A 3-Dimensional Finite Element Analysis Of Maxillary First Molar In Lingual Orthodontics

ObjectiveThe development of fixed lingual orthodontics appliance began in the mid-1970s, largely because of an increased interest in adult orthodontics. These invisible brace were designed in an effort to offer a valuable service to many patients who were unwilling to undergo treatment with labial appliances because of esthetic concerns. During the past 30 years, dramatic progress has been made in bonging technology, precise positioning of brackets, improving the design of a lingual appliance, the application of CAD/CAM in lingual orthodontics and mechanical efficiency. Presently, there are some studies about the biomechanics of upper central incisor, lower canine and mandibular first molar, however, there are no published reports on the mechanical analyses of maxillary first molar. In this study , we established a finite element model, including the maxillary first molar, the periodontal ligament, alveolar bone , and a lingual or buccal tube. All kinds of the orthodontic forces were applied on the lingual or buccal tube. We observed the movement of the maxillary first molar and the stress distribution of the periodontium, to compare the effect of labial vs lingual forces , and then to conduct clinical application.Methods1,In this study , we selected the maxillary first molar of standard permanent dentition tooting producted by Japanese Nission dental products Inc .Geometric models were built by use of the advanced 3-dimensional laser scanning and 3-dimensional computer assisted design technique. The geometric data were introduced into MSC. PATRAN for establishing the finite element model , comprising a maxillary first molar, periodontal ligament, alveolar bone , and a lingual or buccal tube, consisted of 25766 nodes and 105794 elements.2,Diffient kinds of loads were applied at a point of the lingual or buccal tube separately. By the finite element method , the displacment of the maxillary first molar and the stress of the periodontium were calculated and analyzed .Results1,When the mesial force was applied the maxillary first molar , the tooth was tipped mesially ,rotated mesially and lingually in labial technique; In the lingual technique , the tooth was tipped mesially, rotated mesially and buccally. the degree of tipping and rotation of labial technique is bigger than lingual technique. In order to obtain Bodily movement and uniform low stress of Periodontal tissue, it meantime need to apply moments. In labial technique, Mt = 16. 2N.mm, Mt/F=8.1:1, Mr=16 N. mm, Mr/ F=8:1. In lingual technique, Mt = 13.8N.mm, Mt/F=6.9:1, Mr=14.2 N.mm, Mr/ F=7.1:1. When the tooth moved bodily, the displacement of lingual technique was larger than labial technique.2,When the extrusion or intrusion force was applied, the degree of tipping in labial technique was bigger than in lingual technique, the direction of tipping was opposite. When the tooth moved bodily , in labial technique , Mt = 4.95 N.mm, Mt/ F=4.95:1; in lingual technique , Mt = 3.6 N.mm, Mt/F=3. 6:1.3,Regardless of lingual technique and labial technique, the order of stress were mostly root>periodontal ligament>alveolar bone. The stress of labial technique was bigger than lingual technique .The stress of bodily movement was smaller than of tipping and rotation. The order of stress in root and PDL's different section was: cervial region , furcation level>upper of root 1/3 level >midst of root 1/3 level >below of root 1/3 level. The stress of alveolar bone is the biggest in furcation level.Conclusions1,When the maxilly first molar moved bodily in horizontal plane, the M/F of lingual technique was smaller than labial technique. The efficiency of movement in lingual technique was higher than labial technique. It disadvantages control of anchorage and easy to move distally. When the mesial force was applied, the tooth rotated mesially and buccally and it reinforced the anchorage.2,When the tooth moved bodily in vertical direction, the M/F of lingual technique was smaller than labial technique, it was easy to extrude or intrude the maxilly first molar in lingual technique.3,The order of stress in lingual and labial technique were both: root >periodontal ligament>alveolar bone. When the tooth obtained bodily movement , the stress of PDL and alveolar bone were uniform and low. So the bodily movement profits the healthy of tooth and peridontal tissue.4,The stress of labial technique was bigger than lingual technique .So the lingual orthodontics profits the healthy of tooth and peridontal tissue.