8

Standard Surgical Techniques for Augmentation

The degree of difficulty of augmentation surgery depends on the defect shape. The most favorable situation is an inlay graft, followed by an interpositional graft. More challenging is an appositional graft (horizontal augmentation), and the most difficult situation is an onlay graft (vertical augmentation). This ranking relates to the choice of bone graft, the difficulty of soft tissue coverage, and the professional demands placed on the team. Nevertheless, the long-term results of all four procedures are very good, and implants in regenerated bone do not have a worse prognosis than implants in local bone.¹

8.1 Inlay Grafts

External sinus floor augmentation with graft

External sinus floor augmentation is performed via an approach through the facial sinus wall, which allows an open view of the sinus membrane and is therefore also called an open sinus elevation (Figs 8-1 and 8-2). This is not possible with the internal (crestal) approach via the alveolar process, which is therefore referred to as a closed sinus elevation. Sinus floor augmentation is, in type, an inlay graft similar to filling a cyst, with all the advantages for healing of mechanical rest and almost circumferential bony containment. Sinus floor augmentation is also called sinus elevation, sinus lift, or subantral augmentation.

In the posterior maxilla, there is often reduced bone height due to maxillary sinus pneumatization after tooth loss. Bone augmentation of the maxillary sinus floor creates the bone conditions to use rotationally symmetric dental implants of a length analogous to human tooth roots, which can be positioned exactly according to the prosthetic requirements in the center of the masticatory functional load (Fig 8-3). Sinus floor augmentation has an excellent long-term prognosis, with 97.7% implant survival after 3 years in prospective studies at a high level of evidence² as well as 95% after 10 years and 85% after 20 years in a retrospective study.³ Autogenous bone alone or mixed with bone graft substitute showed better histologic bone densities than bone graft substitute alone according to a recent meta-analysis.² The addition of platelet-rich fibrin (PRF)⁴ or platelet rich plasma (PRP)⁵ did not provide any benefit for bone regeneration in sinus augmentation. Sinus floor augmentation has also been described with leukocyte- and platelet-rich fibrin (L-PRF) as an augmentation material.⁶

Fig 8-1 Sinus floor augmentation via external access on the left and via internal crestal access on the right. Control via a maxillary sinus endoscope is optional.

The healing time of a sinus floor augmentation is usually given in the literature as 6 months. However, studies with a high proportion (50%) of autogenous bone scraper chips were able to demonstrate sufficient implant stability after only 8 weeks.⁷ Autogenous bone accelerates healing. According to studies by the author’s group (see chapter 3), an admixture of 25% autogenous bone chips to 75% bone graft substitute is the best compromise, resulting in a healing time of 4 months.

The facial wall of the maxillary sinus is exposed via a lateral approach. The positions of the roots of any teeth still present are marked, and an oval window is planned with a base point near the deepest part of the alveolar recess of the maxillary sinus. The window should not be extended unnecessarily far cranially because slightly below the infraorbital foramen in the facial bone wall of the maxillary sinus, the antral alveolar artery⁸ makes a strong connection to the superior posterior alveolar artery. The bone is flattened first with the ball bur and then, as it approaches the mucosa, with a diamond ball bur. Here, bone can be left in the center of the window so that it can later be swung as a bone lid into the maxillary sinus. This bone plate then ideally lies above the apices of the implants and protects the sinus membrane from perforation. With careful handling, the diamond bur does not injure the mucosa, so that after some time the bone flap becomes mobile with a pedicle on the sinus membrane (also called the Schneiderian membrane after Konrad Viktor Schneider, anatomist, Wittenberg, 1614–1680). Now, using blunt instruments, the mucosa is first detached internally from the bone margins with pressing rather than scraping movements. When the mucosa is circularly mobile, the sharp edges of the bone are deburred all around with the diamond ball bur. The sinus mucosa is then detached from the alveolar recess internally without perforation using curved blunt instruments (eg, Joseph elevator) or special sinus elevation curets. In most cases, due to the additional coronal and lateral atrophy (Fig 8-4), it is necessary to augment the ridge additionally, which can be done by guided bone regeneration (GBR), block grafts, and ridge splitting in the most anterior parts (Figs 8-5 and 8-6).

Fig 8-2 External access. Here, a bone lid was prepared, still attached to the sinus membrane, which acts like a hinge.

Fig 8-3 External sinus floor augmentation. a. Initial situation with unilateral free-end situation without significant crestal bone atrophy. b. Access is via a midcrestal incision, gingival margin incision, and distal relief latereral to the tuberosity. The facial maxillary sinus wall is first ground thin with a steel ball bur. The sinus membrane preparation is performed using a diamond ball bur. c. Using special rounded curets with different angular positions, the sinus membrane is first detached from the bone in a circular fashion and elevated secondarily. d. A mixture of autologous bone and bone substitute (25%:75%), and venous blood is filled in. e. The implants can be placed simultaneously as long as they are still primarily held stable by the residual bone. The limit of minimal residual bone for this purpose depends on the implant system. f. Implant exposure 4 months later. g. Prosthetic restoration. h. Postoperative panoramic tomogram.

Fig 8-4 In case of atrophy of the maxillary sinus floor, the line connecting the alveolar ridges does not change. In the case of atrophy from the crestal side, the altered line connecting the alveolar ridges must be observed and corrected by lateral augmentation in addition to the sinus elevation so that no crossbite occurs. In the case of pronounced crestal atrophy, sinus elevation is contraindicated, and vertical ridge augmentation is preferable instead.

Piezoelectric opening of the facial maxillary sinus wall has the initial advantage that the ultrasonic vibration avoids the the sinus membrane. However, prospective comparative studies have not found lower perforation rates than with the diamond ball method.9

Preparing the sinus membrane opens the subantral space, which is now filled with, eg, a 75%/25% mixture of bone substitute/autogenous bone (see chapter 4). The filling height should correspond approximately to the height of the sinus floor and allow the anchorage of 10- to 12-mm-long implants in the residual bone. Wall closure is achieved by folding back the uninjured mucoperiosteal flap. The periosteum of the sinus membrane also exerts an osteogenic effect.¹⁰ Covering of the window with a barrier membrane offers no advantage according to studies¹¹ and a meta-analysis.¹²

External sinus floor augmentation without graft

The subantral space has such a high healing potential that, according to Stefan Lundgren,¹³ bony filling of the subantral space can be achieved entirely without bone graft (graftless) and by spontaneous filling with autologous blood alone. A meta-analysis showed better implant survival rates without graft, suggesting that a bone graft material may pose additional risks such as infections.¹⁴ A prerequisite is the stabilization of the elevated membrane in a cranial position over the implants. This can be achieved, for example, by simultaneously inserting dental implants to serve a “tenting” function. However, there are also techniques to achieve this stabilization using rigid membranes or a metal or plastic mesh. Implant survival was 95.9% with an average bone height gain of 4 mm.¹⁵ An advantage of the graftless technique is that no foreign material is applied, which consequently cannot cause infections by forming a bacterial biofilm. A meta-analysis comparing the graftless technique with the application of a bone graft showed no difference in implant survival but a significant difference in mean bone gain of 0.7 mm less without a graft.¹⁶

Fig 8-5 Combination sinus elevation with bone splitting. a. In free-end situations in the maxilla, there is usually pronounced horizontal atrophy on the premolars (omega shape of the maxilla). Here, the sinus membrane is already elevated. b. In the ascending part of the maxillary sinus floor of the premolar region, bone splitting can be performed with a Lindemann bur. c. This is completed with the blade chisel, which may penetrate into the maxillary sinus floor. d. This allows an implant with low primary stability to be placed in the first premolar region. The splitting gap and the maxillary sinus floor are filled with a bone substitute material mixture. e. Postoperative panoramic image. f. Panoramic image after prosthetic restoration. The consolidation of the graft with formation of a cranial cortical layer can be seen.

Fig 8-6 Internal sinus elevation with hydraulic technique. a. Water pressure is used to lift the sinus membrane via crestal access, and the subantral space released is filled with bone substitute mixture. b. Diagram showing the internal sinus elevation technique.

In accordance with the original method described above, the facial maxillary sinus wall is first exposed (Fig 8-7). Then, using a piezoelectric device or fine saws or drills, a faceted bone lid is formed using oblique cuts. The oblique cut surfaces allow this lid to be repositioned later so that it clamps and does not fall into the maxillary sinus. After the bone lid is lifted off and placed temporarily in saline solution, the sinus membrane is elevated. Then the dental implants are inserted. In most cases, the subantral space fills with wound blood on its own. Now the bone flap is repositioned. If it does not clamp itself securely, it is secured with histoacryl glue. Alternatively, holes can be drilled for suturing with an absorbable material. This is followed by primary wound closure.

Internal sinus floor augmentation (crestal technique) with the hydraulic technique

Crestal sinus floor augmentation according to Summers,¹⁷ also referred to as the osteotome sinus floor elevation (OSFE), is a minimally invasive technique because it can be performed through the implant osteotomy, which is required anyway, and with a minimal mucosal incision (see Fig 8-6b). A meta-analysis yielded 96.9% implant survival with bone height greater than 5 mm and 92.6% with bone height less than 5 mm.¹⁸ The 10-year results of a prospective study were 90.7% implant survival with bone graft substitutes and 95% with the graftless approach. It was reported as 90.7% for 6-mm implants and 95% for 10-mm implants, although the differences were not significant.¹⁹ The crestal sinus elevation is very well tolerated by patients. As a minimally invasive method, it did not burden patients more than implant placement without augmentation in a clinical study.²⁰

The procedure is somewhat time consuming because each implant site must be operated on individually, so the external technique is time saving in the case of multiple implants. Generally, the existing bone is drilled to about 0.5 mm below the subantral cortex. The experienced surgeon feels the subantral cortex as drilling resistance. A CBCT is recommended to accurately plan this distance in advance. Then the sinus floor is infracted by malleting with an osteotome and deformed cranially, inserting the instruments through the implant osteotomy. The resulting fragments can then be pushed a few millimeters into the maxillary sinus. An attempt can also be made to enlarge the subantral space with blunt elevators by lifting the sinus membrane and then filling with autologous blood or bone grafts. Finally, the dental implant is placed, sealing the access cavity to the maxillary sinus airtight to avoid an oroantral fistula. In most cases, the basic technique results in membrane perforation, but this remains undetected due to lack of visibility. However, this can be diagnosed by probing or irrigation if saline leaks to the nose. Better control of the sinus membrane is allowed by simultaneous endoscopy of the maxillary sinus via a punctate transoral perforation of the facial maxillary sinus wall.

Fig 8-7 Graftless sinus elevation. a. With the aid of a small cutting disc, a faceted bone lid is cut out of the facial sinus wall, lifted off, and stored temporarily under moist conditions. b. The sinus membrane is lifted with special angled blunt curets. The dental implant acts like a tent post and prevents the sinus membrane from falling back into the alveolar recess. The subantral space spontaneously fills with autologous blood. c. The bone lid is repositioned. The faceting and the oblique cut surfaces prevent the flap from falling inward. d. Histoacrylic adhesive is used to secure the lid. e. Postoperative panoramic image following flap exposure with bilateral sinus elevation without grafting.

Fig 8-8 Hydraulic sinus elevation using the Jeder System. a. Panoramic tomogram. b. Jeder technique. The drill tip is under water pressure via a pressure cuff on the contra-angle handpiece, so that the sinus membrane is pushed away at the moment of cortical perforation and is protected. Computer control of the water pressure also allows controlled augmentation volume to be introduced. (Image in b courtesy of Jeder GmbH, Vienna, Austria.)

The critical phases of an internal sinus floor augmentation are firstly the entry into the maxillary sinus and secondly the elevation of the sinus membrane, because membrane rupture can occur during both procedures, with studies showing its occurrence in 28% of cases.²¹ The first risk is increased if the maxillary sinus floor is rippled, oblique, or even septated. Several techniques have been developed to reduce the risk of membrane tears. The most obvious are calibrated burs in half-millimeter increments, which are controlled by CBCT to precisely drill the thin cortical bone of the maxillary sinus and perforate it without touching the membrane. Another approach is stop burs, which decouple and stop turning when counterpressure is lost. Other types of burs transport the bone shavings apically, where they act like a cushion to displace the sinus membrane at the moment of entry. Finally, there is the suggestion of screwing in a fine-threaded implant, which then lifts the maxillary sinus floor very slowly and in a more controlled manner compared with a plunger. The most advanced solution to the entry problem is the contra-angle handpiece of the Jeder System, which holds a small steel drill under constant water pressure maintained at the edges of the osteotomy by seals.²² At the moment of entry of the small steel drill, pressurized water is pumped into the subantral space, pushing the intact membrane in front of it (Fig 8-8).

The second risk is rupture of the membrane during elevation and creation of the subantral space. To reduce the risk of rupture of the membrane during elevation, various techniques have also been developed. One modification of the osteotome method is balloon-assisted sinus floor augmentation. A balloon distributes the pressure of a filling liquid over a large area and can protect the sinus membrane. However, the balloon is a disposable product and relatively expensive. From Israel came the suggestion of a dental implant with a pump channel that exits at the apex. This channel can be filled with bone augmentation material is paste form, which slowly pushes up the sinus membrane while simultaneously building up the bone.

As a clinical synthesis of all these approaches, the author uses the hydraulic method modified from Chen and Cha.²³ In the original method, a diamond ball bur is first used to drill a 3-mm hole at the future implant site up to 1 mm short of the cortical bone. Then the cortical bone is perforated punctiform with a 2-mm ball drill, whereby a water/air mixture enters the drill tunnel with pressure from the handpiece of Chen and Cha,²³ which detaches the sinus membrane. The author of this book proceeds in such a way that after the punctiform perforation, a blunt irrigation needle is inserted into the osteotomy and sealed circumferentially with a moistened swab. A syringe is used to manually inject saline solution, which lifts the sinus membrane. Relatively strong pressure is required for this. Approximately 2 mL of saline solution is injected, recognizable by the graduation of the syringe. A noticeable loss of pressure would indicate a perforation, and in this case one can switch to the lateral technique. Augmentation material can be filled into the raised space of a perforation-free internal membrane elevation through the implant osteotomy. With good technique, impressive membrane-covered domes of bone substitute material (Fig 8-8a) can be built up in this way, with the implant in the center. Patients are usually very satisfied because the approach is minimally invasive and there is hardly any discomfort. However, the tapping noises when advancing the osteotome may annoy the patient.

Due to the reduced field of view compared to the lateral method, the crestal technique is recommended only for experienced surgeons, who can switch to the lateral approach if necessary.

8.2 Interpositional Grafts

Interpositional defects can be created by vertical or horizontal (sandwich) splitting of the alveolar process. In the case of knife edge alveolar ridges, the split segment can also be swung up like a garage door (so-called swing osteotomy). A common feature of interpositional grafts is the creation of a bone bed bordered on two sides by vascularized bone tissue, which doubles the distance of angiogenesis (Fig 8-9). Because bone segments remain pedicled by soft tissue over the periosteum, they are also referred to as osteoperiosteal flaps. Interpositional grafts are also called alveolar ridge expansion because the existing bone is expanded from within. They also work beyond the envelope because they relocate it.

Vertical interpositional bone grafts (sandwich technique)

According to a recent study by the author, the implant survival rate after vertical augmentation by the sandwich method is 96.7% with up to 8.3-mm height gain and hardly any long-term resorption (0.27 mm after 12 years). Wound dehiscence occurred in 12%, but without infection of the bone graft because its depth protects it²⁴ (Fig 8-10). A meta-analysis of 10 studies reported 94% implant survival at 5 years.²⁵ An advantage of sandwich bone grafting is that the soft tissue, and in particular the residual attached gingiva, does not need to be detached from the alveolar ridge (Fig 8-11). The technique can be combined very well with the physiologic midcrestal incision. As a result, the specialized tissues of the marginal periodontium (neuroectodermal cells) are preserved at the subsequent implant emergence site and can form a new soft tissue attachment apparatus around implants here. In addition, the periosteum is not detached on the oral side of the segment. It is assumed that this results in less resorption of the augmented bone height than with overlay grafts.

In the lateral mandible, the buccal compact bone is osteotomized above the nerve plane using the Lindemann bur (Fig 8-12). This is followed by full-depth vertical osteotomies mesially and distally of the segment, extending through to the lingual aspect. Here, one can carefully insert a finger to palpate the floor of the mouth so as not to perforate the lingual mucosa with the drill. Lingually, the horizontal osteotomy is performed with thin blade chisels, because it is too dangerous to use the Lindemann bur in the vicinity of the lingual nerve. The segment usually becomes suddenly mobile after one to two chisel blows, when the lingual compact bone fractures. It must be completely mobile but still pedicled on the lingual soft tissues, which supply it with blood. The lingual periosteum is usually pliable enough to follow the upward movement of the segment without resistance and also allows the segment to be navigated into the desired position to allow dental implants to be placed within the prosthetic axis. Stable fixation of the segment at the desired height is achieved from the vestibular aspect with 1.5-mm Micro titanium plates (KLS Martin). Thereby a box-shaped cavity opens up under the segment, which can be filled with the drill chips and bone substitute material. Then, after 4 months, a loadable implant site is present, and the plates can be removed. The technique can also be used analogously in the anterior maxilla, but there the palatal mucosa is rigid, so distraction osteogenesis is used for height deficits of more than 2 to 3 mm.

Fig 8-9 Bone defects according to the quarter classification. The size of the circle shows the increasing demand on neoangiogenesis; defects larger than 1/4 overtax angiogenesis, so that they ossify only partially or the bone substitute does not heal (see Fig 2-21). The sandwich osteotomy doubles the angiogenesis distance, because both of the connecting bone surfaces are supplied with blood.

Fig 8-10 a. Average bone height gain by jaw region and partially edentulous and edentulous cases. About 2 mm of the original height gain is lost due to remodeling prior to implant placement. b. From the time of implant placement, bone loss after sandwich bone grafting averages only 0.27 mm. c. Implant survival rate and implant success rate according to Kaplan Meier.

Swing osteotomy

In the 3/4 stage (according to the quarter rule; see Fig 1-11), a depressed pointed ridge is still present lingually, which would interfere with pure upward movement. In this situation, a shell technique with block grafts could be used (Fig 8-13). However, as an onlay technique, this is at risk of dehiscence. It is better to use the swing osteotomy. Here, the transport segment is mobilized as described above. However, it is not shifted vertically upwards, but swung up like a garage door. The inclined surface of the atrophied jaw positions itself horizontally and becomes a plateau for the subsequent implant placement. Therefore, the segment must also be of sufficient width, eg, 8 mm wide: 4 mm for the implant and 2 mm each to form the lingual and buccal implant sockets (Fig 8-14).

Fig 8-11 The position of the residual attached gingiva is shown in the center of the alveolar ridge by a short red line. During simultaneous GBR as well as during block placement, this zone moves lingually (shifted mucogingival border). Only in distraction osteogenesis and the sandwich procedure derived from it does the attached gingiva remain in the center of the alveolar ridge, where it stays in the emergence profile of the future implants.

Fig 8-12 Sandwich interposition. a. Initial position with vertical atrophy in bilateral free-end situation in the mandible. Minimal bone height above the nerve (about 4 mm). b. The soft tissue-supported bone segment is stabilized in the cranial position with microplates (KLS Martin). A box-shaped bone cavity opens up. c. Mixture of venous blood, 75% bone substitute (Bio-Oss, Geistlich), and 25% autologous bone chips (from the filter). d. Filled interpositional defect. e. Postoperative panoramic tomography. f. After 4 months, the plates are removed, and the new bone height is used for dental implants. g. Fixed prosthetic restoration. h. Left mandible 10 years later. i. Right mandible 10 years later. j. Panoramic image 10 years later, with no sign of vertical bone resorption in the area of the previous augmentations.

Fig 8-13 The 3/4 atrophy can be treated with a shell or interposition technique (top and middle). In contrast to the sandwich osteotomy (bottom), the segment is swung up like a garage door, which is why the method is called a swing osteotomy.

Horizontal interpositional bone grafts (ridge splitting)

Ridge splitting can be performed simultaneously with implant placement. In a comparative study, splitting had better implant survival (100%) than block placement (92.9%).²⁶ In another study using the split-crest technique implant survival was 97% after 10 years.²⁷

The prerequisite for ridge splitting is two splittable compact lamellae in the CBCT cross-section separated by a layer of cancellous bone. Normally, an excessively narrow stage 2/4 ridge no longer has enough bone to primarily stabilize the implant. With ridge splitting, however, the bone is widened so that it is possible to place the implants in a reasonably stable manner. This makes the overall treatment cheaper and faster than a two-stage procedure. But there is also a price to pay. The disadvantage of ridge splitting is that the splitting direction determines the implant axis, and in the anterior maxilla, with its inclination of about 20 degrees, it does not correspond to the ideal prosthetic axis (Fig 8-15). Therefore, angulated implants must be accepted, and, if necessary, screw-retained prosthetics must be dispensed with, because the screw axes protrude labially in the anterior maxilla after ridge splitting.

Fig 8-14 Interpositional bone graft with swing osteotomy. a. Initial situation with the mandibular right posterior prosthesis out of occlusion due to atrophy and clasp trauma at the canine. b. Panoramic radiograph showing initial situation. Bone height above the nerve is approximately 8 mm. c. Segment osteotomy and swinging up of the segment, pedicled at the lingual soft tissues. d. Interpositional gap filled with bone mixture. e. Incision in the center of the alveolar ridge (with residual attached gingiva) allows for excellent suturing. f. The left side following augmentation. g. Postoperative panoramic image. h. Implant placement on the left side.

Fig 8-14 Interpositional bone graft with swing osteotomy. i. Panoramic image after insertion of normal-length implants (11 mm). j. The midcrestal incision is used as access for all surgical steps. k. The residual trace of the attached gingiva is automatically distributed around the implant like a cuff through the midcrestal incision. The implant emerges at the point where the tooth had already erupted. l. Perfect cuff of attached gingiva, created spontaneously without any soft tissue augmentation. Proper incision guidance saves patients the effort and expense of soft tissue grafting surgery. m. Anterior maxillary prosthesis. n. Mandibular left (left) and right (right) prostheses.

Fig 8-14 Interpositional bone graft with swing osteotomy. o. Prosthetic restoration in the left mandible. p. Prosthetic restoration in the right mandible. q. Occlusal view of the restored mandible. r and s.

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