This longitudinal study assessed the intermaxillary and intraarch relationships from mixed to permanent dentitions during a 4-year follow-up.

The sample comprised 352 children evaluated for crowding, midline maxillary diastema, anterior spacing, overjet, overbite, and sagittal and transverse relationships in mixed (T1) and permanent (T2) dentition. Data between different time points were compared using McNemar and Bowker symmetry tests, with a significance level of 5%.

Of the 352 children evaluated over a 4-year follow-up period, significant changes were observed in the intraarch and intermaxillary relationships from T1 to T2. The intraarch relationship showed significant decreases in crowding (61.3%), maxillary midline diastema (74.3%), and anterior spacing (82.2%) (P <0.0001). Regarding the intermaxillary relationship, statistically significant changes were observed in the overjet (P = 0.003), overbite (P = 0.004), and anteroposterior (P <0.0001) and transverse relationships (P <0.0001). In addition, 43.1% of children had increased overjet at T1 and normal overjet at T2, 29.3% of children with a Class II relationship at T1 and Class I relationship at T2, 70.5% of children with posterior crossbite and normal transverse relationship at T2, and 73.9% of children with anterior open bite and normal overbite at T1 and average overbite at T2.

Significant favorable changes in intraarch relationships were observed during the transition from mixed to permanent dentition. Children also show changes in intermaxillary relationships, with a potential improvement in occlusion of the permanent dentition.

Dental crowding is the most prevalent malocclusion in the mixed and permanent detitions and can have a major impact on dentofacial esthetics. However, adjustments to the development and growth of the dentition can potentiate self-correction of dental crowding during childhood.

To evaluate the physiological behavior of mandibular incisor crowding in the transition from mixed to permanent dentition.

Five electronic databases (PubMed, Scopus, Web of Science, LILACS and LIVIVO) and part of the gray literature (Proquest and Google Scholar) were investigated, based on the eligibility criteria associated with the acronym PECO, until June 2022. The risk of bias was assessed using the ROBINS-E tool and the certainty of evidence, the GRADE tool.

Among the 2.663 studies identified, five were selected for qualitative analysis, of which one have a low risk of bias, and four, a moderate risk. A total of 243 patients were evaluated. Evidence with a high level of certainty was generated indicating a tendency for improvement in mandibular incisor crowding from mixed to permanent dentition, with mandibular incisor crowding decreasing from 0.17 to 4.62 mm on average. The mandibular incisor crowding reduction seems to be associated with the amount of initial crowding and spontaneous dental arch dimensional changes that occur in the mixed dentition and culminate in the increase in arch perimeter, leeway space, incisor protrusion and transverse growth of the maxillary and mandibular arch.

Based on moderate scientific evidence, spontaneous longitudinal changes in dental arch in the transition from the mixed to the permanent dentition demonstrate a spontaneous improvement in mandibular incisor crowding by up to 4.62 mm. These evidence provide a scientific basis for planning only longitudinal follow-up in patients with mild to borderline moderate mandibular incisor crowding in the mixed dentition avoiding overtreatment.

In this study, original leeway space was determined using plaster models prepared from the same individuals over successive years and compared with that reported in an earlier study. The plaster models used for measurement were prepared from a normal dentition group comprising 64 patients and a crowded dentition group comprising 29. The mesiodistal crown width of the deciduous canines, deciduous first molars, and deciduous second molars, as well as that of the canines, first premolars, and second premolars was measured. Leeway space was then calculated and the results compared with that previously reported. The average maxillary and mandibular leeway spaces calculated in the same individuals were 1.46 and 2.66 mm, respectively, whereas those calculated from data collected from different individuals were 0.89 and 2.83 mm, respectively. No direct statistical comparison of leeway space between this and the earlier report was possible. The present results did indicate, however, that it was larger in the maxilla than previously reported. A larger leeway space is advantageous for the normal arrangement of the permanent teeth. While the mesiodistal crown width of some of the lateral segment teeth in the present study was significantly larger in boys than in girls, no significant difference was observed in leeway space between sexes. The mesiodistal width was larger in multiple permanent teeth such as canines in the crowded dentition group, and this difference was significant in boys. On the other hand, no difference was observed in mesiodistal width in the deciduous teeth between the two groups. These results showed a tendency toward larger teeth and less leeway space in the permanent dentition in the crowded dentition group, which may have been a factor in why such crowding occurred.

To study the influence of different force magnitudes on dental arches in cervical headgear (CHG) treatment.

In this controlled clinical trial, patients (n = 40) were treated with CHG with light (L, 300 g, n = 22) or heavy force (H, 500 g, n = 18) magnitude. Subjects were asked to use CHG for 10 hours a day for 10 months. The outer bow of the CHG facebow was raised 10-20 degrees and the inner bow expanded 3-4 mm. Adherence to instructions and force magnitude were monitored with an electronic module (Smartgear, Swissorthodontics, Switzerland). Impressions for study models were taken before (T1) and after (T2) treatment and the study models were scanned into digital form (3Shape, R700 Scanner, Denmark). Measurements were made using the digital models (Planmeca Romexis, Model analyser, Finland).

During the treatment (T1-T2) the upper inter-canine distance increased by 2.83 mm (P = 0.000) and 2.60 mm (P = 0.000) in the L and H force magnitude groups, respectively. Upper inter-molar width increased by 3.16 mm (P = 0.000) and 2.50 mm (P = 0.000) in the L and H groups, respectively. Maxillary total arch perimeter increased by 6.39 mm (P = 0.001) and 6.68 mm (P = 0.001) in the L and H groups, respectively. In the amount of change over time, T1-T2, in the upper arch measurements, no significant difference was found between the groups. Lower inter-canine width increased by 0.94 mm (P = 0.005) and 1.16 mm (P = 0.000) in the L and H groups, respectively; no difference between the groups. Lower inter-molar distance increased by 2.17 mm (P = 0.000) and 1.11 mm (P = 0.008) in the L and H groups, respectively. At the end of the study, upper and lower inter-molar width was larger in the L group than in the H group (P = 0.039 and P = 0.022, respectively).

CHG therapy is an effective method for expanding and releasing moderate crowding of the upper dental arch. The lower arch spontaneously follows the upper arch in widening effects, and minor expansion can also be seen on the lower arch. In the L group, larger inter-molar width was achieved on the upper and lower arch; probably due to better adherence to instructions. Light force is recommended for use in CHG therapy.