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Objective:To evaluate the quantitative effects on torque expression of varying the slot size of stainless steel orthodontic brackets and the dimension of stainless steel wire, and to analyze the limitations of the experimental methods used. Materials and Methods:In vitro studies measuring torque expression in conventional and selfligating stainless steel brackets with a torque-measuring device, with the use of straight stainless steel orthodontic wire without second-order mechanics and without loops, coils, or auxiliary wires, were sought through a systematic review process. Results: Eleven articles were selected. Direct comparison of different studies was limited by differences in the measuring devices used and in the parameters measured. On the basis of the selected studies, in a 0.018 inch stainless steel bracket slot, the engagement angle ranges from 31 degrees with a 0.016 ϫ 0.016 inch stainless steel archwire to 4.6 degrees with a 0.018 ϫ 0.025 inch stainless steel archwire. In a 0.022 inch stainless steel bracket slot, the engagement angle ranges from 18 degrees with a 0.018 ϫ 0.025 inch stainless steel archwire to 6 degrees with a 0.021 ϫ 0.025 inch stainless steel archwire. Active stainless steel self-ligating brackets demonstrate an engagement angle of approximately 7.5 degrees, whereas passive stainless steel self-ligating brackets show an engagement angle of approximately 14 degrees with 0.019 ϫ 0.025 inch stainless steel wire in a 0.022 inch slot. Conclusions:The engagement angle depends on archwire dimension and edge shape, as well as on bracket slot dimension, and is variable and larger than published theoretical values. Clinically effective torque can be achieved in a 0.022 inch bracket slot with archwire torsion of 15 to 31 degrees for active self-ligating brackets and of 23 to 35 degrees for passive self-ligating brackets with a 0.019 ϫ 0.025 inch stainless steel wire. (Angle Orthod. 2010;80:201-210.)

Stainless steel has the largest torque expression, followed by TMA and then NiTi.

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Objective: To better understand the mechanics of bracket/archwire interaction through analysis of force and couple distribution along the maxillary arch. Materials and Methods: An orthodontic simulator was utilized to study high canine malocclusion. Force/couple distributions, referenced to the center of resistance (CR) of each tooth, produced by passive ligation brackets and round wire were measured. Tests were repeated for 12 bracket sets with 12 wires per set. Results: Propagation of the force/couple systems around the arch was minimal. Binding was observed only on the teeth adjacent to the displaced canine. For most of the teeth, reduced resistance to sliding of the passive ligation bracket yielded minimal tangential and normal forces at the bracket and contributed to lower moments at CR. Conclusions: Some potential mechanical advantages of passive ligation systems are suggested for the case studied. In particular, limited propagation around the arch reduces the occurrence of unwanted force/couple systems. (Angle Orthod. 2011;81:953-959.)

The results demonstrate that an increase in wire size does not result in a proportional increase of applied force/moment. This discrepancy is explained in terms of the non-linear properties of CuNiTi wires. This non-proportional force response in relation to increased wire size warrants careful consideration when selecting wires in a clinical setting.

The results of this study suggest some potential mechanical advantages of passive over elastic ligation. In particular, limited propagation around the arch in passive ligation reduces the occurrence of unwanted force/couple systems compared with elastic ligation. These advantages may not transfer to a clinical setting because of the conditions of the tests; additional testing would be required to determine whether these advantages can be generalized.

Introduction: Retention of provisionallycemented implant-supported restorations plays an important role in success of the treatment. Uncemented restorations may cause several problems such as restoration swallowing, increased bone loss and prosthesis failure. Therefore, suitable cement compromising between retention and retrievability as well as extra-means of abutment retention might be preferable for durable implant restorations.Objectives: This study introduced circumferential and axial grooves on implant abutments as retentive promoters and evaluated their effect on the retention of crown copings cemented to implant abutments with provisional luting cements. Materials and methods: Twenty straight titanium implant abutments were divided into 4 groups (n=5): without grooves, with 1 axial groove, with 2 circumferential grooves, and with 3 circumferential grooves. Twenty nickel chromium crown copings were fabricated to fit all 20 abutments. The copings were cemented to each group of abutments with non-eugenol provisional cement. After storage for 24 hours in 100% humidity at 37°C, specimens were subjected to 500 cycles of thermal cycling, then 5000 cycles of compressive load to simulate the thermal and mechanical stresses in the oral environment. Tensile strengths were conducted with a universal testing machine and tensile stresses were recorded in Newton. After the retention test, the copings and abutments were evaluated for cement failure mode with Stereoscopic Microscope. Collected data were analyzed using one-way analysis of variance (ANOVA) and Tukey's HSD tests (α=.05). Results: The mean tensile strength of the three circumferential grooves was significantly higher than the other groups (P<0.001) while there was no significant difference between the axial groove and control group (P=0.999). The cement failure mode was generally adhesive in nature, although some mixed failures were observed. Conclusion The surface modification of an implant abutment by means of circumferential grooves was found to be an effective method of improving the retention of crown copings cemented with non-eugenol cement.