Influence of Clinically Relevant Seating Loads on Shear-Thinning Behavior and Film Thickness of Light-Cure Veneer Cements

This article aims to evaluate the shear rate-dependent rheological behavior of light-cure resin cements used for lithium disilicate veneers and assess its relationship with cement film thickness under standardized and clinically relevant seating loads. Five light-cure resin cements (RXV, CVE, ACV, NXL, and VLE) were tested using rotational rheometry under a standardized baseline gap. Apparent viscosity (η) was determined at 10 s−1 and 100 s−1. Cement film thickness was measured following ISO 4049 under 150 N and under reduced loads of 50 and 30 N. All measurements were performed in triplicate (n = 3 per cement for rheology; n = 3 per cement per seating load for film thickness). Data were analyzed using one-way and two-way analysis of variance (ANOVA), followed by Tukey post hoc tests where appropriate. Linear regression and Pearson's correlation analyses were used to examine load-film thickness trends and viscosity-film thickness associations. The significance level was set at α = 0.05. Viscosity differed significantly among materials at both shear rates (p < 0.001). At 10 s−1, viscosity ranged from 210 ± 2 Pa·s (VLE) to 1820 ± 20 Pa·s (NXL), while at 100 s−1 it ranged from 164 ± 2 Pa·s (RXV) to 440 ± 2 Pa·s (VLE). Four cements showed pronounced shear-thinning behavior (−82.6% to −86.3%), whereas VLE showed an inverse response (-109.5%). Film thickness differed significantly across all seating loads (150 N: p = 0.004; 50 and 30 N: p < 0.001). At 30 N, values ranged from 48.3 ± 3.5 µm (RXV) to 74.7 ± 2.5 µm (NXL). Weak positive associations were observed between viscosity and film thickness under reduced seating conditions (r = 0.25 at 30 N; r = 0.24 at 50 N). Seating load was the main determinant of cement film thickness, while shear rate-dependent viscosity showed a secondary, material-dependent contribution under reduced pressure. Favorable shear-thinning behavior may support improved seating adaptation and more consistent film thickness control during veneer placement.