Study On The Initial Stress Distribution Of Maxillary Anterior Dentition And PDL Loaded By The Molar TIP-Back Bend In Different Angles

Objective To search a new rapid and effective method for model construction,and establish a highly precision 3D finite element analysis model of maxillary anterior dentition and its periodontal tissues, investigate its stress distribution with the effect of the molar tip-back bend in different angles,in order to provide academic evidence for how to use orthodontic force systems becomingly when it needs bite opening .Method1. The maxilla of a healthy young female was scanned with spiral CT in order to obtain the CT tomographic images which were transfered and disposed to build the 3D reconstruction model . The finite element analysis models were created after being meshed and checked.2.The two dimensional coordinates of archwire were established according to the formula[Y=4.0491E-5X4+3.3263E-2X2 ( maxilla) ]. The three-dimentional model was established after being rotated along YZ plane. Setting 3 different angles of molar tip-back bends in order to simulate the bite opening instance and investigate the stress distribution of maxillary anterior dentition and its periodontal tissues .Results1.The high quality model consisted of maxillary anterior dentition segment and periodontal tissues (including periodontal ligament and alveolar bone),which had 640396 elements and 117889 nodes.2. The force results of anterior tooth and molar which were loaded by the molar tip-back bend:1)Originaly the maxillary anterior teeth were pressured by the effect of molar tip-back bends,but the force distribution was uneven. Canine was pressed into the biggest, followed by lateral incisor, the smallest incisor . Meanwhile, the anchorage molar was loaded on the force which was extended medially and intruded distally, and the extend force outweighting the intrusive one.2)The pressures on each teeth of the anterior dentition and uneven distribution trend increased with the increase of loading angle.The net elongation force on molar also increased.3. The changes of three stress index(S1,S3,Von mises) of PDL's different nodes indiciated :1)The periodontal ligament of maxillary anterior dentition were pressured maining.Generally the stresses on the labial side were bigger than the lingual ones , the peak value were on the cervical edge and root tine of labial and lingual side. Generally the maximum stress was on the canine PDL ,and the minimum stress was on the lateral incisor.2 ) With the increasing loading angles of tip-back bend, the stress of each nodes has also increased, and more and more concentrated.It presented the distribution characteristics of incline movement.Conclusion1.The new method was easy to use,especially fit for the construction of complex tissues.Meanwhile,the model provided a good foundation for the research of the biomechanics behavior of maxillary anterior dentition.2. It proved that the instrusion of anterior dentition was also a different teeth movement. The results of this research suggest that, the optimum molar tip-back bend is 30°while on stage I bite opening .3. Maxillary anterior dentition which was loaded by the molar tip-back bend presented a trend of incline movement and the trend increased with the increase of loading angle.In order to achieve bodily instrusion of anterior dentition and establish the efficient force system of bite opening , the class II elastic was necessary at the same time on the clinic.