Design Parameters for Soft Tissue Flaps
To provide adequate exposure and promote rapid healing,the flap must be correctly designed. The surgeon must remember that several parameters exist when designing a flap for a specific situation.
When the flap is outlined, the base of the flap must usually be broader than the free margin to preserve an adequate blood supply. This means that all areas of the flap must have a source of uninterrupted vasculature to prevent ischemic necrosis of the entire flap or portions of it (Fig. 8-1).
The flap must be’ of adequate size for several reasons,Sufficient soft tissue reflection is required to provide necessary visualization of the area. Adequate access also must exist for the insertion of instruments required to perform the surgery. In addition, the flap must be held out of the operative field by a retractor that must rest on intact bone. There must be enough flap reflection to permit the retractor to hold the flap without tension. Furthermore, soft tissue heals across the incision, not along the length of the incision, and sharp incisions heal more rapidly than torn tissue. Therefore a long, straight incision with adequate flap reflection heals more rapidly than a short, torn incision, which heals slowly by secondary intention. For an envelope flap to be of adequate size, the length of the flap in the anteroposterior dimension. usually extends two teeth anterior and one tooth posterior to the area of surgery (Fig. 8-2, A). If a relaxing incision is to be made the incision should extend one tooth anterior and one tooth posterior to the area of surgery (Fig. 8-2, R).
The flap should be a full-thickness mucoperiosteal flap. This means that the flap includes, the surface mucosa, submucosa, and periosteum. Because the goal of the surgery is to remove or reshape the bone, all overlying tissue must be reflected from it: In addition, full thickness naps are necessary because the periosteum is the primary tissue responsible for bone healing, and replacement of the periosteum in its original position hastens that healing process. In addition, torn, split, and macerated tissue heals more slowly than a cleanly reflected full thickness flap.
The incisions that outline, the flap must be made over intact bone that will be present after the surgical procedure is complete If the pathologic condition has eroded the buccocortical plate the incision must be at least 6 or 8 mm away from it. In addition, if bone is to be removed over a particular tooth, the incision must be sufficiently distant from it so that after the bone is removed, the incision is 6 to 8 mm away from the bony defect created by surgery. If the incision line is unsupported by sound bone,it tends to collapse into the bony defect, which results in wound dehiscence and delayed healing (Fig. 8-3).
The flap should be designed to avoid injury to local vital structures in the area of the surgery. The two most important structures that can be damaged are both located in the mandible these are the lingual nerve and the mental nerve. When making incisions in the posterior mandible especially in the region of the third molar incisions should be well away from the lingual aspect of the mandible. In this area the lingual nerve may be closely adherent to the lingual aspect of the mandible and incisions in this area may result in the severing of that nerve, with consequent prolonged temporary or permanent anesthesia at the tongue in the same way, surgery in the apical area of the mandibular premolar teeth should be carefully planned and executed to avoid injury to the mental nerve. Envelope incisions should be used if at all possible, and releasing incisions should be well anterior or posterior to the area of the mental nerve.
Flaps in the maxilla rarely endanger any vital structures.On the facial aspect of the maxillary alveolar process, no nerves or arteries exist that are likely to be damaged. When reflecting a palatal flap, the dentist must remember that the major blood supply to the palatal soft tissue comes through the greater palatine artery, which emerges from the greater palatine foramen at the posterior lateral aspect of the hard palate. This artery courses forward and has an anastomosis with the nasopalatine artery. The nasopalatine nerves and arteries exit the incisive foramen to supply the anterior palatal gingiva. If the anterior palatal tissue must be reflected, both the artery and the nerve can be incised at the level of the foramen without much risk. The likelihood of bothersome bleeding is small, and the nerve regenerates quickly. The temporary numbness usually does not bother the patient. However, vertical releasing incisions in the posterior aspect of the palate should be avoided, because they usually sever the greater palatine artery within the tissue, which results in bleeding that may be difficult to control.
Releasing incisions are used only when necessary and not routinely. Envelope incisions usually provide the adequate visualization required for tooth extraction in most areas. When vertical releasing incisions are necessary, only a single vertical incision is used, which is usually at the anterior end of the envelope component. The vertical releasing incision is not a straight vertical incision but is oblique, to allow the base of t.he flap to be broader than the free gingival margin. A vertical releasing incision is made so that it does not cross bony prominences, such as the canine eminence. To do so would increase the likelihood of tension in the suture line, which would result in wound dehiscence .
Vertical-releasing incisions should cross the free gingival margin at the line angle of a tooth and should not be directly on the facial aspect of the tooth nor directly in the papilla (Fig. 8-4). Incisions that cross the free margin of the gingiva directly over the facial aspect of the tooth do not heal properly because of tension; the result is a defect in the attached gingiva. Because the facial bone is frequently quite thin, such incisions will also result in vertical clefting of the bone. Incisions that cross the gingival papilla damage the papilla unnecessarily and increase the chances for localized periodontal problems such incisions should be avoided.