Effect of repeated screw joint closing and opening cycles and cyclic loading on abutment screw removal torque and screw thread morphology: Scanning electron microscopy evaluation

Purpose: To evaluate the effect of repeated screw joint closing and opening cycles and cyclic loading on abutment screw removal torque and screw thread morphology using scanning electron microscopy (SEM). Materials and Methods: Three groups (n = 10 in each group) of implant-abutment-abutment screw assemblies were created. There were also 10 extra abutment screws as new screws in group 3. The abutment screws were tightened to 12 Ncm with an electronic torque meter; then they were removed and removal torque values were recorded. This sequence was repeated 5 times for group 1 and 15 times for groups 2 and 3. The same screws in groups 1 and 2 and the new screws in group 3 were then tightened to 12 Ncm; this was also followed by screw tightening to 30 Ncm and retightening to 30 Ncm 15 minutes later. Removal torque measurements were performed after screws were subjected to cyclic loading (0.5 × 106 cycles; 1 Hz; 75 N). Moreover, the surface topography of one screw from each group before and after cyclic loading was evaluated with SEM and compared with an unused screw. Results: All groups exhibited reduced removal torque values in comparison to insertion torque in each cycle. However, there was a steady trend of torque loss in each group. A comparison of the last cycle of the groups before loading showed significantly greater torque loss value in the 15th cycle of groups 2 and 3 compared with the 5th cycle of group 1 (P < .05). Nonetheless, torque loss values after loading were not shown to be significantly different from each other. Conclusion: Using a new screw could not significantly increase the value of removal torque. It was concluded that restricting the amount of screw tightening is more important than replacing the screw with a new one when an abutment is definitively placed. © 2018 by Quintessence Publishing Co Inc

Treatment plan in amelogenesis imperfecta: A structured literature review on treatment protocols and dedicating the best possible options

"nAmelogenesis imperfecta is an inherited disease that disturbs the formation of the enamel. It occurs as two main categories, hypomineralized and hypoplastic. Both deciduous and permanent teeth are affected, and the disorder may create unaesthetic appearance, dental sensitivity, and severe attrition. In this article through performing a structured literature review, numerous treatment modalities which so far advocated in rehabilitation of amelogenesis imperfecta in adults and children is discussed. The progressive changes on open bite, the problem of bonding during restorative phase of treatment , the rehabilitation difficulties of deciduous as well as permanent teeth is also discussed in detail and finally the interdisciplinary approach for treatment of this disability is demonstrated and some points for decision making in treatment protocols are suggested