Dynamic analysis of the effects of upper lip pressure on the asymmetry of the facial skeleton in patients with unilateral complete cleft lip and palate

Objective: Our purpose was to assess quantitatively the effect of increased upper-lip pressure on asymmetry of the facial bones in patients with unilateral complete lip-alveolar-palatal clefts. Methods: We collected computed tomographic images from 16 patients with unilateral complete lip-alveolar-palatal clefts and classified them into two groups based on absence/presence of alveolar bone grafting. We categorized eight patients (9.6 ± 2.0 years old) who had not been treated with alveolar bone grafting as the ABG(-) group and the other eight patients (9.3 ± 1.6 years old) who had received alveolar bone grafting as the ABG(+) group. After producing a computer-aided design model for each patient,we applied a uniform load on the anterior aspects of the maxilla,alveolus,and teeth of the model to simulate the upper-lip pressure. Then we calculated the degree of distortion each model presented using the finite element method. We compared the distortion pattern between the ABG(-) and ABG(+) groups. Results: In the ABG(-) patients,asymmetry of distortion between the cleft and noncleft sides was present in wide areas involving the orbit,nasal bone, piriform margin,and anterior wall of the maxillary sinus. In the ABG(+) patients, asymmetry of distortion was limited to rather small areas. Conclusions: In unilateral complete lip-alveolar-palatal clefts patients,the upper-lip pressure works to dislocate the cleft-side segment to a more posterior position than the noncleft-side segment. This finding implies that the increased lip pressure exacerbates facial asymmetry of these patients. The exacerbating effect on facial asymmetry is alleviated by alveolar bone grafting.