Light transmittance through composite and ceramic onlay

: an in vitro study

Abstract

Purpose: This in vitro study aimed to evaluate light transmittance through two different CAD-CAM indirect restorative materials: resin-matrix composite and 3 mol% yttria-stabilized tetragonal zirconia polycrystal (3YTZP) to understand how the intrinsic microstructure and optical characteristics of these materials influence light transmittance and the polymerization potential of the underlying resin-matrix cement. Materials and Methods: Eighteen disk-shaped specimens of both materials were prepared using CAD-CAM techniques. A dual-cure resin-matrix cement was applied under a standardized 60 N load. Both materials had 1.5 mm thickness and were cemented using the same 73 wt% resin-matrix cement. Specimens were light-cured at 900 mW/cm2 for 40s. Light transmittance was analyzed before and after polymerization using a spectrophotometer with an integrated monocromator and during polymerization with a MiniGig device. Complementary optical microscopy was performed to evaluate microstructural characteristics of the materials. Statistical analysis was conducted using non-parametric tests with significance set at p < 0.05. Results: 3YTZP zirconia demonstrated significantly higher light transmittance than the resin-matrix composite, both before and after polymerization (p < 0.001). The resin-matrix composite material showed greater variation in optical behavior, attributed to its heterogeneous filler distribution. Spectrophotometric and MiniGig measurements were consistent, reinforcing the validity of the findings. Optical microscopy revealed a homogeneous polycrystalline structure in 3YTZP, while the resin-matrix composite showed irregularly shaped fillers, contributing to greater light scattering. The presence of resin-matrix cement also reduced transmittance across all specimens. Conclusions: Within the limitations of this in vitro study, 3YTZP zirconia allowed higher light transmission than resin-matrix composite, challenging the traditional notion of zirconia's opacity. Advances in ceramic processing have improved the translucency of modern zirconia, supporting its use in indirect restorations where both mechanical strength and light transmittance are essential. Proper material selection, thickness standardization, and adequate curing protocols are crucial to optimize resin-matrix cement polymerization and restoration longevity.

Date of Award	3 Jul 2025
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Rita Fidalgo-Pereira (Supervisor) & Júlio C. M. Souza (Co-Supervisor)