Chapter 37 Tooth Extraction, Socket Grafting, and Barrier Membrane Bone Regeneration
Two fundamental concepts determine the position of an individual implant within a treatment plan: biomechanics and esthetics. Both of these concepts require adequate bone volume to accomplish their goals. Biomechanics requires key implant positions as the canine and first molar sites. When available bone is not present in those locations, bone augmentation is required. When the goal is an FP-1 restoration with ideal crown contour and soft tissue drape, abundant bone is necessary. If the available bone is inadequate, bone augmentation is indicated. Both factors of biomechanics and esthetics often require ideal available bone volumes.
The primary goal of this chapter is to present clinical guidelines to achieve adequate to ideal bone volumes for implant insertion. The process begins with the extraction of a hopeless tooth and socket grafting and continues to the use of barrier membrane (BM) guided bone regeneration (GBR).
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, or orthodontic failures. The concept of “treat or extract” was addressed in preprosthetic considerations in a previous chapter. Once the extraction of a natural tooth is indicated, methods to maintain or obtain the surrounding hard and soft tissues are indicated.
Over the last decade, interest has increased in atraumatic tooth extractions and socket grafting to maintain bone for implant insertion. Before extraction, exudates should not be present. Antibiotics, prophylaxis, scaling, and root planing may all be necessary before the extraction/grafting appointment.
The process of atraumatic tooth extraction and maintenance (or augmenting) of soft and hard tissues begins with the soft tissue. The cells of the inner layer of the periosteum are responsible for bone remodeling. Whenever the periosteum is reflected, the cells are injured and need to regenerate before the remodeling process begins. The cortical bone receives more than 80% of its arterial blood supply and faciliates 100% of its venous blood return through the periosteum.1 When the bone volume is ideal, the periosteum should not be reflected. However, the periosteum also limits the volume of bone formation. When the periosteum is separated from the bone graft by a barrier membrane, more volume of bone is regenerated. The periosteum helps bone remodeling or bone repair, but it limits bone modeling and regeneration.
The soft tissue drape around the teeth is also affected by the reflection of the periosteum and often shrinks to adapt to the residual ridge form. In fact, the soft tissue is more labile to the trauma and reflection of the tissues than the hard tissues. Therefore the sulcular and surrounding soft tissue should remain undisturbed during tooth extraction to prevent further dimensional loss.
The extraction of a natural tooth begins with an incision within the sulcus, preferably with a thin scalpel blade rather than a blunt periotome, 360 degrees around the tooth, to cut the connective tissue attachment fibers above the bone (Figure 37-1). There are 13 different connective tissue fiber groups around a tooth, of which six directly insert into the cementum of the tooth above the bone. If these fibers are not cut before the extraction, trauma to the soft tissue is imminent; soft tissue tearing may occur as well. The tip of the interdental papilla is avascular and should not be incised when possible. The soft tissue should not be reflected, as soft tissue retraction and shrinkage during initial healing is more evident, especially in the interdental papilla region.
The next step in an atraumatic extraction process is to observe the crown and root anatomy, especially in multirooted teeth. When a tooth is extracted next to adjacent teeth, the pathway of removal is often obstructed by the position of the adjacent tooth. If the tooth to be extracted is not reduced (especially mesial and distal), instruments may chip the enamel (or restoration) of the adjacent tooth and may cause the extraction of the tooth to take an altered pathway of removal, which is more likely to fracture the roots, bone, or both (Figure 37-2). If the roots of the tooth to be extracted are divergent, they should be sectioned and removed as individual units, rather than risking fracture of the roots or surrounding bone (Figure 37-3). When the roots are fractured, there is an increased risk of bone fracture/removal to retrieve them. If bone removal around the tooth is necessary (because the tooth is fractured or decayed to the bony crest), it ideally should be at the expense of the lingual alveolus, not the more labial bone.
Figure 37-2 A, The maxillary lateral incisor requires extraction. The pathway of removal may restrict the extraction or chip an adjacent tooth. B, The distal portion of the lateral incisor was reduced to allow the tooth to move distal, which allows pressure to the periodontal ligament and bone. In addition, there is less risk of adjacent tooth damage.
Figure 37-3 A, The left central incisor with replacement resorption requires extraction. The single tooth root is reduced mesiodistal and separated in two. B, The separated central permits the unresorbed tooth root to be displaced to the mesial when the osteotome is inserted into the distal periodontal ligament space.
Biomechanic concepts have been used to extract teeth for thousands of years and date back to the days of Aristotle (384-322 bc),2 who described the mechanics of the extraction forceps, including the advantages of “two levers acting in contrary sense having a single fulcrum.” This was 100 years before Archimedes reported on the principles of the lever.
Pierre Fauchard (1690-1761) is credited with being the pioneer of scientific dentistry and gave specific instructions for extracting teeth using a dental elevator, a “pelican,” or pincers (forceps).2,3 He describes loosening the tooth with an elevator, then using the claw of the “pelican” (invented by Chauliac in the fourteenth century).4 The pelican handle was positioned both on the tooth and on the gum below the tooth while it was rocked back and forth (which he called “shaking”) before the extraction. Taft described a similar technique using the dental key, which had left and right claws that provided twisting and rocking in both directions.5 This allowed the tooth to be loosened sufficiently to be pulled from the socket with “pincers” (forceps). Modern extraction forceps date from Tomes in 1840 with the development of the anatomical forceps, complete with a handle and beak to fit the neck of the tooth.
The principle of the dental elevator is also not a modern development. Abulkasim (ad1050-1122) was the first to apply a single lever (elevator) under the tooth to force it from its “bed.” It was improved by Ambroise Paré in the sixteenth century to lift out the tooth before using the pelican.5 Although these biomechanical methods to remove teeth are effective, a review of the biomechanical principals is in order to decrease the trauma during the tooth extraction process.
The term “simple machine” is often used to describe basic devices that increase the amount of force applied (e.g., the lever, inclined plane, wheel, screw, pulley). They each transmit or modify force or torque. The most common devices used in the extraction of teeth include levers and inclined planes.
The wedge is technically a moving double inclined plane, which overcomes a large resistance by applying a relatively smaller force than the load necessary to move an object. The mechanical advantage of a wedge depends on the ratio of its length to its thickness. A short wedge with a wide angle moves an object faster; however, it requires more force than a long wedge with a smaller angle. Dental elevators and periotomes use the mechanical advantage of a wedge to initiate the luxation of teeth for their removal.
Periotomes are usually longer and thinner wedges compared with dental elevators and should be used to begin the atraumatic extraction process. Periotomes may be used in a similar manner for extraction of intact teeth or removal of retained root fragments. The long axis of the periotome blade should be inserted into the interproximal region along the root long axis (to protect the facial plate of bone), with the tip of the periotome blade located within the crest of the alveolar bone. The instrument is then pushed into the periodontal ligament space or tapped with a mallet into the periodontal ligament space along the mesial and distal root, severing the periodontal ligament immediately below the alveolar crest and wedging the tooth against the opposing cribriform plate (Figure 37-4, A).
Figure 37-4 A, A periotome is inserted along the tooth root on the mesial and pushed (or tapped with a mallet) to wedge the tooth against the opposing cribriform plate. A similar process is performed on the distal interpositional region of the tooth root. B, Once the periotome acts as a wedge and is in place for 10 to 30 seconds, it is tapped (with a mallet) farther down along the mesial and distal interproximal root surface. C, The periotome is converted into a lever by rotating the handle several degrees, which magnifies the force against the root. The tooth becomes slightly mobile at this stage. D, A traditional dental forceps may remove the tooth after initial mobility is created by the periotome.
A period of 10 to 30 seconds is allowed to elapse while the instrument is in place. This allows biomechanical creep to occur to the ligament and reduces its strength, and because the tooth is pushed against the opposing alveolus, it also begins to expand the bone. This process is much more effective when there is no adjacent tooth contact. Reducing the mesial and distal contacts of the tooth to be extracted not only decreases the risk of damage to the adjacent tooth crown, but also aids in the first step to extract the hopeless tooth. The periotome is then pushed farther down into the periodontal ligament toward the root apex, often using a mallet and light tapping force. This process continues along the crestal one third of the tooth. At the completion of this procedure, the tooth is often slightly mobile (see Figure 37-4, B).
Once the periotome is used as a moving wedge, it may then be converted to a lever (see Figure 37-4, C). The blade of the periotome is often 3 to 4 mm wide. When the handle is rotated, one side of the periotome is applied to the tooth root, the other side to the cribriform plate, and the width of the “wedge” is now the length of a lever, which magnifies the rotation force (moment). The rotation of the periotome handle increases both tooth mobility and the force against the opposite cortical plate to further expand it within physiologic limits.
A single-rooted tooth is most often tapered. As the periotome is tapped down to the cribriform plate and slightly rotated, the tooth often is pushed against the opposing cribriform plate. Because the socket is tapered, the lateral force on one side of the tooth is converted to a coronal direction force on the other side and the root is pushed out of the socket. As a result, the periotome may now be pushed farther apical,1 toward the root apex. When time elapses between each force application, the tooth may even slide up and completely out of the socket. Additional time and elevation may be required if significant tooth mobility is not achieved.
A traditional dental forceps should not be applied to the tooth until significant tooth mobility is achieved. Once the wedge and lever action of the dental elevator is applied to a tooth, most often a dental forceps is used to ultimately grasp and deliberately rock the tooth back and forth and to rotate it as much as conditions will allow. The combination of these tooth movements expands the bony socket and separates the periodontal ligaments. As a consequence, the tooth may be removed (see Figure 37-4, D).
Conventional dental forceps are really two first-class levers connected with a hinge. The forces applied to the forceps handles are the long side of the lever and the beaks on the tooth are the short side of the lever, with the hinge acting as a fulcrum. The force on the handles is magnified to allow the beaks of the forceps to grasp the tooth with great force. None of the force on the forceps handles is used to extract the tooth. Rather, the increased force on the forceps beaks often crushes or fractures the tooth. The forceps hold the tooth, and the surgeon’s hand, wrist, and arm are used to move and extract the tooth. This action would be similar to forcibly pulling a bottle cap off a bottle or pulling a nail from a piece of wood, using only a pair of pliers.
The principles of biomechanics are the basis for the development of a different type of dental forceps called Physics Forceps (Golden-Misch Instruments, Detroit, Mich.). A moment of force in physics represents the magnitude of force applied to a rotational system at a distance from the axis of rotation. The principle of moment M is derived from Archimedes’s discovery of the operating principle of the lever and is defined as
where F is the applied force and r is the distance from the force applied to the object. The concept of a moment arm is key to the operation of the lever, which is capable of generating mechanical advantage. This means that the force applied to an object is affected by the length of the lever arms. The lever arm is the distance from the force input to the fulcrum or from the fulcrum to the force output.
The Physics Forceps is a dental extractor that uses first-class lever mechanics. One beak of the device is connected to a “bumper,” which acts as a fulcrum during the extraction. The bumper is placed most often on the facial aspect of the dental alveolus, at or above the mucogingival junction. The second beak of the extractor is positioned as low as practical on the tooth root, most often on the palatal (lingual) into the gingival sulcus.
Once the treatment is in position around the tooth root, no squeezing pressure is applied to the tooth. Instead, the handles, once in position, are rotated as one unit facially for a few degrees and stopped for approximately 60 seconds (Figure 37-5, A). The torque force generated on the tooth, periodontal ligament, and bone is related to the length of the handle to the bumper (8 cm), divided by the distance from the bumper to the forceps beak (1 cm). As a result, a force on the handle connected to the bumper will increase the force on the tooth periodontal ligament and bone by eight times. No force is required to be placed on the forceps beak, which is on the tooth. Therefore the tooth does not split, crush, or fracture. The 60 seconds of constant force cause biomechanical creep into the bone and periodontal ligament. Once creep has expanded and weakened the periodontal ligament and bone, the forceps handle may be slowly rotated another few degrees. This usually releases and elevates the tooth a few millimeters from the socket within an additional 10 seconds (see Figure 37-5, B). At this point the tooth is loose and ready to be removed from the socket using any pincer-like device (e.g., pick-ups, an extraction forceps, a hemostat) (see Figure 37-5, C).
Figure 37-5 A, The Physics Forceps has a “bumper” on one beak, which is placed below the tooth and acts as a lever. The other beak is placed on the tooth root. The handles of the Physics Forceps act as a lever to rotate the tooth from the socket. The bumper is placed below the tooth, usually at or above the mucogingival junction. The beak is placed low on the tooth root in the gingival sulcus. B, Once in position on the tooth root, the Physics Forceps is used as one unit (no squeezing of the handles). A few degrees of rotation to the facial places moment force on the tooth, which is held for 60 seconds. Another few degrees of rotation are then applied, and the tooth releases and elevates. C, Once the tooth releases from the socket, it is removed with a pincer-like device (e.g., pick-ups, extraction forceps, hemostat).
The extraction of a tooth using the Physics Forceps is similar to the removal of a nail from wood with use of a carpenter’s hammer (instead of pliers). The handle of the hammer is a lever, and the beaks of the hammer fit under the head of a nail (they do not squeeze the head). The hammer head acts as a fulcrum. A rotational force applied to the hammer handle magnifies the force by the length of the handle, and the nail is elevated from the wood.
Unlike a nail in wood, which is parallel and has friction for its full length, a tooth is tapered. Therefore, after it is elevated a few millimeters, the periodontal ligament fibers are broken and the tooth may be easily removed, without additional rotational force. This is important to note, as further rotational force on the forceps may fracture the facial plate of bone.
Creep is a phenomenon whereby a material continues to change shape over time under a constant load. In tooth extraction, creep may occur to bone and the periodontal ligament. Reilly established the creep curve of bone, whereby under a constant load of 60 Mpa, the bone over time responds in three different stages.6 The majority of bone changes occur within the first minute, whereby the initial strain of bone (the change of length divided by the original length) is modified. The greater the force, the greater the deformation of the bone. This process allows the tooth socket to expand and the tooth to exit the socket.
A secondary creep curve allows the bone to further deform when the force is applied for 1 to 5 minutes. The longer the time, the greater the deformation. However, the secondary deformation is only a 10% to 20% difference compared with the initial strain over the first minute. Eventually, the bone will fracture if the load is applied over a longer time frame, representing creep rupture.
The creep curve of the periodontal complex is similar to the creep curve of the bone, whereby the constant load on a tooth over time increases the strain and decreases the strength of the periodontal complex. Therefore, the clinician should not underestimate the values of time and constant force to the tooth ligament and bone in the extraction process.
Once the tooth is extracted, the site may heal by repair or regeneration of the bone. All fibrous tissue from periodontal disease or endodontic origin should be completely removed, as these tissues impair bone formation and delay bone healing for extended periods. Repair occurs when there is injury or conditions of the bone that cause incomplete bone volume to form in the residual ridge. The most common conditions that cause repair are the absence of a labial plate before or as a consequence of tooth extraction. Other factors include a bony wall that is less than 1.5 mm thick (usually the facial), exudate, gross apical pathology, or excessive heat from a dental drill during root extraction. On rare occasions, bisphosphonate drugs or systemic conditions may cause a repair rather than a regeneration process.
The tooth socket with five bony walls regenerates bone by secondary intention, and bone healing in many aspects is similar to secondary intention soft tissue healing. The healing sequence in both hard and soft tissue includes inflammation, epithelialization, fibroplasia, and remodeling. However, socket healing presents unique microvascular features and a sequential pattern of bone formation before remodeling. The inflammatory stage of healing is initiated by the extraction trauma. Oral epithelium surrounds the crestal aspect of the socket and averages 3 mm in thickness in the absence of periodontal disease (the sulcus, junctional epithelial attachment, and connective tissue attachment accounting for approximately 1 mm each). The cribriform plate is composed of cortical-like bone and, after extraction, it is covered with the residual periodontal ligament. The vessels torn during the extraction fill the socket with blood, which coagulates and protects the bone during initial healing. The epithelium around the crest of the alveolus migrates down the socket walls during the first week. The migration continues until it reaches the bed of granulation tissue situated under the blood clot. It then migrates over this granulation tissue until it makes contact with the epithelium migrating from the other sides.
Ohta has proposed four stages of bone regeneration after a tooth is extracted with a healthy surrounding alveolus.7 The time frames presented here have been modified from his dog study to reflect the human sigma of bone. The week following extraction is called the initial angiogenic stage. Initial angiogenesis develops from the broken ends of blood vessels in the residual periodontal ligament covering the cribriform plate. Blood plasma leaks from these broken vessels, and immature fibroblasts aggregate at the plasma-rich regions. The blood clot begins to shrink, and capillaries form sinusoids and granulation tissue, starting from the apex and the surrounding walls of bone. Fibroplasia begins early in the sequence during the first week as a result of the ingrowth of capillaries and fibroblasts. White blood cells kill bacteria and begin to dissolve foreign bodies and bone fragments. With few exceptions, the angiogenesis begins at the bottom of the socket because this area is not severely injured during the extraction and has the greatest source of blood vessels. Within 5 days of the extraction, early granulation tissue composed of immature capillaries and fibroblasts appears at the bottom of the socket and spreads upward along the socket walls. New bone trabeculae also form at the apical portion of the socket during this early stage.
The new bone formation stage begins as early as the third week after extraction.7 At this time, the entire socket is filled with granulation tissue. This period demonstrates the greatest sinusoid formation activity. The forming trabeculae of woven bone first start from the bottom of the socket following the meshwork of newly formed anastomosing sinusoidal capillaries. Bone formation is more rapid at this point, creating a three-dimensional lattice pattern of woven bone. It has been observed that, during this time, the cortical bone of the marginal crest of the socket continues to resorb, especially in the interseptal regions and the thinner facial plate.
The bone growth stage starts 4 to 5 weeks after the extraction.7 New bone trabeculae forming on the walls and apical region have thickened and fill the apical two thirds of the socket. The center of the socket is still woven bone because ossification occurs on randomly formed collagen fibers; hence its lattice appearance. The more organized lamellar bone starts to form from the lining of the socket toward the center of the socket.
The bone reorganization stage occurs at least 6 weeks after extraction.7 The primary bone trabeculae remodel to form thicker secondary spongiosa. This process always begins at the apex of the extraction socket. The complete cortical lining of bone around the socket is not fully resorbed, and remodeling continues for 4 to 6 months after the initial extraction (Figure 37-6).
The timing for these four stages varies among individuals and clinical situations. The number of bony walls around the socket and size of the alveolus greatly influence the regeneration process. Molar sites take longer to completely form bone compared with smaller-diameter anterior sites. Although the period of regeneration for an extraction socket is variable, the clinical sign that the socket regeneration is complete is when the radiographic lamina dura (which represents the cribriform plate) is no longer present. This period is most often 3 to 6 months, dependent upon tooth size, root number, and trauma of extraction.
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 among different reports, but also within each study.8–11 Rather than use the same technique regardless of clinical conditions, when bone repair rather than regeneration is likely, the clinician should provide as many keys to bone grafting as possible to increase the socket.
In 1993, Misch and Dietsh suggested different graft materials and techniques based on the number of bony walls that remained after the tooth is removed.12 A thick five bony wall defect will grow bone with almost any resorbable graft material (RGM); for example an alloplast, allograft, or autograft. When a wall of bone is less than 1.5 mm or a labial plate is missing (four bony wall defect), an autograft or an alloplast or freeze-dried bone (FDB) with BM and GBR increased the predictability of restoring the original bony contour. Becker et al. evaluated demineralized freeze-dried bone (DFDB) alone in extraction sockets, and no evidence of bone formation was observed.13 It appears DFDB alone may be a poor choice for socket grafting. LeKovic et al. compared extractions alone to BM with extractions. At 6 months, crestal bone loss (0.38 versus 1.50 mm) and horizontal ridge resorption (–1.31 versus −4.56 mm) were found.14 A two or three bony wall defect requires an RGM and, at least, some autogenous bone with a barrier membrane. A block graft of cortical autogenous bone fixated into the host bone position is suggested for one bony wall defect (Figure 37-7).
Figure 37-7 The graft materials and techniques for socket grafting are related to the remaining number of bony walls. A thick five wall bony defect may use any resorbable graft material (RGM). Four wall defects require an autograft or mineralized alloplast, allograft, and barrier membrane. A two or three wall bony defect may use some alloplast/mineralized allograft, but should use autograft and a barrier membrane as well. A one wall bony defect is most predictable with a cortical autograft fixated to the host bone.
Regeneration restores complete morphology and bone volume to the residual ridge. This most often occurs when there are five thick bony walls around the extraction site. Most of the keys for predictable bone formation are present under these conditions, and the socket often forms bone in the extraction socket without loss of width or height. The atraumatic extraction of a tooth without pathology provides many of the keys necessary for predictable bone regeneration. The extraction process sets up a regional acceleratory phenomenon (RAP) for healing (which increases the rate of repair and adds bone morphogenetic protein [BMP] to the site); the five bony walls protect the graft from mobility; the torn blood vessels in the periodontal complex leak growth factors into the region (platelet-derived growth factor [PDGF], transforming growth factor [TGF]); the space is maintained by the five walls of the bone; the bony walls provide blood vessels from bone into the site; and the defect size is small (i.e., one tooth). As a result, the only key initially missing is soft tissue closure (Figure 37-8). The soft tissue around the extraction site begins to grow over the clot and granulation tissue of the socket and within 2 to 3 weeks covers the site. For example, a mandibular third molar extraction site often 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.
Figure 37-8 A, Atraumatic extraction of the anterior six teeth found thick, five bony wall defects. Demineralized, cortical bone fibers (Grafton, Lifecell) are placed into the sockets. B, The soft tissue is approximated for primary closure. C, The soft tissue healing after 5 months. D, Reentry into the residual premaxillary ridge observes abundant bone and ridge preservation. E, A core biopsy is taken from a central incisor site. F, Implants are inserted into the premaxillary arch. G, Histology of the core indicates primarily vital bone trabeculae and some residual demineralized freeze-dried bone at 5 months.
(Courtesy M. Sharawy.)
When a labial plate around a socket is missing, the absence of the wall prevents space maintenance, reduces host bone vascularization, and replaces it with soft tissue vascularization. The facial bone level will never grow above the height of bone on the facial cortical plate of the tooth. Bone augmentation procedures must be used to obtain an ideal volume and contour of bone. Sockets with a missing lateral wall are significantly compromised and heal by repair rather than regeneration.
When conditions of repair instead of regeneration are present, socket grafting for ridge augmentation at the time of extraction is indicated.12 Tooth extraction without grafting in these conditions results in residual bone loss as a result of resorption. The maxillary anterior region may be reduced 23% in the first 6 months after an extraction and another 11% over the following 5 years.15 Within 2 years, an average of 40% to 60% of the original height and width of bone may be lost with multiple extractions.16
The first determination after the tooth extraction is complete is the assessment of the thickness of labial and palatal plates of bone and their relative height to the ideal volume desires. When one of the lateral plates of bone is thinner than 1.5 mm, or when height is desired, a socket graft is indicated, even in the presence of five bony walls. A similar socket augmentation procedure also may be used when the labial plate of bone is missing. The two techniques of choice are a BM with a mineralized alloplast/freeze-dried bone (FDB) socket fill or a modified socket seal surgery.
An acellular dermal matrix is selected for a BM when soft tissue augmentation is also desired, or a collagen BM is used when the soft tissue drape is not an issue. A periotome or thin periosteal elevator is used to tunnel under the final bone periosteum and lift the soft tissue off the bone over the thin bony wall. This tunnel should extend several millimeters beyond the desired augmentation site. A BM is then slid into the “pocket” created under the tissue and extends apical, mesial, and distal beyond the extraction site. Approximately 6 to 8 mm of the BM should extend above the marginal tissue.
When the facial plate is thin, the socket may be filled with FDB (e.g., MinerOss, Puros) or a mineralized hydroxyapatite (HA) source (e.g., BioOss, Osteograf-N). 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 walls of bone on the mesial, distal, and palatal provide bone blood vessels to this autograft. The extension of collagen or AlloDerm then covers the top of the socket and is tucked below the palatal tissue. Sutures are then placed over the top of the BM. Primary closure of the soft tissues is not obtained, as the tissues would need to be reflected and advanced over the socket, which would affect the soft tissue drape (Figure 37-9, A to H).
Figure 37-9 A, A radiograph of endodontically treated maxillary central incisor with internal resorption and apical radiolucency. B, The central incisor crown is reduced on the mesial and distal to favor the atraumatic extraction. C, The tooth is atraumatically extracted without soft tissue reflection. The labial wall is less than 1 mm thick. D, A periotome forms a tunnel on the facial cortical bone and extends mesial, distal, and apical to the contours of the extraction site. E, A piece of acellular dermal matrix (Alloderm) is in position, draped over a periotome. F, The acellular dermal matrix is pushed into the facial tunnel and acts as a barrier membrane. G, The extraction socket is filled with a resorbable graft material (DFDB/FDB), consisting of a mixture of 30% demineralized freeze-dried bone (Grafton) and 70% mineralized freeze-dried bone (MinerOss). H, Postoperative radiograph demonstrates the extraction site and graft material in place. I, The soft tissue healing after 5 months. J, A periapical radiograph indicates the cribriform plate of the extraction socket is no longer visible. This indicates the bone reorganization stage of socket repair is complete. K, An implant is inserted into the central incisor site. A “split-finger” tissue flap on the palate is rotated to the mesial. L, A permucosal extension is inserted into the implant body and the tissues approximated. M, After 4 months of healing, an abutment is placed into the implant body. N, A periapical radiograph 9 months after implant insertion. The interseptal bone is maintained adjacent to the implant.
The extraction site may be reentered after 4 to 6 months. The clinical time for reentry is determined by the absence of the cortical lining of the socket (cribriform plate) on a periapical radiograph. Once this has occurred, the implant may be inserted and a regular protocol of healing and restoration used (see Figure 37-9, I to N).
The tuberosity offers a variable amount of trabecular bone. This area is convenient for use in maxillary sinus grafting12,17,18 and also may be considered for smaller areas of ridge augmentation19,20 (Figure 37-10). The cancellous nature of the bone allows it to be molded into an alveolar defect, such as an extraction socket.12 However, the trabecular graft will more often require the use of a barrier membrane in onlay grafting to minimize resorption and stabilize the graft.21 The tuberosity autograft has growth factors for osteoinduction and to accelerate blood vessel growth in the host site.
Figure 37-10 The maxillary tuberosity region is a common bone donor site for bone grafting, when trabecular bone is the desired product. Trabecular bone has growth factors for blood vessels and for regeneration of a bone defect.
The thicker soft tissue in the tuberosity region can mislead the assessment of this donor site. The tuberosity should be evaluated with panoramic or periapical radiographs. The anatomical limitations of this area include the maxillary sinus, pterygoid plates, adjacent teeth when present, and the greater palatine canal. A vertical incision is made posteriorly at the lateral aspect of the maxilla. It extends anteriorly across the tuberosity into the molar region. After reflection of a mucoperiosteal flap, bone may be harvested from the tuberosity with a rongeur or chisel. Removing the graft with a chisel will allow the harvesting of a larger piece of bone. Although the sinus may inadvertently be entered during removal of the graft, coverage of the perforation with the thick mucosa should preclude the development of an oroantral communication. If this is observed at suture removal, the patient is instructed to avoid creating high nasal pressures and should be placed on antibiotics and decongestants to prevent infection and ensure normal drainage. Most often, within 1 month, the oroantral opening will close on its own.
A composite graft socket seal surgery has been developed by Misch et al.22,23 composed of connective tissue, periosteum, and trabecular bone used to seal a fresh extraction socket. A connective tissue graft has the advantage over a keratinized graft by blending into the surrounding attached gingival regions, offering similar color and texture of the epithelium. This is most advantageous in the maxillary anterior region and other aesthetic areas. The composite graft also contains autogenous bone. The major advantage of autologous bone is a more rapid and predictable bone formation via osteogenesis. This technique may be used any time a tooth is extracted and an implant is planned as replacement.
A 6- to 10-mm trephine bur corresponding to the extraction site diameter is used in a slow-speed, high-torque hand piece to harvest a gingival graft with underlying bone. The most common site for the intraoral composite graft harvest is the maxillary tuberosity region (see Figure 37-10). The trephine drill drills through the unreflected, keratinized, attached gingiva and into the bone of the tuberosity region at the prescribed depth related to the thickness of the tissue and the amount of donor bone available. Care should be exerted not to enter the antrum, but that is of little consequence if the antrum is healthy during the process. A trephine bur may be used as a lever to greenstick fracture the bone core from its base, once it is in position within the bone. A Molt elevator may also be used for this purpose. The bone core (usually 5 to 10 mm in height) and the attached soft tissue (about 3 mm in height) is trimmed of its epithelium with a tissue scissors, leaving 3 to 6 mm of connective tissue attached to the bone core.
If the bone core does not fill the extraction socket completely, a mineralized bone graft material (e.g., FDB, bovine bone) may be used in the apical portion of the socket, provided the labial plate is still intact. Because the new bone forms from the apical portion of the socket, this is the least important region to augment. If no bone plate remains in the apical half of the socket, additional autogenous bone should be harvested from an additional intraoral site to overfill the apical half of the socket. The bone of the composite graft (connective tissue attached to periosteum and bone) is compressed and fitted into the remaining portion of the socket. The tissue of the composite graft will seal the socket and remain above the surrounding gingiva. A mallet and blunt instrument should be used to tap it into place and compress the bony core to conform to the crestal contour of the socket. The connective tissue portion of the graft is then sutured to the surrounding gingival tissue with facial and palatal interrupted 4-0 PMA or Vicryl sutures (Figure 37-11). A removable transitional prosthesis should not be permitted to load the tissue during the first few weeks after extraction; otherwise, the composite graft may become mobile and sequestrate. A fixed transitional restoration may use an ovoid pontic design to maintain the interdental papilla height and contour.