Socket Grafting and Alveolar Ridge Preservation

There are 2 fundamental concepts that determine the position of an individual implant within a treatment plan: biomechanics and aesthetics. Both of these concepts require adequate bone volume to accomplish their goals. If the available bone is inadequate, bone augmentation is indicated.
At some point in time, the dental practitioner may decide to remove a natural tooth. Hopeless or unrestorable teeth may be related to periodontal, endodontic, prosthetic, and/or orthodontic failures. Once the extraction of a natural tooth is indicated, methods to maintain (or obtain) the surrounding hard and soft tissues are in order. Over the last decade, there has been an increased interest in socket grafting in order to maintain or obtain bone for implant insertion after a tooth is extracted.

SOCKET GRAFTING

Multiple bone graft procedures and studies have been evaluated for socket augmentation at the time of extraction. However variable results have been observed not only between different reports, but also within each study.1-4 This range of results occur for several reasons, and especially because not all extraction sites have the same clinical condition. Rather than use the same technique, regardless of clinical conditions, the clinician should provide as many of the missing keys to bone grafting as possible to increase the likelihood of success.5 For example, in 1993 Misch and Dietsh6 suggested different graft materials and techniques for socket grafts based on the number of bony walls that remained after the tooth is removed.

Five Thick Bony Wall Defect

Regeneration of the extraction socket restores complete morphology and bone volume to the residual ridge. This most often occurs independent of a graft material when there are 5 bony walls more than 1.5 mm thick around an atraumatic extraction site. This clinical condition is found most often in the posterior mandible and maxillary molar regions. For example, a mandibular third molar extraction site usually has thick lateral walls of bone, and most often the bone area is regenerated in both height and width, with no graft material or regeneration technique in the sockets.
The extraction process of a tooth provides many of the keys necessary to grow bone in the socket under these surrounding bone conditions.5 The surgical insult sets up a Regional Acceleratory Phenomenon5 for healing (which increases the rate of repair and adds bone morphogenetic protein to the site), the 5 bony walls of the extraction socket protect the graft from mobility, the torn blood vessels in the periodontal complex leak growth factors into the region (including platelet derived growth factor and transforming growth factor), the space for the bone regeneration process is maintained for several months because of the 5 surrounding walls of the bone, the bony walls provide blood vessels coming from bone into the regeneration site (which bring in osteoblasts for bone formation), and the defect size is small (ie, one tooth).7

Figure 1. The posterior extraction socket often has 5 thick bony walls. A piece of collagen inserted over DFDB fibers (eg, Grafton) placed in the socket and reverse cross sutures over the top is sufficient to regenerate the bone.

The only initial key element missing for successful bone regeneration is soft tissue closure over the extraction site. The surrounding epithelium around the tooth extraction site begins to grow over the blood clot and granulation tissue of the socket and within 3 to 4 weeks covers the site. To aid in this process, a piece of collagen may be placed within the socket and several sutures placed over the extraction socket to prevent dislodgement during initial healing (Figure 1). When a molar is extracted, fibers of demineralized freeze-dried bone (eg, Grafton) may also be used, since the socket is larger than a premolar site. The extraction site often forms bone under these ideal conditions with very little loss of bone volume width or height.

Five Thin to Four Bony Wall Socket

When a lateral plate around a socket is less than 1.5 mm thick, or is partially to completely missing, the resorption and/or absence of the bony wall prevents space maintenance, reduces host bone vascularization, and replaces it with soft tissue invagination. Unfortunately, this condition is most often observed in the anterior regions of the jaws, especially in the premaxilla. Sockets with a missing lateral wall are significantly compromised, and heal by repair rather than regeneration.7 Bone will not grow above the lateral plate bone level of the extraction site during the repair process without a bone grafting procedure. In addition, when the labial plate of bone is thin or absent, bone resorption in width occurs. For example, the maxillary anterior region may be reduced more than 23% within the first 6 months after an extraction. Within 2 years, an average of 40% to 60% of the original height and width of bone may be lost with multiple extractions.8
When conditions of repair instead of regeneration are present, socket grafting for ridge augmentation at the time of extraction is indicated.7 Tooth extraction without grafting under these conditions results in a decreased residual bone volume as a result of inadequate host conditions and further resorption of the thin bony wall at the site. As a consequence, one of the first determinations after the tooth extraction process is the assessment of the thickness of labial and palatal plates of bone and their relative height to the ideal volume desired. When one of the lateral plates of bone is thinner than 1.5 mm, or additional height is desired, a socket graft is indicated (even in the presence of 5 bony walls).

Technique For 4 to 5 Thin Body Walls

A Barrier Membrane (BM) [eg Memlok (BioHorizons)] in conjunction with a mineralized alloplast or allograft placed within the extraction socket is usually indicated when the surrounding bony wall conditions are not ideal.9 Demineralized Freeze-Dried Bone (DFDB) [eg, Grafton (Osteotech)] alone in extraction sockets under these conditions often provides little evidence of bone formation.10 On the other hand, when a BM is used after the extractions, at 6 months less crestal bone loss and less horizontal ridge resorption is found.9 An acellular dermal matrix (eg, AlloDerm [LifeCell]) is selected for a BM when soft tissue augmentation is desired in addition to bone regeneration or a collagen BM may be used (eg, Memlok, Bio- Horizons) when the soft tissue drape is not an issue.3,4

Figure 2. An x-ray of a maxillary central incisor with internal resorption and a 6-year postoperative implant replacing the other central incisor.	Figure 3. The tooth is removed. Since the labial plate of bone is thin (or absent), a periostome is used to form a subperiosteal tunnel over the site.
Figure 4. A piece of acellular tissue (AlloDerm [LifeCell]) is placed into the tunnel and extends over the socket.	Figure 5. An immediate postoperative radiograph demonstrates the extraction site with FDB (MinerOs) in situ.

The facial tissue may be reflected after the atraumatic extraction and the labial bone defect observed, or a periotome may be used to tunnel under the facial periosteum over the bone and lift the soft tissue from the thin bony wall (Figures 2 and 3). This subperiosteal tunnel should extend several mm beyond the desired augmentation site. A BM is then placed over the site or slid into the “pocket” created under the tissue and extended apical, mesial, and distal beyond the extraction site (Figure 4). Approximately 8 mm of the BM should extend above the marginal tissue.7
When the facial plate is thin, the socket may be filled with a mineralized bone source as freeze-dried bone (FDB) (eg, MinerOss) or an alloplast (eg, BioOss [Osteohealth], Osteograf/N [eg, DENTSPLY Friadent])6,11 (Figure 5). When the labial plate is missing, the FDB may be placed in the apical portion, but particulate autologous bone should be placed in the crestal half of the socket. The tuberosity is usually harvested for this purpose and offers a variable amount of trabecular bone.12
The cancellous nature of the bone from the tuberosity allows it to be molded into an alveolar defect, such as an extraction socket. The tuberosity autograft has growth factors for osteoinduction and to accelerate blood vessel growth in the host site. The socket walls of bone on the mesial, distal, and palatal provide bone blood vessels to this autograft. However, the trabecular graft requires the use of a barrier membrane to minimize resorption and stabilize the graft.
The 8-mm extension of collagen or AlloDerm BM above the extraction site covers the top of the socket graft and is tucked below the palatal tissue. Sutures are then placed over the top of the BM. The membrane is secured in position with reverse cross sutures. The suture needle first penetrates the BM near the margin of the socket, then through the soft tissue from below. The suture is then brought over to the opposite rim of the extraction site, penetrating first the BM, then the tissue from below, brought over the site and tied. A series of 2 to 4 reverse cross-positioned sutures secures the BM over the socket. Primary closure of the soft tissues is not obtained, since the tissues would need to be reflected and advanced over the socket and reduce the aesthetic result of the soft-tissue drape.
The initial socket site does not have an adequate blood supply within the graft to resist bacterial invasion. Therefore, a short-term dose of oral antibiotics is suggested when a socket graft is performed.8 This is especially indicated when the tooth has subclinical signs of periodontal or endodontic pathology. If overt pathology and exudate is noted, the socket graft should be delayed for several weeks after the extraction.

Two To Three Bony Wall Defects

A 2- to 3-bony wall defect is treated very similarly to a 4-wall bony defect. However, since the defect size is larger, more autograft is required in the bone graft, using a layered technique as first suggested by Misch.5,8 Rather than mixing the autograft with other bone graft materials, the first layer on top of the host bone of the 2- to 3-wall bony wall defect is particulate autograft. As a consequence of the defect size, a bone donor site from the ramus or symphysis of the mandible is often required. When inadequate particulate autograft is harvested to completely fill the defect, a 25% DFDB and 75% mineralized bone (eg, FDB) is the second layer of the graft and fills the remainder of the defect, preferably mixed with platelet rich plasma. A barrier membrane is then placed over the site and acts as the third layer of the graft. Primary closure of the soft tissue is required in larger bony wall defects.12
The most common 2- to 3- bony wall defects are multiple extraction sites missing more than the labial bony wall. Since the mesial and distal bony walls are usually present, the host site is more predictable than a one bony-wall defect or onlay graft. A block graft of cortical autogenous bone fixated onto the host bone position is also predictable for this larger size defect.11

IMPLANT INSERTION

Figure 6. A 4-month postoperative radiograph demonstrates a lack of lamina dura from the extraction site and most of the graft is incorporated into the area.	Figure 7. An implant (Biohorizons Maestro) is inserted into the site, 5 months after the socket graft.
Figure 8. 4 months after implant insertion, a crown is cemented onto the implant.	Figure 9. A postoperative x-ray showing the 2 implants and crowns.

The extraction site may be re-entered after 4 to 6 months. The clinical time for re-entry is determined by the absence of the cortical lining of the socket (cribriform plate) on a periapical radiograph (Figure 6). Once this has occurred, the implant may be inserted and a regular protocol of healing and restoration employed (Figures 7 to 9).

CONCLUSION

The socket grafting procedure is becoming a more necessary treatment step in order to restore adequate bone volume for implant insertion. The socket graft technique is dependent upon the clinical conditions observed after the extraction process. One of the more important conditions is the number and thickness of the bony walls surrounding the extraction site.
A thick 5-bony wall defect will grow bone with almost any resorbable graft material. When a wall of bone is less than 1.5 mm or a labial plate is missing (4-bony wall defect), an autograft with an alloplast or FDB and barrier membrane for guided bone regeneration increases the predictability of restoring the original bony contour. A 2- or 3-bony wall defect requires a layered approach with more autogenous bone on the host site, a resorbable graft material over this and a barrier membrane covering the entire graft site. Soft tissue closure is also required for these larger defects. When the socket graft procedure is modified related to defect size and surrounding bony wall conditions, a predictable regeneration/augmentation of bone is obtained. The bone volume is one of the more important factors for ideal implant insertion and restoration.

References

Dr. Misch is a Fellow of 13 different societies, including both the American and the International Colleges of Dentists. He has been president of many implant organizations and is currently the co-chairman of the Board of Directors of the International Congress of Implantologists (ICOI), the world’s largest implant organization. He is also co-inventor of the BioHorizons Dental Implant System and served on the Board of Directors from 1995 to 2006. He has edited 4 books: Contemporary Implant Dentistry editions 1, 2, and 3, and Dental Implants Prosthetics by C.V. Mosby, and over 220 articles. In 1984, he founded the Misch International Implant Institute. He has trained more than 3,500 doctors in his hands-on, yearly forum of education in implant dentistry. He can be reached at (248) 642-3800 or info@misch.com.

Dr. Silc received her DDS from Marquette University and MS in Periodontics from the University of Michigan. She is a Diplomate in the American Board of Periodontology as well as the International Congress of Oral Implantologists. She has done research on dental implant design and published numerous articles in the field of implant dentistry. She maintains a private practice limited to periodontics with an emphasis on cosmetic procedures and implant dentistry in Chicago, Ill. She can be reached at (847) 605-0280 or email at jtsilc@yahoo.com.