Fracture strength and marginal gap comparisons of monolayered and multilayered monolithic zirconia crowns with various milling depths.

PURPOSE: This study aimed to compare the marginal adaptation and fracture strength of monolayered and multilayered monolithic zirconia crowns fabricated at three distinct milling depths. MATERIALS AND METHODS: Eighty-four epoxy resin dies of prepared premolars were fabricated. Crowns were designed in software and milled from two monolayered zirconia materials [3Y-TZP (VITA YZ HT)(3-VYZ) and 4Y-TZP (Priti®multidisc ZrO2 Extra Translucent)(4-ET)], three multilayered zirconia materials [3/5Y-TZP (IPS e.max ZirCAD Prime)(3/5-ZP), 4/5Y-TZP (IPS e.max ZirCAD Prime Esthetic)(4/5-ZPE), and 4/5Y-TZP (Priti®multidisc ZrO2 Multi Translucent Plus)(4/5-MTP)], at three milling depths [above (A), center (C), below (B)], and a zirconia-reinforced lithium silicate glass ceramic block (VITA Suprinity)(VS) (n = 7). After sintering and glazing, marginal gaps (MG) were measured using silicone replica technique. Crowns were cemented with dualcure resin (SpeedCEM Plus, Ivoclar Vivadent), subjected to 5000 thermal cycles. Fracture strength (FS) test was performed perpendicularly to occlusal surface at 1 mm/min. Data were analyzed (SPSS 26, one-way ANOVA, Tukey post-hoc tests, P = .05), and fracture types were classified. SEM analysis was performed on representative specimens. RESULTS: MG differences among groups were insignificant (P > .05). The highest FS values were observed in 3-VYZ (1587.14 ± 228.26 N), 3/5ZP-B (1537.28 ± 268.81 N), and 4-ET (1364.86 ± 196.98 N) (P > .05). The lowest FS values were found in VS (483.86 ± 47.10 N)(P > .05). B-positioned multilayered crowns exhibited numerically higher FS than A or C positions. CONCLUSION: Monolayered (3Y-TZP and 4Y-TZP) or multilayered 3/5Y-TZP zirconia milled from below layer may be preferred for posterior region, whereas multilayered 3/5Y-TZP milled from upper layer and all configurations of multilayered 4/5Y-TZP may be more suitable for anterior.