3D FEA Of Maxillary Dentition By Vertical Control Using Tip-back Bends With Mini-implant

Objective: Malocclusion is a developmental malformation of tooth orjaw in cranial and maxillofacial growth due to the genetic and environmentalfactors. At present, the incidence of children's malocclusion has reached to68%in China. Malocclusion has negative influence on the patient's commonoral function and appearance, adding the psychological burden to the patient.Malocclusion with hyperdivergent, in particular, causes severe facial estheticsand psychological health problem. Malocclusion with hyperdivergent usuallytakes the figures of high-angle face, maxillary prognathism, mandibularretrognathism, deep overbite, deep overjet, open bite, etc. Therefore,Orthodontic treatment is adopted to control the length, width, height andoverall, coordinating the restriction and interaction among them. Sagittalorientation of the treatment cannot be separated from the arch height andwidth control. Perpendicular to the malocclusion more focused on verticalcontrol. Malocclusion with hyperdivergent is a kind of difficult case toorthodontists and molar extrusion is more likely to take place during theorthodontic treatment. So vertical controlling is the key to achieve ideal effectin hyperdivergent.The birth of mini-implant brings new hope to orthodontic areas.Mini-implant can perform the absolute intruding of molar and forward planarrotation of mandibular, improving the appearance of the patient's soft tissueeffectively. Compared with other traditional methods, Mini-implant takes suchsignificant advantages that bringing the orthodontic treatment to a new era.Tip-back bends, a type of V band, is commonly used to open bite. It is usuallyused to control the molar height and anterior teeth movement when theprocedure of en-mass retracts with mini-implant. However, mechanicalmechanism of how tip-back bends affecting the maxillary anterior and posterior by mini-implant is not clear yet. It affects the clinical application.The goal of this experimental application is to perform a better verticalcontrol of arch by the mini-implant and establish a fast and effective treatmentof malocclusion that guiding the clinical operation. Three-dimensional finiteelement method is used to model the maxillary teeth and periodontal tissuewith clinical mini-implant. Simulation of process that tip-back bendsadducting anterior teeth after extraction of the first premolar is then performedunder different bending angle. The stress, strain and the initial displacementthat comes from maxillary teeth and periodontal tissue is obtained. Themechanical mechanism of vertical control to the dental arch by themini-implant and tip-back bends is discussed. This study provides solidtheoretical foundation for future clinical application and research.Meterials and Methods:1Experiment one: Establishing the FEA models of maxillary dentitionincluded appliance of tip-back bends with different angles1.1laboratory equipment:To choice adult male volunteers as the research object who is the normalocclusion, no missing teeth, periodontal healthy. The CT scan from skull tojaw and the results were stored in Dicom.1.2Setting the tip-back bends of stainless steel arch wireCase1: the arch wire with0°tip-back bends.Case2: the arch wire with20°tip-back bends.Case3: the arch wire with40°tip-back bends.1.3Establish3D FEA model:A3D FEA model which including maxillary teeth, PDL, brackets archwire and center hook was establishsd by Mimics10.01, CatiaV5, and Abaqus6.8software.1.4Meshing the models:Maxilla use tetrahedral element, periodontal ligament use bilineartetrahedral unit C3D10M, and the arch wire use hexahedral elements C3D8R.2Experiment two: The effect of teeth and periodontal tissue with different angle tip-back bends:3D finite element analysis2.1Loading conditions: simulated clinical between the maxillary secondpremolar and first molar root from the tooth bad ridge top4mm implant togive150g of force and the direction is30°tilted occlusally.2.2Constraints:The teeth fixed in the maxilla, between the teeth and maxilla,teeth and the appliance is relatively fixed. The friction coefficient μ betweenthe bracket and arch wire is0.2.2.3The Von-Mises stress and displacement distribution of teeth and PDL wasrecorded and analyzed in different conditions.Results:1Experiment one:1.1Establishing three different angle molar tip-back bends:Case1: the arch wire with0°tip-back bends.Case2: the arch wire with20°tip-back bends.Case3: the arch wire with40°tip-back bends.1.2A successful establishment of geometric similarity and biologicalsimilarity higher maxillary dentition (except the first premolar) andperiodontal tissues, appliance, three-dimensional finite element model of thetow hooks.2Experiment two:2.1The Von-Mises stress distribution of teeth, alveolar bone and Periodontalligament2.1.1The stress distribution of teeth: concentration in the crown and bracketbonding.2.1.2The stress distribution of alveolar bone:0°tip-back bends, Max stressappears at the lingual alveolar bone cervical margin of the lateral incisor andcanine;20°and40°tip-back bends, Max stress appears at the alveolar ridgeand root furcation of posterior.2.1.3The stress distribution of PDL: concentration at the tooth cervical margin.But when the PDL loaded too much, the apical area also appears peak region.cervical margin>apical area>middle. 2.2The role of the tip-back bends labial side of anterior teeth, canine and thesecond premolar, molar's palatal root is always the pression zone. The lateralincisor's lingual side and apical, molar mesial root as always the tension zone.2.3The effect of teeth, alveolar bone and PDL under the different cases.2.3.1PDL stress distribution trend with the teeth, alveolar bone stressdistribution in a similar trend in the same tip-back bends, but the force on theteeth> alveolar bone> periodontal ligament.2.3.2With tip-back bends angle increases the Max Von-Mises of teeth,alveolar bone and PDL are increasing.2.3.3When the loaded by0°tip-back bends, main force for anterior teeth(canines are stress value the most, followed by lateral incisors and centralincisors), posterior is almost free from force.2.3.4When the loaded by20°,40°tip-back bends,posterior stress increasedSignificantly, but anterior teeth increased very little. Posterior stressdistribution main at the mesiocclusion of the first molar and the distoclusionof the second molar. The Max Von-Mises stress of the40°tip-back bendswere higher than the20°tip-back bends.2.4The initial displacement of teeth:2.4.1When the loaded by0°tip-back bends, anterior teeth to the lingual, thedistal, to gingival movement, posterior nearly movement.2.4.2the central incisors to the labio, to mesial, to nearly gingival movement,the lateral incisors to the labio, to the distal, to occlusal movement, canine tothe lingual, the distal, to gingival movement, the second premolar to thebuccal, to the distal, to occlusal movement, the first molar to the lingual, todistal, to gingival movement, and upright the second molar to the distal.2.4.3When the loaded by20°,40°tip-back bends, the first molar and secondmolar's displacement are most, and the anterior teeth displacement are isrelatively small. The initial displacement stress of the40°tip-back bendswere higher than the20°tip-back bends.2.4.4Displacement range of maxillary dentition in three dimensions under thedifferent cases to see Table7. Conclusion:1Under the mini-implant with the different tip-back bends angels, The stressdistribution of teeth concentration is at the crown and bracket bonding; Thestress distribution of alveolar bone Max stress appears at the alveolar ridgeand root furcation of posterior; The stress distribution of PDL concentration isat the tooth cervical margin and the apical area.2When the straight arch wire without tip-back bends, anterior teeth to thelingual, the distal, to gingival movement and posterior almostly movementloading by mini-implant.3The role of the tip-back bends incisor to drive down and pour lip, canine todrive down and lingually tip, second premolar elongation, the first molars todrive down and to distal movement, and the second molar to the distal upright.4With the tip-back bends angle increases from0°to20°,40°, the MaxVon-Mises stress values and Max initial displacement for each tooth andperiodontal ligament increases.