Nine-year evaluation of a polyacid-modified resin composite/resin composite open sandwich technique in Class II cavities

The aim of this study was to evaluate in an intraindividual comparison the durability of a polyacid-modified resin composite/resin composite open sandwich restoration in a 9 years follow-up. A polyacid-modified resin composite (PMRC; compomer, Dyract) was placed as an intermediate layer and covered with resin composite (RC, Prisma TPH). A direct RC restoration was used as control.Each of 57 patients, received at least one pair of Class II restorations, one open sandwich and one resin composite control. In total 75 pairs of Class II restorations, 68 premolars and 82 molars, all in occlusion, were placed by two dentists. Most of the cavities were surrounded by enamel. The restorations were evaluated at baseline, 6, 12, 24, 36 months and 9 years by slightly modified USPHS criteria. Survival of restorations grouped on the two different techniques was determined using Kaplan-Meier survival curves.After 9 years, 14 of 135 evaluated restorations were estimated as unacceptable, 6 in the sandwich group and 8 in the control group. Over all annual failure rate during the 9-year period was 1.1%. The survival rate was not significant different between the two techniques (p=0.604). Reasons of failure were: secondary caries (8), fracture of tooth (1), fracture of restoration (2), endodontic treatment (3).Both restorative techniques showed good durability during the 9-year period. No clinical advantage was observed for the sandwich technique.