The mechanical and self-mineralized properties of nanohybrid composite resins used for the dental restoration of class V caries are investigated. The nanorod hydroxyapatite (Nr-HA) hybrid and the microspherical granular dicalcium phosphate anhydrate (DCPA) after silanization were mixed and used as fillers in different kinds of composite resins (abbreviated as DCPA, DCPA+5Nr-HA, and DCPA+10Nr-HA). Their composite strengths were measured via 3-point flexure. Their properties were characterized from environmental samples after water immersion for 24 h and exposure to thermal fatigue between 5 and 55 °C for 600 and 2400 cycles. The resin reinforced with high amounts of Nr-HA (DCPA+10Nr-HA) showed a significant increase in mineralization of the sample surfaces, which consequently enhanced microhardness. The presence of Nr-HA also increased the residual energy of samples during preparation and enhanced their capacity to reprecipitate after immersion and through thermal fatigue. However, the presence of Nr-HA also resulted in high ductility and early failure of the sample, especially in the reinforced group with the highest amount of Nr-HA (DCPA+10Nr-HA). The appropriate additive Nr-HA (DCPA+5Nr-HA) balanced the properties with less difference of strength and residual energy compared with the DCPA group. The additive showed superior capability in enhancing the release of ions and initiating mineralization after immersion with thermal fatigue in vitro. This newly developed composite resin may provide an excellent combination of stress bearing, improved residual energy before the sample fracture, enhanced mineralization capacity, and improved caries-inhibiting capabilities.
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