In vivo tensile testing of fluorapatite and hydroxylapatite plasma-sprayed coatings

A tensile test has been developed to test bioactive coating materials. Hydroxylapatite (HA) and fluorapatite (FA) coatings with various roughnesses were tested using sandblasted titanium (Ti) as a control material. Twelve goats received 7 implants each for 6 (2 goats), 12 (5), and 24 (4) week implantation periods. After 12 weeks the mean tensile strength values were highest for polished hydroxylapatite (HAP) followed by HA > FAP (polished fluorapatite) > FA > Ti, and hydroxylapatite type coatings were found to exhibit significantly higher values than fluorapatite type coatings or titanium implants. After 24 weeks no statistically significant differences could be found between any of the implant types. The order of the mean strength values was now HAP > HA > FA > FAP > Ti. Fracture always occurred between the coating and titanium if bone contact had been established. In conclusion, it is suggested that results from different types of test methods cannot be used to compare different types of bioactive coatings.