Effect of translucency and thickness of lithium disilicate ceramic on light transmission and composite cement polymerization
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Abstract
Objective: To evaluate the effect of translucency and thickness of lithium disilicate ceramic on the light irradiance (LI) and the degree of conversion (DC) of a dual-cure and a light-cure composite cement under two LED lightcuring units (LCUs).
Materials and Methods: IPS e.max CAD discs were prepared in two translucencies (HT-A3, LT-A3) and four thicknesses (2, 3, 4, 5 mm), with no-ceramic controls. Two LED LCUs (Bluephase N G4, polywave; Elipar DeepCure-S, monowave) were used, both delivering ~1100 mW/cm² for 40 s. LI was measured with a light spectrometer (n = 2 per cell). DC of a dual-cure resin cement (Variolink Esthetic DC) and a light-cure restorative composite (Clearfil AP-X) was measured by micro-Raman spectroscopy at six time points (1 min, 5 min, 15 min, 1 h, 24 h, 1 week; n = 3 per cell). Non-parametric tests were used (α = 0.05).
Results: LI decreased with increasing ceramic thickness and lower translucency (Spearman’s ρ = −0.94 to −0.98, p ≤ 0.001) and fell below the detection limit at LT-A3 5 mm under both LCUs. DC increased over time, reaching a pooled mean of ~78% at one week; but the response depended on both cement chemistry and LCU spectrum. Variolink reached the 90% threshold in 6/8 ceramic groups under Bluephase N G4 and 5/8 under Elipar DeepCure-S, while Clearfil AP-X reached it in only 2/8 and 5/8, respectively. The worst-performing condition was Clearfil/LT-A3 5 mm (fitted plateau A = 66.27% under Elipar DeepCure-S).
Conclusion: Within the limitations of this in vitro study, lithium disilicate translucency and thickness markedly reduced LI and modulated DC in a cement- and LCU-dependent manner. Clinicians may consider a dual-cure cement combined with a polywave LCU when cementing thick or low-translucency lithium disilicate restorations.
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