Interfacial adaptation of a Class II polyacid-modified resin composite/resin composite laminate restoration in vivo

The aim of this in vivo study was to evaluate the interfacial adaptation of Class II resin composite open sandwich restorations with a polyacid-modifi ed resin composite as a stress-absorbing layer (PMRC/RC). Twenty Class II b ox-shaped, enamel-bordered cavities were prepared in 10 premolars scheduled to be extracted for orthodontic reasons. An open PMRC/RC sandwich restorat ion was placed in 1 of the cavities of each tooth. The first layer, PMRC, i n the proximal box extended to the periphery in the cervical part of the ca vity. The following RC layers were placed with a horizontally incremental t echnique. The PMRC was excluded from the control cavity. The teeth were ext racted after 1 month and the interfacial adaptation of the restorations was studied with quantitative scanning electron microscope analysis using a re plicate technique. Cap-free interfacial adaptation was observed for the PMR C/RC and RC restorations in cervical enamel in 97% and 73%, respectively (P = 0.006). The gap-free scores for dentin were 87% and 64%, respectively (P = 0.022). Excellent interfacial adaptation was observed in both groups for the occlusal enamel 99% and 100%, respectively. The adaptation to occlusal enamel for the direct resin composite restorations was significantly bette r than to dentin or cervical enamel. A higher frequency of enamel fractures was observed parallel to the cervical margins compared to the occlusal. No dentin fractures were observed in the experimental groups. The PMRC/RC san dwich technique showed a statistically significant improved interfacial ada ptation to dentin and cervical enamel in Class II enamel-bordered cavities. The clinical significance of the differences has to be evaluated.