Etchability of zirconia ceramics and its effect on adhesion: A systematic review and meta-analysis

This review and meta-analysis assessed how chemical etching protocols impact zirconia-resin bonding, examining etchant composition, application conditions, and aging. Two reviewers searched MEDLINE, Embase, Scopus, and Web of Science for in vitro studies in English on chemical etching effects. Following PRISMA 2020 guidelines (PROSPERO: CRD42024543837), studies using acid-based etching on zirconia were included. The main focus was adhesion performance, with a qualitative analysis of factors like etchant type, exposure time and temperature, zirconia type, and primer or cement chemistry. The meta-analysis used mean differences with 95% CI under a random-effects model to explore how etchant strength affects bonding. Out of 1432 screened titles and 110 full texts, 58 studies on zirconia conditioned with weak or strong/mixed acids were included, with 41 providing data for meta-analysis. Etching significantly increased bond strength initially (MD = +2.41; CI = 2.31–2.51) and after aging (MD = +1.15; CI = 1.09–1.20), outperforming no treatment and showing competitive results against alumina air-abrasion, especially after aging. Silica coating yielded higher adhesion baseline and post-aging, but strong acids showed comparable performance in subgroup analyses. 10-MDP primers/cements were crucial for stability. Most studies showed a low bias risk. Although zirconia is not conventionally etchable, zirconia-specific acid formulations can chemically activate the surface and induce grain-boundary dissolution, enhancing bonding compared with untreated and alumina-abraded zirconia and approaching silica-coating performance under optimized conditions.