Biomaterials, Dental Materials, and Device Retrieval and Analysis - Biomaterials Science: An Integrated Clinical and Engineering Approach - page 130

shown that bone integration does not exist for chromium oxide on stainless
steel and is limited for chromium oxides on cobalt alloys. Oxides on titanium
and alloys with and without ion implantation as well as aluminum and zir-
conium oxide ceramics, carbons, and calcium phosphates have shown bone
integration for a wide range of dental implant designs. Several of those bio-
materials have also demonstrated bone integration along very smooth sur-
faces such as aluminum oxide (sapphire), although current systems now are
finished with various shapes and sizes of nano-micro-topographies. Claims
exist about enhanced rates of healing with various surface conditions. Our
overall evaluations indicate most metallic and ceramic biomaterials exhibit
bone integration after several weeks with maturity within a year. Overall, the
magnitudes of bone-to-implant contact (BIC) range from about 20 to above
80% of the implant body section surface areas [24-26]. Our studies support
high or magnitudes of BIC for calcium phosphate-coated (treated) surfaces;
however, our results and those of other controlled studies are inadequate
for correlation with clinical survival evaluations. One recent finding is that
calcium phosphate coatings and post coating loss surfaces of cast cobalt alloy
show bone integration after decades of in vivo function. This is called the
custom osseous integrated implant (COII) system.
Biodegradation phenomena, primarily corrosion of metallics, have been
an issue within some dental implant constructs, with several analyses
initiating in the 1970s [27-37]. Subsequent studies provided guidelines
on “acceptable combinations” from an electrochemical corrosion evalua-
tion viewpoint. These data were expanded considerably, and recent stud-
ies now include alloy combinations tested under electrochemical (galvanic
coupling) conditions. As a general guide (detailed information now avail-
able from product manufacturers), groupings of “acceptable and possible
unacceptable” electrochemical combinations of metallics are summarized
in Figures 5.4 and 5.5. Prior overviews have shown that high noble dental
alloys (Au, Pt, Pd, Ir) when combined (coupled) with titanium alloys and
cobalt alloys (Co-Cr-Mo) do not result in significant corrosion magnitudes
of either part. However, some adverse conditions have been associated with
combined titanium alloy and cobalt alloy compared with stainless steels,
nonprecious (nickel-chromium) alloys (especially with Be), copper alloys,
and amalgams.
A number of patient, technology, and biomaterial issues have been noted
related to biomechanical fractures of intraoral prosthesis (primarily con-
nectors and cantilevers), abutment components, and body sections of dental
implants [38, 39]. Examples of such mechanisms usually present structural
fatigue often caused by surface irregularities, inadequate structural dimen-
sions, and/or fretting and corrosion processes. The extensive use of unal-
loyed titanium at grade I and II property magnitudes were shown to be
at increased risk because of lower strength. The alloys and higher grades
of titanium (III, IV) have shown limited numbers of biomechanical frac-
tures. In some situations, such as the early root-form designs made from