# Effect of Dental CAD-CAM Resin Composite Thickness on the Polymerization Behavior of Dual-Cure Resin Cements for Endocrown Restoration

## TL;DR

Thicker dental resin composites reduce light transmission, leading to poor cement polymerization and potential restoration failure.

## Contribution

This study quantifies how CAD-CAM resin composite thickness affects dual-cure resin cement polymerization in endocrown restorations.

## Key findings

- Transmitted light intensity decreases logarithmically with increasing composite thickness.
- Dual-cure resin cement polymerization significantly decreases when composite thickness exceeds 5.5 mm.
- Self-curing cannot fully compensate for inadequate light transmission in thick composites.

## Abstract

What are the main findings?
Light transmission through CAD-CAM resin composites decreases exponentially with thickness.Dual-cure resin cement polymerization decreases markedly above 5.5 mm thickness.Adequate polymerization occurs when the composite thickness is below approximately 5.5 mm.

Light transmission through CAD-CAM resin composites decreases exponentially with thickness.

Dual-cure resin cement polymerization decreases markedly above 5.5 mm thickness.

Adequate polymerization occurs when the composite thickness is below approximately 5.5 mm.

What are the implications of the main findings?
Self-curing alone cannot compensate for insufficient light under thick restorations.Excessive pulp-chamber extension may increase the risk of debonding and failure.

Self-curing alone cannot compensate for insufficient light under thick restorations.

Excessive pulp-chamber extension may increase the risk of debonding and failure.

This study investigated the effect of CAD-CAM resin composite thickness on the polymerization behavior of dual-cure resin cements used for endocrown restorations. Three commercially available dual-cure resin cements and one light-cure resin cement (for comparison) were polymerized by light irradiation through CAD-CAM resin composite plates of varying thicknesses (1.5, 3.5, 5.5, 7.5, and 9.5 mm). Transmitted light intensity was measured using an optical spectrometer. Polymerization behavior was evaluated immediately after irradiation and after 24 h of aging using Fourier transform infrared spectroscopy to determine the degree of conversion (DC) and Vickers hardness (VH) testing. Transmitted light intensity decreased logarithmically with increasing composite thickness, with less than 1% of incident light reaching the resin cement at thicknesses ≥ 5.5 mm. For the dual-cure resin cements, DC and VH values significantly decreased when the composite thickness exceeded 5.5 mm. Although DC and VH increased after 24 h due to self-curing, values beneath thicker composites remained lower than those beneath 1.5 mm thick composites. The light-cure resin cement failed to polymerize when the composite thickness exceeded 7.5 mm. These results indicate that CAD-CAM resin composite thickness critically influences resin cement polymerization, highlighting the importance of thickness control in endocrown restorations.