Adhesion to Zirconia: An umbrella review

Background The zirconia polycrystalline nature avoids forming a permanent bond with the tooth structure. Thus, creating a solid bond between zirconia and tooth is challenging. The best protocol for zirconia adhesion is unknown due to reporting various data in the previous studies. This Umbrella study compares several systematic/meta-analysis reviews related to the adhesion to zirconia. Methods Electronic databases of PubMed, Medline, Scopus, Cochrane Library, and Google Scholar were searched until December 2021. This procedure was performed considering language restrictions based on PRISMA guidelines. According to the PICO framework, the study question was "Which method of cement usage has the best adhesion to zirconia over time?". The inclusion criteria were all systematic/meta-analysis review articles that compared zirconia for adhesion. In this case, two competent researchers assessed the inclusion and exclusion criteria and the risk of bias for the selected studies. Also, a third one helped resolve their ambiguities. Results The literature survey showed that four systematic/meta-analysis reviews evaluated adhesion to zirconia. A total of 191 articles published during 1998–2020 were considered for the selected systematic studies. After eliminating 28 duplicates, the number of 163 studies remained. These articles applied various surface conditioning methods, including air abrasion protocols and an adhesive promoter. Conclusion Systematic studies showed increased zirconia adhesion after Mechano-chemical pre-treatments and MDP-based resin cement . Also, surface contamination and Artificial aging reduced adhesion factors for zirconia.