UNASSIGNED: Overtreatment design of clear aligner treatment (CAT) in extraction cases is currently primarily based on the clinical experience of orthodontists and is not supported by robust evidence on the underlying biomechanics. This study aimed to investigate the biomechanical effects of overtreatment strategies involving different maxillary anterior teeth intrusion patterns during anterior teeth retraction by CAT in extraction cases.
UNASSIGNED: A finite element model of the maxillary dentition with the first premolar extracted was constructed. A loading method of clear aligners (CAs) based on the initial state field was proposed. The iterative method was used to simulate the long-term orthodontic tooth movement under the mechanical load exerted by the CAs. Three groups of CAs were utilized for anterior teeth retraction (G0: control group; G1: incisors intrusion group; G2: anterior teeth intrusion group). Tooth displacement and occlusal plane rotation tendency were analyzed.
UNASSIGNED: In G0, CAT caused lingual tipping and extrusion of the incisors, distal tipping and extrusion of the canines, mesial tipping, and intrusion of the posterior teeth. In G1, the incisors showed minimal extrusion, whereas the canines showed increased extrusion and distal tipping tendency. G2 showed the smallest degree of posterior occlusal plane angle rotation, while the inclination tendency of the canines and second premolars decreased.
UNASSIGNED: 1. In CAT, tooth displacement tendency may change with increased wear time. 2. During anterior teeth retraction, the incisor intrusion pattern can provide effective vertical control for the lateral incisors but has little effect on the central incisors. Anterior teeth intrusion patterns can alleviate the inclination of canines and second premolars, resulting in partial relief of the roller-coaster effect.

暂无摘要。

BACKGROUND: The most common treatment approaches for patients missing maxillary lateral incisors are implant replacement (IT) and orthodontic space closure (SC). Treatment techniques change and improve over time, and it is of interest to know if improvements differ between the methods.
OBJECTIVE: To compare the aesthetic outcome and other clinical findings in patients with one or two missing maxillary lateral incisors who were treated with a 10-year difference in time, with either orthodontic space closure or implant replacement.
METHODS: A total of 88 patients were included in the study. Forty-four patients treated between 2011 and 2018 were included as the latter cohort (LC). The LC was compared to the early cohort (EC; n = 44), treated between 2001 and 2008. A total of 132 teeth was analysed: 62 teeth in the EC (28 teeth in IT cases and 34 teeth in SC cases) and 70 teeth in the LC (34 teeth in IT cases and 36 teeth in SC cases). Long-term clinical and aesthetic outcomes were evaluated.
RESULTS: An improvement over time was found in crown length, BoP, papilla, the inclination of incisors, and overall appearance in IT cases and in crown colour and overbite in SC cases. A deterioration over time was found in crown length and BoP among the SC cases.
CONCLUSIONS: Among the IT cases, an improvement in outcomes was noted over time. When comparing SC cases the colour of the crown and overbite had improved, while crown length and BoP had deteriorated over time.

The patient presented in this case report is a 10-year-old boy with hyperdivergent skeletal Class II associated with familial genetic agenesis of the second premolars. The treatment plan chosen was to close the spaces of agenesis using a bimaxillary appliance fixed buccally. The advantages and disadvantages of this treatment option were discussed. The result was stable and made it possible to avoid an implant-prosthetic solution, which would undoubtedly have been more restrictive over time.

OBJECTIVE: To assess the success rate of spontaneous space closure after extraction of the first permanent molar (FPM) in the maxilla and the mandible, and to identify the factors that make spontaneous space closure most favorable in each.
METHODS: A retrospective records-based cohort study was conducted through a search of the database of the Public Dental Service, Stockholm County Council, Stockholm, for young adults born between 2000 and 2001, who underwent extraction of one or more FPM between 2006 and 2016. A total of 995 extracted teeth were identified, of which 203 teeth in 155 patients met the inclusion criteria.
RESULTS: Of the 203 extracted teeth, 166 (81.8%) did not receive any orthodontic treatment. The success rate for space closure in orthodontically treated patients was 91.9%. The success rate for spontaneous space closure was 84.3%. All unsuccessful spontaneous space closure in the maxilla occurred in patients older than 12 years. The dental developmental stage of the second permanent molar (SPM) had a statistically significant association with spontaneous space closure in the mandible (P < .001).
CONCLUSIONS: The success rate of spontaneous space closure was high (84.3%) and was higher in the maxilla (94.1%) than the mandible (74.1%). Age at time of extraction and dental developmental stage of the SPM were significant factors for successful spontaneous space closure in the maxilla and mandible, respectively.

This case report describes a complex full-step class II case in a young adult patient treated with lingual straight-wire appliance and upper first molar extraction. As the patient refused a surgical treatment, she was offered the best possible camouflage with the double aim of obtaining an ideal occlusal relationship and maintaining the profile; appropriate biomechanical strategies, including extraction choice and anchorage control during space closure, were needed to achieve the planned results. This case report demonstrates the possibility of successfully resolving severe sagittal discrepancies in an adult patient without surgical treatment by means of a completely invisible non-compliance technique, with the extraction of the most compromised teeth. This report also underlines the need for careful planning during both diagnostic and treatment phases, in order to obtain the best results.

BACKGROUND: This single-centered randomized controlled clinical trial aimed to evaluate the effectiveness of micro-osteoperforations (MOPs) in accelerating the orthodontic retraction of maxillary incisors.
METHODS: Forty-two patients aged 16-40 were recruited and randomly assigned into two groups, one which underwent MOPs (MOPG) in the buccal and palatal region of all maxillary incisors immediately before the start of retraction and one which did not (CG). Eligibility criteria included the orthodontic need for maxillary first premolars extraction and space closure in two phases. The primary outcome of the study consisted of measuring the rate of space closure and, consequently, the rate of incisors\' retraction using digital model superimposition 14 days later and monthly thereafter for the next 4 months. The secondary outcomes included measuring anchorage loss, central incisors\' inclination, and root length shortening, analyzed using cone beam computed tomography scans acquired before retraction and 4 months after retraction. Randomization was performed using QuickCalcs software. While clinical blinding was not possible, the image\'s examinator was blinded.
RESULTS: Twenty-one patients were randomly assigned to each group. However, due to various reasons, a total of 37 patients (17 male and 20 female) were analyzed (mean age: 24.3 ± 8.1 years in the MOPG; 22.2 ± 4.2 years in the CG) during the trial. No statistically significant difference was found between the MOPG and the CG regarding the incisors\' retraction measured at different time points at the incisal border (14 days, 0.4 mm vs. 0.5 mm; 1 month, 0.79 mm vs. 0.77 mm; 2 months, 1.47 mm vs. 1.41 mm; 3 months, 2.09 mm vs. 1.88 mm; 4 months, 2.62 mm vs. 2.29 mm) and at the cervical level (14 days, 0.28 mm vs. 0.30 mm; 1 month, 0.41 mm vs. 0.32 mm; 2 months, 0.89 mm vs. 0.61 mm; 3 months, 1.36 mm vs. 1.10 mm; 4 months, 1.73 mm vs. 1.39 mm). Similarly, no statistically significant differences were detected in the space closure, anchorage loss, central incisors\' inclination, and radicular length between groups. No adverse effect was observed during the trial.
CONCLUSIONS: MOPs did not accelerate the retraction of the maxillary incisors, nor were they associated with greater incisor inclination or root resorption. Trial registration ClinicalTrials.gov NCT03089996. Registered 24 March 2017- https://clinicaltrials.gov/ct2/show/NCT03089996 .

BACKGROUND: This study aimed to assess the impact of aligner activation and power arm length and material on canine and aligner displacement, von Mises stress in the power arm, and principal stress in the periodontal ligament (PDL) during canine tooth distalization using finite element analysis (FEA). The effects of aligner activation and power arm length were primary outcomes, while the effect of the power arm material was a secondary outcome.
METHODS: Aligner activation (0.1 mm or 0.2 mm) was applied without using a power arm in two models. The effects of aligner activation, power arm length (12, 13, or 14 mm) and power arm material (stainless steel [SS] or fiber-reinforced composite [FRC]) on canine distalization were investigated in 12 models by evaluating displacement and stress via ALTAIR OptiStruct analysis.
RESULTS: Greater canine displacement was observed in all models with 0.2 mm than 0.1 mm of aligner activation. When models with the same aligner activation were compared, reduced mesiodistal tipping, increased palatal tipping, and increased extrusion of the canine cusp were observed with increasing power arm length. Moreover, the von Mises stress increased as the power arm length increased. Increasing the aligner activation and power arm length increased the maximum principal stress in the PDL. Power arms of the same length in both materials showed the same results in terms of canine displacement, clear aligner displacement, and maximum principal stress in the PDL. However, under conditions of equal length and aligner activation, the von Mises stress of the SS power arm was higher than that of the FRC power arm.
CONCLUSIONS: Using a power arm in canine distalization reduced mesiodistal tipping but increased palatal tipping and extrusion of the canine cusp. Aligner activation and additional force increased tooth movement and principal stress in the canine PDL. FRC power arms exhibited less von Mises stress than SS power arms.

This study aimed to assess the effect of premolar extraction and anchorage type for orthodontic space closure on upper airway dimensions and position of hyoid bone in adults by cephalometric assessment.
This retrospective study was conducted on 142 cephalograms of patients who underwent orthodontic treatment with premolar extraction in four groups of (I) 40 class I patients with bimaxillary protrusion and maximum anchorage, (II) 40 class I patients with moderate crowding and anchorage, (III) 40 class II patients with maximum anchorage, and (IV) 22 skeletal class III patients with maximum anchorage. The dimensions of the nasopharynx, velopharynx, oropharynx, and hypopharynx, and hyoid bone position were assessed on pre- and postoperative lateral cephalograms using AudaxCeph v6.1.4.3951 software. Data were analyzed by the Chi-square test, paired t-test, and Pearson\'s correlation test (alpha = 0.05).
A significant reduction in oropharyngeal, velopharyngeal, and hypopharyngeal airway dimensions was noted in groups I, III, and IV (P < 0.001), which was correlated with the magnitude of retraction of upper and lower incisors (r = 0.6 - 0.8). In group II, a significant increase was observed in oropharyngeal and velopharyngeal dimensions (P < 0.001). A significant increase in nasopharyngeal dimensions occurred in all groups (P < 0.001). Also, in groups I and III, the position of hyoid bone changed downwards and backwards, which was correlated with reduction in airway dimensions (r = 0.4 - 0.6).
According to the present results, extraction orthodontic treatment affects upper airway dimensions and hyoid bone position. Maximum anchorage decreases airway dimensions while moderate anchorage increases airway dimensions.

OBJECTIVE: A TiNb alloy wire (GUMMETAL® [GM], Toyota Central R&D Labs, Inc., Nagakute, Japan) was recently developed with unique properties for orthodontic applications. This pilot split-mouth randomized controlled trial compared maxillary canine retraction during space closure using sliding mechanics on GM vs. stainless steel (SS) archwires.
METHODS: Subjects who met the inclusion criteria were treated with fixed appliances and maxillary first-premolar extractions between September 2020 and March 2022. After leveling and aligning, maxillary archwires, fabricated by crimping together segments of 0.016×0.022\" GM and SS archwires, were placed and canine retraction initiated using nickel-titanium coil springs. Digital models of the maxillary arch were superimposed at 0, 4, 8 and 12 weeks and the amount of canine movement (mm), rate of movement (mm/month), and 3-dimensional changes (rotational, vertical extrusion, tip) were measured and compared statistically.
RESULTS: Of the 12 subjects recruited, only six completed the study with a median age of 15.8 years (12.0-17.4 years). At 12 weeks, the median canine retraction was 3.41mm (IQR: 2.10, 4.76) with GM versus 3.71mm (IQR: 1.62, 6.45) with SS. The retraction rate was 1.14mm/month (IQR: 0.69, 1.59) with GM, versus 1.24mm/month (IQR: 0.54, 2.15) with SS. The median rotational, vertical and tip changes of the canine were 7.90̊, 0.59mm and 6.15̊ with GM, and 7.25̊, 0.29mm and 2.05̊ with SS. Intergroup differences with all measurements were not statistically significant.
CONCLUSIONS: No significant differences were found between GM and SS during maxillary canine retraction. GM demonstrated clinical potential for space closure mechanics, however, future larger studies are needed.