Influence of post-etching phosphoric acid cleaning on resin bond strength to glass-ceramics: a systematic review of in vitro studies

Hydrofluoric acid (HF) etching is widely used to condition glass-ceramics, but residual salts may compromise adhesion. Phosphoric acid (PA) cleaning has been proposed to clean and improve bond strength; however, its effectiveness remains uncertain. This systematic review aimed to evaluate the influence of PA cleaning after HF etching on the bond strength of resin to glass-ceramics. A comprehensive search of four electronic databases: PubMed, Scopus, Embase, and Web of Science, as well as manual searches, was performed to identify relevant studies published through November 2024. The PICO strategy used was P- glass-ceramics; I-phosphoric acid cleaning after hydrofluoric acid etching; C- no post-etching cleaning; O- bond strength and S- in vitro studies evaluating the effect of phosphoric acid cleaning on the bond strength of HF-etched glass-ceramics. A total of 12 studies were included. HF concentrations ranged from 5–10%, and 37% PA was the most used cleaning agent. Five studies reported improved bond strength when PA was combined with ultrasonic bath cleaning, and three studies reported improvement with PA alone. In contrast, four studies found no improvement in bond strength after PA cleaning. After thermocycling, the positive effects of cleaning protocols were reduced or no longer statistically significant. Failure mode analysis predominantly showed adhesive failures across all protocols. PA cleaning alone did not improve bond strength or reduce adhesive failures, but when combined with ultrasonic cleaning or applied actively with a microbrush, it enhanced bond strength and increased mixed/cohesive failures. However, these effects were not sustained after thermocycling.