An evaluation of various zirconia surface treatments for enhancing orthodontic bonding

To assess the impact of various surface treatments of zirconia crowns on shear bond strength (SBS) of orthodontic brackets, both with and without thermocycling.

A total of 36 zirconia crowns were digitally constructed to mimic upper first premolars. The specimens were categorized into three groups (n = 12/ each) based on surface treatment: the sandblasting (S) group, the Nd:YAG Laser (L) (1064 nm,3W,10 Hz) group, and the combined sandblasting and laser (SL) group. One specimen/each group was examined using a scanning electron microscope. Metal orthodontic brackets were bonded to treated zirconia using universal orthodontic adhesive. Each group was subcategorized into non-thermocycled (n = 6) and thermocycled (n = 6) groups. Thermocycling (between 5 and 55 °C) was applied for 500 thermal cycles. The SBS and adhesive remnant index score (ARI, ranging from 0–3) were measured and recorded. The statistical analysis of SBS was conducted using a two-way analysis of variance, while the ARI scores were analyzed using the Kruskal–Wallis test.

The results revealed a significant interaction between the surface treatment and thermocycling on SBS (P = 0.031). The SL group exhibited the highest SBS prior to thermocycling (16.74 ± 2.44), followed by the L group (14.75 ± 2.48) and then the S group (10.38 ± 1.17). The SBS values exhibited a significant decrease following thermocycling, with the S group (5.9 ± 0.25) demonstrating the lowest values. The distribution of ARI scores showed a significant difference between the S group without thermocycling and both the L and SL groups without thermocycling (P = 0.004).

Although the combination of sandblasting and Nd laser treatment has been proven to be the most effective in achieving clinically acceptable SBS, the SBS did not differ significantly compared to laser treatment alone after thermocycling. This suggests that zirconia laser treatment with an Nd laser can be an effective in-office procedure for orthodontists. Future clinical trials are necessary to verify these in vitro findings.