Search

ABSTRACTThis study investigates the effect of bracket bonding-debonding on the tribological properties of human tooth enamel, when two different adhesives are applied. The nano-scratch experiment was performed on the enamel at untreated and under the bracket regions to obtain wear resistance, scratch hardness and friction coefficient. The results indicated that the tribological properties of the enamel vary significantly after bracket bonding-debonding. However, no significant difference exists between the effects of bracket bonding by the nano-composite and the composite adhesives on the tribological properties. Therefore, considering the mechanical and physical properties of the nano-composite adhesive, its bond strength for orthodontic bracket bonding and the influences on the enamel after removing the bracket, the use of nano-composite adhesive is suitable for orthodontic treatments.

Modified ring (MR) specimen was suggested for investigating the mixed-mode (I/II) fracture behavior of brittle materials by rotating the crack orientation with respect to the loading direction. Crack tip fracture parameters (KI, KII, and Tstress) of MR were calculated for different geometric dimensions. To verify the numerical modeling procedure, two sets of comparisons were drawn between the results of prior studies on MR Mode Ifracture behavior and those of this study, showing good agreement between the results. Through some graphs, the effects of geometric parameters on YI, YII, and T*(dimensionless crack tip parameters) and also on βII(pure Mode IIcrack angle) were studied. In addition, the biaxiality ratio (B), as an influential factor in the generalized maximum tangential stress (GMTS) criterion, was calculated for the whole range of mode mixity in the MR specimens. Next, fracture behavior of the specimen was discussed by means of the GMTS criterion in terms of the results obtained for the biaxiality ratio (B). At the end, as an appendix, the entire results obtained for YI, YII, T*, and βIIwere presented.

In recent decades, the development of new biomaterials for medical applications has been one of the challenging tasks for biomaterial scientists. Functionally graded biomaterials (FGBM) have been receiving an increasing attention due to their unique advantage, being able to satisfy the requirements of both mechanical and biocompatibility properties simultaneously. This paper evaluates the motion range and stress distribution of FGBM and non-FGBM artificial discs in response to different loading conditions i.e. compression, bending moment and torsion. In order to ensure the accuracy of analytical solution, the numerical solution was performed using finite element method and good agreement was found between the analytical and finite element results. In addition, the experimental data reported in the previous literature were used to predict the optimal model of artificial FGBM disc using the proposed analytical solution. The results of this study suggest that FGBM parameters can play an important role in achieving the goal of mechanical function optimization. [ABSTRACT FROM AUTHOR]