T. Aksoy

Fracture toughness determination of composite resin and dentin/composite resin adhesive interfaces by laboratory testing and finite element models

OBJECTIVES The reliability and validity of the adhesive bond toughness of dentin/composite resin interfaces were studied from the standpoint of fracture mechanics. METHODS The fracture toughness (KIC) and fracture energy (JIC) values of two different composite resins (Brilliant Dentin and P50) were determined by using single edge notch (SEN) specimens loaded in three point bending and the results were analyzed by the t-test method (p < 0.1). The fracture loads of dentin/composite resin interface with different initial crack lengths were obtained experimentally. The adhesive fracture energy (J(adh)), residual fracture energy (J(res)) and effective (total) fracture energy (J(eff)) for the symmetrical bimaterial (SBM) joint specimen for dentin/composite resin interfaces were calculated and the applied fracture energy (J(appl)) values under the mastication force were obtained for the axisymmetric tooth models. All numerical calculations were carried out by the finite element method and software programs were prepared according to fortran 77. RESULTS The fracture toughness and energy values obtained experimentally for Brilliant Dentin were found to be higher than those for P50. It was seen that, calculated J values (J(adh) and J(res)++) changed with the crack length; but the effective fracture energy (J(eff)++) was independent of the crack length, as expected. The applied fracture energy (J(appl)) and effective fracture energy (J(eff)) are considerably smaller than the experimentally determined JIC values of composite resins. SIGNIFICANCE The bonded interface tends to produce microscopic flaws which could act as critical stress risers promoting interfacial failures. The initiation and propagation of such flaws under the mastication forces can be followed by fracture toughness (KIC) or fracture energy (JIC) in linear elastic fracture mechanics (LEFM).

An investigation of temperature and stress distribution on a restored maxillary second premolar tooth using a three-dimensional finite element method

This paper presents the stress analysis of the maxillary second premolar tooth under thermal loading as a result of hot/cold liquid in the mouth using the three-dimensional (3D) finite element method (FEM). The tooth was considered to be in a restored state with composite resin and amalgam on glass-ionomer as the base material. In the first step of the study, the temperature changes as a result of hot/cold liquid in the mouth were calculated. The thermal stress distributions owing to the temperature changes were then obtained. All calculation programs were prepared by the authors using FORTRAN 77. The tooth was assumed to be isotropic, homogeneous, elastic and unsymmetric. The distribution of temperature and stress were plotted for some critical points.

Wear and Friction Properties of Multilayer Hard Coatings by HTCVD Method

This paper concerns the wear and friction properties of multilayer hard coatings on WC(Ti, Ta, Nb, W)C-Co hard metal substrates for cutting tool applications. The multilayer hard coatings with TiCN+TiC+TiCN+Al2O3+TiN configuration were deposited at the temperatures of 800-1000 o C by using a high temperature chemical vapour deposition (HTCVD) process. The multilayer coatings were characterized by X-ray diffraction, and scanning electron microscopy (SEM). It was found that all multilayer coatings have a dense and homogeneous surface morphology. The multilayer hard coatings (BK-247) with 7.5 μm showed the best wear resistance under 50 N. It as also determined that the Ti-410 specimens with 10.5 μm thick had the best wear resistance at 200 N.