The effect of three different calcium phosphate implant coatings on bone deposition and coating resorption: a long-term histological study in sheep

: The present study investigated the hypothesis that hydroxyapatite (HA), tricalcium phosphate (TCP), and a HA‐gel coated on endosseous titanium (Ti) implants by spark discharging (SD) and dip coating would achieve predictable osseointegration without evident bioresorption of the coatings on the long term. A costal sheep model was used for the implantation of the HA/SD, HA/TCP/SD, and HA‐gel/SD specimens, which were retrieved 6 and 12 months following implantation. HA and Ti coatings on implants obtained by conventional plasma spraying (HA/PS, Ti/PS) were used as controls. Microscopy showed that osseointegration was achieved from all types of implants. No evidence for bioresorption of the HA/SD, HA/TCP/SD, and HA‐gel/SD coatings was present but cohesive failure with disruption of the coating/implant interface was seen. A statistical analysis of the histomorphometrical data showed no time‐dependent effect, however. HA/PS coatings achieved significantly higher bone–implant contact (BIC) percentages of the total implant surface (toBIC) than the other types of coatings (P=0.01). If the BIC percentages were traced separately for implant portions placed into cortical and cancellous bone (coBIC and caBIC, respectively), detailed analysis showed that the caBIC values of HA‐gel/SD and HA/PS coatings were significantly higher than that of the other types of coatings (P=0.01). CaBIC values were highly correlated with toBIC values (P