The effect of polymerization shrinkage during veneer placement

This study evaluated the relationship of polymerization shrinkage during composite resin veneer placemeiu to direction of the polymerizaiion tight source. Fifty maxillary permanent incisors were obtained and divided into five groups of ten. Groups I and H had preparations placed in enamel Groups III, IV, and V had preparations placed in deniin. In groups 1 and III. an unfilled bonding resin was placed and polymerized from the facial aspect, followed hy placement and polymerization of a hybrid composite resin. Groups II and IV were initially polymerized from the lingual direction. In group V. the unfilled resin and hybrid composite resin were polymerized simultaneously from the facial aspect. Staiistical analysis indicated ihat there was significantly less axial microgap formation during lingual polymerization when ihe preparation remained in dentin. but demonstrated that there was no siatisiically significant difference when the preparation remained in enamel.