Enamel-like Polymer-Infiltrated Ceramic Materials for Dental Applications

Polymer-infiltrated ceramic network (PICN) composites are recognized for their mechanical properties, closely resembling natural tooth enamel. However, the low fracture toughness of current PICN materials limits their broader use. This study draws inspiration from the natural enamel rod-sheath architecture to develop bionic PICN composites with an enamel-like structure, enhancing their fracture toughness for dental restorations. By simulating the morphology and arrangement of enamel rods, 3 types of zirconia ceramic scaffolds were designed and manufactured by digital light processing technology, which featured a straight-rod structure, a gnarled-rod structure, or a natural rod distribution structure. The scaffolds were surface treated and resin infiltrated to obtain enamel-structured PICN material, wherein the infiltrated resin formed a rod-sheath structure. With VITA Enamic (VE) as control, the enamel-like composites were characterized in detail for their microstructure, flexural strength, fracture toughness, flexural modulus, friction and wear properties, adhesive properties, and cell compatibility. Results show that the PICN with the natural rod distribution structure had the highest flexural strength and fracture toughness among the 3 PICN composites, but there was no significant difference in their moduli. Its strength and modulus were slightly lower than those of VE, but its toughness was 7.0 ± 0.6 MPa·m^1/2, around 7 times that of VE. The fracture mode in the ceramic phase was mainly transgranular, while ductile fracturing of the resin phase contributed to toughening. Furthermore, it exhibited superior wear resistance when compared with VE and bovine enamel. After sandblasting and priming, its bond strength to bovine dentin was comparable to that of VE after standardized treatment. Cytotoxicity assays confirmed high cell viability and healthy morphology. Overall, these results indicate that the newly developed PICN composites offer significant improvement over current dental materials, making them promising candidates for bonded prosthetic applications.