Surface characteristics of resin-coated composite restorations

Twenty-four maxillary anterior composite restorations from a clinical study of resin coating were examined at the time of baseline evaluation and at 23 months; electroplated positive replicas, impression negative replicas, and SEMs were used for evaluation. Coated restorations had smooth surfaces after 23 months, in comparison with rough surfaces of uncoated restorations. Defects in some of the resin coatings were found at the time of baseline evaluation; these included isolated areas of the composite or etched enamel that were not covered by the resin. Later examinations showed cracking of part of the edges of resin coating, development of bare areas, thinning of the coating edges, or generalized loss of the protective coating. The defects seen immediately after placement of the coatings were probably caused by errors in technique that include: application of the resin in a layer that was too thin; surface contaminants in the area of application; moisture on the surface of the composite or enamel; and areas of inadequate enamel etching were adjacent to the cavosurface margin of the composite. The appearance of bare spots or total loss or thinning of the resin coating edges during the later examinations is caused by wearing or abrading of the resin coatings from natural or mechanical causes. This seems to be a function of the initial coating thickness and its location on the tooth.