Compressive modulus, translucency, and irradiance transmittance of clear PVS materials used for resin injection molding technique.

Objectives: To evaluate the compressive modulus, translucency, and light curing irradiance transmittance of four clear polyvinyl siloxane (PVS) materials used for the injection molding technique at varying thicknesses, and to assess the correlation between color parameters and irradiance transmittance.

Materials and methods: Four clear PVS materials (Exaclear, Clear Bite Matrix, Affinity Crystal, and Memosil 2) were used in this study. Compressive modulus was measured by compressing cylindrical PVS specimens (n = 9; d = 10 mm; t = 6 mm) up to 30% strain using a universal testing machine. For the translucency analysis and irradiance transmittance, specimens (n = 5) were fabricated with five different thicknesses (d = 12 mm and t = 2, 4, 6, 8 and 10 mm). The L*, a, *b* values of specimens were obtained using a CIELab spectrophotometer (CMD-700, Konica Minolta) with calibrated white and black tiles; the translucency parameter was calculated. The same specimens were placed onto a spectrophotometer (MARC Light Collector) to measure irradiance transmitted through the specimens from a light curing unit (Valo Corded, Ultradent). Data were analyzed using analysis of variance (ANOVA) with Tukey post hoc test and the correlation between translucency and irradiance transmittance of materials for each thickness was evaluated using Pearson's correlation.

Results: Compressive modulus differences in PVS materials were significant (one-way ANOVA: df = 3, F = 76.27, p < 0.001); Affinity and Memosil 2 were highest with no significant difference between them (Tukey: t = -1.62; p = 0.382). Clear Bite was higher than Exaclear (Tukey: t = -3.70; p = 0.004). Exaclear was lowest. Translucency decreased with thickness (Two-way ANOVA: df = 3, F = 586.53, p < 0.001; thickness: df = 4, F = 1389.34, p < 0.001). Exaclear was most translucent at all thicknesses. L*, a*, b* values varied by material and thickness (L*: df = 3, F = 1213.32, p < 0.001; a*: df = 3, F = 10766.8, p < 0.001; b*: df = 3, F = 3260.42, p < 0.001). Memosil 2 had lowest b* values. Irradiance transmittance was affected by material and thickness (Two-way ANOVA: df = 4, F = 2388.86, p < 0.001). Exaclear had highest irradiance transmission, surpassing control at >6 mm. Violet/blue irradiance ratio decreased with thickness; Exaclear maintained a constant ratio, indicating preserved violet irradiance. There was a strong positive correlation between translucency and light irradiance (Pearson's r = 0.97, R² = 0.86-0.96). Radiant exposure analysis suggests adjusting the curing time based on PVS thickness for optimal exposure (10 J/cm²) is achievable within 13-14 s for <2 mm and 21-30 s for 8-10 mm with Clear Bite, Affinity, and Memosil 2; whereas Exaclear requires less time.

Conclusions: Compressive modulus in clear PVS materials varied by type; Affinity and Memosil 2 demonstrate higher modulus, offering more stability of the clear mold. Translucency and irradiance transmission through clear PVS materials decreased as their thickness increased, yet Exaclear exceled in maintaining high translucency and superior light transmission capabilities. Additionally, there is a strong positive linear correlation between translucency and light irradiance transmittance, offering a method to adjust curing times effectively based on material translucency.

Clinical significance: The light curing time to adequately polymerize composite through clear impression material may need to be increased, particularly with thicker matrices or less translucent materials.