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Background <p>Full-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.</p> Methods <p>Eighty 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&#xa0;°C and 55&#xa0;°C. The wear cohort underwent 150,000 chewing cycles at 50 N and 1.2&#xa0;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.</p> Results <p>Mean 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 (<i>p</i> = 0.68), whereas both showed lower wear scores than SSC (<i>p</i> = 0.04) and BioFlx (<i>p</i> = 0.01). SSC also showed lower wear scores than BioFlx (<i>p</i> = 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 (<i>p</i> &lt; 0.001). BioFlx and SSC did not differ significantly (<i>p</i> = 0.093), while both exceeded the zirconia groups (<i>p</i> &lt; 0.001). NuSmile exceeded ProfZr (<i>p</i> = 0.043).</p> Conclusions <p>Under 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.</p>

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Wear resistance and fracture strength of BioFlx, zirconia and stainless steel crowns for primary molars after thermomechanical aging: an in vitro comparative study

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月23日

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  • Alp Abidin Ateşçi,
  • Dilek Özge Yılmaz,
  • Berk Gergit,
  • Münevver Çoruh Kılıç,
  • Hüseyin Şimşek

摘要

Background

Full-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.

Methods

Eighty 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.

Results

Mean 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).

Conclusions

Under 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.