In vitro, conventional, microfilled and experimental composite resin specimens were subjected to toothbrush-dentifrice abrasion. Subsequently, height loss was recorded, and the appearance of the abraded surfaces was studied by light and scanning electron microscopy. In the experimental composite, which had a polymer-impregnated porous glass filler, the glass phase showed flat surfaces. These surfaces were more smooth and lustrous than the surrounding resin. They also showed a rounding-off in the periphery. In the experimental composite smoothness and luster were therefore favored by the presence of large continuous areas of glass in the surface. It was possible to demonstrate the extension of the flat glass areas by the use of optical microscopy. In the conventional composite partly exposed irregular or rounded glass particles were frequent. A microfilled composite showed, except for frequent pores, a relatively smooth and lustrous surface. The wear rate of this material was, however, comparatively high.

An abrasive wear test for composite resins was proposed. A slurry of glass pearls and abrasive particles were used. The abrasive effect was examined for different particle sizes. Particle sizes were found which gave the same order of wear as found clinically for an amalgam, a composite resin, and unfilled resin.

In an attempt to find an explanation for an experimentally found strong connection between the extension of the loaded area and the load required for fracture, an analysis of the diametral compression test was carried out by means of the finite element method. The distribution of the stresses in a quadrant of a circular specimen section was studied for varying contact surface but at a given load distribution within this surface. Below a limit value for the width of the contact surface tensile stresses appeared peripherically outside the contact area, which had a magnitude exceeding those stresses which are centrally located and should normally initiate fracture. For that reason, peripheral fracture initiation must be regarded as a possibility. Only marginal importance could be attached to changes in the extension and magnitude of the central tensile stresses, as compared with the potential impact of the peripheral tensile stresses.

Veneers were made from sheets consisting of a three-dimensional network of sintered ultrafine glass fibers. The sheets were molded by a vacuum-pressure technique and then impregnated with a liquid resin. Impregnation was performed with a method that enabled the depth of penetration to be monitored. The resin was cured with UV radiation under N2 protection. By the use of TiO2-containing resins the veneer achieved an enamel-like appearance. An in vitro toothbrush dentifrice abrasion test showed a high wear resistance and persisting surface luster. Scanning electron and light microscopy showed fairly smooth and flat light-reflecting glass structures in the surface.

A long-term study was performed on the abrasion of dental composites stored in different solutions for six months. No difference in wear resistancewas noticeable between the water and lactic acid group. But the composite with regular filler showed reduced wear resistance when compared with a microfiller composite.