Aetiology and pathology
Residual ridge resorption occurs in the mandible and maxilla after removal of the natural teeth and might be considered as a form of disuse atrophy. The resorptive process occurs at different rates in the maxilla and mandible such that the mandible commonly resorbs at a rate of 4: 1 to that of the maxilla. This process will continue indefinitely and can be affected by various factors including hormone levels, smoking and some as yet unidentified factors.
When severe resorption occurs, the mandible in particular becomes very thin and all that may remain is its lower border. In such circumstances the mandible is described as being pipe-stemmed and the inferior alveolar nerve comes to lie on its superior surface. This can present the patient and clinician with several problems including possible physiological fracture of the severely weakened bone or pain from pressure on the nerve which is now placed superficially.
The placement of implants into the edentulous ridges or maintenance of roots as overdenture abutments has been shown to preserve bone and prevent this severe bony resorption occurring. Attempts to apply bone grafts using autogenous as well as artificial bone, and the use of barrier membrane materials have all been tried in an attempt to augment resorbed ridges.