Monomer conversion of pre-heated composite

The potential for maximizing conversion of room-temperature, photoactivated resin composite in the oral environment is limited. Pre-heating composite prior to light-curing is hypothesized to increase monomer conversion and reduce the duration of light exposure. Composite temperature was controlled at between 3°C and 60°C prior to exposure with a conventional quartz-tungsten- halogen curing unit: 5, 10, 20, or 40 sec. Monomer conversion was calculated from infrared spectra at O mm (top) and 2-mm-deep surfaces 5 min after light initiation. A strong, positive correlation existed between temperature and monomer conversion: top r² = 0.999, 2 mm r² = 0.998. Conversion ranged from 31.6% (3°C) to 67.3% (60°C). The duration of light exposure, reduced by 50 to 75% with pre-heated composite, yielded the same or significantly higher conversion (p = 0.001) than with control (22°C, 20 sec). Both hypotheses were accepted: Pre-heating composite prior to photoactivation provides greater conversion requiring reduced light exposure than with room-temperature composite.