In recent years, clear aligner technology has been maturing and is rapidly gaining popularity in the orthodontic market for its aesthetic and removable properties. However, despite the background of its large-scale clinical application, mechanical properties of clear aligners need to be studied in depth. This paper reviews the factors influencing mechanical properties of clear aligners and the current status of research to provide evidence-based guidance for clinical application.

BACKGROUND:The reciprocal force generated by the molar distalization with clear aligners can lead to anchorage loss.The effect of arch shapes and missing second premolars on anchorage has not been reported. OBJECTIVE:To analyze the effect of arch shapes and missing second premolars on anchorage during molar distalization with clear aligners using the finite element method. METHODS:Cone-beam CT data from an adult male were acquired from the database to establish the maxilla-upper dentition-periodontium-rectangular attachment-clear aligner model.The distal movement amount designed on the bilateral second molars was set to 0.25 mm.First,there were two groups in the study:second premolar bilateral presence and absence groups.Then,four subgroups in each group were created:tapered arch,ovoid arch,square Class Ⅱ Division 1 arch,and Class Ⅱ Division 2 arch groups.The Ansys software was used to calculate the displacement of the anchorage tooth and the stress of the periodontal ligament. RESULTS AND CONCLUSION:Mesial tipping and extrusion of first molars and premolars,labial inclination and intrusion of anterior teeth occurred during the upper second molar distalization with clear aligners.When the bilateral second premolars were missing,the mesial displacement of first molars increased significantly while that of first premolars and anterior teeth decreased in all groups.The square Class Ⅱ Division 1 arch group showed the least anterior labial inclination,while the tapered arch group showed the most.There was no significant difference between the ovoid arch group and the tapered arch group.Moreover,the magnitude of tipping in the square Class Ⅱ Division 2 arch group was slightly higher than that in the Class Ⅱ Division 1 arch group.The stress of the periodontal ligament of the anchorage teeth was concentrated on the cervical and apical regions of the teeth.And the lowest stress level was detected in the square arch group.Compared with the other groups,the stress on the labial cervical area of the periodontal ligaments was also significantly relieved in the square arch group.To conclude,the square arch is more favorable in terms of anterior anchorage control and periodontal ligament stress distribution.Anterior labial inclination efficiency can be increased in cases of Class Ⅱ Division 2 by designing the anterior labial inclination in conjunction with molar distalization.If the second premolar is missing during molar distalization,it is not conducive to opening up the space in the area of the missing tooth.

BACKGROUND:The thin alveolar bone in the lower anterior region increases the risk of labial bone resorption when intruding the teeth with clear aligners.The effect of sagittal overcorrection design on the labiolingual control of mandibular anterior teeth intrusion has not been fully investigated. OBJECTIVE:To explore the effect of overcorrection on the changes in the displacement and stress of the mandibular anterior teeth,especially the cervical and apical regions. METHODS:Through a male volunteer cone-beam CT data,the three-dimensional reconstruction of the mandible and teeth was conducted in the MIMICS and GEOMAGIC software.Moreover,the models of periodontal ligaments,attachments,and appliances were created in the SOLIDWORKS software.First,the study was divided into canine intrusion group and incisor intrusion group.Then,the overcorrection(0°,1°,2°)was designed on the bilateral mandibular central and lateral incisors.A total of six models were established.The models were assembled and imported into the ANSYS software to analyze and calculate the displacement and stress level. RESULTS AND CONCLUSION:(1)In the canine intrusion group,canines intruded and tipped lingually while incisors extruded and tipped lingually.In the incisor intrusion group,canines extruded and tipped lingually while incisors intruded and tipped lingually.(2)Without overcorrection,the incisors necks moved lingually while apexes moved labially.With overcorrection,the incisors tended to be upright,followed by labial tilt.The least cervical and apical displacements were detected under 1° overcorrection.(3)With overcorrection,the incisal cervical stress concentration area shifted from labial to lingual in the canine intrusion group,whereas the stress concentration area shifted from lingual to labial in the incisor intrusion group.(4)The incisors tended to tilt lingually when intruding the mandibular anterior teeth with clear aligners.The sagittal overcorrection design was conductive to maintain the stable position of incisors.However,the amount of overcorrection should be moderate.Excessive overcorrection might increase the labial inclination tendencies of incisors.

Aged, 80 and over ; Female ; Humans ; Thyroid Neoplasms ; surgery ; Trachea ; surgery

The olfactory bulb (OB) is the first relay station in the olfactory system. In the OB, mitral/tufted cells (M/Ts), which are the main output neurons, play important roles in the processing and representation of odor information. Recent studies focusing on the function of M/Ts at the single-cell level in awake behaving mice have demonstrated that odor-evoked firing of single M/Ts displays transient/long-term plasticity during learning. Here, we tested whether the neural activity of M/Ts and sniffing patterns are dependent on anticipation and reward in awake behaving mice. We used an odor discrimination task combined with in vivo electrophysiological recordings in awake, head-fixed mice, and found that, while learning induced plasticity of spikes and beta oscillations during odor sampling, we also found plasticity of spikes, beta oscillation, sniffing pattern, and coherence between sniffing and theta oscillations during the periods of anticipation and/or reward. These results indicate that the activity of M/Ts plays important roles not only in odor representation but also in salience-related events such as anticipation and reward.