Marginal gap, internal fit, and fracture resistance of screw‐retained single implant crowns cemented to titanium base abutments: An in vitro investigation

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PURPOSE: To evaluate the marginal gap, internal fit, and fracture resistance of screw-retained single implant 3Y-TZP and 5Y-TZP zirconia crowns with different cement gap thicknesses. MATERIALS AND METHODS: Forty screw-retained single implant crowns, supported by forty implants and abutments, were constructed and divided into two groups (n = 20) according to the zirconia type (3Y-TZP vs. 5Y-TZP), and then into two subgroups according to the cement gap thickness, 40 and 60 µm. The cement gap initiation point was located 1 mm from the abutment's finish line, with a standardized zero end gap. Maxillary first premolar crowns were milled, and prefabricated screw access channels were used for the titanium-base group. ANOVA and Tukey tests were used to analyze the data. RESULTS: The 3Y-TZP40 (7.59 ± 0.28 µm) and 5Y-TZP40 (8.30 ± 0.50 µm) revealed less marginal gap (p < 0.001) compared to the 3Y-TZP60 (13.83 ± 0.15 µm) and 5Y-TZP60 (14.15 ± 0.59 µm). When the internal fit (µm) was evaluated, 3Y-TZP40 revealed a better internal fit compared to 3Y-TZP60 and 5Y-TZP60 in the axial area and total internal fit (p < 0.05). 3Y-TZP40 (2071.61 ± 115.89 N) and 3Y-TZP60 (2091.36 ± 44.12 N) revealed higher (p < 0.01) fracture resistance than 5Y-TZP40 (1634.80 ± 105.10 N) and 5Y-TZP60 (1655.32 ± 43.34 N). The two-way ANOVA revealed that cement gap thickness was a significant factor (p < 0.05) when measuring the marginal gap and axial and total internal fit. The type of zirconia was significant in the marginal gap and fracture resistance. CONCLUSION: 3Y-TZP exhibits superior fracture resistance to 5Y-TZP. A thinner cement gap enhances marginal adaptation and internal fit, which can improve clinical longevity.