Two-dimensional finite element stress analyses were employed to study the human mandible. Two models, three teeth loading conditions and three distributions of masticatory muscles are presented. Finite element analyses are compared with photoelastic experiments to indicate correspondence between both results. High stress concentrates in the mandibular angle, condylar region, retromolar area and dental orown.

The human venous valve of the brachial,femoral and long saphenous veins wereexamined with light,transmission and scanning electron microscopy.The observationshows that the venous valve is composed of three functional layers covered withendothelium on both surfaces.A loosely structured layer is located underlying theendothelium.A network mainly containing randomly oriented elastic fibers was foundnear the side towards the lumen.To the side towards the venous wall,there is adense layer composed of eircumferentially and transversly oriented collagen bundles.Some smooth muscle cells extend from the wall of the vein to the base of thevenous valve.The elastic fibers and smooth muscle cells together with the collagenfibers contribute to the mechanical load-bearing performance of the valve and to thepassive closing and openning mechanism.In addition,the smooth muscle cells mightplay an active role in the normal functioning of the valve.The scanning and transmission electron microscopy of venous valve showdifferent arrangement of the endothelium.On the surface of the valve next to the wallof the vein,the endothelial cells are transversely arranged,while on the othersurface over which the current of blood flows,the cells are longitudinally arrangedin the direction of the current.These accord with the role of fluid mechanics.12 normal venous valves were tested by universal testing instrument (Instrontype 1122).The mean value of the maximum tension of the valve is 1 N.Theaverage value of the tensile ultimate strength is 10N/mm~2.