Factorial analysis of variables affecting bone stress adjacent to mini-implants used for molar distalization by direct anchorage-A finite element study.

OBJECTIVE: The aim of this study was to investigate the stresses on mini-implant, cortical bone, and cancellous bone for maxillary molar distalization using an orthodontic implant in a finite element model for different angulations and depths of insertion. METHODS: A three-dimensional finite element method was used to simulate overall orthodontic tooth movements by using ANSYS software. The maxillary bone and the molars were reproduced using CT scan images and conversion of the same into STL file was done. Finite element model was generated and the effect of forces was studied on the model for different depths and angulations of mini-implant insertions. The distalization force was exerted by an open-coil spring and the direct skeletal anchorage was provided by a mini-implant. Mini-implants were placed in depths of 5 mm, 7 mm, and 9 mm inside the bone and insertion angles of 30°, 60°, and 90°. Stresses on mini-implant and extent of stress on the surrounding bone were assessed by the software. RESULTS: 1. Least stress was found when the mini-implant was inserted at an angle of 30°, as it is nearer to the stronger cortical bone. 2. As the length of the mini-implant increases, accompanied by the increase in the depth of insertion, a decrease in stress in the mini-implant, cortical bone, and cancellous bone was noticed. CONCLUSION: An increase in the insertion angle from 30° to 90° increases the stresses on both the implant and the cortical bone. A higher depth of thread in the bone helps in reducing the stress on the implant, cortical bone, and cancellous bone. This helps in improving the primary stability of the mini-implant and its life.

"Effect of grape seed and green tea on shear bond strength of brackets bonded to bleached enamel with and without Lase Peroxide Lite" - An in vitro study.

OBJECTIVE: To investigate the effect of antioxidants on shear bond strength of brackets bonded to bleached enamel with and without titanium dioxide nanoparticles (Lase Peroxide Lite). MATERIALS AND METHODS: One hundred and five human maxillary premolars were randomly divided into seven groups (n = 15). Group I served as control, in group II-A bleaching was performed with Opalescent Boost. In group II-B and C, bleaching was performed with Opalescent Boost followed by application of 5% grape seed and 10% green tea extracts, respectively. Group III-A bleaching was performed with Lase Peroxide Lite. Group III-B and III-C bleaching was performed with Lase Peroxide Lite followed by application of 5% grape seed and 10% green tea extracts, respectively. Brackets were bonded with composite resin and cured with light emitting diode (LED) light. Shear bond strength of brackets was tested with a Universal testing machine. RESULTS: There was statistically significant difference in the shear bond strength among the seven groups included in the study. There is a statistically significant decrease in shear bond strength in group II-A (8.2 ± 1.6 Mpa), group III-A (8.6 ± 2.1 Mpa) when compared with group I-A (15.9 ± 1.4 Mpa). Among all experimental groups, group II-A showed the lowest mean shear bond-strength values (8.2 ± 1.6 Mpa) (P < 0.005). Group III-C (14.9 ± 2.2 Mpa) has significantly higher shear bond strength. CONCLUSION: Bleaching reduced the shear bond strength of brackets below acceptable level while application of grape seed and green tea extracts has recovered the shear bond strength.