First-principles study on Sr-doped hydroxyapatite as a biocompatible filler for photo-cured dental composites

Abstract

The first-principles calculations based on density functional theory with generalized gradient approximation were carried out to investigate the fundamental features of hydroxyapatite, the primary constituent of human bone and tooth, for use in light-curable dental composites. Moreover, the influence of strontium incorporation into hydroxyapatite on structural, electronic and optical properties of hydroxyapatite was comprehensively studied while we believe this substitution can promote radiopacity and remineralization ability of apatite. After geometry optimization, the computed structural parameters are found to yield a satisfactory agreement with the reported experimental results indicating the accuracy of the calculations. The elastic characteristics demonstrate that both hexagonal apatites possess higher Young’s modulus and Poisson’s ratio compared silica glass which is known as traditional filler used in dental composites. The analysis of the electronic density of states reveals that some variation in macroscopic mechanical properties can arise from difference between d state energy of calcium and strontium elements. Moreover, the origins of optical features affecting the curing depth of composite have been discussed in terms of the dielectric function and refractive index. The weak energy loss in the range of 3–3.5 eV demonstrates that these biocompatible fillers can provide an increased curing depth when are used in a UV-LED cured restorative dental materials.