Biomechanical effects on maxillary protraction of the craniofacial skeleton with cleft lip and palate after alveolar bone graft

Objective To explore the biomechanical effects of maxillary protraction on the craniofacial skeleton in patients with unilateral cleft lip and palate (UCLP) after alveolar bone graft (ABG) and resorption of ABG, thus to provide theoretical basis for the clinical application of maxillary protraction, which can improve the facial deformity of the UCLP patients. Methods A finite element model of a UCLP patient's skull was generated using data from spiral computed tomographic (CT) scans. Based on this finite element model, another 6 ABG finite element models were constructed to simulate ABG and resorption of ABG, respectively (nonresorption model, upper one-third resorption of the grafted bone model, upper two-thirds resorption of the grafted bone model, lower one-third resorption of the grafted bone model, lower two-thirds resorption of the grafted bone model, upper one-third and lower one-third resorption of the grafted bone model). Two additional models were developed to simulate maxillary protraction with expansion and maxillary protraction alone. All models were loaded with orthopedic force (30 degrees downward and forward to the occlusal plane, 500 g per side) on the region of alveolar of maxillary canine. Results Before ABG, the cleft side showed larger displacement than the noncleft side, when it came to the stress distribution in the craniofacial suture, it showed an asymmetric pattern as well. After ABG, the displacement difference between the cleft side and the noncleft side decreased, and the stress distribution in the craniofacial suture showed more symmetric than that before ABG. The pterygopalatine suture obtained the largest value, followed by zygomaticotemporal, zygomaticomaxillary, and zygomaticofrontal sutures among the observed sutures. Higher stresses and pronounced forward displacement were generated in the craniofacial sutures after maxillary protraction with expansion. Conclusions Maxillary protraction after ABG performed a more favorable outcome. Among the ABG models, nonresorption model showed the best effect after loading maxillary protraction force, and resorption in the lower region of the grafted bone showed a better effect than resorption in the upper region of the grafted bone. Maxillary expansion could effectively facilitate the orthopedic of the maxillary protraction presumably.