Marginal adaptation of zirconia-reinforced lithium silicate overlays with different preparation designs

Objective Following the advent of strong adhesive bonding, the conservative tooth preparation designs without a retentive form gained increasing popularity. This study aimed to evaluate the marginal adaptation of zirconia-reinforced lithium silicate (ZLS) overlays with different preparation designs. Materials and methods Forty sound human maxillary first molars were collected and divided into four groups (n = 10) according to their preparation design for the fabrication of ZLS overlays: (O) anatomical occlusal reduction, (OS) anatomical occlusal reduction with rounded shoulder, (OG) anatomical occlusal reduction with a central groove, and (OSG) anatomical occlusal reduction with rounded shoulder and central groove. A video measuring machine (VMM) was used to measure the marginal gap. Statistical analysis was carried out using one-way ANOVA followed by pairedttest and Tukey's test (alpha = .05). Results The gap size was significantly different between the groups both before (P= .004) and after (P= .008) cementation, and it was significantly smaller in group O than group OSG (P= .002 before andP= .004 after cementation). Marginal gap increased in all groups following cementation (P< .001). Conclusions Group O showed comparable marginal adaptation with groups OS and OG while group OSG with the most complex design showed the lowest marginal adaptation for ZLS overlays. Clinical Significance According to the results of this in vitro study, it may be stated that for defect-free teeth requiring occlusal restoration, the occlusal surface preparation alone would suffice to achieve optimal marginal adaptation, and retentive and more invasive preparation designs are not required.