Alveolar ridges are bony structures in the upper (maxilla) and lower (mandible) jaws that contain the tooth sockets. They provide the foundation and support for teeth.
Anatomy and Purpose of the Alveolar Ridges
The alveolar ridge consists of alveolar bone, covered by gingiva (gum tissue). Within this bony ridge are the tooth sockets (alveoli), shaped to cradle each tooth’s root. The alveolar bone itself is composed of approximately 65% inorganic material, primarily hydroxyapatite crystals, and about 35% organic material, largely consisting of type I collagen.
The primary function of these ridges is to securely anchor the teeth within the jaw, allowing them to withstand the forces of chewing and biting. This support is also important for clear speech and for protecting the delicate nerves and blood vessels that nourish the teeth. Continuous stimulation from chewing forces transmitted through the tooth roots helps maintain the density and shape of this specialized bone.
Changes to the Ridge After Tooth Loss
When a tooth is removed or lost, the alveolar ridge undergoes a process of resorption (atrophy). This occurs because the tooth root’s absence removes the natural stimulation needed to maintain the bone, leading to its gradual reabsorption.
Resorption occurs in two phases. First, the bundle bone lining the socket is reabsorbed and replaced by woven bone. Then, resorption from the outer and inner bone walls causes the ridge to narrow and shorten. Most changes (about two-thirds of tissue reduction) occur within the first three months after extraction, continuing at 0.5-1.0% per year. This bone loss is often more pronounced on the buccal (cheek-facing) side of the jaw.
Changes to the alveolar ridge have consequences for oral function and facial appearance. A diminished ridge makes fitting removable dentures difficult, leading to instability and discomfort. An atrophied ridge may lack sufficient bone volume for dental implants, which need a stable foundation. Over time, significant bone loss can also contribute to alterations in facial structure, such as a sunken appearance around the mouth, changes in lip support, and the formation of wrinkles.
Maintaining and Rebuilding the Alveolar Ridge
Dental professionals address changes after tooth loss by preserving or restoring the alveolar ridge. Socket preservation is a common preventative measure, often performed immediately after tooth extraction. It involves cleaning the empty socket and filling it with bone graft material. A barrier membrane is placed over the graft to protect it and guide bone regeneration, followed by suturing. Its aim is to minimize natural bone resorption after extraction, creating a suitable site for future dental implants and often avoiding more extensive grafting later.
When significant bone loss has occurred, ridge augmentation rebuilds the height and width of the alveolar ridge. It involves exposing the deficient bone and placing bone graft material onto the existing ridge. Similar to socket preservation, a membrane may be used to contain the graft and encourage new bone formation. The goal is to restore adequate bone volume, providing a stable foundation for dental implants or improving the fit and comfort of conventional dentures. The bone graft material can come from various sources, including:
- Autografts (the patient’s own bone)
- Allografts (from human donors)
- Xenografts (from animal sources, such as bovine)
- Synthetic materials (e.g., hydroxyapatite or tricalcium phosphate)