The effect of resin composite pre-heating on monomer conversion and polymerization shrinkage.

OBJECTIVES

To determine monomer conversion and polymerization shrinkage of a resin composite after different pre-heating procedures and storage intervals.

METHODS

For a commercial resin-based composite the immediate (5 min) and final (24h) degree of conversion was measured on top and bottom surfaces utilizing FTIR spectroscopy. Composite pre-heating temperatures were selected between 10 and 68 degrees C. Polymerization shrinkage was measured according to Archimedes' principles of buoyancy after 5 min at respective pre-heating temperatures and after 24h dark and wet storage at 37 degrees C. Intra-cavity temperature development was monitored using a K-type thermocouple.

RESULTS

No significant increase in immediate as well as in final degree of conversion were measured from composite pre-heating at 68 degrees C compared to 54 and 39 degrees C. Linear correlations were detected immediately after photo-polymerization and on the top surface after 24h storage. Polymerization shrinkage as a function of pre-heating temperatures exhibited a linear correlation after 5 min, but no statistically different behavior after 24h.

SIGNIFICANCE

Pre-heating of resin composites does not increase degree of conversion over time. It can be clinically beneficial, due to a superior marginal adaptation. This advantageous effect of reduced material paste viscosity has to be clinically addressed, since temperature rapidly drops to the physiological level upon removal from the pre-heating device.