[Thermal expansion of restorative composite resins under the dry and wet conditions (author's transl)].

Linear coefficients of thermal expansion (beta) of twelve restorative composite resins, one Bis-GMA based resin and one self-curing acrylic resin were determined in the temperature range of 4 to 60 degrees C under the dry and the wet conditions on a thermomechanical analyzer. The results were as follows. 1) The thermal expansion curves obtained were nonlinear, and the transition appeared at about 40 degrees C. 2) beta reduced with the elapse of stored time and the number of times of measuring run. It appears that these phenomena were attributable to decrease of monomer remained in each case. 3) beta under the wet condition was larger than one under the dry condition, when specimens were stored for 20 days in each condition at 37 degrees C. Values of beta for composites ranged from 16.1 to 35.3 x 10(-6)/degrees C under the dry condition and from 18.1 to 55.4 x 10(-6)/degrees C under the wet condition. 4) beta of composites varied with filler content and kinds of filler and resin used. Value of beta reduced with increase of filler content, and was lower for Bis-GMA based composite resin than for MMA based composite resin.