Marginal gap evaluation of zirconia and metal short crowns with varying total occlusal convergence and auxiliary preparation features: an in-vitro study

Abstract

Marginal adaptation is one of the important factors in determining the long-term success of dental restorations. Despite extensive research, conflicting evidence exists regarding the influence of material type, total occlusal convergence (TOC), and auxiliary preparation features on marginal gaps of definitive crowns. This in-vitro study aimed to evaluate and compare the marginal gaps of zirconia and metal short crowns fabricated using digitally across preparations with varying TOC angles (10° and 20°) and auxiliary features (groove and box). Eighty short crown specimens were distributed across eight groups ( n = 10 each): zirconia and metal crowns at 10° and 20° TOC, with auxiliary groove or box preparations. Mandibular first molar typodont teeth were prepared under standardized conditions. Zirconia crowns were milled via CAD-CAM (Ceramill Zolid PS), and metal crowns were fabricated from digitally milled wax patterns using the lost-wax technique (Wiron Light). Marginal gaps were measured at seven equidistant buccal and lingual, and five mesial and distal points under 100× stereomicroscopic magnification. Data were analyzed using one-way ANOVA, Tukey’s post-hoc test, unpaired Student’s t-test, and paired t-test (α = 0.05). One-way ANOVA showed a statistically significant difference in marginal gaps among all groups across all surfaces ( p < 0.05). Metal crowns demonstrated significantly higher marginal gaps (145.71 ± 54.50 μm) than zirconia crowns (104.02 ± 50.19 μm) ( p = 0.001). The zirconia crown with 20° taper and buccal groove (Z20G) showed the lowest marginal gap (71.6 ± 48.2 μm), while the metal crown with 20° taper (M20) recorded the highest (178.0 ± 61.5 μm). Marginal gap of short crowns is significantly influenced by material type, TOC, and auxiliary preparation design. Zirconia crowns with 20° taper and buccal grooves demonstrated accurate marginal fit, with taper angle, and auxiliary features significantly influencing marginal gap accuracy.