A preliminary evaluation of the structural integrity and fracture mode of minimally prepared resin bonded CAD/CAM crowns

PurposeThis study was a preliminary evaluation of two minimal preparation designs proposed for ceramic and composite resin bonded CAD/CAM crowns. It compared the structural integrity and fracture mode of teeth restored with traditionally and minimally prepared resin bonded CAD/CAM crowns fabricated from the same material hypothesizing that teeth restored with minimal resin bonded crowns would demonstrate the same fracture strength to teeth restored with traditional resin bonded crowns.Materials and methodsForty intact maxillary molar teeth were used and divided in four groups. Two groups were prepared according to a traditional crown preparation design and two groups were prepared according to minimal preparation designs. A resin composite (Paradigm MZ100, 3M ESPE) and a leucite glass–ceramic (ProCAD, Ivoclar Vivadent) were used for the fabrication of the crowns using CEREC Scan. Crowns of ceramic were cemented using Variolink II (Ivoclar Vivadent) and crowns of composite with Rely X Unicem Aplicap™ (3M ESPE) and loaded until fracture. Load data was analysed using ANOVA comparing crowns of the same restorative material. The mode of fracture was also recorded and analysed (Kruskal–Wallis).ResultsFor the composite system the mean fracture load and SD was 1682 N (±315) for the traditional and 1751 N (±338) for the minimal crowns. For the ceramic system the mean fracture load and SD was 1512 N (±373) for the traditional and 1837 (±356) for the minimal crowns. No statistically significant difference was found between the two designs for each system. Nonparametric analysis (Kruskal–Wallis) of the fracture mode showed no statistical significant difference between designs for either material (p > .05).ConclusionWithin the limitations of this experimental design, it was found that minimally prepared resin bonded CEREC crowns demonstrated equal fracture resistance and mode of fracture to that of crowns bonded to traditionally prepared teeth.