[Observation of Carabelli's trait on permanent maxillary molars].

PURPOSE: To investigate the prevalence of the Carabelli's trait in a Chinese population. METHODS: Direct intraoral examination was conducted on 2758 Han Chinese people. The expression of Carabelli's trait was divided into 5 grades. Software SPSS 13.0 software package was used for statistical analysis. The trait frequency differences between two genders, between right and left sides were evaluated using Chi-square tests. Correlations in the presence of the trait between bilateral antimeric teeth and between first and second molars at the same side were determined by Kendall test. RESULTS: The trait frequency was 36.18% (40.73% of the males and 32.13% of females) for the first and 1.39% (1.82% in males and 0.99% in females) for the second molars by individual counting method. Sex difference was statistically significant for the first molars (P<0.01). The bilateral concurrence rate was 72.97% and 48.57% for the first and second molar, and the bilateral correlation coefficient tau was 0.77 and 0.65, respectively. The correlation between the first and second molar in the same teeth district was weak (tau=0.13, P<0.01). CONCLUSIONS: Evaluating the prevalence of Carabelli's trait in Chinese populations by using a standardized method has great anthropological significance.

[Experimental study of preparation errors during instrumentation of artificial curved root canals with stainless steel K files].

PURPOSE: To investigate the features and rules of preparation errors developed from instrumentation of curved root canals. METHODS: 8 curved artificial root canals were prepared with stainless steel K files by the step-back technique,the root canals were digitally photographed,the images were analysed by the software Image-Pro Plus,the shapes and positions of the root canals were measured and analysed.SPSS 10.0 software package was used for statistical analysis, paired-samples t test was used to compare the difference of the means among sample groups. RESULTS: After root canal preparation,the mean value of the angles of canal curvature decreased from 36.21 degrees to 21.98 degrees , while the mean value of the radius of the canal curvature increased from 6.25mm to 11.35mm; the canal axes transported and intercrossed with the original axes at 2 points and created 3 intersection zones.The taper of the root canals was destroyed and a series of instrumentation defaults were created. CONCLUSION: The cause of preparation errors was the transportation of the root canal instruments leaded by the elastic force and cutting effects.

[Curve analysis and geometric measurement of root canal curvatures].

PURPOSE: To study the anatomical features of curved root canals. METHODS: According to Nagy's classification,the root canals were divided into 4 types:type I (straight), type C (continuously curved), type J (apically curved) and type S (multicurved). Each type had a sample selected from extracted permanent teeth. Digital radiographs were taken at buccolingual and mesiodistal directions with a K-file inserted into the root canal. The images were treated by Photoshop7.0 and CorelTRACE10 softwares, after that a CAD/CAM software UG NX V1.0 was applied to extract the 2D curves of the root canal axis from the images,then the 3D curves of the root canal axis were built up accordingly. The curvature of the curves was analysed and the geometric parameters were measured by UG. RESULTS: The curvature values of type I root canal were very low; the curvature of type C root canal reached a peak on the middle part,it decreased slowly towards the two ends; type J root canal had a curvature peak near the root apex, and the middle 1/3 and neck 1/3 parts of the root canal were "curvature flat zones". Type S root canal had a curvature inflection,and beside it were 2 curvature peaks at opposite directions. The geometric parameter values of the same root canal's 2D and 3D axis were different. CONCLUSION: Each point on the root canal axis had a curvature value and a vector of tangent, different root canal forms had different rules of curvature distribution, just 1 or 2 parameters couldn't describe a curved root canal completely.