Résumé
BACKGROUND: Using interproximal enamel reduction, adding attachments and over-correction are major methods to improve the efficiency of correcting tooth torsion when using clear aligners in the clinic. However, the choice and placement of attachments depend on the experience and habits of orthodontists, and whether the effects are different has not been reported. OBJECTIVE: To explore the effects of rectangular attachment with different thicknesses and locations on the left maxillary canine tooth torsion in clear aligner by three-dimensional finite element analysis. METHODS: The finite element models of the clear aligner-attachment-maxillary canine-periodontal ligament-spongy bone-cortical bone and the clear aligner-maxillary canine-periodontal ligament-spongy bone-cortical bone were established according to the scanning data of in vitro maxillary canine. The models with attachments were divided into four groups based on different thicknesses of attachment, namely 0.5, 0.75,1.0, and 1.5 mm groups. The placement positions were divided into five areas: mesial, distal, occlusal, median, and gingival of canine. 2° clockwise rotation of the tooth axis (X axis) was applied to the clear aligner. The action of the appliance and the canine were calculated by MSC.Marc.Mentat software. Then, the nephograms of stress and displacement, and the maximum stress and displacement values were collected. RESULTS AND CONCLUSION: (1) Whether the rectangular attachment was used or not, the two models’ distribution of canine’s displacement and periodontal stress were the same. The stress values of periodontal ligament were all higher than those without rectangular attachment. (2) With the thickness of rectangular attachment increasing, the maximum displacement values of the canine increased gradually, which were 42.94, 49.32, 52.52 and 59.39 urn, respectively. (3) When the rectangular attachment was placed in different positions, the maximal displacement of canine teeth the attachment of which was placed on the median was almost the same with that of the gingival side. While the changes in the mesial and distal directions were irregular. (4) The use of rectangular attachments makes no effect on the movement of instant canines, which only plays a synergistic role in the control of canine tooth torsion. The thickness of the attachment has a certain effect on the torsion of appliance. When the thickness increases, the maximum displacement of the canine tooth and the stress of the periodontal ligament are increased. In the vertical direction, the closer of the placement is to the crown, the better the control of the rotated canine is.
Résumé
Objective To analyze effects of different elastic modulus, thickness and tooth movement on deformation of the invisible dental appliance by finite element method, so as to provide theoretical references for orthodontic doctor to formulate the orthodontic treatment scheme. Methods A total of 12 finite element models of invisible appliances were established with 4 kinds of thickness and 3 kinds of elastic modulus. The displacement load of the tilting movement was applied to the 12 models, and the maximum Von Mises stress and deformation of the appliance were analyzed; the deformation of the appliance was analyzed by applying the displacement load of inclined, parallel and intrusion to the optimal model. Results The maximum Von Mises stress increased with the elastic modulus and thickness of the invisible appliance increasing. The deformation decreased with the appliance thickness increasing. When the tooth was under inclined and parallel movement, the maximum deformation was found in the corresponding part of the tooth. Some of the corresponding parts of the immovable teeth were deformed to the lip convex side and some to the tongue side with internal concave deformation, and the appliance deviated seriously to top of the crown when the tooth was under intrusion movement. Conclusions The optimum thickness of invisible dental appliance was 0.75 mm, and the elastic modulus 816.31 MPa that currently used in clinic was suitable. In the digital model, the tongue side of the teeth corresponding to the labial protruding part and the lip side of the tooth corresponding to the concave side of the tongue side can be thickened, and the invisible appliance can be optimized by using the thickened digital model.
Résumé
@#Accurate positioning of brackets is a necessary condition for ideal orthodontic treatment. Traditional bracket bonding technology has certain limitations, such as long operation time and poor accuracy. Indirect bonding technology is a method that bonding brackets on the model through intraoral impression or scanning, and then the brackets are accurately bonded to the tooth crowns using a transfer tray. In this article, the progression of transfer trays and adhesive agents, the application of digital technology in indirect bonding technology, indirect bonding for invisible appliances, and the prospect of this technology are reviewed. The literature review results show that indirect bonding technology can locate the bracket accurately, the operation is simple, the patient’s experience is comfortable, and the clinical efficiency can be significantly improved, the photocurable adhesive is an ideal adhesive for indirect bonding technology. With the development of digital technology, indirect bonding technology will be able to locate the brackets with increasing accuracy, thus achieving the "digital precision movement" of the teeth. The bonding technology of invisible appliance accessories is essentially a type of indirect bonding technology, It requires indirect bonding technology and digital technology to highly fit the needs of computer design accessories for the visual tooth movement and the use of indirect bonding technology to accurately bond accessories, ultimately achieving the desired tooth movement. Indirect bonding technology will play an increasingly important role with the development of digital technology and invisible correction technology.
Résumé
Objective:To investigate the effects of bracketless invisible appliance(BI),self-ligating bracket(SB) and conventional brackets(CB) on periodontal indices(PI) and inflammatory cytokine levels in gingival crevicular fluid(GCF) in adult orthodontic patients.Methods:90 orthodontic patients were randomly divided into CB,SB and BI groups(n =30).The subjects in the 3 groups accepted invisalign,Demon Q self-ligating brackets and conventional MBT brackets respectively.Plaque index(PLI),probing depth (PD) and interleukin-13 (IL-3),tumor necrosis factor-α (TNF-a) in GCF were analyzed before treatment,l,3 and 6 months after treatment,and after appliance removed respectively.Results:1 to 6 months after treatment,PI,IL-β and TNF-α rose constantly in CB and SB groups and reached to their top 6 months after treatment.There were no statistical differences between CB and SB groups 1 months after treatment,while PI,IL-β and TNF-α of SB group were lower than those of CB group 3 and 6 months after treatment and after therapy completed.PLI、IL-1 β and TNF-α of BI group were significantly increased 6 months after treatment.However,each index of BI group was significantly reduced compared with SB and CB groups after treatment.Conclusion:The SB has fewer disadvantages on peridentium than CB,while the BI is more conductive to protect the periodontal health status than SB and CB.
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Invisible appliance technology is the latest product resulting from image processing, computer-aided design and rapid prototyping technology in the field of orthodontics, and its development conforms to people’s pursuit for clinical treatment with modern concept of being beautiful, comfortable and healthy. The invisible appliance technology now has been widely used for treating different types of clinical orthodontic malocclusions by doctors, but researches on its clinical efficacy, biological and biomechanical mechanism still show quite deficiency. In this paper, the progresses of biomechanical research on invisible appliance technology were reviewed with the purpose to provide theoretical references for the reasonable, scientific and effective application of invisible appliance technology in clinic.
Résumé
Objective To analyze the mechanical effect of invisible appliances with different material hardness and provide theoretical basis for selecting the suitable material for invisible appliance and its clinical application. Methods Three different three-dimensional (3D) finite element models of invisible appliance were established, of which the elastic modulus was chosen as 415.6, 816.308 and 2 400 MPa, respectively. In these models, the upper central incisors were all designed to move 0.3 mm mesially. Then 3D nonlinear finite element method was used to analyze the stress-distribution in invisible appliance, teeth and periodontal ligament and the instant displacement of every tooth. The comparative study was made among three invisible appliances with different hardness． Results Under experimental condition, the most instant stress and displacement of teeth was the upper central incisor, with initial displacement greater in crown section than that in apical section and the greatest displacement was 0.17 mm. The tendency of central incisor movement was tipping in all situations. The movement of lateral incisor had the second greatest distance (the greatest displacement was 0.10 mm) and the tendency of its movement was in the opposite directions of aimed teeth. When elastic modulus of material decreased, the stress on the invisible appliance increased. The stress in periodontal ligament and the displacement of aimed teeth were also increased. Conclusions If the hardness of invisible appliance increases, the displacement of the designed tooth and treatment efficacy increases, but the appliance with more hardness couldn’t provide better ability in controlling of orthodontic tooth movement. The study suggested clinicians should use attachments or cooperate with fixed appliance to help move teeth bodily.