Anterior Maxillary Segmental Distraction Osteogenesis On Cleft Lip And Palate:A Three-Dimensional Finite Element Analysis

Purpose:(1)To construct a finite element model(FEM)of human craniofacial complex with unilateral cleft lip and palate and simulate anterior maxillary osteotomy and alveolar bone graft for subsequent biomechanical evaluation of anterior maxillary segmental distraction osteogenesis(AMSD)on cleft lip and palate.(2)To investigate the biomechanics of AMSD on craniofacial complex with cleft lip and palate undergoing alveolar bone graft resorption through displacement pattern of surface landmarks of dentition and alveolus and stress distribution over graft site and provide guidance for clinical application of AMSD under graft resorption.(3)To investigate the biomechanics of AMSD on craniofacial complex with cleft lip and palate with intraoral appliance(IA)and rigid external distraction(RED)device through displacement pattern of surface landmarks of dentition,alveolus and maxillofacial structures and stress distribution over graft site and explore indications of distractor selection for clinical purpose.Method:(1)The geometric model was developed in with spiral-CT scan data of a unilateral cleft lip and palate patient.The model was later imported to HyperMesh12.0 and Solid Edge ST7 for addition of osteotomy line and alveolar bone graft simulation,respectively.Creation of 3-D FEM mesh and definition of material properties were completed using HyperMesh12.0.(2)Distraction force,simulating AMSD with IA,directed anteriorly and parallel to the occlusal plane,with magnitude of 10 N was loaded to bilateral first bicuspids cervices in the 6 models with different states of graft resorption.Displacement of surface landmarks of dentition and alveolus and von Mises stress distribution over graft were analyzed.(3)Distraction force directed anteriorly and parallel to the occlusal plane,with magnitude of 10 N was loaded to bilateral first bicuspids cervices and bilateral canine apexes simulating AMSD with IA and RED respectively in the model with no resorption.Displacement of surface landmarks of dentition,alveolus and maxillofacial structures and von Mises stress distribution over graft were analyzed.Results:(1)A 3-D FEM of human craniofacial complex with unilateral cleft lip and palate was constructed with simulation of anterior maxillary osteotomy and alveolar bone graft for various experimental purposes.(2)Displacement results showed that the model with intact graft exhibited the most favorable outcome regarding symmetry of sagittal displacement and counter-clockwise rotation of anterior segment,stability of arch in transversal dimension and elimination of step across graft site,which deteriorated in the order of model with graft resorption of upper 1/3,upper 2/3,and lower 2/3.Stress results showed that the highest von Mises stress over graft was found in the model with graft resorption of lower 2/3,followed by the model with graft resorption of upper 2/3,lower 1/3,upper 1/3 and no resorption.(3)In IA and RED model alveolus showed less,more forward displacement than dentition,respectively.More forward displacement was noted at piriform aperture,nasion,infraorbital margin,zygomatic body and temporal process of zygomatic bone in RED model than IA model.Both in IA model and RED model expansion was observed throughout anterior maxillary segment.Vertically,significant upward movement of anterior maxillary segment that increased anteriorly occurred in IA model while only slight downward displacement was seen in anterior segment of dental arch,and upward in middle in RED model.Higher von Mises stress was noticed at graft in RED model than IA model.Conclusions:(1)When applying IA for AMSD,as the level of resorption lowered and remaining graft volume diminished,asymmetry of displacement,expansion of arch,step across cleft and stress concentration at graft became obvious.(2)IA causes counter-clockwise rotation of anterior segment and isindicated for moderate maxillary hypoplasia with normal incisor display and acceptable profile.(3)RED leads to clockwise rotation of anterior segment and is thus recommended for severe maxillary hypoplasia needing large distraction amount for basal bone elongation,expansion of arch,control in vertical dimension and improvement of midface concavity.