In vitro evaluation of compressive strength and microleakage of stainless steel and BioFLX crowns used for restoring primary molar teeth

Background: The restoration of primary molar teeth requires crowns with adequate mechanical strength and marginal sealing ability. This in vitro study aimed to compare the compressive strength and microleakage of stainless-steel crowns (SSC) and BioFLX crowns used for restoring primary molar teeth. Methods: Forty-eight typodont primary mandibular second molar teeth were divided into two groups (n = 24) according to crown type: SSC and BioFLX. Each group was further subdivided into compressive strength and microleakage subgroups (n = 12). All teeth were prepared using standardized protocols and cemented with resin-modified glass ionomer cement. After thermocycling for 10,000 cycles between 5 ◦C and 55 ◦C, compressive strength was measured using a universal testing machine. Microleakage was evaluated by 0.5%basic fuchsin dye penetration under 25× magnification using a dental microscope, and measurements were performed with ImageJ software. Data were analyzed using independent t-tests with a significance level set at p < 0.05. Results: SSC crowns exhibited significantly higher compressive strength (56.07 ± 10.48 MPa) than BioFLX crowns (46.17 ± 10.57 MPa) (p = 0.032). Microleakage analysis revealed lower dye penetration in SSCs (11.65 ± 0.53%) compared with BioFLX crowns (12.56± 0.88%) (p = 0.006). Conclusions: Although stainless-steel crowns demonstrated superior compressive strength and marginal seal, the microleakage values of BioFLX crowns were within ranges reported for esthetic pediatric crowns with documented clinical success. Considering their comparable dye-penetration percentages and ability to withstand forces exceeding typical pediatric masticatory loads, BioFLX crowns may be regarded as a clinically acceptable esthetic alternative for the restoration of primary molars under standardized in vitro conditions.

Stainless-steel crown; BioFLX crown; Primary molar; Compressive strength; Microleakage; Pediatric dentistry

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