Abstract: We found six publications involving a total of 47 participants requiring maxillary advancement of 4 mm to 10 mm. All of them related to a single trial performed between 2002 and 2008 at the University of Hong Kong, but not all of the publications reported outcomes from all 47 participants. The study compared maxillary distraction osteogenesis with orthognathic surgery, and included participants from 13 to 45 years of age. Results and conclusions should be interpreted with caution given the fact that this was a single trial at high risk of bias, with a small sample size. The main outcomes assessed were hard and soft tissue changes, skeletal relapse, effects on speech and velopharyngeal function, psychological status, and clinical morbidities. Both interventions produced notable hard and soft tissue improvements. Nevertheless, the distraction group demonstrated a greater maxillary advancement, evaluated as the advancement of Subspinale A-point: a mean difference of 4.40 mm (95% CI 0.24 to 8.56) was recorded two years postoperatively. Horizontal relapse of the maxilla was significantly less in the distraction osteogenesis group five years after surgery. A total forward movement of A-point of 2.27 mm was noted for the distraction group, whereas a backward movement of 2.53 mm was recorded for the osteotomy group (mean difference 4.8 mm, 95% CI 0.41 to 9.19). No statistically significant differences could be detected between the groups in speech outcomes, when evaluated through resonance (hypernasality) at 17 months postoperatively (RR 0.11, 95% CI 0.01 to 1.85) and nasal emissions at 17 months postoperatively (RR 3.00, 95% CI 0.14 to 66.53), or in velopharyngeal function at the same time point (RR 1.28, 95% CI 0.65 to 2.52). Maxillary distraction initially lowered social self-esteem at least until the distractors were removed, at three months postoperatively, compared to the osteotomy group, but this improved over time and the distraction group had higher satisfaction with life in the long term (two years after surgery) (MD 2.95, 95% CI 014 to 5.76). Adverse effects, in terms of clinical morbidities, included mainly occlusal relapse and mucosal infection, with the frequency being similar between groups (3/15 participants in the distraction osteogenesis group and 3/14 participants in the osteotomy group). There was no severe harm to any participant. This review found only one small randomised controlled trial concerning the effectiveness of distraction osteogenesis compared to conventional orthognathic surgery. The available evidence is of very low quality, which indicates that further research is likely to change the estimate of the effect. Based on measured outcomes, distraction osteogenesis may produce more satisfactory results; however, further prospective research comprising assessment of a larger sample size with participants with different facial characteristics is required to confirm possible true differences between interventions.

Plain-language summary: The evidence on which this review is based is up to date as of 15 May 2018. We found six relevant articles to include in this review. All are related to one single study conducted in Hong Kong between 2002 and 2008. The study involved 47 participants aged 13 to 45 years of age. It investigated the effects of the two surgical procedures on alteration of face morphology, stability of upper jaw after surgery, speech and velopharyngeal function (ability to close the gap between the soft palate and nasal cavity to produce sound), psychological status of the participants and clinical side effects. Both procedures were effective in producing better facial structure in cleft patients. Upper jaw was more stable in the distraction osteogenesis group than the conventional osteotomy group five years after surgery. There was no difference in speech and velopharyngeal function between the procedures. Social self esteem in the maxillary distraction group initially seemed to be lower than in the conventional surgery group, but this improved over time and the distraction group had higher satisfaction with life two years after surgery. Side effects included deterioration of the fit between the teeth when the mouth is closed and infection of muscous membranes of the nose and mouth, but the frequency of these problems was similar between groups. There was no severe harm to any participant. We judged the quality of the evidence to be very low. The one study was small and there were concerns about aspects of its design and reporting; therefore we have found no reliable evidence as to which procedure should be regarded superior. High quality clinical trials, which involve lots of people, and different face types, are required to guide decision making.