Three-dimensional Finite Element Analysis Of Maxillary Dentition En-masse Retraction With Infrazygomatic Crest Micro-implant Under Different Patterns

Objective This paper analyzes the movement trend of each tooth during the distal displacement of maxillary dentition under different loading modes using the three dimensional finite element technique,in order to explore the best method of en-masse retraction of maxillary dentition,provide reference for clinical designing orthodontic scheme rationally,and try to analyze the biomechanical principle inside preliminarily.Methods A three-dimensional finite element model of straight wire arch bracket and nasal maxillary complex was established.The size of stainless steel bracket groove was set as 0.019*0.025-inch,the arch wire was 0.019*0.025-inch Stainless Steel.The sagittal position of the simulated micro-implant was located at the buccal tip of the first molar of maxillary,and the vertical positions(base on the top edge of arch wire)were 0 mm and 7 mm.The traction hook was located between the lateral incisor and the canine,and between the canine and the first premolar in sagittal direction,with a vertical height of 7mm,0 mm and-7 mm.The traction force was 150 g,and the direction was from the traction hook to the micro-implant.The middle point of the incisor margin(C1),the middle point of the lateral incisor margin(C2),the cusp of the canine(C3),the buccal cusp of the first premolar(C4),the buccal cusp of the second premolar(C5),the proximal buccal cusp of the first molar(C6),the proximal buccal cusp of the second molar(C7)and the root cusp of the above mentioned teeth(proximal/buccal)were set as the displacement evaluation markers.A three-dimensional coordinate system was established to extract the displacement value and the stress distribution cloud map of each marking point for analysis.Results The pattern of 7 mm height micro-implant or 7 mm height traction hook had an intrusive effect on the upper anterior teeth,and the combination pattern of 7 mm height micro-implant and 7 mm height traction hook had a better intrusive effect.When 0 mm height traction hook and 0 mm height micro-implant were used,the upper anterior teeth were slightly extended.When using a traction hook with a height of-7 mm and a micro-implant with a height of 0 mm,the upper anterior teeth were extended.When using the traction hook with a height of-7 mm and the micro-implant with a height of 7 mm,traction hook was located between the lateral incisors and the cccanine,the upper anterior teeth were extended,when the traction hook was between the canine and the first premolars,and the upper teeth were slightly intruded.Conclusion Traction hook height will impact upper anterior teeth overbite and torque,high micro-plant with high traction hook can significantly intrude teeth,which is suitable for patients with gingival smile,but it is needed to pay attention to the teeth after the traction hook,preventing the excessive extension.The horizontal position of the traction hook affects the sagittal position of the posterior teeth more than that of the anterior teeth.It is hoped that cases where the teeth are expected more retrusion can be considered to adjust the traction hook backward.