The effects of thermal stress on the marginal leakage of resin composite restorations in bovine teeth were investigated by a method that preserved the specimens. The changes in marginal leakage of specimens with increasing numbers of thermal cycles were measured by an electrical conductivity method. Four brands of posterior resin composites were used to fill cylindrical cavities (2.0 mm in diameter and 1.5 mm in depth) on the labial surfaces of bovine incisors, according to the manufacturer's instructions. Thermal cycling stress was applied to the specimens for up to about seven weeks (9000 cycles). During this time, the electrical conductance between the pulp and a drop of physiological saline solution covering the resin restoration was measured periodically by application of an electrical potential (60 Hz, 10 Vp-p). Thermal stress increased the marginal leakage gradually, rather than step-wise. Even before application of any thermal stress, wide variations of marginal leakage were found among different specimens restored with the same brand of resin. Specimens with less initial leakage showed less increase in leakage, and vice versa, throughout the experimental period.

Elastic waves emitted by microfracturing are called acoustic emission ( A E ) . Recently A E techniques have been extensively applied to concrete engineering as a non-destructive testing ( N D T ) method. A key aspect of A E is that the nucleation of internal cracks is direct1.v detected by a surface observation. In conventional A E techniques, such A E parameters as event count (activity), amplitude, energy and spectra are correlated with the ,failure process of materials. Thus, A E characteristics are utilized,for NDT. The A E source (crack) is also located by employing a multichannel (more than 5 ) A E detecting and recording system. In this Paper an advanced A E analysis procedure is proposed. In addition to crack locations, crack types and crack orientations are determined from A E relative amplitudes of the ,first motions. The procedure classifies cracks into tensile cracks and shear cracks. Based on information of the crack type, the crack orientation is determined; this is the direction of crack opening in the case of tensile cracks, and the direction of sliding motion in the case of shear cracks. The proposed procedure is applied to a pull-out test of an anchor-bolt from a concrete block and a cylinder-tensile test. In the pull out test the opening directions of the tensile cracks is perpendicular to the failure surface, while the directions of sliding motion of the shear cracks are parallel to the failure surface. In the cylinder-tensile test the opening directions of the tensile cracks are perpendicular to the loading direction and all sources are located near the final plane. The proposed procedure is therefore able to determine the microcrack kinematics generated in concrete.

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