Bond strength of orthodontic brackets to CAD/CAM ceramics following various surface treatments

Abstract

Objectives: This study evaluated the shear bond strength (SBS) of two types of orthodontic brackets (ceramic and metal) bonded to two CAD/CAM ceramic materials (feldspathic ceramic and lithium disilicate glass-ceramic), each subjected to different surface treatments, and assessed adhesive remnant index (ARI) scores. Materials and methods: Sixty-four ceramic discs (1 mm thick; n = 32 per material) were prepared. Surface pretreatments were alumina air abrasion followed by phosphoric acid etching or hydrofluoric acid etching. Each subgroup was bonded with metal or ceramic brackets using a light-cured adhesive. SBS was measured with a universal testing machine, and ARI was assessed under a stereomicroscope. Three-way ANOVA tested the effects of ceramic type, bracket type, and surface treatment (α = 0.05), and chi-square tests compared ARI distributions. Results: The results demonstrated that the ceramic type significantly influenced SBS (p = 0.004). Lithium disilicate glass-ceramic exhibited higher SBS values than feldspathic ceramic. Bracket type also had a significant effect on SBS, regardless of ceramic type or surface treatment (p = 0.001). However, the applied surface treatments did not produce a significant difference in SBS (p = 0.546); phosphoric acid etching after alumina air abrasion yielded comparable results to hydrofluoric acid etching. ARI scores did not differ significantly among groups, and debonded surfaces showed no gross ceramic damage under stereomicroscopy. Conclusions: Ceramic type and bracket type significantly affected SBS, whereas surface pretreatment did not under the tested conditions. Clinical relevance: Balancing adequate bracket retention with safe debonding is essential for ceramic restorations. Comparable SBS between the two pretreatments and the absence of visible ceramic damage support conservative, clinically oriented conditioning protocols.