PubMed · 5273417
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P D Bernard, M Collas. 1970. [Root canal triangles].. https://pubmed.ncbi.nlm.nih.gov/5273417/
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The use of an ultrasonic apical preparation technique has been advocated recently. Root-end preparations in 30 extracted single-canaled human teeth were evaluated, comparing those prepared with ultrasonic instrumentation alone, or in combination with rotary bur preparation, to those prepared with rotary instrumentation alone. Specimens were evaluated for the presence of debris, smear layer, and the smoothness and uniformity of the preparations. The apical preparations were completed according to the varying techniques, examined, and photographed under scanning electron microscopy. Those cavities prepared with the ultrasonic, either alone or in combination with rotary instrumentation, showed the presence of significantly less smear layer compared with those made by burs alone. Cavities prepared with ultrasonic instrumentation in combination with rotary instrumentation contained significantly less debris than those prepared with rotary instrumentation alone. There were no significant differences between the techniques in the smoothness or uniformity of the preparations.
The mesiobuccal roots of 50 randomly selected maxillary first molars were examined to assess the incidence and position of the canal isthmus. Transverse serial sections of the apical 6 mm of each root were prepared in 1-mm increments. The apical side of each section was stained with methylene blue dye, viewed with a surgical operating microscope, and videotaped. Forty percent of the roots had one canal, whereas 60% had two canals. None of the sections had more than two main canals. The incidence of an isthmus was highest in the apical 3- to 5-mm levels. In teeth that had two canals, the 4-mm sections contained a complete or partial isthmus 100% of the time. The concept of a partial isthmus was presented. Failure to deal with the isthmus may explain why some posterior teeth do not heal completely following endodontic surgery.
Various techniques for root canal instrumentation may have different effects in cleaning curved root canals, especially their apical portions. One hundred thirty-five mesiobuccal canals with an average curvature of 25 degrees from human mandibular molars were treated with step-back, crown-down pressureless, or balanced-force techniques with 2% sodium hypochlorite used as an irrigant. The cleaning efficacy of these techniques was evaluated by counting the remaining surface debris under a stereomicroscope with a calibrated eyepiece micrometer. The results indicated that the apical portion of the canal was less clean than the middle and coronal portions regardless of the technique performed and that the balanced-force technique produced a cleaner apical portion of the canal than did the other techniques studied.