ArticleBMC oral health2026
Wear resistance and fracture strength of BioFlx, zirconia and stainless steel crowns for primary molars after thermomechanical aging: an in vitro comparative study.
Article in BMC oral health, 2026. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Not yet cited in PubMed.
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Abstract
backgroundFull-coverage restorations are often required for primary molars with extensive carious destruction. Stainless steel crowns remain the long-standing reference, while prefabricated zirconia and polymer-based crowns have become tooth-colored alternatives. Direct comparisons under a single thermomechanical protocol, with separate wear and fracture cohorts, remain limited. This in vitro study quantified post-aging occlusal wear and compressive fracture load in four prefabricated crown systems for mandibular second primary molars.
methodsEighty crowns were tested, with 10 specimens per material for each outcome: two prefabricated zirconia crowns, one polymer-based crown, and one stainless steel crown. Identical resin dies were 3D-printed and all crowns were luted with glass-ionomer cement. All specimens underwent 10,000 thermal cycles between 5 °C and 55 °C. The wear cohort underwent 150,000 chewing cycles at 50 N and 1.2 Hz, and wear was scored on a 0-3 scale by two blinded examiners. The fracture cohort was loaded to failure. Wear scores were compared using Kruskal-Wallis and Dunn-Bonferroni tests; fracture loads were analyzed using one-way ANOVA and Tukey HSD.
resultsMean wear scores were 1.1 ± 0.3 for NuSmile, 1.2 ± 0.4 for ProfZr, 1.7 ± 0.4 for SSC, and 2.2 ± 0.4 for BioFlx. The zirconia groups did not differ significantly (p = 0.68), whereas both showed lower wear scores than SSC (p = 0.04) and BioFlx (p = 0.01). SSC also showed lower wear scores than BioFlx (p = 0.03). Mean fracture loads were 3148.4 ± 643.4 N for BioFlx, 2703.4 ± 243.1 N for SSC, 1076.1 ± 186.9 N for NuSmile, and 565.5 ± 159.6 N for ProfZr (p < 0.001). BioFlx and SSC did not differ significantly (p = 0.093), while both exceeded the zirconia groups (p < 0.001). NuSmile exceeded ProfZr (p = 0.043).
conclusionsUnder this in vitro model, zirconia crowns showed the lowest wear scores, whereas BioFlx and SSC showed the highest fracture loads. Each material demonstrated a distinct mechanical profile. Laboratory rankings alone should not guide clinical recommendations; long-term clinical studies are needed.
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