The Three-dimensional Finite Element Analysis Of Intruding Lower Incisors By Invisible Appliance

Objective: By simulating the design characteristics of invisible appliance,a three-dimension finite element model of the lower anterior teeth with invisible appliance was established.On the one hand,this study observed the movement trend and stress distribution of 6 lower anterior teeth under the stepwise depression and global depression;on the other hand,this paper discussed its movement trend and stress distribution of 6 lower anterior teeth in different force position.Finally,it provided reference for clinical orthodontic treatment.Methods: One young female volunteer was selected and scanned her maxillofacial region with CBCT.A 3D finite element model of mandibular,lower dentition and invisible appliance with good geometric similarity,high accuracy and biomechanical characteristics was established by using the software of Mimics,Geomagic Studio and Abaqus.A force was added to the midpoint of the incisal edge of the lower anterior teeth along the long axis of tooth.Then this paper needs observing the displacement trend and the stress condition of the lower anterior teeth under the different methods of intrusion.When the force location was adjusted to the lingual cingulum,the displacement trend and stress condition of 6 lower anterior teeth were required to be observed and analyzed.Results:1.The stress distribution of the periodontal ligament in the lower anterior teeth was approximately same under the stepwise depression and global depression of invisible orthodontic appliance,which was averagely distributing around 1/3 of the tooth neck;2.The lower anterior teeth in different methods of intrusion showed the movement tendency of labial depression under the force of depression;3.The displacement tendency of anterior teeth and the stress distribution of periodontal ligament under the condition of global depression were larger than that of stepwide depression;4.When the stressing point of depression was located at the protuberance of the tongue,the stress distribution of periodontal ligament was less than it in the the middle of incision,but the distribution of periodontal ligament was more even relative to it in the middle of incision.The lower anterior teeth tended to move along the long axis of the tooth under the force of depression.Conclusion: In the process of intruding the lower anterior teeth with invisible appliance,thegroup of global depression has more stress distribution and displacement trend of lower anterior teeth and periodontal ligament than the other one,which means it needs more anchorage.The pressure zone design on invisible appliance can effectively control the torque of anterior teeth and realize overall intrusion.