Retention of Bioflx, Zirconia, and Stainless Steel crowns using two different luting cements in primary molars: an in vitro study

BACKGROUND: Different crown types are used for the full-coverage restoration of primary teeth with extensive caries. Bioflx crowns are hybrid polymer-resin crowns designed to combine the benefits of Stainless Steel and Zirconia. The longevity and clinical efficacy of dental restorations are significantly affected by crown retention. We aim to assess the retention of Bioflx, Zirconia, and Stainless Steel crowns using two different luting materials. METHODS: Fifty-four (n = 54) freshly extracted mandibular second primary molars were divided into three main groups (n = 18): Bioflx crowns, Zirconia crowns, and Stainless Steel crowns (SSCs). Each group was further subdivided into two subgroups (n = 9), using either Conventional Glass Ionomer luting cement (GIC) or Resin Modified Glass Ionomer luting cement (RMGIC). A retention test was performed to determine the retentive force required for crown removal after the samples underwent 2,000 cycles of thermocycling. A stereo light microscope was used to examine the debonding failure. Data were analysed using two-way analysis of variance (ANOVA) and Pearson's chi-square test. RESULTS: Stainless Steel crowns exhibited the highest retention in both subgroups (GIC = 307.44 ± 53.58 N, RMGIC = 324.11 ± 52.04 N). Bioflx crowns outperformed Zirconia crowns (Bioflx: GIC = 138.11 ± 30.87 N, RMGIC = 218.11 ± 34.61 N; Zirconia: GIC = 35.50 ± 5.14 N, RMGIC = 131.78 ± 11.91 N). All differences between the GIC and RMGIC subgroups were significant (p < 0.001), except for Stainless Steel crowns (p = 0.5). RMGIC had greater retention values than GIC in all groups, and the difference was significant (p < 0.001), except for the SCCs group (p = 0.5). CONCLUSIONS: Stainless Steel crowns showed the highest retention across all tested luting cements, followed by Bioflx crowns, which exhibited superior retention compared with Zirconia crowns. RMGIC showed superior retention compared with GIC.