Influence of Veneer Thickness on Double Bond Conversion of Preheated Composite and Self-Adhesive Resin Cement Under Lithium Disilicate Restorations: An In-Vitro Study.

Introduction: This study evaluated the influence of lithium disilicate restoration thickness on the degree of conversion (DC) of a self-adhesive dual-cured resin cement (Bifix SE®; VOCO GmbH, Cuxhaven, Germany) and a preheated composite resin (VisCalor Bulk®; VOCO GmbH, Cuxhaven, Germany). Methods: Sixty IPS e.max CAD (LTB1) specimens (2 mm, 4 mm, 6 mm; n D 10 per group) were fabricated and divided into six groups. Groups 1–3 were luted with Bifix SE, and Groups 4–6 with preheated VisCalor Bulk. Specimens were conditioned with 5% hydro_uoric acid and silane, then cemented and light cured. Raman spectroscopy was used to determine DC. Results: Two-way ANOVA showed ceramic thickness significantly reduced DC% (F(2,54) D 17.053, p < 0.001), and luting agent type was also significant (F(1,54) D 360.679, p < 0.001), with VisCalor Bulk achieving higher DC than Bifix SE at all thicknesses. Conclusions: Increasing lithium disilicate thickness negatively affected polymerization. Preheated VisCalor Bulk performed better, making it preferable under thicker ceramic restorations.