Use of mandibular chin bone for alveolar bone grafting in cleft patients

Cleft alveolus is a condition in which there is a break in the continuity of the alveolar process. This condition is usually congenital. Cleft alveolus is the anomaly resulting from the lack of fusion between the medial nasal process and the maxillary process, and it is usually associated with a cleft lip or palate or both [1]. As a result, a problem can occur, such as oral fluid outflow through the nose, nasal secretions entering the mouth, tooth eruption at the rupture site, and alveolar collapse. Cleft alveolus is usually not addressed by the surgical correction of the cleft lip or cleft palate alone. After surgical repair of the cleft lip or cleft palate, the oronasal fistula should be closed and the continuity of the alveolar bone restored. The alveolar bone graft and distraction osteogenesis (DO) are the most common treatments of cleft alveolus [2–4].

DO can reconstruct both the alveolar bone and soft tissue [2, 5]. However, this method increases the treatment period, and DO devices can cause discomfort. Also, additional bone grafting could be necessary in the future. Thus, the alveolar bone graft is still mainly applied for the treatment of cleft alveolus. Through the alveolar bone graft, the aforementioned problems can be solved with intact maxillary arch formation, stabilization of the bone, and the improvement of the face by a proper bone support of the nose and lips [6–9]. The ideal bone graft material for alveolar cleft reconstruction is still controversial. Various bone graft materials such as autogenic, allogenic, xenogenic, and alloplastic grafts have been used in alveolar bone graft. However, autogenic bone is still mainly selected for alveolar bone graft despite the problems of unpredictable atrophy and loss of bone structure [10, 11].

Various types of autogenous bone may be used as grafting materials in alveolar cleft [12]. The iliac bone as the endochondral bone is the most popular, but some authors have reported that the intramembranous bone is more advantageous than the endochondral bone [11, 13, 14]. Hemar et al. performed calvarial bone grafting for maxillofacial reconstruction in 71 patients and had a follow-up of 2 to 6 years [15]. Their results look better than endochondral bone grafting with bones such as the iliac crest, ribs, and tibia. Zins and Whitaker reported that their endochondral bone showed a reduction of three to four times that of intramembranous bone in animal models [16]. It was thought that this difference was caused by the micro-architecture of mineralized matrix and quality of grafted bone. On the other hand, several studies that included long-term observation of cranial bone grafting show no particular advantages compared with iliac bone grafting [17, 18]. As such, there is still controversy regarding the result of alveolar bone graft depending on the type of bone used. Therefore, to get more than a good surgical outcome, you will need to think about the type of bone to be transplanted.

In this retrospective study, we evaluated and compared the outcomes of the different types of ossification processes that were performed using endochondral bone (iliac bone or rib bone) grafting or intramembranous bone (mandibular bone) grafting in alveolar cleft patients. Our goal was to find the most favorable conditions for successful bone grafting.

Fifteen patients had received orthodontic treatment: six from the intramembranous bone graft group and nine from the endochondral bone graft group. The space closure was performed by moving the teeth to four of the six patients in the intramembranous bone graft group (66.7 %) and six of the nine patients in the endochondral bone graft group (66.7 %). Nine patients from the endochondral bone graft group had non-erupted teeth, and eight of these patients had non-erupted teeth that erupted after a year. Six patients from the intramembranous bone graft group had non-erupted teeth, and all teeth were erupted after a year. The wound dehiscence occurred in three patients: one from the intramembranous bone graft group and two from the endochondral bone graft group. Although all patients healed during 2 ~ 3 months after surgery; sever reduction of grafted bone occurred until type III or type IV. And one patient received an additional bone graft surgery during the follow-up period. There were no serious complications except for mild infections following surgery in other patients.

In this study, the height of the interdental bone septum in the mesial teeth and distal teeth of the alveolar cleft were compared and evaluated through the radiographs taken immediately after surgery, 6 months after surgery, and 1 year after surgery [11, 19]. This method has been used in several studies to evaluate the results of alveolar bone grafting [21–23]. In this study, if more than 50 % of the graft bones remained 1 year after surgery, we considered it a successful alveolar bone graft. As a result, the success rate of the intramembranous bone graft was 91.67 % and that of the endochondral bone graft was 83.33 %. In comparison with other studies that reported a success rate of 80 to 90 %, both groups showed a similar result [24].

Although not statistically significant, the success rate of intramembranous bone was higher than that of the endochondral bone. Grafted bones were exposed in three patients after surgery. Two patients underwent the iliac crest bone graft, and one patient received the chin bone graft. Severe reduction of the graft bone was observed until type III or type IV in all patients. If the size of the cleft site is large, the excessive tension causes the failure of the primary closure, especially in the palatal side. That is, the size of the alveolar cleft rather than the type of the grafting bone was seen as having a greater effect on the result of the surgery [22, 24].

The interdental bone septum height tended to decrease in the intramembranous bone more than the endochondral bone at 6 months after surgery; however, the endochondral bone decreased more than the intramembranous bone at 1 year after surgery. The mean resorption rate of the area of the grafted bone also tended to decrease in the intramembranous bone more than the endochondral bone at 6 months after surgery. That is, initially, the intramembranous bone is absorbed more rapidly; however, the intramembranous bone is more stable than the endochondral bone in the long-term follow-up. In this regard, one of the most important factors that can affect the outcome of a bone graft is its revascularization. When the graft becomes newly vascularized, nutrients, gas, and undifferentiated mesenchymal cells are transported into the defect and bone regeneration is promoted [25, 26].

In several previous studies, the endochondral bone grafts were more rapidly revascularized than the intramembranous bone grafts in animal models [18, 27]. This would explain the result of the initially greater volume maintenance of the endochondral bone grafts. However, after revascularization, it is considered that that the volume of intramembranous bone is maintained better than that of the endochondral bone due to the differences of micro-architecture of the mineralized matrix of bone [16].

The ilium which can be harvested in large quantities at a time, and is easy to work with due to both the cortical and cancellous bone, is the most popular; however, it has problems such as the gait disturbance and formation of scar tissue around the mouth [28–30]. Some surgeons used the calvarial bone of the intramembranous bone rather than the ilium of the endochondral bone, because of the similarity of the bones’ histology and development [31]. In addition, the autogenous bone harvested from the mandibular ramal or chin area can be used for bone grafting [32]. The mandibular bone has a good result compared to iliac surgery, and it has the advantage of a shorter operative time and hospital stay, as well as no extraoral scar formation [33]. But, if a great amount of grafting bone is required, the mandibular bone cannot be used because only a small amount can be collected. In this study, we used the mandibular bone and not the calvarial bone, and all patients with bilateral cleft received the iliac bone graft.

In this study, the heights of the interdental bone septum were measured 6 months and 1 year after surgery. Other studies have shown that absorption of graft bone occurs mainly during the first 6 months, and there are no significant changes of the bone between 6 months and 1 year following surgery [34]. Therefore, the follow-up period of 1 year is sufficient to test this result. But the limitations of this study were that it has a small number of samples and the width of the bone could not be assessed using radiographic images.

In this study, the results of the alveolar bone graft were that there is no significant difference according to the type of graft bone used. Although significant bone resorption was observed with the passage of time following alveolar bone grafting, the amount of absorption was not enough to affect the successful outcome. The failure of soft tissue cover in the recipient site largely influences the outcome of the alveolar bone graft. As a result, both the intramembranous bone (mandibular bone) and the endochondral bone (iliac bone or rib bone) can successfully be used for bone grafting of the alveolar cleft. It is important to select the appropriate bone according to the size and shape of the alveolar cleft site and condition of the patient. If appropriate to the size of the recipient site, the chin bone is a useful graft material in the alveolar cleft, as is the iliac bone.