enhancement to traditional film-based radiography by allowing the user to increase image size as well as other viewing features that improve the clinician’s diagnostic capabilities. As a result of their ability to be efficiently displayed chairside, digital radiographs are also excellent for patient education.
Each clinician must have a clear vision of tooth morphology to help guide his or her hands and instruments to the right location(s). While this knowledge can be gained from reading texts and journal articles, practical knowledge only comes from two hands-on exercises. The first requires the practitioner to examine the external anatomy of extracted teeth; the second requires the clinician to perform access preparations on these extracted teeth in a clinical rather than laboratory environment in order to heighten one’s coordination and skills. Placing the tooth in a dentoform of some type and attaching it to the dental chair adds greater clinical reality to this experience. The clinician must always remember that the internal anatomy of the tooth dictates its external access shape (Figure 2).
New stainless steel burs are essential for initial access in natural tooth structures. The clinician should “think small” when selecting burs so that errors do not result in irreversible defects (ie, irreparable perforations). A high-speed #2 regular-length round bur with copious water spray is ideal for this purpose and also minimizes chances of chipping porcelain. It is also important to replace burs at the first sign of a decrease in their cutting efficiency.
It is almost never necessary to resort to a long-shank bur for access, which exponentially increases the risk of perforation (Figure 3). A helpful hint is for the clinician to place the regular-length bur against a plain-film radiograph to determine how far the bur can enter the tooth before the risk of a possible perforation can occur, especially in the case of a calcified chamber.
Access procedures should always be performed under a rubber dam to increase visualization, prevent saliva from entering the RCS, and preclude the patient from aspirating or swallowing small instruments. It is also a critical medicolegal requirement.
Knowledge of the radiographic and general morphology of the tooth as well as the tooth’s alignment in the arch is essential. One helpful hint is for the practitioner to examine the root eminence(s) in the keratinized tissue prior to rubber dam placement. The operator can observe the root alignment and help him or her in subsequent alignment of the bur when establishing the access preparation.
It is important to position the bur two-dimensionally in a buccolingual and mesiodistal dimension before beginning tooth removal. The clinician should then periodically evaluate the axis of entry to ensure it is still in the proper alignment. It is easy to develop “tunnel vision” during access preparation and lose sight of the alignment, thereby creating a therapeutic misadventure.
After the #2 bur is felt to “slip” into the pulp chamber, it is removed and replaced with a high-speed, safe-ended diamond bur. This bur is placed into the previously established opening and moved circumferentially while the safe-ended tip rests against the floor of the chamber. This procedure establishes the external outline form, since it is being dictated by the internal anatomy. Resting this bur on the floor also precludes risk of perforation either laterally or apically, as long as it remains on the floor of the chamber at all times. The bur can also be inclined against the axial walls to allow straight-line access into the RCSs.
Ultrasonic instrumentation plays a critical role in refining access preparations as well as removing dentin that obscures RCSs. As there are many units and tips available, the clinician should choose a base unit with a wide range of power settings so that tips do not break even when low power settings are selected. The tip with a rounded end may be beneficial in locating the RCS in a calcified chamber since it creates few “sticks” like those made if a pointed tip is used.
When the clinician has a limited view of the treatment site or when obstructed by the anatomy of the intraoral environment, locating RCSs can be challenging. Using the aforementioned recommendations in a proper endodontic sequence, however, can enable each practitioner to achieve successful results and expand the range of treatments offered to his or her patient population.
*Professor and Program Director, Post-Graduate Endodontics, University of Missouri at Kansas City School of Dentistry, Kansas City, MO.