RESUMO
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.
RESUMO
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.