Because of the conflicting evidence concerning the effectiveness of ultrasonics in root canal therapy, other methods of disinfecting and debriding canals properly must be studied. Such research might include better ways to deliver irrigants and disinfecting solutions.
Cleaning and shaping are important, interdependent steps in root canal treatment. Cleaning, as demonstrated by an intracanal surface free of smear layer, can be done only after root canals have been sufficiently enlarged to accommodate adequate irrigation needles. Canal preparation is optimized when mechanical aims are fulfilled and enlargement is acceptable; such aims include avoiding both significant preparation errors and weakening of the radicular structure, which can result in fractures.
Taken together and performed to a high standard, the procedures described in this chapter lay the foundation for biologic success in both straightforward (Fig. 9-77) and more complicated (Fig. 9-78) clinical cases. Recall radiographs confirm favorable outcomes, or biologic success (i.e., the prevention or healing of periradicular periodontitis) over the years. Similarly, adherence to the principles discussed leads to predictable outcomes for root canal treatments.
Date Added: 28 February 2007
Karl Keiser, DDS, MS, University of Texas Health Science Center at San Antonio
The effect of root canal curvature on the efficacy of irrigation
The ultimate biologic goal of endodontics is to prevent or cure apical periodontitis.1 In most cases, apical periodontitis is caused by microbial factors.2-4 Endodontic therapy should be aimed at preventing the ingress of microbes in vital cases and reducing the number of bacteria and other microbes in the root canal system in necrotic cases. The former requires attention to the creation and maintenance of an aseptic operating field through the use of surface disinfectants and rubber dam isolation. The latter involves chemomechanical preparation of the root canal system using physical and chemical means. Much emphasis has been placed on the increased ability to clean and shape canals with newly developed nickel titanium (niti) rotary files; however, it is still impossible physically to reach all aspects of the complex internal dental anatomy.5 Chemical disinfection remains a critical aspect of root canal preparation.
A variety of irrigants have been proposed for use in clinical endodontics. Because of its broad spectrum of antimicrobial activity and ability to dissolve tissue remnants, sodium hypochlorite is widely used.6 Because it is also quite cytotoxic, pressure in the irrigating device must be minimized to avoid expression of the solution into periradicular tissues. This expression may result in an inadequate distribution of the irrigant, especially in the apical regions of the canal system. This is likely influenced by anatomic features, such as the degree of curvature of the root.
Using an in vitro real-time imaging model, Nguy and Sedgley7 recently addressed this question. Thirty-three single-rooted mandibular premolars were grouped according to degree of canal curvature, then accessed and instrumented using a crown-down technique to an apical size of 0.27 mm with 4% tapered niti rotary endodontic files and sodium hypochlorite irrigation. The smear layer was removed in an ultrasonic bath of 17% EDTA, and the teeth were sterilized by autoclave. Pseudomonas fluorescens 5RL suspensions were introduced into the prepared canals using pipet tips that fit loosely at working length. These bacteria have been constructed to contain a luminescent enzyme system that emits detectable photons, allowing real-time quantification. A standardized irrigation protocol was followed for each tooth. Using a sterile 30G safe-ended endodontic irrigating needle placed 1 mm short of working length, 6 mL of sterile saline was delivered at the rate of 1 mL/20 s. After irrigation, the canal contents were immediately aspirated. Bioluminescence was measured before inoculation to determine background counts, after inoculation, and once more after irrigation. The same procedures were repeated after instrumentation to an apical size of 0.36 mm and again after instrumentation to an apical size of 0.46 mm. Bacterial counts were correlated with apical preparation size and degree of canal curvature. In canals with greater curvature, irrigation was significantly less effective in the smaller (0.27 mm) apical preparations.
This study suggests that as canal curvature increases, the ability to irrigate the prepared canal adequately is enhanced with larger apical preparation sizes. This is a two-edged sword, however, because as canal curvature increases, the potential for procedural errors, such as canal transportation, also increases. Apical transportation of a curved canal leaves undébrided, potentially infected space in the terminal region. Care must be taken to balance preparation size with anticipated mechanical difficulties during the preparation. Increasing the efficacy of the irrigation process, such as by increasing irrigant volume8 and ultrasonic energization,9 also should be considered.
1. Orstavik D, Pitt Ford TR: Apical periodontitis: Microbial infection and host responses. In Orstavik D, Pitt Ford TR (eds): Essential Endodontology. London, Blackwell Science Ltd, 1998, p 1.
2. Kakehashi S, Stanley HR, Fitzgerald RJ: The effects of surgical exposures of dental pulps in germ-free and conventional rats.Oral Surg Oral Med Oral Pathol 20:340-349, 1965. MedlineSimilar articles
3. Moller AJ, Fabricius L, Dahlen G, et al: Influence on periapical tissues of indigenous oral bacteria and necrotic pulp tissue in monkeys. Scand J Dent Res 89(6):475-484, 1981.
4. Fabricius L, Dahlen G, Sundqvist G, et al: Influence of residual bacteria on periapical tissue healing after chemomechanical treatment and root filling of experimentally infected monkey teeth. Eur J Oral Sci 114(4):278-285, 2006.
5. Peters OA, Laib A, Gohring TN, et al: Changes in root canal geometry after preparation assessed by high-resolution computed tomography. J Endod 27(1):1-6, 2001.