# Effect of Storage Time After Surface Treatment of Zirconia on Surface Free Energy and Bond Strength of Composite Cement

## TL;DR

This study shows that delaying cementation after zirconia surface treatment reduces surface energy and bond strength, suggesting immediate cementation is best.

## Contribution

The study reveals how storage time after zirconia surface treatment affects surface energy and bond strength, offering practical recommendations for dental applications.

## Key findings

- Surface free energy of zirconia decreases with prolonged storage after surface treatment.
- Storage time significantly affects bond strength of composite cement, particularly for KHF2-etched zirconia.
- Adhesive failures to cement increase with longer storage times, though not always statistically significant.

## Abstract

Surface treatment of zirconia before cementation can be performed using different methods, e.g. airborne particle abrasion (APA) or various etching protocols. This study evaluated the effect of storage time between surface treatment and cementation on the surface free energy (SFE) of zirconia, the bond strength of composite cement, and failure mode.

Rod-shaped zirconia specimens were fabricated and assigned to two surface treatment groups: APA (n = 80) and hot etching with potassium hydrogen difluoride (KHF2, n = 80). Each group was divided into four storage time subgroups: immediate, 24 h, 1 week, and 1 month. After storage, specimens were either analyzed for SFE (n = 10) or cemented for shear bond strength (SBS) testing and failure mode evaluation (n = 10).

Two-way analysis of variance (ANOVA) showed a significant effect of both surface treatment and storage time on SFE (P < 0.05), with KHF2-etched zirconia exhibiting the highest values across all time points. In both groups, SFE gradually decreased with increased storage. Surface treatment did not significantly affect SBS (P > 0.05). Storage time significantly influenced SBS (P < 0.05), specifically for KHF2-etched zirconia; post-hoc comparisons showed higher SBS after 1 week than at immediate testing (P < 0.05). Although adhesive failures to cement increased with longer storage time for KHF2-etched specimens, this trend was not significant (P > 0.05). For APA specimens, the highest incidence of adhesive failures (n = 9) to cement occurred after 24 h of storage.

Given the significant decrease in SFE with prolonged storage and adhesive failures to zirconia tended to increase over time, minimizing the interval between surface treatment and cementation is recommended.