A Finite Element Analysis Study Comparing 3 Internal Fixation Techniques in Mandibular Sagittal Split Osteotomy

Purpose: To analyse, and compare using finite element analysis, the biomechanical properties of the 1.7 mm miniplate fixation against 2 conventional fixation techniques (2.0 mm bi-cortical screws and 2.0 mm miniplate) used in the mandibular sagittal split osteotomy. Methods: A 3-D virtual mandible model was constructed using images from CT scan. Sagittal split osteotomy was carried out virtually, and the fixation techniques were applied onto the model. 9 virtual models consisted of the 3 fixation techniques with mandibular movements of 3 mm setback, 3 mm advancement and 7 mm advancement were developed. Bite forces of 50, 75 and 100 N were applied for incisor bite simulation and 100, 200 and 300 N for molar biting force. Finite element analysis was carried out in Solidworks, and readings of stresses and displacement were recorded. Wilcoxon rank sum test was applied and P-value of 0.05 was set for statistical analysis. Results: In this manuscript the authors have compared 3 internal fixation techniques in mandibular sagittal split osteotomy. There was a statistically significant difference for both stress and displacement readings between the 1.7 mm miniplate, the 2.0 mm bi-cortical screws and the 2.0 mm miniplate for all mandibular movements. For the 1.7 mm miniplate vs 2.0 mm bi-cortical screws, the stress reading was (P = 3.063e-08, W = 314), and for displacement was (P = 5.811e-05, W = 282). For the 1.7 mm miniplate vs 2.0 mm miniplate, the stress reading was (P = 9.862e-4, W = 263) and for displacement was (2.05e-2, W = 235). Conclusion: The 1.7 mm miniplate has adequate strength to be used in mandibular sagittal split osteotomy, although statistically less rigid when compared to the conventional 2.0 mm miniplate and 2.0 mm bi-cortical screws, especially in larger movements.

Assessment of undergraduate students’ tooth preparation for full veneer cast restorations

Purpose: To evaluate tooth preparation for full veneer cast restorations performed by final year dental students in Sudan. Materials and Methods: 117 stone dies from two different dental institutions were collected and evaluated. Polyvinylsilioxane impression material was used to produce two impressive replicas of which one was sectioned in faciolingual plane and the other in mesiodistal plane. Occlusal clearance was measured using a digital caliper. Amount of axial preparation was also measured. Impression silhouettes that were produced using an overhead projector were used to measure convergence angle. Working casts were examined for smoothness and evenness of the preparations, existence or absence of additional features of retention and the finishing line were evaluated for its position and continuity. All obtained data were statistically analyzed by using T-test, ANO-VA, and Pearson Chi square tests. P-values ≤ 0.05 were considered as statistically significant. Results: Average taper of the examined preparations was 39.98?, with 44.1? in the faciolingual, and 35.8? in the mesiodistal dimensions. Preparations for full coverage restorations were over prepared. 38.5% of the total number of preparations were found to have finishing lines in the sub and supra gingival positions. 19.66% were unable to maintain continuity of the finishing line all around the preparation. All preparations were generally smooth with no sharp angles, and 1.7% of the preparations had additional retentive features. Conclusion: Within the limitations of this study, it could be concluded that the convergence angle and finishing line preparations were less than adequate in a sizeable proportion of the preparations examined.