Hydroxyapatite‐based dental inserts: Microstructure, mechanical properties, bonding efficiency and fracture resistance of molars with occlusal restorations

Abstract

AbstractThis study aimed to (1) comparatively analyze properties of Sr‐ and Mg‐substituted hydroxyapatite (HAP)‐based dental inserts; (2) evaluate insert bonding to restorative materials, and (3) evaluate the effect of doped HAP inserts on fracture resistance (FR) of human molars with large occlusal restorations. By ion‐doping with Sr or Mg, 3 insert types were obtained and characterized using XRD, SEM, Vickers hardness and fracture toughness. Shear bond strength (SBS) was determined between acid etched or unetched inserts and following materials: Maxcem cement (Kerr); Filtek Z250 (3M) bonded with Single Bond Universal (SBU; 3M) or Clearfil Universal (Cf; Kuraray). Modified Class I cavities were prepared in 16 intact molars and restored using insert + composite or composite only (control) (n = 8/group). FR of restored molars was determined by static load until fracture upon thermal cycling. Fracture toughness was similar between Sr/Mg‐doped inserts (0.94–1.04 MPam−1/2 p = .429). Mg‐doped inserts showed greater hardness (range 4.78–5.15 GPa) than Sr6 inserts (3.74 ± 0.31 GPa; p < .05). SBS for SBU and Cf adhesives (range 7.19–15.93 MPa) was higher than for Maxcem (range 3.07–5.95 MPa) (p < .05). There was no significant difference in FR between molars restored with insert‐containing and control restorations (3.00 ± 0.30 kN and 3.22 ± 0.42 kN, respectively; p > .05). HAP‐based inserts doped with Mg/Sr had different composition and mechanical properties. Adhesive bonding to inserts resulted in greater bond strength than cementation, which may be improved by insert acid‐etching. Ion‐doped HAP inserts did not affect FR of restored molars. In conclusion, HAP‐based dental inserts may potentially replace dentin in large cavities, without affecting fracture resistance of restored teeth.