The use of titanium in medical applications began in the 1930s and is based on its biocompatibility, density, mechanical properties, and corrosion resistance (Ref 15.1, 15.2). Titanium has outstanding resistance to corrosion and fatigue corrosion in the human body (body fluids are 0.9% saline solution). It also has good tissue tolerance and is compatible with human bone. As a surgical implant material, tissue compatibility and sterilization capability are key attributes, which have led to its growing acceptability. Many medical instruments are also made of titanium because of its special combination of physical, chemical, and mechanical properties. In the dental field, the high strength and low modulus of titanium have been central to its successful use. The use of titanium as a surgical implant material began in the 1930s, well before the commercial industry was founded in 1950. The first experimental implants were laboratory-produced unalloyed titanium pegs that were implanted in a cat’s femur. This trial, along with many subsequent evaluations, demonstrated titanium biocompatibility.
This property, along with its favorable density and mechanical properties (high strength and modulus nearly that of bone), led commercially pure titanium and its alloy Ti-6Al-4V ELI to be included in the ASTM F 67 and F 136 specifications, respectively, for surgical implant material. These alloys are now used in applications such as total hip replacements, shoulder prostheses, finger joints, knee replacements, heart valves, pacemaker cases, artificial ribs, nails, screws, and pins. A titanium valve assembly is a vital component of the Jarvik 7 artificial heart. In addition, titanium wire mesh and metal wool pads are used in facial reconstructive surgery.
Titanium is also used in external prostheses based on its low density and high strength. The weight reduction over stainless steel at no sacrifice in strength is a major benefit to patients who wear external prostheses. Titanium tubules are used to make lightweight crutches and wheelchairs. Based on strength and weight, titanium has replaced both aluminum and stainless steel in this application. In dental applications, titanium is used in several ways, including orthodontic wire, medical and dental instruments, crown material, and implants placed in the jaw as anchors for artificial teeth.
Braces used for orthodontic repositioning of teeth are made of several types of titanium alloy wire. Beta-titanium alloy Ti-3Al-8V-6Cr-4Zr-4Mo wire is used in orthodontic appliances for its low modulus and high strength. Nitinol (Ti-55Ni) shape-memory alloy is used for its high strength, low modulus, and its ability to return to a preformed shape induced by the warmth of the mouth. Both types of orthodontic wire reduce the number of adjustments required for a set amount of dental movements compared with traditional orthodontic wire.
The use of titanium dental implants is also gaining prominence. The procedure involves screwing a titanium anchor into the jawbone, forming a root. A smaller titanium screw is then tightened into the anchor to serve as an abutment to which the artificial tooth or teeth are attached. The procedure is used to replace one or more teeth using one or more anchors. In addition to providing nearly natural teeth that do not wobble or irritate, the implants help minimize jawbone erosion, common to denture wearers.
Titanium is used increasingly in medical and dental instruments . Because of its low density, surgical instruments are lighter when made of titanium. This lighter weight is an important factor in reducing surgeon fatigue during lengthy surgical procedures. The ability of titanium to be sterilized repeatedly and its “springy” quality are also important considerations in its selection.
