Buccolingual angulation and intermolar width changes in the maxillary first molars of untreated growing children

Evaluation of Buccolingual Inclinations of First Molars Among Different Vertical Facial Patterns in Class II Division I Subjects

Background Knowing the characteristics of vertical patterns is crucial to provide the best orthodontic treatment. Cone beam computed tomography (CBCT) offers a valuable tool for evaluating true buccolingual inclinations. The current study investigates the buccolingual inclination of first molars in adult subjects with different vertical facial patterns. Methods CBCT scans of 66 adult patients (31 males, 35 females) with a mean age of 31.6 years (SD: 6.4 years) exhibiting skeletal class II division I maxillomandibular relationships were employed. Participants were categorized into three groups based on linear and angular measurements: normodivergent group (n=22), hypodivergent group (n=22), and hyperdivergent group (n=22). The independent samples t-test and Mann-Whitney U-test were conducted to investigate statistical differences in terms of buccolingual inclination between the three vertical patterns. Results Statistically significant differences were observed in the buccolingual inclinations of both maxillary and mandibular first molars in the hypodivergent group compared to the other groups (p<0.05). Conclusions In patients with class II division I sagittal relationships, the buccolingual inclinations of the first molars exhibit similarities between normodivergent and hyperdivergent groups. However, these inclinations differ significantly in hypodivergent adult subjects.

Three-dimensional analysis of posterior tooth inclinations in transverse and sagittal relationships: A cross-sectional study

OBJECTIVE

To compare tooth inclinations in different sagittal skeletal patterns and transverse maxillary relationships three-dimensionally.

METHODS

A cross-sectional study carried out with 132 three-dimensional digital models in the complete permanent dentition divided into six groups (n=22); three groups with maxillary atresia: G1- skeletal class I, G2- skeletal class II and G3-skeletal class III; three groups without maxillary atresia: G4- skeletal class I; G5- skeletal class II and G6- skeletal class III. The comparison between the skeletal pattern was performed by the non-parametric tests of Kruskal Wallis and Dunn and between the groups by the non-parametric test of Mann Whitney.

RESULTS

Subjects with skeletal class II and maxillary atresia had a greater lingual inclination of the maxillary teeth than those with class I and III; Subjects with skeletal class II without atresia had a less lingual inclination of the mandibular molars than the other classes (p<0.05). The maxillary premolars showed no variation in dental inclination with atresia, independent of the skeletal class in G1, G2, and G3 (p>0.05). The mandibular premolars showed that the groups without atresia G4, G5, and G6 presented no significant difference (p>0.05). Lower premolars in skeletal class III malocclusion individuals with atresia had a more negative inclination than the others.

CONCLUSION

There is a difference in the inclination of posterior teeth between individuals with and without maxillary atresia and skeletal classes I, II, and III.

Longitudinal changes in the dental arch width and symmetry in identical and fraternal twins

INTRODUCTION

This study aimed to assess growth-related dental and symmetry changes in the dental arch within and between identical and fraternal twins in mixed and permanent dentition.

METHODS

Three-dimensional scanned dental models of eligible subjects were selected from the Forsyth-Moorrees Twin Study sample. This retrospective cohort study was carried out on 36 identical (18 pairs) and 28 fraternal (14 pairs) twins in mixed dentition and 36 identical (18 pairs) and 38 fraternal (19 pairs) twins in permanent dentition stages on the basis of the availability of the dental casts scanned each year from each group (Table I). Linear measurements from dental casts were performed in patients aged 8-16 years. Student t test and Pearson's correlation were used to compare the symmetry between and within the identical and fraternal twins. The resemblance and heritability patterns were retrospectively obtained from the Pearson correlation coefficient and Falconer's heritability test (H2 = 2 × b). Adjusted mixed-effects estimates and 95% confidence intervals were calculated to test the association between age and dental parameters for both mixed and permanent dentition groups.

RESULTS

Intercanine and intermolar widths significantly increased (P <0.05) during the mixed dentition but became stable after 13 years old. No statistically significant differences were found in arch symmetry between the 2 groups (ie, identical and fraternal) in any of the included measurements. Evaluation of the resemblance and heritability pattern showed nonsignificant results for all variables measured (H2 range, -0.67 to 0.56).

CONCLUSIONS

The dental arch becomes wider at a higher rate in the canine region than the molar region in both the mixed and early permanent dentition. The dental arches of twins develop symmetrically, and their growth is not mainly affected by genetics. Asymmetrical teeth will maintain their relative position to reference planes throughout growth.

Genetic contribution to palatal morphology variation using three-dimensional analysis in Australian twins

OBJECTIVE

This study aimed to provide insight into the relative contributions of genetic and environmental factors to palatal morphology variation in a cohort of Australian twins.

METHODS

Healthy Australian twins, aged 12-15 years (45 monozygotic, 46 same sex dizygotic, and 32 opposite-sex dizygotic) were included in the study groups. A scanner was used to obtain three-dimensional data of the maxillary arch. Palatal depth was defined by a line to the deepest point measured from the reference plane at the mid-point of the inter-pre-molar or inter-molar line. This line was then divided into 10 equal sections in order to created 10 different depths for each palatal width. Each palatal width was divided into anterior and posterior areas. Univariate genetic analysis, using the OpenMx structural equation modelling package in R, was carried out on the quantitative data using the normal assumptions of a twin model.

RESULTS

Heritability estimates for anterior palatal width ranged from 0.75 to 0.80, and from 0.78 to 0.86 for posterior palatal width. Estimates for anterior and posterior palatal depth were 0.72 and 0.86, respectively.

CONCLUSIONS

Palatal morphology tends to have a moderate to relatively high genetic contribution overall. Palate height has a higher genetic contribution posteriorly than anteriorly. The width of the deep palate is under marginally less stringent genetic regulation than the width of the shallow palate.

Quad-helix compression to decompensate molar inclination prior to skeletal expansion

OBJECTIVES

To demonstrate that patients without posterior crossbite (PCB) but with maxillary transverse deficiency, not previously observed due to an increased curve of Wilson, can benefit from the same palatal expansion as patients with PCB, after correction of the buccal inclination.

MATERIALS AND METHODS

A total of 41 patients presenting a maxillary skeletal transverse deficiency were treated: 26 without PCB and 15 with PCB. In the non-PCB group, quad-helix compression was followed by a Hyrax expander (QH+HY), whereas the PCB group only underwent Hyrax expander treatment (HY). The maxillary intercanine, interpremolar, intermolar widths (cusp tips and gingival level) and molar inclination were measured at baseline and at the end of treatment in both groups.

RESULTS

No significant differences were found between groups at the end of treatment, and no PCBs remained. The same maxillary expansion was achieved in the QH+HY and HY groups in the region of the canines, at both the gingival (3.4 ± 2.0 vs. 3.4 ± 2.7 mm; P = 0.999) and cusp tip levels (4.5 ± 3.1 vs. 3.8 ± 2.2 mm; P = 0.981). The molar inclination in the QH+HY group decreased, while there was a slight increase in the HY group (-6.50° ± 5.34° vs. 2.3° ± 4.1°; P < 0.001).

CONCLUSIONS

Some patients with maxillary transverse deficiency do not present with PCB, due to an increased curve of Wilson. However, these patients require skeletal expansion similar to that of patients with a bilateral PCB. The curve of Wilson should be flattened prior to expansion in order to increase the amount of maxillary skeletal expansion.

Evaluation of Growth and Development of Late Mixed Dentition Upper Dental Arch with Normal Occlusion Using 3-Dimensional Digital Models

Objective

The purpose of this study was to observe the three-dimensional growth and development of the maxillary arch in 10-year-olds with normal occlusion during the late mixed dentition stage.

Methods

Forty-four 10-year-old students (22 males and 22 females) who had normal occlusion during late mixed dentition were selected from an elementary school in Beijing, China. Once per year for three consecutive years, a dental cast was obtained from each subject, and the cast was scanned with a 3D digital scanner (R700 3D). The three-dimensional measurements of the maxillary dental arch and the inclination of the bilateral maxillary first molars were obtained from the digital model.

Results

The upper anterior arch length (UAAL), upper total arch length (UTAL), upper inter primary or permanent canine width (UICW), upper intermolar width (UIMW), and upper dental arch length (UDAL) increased by 0.959 mm, 0.583 mm, 0.955 mm, 1.462 mm, and 2.46 mm, respectively, over the two years (P < 0.001). UR6BL and UL6BL decreased by 4.416° and 7.133°, respectively, over the two years (P < 0.001). The values of the UICW and UIMW were 1.67 mm and 1.86 mm, respectively, larger in males than in females at 12 years old (P < 0.01). The change in the UTAL was 0.431 mm greater in males than in females over the 2 years (P < 0.05).

Conclusion

The UAAL, UTAL, UICW, UIMW, and UDAL in 10- to 12-year-olds with normal occlusion increased with age. The buccolingual inclination of the bilateral maxillary first molars inclined to the palatal side with age. The UICW and UIMW were larger in males than in females at 12 years old. The male UTAL increased more than the female UTAL over the 2 years.