Effect of reaction layer removal methods on bond strength of pressed lithium disilicate ceramic to resin cement

Abstract

The aim of this study was to evaluate the impact of reaction layer removal methods on the immediate and long-term bond strength of pressed lithium disilicate ceramics, with or without 5% hydrofluoric acid (HF) etching. For this, sixty lithium disilicate ceramic discs (Ø= 12 mm, thickness= 1.2 mm) were assigned to 6 groups based on removal method and surface pretreatment: CTRL (polishing only), CTRL + HF (polishing + HF etching), GB (grit-blasting), GB + HF (grit-blasting + HF), LCA (grit-blasting + 0.6% HF + 1.7% H₂SO₄), and LCA + HF (LCA + HF). Resin cement cylinders were built, light-cured, and tested for microshear bond strength (μSBS) after 24 h or 90 days (with 10,000 thermal cycles). Surface topography, chemical composition, and failure modes were assessed. No significant difference in bond strength was observed between groups at baseline (p> 0.05). After aging, LCA + HF and GB + HF showed the highest μSBS, with no significant difference from CTRL + HF and LCA. GB had no significant difference from CTRL + HF and LCA. CTRL had the lowest bond strength (p< 0.05). All groups showed a decrease in bond strength after aging, but HF etching minimized this decrease. Higher amounts of Mg and P were found in the reaction layer presence. Therefore, grit-blasting or low-concentration acid immersion combined with grit-blasting are effective methods for removing the reaction layer without affecting bond strength. However, HF etching is crucial for reliable long-term bond strength.