Ogiso M, Yamashita Y, Matsumoto T
Department of Fixed Prosthodontics, Faculty of Dentistry, Tokyo Medical and Dental University, Japan.
J Biomed Mater Res. 1998 Jan;39(1):23-31. doi: 10.1002/(sici)1097-4636(199801)39:1<23::aid-jbm4>3.0.co;2-k.
In our previous comparative push-out test of HA-coated implants and dense HA implants in dog bone, the ratio of the push-out value of the HA-coated implant to that of the dense HA implant decreased with time due to weakening of the HA coating as compared to the dense, more durable HA. The aim of this study was to investigate by histological examination of HA-coated implants in dog bone, using TEM, how this weakening of the HA coating occurs. The HA coating before implantation is composed of an amorphous glassy phase and a crystal phase scattered within the glassy phase. After implantation, the crystal phase remained almost unchanged. However, in the glassy phase, crystallization occurred and progressed with time. By 3 weeks after implantation, this crystallization already had started in the surface portion of the HA coating where it was covered by bone and also where it still touched the soft tissue. By 10 months, the crystallization had progressed to the deeper portion of the HA coating and had expanded to most of the glassy phase except for the narrow portions along the substrate-coating interface. These findings suggest that a progression of crystallization in the glassy phase causes stress accumulation within the HA coating, especially in the interface between the HA coating and the substrate, and that this stress accumulation results in a weakening of the HA-coated implant.
在我们之前对狗骨中羟基磷灰石（HA）涂层植入物和致密HA植入物进行的比较推出试验中，与致密、更耐用的HA相比，由于HA涂层的弱化，HA涂层植入物的推出值与致密HA植入物的推出值之比随时间下降。本研究的目的是通过使用透射电子显微镜（TEM）对狗骨中的HA涂层植入物进行组织学检查，来研究HA涂层的这种弱化是如何发生的。植入前的HA涂层由非晶玻璃相和分散在玻璃相中的晶相组成。植入后，晶相几乎保持不变。然而，在玻璃相中，结晶随着时间的推移而发生并进展。植入后3周，这种结晶已经在HA涂层被骨覆盖的表面部分以及仍与软组织接触的部分开始。到10个月时，结晶已经进展到HA涂层的更深部分，并扩展到除了沿基底-涂层界面的狭窄部分之外的大部分玻璃相。这些发现表明，玻璃相中结晶的进展会导致HA涂层内尤其是HA涂层与基底之间的界面处的应力积累，并且这种应力积累会导致HA涂层植入物的弱化。
