Sintered dental inserts based on ion-doped hydroxyapatite as dentin substitutes

Abstract

The main drawback of resin-based composites (RBCs) widely used in restorative dentistry presents their volumetric shrinkage during the polymerization that can lead to clinical failures of restorations such asmarginal gap formation, bacterial microleakage, fractures, and postoperative sensitivity. To address this problem, sintered hydroxyapatite based dental inserts were introduced in the central part of molar teethrestoration, due to chemical and structural similarities with inorganic part of teeth. The fabrication of bioceramic dental inserts based on HAP doped with Sr and/or Mg ions presents a way to obtain a dentin substitute that has even greater resemblance to the biological apatite in dentin. However, ion-substitutions arise lattice strain that can have a signifi cant impact on phase composition and properties of apatite materials, especially upon thermal treatment, which could be determining for their further application. The aims of this study were to comparatively analyze physico-chemical and mechanical properties of the Sr- or Mg-, and Sr+Mg substituted HAP based dental inserts; and evaluate their possible application as dentinsubstitutes. Mono (5 mol. % Sr or Mg ions) and binary- (3 mol.% Sr and 3 mol.% Mg ions) doped HAP nanoparticles were hydrothermally obtained, isostatically pressed into compacts and eventually sintered at 1200°C to obtain dental inserts. The inserts are meant to be adhered to the cavity walls as well as topped with resin composite for sealing and esthetic purposes. Bonding ability of obtained inserts with different commercialrestorative materials, as well as fracture resistance of human molars restored with doped HAP inserts was investigated. Ion doping was found to infl uence phase compositions of sintered inserts, leading to different mechanical properties and etching behavior of inserts. All inserts showed fracture toughness and bonding ability torestorative materials similar to dentin, while the highest bond strength was obtained for HAP insert doped with 5 mol% Mg (Mg-HAP) bonded to. Fracture resistance of human molars restored with Mg-HAP wasshown to be similar to the fracture resistance of the conventionally restored molars. In conclusion the obtained hydroxyapatite based dental inserts present promising materials for application as dentin substitutes inrestorative dentistry, which have the potential to extend the durability of the restoration.