Influence of different evaluation pastes on the bond of resin cement to lithium disilicate ceramic: An in vitro study.

STATEMENT OF PROBLEM: Residue from evaluation pastes may remain on the bonding surface of indirect restorations, requiring specific cleaning protocols. However, it is not clear how much the composition of different evaluation pastes affects the bond strength to resin cement.

PURPOSE: The purpose of this in vitro study was to determine the effectiveness of using 37% phosphoric acid to clean different evaluation pastes and its effect on the long-term bond strength of lithium disilicate ceramics to resin cement.

MATERIAL AND

METHODS

Lithium disilicate slices (IPS e.max CAD) with simulated computer-aided design and computer-aided manufacturing (CAD-CAM) topography were crystallized, etched (20 seconds - 5% hydrofluoric acid -HF), and received the application of different evaluation pastes (CTRL - no contamination; AC - Allcem; NX - NX3; ML - Multilink; RX - RelyX). All specimens were actively cleaned for 60 seconds with 37% phosphoric acid, except for the CTRL group. After applying silane, resin cement cylinders were produced and light-polymerized. Micro-shear bond strength testing was carried out on half of the cylinders (n=40) at baseline (24 hours) and after aging (220 days of water storage at 37 °C and 25 000 heat cycles between 5 °C and 55 °C). Failure modes, surface topography via scanning electron microscopy (SEM), and chemical composition through energy-dispersive X-ray spectroscopy (EDS) were assessed. Statistical analysis used 2-way analysis of variance (ANOVA) and Bonferroni post hoc tests (α=.05).

RESULTS

At baseline, the AC and NX groups exhibited bond strength similar to the CTRL group. All groups experienced a considerable decline in bond strength after aging, but there was no difference between the AC group and the CTRL group. In both scenarios, the RX and ML groups displayed the weakest bonds. SEM analysis revealed similar surface topography, confirming the EDS results, where similar elemental composition was observed among the groups.

CONCLUSIONS

Cleaning lithium disilicate surfaces with 37% phosphoric acid after contamination with an evaluation paste is not universally effective for the tested pastes. Some pastes leave a residue that still compromises bond strength in the long term. Therefore, alternative cleaning methods should be considered.