| Research Abstract |
The conventional plasma-sprayed HA coatings have been associated with several problems including resorption, fracture, and fatigue. To increase the chemical stability of these coatings, the high crystalline HA coating has been recently developed. However, because the durability of the coatings is thought to be greatly affected by their structure, we investigated various coatings including an available high crystalline coating. The materials examined included Integrals (Sulzer Calcitek Inc.) as a typical HA coating that were produced in 1995 and 1998, MP-1 (Sulzer Calcitek Inc.) with high crystalline HA coating, Integrals that were autoclaved at 200℃ or 125℃ for 24 hr, and dense HA (Apaceram). These samples were examined by XRD, FTIR, SEM, and TEM analysis. The dense HA is composed of HA grains with a perfect crystalline structure and with almost no loss of OHィイD1-ィエD1 groups. TEM findings revealed that the HA grains have a size of approximately 0.4μm×0.6μm and are closely bounded to ea
… More
ch other. Integral 1998 (125℃・24hr) is crystallized except the small areas near the substrate. However, more and larger cracks and pores infiltrated by embedding resin compared to the unautoclaved Integrals are visible in the crystallized area. Crystallization occurred sporadically in the peripheral area of the remained amorphous phase. In the coating of Integral 98 (200℃・24hr), amorphous phase completely disappeared. Most of the crystallized area are composed of various crystals, approximately 50nm to 0.5μm. In such areas, there are many fine cracks infiltrated by embedding resin among crystals, in addition to large cracks. Furthermore, fine crystals of smaller than 50nm alternated to void spaces, exist in the sites corresponding to the lower atomic density layers in the amorphous phase of the Integral. Such layers are not so many in Integral 98 (200℃・24hr). However, Integral 1995 (200℃・24hr) has many layers of fine crystals. The structural differences between both ceramics originate in the differences between Integral 95 and Integral 98. Some crystals in the crystallized area show the crystal lattices with 8.2Å intervals and 1/3 lattices. However, continuation of these crystal lattices is interrupted and their direction changes slightly at narrow ranges. This means that the crystallinity of the crystallized area is low. The structure of MP-1 coating is almost same as that of Integral 95 (200℃・24hr). There are many layers of fine crystals like Integral 95 (200℃・24hr), in addition to wide areas composed of various crystals, approximately 50nm to 0.5μm. Large cracks, big pores, and fine cracks exist throughout the coating. Based on these results, we can conclude that the plasma-sprayed HA coating can be easily crystallized after autoclaving. However, this crystallization weakens the mechanical properties of the coating due to increased porosity and the formation of cracks. Whether or not the durability of the high crystalline HA coating is higher than that of the conventional coating should be judged by the results of their long-term clinical use. Less
|
