Differences in skeletal growth patterns: an exploratory approach using elliptic Fourier analysis

[Frequency of retained third molars in relation to facial biotype. a cross-sectional study]

Objective

This study aims to determine the frequency of retained third molars in relation to facial biotype, the data were collected by using the patients' 2D studies (panoramic and cephalometric) attending the imaging center ZETA-EXMED in the period November 2018 to December 2021, in the city of Lima, Peru.

Methods

The type of study used for this research are observational, descriptive, cross-sectional, and retrospective. For the present study, 6000 cases were evaluated, each case consists of one panoramic radiographic image and one cephalometric image, both taken to the patient on the same date, of these, only 150 cases that met the selection criteria were included in this study. Measurements about frequency of retained third molars in relation to facial biotype were done by a trained and calibrated researcher, using NemoCeph software for the cephalometric tracing. The statistical analysis was done using SPSS program version 1.0.0.1401 (SPSS Inc., USA) and the Chi square test (p <0.05).

Results

Of the 150 cases observed, 91 were women (60.66%) and 59 were men (39.33%). According to the results, dolichofacial biotype had the highest frequency among males with a total of 27 cases (45.80%), while the brachyfacial biotype was more prevalent among females, with a total of 35 cases (38.50%). In addition, out of the total number of retained third molars evaluated (403 pieces), 141 were present in cases with dolichofacial biotype, followed by the mesofacial biotype with 139 pieces and finally the brachyfacial biotype with 123 pieces. Regarding the evaluation of retained third molars according to their position and facial biotype, 63 retained third molars were found in mesioangulated position and 28 retained third molars in dolichofacial / distoangular position, followed by 48 pieces in the vertical position in brachyfacial.

Conclusions

There is not significant association between the quantity of retained third molars and their positions, in relation to facial biotype, although there is a significant association between facial biotype and the patient's sex, so it was concluded that Dolichofacial biotype has the highest frequency in males, while the Brachyfacial biotype is seen more frequently among females.

Mandibular shape prediction model using machine learning techniques

OBJECTIVE

To create a mandibular shape prediction model using machine learning techniques and geometric morphometrics.

MATERIALS AND METHODS

Six hundred twenty-nine radiographs were used to select the most appropriate craniomaxillary variables in different craniofacial pattern classifications using a support vector machine. To obtain the three-dimensional mandibular shape, a Procrustes fit was used on 55 tomograms, in which 17 three-dimensional landmarks were digitized. A partial least square regression was employed to find the best covariation between craniomaxillary angles and the symmetric components of mandibular shape. The model was applied to a new sample of six tomograms and evaluated by the mean absolute error. Each mandible predicted was assessed using the Hausdorff distance (HDu) and a color scale. The model was also exploratively applied to six new radiographs.

RESULTS

Covariation was 88.66% with a significance of < 0.0001 explained by twelve craniomaxillary variables. Low differences between the original and predicted models were obtained, with a mean absolute error of 0.0143. The mean distance between meshes ranged from 0.0033 to 0.0059 HDu and each color scale demonstrated general similarity between the surfaces.

CONCLUSIONS

This approach offered promising results in obtaining a mandibular prediction model that enhances shape properties in an economical way and is applicable to a Latin American population. Clinical proof of this method will require further studies with larger samples.

CLINICAL RELEVANCE

This method offers a reliable, economic alternative to traditional mandibular prediction methods and is applicable to the Latin American population.

Biotypic classification of facial profiles using discrete cosine transforms on lateral radiographs

OBJECTIVE

The aim of the study was to use discrete cosine transforms to graph soft tissue curves in lateral cephalometric radiographs and, with the obtained mathematical values, to group these curves by both traditional biotypes and cluster systems, in order to evaluate discriminatory capacity in terms of accuracy.

DESIGN

A sample of 625 lateral radiographs of adult patients (319 women and 306 men) was classified by facial biotype based on the ANB angle and mandibular plane angle. The curves of the facial profile were digitized with 50 equidistant points and discrete cosine transform was applied to analyze these curves mathematically for the determination of the accuracy of the classification of traditional biotypes. Phylogram cluster analysis was then performed for hierarchical grouping and accuracy was determined through cross-validation.

RESULTS

Grouping by biotype was performed for men and women separately. Although significant, accuracy did not surpass 71.4%. In the groups by clusters, significant results were achieved when performing four analyses for men and two for women. The best accuracy regarding classification power and qualitative distinction was 89.5% for men and 94% for women.

CONCLUSIONS

Discrete cosine transforms using a cluster system had greater discriminatory capacity in terms of accuracy compared to traditional grouping considering the ANB angle and mandibular plane angle. This exploration can be useful for the creation of a soft-tissue facial reconstruction software for the Latin American population.