Hardness of model dental composites - the effect of filler volume fractionand silanation

The relationship between structure and mechanical properties for dental com posites has often proved difficult to determine due to the use of commercia lly available materials having a number of differences in composition i.e. different type of resin, different type of filler, etc. This makes a scient ific study of any one variable such as filler content difficult if not impo ssible. In the current study it was the aim to test the hypothesis that har dness measurements of dental composites could be used to monitor the status of the resin-filler interface and to determine the efficacy of any particl e silanation process. Ten model composites formulated from a single batch o f resin and containing a common type of glass filler were formulated to con tain varying amounts of filler. Some materials contained silanated filler, others contained unsilanated filler. Specimens were prepared and stored in water and hardness (Vickers') was determined at 24 h using loads of 50, 100 , 200 and 300 g. Composites containing silanated fillers were significantly harder than mate rials containing unsilanated fillers. For unsilanated products hardness was independent of applied load and in this respect they behaved like homogene ous materials. For composites containing silanated fillers there was a mark ed increase in measured hardness as applied load was increased. This sugges ts that the hardness-load profile could be used to monitor the status of th e resin-filler interface. (C) 1999 Kluwer Academic Publishers.