Hydroxyapatite and their use as coatings in dental implants: A review

At present, no standard manufacturing guideline exists for depositing hydro xyapatite (HA) on implant surfaces. Although animal and in vitro studies ha ve reported on the benefits of using HA-coated implants as well as the risk s of dissolution, these short-term studies did not demonstrate that the dis solution of the HA coating leads to a loss of implants. In addition, many i n vivo and clinical studies did not include the chemical and structural cha racterization of the coatings, and thus comparisons between studies are dif ficult. In the clinics, the recommendation is that HA-coated screw implants be used for the anterior maxilla and posterior mandible where the bone depth excee ds 10 mm and when the cortical layer is thinner and spongiosia is less dens e. In the posterior maxilla or when the cortical layer is very thin with lo w density, the use of HA-coated cylindrical implants is recommended. Howeve r, there are concerns for using IIA-coated implants. The clinician needs to take into consideration the enhanced bacterial susceptibility of IIA coati ngs compared with titanium implants. In addition, the clinician needs to co nsider the possible failure of FIA coatings as a result of coating-substrat e interfacial fracture. Finally, besides the surgical skills, it is also im portant that the clinical investigators be well versed with the materials c haracterization needed for HA-coated implants, the problems associated with the current HA coatings, and the indications for use. In addition, the cor relation between well characterized coatings and their effect on bone forma tion rate and long-term implant success, coating-implant interfacial streng th, and alternative superior coating process need to be investigated furthe r.