Evaluation of the effect of two preparation designs on the fracture resistance and marginal adaptation of two types of ceramic crowns using CAD/CAM technology (In vitro study)

Abstract Background Recently, prosthodontic approaches involve more conservative procedures that include less invasive finish line preparations that use less ceramic thickness. Aim of the study: This in vitro study aimed to evaluate the effect of vertical preparation and modified vertical preparation designs on the marginal adaptation and fracture resistance of two types of ceramic crowns using CAD/CAM technology. Materials and methods Two typodont maxillary first premolars were embedded in acrylic resin. Forty positive replicas of epoxy resin dies were used that were divided into two groups depending on the preparation design (n = 20); Group V (Vertical): dies with feather edge finish line and Group MV (Modified vertical): dies with feather edge finish line, where a reverse shoulder of 1 mm depth was placed on the buccal surface 1.5 mm from the occlusal surface. Each group was further subdivided into two subgroups according to the type of ceramic material (n = 10): Subgroup Va and subgroup MVa for lithium disilicate (e.max CAD) and subgroup Vb and subgroup MVb for zirconia (zolid ht+). All crown restorations were fabricated using CAD-CAM technology. The marginal adaptation was measured before cementation and after cementation and aging using a stereomicroscope. To evaluate fracture resistance, each crown was placed under compressive load using a universal testing machine. Data was gathered and statistically analyzed. Results For Marginal adaptation (µm), there was no statistically significant difference shown between the study subgroups neither before cementation nor after cementation and aging. According to three-way ANOVA, there was no significant effect of the preparation design (p = 0.516) and material (p = 0.269) on the marginal adaptation with significant effect of the cementation (p < 0.0001). For Fracture resistance evaluation, results revealed a significant difference between study groups (p < 0.0001). According to two-way ANOVA test, Subgroup (MVb) showed the highest result followed by subgroup (Vb) and subgroub (MVa) and the least was subgroub (Va). The modes of fracture had no statistically significant difference among the four studied subgroups (p = .982). Conclusions Modified vertical preparation design could be a better conservative choice over other preparation designs.