BACKGROUND: The aim of this study is to conduct a comparative evaluation of different designs of clear aligners and examine the disparities between clear aligners and fixed appliances.
METHODS: 3D digital models were created, consisting of a maxillary dentition without first premolars, maxilla, periodontal ligaments, attachments, micro-implant, 3D printed lingual retractor, brackets, archwire and clear aligner. The study involved the creation of five design models for clear aligner maxillary anterior internal retraction and one design model for fixed appliance maxillary anterior internal retraction, which were subsequently subjected to finite element analysis. These design models included: (1) Model C0 Control, (2) Model C1 Posterior Micro-implant, (3) Model C2 Anterior Micro-implant, (4) Model C3 Palatal Plate, (5) Model C4 Lingual Retractor, and (6) Model F0 Fixed Appliance.
RESULTS: In the clear aligner models, a consistent pattern of tooth movement was observed. Notably, among all tested models, the modified clear aligner Model C3 exhibited the smallest differences in sagittal displacement of the crown-root of the central incisor, vertical displacement of the central incisor, sagittal displacement of the second premolar and second molar, as well as vertical displacement of posterior teeth. However, distinct variations in tooth movement trends were observed between the clear aligner models and the fixed appliance model. Furthermore, compared to the fixed appliance model, significant increases in tooth displacement were achieved with the use of clear aligner models.
CONCLUSIONS: In the clear aligner models, the movement trend of the teeth remained consistent, but there were variations in the amount of tooth displacement. Overall, the Model C3 exhibited better torque control and provided greater protection for posterior anchorage teeth compared to the other four clear aligner models. On the other hand, the fixed appliance model provides superior anterior torque control and better protection of the posterior anchorage teeth compared to clear aligner models. The clear aligner approach and the fixed appliance approach still exhibit a disparity; nevertheless, this study offers a developmental direction and establishes a theoretical foundation for future non-invasive, aesthetically pleasing, comfortable, and efficient modalities of clear aligner treatment.

OBJECTIVE: To compare the effect of maxillary incisor intrusion and retraction with controlled tipping (CT) versus bodily movement (BM) in extraction cases on alveolar bone height and thickness, using cone-beam computed tomography (CBCT). Correlations between changes in alveolar dimensions and crown or root retraction, incisor inclination, and intrusion were also investigated.
METHODS: In all, 144 incisors of 36 women were retrospectively evaluated. All patients were treated with anterior intrusion and retraction with either controlled tipping (CT) (group 1) or bodily movement (BM) (group 2). CBCT scans were taken before and after retraction and intrusion and measurements of alveolar bone height and thickness at the level of mid-root and root apex were measured. The prevalence of dehiscence was also calculated.
RESULTS: Labial bone thickness (BT) increased at the level of the root apex with increased total BT in the CT group (p < 0.05). The BM group showed decreased palatal BT. Significant vertical bone loss with an increased incidence of dehiscences occurred on the palatal side in both groups. Changes in palatal bone area was negatively correlated with the amount of root apex retraction, while the total BT at the level of root apex was positively correlated with amount of intrusion.
CONCLUSIONS: Bodily retraction can result in reduced palatal bone dimensions and an increase risk of iatrogenic sequelae following anterior retraction in extraction cases. Vertical bone loss and an increased incidence of dehiscences is to be expected following anterior retraction. Careful attention must be paid to the bone boundary conditions to avoid moving the incisors out of the alveolar housing.
UNASSIGNED: ZIELSETZUNG: Vergleich der Auswirkungen der Intrusion und Retraktion des oberen Schneidezahns mit kontrolliertem Kippen („controlled tipping“, CT) und körperlicher Bewegung („bodily movement“, BM) bei Extraktionen auf die Höhe und Dicke des Alveolarknochens mithilfe digitaler Volumentomographie (DVT). Ferner wurden Korrelationen zwischen Veränderungen der Alveolardimensionen und Kronen- bzw. Wurzelretraktion, Schneidezahnneigung und Intrusion untersucht.
UNASSIGNED: Insgesamt wurden 144 Schneidezähne von 36 Frauen retrospektiv ausgewertet. Alle Patientinnen wurden mit anteriorer Intrusion und Retraktion entweder mit CT (Gruppe 1) oder BM (Gruppe 2) behandelt. Vor und nach der Retraktion und Intrusion wurden DVT-Aufnahmen angefertigt sowie Höhe und Dicke des Alveolarknochens auf der Höhe der mittleren Wurzel und der Wurzelspitze gemessen. Zudem wurde die Prävalenz der Dehiszenz berechnet.
UNASSIGNED: Die labiale Knochendicke (BT) nahm auf Höhe der Wurzelspitze zu, wobei die Gesamt-BT in der CT-Gruppe zunahm (p < 0,05). In der BM-Gruppe war die palatinale BT verringert. Auf der palatinalen Seite kam es in beiden Gruppen zu einem signifikanten vertikalen Knochenverlust mit einer erhöhten Inzidenz von Dehiszenzen. Die Veränderungen der palatinalen Knochenfläche waren negativ mit dem Ausmaß der Wurzelspitzenretraktion korreliert, die Gesamt-BT auf Höhe der Wurzelspitze dagegen positiv mit dem Ausmaß der Intrusion.
UNASSIGNED: Körperliche Retraktion kann zu einer Verringerung der palatinalen Knochendimensionen und zu einem erhöhten Risiko iatrogener Folgeerscheinungen nach anteriorer Retraktion bei Extraktionen führen. Nach einer anterioren Retraktion ist mit einem vertikalen Knochenverlust und einer erhöhten Inzidenz von Dehiszenzen zu rechnen. Um eine Verschiebung der Inzisiven aus ihrem alveolären Umfeld zu vermeiden, ist eine sorgfältige Berücksichtigung der Knochenrandbedingungen erforderlich.

OBJECTIVE: To elucidate the relationships and factors affecting the proximity between the incisive canal (IC) and maxillary central incisors and to predict the probable outcomes after anterior tooth retraction using cone beam computed tomography (CBCT).
METHODS: Retrospective CBCT data taken before and after maxillary anterior retraction in 36 patients were used in this study. The incisive canal length (ICL), maxillary central incisor length (TL), angles between the palatal plane and axes of the maxillary alveolar border (θ1), IC (θ2), and maxillary central incisor (θ3), retraction distance (TDE), distance from the maxillary central incisors to the IC (D), cross-sectional area of the IC (CSA), and volume of the IC were evaluated. Comparison of the parameters between contact and noncontact groups were examined. Logistic regression was performed to analyze the probable outcome prediction.
RESULTS: All parameters significantly decreased after anterior retraction, except for the ICL. Eighteen roots in 12 patients contacted the IC. The θ1, θ2, θ3, and D values at all levels were significantly lower, whereas the TDE, midlevel and oral opening CSA, and volume were significantly higher in the contact group compared with the noncontact group. The larger the pretreatment θ1 and θ3 were, the higher was the chance of incisors not contacting the IC.
CONCLUSIONS: Maxillary central incisors not contacting the IC after anterior retraction was positively associated with larger degrees of pretreatment maxillary alveolar bone angle and maxillary central incisor angle.

To evaluate the effect of friction vs frictionless mechanics on the rate of anterior segment retraction (ASR) in patients with bimaxillary protrusion.
Thirty females (18.3 ± 3.7 years) with bimaxillary protrusion were randomly allocated into the friction group, using elastomeric power chains, and the frictionless group, using T-loop springs for ASR. Eligibility criteria included absence of skeletal discrepancies and any systemic diseases or medications, among others. Randomization in a 1:1 ratio was generated by Microsoft Excel. Opaque sealed envelopes were sequentially numbered for allocation concealment. Only blinding of the outcome assessor was applicable. Activations were done every 4 weeks until completion of ASR. The primary outcome was the rate of ASR measured on digital models. Anchorage loss, molar rotation, and pain experienced were also assessed.
Two patients were lost to follow-up. The rate of ASR was 0.68 ± 0.18 mm/mo in the friction group vs 0.88 ± 0.27 mm/mo in the frictionless group, with no significant difference. A significant difference in anchorage loss of 1.63 mm and molar rotation of 7.06° was observed, being higher in the frictionless group. A comparable pain experience associated with both mechanics was reported.
No difference in the rate of ASR or pain experience was observed between friction and frictionless mechanics. However, extra anchorage measures should be considered when using frictionless mechanics as greater anchorage loss and molar rotations are anticipated.