COMPARISON OF THE TISSUE REACTION TO IMPLANTS MADE OF A BETA-TITANIUMALLOY AND PURE TITANIUM - EXPERIMENTAL-STUDY ON RABBITS

Commercially pure titanium (Ti cp) has been used successfully as an im plant material in fracture fixation devices for many years. Ti cp is c omparatively soft, but the mechanical properties, such as strength and ductility, can be adjusted by different means over a wide range. Tita nium changes its crystal structure from a hexagonal (alpha) phase to t he cubic (beta) phase at about 882 degrees C. Cubic titanium has the a dvantage of being very malleable (ductile), but in order to stabilize it at room temperature, additions of suitable alloying elements are re quired. In this study the soft tissue reaction to implants made from a beta titanium alloy (Ti-Mo-Zr-Al) with four different surface treatme nts is evaluated. The results are compared to Ti cp implants having th e same surface conditions, and to electropolished stainless steel plat es as controls. A minimum of four small plates of each group were impl anted in rabbit tibiae for 3 months. Histomorphometric results show th at the thickness of the soft tissue reaction layer, and the number of blood vessels, connective tissue cells (fibroblasts, fibrocytes), lymp hocytes, and foreign body giant cells are not significantly different between beta titanium and Ti cp plates. For stainless steel plates the soft tissue reaction layer is thicker, and the numbers of macrophages and connective tissue cells are higher. Excellent biocompatibility wa s observed for this beta titanium alloy. The mechanical properties of this alloy surpass those of Ti cp, and because of the good tissue tole rance, this material seems to be advantageous and should enter into cl inical testing.