Try-in procedure and surface treatment strategies: Optimizing the fatigue behavior of lithium disilicate restorations

This in vitro study evaluated how different surface treatments during try-in affect the fatigue behavior of lithium disilicate ceramic. Disc-shaped lithium disilicate specimens were fabricated and allocated into 4 groups: (1) CTRL - try-in paste removed with 37% phosphoric acid (H₃PO₄), followed by etching with 5% hydrofluoric acid (HF) and silane treatment; (2) HFSIL PRE - HF and silane applied before try-in, followed by H₃PO₄ cleaning; (3) HFSIL PRE + SIL POST - same as HFSIL PRE, with an additional silane application after paste removal; and (4) HFSIL PRE + HFSIL POST - HF and silane applied both before and after try-in. Specimens were bonded to fiber-reinforced epoxy resin discs with resin cement. Baseline (24-h water storage) and aged (25,000 thermal cycles) samples underwent fatigue testing (n = 15; 20 Hz, initial load 200 N, step size 50 N, 10,000 cycles per step) to measure fatigue failure load (FFL) and cycles for failure (CFF). Monotonic test (1 mm/min) was also performed to determine maximum load. At baseline, no significant differences in fatigue behavior were observed among the groups. After aging, HFSIL PRE group demonstrated superior fatigue behavior compared to HFSIL PRE + HFSIL POST group. No significant differences were found between CTRL, HFSIL PRE, and HFSIL PRE + SIL POST. Aging significantly reduced FFL and CFF across all groups. These results suggest that a surface treatment protocol involving single etching and silane application during try-in optimizes the mechanical performance of lithium disilicate restorations. Re-etching with HF after try-in is unnecessary and may impair fatigue performance.