## 4 Discussion
Dental age is our main consideration for determining the timing of surgery. According to our results, after perioperative orthodontic treatment, the 1-year volume change in the EGPP group reached 69.8%, which was not significantly different compared with that in the SABG group (79.4%). The Bergland scale assessment revealed that most patients in both groups were classified as type I; the canine eruption rate was also not significantly different in both groups. These results were compatible with the CT image study. Our data proved that combined with orthodontic treatment, the bone formation in the EGPP group was similar to that in bone grafting. The osteogenesis phenomenon after orthodontic treatment is described in the literature. [PERSON] et al. found that early secondary gingvaalveolaroplasty promotes adequate bone growth in the alveolar and nasal regions [24]. The rate of permanent tooth eruption remains normal [18]. [PERSON] et al. presented that the bone created via orthodontic treatment appeared to have sufficient stability in horizontal and vertical directions at long-term follow-up [25]. The biophysical mechanism is the regulation of bone remodeling by signaling factors. Tooth loading during orthodontic treatment causes hypoxia, which initiates an inflammatory cascade, inducing osteoblast deposition in the tension area and osteoclast resorption in the compression area [26]. The idea of EGPP for the alveolar cleft instead of bone grafting came from the experience in some patients in whom alveolar fistula repair was difficult, such as very long and deep fistulas and wide alveolar gaps in syndromic patients that cannot cooperate with perioperative orthodontic treatment, and graft infection due to poor oral hygiene. Instead of SABG, EGPP was performed in these patientsto prevent graft infection from difficult wound closure. During follow-up, bone formation was found in most of these patients after the EGPP. Another crucial point is how wide the dissection area is in EGPP. Without bone grafting, the nasal floor, as the roof of the cleft, may collapse and contact with the palatal mucosa floor, as the redundant soft tissue causes obliteration of the cleft space, allowing less bone growth. EGPP enables deep dissection to the most posterior part of the cleft and excision of redundant soft tissues as much as possible. The tensile force of the nasal floor and palatal mucosa become high, preventing the collapse of the cleft space. Hence, the bone is allowed to regenerate within the space during orthodontic treatment without impediment by soft tissue. If the dissection in GPP is not extensive enough or if the soft tissue is not trimmed adequately, alveolar bone growth is compromised. Another alternative method to replace or enhance autogenous bone graft is recombinant human bone morphogenetic protein-2 (rh-BMP2) [27]. From a recent meta-analysis, the rh-BMP2 graft showed comparable effectiveness to autologous bone in terms of bone graft volume and height, but provides a shorter hospital stay due to the absence of a donor site [28]. EGPP also reduces hospital stay, and in this study, no complications after EGPP were reported. The limitations of this study were the small sample size and short follow-up period. The method error assessment was not conducted. Further study with larger sample size and long-term follow-up is needed.