The morphological effect of calcium phosphates as reinforcement in methacrylate-based dental composite resins on mechanical strength through thermal cycling

Abstract The rationale of this study was based on the hypothesis that mechanical strength and ion release in dental composite resins containing 50 wt% calcium phosphate fillers, including spherical micrometer-scale modified dicalcium phosphate anhydrous (Ms-DCPA) and synthetic micro- and nanometer-scale rod-like hydroxyapatite (HA) (respectively abbreviated as Mr-HA and Nr-HA), led to a superior ability to re-precipitate. The reinforced resin properties were measured before and after immersion for 24 h and further exposure to thermal fatigue between 5 and 55 °C for 600 and 2400 cycles. The groups of resins reinforced with Mr-HA and Nr-HA showed a significant increase in their microhardness and ability to re-precipitate after immersion and through thermal fatigue. The 50% Mr-HA sample had the highest anti-decline ability for flexural strength and modulus after thermal fatigue among all three types of fillers, whereas the Nr-HA sample had the lowest flexural strength and modulus. Filler morphologies that had a higher aspect ratio of length to width had better re-mineralization ability after immersion, but the Mr-HA sample showed the advantage of avoiding the agglomeration problems that occurred in the case of Nr-HA. Micro-rod HA-reinforced composite resins have superior potential applications in dental caries restoration.