Loss of substance of dental composite restorations

A method for the direct in vivo measuring of loss of substance of Class I and II restorations was tested. On models of the teeth involved, silver caps were made. The occlusal surface was relieved by a piece of tinfoil. With the silver cap, silicone impressions were made for baseline registration and also at 3 recall periods, 6, 12 and 18 months after baseline registration respectively. The average thickness of the loss of substance was computed by the weight, the density and the thickness of both the enclosed impression material and the piece of tinfoil. The results show the in vivo repeatability of the test method to be in good agreement with data obtained in a previous in vitro study. The error of the test method accounts only for a relatively small part of the total experimental variance (7, 9 and 12%). The wear values show that the method registers, with adequate accuracy, wear rates of approximately 20 μm/year. Because of its simplicity, inexpensiveness and accuracy, the method is highly productive and suitable for clinical screening tests of the wear behaviour of restorations, especially for the registration of losses of substance of posterior composites.