7
Soft Tissue Management and Augmentation
In the contaminated environment of the oral cavity, an avascular bone block graft requires a closed soft tissue covering that is as bacteria-proof as possible for trouble-free healing. The soft tissue covering keeps bacteria out in a phase in which the grafted material does not yet have its own defense and vascularization. In some cases, blood vessels grow from the soft tissue into the graft, as a result of which the osteoclasts and osteoblasts required for incorporation appear.
7.1 Dimensions of the Soft Tissue around the Dental Implant
As a rule of thumb, the soft tissue height in the edentulous region is 1.5 mm. If the gingiva can rest on one side against a crown on the vestibular surface, it rises to 3 mm, which corresponds to the average value of the biologic width. If it can support itself between two teeth on both sides, it rises 6 mm above the bone, which is easy to remember because the amount doubles in each case (Figs 7-1 and 7-2).
There is little human data on true soft tissue dimensions, which is also due to the clinical measurement inaccuracy of periodontal probes. The soft tissue thickness of edentulous areas in the implant site can be inferred from clinical studies to be about 2 mm, depending on the biotype.1 There are animal experimental data on the biologic width at dental implants, which have been measured very accurately histologically. According to this, the biologic width is about 2 mm of junctional epithelium and 1.3 to 1.8 mm connective tissue plus the sulcus depth.2 The Tarnow rule on teeth stated that a contact point 5 mm above the bone crest had a greater than 98% probability of a papilla, >6 mm had a 56% probability, and >7 mm had a 27% probability.3 These measurements were repeated by Tarnow for the space between an implant and a tooth, and these were slightly lower, with 100% at <5 mm and 50% probability at >5 mm papilla height above the bone.4 A recent meta-analysis showed a 95% probability that the papilla will rise 5.94 mm above the bone.5 Between two adjacent dental implants, only 3.4 mm of soft tissue height can be expected,6 which is why this situation should be avoided in the anterior region by inserting pontics or bridge attachments if possible.
Fig 7-1 The mean values of the biologic width in millimeters on the tooth on the left and on the implant on the right. The soft tissue attachment apparatus consists of a connective tissue zone, inner marginal epithelium, and free gingiva. For the implant it is indicated that the bone can be thicker and higher than at the tooth. The coronal starting point for the apical marginal epithelium is usually the abutment gap, as this generates an inflammatory infiltrate via escaping bacterial toxins, which leads to detachment of the marginal epithelium coronal to the gap.
7.2 Access Incision Guidelines
As access incisions, the exact midcrestal incision in edentulous areas and the sulcular incision on teeth takes into account the blood supply conditions in the alveolar process7 (Fig 7-3). The midline of the alveolar ridge can be recognized by the linea alba, meaning “pale line,” whose appearance is caused by the minimal blood supply in the tissue underneath. This is due to scar healing after the two occurrences of both tooth eruption and tooth loss, at least in the anterior jaw, where the primary and permanent teeth were present prior to edentulism (Fig 7-4).
When there was still a tooth in the edentulous segment, the vestibular gingiva was vascularized externally by vessels from the labial artery, and the palatal gingiva was vascularized internally by the palatine artery, with similar nerve development. Tooth loss does not change this; anastomoses rarely form between these supply areas after tooth extraction. Shifting the incisions palatally or vestibularly may cause wound margin necrosis of the protruding, poorly perfused flap margin. This portion of the flap likely is saved in such displaced incisions in the edentulous ridge by connecting it longitudinally as in a bridge flap. Blood flow to the wound margin is essential for soft tissue healing, and this should be the most important criterion for incision placement. Vertical relief incisions should be used sparingly and, if possible, not at all in the esthetic area. It is better to place relief incisions in the labial frenum and retromolar area.
If teeth are adjacent to an edentulous jaw section, the midline incisions are continued intrasulcularly as a gingival margin incision. The gingival margin incision is bacteria-proof after only 24 hours due to the high rate of cell division in the junctional epithelium, as these cells attach to the tooth with hemidesmosomes. In addition, the marginal gingiva is by nature the zone of confrontation with plaque bacteria and is immunologically best prepared (Fig 7-5).
The scar in the sulcus has already been created by the erupting tooth, so the surgeon does not create any new scars, as in the case of the alveolar midcrestal incision. Both the midcrestal incision and the sulcular incision leave no visible scars and do not cut any important vessels. Thus, the flap in between remains scar-free and unaffected in its nervous and vascular architecture. This is important in case further interventions are needed at this site later in life, which would not be uncommon with implants. Augmentation surgery is not always the last intervention at this site in the patient’s life. Perhaps peri-implantitis treatment or other revision treatment will need to be performed a few years later. If the bone augmentation procedure is so critical that it can only be healed with atypical soft tissue flaps such as vestibular incisions, then in case of doubt the augmentation procedure should be focused on rather than the incision, or the former should be adapted to the soft tissue anatomy. As a surgeon, the following applies once again: Primum non nocere!
Fig 7-2 Approximate soft tissue thickness as a rule of thumb in the edentulous, vestibular, and interdental regions, which doubles each time. By bringing the bone to the correct height, these figures can be used to control the soft tissue height and achieve optimum esthetics.
Fig 7-3 The gingival margin incision (sulcular incision), together with the alveolar ridge incision, causes the least damage to the natural blood flow pathways and the innervation of the gingiva. In a sense, the midcrestal incision is the sulcular incision of the edentulous ridge, because the palatal and buccal gingival flaps have previously shrunk to the center in the course of alveolar healing, thus taking their vascularization (red) and innervation (yellow) with them.
Fig 7-4 In the edentulous jaw, there is hardly any anastomosis beyond the center of the alveolar ridge. In the center of the alveolar ridge, therefore, the linea alba is found as a zone of low blood supply and favorable for incision.
Fig 7-5 The sulcular incision is located in a natural scar already created by the erupting tooth, and no additional scars are created by the sulcus incision. In addition, the sulcus incision can heal within 24 hours in a bacteria-proof manner because the inner junctionall epithelium has a high cell division rate and can quickly form hemidesmosomes to the tooth or restoration. Finally, the sulcular incision is in the region of natural defense against plaque bacteria, so the immune system is already present. This all explains the enormously reliable and rapid healing of a sulcular incision.
7.3 Flap Types
In the implant placement and bone grafting phase, it makes sense to preserve the alveolar ridge periosteum of the intact mucoperiosteal flap by gentle subperiosteal preparation (Fig 7-6). Partial-thickness flaps are generally not indicated in bone augmentation surgery. There are several reasons for this. There is hardly any bleeding in the subperiosteal layer, so the wound remains dry and clear. The intact periosteum protects the nerves and vessels behind it, such as the mental nerve. Due to the fully permanent detachment of the mucoperiosteal flap, the juga alveolaria (alveolar yokes) are clearly visible, which is a good orientation aid, eg, for assessing the axis of adjacent teeth next to the implant site. In addition to serving as a membrane, the periosteum is also a good structure for positional stabilization of particulate bone grafts.
The alternative, further preparation not beneath but on top of the periosteum to form a split-thickness flap, takes place directly in the blood-bearing layer of the flap and destroys part of its vascular architecture. The extent to which this also compromises the nerve supply and thus the sensitivity of the marginal gingiva is largely unknown. Split-thickness epiperiosteal flaps have little place in bone augmentation surgery. The advantage of split-thickness flaps is their mobility due to the elasticity of the vestibular alveolar mucosa. Therefore, split-thickness flaps are a good alternative for coverage of extraction sockets in case of a history of bisphosphonate use or for fistula coverage in the maxillary sinus. Another advantage is that a perfused periosteum remains on the maxillary bone, which is why this flap provides good soft tissue support for nourishing a soft tissue graft. The split-thickness flap is therefore the standard flap in periodontal plastic surgery. The mobility of the gingiva on the periosteal support is also the reason why this flap is popular for implant uncovering.
Fig 7-6 Full-thickness flaps (mucoperiosteal flaps, left) are more suitable for general oral surgery, bone augmentation, and implant placement in phase 1. This preparation heals without scarring and can be repeated several times without changes for the patient. Partial-thickness flaps (right) are used less frequently, especially for implant uncovering (phase 2) and periodontal plastic surgery, where a vascularized bed on the periosteum is needed for soft tissue grafts. Otherwise, epiperiosteal preparation destroys the natural soft tissue architecture and its vessels.
Both flaps, full thickness and partial thickness, can be displaced laterally, apically, and coronally. Apically positioned flaps are used, for example, in surgical crown lengthening or in peri-implantitis therapy for pocket elimination. Periosteal sutures are required to position a flap apically. Coronally positioned flaps are used for recession coverage, for example. To anchor a flap coronally, double crossed sutures are required, which are placed on the interdental contact point for tight adaptation. In the case of loose contact points, non-bonded composite bridges are placed on the contact point to prevent the gingival pull-up sutures from slipping.
7.4 Vestibuloplasty and Other Soft Tissue Plastic Surgery
If the partial-thickness flap is prepared further apically on the periosteum, the muscle attachments of the buccinator muscle reach halfway up the tooth roots. Vestibuloplasty begins when the dissection is deeper than this muscle and the muscle fiber attachments are separated from the bone. Vestibuloplasty is indicated in the edentulous jaw to improve the denture support. If performed in partial areas of the jaw, the technique is performed to obtain a periosteal surface that can be covered with a mucosal graft with the aim of widening the attached gingiva. In the mandible, when the attachment of the mylohyoid muscle is separated lingually, it is referred to as lowering of the floor of the mouth (Fig 7-7).
Further soft tissue plastic surgery, such as ligament correction by Z-plasty or V-Y plasty, is rarely indicated in augmentation surgery because the underlying ligaments usually disappear by themselves in the course of flap coverage of the augmented bone.
Fig 7-7 Definition of lowering of the floor of the mouth or vestibuloplasty by severing the muscle attachments of the mylohyoid or buccinator muscles.
7.5 Flap Tension and Mobilization
A problem of all overlay bone grafts in contrast to interpositional grafts is the flap tension generated in the soft tissue to cover the additional volume. Flap tension causes compression of the capillaries on a microscopic scale. This can be thought of as similar to a wire mesh. If this is stretched in the longitudinal direction, the mesh closes more and more until the tubes of the capillaries contained therein are closed off. This is how necrosis of the flap tip and the wound dehiscence develop.
Anything that impairs local tissue blood flow, such as nicotine use, uncontrolled diabetes mellitus, history of tumor irradiation, or points and sharp edges below the flap, can promote dehiscence. The flap should be well cushioned from below, eg, by smoothing the bone or placing collagen membranes. The effect of a sharp edge, eg, a protruding particle of a bone graft substitute, is to concentrate force on a point of the tissue, resulting in a pinpoint depression of blood flow. When this pressure is applied for some time, ischemic necrosis of the flap is thus produced.
Surgical flap procedures
The flap tension should be relieved by particularly gentle tissue mobilization. To do this, the flap is grasped with a fine Gillies single hook retractor and pulled over the augmentation on a trial basis. This shows how much length is missing. The flap should never be grasped with tweezers because they unnecessarily compress the edge of the tissue to hold it! One can least afford such an unnecessary trauma at the edge of the flap, where the primary wound healing is to take place later.
The flap is held tightly with the single hook in one hand. The taut periosteum is seen as the limiting structure. With a fresh 15c scalpel in the other hand, the taut periosteal fibers are now cut individually under visual control. This brings about 5 mm of flap extension, which can be seen immediately under traction with the single hook. This is done very carefully, as the nerves (eg, mental nerve) and blood vessels running behind the periosteum must not be damaged under any circumstances. The scalpel should be able to avoid these because they lie more loosely than the taut periosteal fibers. Blood vessels that are inadvertently injured in the deep opening of the periosteum are responsible for the cheek hematomas of some patients after augmentation procedures. They are largely avoidable with a proper surgical technique; at the very least, such hemorrhages should be carefully stopped intraoperatively by means of bipolar coagulation. Another mistake in periosteal incisions is perforations into the vestibule. It is best to ensure that both sides of the flap are well visible and to work only in the uppermost periosteal layer.
The single hook is now inserted again for testing. If the flap is still too short or is under too much tension, closed Metzenbaum dissecting scissors (with round ends) should be inserted into the periosteal incision and used to spread the tissue in a submucosal direction. If this is still not enough, one can insert a blunt elevator into the periosteal incision and elevate the flap. One should never make a deep incision in this situation because the restraining structure in the maxillary vestibule is often the infraorbital nerve, which at most should be stretched slightly but not cut. In the end, the flap should be able to be pulled loosely with the single hook over the augmentation with some excess; this indicates the mobilization is correct.
7.6 Suture Technique and Material
Sutures that are too tight or too taut have a similar effect on blood flow as harmful flap tension. In surgical courses and books, enormous emphasis is sometimes placed on suturing techniques and elaborate interlacing of sutures is presented in drawings. In nature, however, blood must still be able to flow between the stitches and loops of the sutures; otherwise, the tissue becomes necrotic. The transverse lines that are sometimes seen after the sutures are removed, and that are often drawn in popular depictions of scars, are the zones of necrosis where the tissue directly under the suture has been squeezed and has become necrotic. So every suture creates a trauma; one should be aware of that.
The suture technique should be selected in such a way that, as far as possible, there is an optimum ratio between the tightness of the suture against the oral cavity and the strangulation of the microcirculation at the wound margin. This can be achieved, for example, by fine sutures (5-0) at the wound margin, supplemented by somewhat stronger holding sutures (4-0) in the flap periosteum away from the wound margin, which absorb the tension. However, less is often more. Although it appears simple, the interrupted suture strikes a very good balance between trauma and flap adaptive force. It is surpassed only by the continuous (spiral) suture, which uses half the number of stitches. “It can only heal between the sutures,” was a popular saying of the author’s teacher Prof. Dr. Dr. Franz Härle. This meant that it was better to have a few well-placed, strong sutures than countless small sutures under the microscope.
In the end, suturing depends on a clean macroscopic adaptation of perfused wound edges. Ultimately, it is probably illusory to believe that sutures can be used to close the wound in a bacteria-proof manner; at least in the stitch holes, the bacteria can penetrate along the suture into the depths. A surgical suture must, along the threads, always leave gaps in the woung margin for circulation, and at these points the tissue layers lie more loosely against each other. Tight sutures are most likely to work in the attached gingiva, because here the tissue elasticity of the alveolar mucosa does not allow the muscles of the cheek to pull the wound open.
In practice, bone augmentation wounds are on average sutured with atraumatic 4-0 pseudomonofilament polyamide with a sharp needle (eg, Supramid, Resorba; Fig 7-8). For smaller bone grafts, the thickness 5-0 or 6-0 is also sufficient, but these threads are then no longer twisted pseudomonofilament but monofilament, which results in poorer knot strength. Pseudomonofilament means that a thread is twisted like silk, but coated with plastic. Purely twisted polyfilaments, such as absorbable polylactide filaments, accumulate an enormous number of bacteria after some time8 and have a wicking effect into the interior of the tissue.9,10 Thus, they do not heal as irritation-free as monofilament or pseudomonofilament types.
It is also important to have a defined final strength of the knotted loop, which should not loosen again over time. This is particularly important for sutures in the attached gingiva and at the gingival margin. The rubbery elasticity of some suture materials is rather counterproductive in these areas.
Fig 7-8
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