The alveolar process of the jaw develops along with the eruption of teeth, ongoing root formation, and subsequent growth. The alveolar bone, periodontal ligament, cementum, and tooth constitute a developmental unit, as they form together. The dimension of the alveolar process differs significantly among the various regions of the jaw, with the tooth type correlating to the size of the alveolar process. Genetic factors may also play a role in determining the alveolar process dimension. The alveolar process is composed of two types of bone: the alveolar bone proper (known histologically as bundle bone) and the supporting bone. The bundle bone comprises the inner portion of the alveolar socket while the remaining part of the alveolar process consists of supporting bone. The bundle bone is a periodontal tissue similar to cementum that connects the periodontal ligament to the alveolar bone. When a tooth is removed, the developmental unit is altered, and the alveolar process resorbs.

Adequate dimensions of the alveolar ridge promote implant placement in the proper three-dimensional position and provide proper mechanical support for the implant and soft tissues. Resorption of the alveolar process is an inevitable consequence of tooth extraction. Preventing or reducing this resorption is desirable, as bone walls of adequate thickness contribute to long-term success in implant dentistry. Ridge preservation may be defined as a procedure that aims to preserve the ridge volume existing at the time of extraction.

After completing this ITI Academy Module, you should be able to: describe ridge alterations following tooth extraction; describe indications for ridge preservation; describe techniques for ridge preservation; describe complications of ridge preservation procedures.

The alveolar socket healing process following tooth extraction leads to dimensional alterations at the extraction site. The result of these alterations is a reduction in the alveolar ridge dimensions that is a combination of hard and soft tissue changes. This reduction occurs in both the horizontal and vertical dimensions. The amount of atrophy is influenced by various factors. Of these, the thickness of the socket wall is fundamental in the alveolar resorption process. If it is thin (for example, less than 1 mm), it will quickly resorb, allowing the soft tissue to collapse into the space previously occupied by the tooth root. If it is thicker (that is, greater than 1 mm), osteoclastic activity will not completely resorb the wall, and a portion of the space previously occupied by the root may be preserved.

Alveolar ridge alterations are typically characterized by greater reduction along the buccal surface than on the lingual or palatal aspect. Changes in vertical bone height are usually moderate. A systematic review on the amount of change in height and width of the residual ridge after tooth extraction found that the mean reduction in height was approximately 1.7 mm. On the contrary, changes in horizontal ridge width are more significant. In the same systematic review, the mean reduction in alveolar ridge width was calculated to be approximately 4 mm. Two-thirds of this reduction will occur within the first 3 months after tooth extraction.

Araújo and Lindhe described alterations in the edentulous ridge profile following tooth extraction in an experimental study in a dog model. Over 8 weeks of healing, the margin of the buccal wall shifted apically by approximately 2 mm, as indicated by the yellow arrow. Bone loss during socket healing is greater along the buccal than the lingual wall for several reasons. First, the crestal portion of the buccal bone wall is primarily comprised of bundle bone, especially in the anterior region. Bundle bone is a tooth-dependent tissue that completely resorbs after tooth extraction. On the contrary, bundle bone typically comprises a smaller proportion of the lingual or palatal socket wall. Also, the lingual bone wall of the socket is thicker than the buccal wall.

Many factors have been suggested as having an influence on post-extraction ridge reduction. These include pre-existing pathological processes such as periapical lesions that have damaged the bone prior to extraction and that result in atypical ridge atrophy. Other factors include the presence of a thin bone phenotype and the number of missing teeth. The more teeth that are missing, the greater the atrophy. Excessively traumatic tooth extraction procedures also contribute to ridge reduction.

Ridge Alterations Following Tooth Extraction, Key Learning Points: Tooth loss results in significant alveolar ridge alteration or alveolar atrophy. The loss of bone width is greater than the loss of bone height. The amount of ridge alteration is dependent on the thickness of the alveolar bony walls. Dimensional changes are more pronounced on the buccal aspect of the socket because the buccal bone wall is thinner than the lingual or palatal wall. Multiple factors influence ridge resorption, including pre-existing pathological processes, thin bone phenotype, number of missing teeth, and traumatic extraction.

Post-extraction dimensional alterations occur mainly due to resorption of the socket walls. As discussed in the first Learning Objective, these alterations are more significant during the first 3 months of socket healing and are observed predominately at the buccal aspect of the ridge. Ridge preservation procedures have been shown to modify these bone modeling events, thereby partially preventing the reduction in marginal ridge dimension that occurs following tooth removal and reducing the need for further reconstructive procedures. It is important to note that ridge preservation can have a significant impact on the decrease in horizontal ridge width following tooth extraction, but it has only a minor impact, if any, on the decrease in vertical ridge height. Ridge preservation has its limitations, however. It cannot preserve the full thickness of a buccal bone wall, and it cannot prevent the loss of a very thin buccal wall, as is often seen in esthetic areas or in patients with a thin periodontal phenotype. In these situations simultaneous bone augmentation may still be needed at the time of implant placement, especially in anterior regions.

A ridge preservation procedure is indicated when it is desirable to preserve the dimension of the ridge for a pontic site, or when implant placement needs to be deferred. Implant placement may be delayed due to loss of bone or if the socket morphology prevents implant placement in an ideal prosthodontic position; in young patients in whom active growth and development is still occurring; when the patient cannot afford implant therapy; or because placement is contraindicated by medical health issues. In these situations a ridge preservation procedure is indicated to reduce the bone modeling that will inevitably occur while the patient is waiting for implant placement. Implant placement in post-extraction sites can usually be managed with bone augmentation procedures with high predictability, provided that at least two intact bone walls remain. However, as the time interval from extraction to implant placement increases, progressive ridge resorption may result in loss of bone volume to a degree that simultaneous bone augmentation becomes less predictable. If a long interval between extraction and implantation is anticipated, a ridge preservation procedure may be performed to increase the predictability of subsequent augmentation procedures.

Whenever there are indications, there are also contraindications. For example, the patient may have medical conditions that limit nonessential surgical procedures, such as procedures other than the necessary tooth extraction. These medical conditions may also limit later potential implant placement. Acute infection at the extraction site must be resolved so that implant placement and simultaneous or staged bone augmentation are performed in noninfected sites. It may not be a contraindication, but if an implant is to be placed at the time of extraction or within 6 to 8 weeks afterwards, there appears to be little benefit in performing a ridge preservation procedure. In some patients, such as those with a thick periodontal phenotype exhibiting thick socket walls, unassisted socket healing is likely to result in a sufficient amount of bone for implant placement. In these patients a ridge preservation procedure is not necessary.

Indications for Ridge Preservation, Key Learning Points: Ridge preservation procedures do not completely prevent resorption. Some resorption inevitably occurs, mainly due to loss of the buccal bone wall. Ridge preservation primarily impacts the horizontal ridge width. Ridge preservation reduces the need for further reconstructive procedures, but bone augmentation at the time of implant placement may still be needed. Ridge preservation is not indicated when implant placement will occur soon after extraction or in patients with a thick phenotype and thick socket walls.

Tooth extraction should be performed in such way as to prevent damage to the buccal wall. An intact buccal wall will provide proper protection for fragile healing tissues. Surgical trauma from the extraction induces microtrauma in the surrounding bone, which accelerates bone resorption. A flapless low-trauma tooth extraction approach is therefore recommended when using early implant placement protocols as well as in cases of immediate implant placement in sockets with thick facial bone wall phenotypes in order to avoid additional bone loss at the superficial bone wall. Raising a flap in itself may induce superficial resorption of the bone surface. At the time of extraction any remaining pathology inside the socket must be removed. An instrument such as a Luer curette should be used to explore for residual pathologic tissue and to debride the inner walls of the alveolar socket.

To prevent reduction in the alveolar ridge dimension a graft material is placed into the extraction socket. This material could be autogenous bone, a biomaterial of allogeneic or xenogeneic origin, or an alloplastic bone substitute. The literature is inconclusive as to which material provides the best outcome, but in general the material should be slow resorbing, biocompatible and osteoconductive. This histological image shows the graft material surrounded by the host bone. Graft materials with high resorption rates allow for the formation of bone with no residual graft particles at the time of implant placement, but their ability to sustain alveolar ridge volume in the long term may be inferior to that of mineralized grafts.

The material selected should act as a permanent scaffold for bony ingrowth and maintain most of the original ridge dimension. The biomaterial should not be removed by osteoclastic activity but instead remain in the socket and be incorporated into the host bone. The use of osteoconductive and mineralized graft materials do not accelerate bone healing but may allow for better preservation of the ridge volume, which is highly desirable for both the esthetics and function of the future implant prosthesis.

After placing the graft material into the socket, the socket entrance should be closed to protect the graft and avoid its displacement. Before closure, the graft may be covered by a membrane. The membrane can be resorbable, most often a collagen membrane, or nonresorbable, typically an expanded polytetrafluoroethylene (or ePTFE) membrane. Resorbable membranes are preferable to nonresorbable membranes, as the use of a nonresorbable material is more demanding in regard to soft tissue closure. There is also a higher incidence of soft tissue dehiscence when a nonresorbable membrane is used.

After placement of the membrane the area should be protected by soft tissue closure. For this step a free gingival graft may be retrieved from the palate or the maxillary tuberosity. A coronally advanced flap or a pediculated split-thickness palatal flap may also be used to close the socket entrance. It should be taken into consideration that a coronally advanced flap may alter the mucogingival junction at the buccal side, resulting in a compromised esthetic result. As an alternative to use of a membrane or flap advancement to close the socket entrance, a soft tissue substitute such as a resorbable polylactide-polyglycolide acid sponge can be used.

If the buccal bone is intact after tooth extraction, a flapless approach may be used for the ridge preservation. First, after gentle reflection of the soft tissue, the membrane is placed between the outer bone surface and buccal soft tissue. Next, the graft material is placed into the socket. The procedure is finalized by placing the membrane under the soft tissue along the circumference of the socket. Note that the membrane provides the soft tissue seal in this technique.

If the buccal bone is deficient after tooth extraction, a full-thickness mucoperiosteal flap must be raised and a membrane placed to cover the socket and graft material and to serve as a buccal wall during the first weeks of healing. A resorbable or nonresorbable membrane can be used. During flap closure, complete covering of the membrane with soft tissue must be accomplished.

After placing the biomaterial in the extraction socket and subsequently covering the area with a membrane and a flap or solely with a soft tissue substitute material, the area should be left to heal for 4 to 6 months prior to implant placement. The healing period depends on the size of the extraction socket. It is recommended that a molar socket be allowed to heal for 6 months, and a lateral incisor socket for 4 months. In general, ridge preservation procedures are accompanied by varying degrees of bone formation and residual graft material in the extraction socket. This depends on the materials and techniques used. Ridge preservation procedures do not prevent 100% of the ridge alteration that takes place following tooth extraction. Thus, even if enough bone is preserved for implant placement, some flattening of the ridge should be expected. In maxillary anterior regions, additional procedures such as contour augmentation or soft tissue grafting may be required at the time of implant placement to compensate for this deficiency.

Techniques and Healing Outcomes, Key Learning Points: Minimally invasive tooth extraction techniques should be used to avoid unnecessary damage to the socket walls. Sockets should be grafted with biomaterials that can be incorporated into bone to act as a permanent scaffold for the host bone. The graft material must be protected by a membrane, a complete soft tissue seal, or a soft tissue substitute material. A barrier membrane should be used to compensate for the lack of a buccal socket wall. Further tissue augmentation may be needed at the time of implant placement, even if there is adequate bone for proper implant positioning.

Ridge preservation may on occasion result in complications. These are mostly related to healing and bacterial contamination of the wound. Common complications include infection, dehiscence of the soft tissue covering the extraction socket, necrosis of gingival grafts, exposure of the membrane covering the graft material, and exposure of the graft material itself.

Infection may be due to contamination during treatment, particularly if a flap was raised, or lack of sufficient oral hygiene in the initial healing period. If typical clinical signs of acute inflammation are observed, that is, swelling, pain, and suppuration, the patient should be treated by mechanical and antiseptic plaque control at the site. The origin of the potential suppuration must be identified; this is most often the soft tissue covering the outer buccal bone surface. Copious irrigation of the infected site with chlorhexidine should be performed with a syringe and blunt-end needle to remove bacteria, pus, and contaminated biomaterial. Treatment with systemic antibiotics may be needed. If the origin of the infection is the socket, all infected biomaterial should be removed and the ridge preservation procedure should be considered lost. The plaque control procedure should be performed until there no clinical signs of acute inflammation. Antibiotic therapy should also be implemented. If infection results in incomplete ridge preservation, a ridge augmentation procedure should be performed at the time of implant placement.

Whenever a flap is raised and advanced, a soft tissue dehiscence may occur as a result of too much tension in the flap. This dehiscence can result in exposure of an applied membrane. If the membrane is resorbable, the soft tissue dehiscence and the exposed membrane should be treated by mechanical and antiseptic plaque control of the site. Normally, the soft tissue will heal by secondary intention without further complications. If the membrane is nonresorbable it should be removed, as it is not possible to control an eventual infection in the exposed area. A free gingival graft may become necrotic during healing due to lack of proper vascularization. The necrotic graft must be removed as it attracts bacteria, which may induce an infection. Loss of the soft tissue seal over the socket, including necrosis of free gingival grafts, is not clinically important if the seal has been maintained for the first 15 days after tooth extraction.

Complications, Key Learning Points: Although unlikely, complications may occur after ridge preservation. Loss of the socket seal is significant if it takes place within the first 15 days of healing. Postoperative infections are often related to bacterial proliferation outside the socket secondary to flap elevation. If the origin of an infection is the grafted socket, all graft material should be removed. If the ridge preservation outcome is not ideal, a ridge augmentation procedure should be performed at the time of implant placement.

Ridge Preservation Techniques, Module Summary: Ridge preservation procedures are effective at limiting horizontal resorption of the ridge. Bone grafts and bone substitutes used for socket grafting should have slow resorption rates. A barrier membrane should be used to compensate for the lack of a socket wall. A complete soft tissue seal is required to ensure optimum results; this can be achieved by flap advancement, a membrane, or a soft tissue substitute material. In maxillary anterior regions, additional grafting may be required at the time of implant placement for contour augmentation. Ridge preservation is not free of complications; potential complications include loss of the socket seal, loss of the biomaterial, postoperative infection, and incomplete ridge preservation.