No abstract

The excellent corrosion resistance of titanium and its alloys to physiological chloride solutions is well documented. Occasionally, however, titanium compounds have been found in tissue adjacent to titanium implants. These findings were reported to be unrelated to wear processes, suggesting that either the metal or its passive film was dissolving. The unpredictability of these findings further suggests that preimplantation surface treatments and/or variations in the physiological environment may be factors. T o determine a mechanism by which titanium can be released from an implant, a study was initiated which employed electrochemical techniques, Auger electron spectroscopy (AES), and replica transmission electron microscopy (RTEM). Specifically, the purpose was t o characterize the passive film on titanium and Ti-6A1-4V, and to determine if there is dissolution of the film or metal in a static unstressed state. Passive film behavior of commercially pure titanium, Ti-6A1-4V and nitrided Ti-6A1-4V was studied by anodic polarization and pulse potentiostatic capacitance techniques in Ringer's solution at 37OC with and without physiological additions of several amino acids. Solution Poz, pH, and specimen surface finish were varied to include all probable in v i m conditions. In all tests, potentiostatic anodic polarization of each material yielded potential-current density curves which showed passivity over the entire experimental range. This range greatly exceeded the oxygen-reduction reversible electrode potential. No breakdown potentials were observed. The passive current density was not significantly affected by varying the experimental parameters. AES as well as charge and capacitance measurements showed that the electtochemical reaction which occurred was growth of the passive film. The data indicated that the effective electrochemical area of each specimen was less than its geometrical area, and was dependent on both pH and surface finish. The findings of this study showed that, under static conditions, titanium and Ti-6A1-4V should withstand exposure to physiological chloride solutions a t body temperature indefinitely. Furthermore, the findings

The tissue-implant interfaces of functional and non-functional endosseous dental implants were compared histologically for up to one year post-operatively. Nonmineralized connective tissue zones (a "fibrous capsule") existed in all functional interfaces. Direct, or nearly direct, bone apposition to implants occurred in non-functional interfaces. The origin of this result and its significance in dental implantology is discussed.

A microelectrode technique has been developed to enable the study of stress-generated potentials (SGP) in bone to a spatial resolution of 5 micrometers. The technique has been used to measure the electrical potentials as a function of bone micromorphology in four-point bending. Electric fields ranging from 30 to 10(3) times greater than is measured by conventional macroscopic methods have been discovered at the Haversian canals for human and bovine cortical bone. The amplitude and direction of the electric field in the osteons depend specifically upon the amplitude and the sign (i.e., compression or tension) of the stress. The implications of this finding with regard to the origin of SGP and their possible physiological significance are considered.

SummaryMeasurements of Haversian osteons in human tibia1 cortical bone sperimens from seven donors demonstrate that, for this study: 1) Haversian osteonsl area, as a proportion of cross-sectional area of cortical bone, increases with the age of the donor, whether or not the area of the central Haversian canal is taken into account.2 ) Haversian canal area, as a proportion of cross-sectional area of cortical bone, either remains the same or increases with the age of the donor.3) The number of osteons present per u n i t cross-sectional area has no observable age dependence. 4)The percent inorganic content or cortical bone increases with the age of the donor.Optical studies on thin sections of cortical bone, utilizing crossed polarizing filters, suggest that the classification of osteons as light, dark and intermediate, as proposed by others (Anat. Rec., 161, 377 (1968)) is incorrect in that only one general type of Haversian osteon structure was detected in this study.