Stainless-steel crowns (SSCs) are the most durable restorative option for deciduous teeth, although they are unsightly. However, prefabricated zirconia crowns (ZCs) look more pleasant but require substantial dental preparation. Recently, BioFlx crowns have been introduced as a white-colored alternative to SSCs, providing both flexibility and aesthetics. However, clinical trials have not assessed their oral cavity load-bearing capacity and suitability for repairing severely decayed deciduous teeth. To address this gap, the present study compared the shear stresses generated by BioFlx crowns, ZCs and the gold standard SSCs when restoring extensively decayed deciduous teeth using finite element analysis (FEA). The restoration was represented by three finite element models with the identical tooth structure: BioFlx, SSC and ZC, constructed using a Trios 3 scanner and exported for analysis using ANSYS. The FEA results showed that ZCs had the maximum axial static load stress at 40.91 MPa, followed by SSCs at 39.331 MPa and BioFlx at 14.009 MPa. ZCs produced 2.932 MPa at 45◦, SSCs 3.005 MPa and BioFlx 0.3227 MPa. ZCs had a maximum primary stress of 3.055 MPa at 0◦, while SSCs and BioFlx had 2.3 and 0.3017 MPa, respectively. Deformation analysis revealed that under a load direction of 90◦, SSCs deformed by 5.978 mm, ZCs by 5.971 mm and BioFlx by 5.971 mm. When the load was applied at an angle of 45◦, SSCs deformed by 6.527 mm, ZCs by 5.444 mm and BioFlx by 5.447 mm. SSCs deformed 5.452 mm at 0◦ load, while ZCs and BioFlx deformed 6.472 and 6.479 mm, respectively. Based on these findings, BioFlx crowns, in combination with the underlying core material, can withstand maximum loads, suggesting that a mutilated primary posterior tooth restored with glass ionomer cement and a BioFlx crown may be a viable option for frequent clinical use.