The investigation of the mechanical properties of resin-based restoration materials used in primary teeth

OBJECTIVE: This study aimed to compare, under in vitro conditions, the microhardness, microleakage, and microtensile bond strength of resin-based restorative materials currently used in pediatric dentistry on primary teeth. MATERIALS AND METHODS: In this in vitro study, four different restorative materials in compule form (Dyract XP, Neo Spectra ST HV, Filtek One Bulk Fill, SDR Plus) were applied to caries-free human primary second molars. Initial Vickers microhardness measurements were performed on a total of 32 specimens (eight per group), followed by repeated measurements after 10,000 thermal cycles. For the microleakage test, Class II cavities were prepared and restored in eight primary second molars per group, and the specimens were subjected to 500 thermal cycles. The specimens were immersed in 0.5% basic fuchsin for 24 hours and sectioned mesiodistally for microleakage evaluation. In the microtensile test, twenty sticks measuring 1×1 mm² were prepared for each of the four material groups, and fracture values were obtained using a testing machine. Microleakage and fracture analyses were performed with a stereomicroscope. RESULTS: A statistically significant decrease in microhardness values was observed in all materials after thermal cycling (p<0.05). Neo Spectra ST HV showed the highest microhardness before and after aging, while SDR Plus showed the lowest. The greatest decrease in hardness was observed in Neo Spectra ST HV, and the least in SDR Plus (p<0.05). In terms of bond strength, Neo Spectra ST HV showed the highest mean, while Dyract XP showed the lowest, and the difference between them was statistically significant (p<0.05). Adhesive failure was the most frequent failure type, with no significant difference between groups (p>0.05). While no difference was detected among groups in occlusal microleakage, significant differences were found in gingival microleakage; the highest leakage was observed in Dyract XP, and the lowest in SDR Plus and Filtek One Bulk Fill (p<0.05). CONCLUSION: After thermal cycling, the microhardness of all materials decreased. Neo Spectra ST HV exhibited the highest microhardness and bond strength. Gingival microleakage was lowest in SDR Plus and Filtek One Bulk Fill. The study demonstrates that the physicomechanical properties of restorative materials are decisive for clinical success.