Suitability of different tooth replicas for endodontic training: perceptions and detection of common errors in the performance of postgraduate students.

AIM: To compare the perceptions of students when using five different tooth replicas and to detect common errors in the performance of students that might be attributed to a specific type of tooth replica. METHODOLOGY: Five groups (n = 10 each) of artificial first maxillary molars (DEPT, DRSK, Nissin, DENTALIKE and TrueTooth) were used. All 50 teeth were mounted individually in opaque containers, distributed in 10 packages containing a sample from each with an assigned random order for students to perform root canal treatments. Ten postgraduate students each performed a root canal treatment on the five replicas, in the assigned order, and completed a satisfaction questionnaire. Three trained and calibrated endodontic educators, each with more than 15 years of experience, evaluated their performance using a grading rubric and completed a questionnaire to detect common errors attributed to a specific tooth replica. Inter-rater reliability was calculated with the interclass correlation coefficient for both consistency and absolute agreement. A two-way related measures anova was used to assess the interaction amongst evaluators and tooth groups on the average scores of students. Post hoc T3 Dunnet was used to compare groups. The perceptions of students amongst groups were compared with chi-square and linear-by-linear association tests. RESULTS: Inter-rater reliability was very high for both consistency (ICCC = 0.939; 95% confidence interval (CI) 0.902-0.964) and absolute agreement (ICCA = 0.940; 95% CI 0.904-0.965). No significant differences were found amongst the ratings of evaluators; however, students performed differently when using the various tooth replicas (P < 0.05). Overall, 60% of students preferred the DRSK replica for root canal treatment training purposes, followed by DENTALIKE (30%). The least preferred was TrueTooth (70% responses) due to its complex anatomy and poor resistance to instruments and heat pluggers. Evaluators detected several common errors in specific tooth replicas and preferred tooth replicas manufactured based on microCT scans of natural teeth. CONCLUSIONS: Tooth replicas manufactured based on microCT scans of natural teeth (TrueTooth and DENTALIKE) had much better acceptance amongst evaluators, although students rated and performed less well in TrueTooth replicas due to their greater level of difficulty.

Complex effects of imatinib on spontaneous and oxytocin-induced contractions in human non-pregnant myometrium.

Human myometrium includes two important cell populations involved in its contractility: smooth muscle fibers and interstitial cells. The pacemaking mechanism is not yet identified, but it is possible that myometrial smooth muscle cells contract in response to a signal generated by c-kit positive interstitial cells. The aim of this study was to investigate the effects of imatinib as a c-kit receptor antagonist on the spontaneous or oxytocin (OT) induced contractions of human non-pregnant myometrium in vitro. Myometrial strips were obtained from non-pregnant women (reproductive age) undergoing hysterectomy for benign indications. The strips were suspended in organ baths for recording of isometric tension. Imatinib effects were assessed on spontaneous contraction and after preexposure to OT.Direct exposure of myometrial strips to imatinib inhibits both amplitude and frequency of contractions (80-320 µM) in a dose dependent manner. Amplitude reverted back to 90% of the baseline amplitude by consequent addition of imatinib (until 480 µM). Total inhibition of myometrial contraction was obtained after addition of OT 60 nM. If myometrium was pre-exposed to OT (320 nM), imatinib 80-160 µm increased amplitude, while decreasing frequency. These data provide evidence that telocytes may be involved as modulators of the spontaneous contractions of the non-pregnant human uterus, via a tyrosine-kinase independent signaling pathway.

The influence of bone and bone cement debris on counterface roughness in sliding wear tests of ultra-high molecular weight polyethylene on stainless steel.

Studies of explanted hip prostheses have shown high wear rates of ultra-high molecular weight polyethylene (UHMWPE) acetabular cups and roughening of the surface of the metallic femoral head. Bone and bone cement particles have also been found in the articulating surfaces of some joints. It has been proposed that bone or bone cement particles may cause scratching and deterioration in the surface finish of metallic femoral heads, thus producing increased wear rates and excessive amounts of wear debris. Sliding wear tests of UHMWPE pins on stainless steel have been performed with particles of different types of bone and bone cement added. Damage to the stainless steel counterface and the motion of particles through the interface have been studied. Particles of bone cement with zirconium and barium sulphate additives and particles of cortical bone scratched the stainless steel counterface. The cement particles with zirconium additive produced significantly greater surface damage. The number of particles entering the contact and embedding in the UHMWPE pin was dependent on particle size and geometry, surface roughness and contact stress. Particles are likely to cause surface roughening and increased wear rates in artificial joints.