Hendrik Terheyden and Maxime Champy

The early plating systems were made of stainless steel (Spiessl, 1969; Becker and Machtens, 1973; Champy, Wilk, and Schnebelen, 1975) or of Vitallium (Luhr, 1968). Removal of the hardware, once the fracture had consolidated and the plate had ceased to function, was advocated as part of the total treatment (Champy et al., 1976; Alpert and Seligson, 1996). Subsequently, the evolution of plating systems was characterized by smaller implants, often placed in inaccessible areas, improved surgical techniques, and the use of titanium (Weber et al., 1990; Oikarinen, Ignatius, and Silvennoinen, 1993). Titanium is the preferred metal for bone appliances (Zitter and Plenk, 1987). The seminal discovery that titanium develops a direct bony anchorage has had a decisive impact on dental implantology (Brånemark, 1983). Titanium is one of the most biocompatible and corrosion-resistant metals (Rae, 1986; Alpert and Seligson, 1996). Titanium has an elastic modulus closer to that of bone than other metals used in bone surgery (Katou et al., 1996; Haug, 1996). Thus, retention of titanium hardware seemed possible and controversy about elective removal of asymptomatic plates has developed as a consequence (Hildebrand and Champy, 1987; Haug, 1996).

Removal of symptomatic plates is not controversial. Symptomatic plates are those involved in infection, dehiscence, or extrusion (MacLeod and Bainton, 1992), and loose, fractured, or migrating plates. Similarly, there is no controversy about the removal of plates that cause pain, temperature sensitivity, and foreign body reactions (Alpert and Seligson, 1996). Elective removal of asymptomatic plates is more difficult to agree with, but may be necessary in a few indications. Material at the alveolar process can interfere with dentures and is subject to extrusion after tooth loss and subsequent atrophy of the ridge. In the growing craniofacial skeleton, plates can become buried or dislocated into the brain (Hönig, Merten, and Luhr, 1995; Yaremchuk and Posnick, 1995) or cause growth restriction (Yaremchuk et al., 1994).

According to Semlitsch (1987), titanium in plates is usually alloyed as Ti–6Al–4V (6 % aluminum and 4 % vanadium) or Ti–6Al–7Nb (6 % aluminum and 7 % niobium). Commercially pure titanium (cpTi) is 99.99 % pure. However, the remaining 0.01 % is unspecified (Moberg, Nordenram, and Kjellmaru, 1989). Unlike stainless steel (Fe–Cr–Ni alloy) or Vitallium (Co–Cr alloy), titanium is virtually free from pitting and crevice corrosion (Gerstorfer and Weber, 1988; Haug, 1996). Titanium spontaneously forms a film of oxides approximately 10 µm thick, which protects against acids under body conditions (Scales, 1991). Although cpTi and alloys are different metals with different electrochemical potentials, their combined use appears not to produce a galvanic effect (Haug, 1996). Despite these properties, however, metal release occurs in maxillofacial applications from bending of the plates and from movement of the screws against them (Solar, Pollak, and Korostoff, 1979) or against the bone (Muster et al., 1987; Galante et al., 1991). Titanium is one of the least wear-resistant metals currently in use as bio-material (Rae, 1979) and is susceptible to fretting corrosion (Agins et al., 1988). Fretting corrosion is considerably enhanced in the presence of hydrogen peroxide (H₂O₂). Activated macrophages are a possible source of H₂O₂ (Tengvall et al., 1990; Montague et al., 1996).

Titanium in ionic form is cleared through the kidneys (Jacobs et al., 1991). Titanium ions exhibit lower toxicity to osteoblasts than aluminum, vanadium, and chromium (Maurer, Merritt, and Brown, 1994; McKay et al., 1996; Thompson and Puleo, 1996; Ito et al., 1995). Elevated titanium in blood (Jacobs et al., 1991) and in hair (Trinchi, Nobis, and Cecchele, 1992) was measured in patients with loose joint replacements. Concentrations of 0.1–100 ng/mL of Ti ions in joint fluid after hip replacements have been reported (Jacobs et al., 1991).