Electrical Implications of Corrosion for Osseointegration of
Titanium Implants*
Summarized by: Dr. Yael Abramovich
The success rate of dental and orthopedic titanium implants depends on the
integration of the surrounding bone tissue with the metal implant. For compromised
patients this ability had lower success rate. It has been found that electrical
stimulation of bone can control growth and healing and promote osseointegration.
Biopotentials
Natural electrical properties that control the growth and development of different types of
cells and tissues are called Biopotentials (Figs.1a, 1c). Injury to the tissue will change the
normal potential patterns of the intact tissue; the currents will persist until the wound has
healed. These potentials can span hundreds of microns and are generated by current or
ions flowing through the injured tissue. These potential are called Injury potential (Figs
1b, 1d).
Figure 1. Schematic shows:
(a) Electrical potential of a cell across an intact plasma membrane (Vm).
(b) A cell with a localized injury to the plasma membrane (V).
(c) Transepithelial electrical potential (Vtep) across an intact cell layer of the skin
(d) A short circuit caused by a wound.
Electrical Signals in Bone
Mechanical forces affect the process of bone remodeling. Areas of bone under stress tend
to grow, while those not under stress are usually resorbed. This is probably due to a
change in the physical stress and the biochemical activation of specific bone cells. At the
same time, negative polarity is greater in areas of bone under stress than in those under
minimal or no stress, Fig 2 shows negative and positive polarity due to orthodontics
forces. Negative polarity may be the cause of bone growth, whereas positive polarity
causes bone resorption. In other words, electrical signals could provide feedback for bone
remodeling.
Figure 2. Schematic of: Stress and polarization of bone and periodontal ligament
resulting from orthodontics treatment.
Electrical Bone Stimulation
The roles of these electrical signals in bone growth and development have been examined
in various studies of bone repair, in which cells and tissues were electrically stimulated.
Some studies have maintained that improved bone growth after electrical stimulation
depends on the levels of bone morphogenetic proteins and of calcium intracellular and
extracellular.
Titanium implants can be used as cathodes for direct current electrical stimulation. In an
animal experiment, a device fitted inside a dental implant supplied electrical stimulation
to the mandibular bone. When compared to the control group , the electrical stimulation
increased bone formation and bone-to-implant contact.
Electrical Implications of Corrosion
Metals are in common use for dental and orthopedic implants. However, metallic devices
tend to corrode in certain environments. Titanium is corrosion-resistant under controlled
environments in the absence of load. In the human body, the physiological environment
in combination with pressure on the implant may increase corrosion. Extreme acidic
conditions, friction between implant and bone, and galvanic corrosion between titanium
implants and other metals could adversely affect the dental implants.
Passivity of Titanium
Certain metals like titanium, oxidize easily forming a layer that protects the surface of the
metal from further oxidation. This passive behavior gives titanium its high resistance to
corrosion. Metals can have stable passivity, where the oxide layer heals itself
immediately after sustaining damage, or unstable passivity, where the oxide layer does
not heal and the bare metal is exposed to active corrosion.
Various studies have shown that the surface characteristics of the implant, such as
roughness, chemistry, and energy, directly influence tissue reaction. New methods of
surface modification have led to a significant improvement in metallic implants.
Clinical Relevance of Corrosion
Electrical currents are directly related to the pressure on the implant such a pressure can
generates abnormal corrosion. Such pressure normally results from the forces exerted
after every bite. Function implants cause cells and tissues to be exposed to extended
periods of abnormal electrical signals, which may provide another explanation for the
failure of implants due to inflammations and bone resorption. As treatments such as early
implant loading become popular, the pressure of mastication on the bone through the
implant can enhanced the electrical signals and affect both the early and later stages of
osseointegration.
Several methods are being used to reduce implant corrosion. These include new and
improved types of metallic alloys, modifications that stabilize surface reactivity, or
electrical protection of implants.
Understanding the electrical processes in cells and tissues and how they affected by
abnormal electrical signals generated by the use of implants, is important for farther
development of a long-term and better solutions for the patient.
*Gittens RA, Olivares-Navarrete R, Tannenbaum R, Boyan BD, Schwartz Z. (2011).
Electrical Implications of Corrosion for Osseointegration of Titanium Implants.
J Dent Res. 90(12):1389-1397.