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.