Chang Y L, Lew D, Park J B, Keller J C
School of Dentistry, National Yang-Ming University, Taipei, Taiwan.
J Oral Maxillofac Surg. 1999 Sep;57(9):1096-108; discussion 1108-9. doi: 10.1016/s0278-2391(99)90333-6.
The level of crystallinity in hydroxyapatite (HA) is thought to be responsible for its degradation in the physiologic milieu. The purpose of this study was to compare the in vivo bony response to HA coatings of varying levels of crystallinity and determine the optimum composition for promoting osseointegration.
Cylindrical implants of sand-blasted CP titanium and HA-coated titanium of 50% (low), 70% (medium), and 90% (high) crystallinity were inserted into the canine femur for 1, 4, 12, and 26 weeks. Morphometric analysis of undecalcified sections determined the percentage of bone contact with the implant surface. A pullout test was used to measure the interfacial attachment strength of the bone-implant interface. Scanning electron microscope (SEM) examination of the implant surface aided in identifying the failure mode. Coating thickness was measured under light microscopy to determine whether degradation occurred.
No significant differences could be found in the percentage of bone contact and interfacial attachment strength between the three types of HA-coated implants throughout the four implantation periods. A significantly higher percentage of bone contact on HA-coated implants than on uncoated titanium implants was noted at 4 weeks. (ANOVA, P<.05). HA-coated implants were also found to have significantly higher interfacial attachment strength than titanium implants at 4, 12, and 26 weeks. Coating thickness decreased gradually with time. The most noticeable reduction was found on the low-crystallinity coatings during the first 4 weeks. Failure of the bone-coating-implant complex occurred mostly within the coating or near the coating-implant interface.
HA coatings on metal implants enhance osseointegration in the early stage of bone healing and provide strong bone-bonding capability, although titanium implants had about the same level of bone contact in the later stage of healing. Crystallinity of HA coatings has no significant influence over the bone formation capacity and the bone bonding strength. However, an HA coating of higher crystallinity is more desirable in providing durability and maintaining osteoconductive properties.
人们认为羟基磷灰石（HA）的结晶度水平是其在生理环境中降解的原因。本研究的目的是比较不同结晶度水平的HA涂层在体内的骨反应，并确定促进骨整合的最佳成分。
将喷砂处理的纯钛圆柱形植入物以及结晶度为50%（低）、70%（中）和90%（高）的HA涂层钛植入物插入犬股骨中1、4、12和26周。对未脱钙切片进行形态计量分析，确定与植入物表面接触的骨的百分比。采用拔出试验测量骨-植入物界面的界面附着强度。通过扫描电子显微镜（SEM）检查植入物表面，以确定失效模式。在光学显微镜下测量涂层厚度，以确定是否发生降解。
在整个四个植入期内，三种HA涂层植入物之间的骨接触百分比和界面附着强度没有显著差异。在4周时，HA涂层植入物上的骨接触百分比显著高于未涂层的钛植入物。（方差分析，P<0.05）。在4、12和26周时，还发现HA涂层植入物的界面附着强度显著高于钛植入物。涂层厚度随时间逐渐减小。最明显的减少发生在低结晶度涂层的前4周。骨-涂层-植入物复合体的失效大多发生在涂层内或涂层-植入物界面附近。
金属植入物上的HA涂层在骨愈合早期增强了骨整合，并提供了强大的骨结合能力，尽管钛植入物在愈合后期的骨接触水平大致相同。HA涂层的结晶度对骨形成能力和骨结合强度没有显著影响。然而，较高结晶度的HA涂层在提供耐久性和维持骨传导性能方面更可取。
