Three-dimensional Finite Element Analysis Of Maxillary Molar Distalization Using Different Attachments With Plastic Aligner

Objective: To analyze the displacement patterns and stress distribution of maxillary tooth with different attachments and plastic aligners during molar distalization.Materials and Method: Three-dimensional finite models of maxilla molar distalization with plastic aligners were constructed.A according to the shapes of different attachments,four models were set up: non-attachment(model A),horizontal rectangular attachment(model B),vertical rectangular attachment(model C)and combined attachment(model D).The 3D coordinates were based on the occlusal plane: x(transverse plane),y(anteroposterior plane),and z(vertical plane).Positive values for x,y,and z indicated palatal,distal,and upward displacements,respectively.Crown displacements of were collected from the mesiobuccal cusp of the molar and the mesial cusp of other teeth.Root displacements were collected from the mesiobuccal tip of the molar and the tip of other teeth.The displacement patterns and stress distribution of the maxillary tooth were analyzed in the Ansys workbench.Results: 1.In the horizontal direction,the second molar all showed a tendency of inclination towards buccal movement of the crown and towards palatal movement of the root in the four groups.The maximum displacement of crown and root were in group C,and the minimum displacement was in group A.In sagittal direction,the displacement of the crown and root in group D was the smallest among the four groups,while the displacement of the crown in group C was the largest.However,the displacement of the buccal crown was much larger than that of the palatal crown,indicating that the second molars in group C experienced a mesiodistal torsional movement trend after the application of load.In the vertical direction,the maximum displacement value was located in the parietal buccal apex and parietal buccal root apex of group C,and the minimum displacement value was located in the parietal palatal apex and parietal palatal root apex of group D.2.The displacement rotation centers of the second molar with models A and B were located at the root furcation.In model C,the displacement rotation center of the buccal sides was located at the middle third of the mesiobuccal root,and the palate side was located at the coronal third of the palate root.In model D,the displacement rotationcenter of the buccal and palate side were located at the middle thirds of root.3.All the displacements of the anchorage tooth in the four groups tended to show mesial tipping movement.(4)The stress distribution of the PDL demonstrated that models B and D was more uniform than model A and C.Models with attachments showed greater tooth displacement patterns than models without attachments.Conclusions: The different attachment forms have different effects on the movement of the teeth.Applying attachments was more efficient for tooth displacement patterns.The second molars of the four groups all showed a clockwise tendencies of distal crown tipping and mesial root tipping.The model with a combined attachment of tooth movement was the most efficient,followed by traditional attachment models.