Oram, David Anthony; (2001) Composite resin inlays: A study of physical properties and effect on cavity design. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Composite resins, while popular on aesthetic grounds, have shown a number of problems including wear, shrinkage and long term degradation. Extra-oral polymerisation has been proposed as a means of reducing bulk polymerisation shrinkage whilst enhancing mechanical properties. However, there still exists a problem with shrinkage associated with the resin cement lute. There are problems obtaining measurement of the cement lute thickness, particularly over the whole fit surface of the restoration. The observed discrepancies between the cavity surface and the fit of the inlay are variable. This study investigates some physical properties of three inlay systems, and attempts to determine the effect of cavity configuration on the dimensional change of the inlay during polymerisation. The physical properties evaluated were flexural strength and hardness to confirm the effect of extra oral polymerisation on the composite. The water sorption and solubility were also determined. Linear shrinkage was measured in different dimensions to determine the effect of the constraining influence of a mould. The apparent cement lute thickness of the inlays in a stylized cavity was assessed using a laser scanning profilometer. An addition silicone impression rubber of similar viscosity to resin cement was used as the luting medium. The greatest shrinkage occurred in width rather than length. Highest values for shrinkage were observed in the system polymerised by heat and pressure. A high solubility value for the heat and light polymerising system (0.53%) was recorded which also showed the lowest water sorption (0.92%). The heat and pressure system had similar solubility values (0.51%), but high water sorption (1.54%). The flexural strength was found to decrease in all samples over a period of 6 months in aqueous solution, the greatest reduction occurring in the laboratory heat and light system. Surface hardness also decreased after 6 months immersion in water. In all cases substantial cement lute thickness was observed and this varied with the cavity configuration. The effect of cavity design on these materials is not clear.

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