Autogenous
Closure of OAF can be achieved using different flap techniques, each of which presents both advantages and limitations. Three types of flaps are most widely used: a buccal flap, a buccal fat pad (BFP) flap, and a palatal flap.
In 1936, Rehrmann [
11] described the use of a buccal advancement flap. Krompotie and Bagatin reported that the rotating gingivovestibular flap can also be applied for closure of an antrooral fistula. This technique is a modification of a vestibular flap with the aim of preventing the lowering of the vestibular sulcus, which regularly accompanies the application of vestibular flaps [
12]. The flap with its simplicity, reliability, and versatility is the most commonly used method for OAF closure [
5,
13].
In this technique, a broad-based trapezoid mucoperiosteal flap is created after excising the epithelialized margins and giving two vertical release incisions to develop a flap with adequate dimensions to be sutured over the defect. Its broad base enables a better blood supply to the flap. Flap coverage is improved by horizontal periosteal incisions. Falci et al. described a modification of this technique for OAF closure. The mucosal margins of the fistula were sutured together prior to the reflection of the buccal flap. Then, the buccal flap was pulled over this sutured site and tucked under the palatal flap, which was elevated simultaneously with the buccal flap [
13]. Killey, in 1972, studied 362 cases using this technique. The results revealed success in 336 (93%) cases [
5]. However, the potential disadvantage of using this flap for OAF closure is the reduction of buccal sulcus, which makes it difficult to use prosthesis in the future [
1]. Other disadvantages include postoperative pain and swelling as a result of the reflection of a mucoperiosteal flap. Currently, a reduction in the buccal sulcus can be overcome by implant-retained overdentures.
Môczáir [
14] described closing alveolar fistulas by the buccal sliding flap, shifting the flap one tooth distally. This technique produces only a negligible change in the depth of the buccal vestibule. A drawback of this approach is that it requires a large amount of dentogingival detachment in order to facilitate the shift, which may result in gingival recession and periodontal disease.
The first description of a technique for closing oroantral fistula using a full-thickness palatal flap based on greater palatine artery dates back to Ashley [
15]. Advantages of the palatal flap include high vascularity, generous thickness, and quality of tissue. Moreover, this flap is more resilient, less prone to infection, very resistant to lacerations, and does not lead to lowering of the vestibule. However, the most significant disadvantages are flap necrosis [
15], exposed bony surface, pain, and development of surface irregularities as a result of secondary epithelialization post operatively [
2]. In 1980, Ehrl employed this technique with wide fistulas of 1 cm in diameter [
16]. The technique consists of excising the epithelium from its edges and incising the palatal fibro-mucosa so as to create a flap with a posterior base, supplied by the greater palatine artery. The anterior extension of the flap must be wide enough to exceed the diameter of the bony defect and long enough to allow lateral rotation. Tension-free suturing should be performed [
8].
The palatal flap has different forms that can be classified by thickness, namely, mucoperiosteal, or by the direction of movement, namely, straight advancement flap, rotation advancement flap, hinged flap, pedicled island flap, anteriorly based flap, submucosal connective tissue pedicle flap, and submucosal island flap.
The palatal mucoperiosteal rotation flap is particularly recommended for the late repair of oroantral fistula [
8]. The base of the flap should be broad enough to cover the defect. A full-thickness palatal flap is typically performed lateral to vascular supply and 3 mm apical to the marginal gingiva of the teeth. The mucoperiosteal flap is raised from the anterior to posterior, rotated, and sutured to secure a tension-free closure of the fistula. [
8]. With this technique, kinking formation at the rotation point and the base of the flap may compromise the vascular supply [
8]. The most important advantages of the technique are rich vascularization, excellent thickness, and easy accessibility.
The palatal straight advancement flap is of limited use due to the inelastic nature of the palatal tissue, which reduces its lateral mobility. For the same reason, it is suitable for the closure of minor palatal or alveolar defects [
17].
The palatal hinged flap has been used successfully to close small fistula of the hard palate, i.e., those less than 2 cm in diameter in a one-stage operation [
18]. The procedure is based on raising a full-thickness flap directly adjacent to the fistula based along one fistula edge and turning this like a hinge over the fistula so that its buccal surface will lie uppermost in the fistula. The main advantage of this technique is that only a small raw area for granulation is left behind following closure of OAF.
Another single-stage local flap is the palatal pedicled island flap. It offers the great advantages of a rich vascular supply, adequate bulk, and mobility. In elevating the flap, incisions are performed according to the amount of donor tissue required to resurface the oral fistula. Incisions can be made at the junction of the hard and soft palate and within 5 mm of the dentition. This allows for harvesting a flap that can be rotated 180° without strangulation of the vascular pedicle. This procedure is the preferred flap for many surgeons because of its versatility, simplicity, and mobility [
19]. The technique is ideal for the closure of posterior fistula due to its ability to transfer large well-vascularized area of tissue. Furthermore, the donor site defect, which overlies the hard palate, decreases the donor site morbidity. Therefore, use of this procedure is limited in closure of anterior defect as a result of stretching of these vessels when the flap is advanced too far anteriorly. The palatal anteriorly based flap is particularly useful for closure of large oroantral fistula and correction of defects at the tuberosity region. The procedure involves a lateral transposition of mucoperiosteum of the posterior third of the hard palate with an anteriorly based palatal flap. The flap is raised to bridge large defects without leaving any considerable exposed raw area [
20]. The modified submucosal connective tissue flap was designed by Dergin et al. [
21] for closure of OAF. Elasticity of the flap prevents folding formation and allows for better manipulation and adaptation in the closure of an OAF in the second and third molar region. Another advantage is that no palatal acrylic plate is required postoperatively. In this technique, an H-type window-like incision is made in the palatal mucosa 4 mm from the gingival margins of the posterior teeth, with the medial incision 2–3 mm from the midline. After excising the fistula wall and curetting the granulation tissue, the mucosa of the two minor flaps of the H-type window-like incision is raised and separated from the underlying connective tissue without jeopardizing the continuity of the mucosal flap. The underlying vascularized connective tissue is dissected in the premolar-canine region, where the incisive and greater palatine arteries anastomose. The connective tissue is raised with periosteum and rotated. The rotated flap is passed through a full-thickness tissue tunnel that had been previously prepared on the palatal side of the OAF. The flap is inserted under the buccal mucosa and sutured without any tension. The H-type minor flap is also sutured and left for primary healing. Hara and Ito designed the submucosal connective tissue pedicle flap by dividing the flap into an upper mucosal layer and underlying connective tissue layer to overcome the problem of bone exposure at the donor site [
22]. The technique is achieved by separating the full-thickness palatal flap into a mucosal layer and an underlying connective tissue layer. The submucosal connective tissue flap is used to close the fistula, and the mucosal part of this flap is then returned to its original position and sutured in place to obtain primary closure. They reported that the healing at the donor site occurred within 1 month [
22]. The disadvantages of this technique are the difficulty of the dissection and possibility of injuring the blood supply [
22]. A submucosal island flap is indicated in the closure of a large oroantral fistula. With this technique, a palatal pedicle flap based on the greater palatine vessels is formed. Depending on the size, shape, and location of the fistula, the anterior part of the submucosal connective tissue flap is made. In addition, the anterior part of the submucosal connective tissue is used to design the island flap. After raising the palatal mucoperiosteum, the island flap is passed under the alveolar tissue bridge across the defect and sutured to the edge of the fistula without tension. The significant advantages of this flap are ample blood supply and mobility without tissue bunching [
23]. In addition, healing is satisfactory without denuded bone. Yamazaki concluded that the dissection of the palatal flap into the epithelial layer and the underlying connective tissue does not pose technical difficulty [
23]. A palatal pedicle flap is used to close an OAF with the advantages of preserving keratinized mucosa and buccal sulcus depth in the area of the fistula. The flap is a one-stage procedure. Preoperative procedure includes making a self-curing acrylic resin plate over the patient’s cast model. The first surgical step is excision of the epithelial fistula wall, followed by division of the flap on the palatal mucosa through an incision, superficially to the periosteum. The flap is passively positioned and thoroughly sutured. The donor site is then protected with surgical cement and held in place by the self-curing acrylic resin plate. The acrylic plate is fixed with bone screws and maintained in place for 10 days [
24]. The ratio of length to thickness of the flap is critical for the survival of the palatal pedicle flap, thus splitting of the flap should be carried out very judiciously [
24]. The Random palatal flap is considered an adequate option for closure of oroantral fistula in difficult locations such as in the tuberosity area. Lee et al. reported a success rate of 76% of random palatal flaps in 21 patients [
25]. He pointed out that the most important factor determining the clinical outcome of palatal flaps was an appropriate length to width ratio. The random palatal flap is based on the anastomoses spread throughout the palate; all rely on greater palatine artery for nutrition. The buccal fat pad (BFP) is a lobulated mass of adipose tissue surrounded by a thin fibrous capsule, located between the buccinator muscle medially, the anterior margin of the masseter muscle, and the mandibular ramus and zygomatic arch laterally [
26]. The buccal pad of fat is exposed through a 1 cm long vertical incision in the reflected periosteum posterior to the zygomatic buttress. Thereafter, it is gently manipulated by pressing extraorally below the zygomatic arc. Finally, the fat pad is sutured to the palatal tissue, covering the oroantral fistula [
27]. The BFP derives its blood supply from branches of the superficial temporal, maxillary, and facial arteries. The advantages of this technique include good epithelialization of the uncovered fat and a high rate of success due to the BFP’s ample vascularity and proximity to the recipient site. Other beneficial features of the BFP flap are the straightforward harvest and minimal dissection required to harvest and to mobilize the flap [
28]. The study of the long-term effectiveness of the BFP technique in the closure of large OAFs supported these features [
29]. The disadvantage is the decrease in the vestibular height. It has been concluded that closure of large defects could involve complications such as graft necrosis or new fistulas [
30]. The buccal fat pad is a feasible option for cases with damage to the alveolar buccal or palatal mucoperiosteum, cases that have failed with other methods, and repairs of large defects in the tuberosity area [
31]. However, success of the buccal fat pad is extremely influenced by the communication size [
32].
Free mucosal grafts (FMG) or connective tissue grafts (CTG) are suitable for the closure of small to moderate size defects in the premolar area as well as small to medium size-persistent defects. In contrast to the techniques described so far, the harvested grafts are not directly vascularized. The flap initially receives its nutrients within the
first three postoperative days by diffusion alone, so-called plasmatic circulation. After day 3, the nutrition is provided by the ingress of blood capillaries from the recipient bed for revascularization. However, the size of the defect and the thickness of the graft play a crucial role in plasma circulation and nutrition of the transplanted cells. The main donor site for FMG/CTG is the palate, the maxillary tuberosity or edentulous alveolar ridges. Struder demonstrated that the thickest part of the palate and the most favorable donor site is in the premolar area [
33]. The thickness of the mucosa decreases distally and becomes thicker once more in the area of the tuberosity. However, the inadequate area is small compared to the premolar area. To perform a FMG, the wound margins of the recipient bed are de-epithelialized according to the techniques already described and the defect to be closed is measured. Using a template, the size of the defect can be projected onto the palatal premolar area and the graft can be harvested. Within 3–4 weeks, the palatally exposed site heals completely above the free granulation. The donor site of the subepithelial connective tissue graft extends from the canine region to nearly the palatal root of the first molar. Free mucosal grafts (FMG) are suitable for closing the OAF to the maxillary second premolar region. Laterally, a distance of 2 mm from the gingival margin should be considered the minimum and a minimum 2-mm zone of the
marginal gingiva should be maintained at the donor site. Medially, the boundary is the vascular-nerve bundles, which, depending on the anatomy of the palate, are 7, 12, or 17 mm away from the palatal cemento-enamel junction. After the incision, the subepithelial connective tissue is dissected and harvested according to the size of the defect. The harvested grafts (FMG/CTG) are then placed on the defect and adapted by sutures on the de-epithelialized wound margins. The pedunculated subepithelial connective tissue graft is particularly
well suited for covering defects in the molar region. Similar to a non
-pedunculated graft, this technique also uses a variety of incision techniques. In our polyclinic, we prefer to use the “trap door” technique favored by Wachtel [
34]. According to Wachtel’s technique, an incision is performed at a distance of 2 mm from the gingival margin and extends, according to the extent of the defect, to the canine region. Subsequently, the scalpel is then angled off; a mucosal flap is prepared about 1.0–1.5 mm medially and a step approximately 1.5 mm is made. The subepithelial graft is then prepared mesially, medially, laterally, and basally. An
undermining “
bridge” between the alveolus or defect and the incision is prepared in the mucosa, and the graft is then placed under the bridge in the defect and fixed at the wound margins with sutures. As with the pedunculated palatal rotation flap, the blood supply to the graft is provided through the greater
palatine artery, the anastomosis of the nasopalatine artery and sphenopalatine artery. In addition to the preservation of the vestibule and the associated favorable prosthetic options, the pedunculated subepithelial connective tissue graft is applicable to the majority of possible defects. Considering the blood supply by the greater
palatine artery, clinicians and patients can expect a high probability of graft success. Due to its high elasticity, the graft can be effortlessly adapted free of tension [
8]. With the use of this technique and the application of a step according to Wachtel, the wound margins can be optimally adapted and wound healing can be ensured by primary intention. Furthermore, there is no free exposed area so postoperative complaints are low [
35]. The disadvantages of this technique include the long duration, high costs, and the ability of the
surgeon [
35]
.
The tongue is an excellent donor site for soft tissue defects of the oral cavity, due to its pliability, position, and abundant vascularity. Tongue flaps can be created from the ventral, dorsal, or lateral part of the tongue [
36]. The surgical design of the flap is dictated by the location of the defect. A lateral tongue flap has been described as a suitable method for the closure of large OAF [
37]. The tongue flap has reported success rates varying from 85 to 95.5% [
37]. Complications of the technique include hematoma formation that can compress the pedicle leading to necrosis of the flap, wound dehiscence, and temporary loss of tongue sensation and taste [
38]. Additional disadvantages are the requirements for general anesthesia and multiple operations. The temporalis muscle flap is another distant flap, which can be used for closure of orofacial region defects. It has been indicated for one-stage closure of large oroantral communications. The temporalis fascia is sectioned above the arch to permit flap rotation. It is then brought into the oroantral fistula through a tunnel created in the infra temporal fossa. The temporalis muscle flap is far less bulky, well-vascularized, and more pliable; with minimal functional and esthetic sequelae; and in closer proximity to the oral cavity [
39].
The use of bone autografts for closing OAFs has been recommended in the literature [
40]. This procedure is indicated in closure of defects larger than 10 mm or in the case of failure of conservative methods to close the defect [
41]. Autografts harvested from the extraction socket, retromolar area, zygomatic process, chin, or distant sites like the iliac crest have been used for repairing the bony defect in maxilla [
9,
42]. Harvesting bone from intraoral donor areas offer the advantage of reducing the demands made on patients postoperatively.
Closure of OAF with a bone graft harvested from the iliac crest should be indicated for large defects because of the significant inherent donor site morbidity, prolonged postoperative pain, and possible sensory disturbance [
40,
43]. The use of monocortical bone grafts harvested at a chin site block for closure of an OAF is recommended for patients affected by maxillary atrophy requiring sinus augmentation before implant placement [
9]. A monocortical block graft is harvested at the chin by using a trephine with an inner diameter matching the size of the round bony defect. The graft is then press-fit into the defect. Soft tissue closure is established by using a flap.
A retromolar bone graft is a viable procedure for OAF closure. However, harvesting of a retromolar bone can occasionally be combined with removal of the third molar, which may affect acceptance of the procedure by patients [
44]. When compared to chin bone grafts, the significant disadvantage of the retromolar donor area is the confined amount of bone available [
45]. The incision is made medial to the external oblique ridge in an anterior direction and terminated in the first molar area to avoid interference with the mental nerve branches. A mucoperiosteal flap is elevated, and the exposed bone area is evaluated in consideration of the amount of bone needed at the defect site. A microreciprocating saw is used to make the osteotomies. The bone block is carefully lifted to ensure that the inferior alveolar nerve is not trapped within the graft. Osseous irregularities are trimmed with chisels or by using a large bur. The flap is repositioned and sutured [
45].
Zygomatic bone is a suitable donor site for OAF closure. The technique is indicated when a modest amount of bone is needed [
46]. In this procedure, an incision is made through the alveolar mucosa about 5 mm above the mucogingival junction, starting between the first and second molars, and proceeds anteriorly to the first premolar area. A full-thickness flap is raised with a periosteal elevator. The dissection extends to the inferior aspect of the infraorbital nerve and around the inferior half of the body of the zygoma. The lateral border of the maxillary sinus is visualized, and the inferior border of the orbital rim is palpated. Bone harvesting is started just above the inferior border of the zygomatic rim and lateral from the maxillary sinus. The incision is closed with running or interrupted resorbable sutures [
46].
This method offers the advantage of proximity of the donor area to the recipient area, which minimizes surgical time and patient discomfort [
46]. Moreover, surgical postoperative complications after zygomatic bone harvesting are minimal.
Recently, auricular cartilage graft has been used for the closure of OAFs. A full-thickness flap is raised at the defect site [
47]. A semicircular incision is then made posteriorly over the conchal cartilage. The conchal cartilage with overlying perichondrium is exposed with a blunt dissection. The harvested auricular graft is then adapted on the defect site and sutured with the surrounding tissue. The mucoperiosteal flap is then advanced and sutured with the palatal tissue. The technique is biocompatible, highly resistant to infection, and easy to harvest. Additionally, it does not require vascularization for the integration to the recipient site. Consequently, there is a decrease in the failure rate of the graft [
47]. A disadvantage of this procedure is the potential formation of a defect at the donor site.
The use of septal cartilage especially for larger oroantral fistulas was documented [
48]. A buccal mucoperichondrial flap is raised, generally starting two teeth mesial and ending, and if feasible, one tooth distal to the site of the fistula. An incision is performed at the caudal end of the septal cartilage, and a mucoperichondrial flap is raised on one side. A cartilage island is outlined and dissected free. The cartilage is trimmed and insinuated into defect as a horizontal plate [
48]. Saleh et al. obtained a success rate of 95.7% in their study using septal cartilage [
48].
According to Aladag et al., the modified Caldwell-Luc Approach is a satisfactory method to close oroantral defects [
49]. In the technique, which includes endoscopic examination using the Caldwell-Luc approach, the inside of the maxillary sinus is explored fully. The bone graft can be harvested from the bone of the anterior wall of the maxillary sinus by accessing the surgical entry tract. The positive features of the technique include the use of autogenous grafts, easy and adequate harvesting of the graft along the surgical route, and no need for a flap. Among its disadvantages are the fact that it requires endoscopic surgical equipment and experience.
An autogenous bone graft and platelet-rich fibrin (PRF) membrane as a treatment strategy for closure of OAF has also been proposed [
50]. PRF is a product of centrifuged blood. The biochemical components of PRF are well-known as factors acting synergistically in the healing process. This includes platelet-derived growth factor (PDGF), whose components are the reason why PRF has anti-inflammatory properties. The PRF membrane covers the graft, while the components contained in it have positive impact on its integration. A trapezoidal mucoperiosteal flap is formed in the oral cavity vestibule. The alveolar width of alveolus and the average height of alveolar bone lamina from the side of the oral cavity vestibule and from the side of the palate are measured intraoperatively. The next stage depends on the cavity diameter and involves collection of monocortical bone blocks from the mental protuberance or mandible oblique line. The bone blocks are formed in a way which makes it possible to wedge them in the cavity and tightly close the defect. The graft is stabilized using a bicortical screw or a titanium mini-plate. Bone irregularities are smoothed. The graft and surrounding bone are covered with a PRF membrane. Thereafter, the membrane is tightly sutured without tension the vestibule flap [
50].
More recently, triple-layered was introduced by George [
51]. This novel technique uses leucocytes-platelet-rich fibrin (L-PRF) membrane concomitantly with the buccal advancement flap and buccal fat pad. The platelet-rich fibrin membrane is placed over the buccal fat pad and completely covered by a buccal advancement flap. The positive feature of the L-PRF membrane is expediting the healing process by producing growth factors and leucocytes.
The use of PRF alone as a clot and a membrane for the closure of OAFs was documented by Assad et al. [
52]. They advocated closing OAFs by using PRF individually. PRF was prepared by taking blood samples into glass-coated plastic tubes without anticoagulant. The samples were centrifuged immediately. A fibrin clot was formed in the middle part of the tube. Then, it was separated from other acellular plasma and red blood cells. Thereafter one third of the fibrin was cut off and inserted gently into the OAF. The remaining two thirds of the clot were pressed gently with sterile dry gauze to drive out the fluids and form the membrane. The OAF site was covered with the membrane which was sutured to the gingival margins. PRF can be considered an autologous biomaterial and as well as a membrane. PRF as a membrane and grafting material facilitates formation of mineralized tissue due to osteoconductive and/or osteoinductive properties possibly inherent in PRF.
Synthetic closure of OAFs
Various synthetic materials have been used for OAF closures. Use of gold foil and gold plate for the closure of OAFs was reported for the first time by Goldman and Salman, respectively [
59,
60]. It is a simplified technique for the closure of oroantral fistulas. The technique consists of elevating the mucoperiosteum to expose the bony margins of the fistula. Then, the opening is covered with an overlapping margin of burnished gold foil.
The mucoperiosteal flaps are sutured across the gold foil without attempting to realize primary closure. Gold foil acts as a bridge for overgrowing sinus mucosa. After 6 weeks, the foil is exfoliated. A
disadvantage of this
technique is that it is
rather costly and the complete closure and healing requires a long period [
57]
.
Aluminum plates were suggested for OAF closures [
61]. According to Steiner, 36-gauge pure aluminum plate is used as a protective plate to aid in closure, using the same technique as in the gold procedure. Buccal and palatal tissues are approximated by sutures. Accordingly, the aluminum plate is constantly visible. After several weeks, the aluminum plate is removed from its initial position as a result of formation reparative tissue underneath. In addition to malleability and smoothness features, aluminum is inexpensive.
Tantalum is a highly biocompatible metal. It has been used for closures of OAFs by McClung and Chipps [
62]. Along the same lines as the gold technique, tantalum foil is used as a protective plate to aid in closure. The Tantalum foil was removed after 9 weeks. They reported formation of granulation tissue following the closure.
Closure of OAFs by titanium plate with transalveolar wiring fixation was documented [
63]. The results revealed good bony and soft tissue healing. Further, the use of two different materials titanium plates and stainless steel wires did not result complication or distaste because of galvanic current.
Polymethylmethacrylate has been introduced as an alternative technique for closing OAFs [
64]. After 24 h of immersion in a sterilizing solution, the polymethylmethacrylate plate is placed over the defect. Mucoperiosteal flaps are then replaced without attempting to cover the acrylic plate. The polymethylmethacrylate plate is removed as soon as the edges become exposed. One of the common disadvantages of this technique is the required time for preparation.
Recently, a dual otorhinolaryngological/oral approach was described in a patient with an OAF complicated by maxillary sinusitis [
65]. The investigators used the functional endoscopic sinus surgery (FESS) technique in combination with a titanium mesh to obtain optimal reconstruction and stabilization of soft tissue. A full-thickness vestibular flap was elevated, and the titanium mesh was fixed on the defect. Mesh removal was conducted after 6 to 18 months of healing based on clinic and radiographic evidence of OAF closure. The main disadvantage of this technique is the second surgery needed to remove the mesh. Despite this drawback, use of a titanium mesh assures predictable healing, mechanic scaffolding, and tissue stability.
Zide and Karas used nonporous blocks of hydroxylapatite to close oroantral fistulas by carving the blocks to fit the bony defect and encircling them with a wire for stability when needed [
66]. The investigators reported natural extrusion of the blocks without recurrence of a fistula [
10]. The technique offers a number of advantages, including ability to have a press-fit graft closure and no morbidity associated with a second-site surgery.
Various sizes of hydroxylapatite implants have also been used to close oroantral fistulas [
67]. Further, the remaining space in the socket was filled by hydroxylapatite granules. Oral mucosa was approximated without complete closure [
10]. Considering extrusion, the technique resulted in no cases of hydroxylapatite implant extrusion. Disadvantages include high costs and the need for various implant sizes to allow for size selection.
The use of a bioabsorbable root analog made of β-tricalcium phosphate for closure of oroantral fistulas was proposed by Thoma et al. [
68]. The root replicas were fabricated chair side, using a mold of the extracted tooth [
10]. The investigators reported that the healing was uneventful. However, fragmentary roots or overly large defects prevent replica fabrication or accurate fitting of the analog. The technique is simple and fast.