Mechanical and Chemical Surface Treatment of Zirconia Crowns for Orthodontic Metal Bracket Bonding - A Review of Shear Bond Strength

AIM: This review evaluates mechanical and chemical surface treatments to improve shear bond strength (SBS) between orthodontic metal brackets and zirconia crowns, aiming to identify protocols enhancing adhesion and clinical reliability. METHODS: A systematic search of PubMed and Google Scholar (2015–2025) identified in vitro studies reporting SBS (MPa) for zirconia–metal bracket interfaces following defined surface treatments. Thirty studies met inclusion criteria. Data were analysed by mechanical treatment (sandblasting [SB], grinding [GD]), chemical etching (hydrofluoric acid [HF], phosphoric acid [PP]), and primers (zirconia primer [ZP], Monobond [MB]). RESULTS: SB was the most studied mechanical method, generally yielding higher SBS than GD or HF, though outcomes varied by protocol and zirconia type. ZP and MB primers significantly increased SBS when combined with SB or GD; MB often matched or exceeded ZP performance, sometimes achieving comparable results alone. HF and PP alone showed inconsistent benefits unless combined with primers. SBS varied across zirconia types (3Y, 4Y, 5Y-TZP) and bracket materials, with composite and ceramic brackets exhibiting lower SBS than metal brackets. CONCLUSION: Optimal bonding to zirconia requires combined mechanical and chemical treatments. SB followed by primer application, particularly ZP or MB, yielded the most consistent results. MB demonstrated high versatility, performing well with or without SB. Outcomes depend on zirconia type and bracket material, underscoring the need for substrate-specific bonding protocols.