An increasing number of endodontic leakage studies have been published. In the 1990 volumes of Journal of Endodontics and International Endodontic Journal, there was one leakage study to every 4.3 scientific articles. The most popular method was linear measurement of tracer (dye or radioisotope) penetration along a root filling. Comparing some data on linear measurement of dye penetration following the cold lateral condensation of gutta-percha that were published between 1980 and 1990, a high level of variation has been found, although the experimental methods used in these studies were quite similar. In almost all studies evaluating various techniques, the cold lateral condensation technique has been used as a standard control for comparison. The reliability of these results is questionable. The problems with such studies are discussed. It seems that more research should be done on leakage study methodology, instead of continuing to evaluate the sealing ability of different materials and techniques by methods that may give little relevant information.

Endodontic leakage studies reconsidered. Part I. Methodology, application and relevance.

Fatigue Resistance of Engine-driven Rotary Nickel-Titanium Instruments Produced by New Manufacturing Methods

It is assumed that above a critical level, microleakage causes periapical disease and jeopardizes periapical tissue repair. The purpose of this investigation was first to find out to what degree obturation prevents leakage of bacteria-sized particles or large protein molecules, and second if leakage of the commonly used dye methylene blue is comparable with that of a small bacterial metabolic product of similar molecular size. Sections, 9 mm long, obtained from 46 extracted human incisor roots had their root canals prepared in a standardized manner and obturated in four experimental ways using gutta-percha. The root sections were mounted in the middle of tubes that were closed at both ends with rubber membrane stoppers, which permitted sampling from the apical reservoir. The coronal reservoir was filled with a solution of 1 mg/ml latex beads, 4 micrograms/ml endotoxin, 0.5 per cent butyric acid, 0.1 per cent valeric acid and 0.1 per cent methylene blue water. After 1 and 2 weeks, samples were taken from the apical reservoir and tested for the presence of latex beads by phase-contrast microscopy, for endotoxin with a limulus lysate test, for butyric acid with gas-chromatography and for methylene blue with spectrophotometric analysis. Leakage of bacteria-sized particles and large-sized protein molecules could be prevented only when both sealer and pressure were used in obturating root canals with gutta-percha. Leakage of butyric acid proved to be comparable with leakage of methylene blue; microleakage of these small molecules could not be prevented in this study whatever method of filling was used.

Particles and molecules in endodontic leakage.

Influence of entrapped air on the accuracy of leakage studies using dye penetration methods.

Instrument fracture can be an unpleasant mishap during non-surgical root canal treatment. While most stainless-steel instruments appear to fail by excessive amounts of torque, the combined action of torsional stress and cyclic loading (i.e. fatigue, as a result of rotational bending, or repeated torsion) is responsible for the breakage of NiTi rotary files in use. Factors affecting the incidence and mode of failures include the instrumentation technique, use of torque-controlled motor, the dimension and surface condition of the instrument, rotation rate, radius (and, to a certain extent, angle) of canal curvature, and the presence of a straight-line access and a ‘glide path’ to the apical portion of the canal. If breakage should occur clinically, the patient should be informed of the incident and consideration should be given as to whether or not to remove the fragment. Managed properly, the presence of a broken fragment per se may not adversely affect the outcome of root canal treatment. This review examines the various aspects (including mechanisms, contributing factors, prognosis and management) of instrument fracture. Emphasis is placed on the separation of nickel–titanium rotary files and ways to prevent this in the clinical situation.

David J. Ishley

Papers

Separation Incidence of Protaper Rotary Instruments: A Large Cohort Clinical Evaluation

An in vitro assessment of the quality of apical seal of thermomechanically obturated canals with and without sealer.