Are zirconia crowns the superior choice when restoring primary posterior molars?

Data sources: Electronic database searches were carried out using predefined search terms using Embase, Google Scholar, Medline, The Cochrane Library, The Cochrane Central Register of Controlled Trials and Latin American and Caribbean Health Sciences Literature. The Trip medical database was also used to identify randomised control trials investigating stainless steel and zirconia crowns. Studies published from 1 January 2000 until 6 June 2021 were included, and reference lists of included studies analysed to ensure data saturation along with grey literature searches.Study selection: Inclusion criteria included research published in English only, randomised control trials investigating the clinical and radiographic effectiveness of zirconia crowns compared to stainless steel crowns, the rehabilitation of pulp-treated posterior primary teeth and randomised control trials with children in good health.Expert opinion, case reports and reviews were excluded. Studies with a follow-up period of less than 12 months, studies including children with special care requirements or non-compliant children were also excluded.Data extraction and synthesis: Two reviewers (AKP, VKC) were involved with the primary search of abstracts and titles independently; both reviewers were involved in full text assessment. Disagreements were resolved by a third reviewer (NRV). The study characteristics, number of teeth evaluated, follow-up duration, type of zirconia and stainless steel crowns, outcome assessed and outcome results were extracted.Extracted data was analysed using Review Manager, Version 5.3 and dichotomous data was summarised as risk ratios with 95% confidence intervals. Continuous data was summarised as mean difference. Heterogeneity was summarised by I2 scores and a random-effects model and Mantel-Haenszel statistical test was used.Results: From the initial 641 studies screened, six studies met the inclusion criteria for the systematic review and were included for analysis. Risk of bias assessment for the included studies was graded as 'low' for three of the six included studies and 'some concern' for the remaining three studies. This was based upon allocation concealment in the randomised control trials.Clinical failures were observed in 63 of 497 events. Rehabilitation with zirconia crowns may result in less clinical failures than stainless steel crowns: risk ratio 0.48; 95% CI (0.15-1.52) p = 0.021. Gingival health was better with zirconia rather than stainless steel crowns: risk ratio 0.32; 95% CI (-0.42-0.23) p <0.001.Conclusions: Primary posterior teeth restored with zirconia crowns may have 52% less risk of experiencing clinical failures than teeth with stainless steel crowns and better gingival health than stainless steel crowns, observed after 12 months. However, due to the low quality of included studies and 'very low' grade rating of the evidence provided, further clinical trials are required to provide further evidence on the clinical and radiographic effectiveness of zirconia and stainless steel crowns.