REDUCTION OF CUSP DEFLECTION RESULTING FROM COMPOSITE POLYMERIZATION SHRINKAGE, USING A LIGHT-TRANSMITTING CONE

For investigation of whether the use of a transparent plastic cone (Li ght-tip) influenced cusp deflection, as compared with a conventional m ethod (control), the following experiments were performed. Mesiodistoc clusal (MOD) cavities were prepared in 10 extracted premolars, and sta inless steel pins were placed on the cusps. The cavities were bonded w ith Scotchbond Multipurpose, and the distance between the pins was mea sured. Control restorations using P-50 were placed in three increments , each increment having been polymerized for 40 s. For placing the tes t restorations, the Light-tip was fitted to the end of the curing wand and pressed into the resin in the proximal box, and the curing light was turned on. The next increment filled the recess created after the removal of the cone in the resin, and curing was performed with the pl astic cone in the occlusal box. The third increment was cured without the cone. Each tooth was used for four restorations. In 16 of 20 cases , a significantly decreased cuspal flexure was found when the cone was used. The flexure decreased 24%, as compared with control.