Hydroxyapatite (HA) is used as a biomaterial in orthopedic applications bec
ause it is similar in composition to bone mineral; however, carbonate apati
te (CHA) is closer in chemical composition to bone mineral because bone min
eral contains significant amounts of carbonate, yet there have been few rep
orts comparing biological responses to HA and CHA. It is generally agreed t
hat bone forms a bond of some kind to HA, and there is conflicting evidence
as to whether HA is resorbed in vivo or not. However, comparative reports
generally agree that beta-tricalcium phosphate (beta-TCP) is removed faster
than HA from an implant site by an undetermined combination of resorption
and/or dissolution. The work reported here attempts to provide the first di
rectly comparable subcutaneous dissolution data for dense sintered HA, beta
-TCP, and CHA in rats. The weight losses of HA, beta-TCP, and 3.2 wt % CHA
were approximately 60, 520, and 320 mg m(-2) day(-1), respectively. Histolo
gical sections did not show any evidence of giant cells, and all of the sam
ples were encapsulated with fibrous tissue. beta-TCP and (to a lesser degre
e) CHA were found to be resistant to dissolution around the edges of the sa
mple. An X-ray analysis did not indicate that any phase transformation had
occurred in the dissolution resistant region. (C) 2000 John Wiley & Sons, I
nc.