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Assessments of the practical deficiencies of polymethylmethacrylate in service have been carried out by several workers. Some of these studies and one further one have been compared so as to seek any common factors, especially those concerned with the age of the appliance at failure. Times of vulnerability for different types of dentures have been demonstrated, and the scope for time-based studies in the laboratory and in service has been discussed.

The historical development and important properties of composite resins are briefly reviewed. Experimental work has been undertaken to examine the marginal adaptation of three commerically available composite resins in 100 Class II and Class V restorations; dye penetration tests were used and measurement of the gap at the tooth/restoration interface as recorded in photographs obtained by scanning electron microscopy of replicas. In Class V restorations showing marginal leakage by dye penetration the gap at the tooth/restoration interface was in all cases greater cervically than occlusally. The results underline the uncertainly of obtaining a good marginal seal with composite resins both peripherally and along internal line angles.