THE INFLUENCE OF SIMULATED CLINICAL HANDLING ON THE FLEXURAL AND COMPRESSIVE STRENGTH OF POSTERIOR COMPOSITE RESTORATIVE MATERIALS

Objectives. The aim of this study was to investigate the influence of clinical handling on the flexural and compressive strengths of two com mercially available posterior composites. Methods. Since the manufactu ring of test specimens in a truly clinical situation presents many pro blems, an in vitro model was developed, consisting of a phantom-head s et-up in a clinical operatory. Two composite materials, recommended fo r use in posterior teeth, were used: P50 APC (3M Dental Products) and Herculite XRV (Kerr, Dental Manufacturing). Beam specimens for 3-point bending tests of both materials and cylindrical specimens for compres sion tests of P50 were made both under ideal laboratory circumstances and under simulated clinical circumstances. Results. The difference in mean flexural strength between laboratory prepared and the quasi-clin ically prepared specimens was highly significant for both composites ( p < 0.002). The reduction in mean flexural strength for the specimens handled in a clinical manner was 15% of the flexural strength of the P 50 specimens made under laboratory conditions, and the difference for Herculite XRV was 29%. No difference in compressive strength could be shown between the laboratory-fabricated and the quasi-clinically made specimens of P50. Significance. The relative flexural strength of comp osite materials in a clinical situation may differ significantly from that predicted from mechanical properties measured in vitro.