Biomechanical Classification System And Individualized Treatment For Maxillary Canine Impactions

Maxillary canine impaction is a condition in which a canine is embedded in the maxillary alveolus so that its eruption is prevented or the tooth is locked in position by bone or by the adjacent teeth. The impacted canine affects the function and aesthetic of oral cavity.The treatment is usually a challenge to orthodontists. The research in existence about the impacted canine mostly focus on the orientation of impacted tooth and the treatment.But biomechanical mechanism on traction of impacted canine is not clear . In order to realize dynamic simulation and biomechanical quantization of the process during traction of impacted canine, imaging engineering method, nonlinear finite element method, and experimental mechanics method were used to inquire this problem. The aim of this study was to establish a biomechanical classification system for maxillary canine impactions. The classification system will guide the precise diagnosis and development of individualized orthodontic appliance for impacted canines.Methods:Part I: To show the 3D shape, size and position of the displaced canines, Surface Shaded Display method was used to reconstruct the dentomaxillofacial CT data of 102 patients with maxillary impacted canines. Based on the analysis of 121 impacted canines' spatial relationship to adjacent teeth, a 3D CT image classification system for maxillary canine impactions was established. Patients with impaction of maxillary canines were divided into two groups. 42 patients were in palatal group and 60 patients in labial group. The control group comprised 50 untreated patients who were matched for age and sex exhibiting normally erupted and undisplaced maxillary canines. MIMICS software was used to measure the 3D CT images of jaw and teeth. The maxillary anterior teeth size, maxillary arch and jaw width were measured and analyzed statistically among the three groups.Part II: Based on the CT data of 2 patients with different maxillary impacted canines, the dummy model of maxillary dentition, periodontal tissue and Edgewise appliance were set up by reverse engineering software and the rapid prototyping technology. A hyperelastic model was applied to build the nonlinear constitutive model of periodontal ligament.Forces of 60g, 75g, 100g, 120g and 150g were exerted to the finite element models of different impacted canines from different driections. ABAQUS software was use to analyze stress changes of their periodontal ligament. The results of the simulations were tested by experiments of digital speckle pattern interferometry.Part III: A computer-assisted surgical navigation system for exposure of impacted teeth was developed by using 3D image guided technology, and an accuracy test was performed. According to biomechanical characteristics in the procedure of impacted maxillary canine movements produced by orthodontic load, a evaluating criterion for difficulty in therapy was established and a set of individualized orthodontic appliance for repositioning of impacted maxillary canines was designed by using computer-aided technology.Results:1. A database for 3D CT image of different maxillary canine impactions was established. In this database, all anterior teeth size of the labial group was the largest in three groups. In the palatal group, the central and lateral incisors were significantly narrower than that of controls but the size of canine showed no was significantly smaller in patients with impacted canines compared to the control group. The width of arch between 1st molar and jaw was almost normal in three groups.2. Three-dimensional finite element model of maxillary dentition, periodontal ligament, alveolar bone and Edgewise appliances were set up by CT scanning and reverse engineering technology. Through nonlinear finite element analysis and electronic speckle pattern interferometer to conduct a preliminary verification, the result was similar. That means that the method of finite element analysis was reliable.3. The result of nonlinear finite element analysis showed that when the long axis of the maxillary impacted teeth has angle with the direction of the force, the angle is larger, the maximum stress is larger and the stress distribution concentrates more. The angle between the orientation of the traction and the long axis of the impacted canine is smaller, the stress distribution is more average.According to this result, a novel biomechanical classification system for maxillary canine impactions and evaluation system for difficulty in maxillary impacted canines'therapy were established.4. A novel positioning method and device for impacted teeth was designed. A set of surgical navigation software for department of stomatology was developed and proved to be able to guide the surgical exposure of impacted teeth precisely.5. A design proposal of individualized orthodontic appliance for impacted maxillary canines which is comprised of a rotatable bracket and cantilever beam forcing device was created.Conclusion:1. There is a distinction of dentomaxillofacial morphology between palatal and labial canine impactions. The changes of maxillary lateral incisors and arch width between the 1st premolar showed significant associations with the maxillary canine impaction.2. Based on the CT image and reverse engineering ,the method through nonlinear finite element analysis and electronic speckle pattern interferometer to test is feasible.The model can be used to biomechanics analysis for numerical simulation of different impacted maxillary canine movements produced by orthodontic load.3. The impacted canines' spatial relationship to adjacent teeth determines the characteristics of stress distribution on periodontal ligament. When the long axis of impacted canine is in line with the desired direction of the force,,there are more advantage to the eruption of the impacted canine.4. The biomechanical classification system for maxillary canine impactions was established based on 3D CT image and results of biomechanical analysis. This concise classification has a basement of science theory. It will play an important role in diagnosis and the treatment of impacted canines in the future.5. Computer-assisted surgical navigation system, difficulty evaluation system and individualized orthodontic appliance will contribute to realize the individualized diagnosis and treatment for impacted maxillary canines, and has good perspective in clinical application.