Clinical significance of corrosion
Although titanium alloys have better corrosion properties
compared to Co-Cr and stainless steel (other implant
materials) their corrosion leads to dissolution of titanium
and other alloying elements like aluminum, vanadium,
niobium, molybdenum etc [67] causing localized to
generalized host response as illustrated in Figure 6. The
leached ions may induce potentially osteolytic cytokines
into tissues leading to implant loosening [67] and may
even cause severe allergic reactions or hypersensitivity
[67]. Incidence of tumors and malignancies has also been
reported in the literature but are few.
Fracture of Dental Implant
Fracture of dental implant/prostheses is a very rare
phenomenon more often associated with mechanical
function and previously use of screw preload systems toclamp flat to flat abutment implant junctions. They can
have serious clinical complications. Corrosion can
severely limit the fatigue strength and ultimate tensile
strength of the material leading to its mechanical failure.
As reported by Green[68], the end-osseous implant
superstructures, leached metal ions into the surrounding
tissues as an event to corrosion, leading to fatigue fracture,
following four years of functional loading into the oral
cavity. Yokoyama et al.[ 69] on the other hand investigated
the delayed fracture of titanium implant into the oral
environment owing to hydrogen embritlement and
environmentally induced cracking (EIC).
Bone loss and osteolysis
Olmedo, Fernandez and Guglidomotti [70] have
speculated the corrosion induced ionic leaching to be
responsible for peri-implantitis and treatment failure.
As already explained in Figure 6. the particles that are
leached as a result of corrosion process are
phagocytosized by macrophages (under the influence of
host response) and release mediators of inflammation in
the form of cytokines (host defense) [67] through the
inflammatory cascade which inhibit the production of
osteoblasts causing increased activity of the bone
destroying cells leading to peripheral osteolysis and
loosening of the implant.
Localized pain and inflammation (swelling)
Watterhehn et al .[71] have studied the effect of ionic
release as a result of corrosion, causing localized pain
and swelling with or without infection in the region of
implant insertion. Figure 7 shows the localized
inflammatory response to a freshly inserted implant in the
right lateral incisor region (12 region). [71]
Cytotoxic tissue response
Corrosion release of the several substitutional alloying
elements from various titanium alloys used in dentistry
have been widely known in literature. Watterhehn et al.
[71-76] have reported these metal ion release to be
associated with carcinogenic and mutagenic activity of
the oral cavity as shown in Figure 8.
Several studies have further shown that the cellular uptake
of hexavalent chromium is many folds greater than the
trivalent chromium ion and its increased uptake causes
reduction of the alkaline phosphatase activity of the
osteoblastic cells [77-79].