A mechanical and histological study of functionally graded hydroxyapatite implant coatings.

摘要

Ever since Dr. Branemark discovered that titanium was biocompatible with bone, extensive research has been done to improve the osseointegration of dental implants. As advances in medicine continue, the average life span of the population is ever increasing. Today, people of all ages are investing more money and time into dental treatment than ever before. Patients are becoming more educated on dental treatment options and expect the best treatment possible. As a result, the replacement of missing teeth with implants is becoming more and more commonplace in dental practices.; The purpose of the present study is to evaluate bone-implant interaction of functionally graded, thin film hydroxyapatite (HA) coatings in an animal model. The rationale for the graded coatings is such that they elicit different biological responses from different layers within the thin film (less than two microns). As such in this study, the graded coatings consist of an initial layering of crystalline HA coatings followed by the layering of an amorphous coating on the crystalline HA surface. Controls for this study are (a) plasma-sprayed HA, (b) amorphous HA, (c) crystalline HA, and (d) non-coated Titanium (Ti). The long-term goal is to improve the bone-implant interface leading to improved design and construction of implants and improved long term success. With this development it is expected that dental implants will be restored following shorter post-operative healing periods and patients will more quickly regain masticatory function resulting in the overall improvement of physical and mental health.; This study focused on mechanical and histological analysis of HA-coated and non-coated Titanium implants placed into the left femur of 40 male Sprague-Dawley rats. The rat was selected for this experiment because the specimen is affordable and historically proven to be a very good model for initial evaluation of the bone healing response to metal and metal coated implants. In vivo experimentation is preferred for these studies because bone wound healing is a complex process requiring the interaction of many cell types and factors. These conditions can not presently be predictably duplicated with in vitro experimentation.; In this study, two implants were placed into the left femur of each rat. At two time intervals (three weeks and nine weeks after implantation) 20 rats were euthanized and the femur containing the implants excised. A total of 40 implants were yielded at each time point. Since there were five groups (titanium, plasma sprayed HA, amorphous HA, crystalline HA and graded HA), there were eight implants per group per time point (40/5 = 8). Of these eight implants per time point per group, six were used for mechanical testing and two for histological evaluation. To evaluate the interfacial strength of the implants at the bone-implant interface, push-out test were performed. The evaluation of the bone response to implant was done using histological analysis.; At three weeks following implantation, there was no significant difference in the interfacial strength between the different implants. The interfacial strength had increased in all groups by nine weeks. The plasma sprayed HA implants had the greater interfacial strength followed by the graded HA, crystalline HA, amorphous HA and titanium implants. At three weeks post implantation, the presence of connective tissue at the tissue-implant interface was noted for all implant groups tested. By nine weeks post implantation, all HA coated implants exhibited more bone formation at the bone-implant interface when compared to the non-coated Ti implants. The greatest response was seen in the plasma sprayed implants. A similar response was seen between the graded and crystalline as well as the amorphous and pure titanium. This study suggested that graded HA is a viable option for implant coatings.