Effect of thickness on irradiance loss and temperature rise in indirect restorative materials: an in vitro study.

Background: The polymerization extent of resin cement used for bonding indirect restorations is contingent upon the light transmittance of the indirect restoration materials and the light intensity of the employed light device. The temperature increase during the polymerization of these resin cements via light is a critical factor in preserving pulp health. The present study aimed to assess the optical properties of different thicknesses of indirect restorative materials such as feldspathic ceramics [Vitablocs Mark II, (VBM)], indirect composites [Gradia, (GRA)] and 3D printing resins [VarseoSmile Crown Plus, (VSC)] and the temperature rise on the undersurface of the materials during LED light application.

Methods: The irradiance loss, absorbance, and absorbance coefficient values of three indirect restorative materials (VBM, GRA, and VSC) with four different thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were analyzed. A Valo Cordless (Ultradent, USA) LED light device was used as the light source. Light transmittance was measured using a radiometer, and the averages were recorded. The temperature variation (Δt) was recorded using a K-type thermocouple during light application. Data were statistically analyzed at a significance level of 0.05.

Results: It was revealed that irradiance loss and absorption values increased, and absorption coefficient values decreased with the increase in thickness in the material groups. The irradiance loss values for VBM and GRA were comparable across all thicknesses. The irradiance loss value for the VSC group was comparable to that of the GRA group and distinct from the VBM group across all thicknesses, except at 0.5 mm (p < 0.05). The assessment of thickness and material groups regarding temperature increase revealed that temperature differential values diminished with more thickness, although no significant difference was seen between the groups (p > 0.05).

Conclusion: The absorbance and irradiance loss values of indirect restorative materials escalated with greater thickness, particularly in the VSC group. The efficacy of light-polymerized resin cements may be negatively impacted; therefore, it is advisable to prolong the curing duration for thicker materials. Moreover, as the thickness grows, the thermal exposure of the materials diminishes, resulting in a reduced danger to pulp health.