Prosthetic Temporomandibular Joints: Materials, Design, and Clinical Considerations

Total temporomandibular joint (TMJ) replacement is an established reconstructive option for patients with end-stage joint disease, ankylosis, failed autogenous grafts, inflammatory arthropathies, or multiple prior TMJ surgeries. Modern prosthetic TMJ systems are designed to restore mandibular function, improve pain, and provide long-term joint stability using durable biomaterials and biomechanically sound designs.

This article reviews the Christensen and Lorenz total TMJ prosthetic systems, focusing on material composition, fixation principles, and clinical implications.

Christensen Total TMJ Prosthesis

The Christensen total TMJ prosthesis is a modular system that has evolved over time. The fossa component is composed of cobalt-chromium alloy, selected for its strength, wear resistance, and long-term durability.

Historically, both precured polymethylmethacrylate (PMMA) and cobalt-chromium condylar elements have been used with this system. The currently utilized “universal” condylar prosthesis consists of:

• A polymethylmethacrylate (PMMA) condylar head

• A cobalt-chromium ramus component

This combination allows for load transfer through the metallic ramus while maintaining a smooth articulating surface at the condylar head.

Although patient-specific TMJ prostheses can be fabricated using CAD-CAM technology, the Christensen system also offers stock components, allowing flexibility in surgical planning and reduced fabrication time in appropriate cases.

Lorenz Total TMJ Prosthesis

The Lorenz total TMJ prosthesis is composed of a cobalt-chromium ramus component designed for rigid fixation and long-term stability. The bone-contacting surface of the ramus is roughened with a titanium plasma spray coating, which promotes osseointegration and enhances mechanical fixation.

The fossa component is manufactured from ultra-high molecular weight polyethylene (UHMWPE) and is secured to the temporal bone using screws. UHMWPE is widely used in orthopedic joint replacements due to its low friction, high wear resistance, and favorable long-term performance.

Polymethylmethacrylate bone cement may be used to fill voids between the prosthesis and host bone when necessary; however, it is important to note that the cement is not designed to function as a load-bearing material.

Clinical Considerations in Prosthetic TMJ Selection

Both systems rely on metallic ramus components for structural support and non-metallic fossa or articulating surfaces to reduce wear. Key factors influencing prosthesis selection include:

• Severity of joint destruction

• Prior TMJ surgeries

• Presence of ankylosis or inflammatory disease

• Need for stock versus patient-specific components

• Surgeon familiarity and experience with the system

Total TMJ prostheses are typically reserved for end-stage pathology, where autogenous reconstruction is unlikely to succeed or has already failed.

Comparison Table: Christensen vs Lorenz TMJ Prostheses

Board and Exam Pearls

• Cobalt-chromium provides strength and wear resistance

• UHMWPE is used for low-friction fossa articulation

• PMMA cement is not load-bearing

• Titanium plasma spray enhances bone-prosthesis integration

• Total TMJ prostheses are indicated for end-stage joint disease

Conclusion

Modern prosthetic TMJ systems provide reliable reconstruction for patients with severe joint pathology. Understanding the material properties, fixation strategies, and biomechanical design of available systems is essential for safe surgical planning and optimal long-term outcomes.