Pneumatization within a maxillary sinus graft: a case report

Discussion

In order to determine the potential cause of the pneumatization within the maxillary sinus graft reported in this case, various factors influencing the success of bone remodeling must be considered.

Later stage complications such as wound dehiscence, oroantral fistula, and postoperative maxillary cysts (mucocele) are relatively common [9]. A small oroantral fistula usually closes spontaneously if the patient is medicated with antibiotics and chlorhexidine solution. In the present case, the presence of an oroantral communication was observed 3 months postoperatively. The patient was not aware of this communication and was only informed of this during the clinical review. Therefore, since a spontaneous closure was not possible in this case, surgical measures for its correction were planned, along with administration of antibiotics.

Since the patient was submitted to a CT scan for treatment planning, a new CT scan was indicated only after 6 months postoperatively, for biosafety reasons [10]. This initial diagnosis of a cyst was rational, since cysts are common after stimulation or inflammation of the maxillary sinus [9]. However, the graft was completely pneumatized, with hard walls surrounding the void, mimicking the formation of an additional maxillary sinus within the existing one, but without any Schneiderian membrane—which made it difficult for the collection of a sample for an histopathological differential diagnosis. Upon surgical access of the suspected cyst, it was possible to confirm that a hollow cavity in which only the peripheral particle material inserted as a maxillary sinus filler was present. Regarding this matter, it can be assumed that there was insufficient irrigation to allow cell migration to the center of the graft. Therefore, this region lacked the defense and nutrition necessary for the maintenance of tissue volume. In other words, the lack of angiogenesis or vasculogenesis in the central region of the graft, a key part to new bone formation, led to this pneumatization within the graft.

Any type of local infection can compromise grafts, and this likely occurred in the present case, generating purulent material that was expelled by a fistular process, finding an easy route into the oral cavity, leading to oroantral communication. One factor that may have influenced the lack of neovascularization is that the patient had a widespread vitamin deficiency, which was found after blood analyses request. Another important factor is that the patient, despite having omitted during the interview, was an alcoholic. Alcoholic patients are generally more prone to failure in bone grafting surgery [11].

Three months after the graft surgery of maxillary sinus, as there was a perceived oroantral communication, the insertion of a fibrin sponge was performed. As pneumatization occurred only on the left side, it could be suggested that the cause of angiogenesis absence could be influenced by the insertion of the sponge in the oroantral communication closing operation. However, Gelatamp® is used for treatment of wounds, since colloidal silver acts releasing silver ions, which act against a broad spectrum of bacteria [12]. Furthermore, the use of topical silver has a popular widespread use for being effective against infections [13]. In our case, its use was intended to speed up the healing and closure of the oroantral communication, favoring the process of cure and prophylaxis of wound. Also, the sponge has hemostatic properties [14], and for this reason, it is used after dental extraction, acting as a scaffold in the alveolus for the installation and proliferation of cells. Within this scaffold, the environment would be favorable and conducive to bone formation and would not prevent the formation of new bone; therefore, the sponge could not have prevented the vascularization of the area. In this case, a minimum piece of sponge was placed solely to assist in healing of the epithelium and connective tissue. For the replacement of bone graft biomaterial by natural bone, an invasion of the osteoblasts accompanied by the formation of new vessels is required [7]. This neovascularization is an essential prerequisite for the formation of new bone of sufficient quality [15] and it may be accomplished with the use of sponge with colloidal silver, which perhaps was not large enough in this case to exercise that function. The bone cells lie within a complex matrix composed of a mineralized component (hydroxyapatite) and a non-mineralized component (predominately collagenous). The non-mineralized component (comprising approximately 30 % of the matrix) is responsible for the growth and differentiation of osteoblasts, osteocytes, and osteoclasts, in addition to bone remodeling [16]. In this component, a large number of angiogenesis regulatory factors interact in a coordinated manner to induce the formation of vessels [17]. The diffusion of fluids and blood perfusion is key for the successful formation of new bone. Therefore, in the present case, it can be suggested that angiogenesis was insufficient for the induction of new bone formation, leading to the formation of a pseudocyst.

In support of this, one report in 1996 [18] proposed several requirements for successful bone grafts. These included the presence of osteoblasts on site, sufficient blood supply for graft nutrition, material stability, and the maintenance of soft tissue closure by suturing without tension. Therefore, the survival of any type of grafting cell relies on processes such as the diffusion of fluids and blood perfusion. In the reported case, tissues were coopted adequately without tension, the material was stable, and the presence of osteoblasts was likely inhibited by a lack of nutrition. In addition to angiogenesis, vasculogenesis can also result in the formation of new blood vessels. Angiogenesis occurs through the branching of pre-existing blood capillaries, while vasculogenesis takes place through the differentiation of undifferentiated endothelial cells [19]. Vascularization of the grafted area begins with the migration and proliferation of endothelial cells. These cells form a network of new bone capillaries because one of the functions of these cells is to regulate angiogenesis. In the present case, bone maturation was not evident in the center of the grafted area where vascularization was most difficult to occur.

The initial process of angiogenesis is diffusion. However, diffusion can only occur at a distance of up to a maximum of 200 μm in the matrix. Therefore, for large tissue reconstruction, the survival of the central reconstruction cells is limited by initial vascularization difficulties [20]. Consequently, due to limited initial vascularization, diffusion into the center of large tissue growth is limited making it difficult for the survival of more centralized cells [21]. Thus, it can be concluded that angiogenesis is essential for successful bone grafting. In the present case, it is likely that angiogenesis did not occur in the center of the graft, leading to the pneumatization of the bone graft in grafted maxillary sinus.