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 degrees C and 60 degrees 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 0 mm ( top) and 2- mm- deep surfaces 5 min after light initiation. A strong, positive correlation existed between temperature and monomer conversion: top r(2) = 0.999, 2 mm r(2) = 0.998. Conversion ranged from 31.6% ( 3 degrees C) to 67.3% ( 60 degrees 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 degrees 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.847663667