The influence of cavity design for cusp coverage on fracture strength of weakened maxillary first premolars using two esthetic restorative systems (CAD/CAM hybrid ceramic and nanohybrid composite) (An in vitro study)

Abstract

Background: Maxillary first premolar with wide MOD cavity more susceptible to fracture. The aim of this study was toassess the influence of cavity design for cusp coverage on the fracture resistance of weakened maxillary firstpremolar restored with CAD/CAM hybrid ceramic versus nanohybide composite.Materials and Methods: Fifty six intact maxillary first premolars of approximately comparable sizes were divided intoseven groups eight for each: Group A: Intact teeth (control group); Group B: teeth prepared for MOD inlay; Group C:teeth prepared for MOD onlay covering the lingual cusp; Group D: teeth prepared for MOD covering buccal andlingual cusps ,the previous three groups indirectly restored with nanohybrid composite (3M ESPE Z 250 XT); GroupE,F,G prepared with the same design as group B, C, D respectively and restored with CAD/CAM hybrid ceramic(VITA ENAMIC).Results: An axial compression test was used to measure the fracture strength of experimented teeth. The readingswere analyzed statistically by t-test, one way ANOVA and LSD, then the mode of fracture had been examined. Theresults showed that sound teeth in group (A) had more fracture resistance values than all experimental groups andthe difference were highly significant with group (B, E, F, G).When the influence of cavity design tested amongcomposite groups it showed highly significant difference between group (B) and (C)and the highest fractureresistance value was for group(C), whereas the influence of cavity design among Enamic groups showed highlysignificant difference between group (E) and (G) the highest fracture resistance value was for group(E).T-testbetween similar designs showed non-significant difference between MOD groups and highly difference betweenother groups.Conclusions: Cusp coverage increased the fracture resistance of composite groups but result in non-restorablefracture, while Enamic total onlay presented promising fracture resistance with favorable mode of fracture