The purpose of this study was to assess dentin removal during root canal preparation by different operators using a NSK reciprocating handpiece. Eighty-four human single-rooted mandibular premolars were hand instrumented using Triple-Flex stainless-steel files (Kerr) up to #30, weighed in analytical balance and randomly assigned to 4 groups (n=21). All specimens were mechanically prepared at the working length with #35 to #45 Triple-Flex files (Kerr) coupled to a NSK (TEP-E10R, Nakanishi Inc.) reciprocating handpiece powered by an electric motor (Endo Plus; VK Driller). Groups 1 to 4 were prepared by a professor of Endodontics, an endodontist, a third-year dental student and a general dentist, respectively. Teeth were reweighed after root canal preparation. The difference between weights was calculated and the means of dentin removal in each group were analyzed statistically by ANOVA and Tukey's test at 5 % significance level. The greatest amount of dentin removal was found in group 4, followed by groups 2, 3 and 1. Group 4 differed statistically from the other groups regarding dentin removal means [p<0.001 (group 1); p=0.005 (group 2); and p=0.001 (group 3)]. No statistically significant difference was found between groups 1 and 2 (p=0.608), 1 and 3 (p=0.914) and 2 and 3 (p=0.938). In conclusion, although the group prepared by a general dentist differed statistically from the other groups in terms of amount of dentin removal, this difference was clinically irrelevant. The NSK reciprocating handpiece powered by an electric engine was proved an effective auxiliary tool in root canal preparation, regardless of the operator's skills.
Introduction The knowledge of the organization of the masseter muscle (MM) and the temporal muscle (TM) is extremely important when related to the study of the stomatognathic system. Moreover, some authors have shown that mastication is of great importance, not only for the intake of food but also for the systemic, mental and physical functions of the body. Materials and Methods We have decided to analyze the biomechanical potential (length of the force arm, muscular work and mechanical advantage) of the MM and TM in the mandibles of mesofacial subjects (n = 34). Results Our results show that the MM exhibits a better biomechanical potential than the TM (p = 0.0001). Conclusion With these data, orthodontists may develop a specific treatment plan and get better results, especially in cases of patients in whom the biomechanical pattern of the temporomandibular joint is unfavorable.
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