Predictability of expansion movements performed by clear aligners in mixed dentition in both arches: a retrospective study on digital casts.

BACKGROUND: to evaluate the predictability of expansion achieved in patients in early mixed dentition treated with Clear Aligners (CA), analyzing the efficiency of the expansion at the end of the first set of aligners and at the end of the therapy in the upper and lower arch. METHODS: 36 patients (20 F, 16 M; mean age 8.3 ± 1.5 years) were selected retrospectively from the Department of Orthodontics of the Hospital of Rome "Tor Vergata". All subjects were treated with CA with no other auxiliaries than attachments. For each patient a standardized sequential expansion protocol was planned for both arches. Digital dental casts were created at three observation periods from an intraoral scanner: prior to treatment (T0), at the end of the first set of aligners (T1), at the end of treatment (T2). The 3D models in planned position determined by the first Clincheck (CC) were obtained for comparison with T1 and T2. Six linear transversal measurements were used to evaluate the dimensional changes and the predictability of expansion movements, comparing T1-CC and T2-CC. RESULTS: a statistically significant increase within the pre-treatment and the final outcomes for all the variables examined was found. In the upper arch, the greatest level of predictability was detected at the level of the first (46.44%) and second deciduous molar width (44.95%) at T1. The analysis of T2-CC changes showed a significant increase in the percentage of predictability of expansion at the level of the first permanent molars, at mesial (54.86%) and distal (58.92%) width. In the lower arch, a higher percentage of predictability than the upper arch was reported at T1-CC and T2-CC, with the greatest values at the level of second (T1-CC: 48.70%; T2-CC: 75.32%) and first deciduous molar width (T1-CC: 45.71%; T2-CC: 72.75%). CONCLUSIONS: CA can induce significant transversal increments. The predictability of expansion is variable, but it did not exceed the 50% during the first set of aligners. It was necessary to apply refinement set to achieve a good predictability for expansion of about 70%. The expansion in the lower arch was observed to be more predictable than in the upper arch.

Mandibular morphometric analysis in open bite early treatment relapse subjects: a retrospective observational pilot study.

BACKGROUND: The purpose of this retrospective study was to evaluate the mandibular shape differences between a group of success and a group of failure Anterior Open Bite (AOB) malocclusion early orthodontic treatment in growing subjects, in order to identify mandibular features of relapse. METHODS: Twenty three patients (7 males, 16 females, 9.3 years ±1,5 years) were enrolled from the Department of Orthodontics at the University of Rome Tor Vergata. Inclusion criteria were: white ancestry, overbite < 0 mm, mixed dentition phase, end-to-end or Class I molar relationship, first skeletal class assessed on lateral cephalograms (0° < ANB < 4°), cervical skeletal maturation CS1-CS2, no previous orthodontic treatment, no congenital diseases. Pre-treatment (T1) lateral cephalograms were acquired. Each patient underwent early orthodontic treatment with Rapid Maxillary Expander (RME) and Bite Block (BB) or Quad-Helix Crib (QHC) until open bite correction. Radiographic records were recollected at T2 (permanent dentition, skeletal cervical maturation CS3-CS4). Mean interval time T2-T1 was 4.2 years ±6 months. According to treatment stability, a Relapse Group (RG 11 patients, 3 M, 8F; 13.7 years ±8 months, 7 subjects treated with RME/BB, 4 with QH/C) and a Success Group (SG, 12 patients, 4 M, 8F; 13.4 ± 10 months, 7 subjects treated with QH/C, 5 with RME/BB) were identified. On the lateral radiographs the mandibular length (Co-Gn), the inferior gonial angle (NGo^GoMe) and the antegonial notch depth (AND) were analyzed. Then the mandibular Geometric Morphometric analysis (GMM) was applied. Intergroup statistically significant differences were found using student's t-tests. Procrustes analysis and principal component analysis (PCA) were performed for the GMM. RESULTS: At T1 no statistically significant differences were found between RG and SG, however higher values of antegonial notch depth were found in RG. T2-T1 comparison showed in RG statistically significant increases in Co-Gn (p = 0.04), NGo^GoMe angle (p = 0.01) and antegonial notch depth (p = 0,04). PC1 confirmed the increase in the antegonial notch depth in RG when compared to SG at T2. CONCLUSIONS: The increased antegonial notch depth associated with the increased mandibular length and the increased gonial angle could be responsible of relapse of early orthodontic treatment in open bite growing subjects.