A cone-beam computed tomography analysis of angulation and inclination of whole tooth and clinical crown in adults with normal occlusion

Three-Dimensional Comparative Analysis of Root Parallelism in First Premolar Extraction Cases: Clear Aligner Versus Fixed Orthodontic Appliance

OBJECTIVE

To compare the three-dimensional root parallelism (mesiodistally and buccolingually) between orthodontic therapy with the Invisalign clear aligners (CA) and fixed appliances (FA) among the first premolar-extraction patients, using cone-beam computed tomography (CBCT).

MATERIALS AND METHODS

Sixty participants with similar American Board of Orthodontics discrepancy index scores as baseline characteristics were included and divided into CA and FA groups (30 per group). Post-treatment mesiodistal and buccolingual root parallelisms were analysed through CBCT using Invivo 6.0.3 software. Descriptive and analytical statistics were performed with a p < 0.05, considered statistically significant.

RESULTS

Mesiodistal dental root parallelism in the U1-U2 and L1-L2 pairings between CA and FA groups were found to be significantly different with inferior parallelism in the CA group (p < 0.05). Conversely, the U3-U5 and L5-L6 pairings exhibited superior parallelism in the CA group (p < 0.05). However, other pairings, including U1-U1, U2-U3, U5-U6, U6-U7, L1-L1, L2-L3, L3-L5, and L6-L7, showed no significant differences in mesiodistal parallelism between groups (p > 0.05). Regarding the buccolingual dental root parallelism, significant differences were also noted in the U5-U6 and L5-L6 pairings with superior parallelism in the CA group (p < 0.05). However, in the U1-U1, U2-U3, U3-U5, U6-U7, L1-L1, L2-L3, L3-L5, and L6-L7 pairings, no significant differences in buccolingual parallelism were observed (p > 0.05).

CONCLUSION

In this study, our findings indicate that in cases involving the extraction of first premolars, Invisalign clear aligners may offer comparable or even superior three-dimensional root parallelism compared to fixed orthodontic appliances, with the exception of the mesiodistal dimension in upper and lower incisors, where their performance is less effective.

Monson's sphere in Chinese young adult females with individual normal occlusion: a preliminary study using digital models

BACKGROUND

This study investigated the characteristics of Monson's sphere in Chinese young adult females with individual normal occlusion to provide a reference for oral rehabilitation in prosthodontic and orthodontic treatments.

METHODS

Points at the dental cusps and incisal edges were selected from 51 digital mandibular dental models of Chinese young adult females (aged 18-22 years) with individual normal occlusion. Monson's spheres were fitted to the selected points based on the least-squares principle and the radii were calculated. The deviation of each selected point from its relative spherical surface was also calculated. The radii and deviations of these points were examined using conventional descriptive statistics and distributions of the most deviated points inside and outside the spheres were analyzed.

RESULTS

The mean radius of Monson's sphere in Chinese young adult females was 79.60 ± 14.13 mm. The deviation of each selected point from its relative sphere surface was 0.38 ± 0.30 mm. The maximum deviations inside and outside the sphere were 0.93 ± 0.25 mm and 0.95 ± 0.30 mm, respectively. The most deviated points outside the spheres were mainly distributed at the distolingual cusps of the mandibular second permanent molars (31.37%), while those inside the spheres were mainly distributed at the mesiolingual cusps of the mandibular first permanent molars (45.10%).

CONCLUSIONS

The radius of Monson's sphere in Chinese young adult females was smaller than the classic four-inch value suggested by Monson. Deviation was observed from all selected points to their Monson's sphere surface, with the most deviated points distributed primarily in the molar region.

Three-dimensional evaluation of a virtual setup considering the roots and alveolar bone in molar distalization cases

We aimed to evaluate root parallelism and the dehiscence or fenestrations of virtual teeth setup using roots isolated from cone beam computed tomography (CBCT) images. Sixteen patients undergoing non-extraction orthodontic treatment with molar distalization were selected. Composite teeth were created by merging CBCT-isolated roots with intraoral scan-derived crowns. Three setups were performed sequentially: crown setup considering only the crowns, root setup-1 considering root alignment, and root setup-2 considering the roots and surrounding alveolar bone. We evaluated the parallelism and exposure of the roots and compared the American Board of Orthodontics Objective Grading System (ABO-OGS) scores using three-dimensionally printed models among the setups. The mean angulation differences between adjacent teeth in root setups-1 and -2 were significantly smaller than in the crown setup, except for some posterior teeth (p < 0.05). The amount of root exposure was significantly smaller in root setup-2 compared to crown setup and root setup-1 except when the mean exposure was less than 0.6 mm (p < 0.05). There was no significant difference in ABO-OGS scores among the setups. Thus, virtual setup considering the roots and alveolar bone can improve root parallelism and reduce the risk of root exposure without compromising occlusion quality.

Genetics of three-dimensional tooth inclination and angulation in orthodontic patients with Class I Occlusion: A cross-sectional study

PURPOSE

This cross-sectional study aimed to utilize quantitative polymerase chain reaction (qPCR) to investigate the influence of genetic variance over teeth inclination and angulation in orthodontic patients with Class I occlusion.

MATERIALS AND METHODS

DNA was extracted from adolescent patients seeking orthodontic treatment in a single institution (from July 2018 to April 2020), who had CBCTs taken as part of initial standardized records. Patients had permanent dentition, Class I skeletal and dental classifications, with normal vertical and transverse skeletal dimensions, normal incisors inclination, no to mild crowding or spacing. qPCR was performed using genetic markers for candidate genes EPB41, TGFβ3, GHR and PAX9. Three-dimensional teeth inclinations (TI) and angulations (TA) were evaluated using Invivo6 software and correlated with genotypes. Reliability of TI and TA was assessed using intraclass correlation coefficients (ICC). Mixed models and multiple linear regression analyses were used to assess the association between each single nucleotide polymorphisms (SNP) with tooth inclination (TI) and with tooth angulation (TA). The results were evaluated at the significance level of P<0.05.

RESULTS

Twenty four adolescent patients with mean age of 13.4±2.4 years were included in the study. ICC showed adequate intra-examiner reliability for TI and TA (0.806<r<0.988, P<0.001). Multiple linear regression analysis showed a significant association between TI and homozygous-T polymorphism for PAX9 (P=0.028) and homozygous-G polymorphism for GHR (P=0.028). Also, a significant association between TA and homozygous-A polymorphism for EPB41 (P=0.019) and homozygous-G polymorphism for GHR (P=0.001) was evident.

CONCLUSIONS

Autosomal recessive patterns of inheritance for PAX9 and GHR with TI and for EPB41 and GHR with TA were shown. This study offers insight toward the hierarchical nature of epigenetic interactions between heredity and the environment in determining the three-dimensional positions of teeth in orthodontic patients with Class I occlusion.

Comparison between the designed and achieved mesiodistal angulation of maxillary canines and posterior teeth and influencing factors: First premolar extraction treatment with clear aligners

INTRODUCTION

This study aimed to compare the designed and achieved mesiodistal angulation of maxillary canines and posterior teeth (MCPT) for first premolar extraction with clear aligner treatment and identify the main influencing factors for preventing MCPT tipping toward the extraction space.

METHODS

A total of 21 adults with first premolar extraction were recruited. The designed and achieved tooth movement of MCPT was measured by superimposing their respective pretreatment and posttreatment cone-beam computed tomography images and compared with the designed tooth movement in ClinCheck using the paired t test and scatter plot analysis. Influencing factors, including dental arch length change, canine distalization, and initial mesiodistal angulation, were analyzed using the linear mixed-effect model.

RESULTS

Designed distal crown tipping (second premolar, 10.73 ± 3.22°; first molar, 9.83 ± 3.60°; second molar, 7.18 ± 2.36°) significantly increased the distal inclination of the second premolar (2.50° ± 5.15°; P ＜0.001), first molar (1.07° ± 4.14°; P ＜0.001), and second (0.70° ± 3.78°; P ＜0.001). Furthermore, mesial tipping (8.59° ± 6.03°; P ＜0.001) achieved appropriate distal crown tipping of canines (-6.43° ± 5.04°; P ＜0.001). The implemented preliminary formulas showed that shortening of the dental arch length, the distance of canine distalization, and initial mesiodistal angulation were closely related to the antitipping design.

CONCLUSIONS

Designed distal crown tipping of posterior teeth and mesial crown tipping of canines might prevent unwanted crown tipping toward the extraction space during space closure. The proposed preliminary formula could guide antitipping designs in clear aligner treatment.