A HISTOMORPHOMETRIC STUDY ON OSTEOCONDUCTION AND OSSEOINTEGRATION OF TITANIUM-ALLOY WITH AND WITHOUT PLASMA-SPRAYED HYDROXYAPATITE COATING USING BACKSCATTERED ELECTRON IMAGES

A quantitative evaluation, at the scanning electron microscopic (SEM) level, was made of the osteoconduction and osseointegration of Ti-6Al-4V implants with and without plasma-sprayed hydroxyapatite coatings (HACs). By employing the Chinese Coin implant model in the lateral femora cortices of canines, different biological properties between HA-coated and uncoated Ti-6Al-4V implants could be compared in one specimen. After 4, 6 and 12 weeks, the implants with surrounding bone were removed and assessed histologically in undecalcified sections under SEM. The osteoconductivity and the ability of osseointegration of implants were histomorphometrically analysed from back-scattered electron images (BEIs) and represented in terms of the new bone healing index (NBHI) and apposition index (AI), respectively. Throughout all implant periods, the HA-coated Ti-6Al-4V implants revealed higher NBHI than the uncoated ones, it appearing that the HA-coated Ti-6Al-4V implant was more osteoconductive than the Ti-6Al-4V was. For HA-coated implant, the evidence of direct bone-to-HAC contact was observed, However, at the bone/Ti-6Al-4V interface, there intervened a fibrous membrane without calcium content, indicating that the Ti-6Al-4V implant was not osseointegrated in the SEM field of view. The maximum value of AI was reached 6 weeks after implantation for HA-coated implant, implying that the HAC had a stimulating influence on bone apposition within 6 weeks of healing. The signs of partial dissolution of HACs within the remodelling canals were evident at the HAC-bone interface 12 weeks after implantation, accounting for the slight decrease in NBHI and the obvious decrease in AI for HAC implant.