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The aim of thes; study was to observe initial stage of wedge-shaped defects under scanning electron microscopy without prior samples preparation. There were revealed special features of structure of enamel and cement at initial stage of wedge-shaped defects in comparison to normal tissues.

Since clinical evaluation of wear turns out to be particularly time consuming, a standardized method was developed to model oral mastication. So-called artificial mouth was used to assess the extent of wear caused from different restorative materials in contact with bovine enamel. Ball heads manufactured from modern veneering ceramics, gold alloy, amalgam and resin composite materials were loaded with a contact load of 50 N for 200,000 chewing cycles. Additional thermo-cycling (5 degrees /55 degrees C) for 2,500 cycles was conducted in the artificial mouth. The worn surfaces, both on the material specimens and on the antagonist bovine enamel surfaces were volumetrically scanned under a laser microscope. Negligible wear rates were observed for the veneering ceramics and for the gold alloy. Most veneering ceramics as well as the resin composite materials caused low wear on the antagonist enamel surfaces. In contrast, the antagonist enamel was significantly damaged in contact with amalgam or some of the ceramic materials. However, modern veneering ceramics as well as gold alloys might be recommended in occlusally loaded contact with the antagonist enamel, whereas resin composite materials might be indicated for non load-bearing areas. Ceramics are contraindicated in case of bruxism.

The authors compare the effects of natural (porcine) and synthetic (Toinex, USA, and Eschalon, France) bristle and rough toothbrushes on the tooth enamel and dentin in the course of toothbrushing. No abrasive effects were detected when brushing normal teeth in clear water. The rate of enamel and dentin abrasion in tooth powder or tooth paste suspension depended on the shape of bristle cut and particularly on the toothbrush roughness.

The dentin resistance against abrasion was studied as related to its microhardness. Sections of 15 intact teeth were investigated (central upper incisors). Water suspensions (40% weight-to weight) of dicalcium phosphate (DCP, FRG; and DKF-1 and DKF-2, USSR) were used as abrasives. Dentin microhardness was measured with a PMT-3 device, and abrasion assessed with profilographic technique. Dentin abrasion was related to its microhardness and to the kind of abrasive used. Dentin abrasion increased as its microhardness decreased. DCF showed minimal abrasive effect, DKF-2 had maximal effect with DKF-1 keeping the intermediate position.