Comparison of two measurement methods (triple scan method and silicone replica technique) for assessing the internal and marginal fit of zirconia copings fabricated with different convergence angles: an in vitro study

Studies investigating the effect of convergence angles on the marginal and internal gaps of fixed dental prostheses using Triple scan method (TSM) and Silicone replica technique (SRT) are limited. Although several methods exist to evaluate the internal and marginal adaptation of zirconia copings, comparative data between digital and conventional approaches remain limited. Twenty zirconia copings were fabricated by a computer-aided design and computer-aided manufacturing system on stainless steel abutment dies at two TOCs (10° and 20°). Each group included 10 samples. The internal and marginal gaps were assessed using SRT and TSM. TSM was performed first, followed by SRT, to avoid any interference from silicone residues. A Paired t-test was used to compare the two methods in measuring the fit and A mixed-model ANOVA was used to assess the influence of measurement method and convergence angle on fit values, while accounting for the type of gap (marginal or internal). the agreement between the two methods was examined using the Bland-Altman plot (α = 0.05). A linear mixed-effects model with coping as the random effect (accounting for repeated measurement method and anatomical location within each coping) showed a significant main effect of measurement method on internal gap ( p < 0.001) and a significant method-by-location interaction ( p < 0.001), but no significant effect of convergence angle ( p = 0.117) and no significant convergence-angle interactions (all p > 0.17). Marginal gap showed no significant effects ( p > 0.15) and variance heterogeneity was present. The Bland-Altman plot indicated that the mean differences in the marginal gap measurements were − 10.227 μm for the 10 degrees group and − 0.13 μm for the 20 degrees group. The limits of agreement for the mentioned groups were 17.932 to -38.639 μm and 32.747 to -33.006 μm respectively. Within the limitations of this in vitro study, both TSM and SRT provided clinically acceptable marginal and internal fit results, with internal gaps being independently affected by measurement method and convergence angle. TSM produced slightly higher internal gap values than SRT, an effect that varied by anatomical location; this in vitro study did not establish the accuracy, validity, or clinical reliability of either method.