To develop an experimental model by negative replica technique (Schilder-Yu) to study the action of file tip on dentine in vitro
Yu, Henry C.
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An experimental model was developed to study the action of mechanical debridment of the root canal system by a negative replica technique (Schilder-Yu) for SEM examination in vitro. The technique allows the option of repeating the procedure at predetermined intervals and observing morphological changes of the same specimen. A newly developed impression material, polyvinyl siloxane, is used with the aid of orthodontic wire to obtain a negative replica in an artifical canal in dentine. The negative replica of the pre-instrumented canal and post-instrumented canal is compared under SEM. The results of the observations are: (1) The replica is proven stable under the hostile environment inside the vacuum chamber of SEM. (2) The reproducibility is detailed enough to capture the intra-tubular spaces. (3) The material handles well clinically and exhibits no electron "burning." (4) It does not adhere or react with metallic, organic or human hard tissues. (5) The file tip angles of #60, #70, #80 files of Kerr, Unitek, Star and Union Broach range widely in size yet fall within the ADA requirement. (6) The file tip design varies between a "sharpened pencil" or an "Egyptian pyramid". Only Kerr and Star are consistant in the tip design, while Unitek and Union Broach vary between sizes and batches. (7) The width at D1 measures inconsistantly between batches and brands. (8) That results in inconsistancy in the final size of the canal after instrumentation. (9) The final shape of the artificial canal does not have the traditional "Washington Monument" shape, but instead it shows a uniform two stage flare similar to the body of a rifle bullet. The tip can vary from a single cone tip to a double cone tip with different lengths of bevels and minor ridges. (10) The debrided dentine from each canal shows no significant difference in weight. (11) The wear on the tips of the larger files (#60-#80) is less than the smaller sizes (#10-#30). They show some smoothing at sharp corners, and limited bending of edges. Chipping is not observed.
Thesis (D.Sc.D.)--Boston University Henry M. Goldman School of Graduate Dentistry, 1984 (Department of Endodontics).Includes bibliography: leaves 91-101.
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