Korean J Orthod.  2023 May;53(3):185-193. 10.4041/kjod22.208.

Covariance patterns between ramus morphology and the rest of the face: A geometric morphometric study

• Krüsi M
• Halazonetis DJ
• Eliades T
• Koretsi V

• KMID: 2542813
• DOI: http://doi.org/10.4041/kjod22.208

Abstract

Objective
The growth and development of the mandible strongly depend on modeling changes occurring at its ramus. Here, we investigated covariance patterns between the morphology of the ramus and the rest of the face.
Methods
Lateral cephalograms of 159 adults (55 males and 104 females) with no history of orthodontic treatment were collected. Geometric morphometrics with sliding semi-landmarks was used. The covariance between the ramus and face was investigated using a two-block partial least squares analysis (PLS). Sexual dimorphism and allometry were also assessed.
Results
Differences in the divergence of the face and anteroposterior relationship of the jaws accounted for 24.1% and 21.6% of shape variation in the sample, respectively. Shape variation was greater in the sagittal plane for males than for females (30.7% vs. 17.4%), whereas variation in the vertical plane was similar for both sexes (23.7% for males and 25.4% for females). Size-related allometric differences between the sexes accounted for the shape variation to a maximum of 6% regarding the face. Regarding the covariation between the shapes of the ramus and the rest of the face, wider and shorter rami were associated with a decreased lower anterior facial height as well as a prognathic mandible and maxilla (PLS 1, 45.5% of the covariance). Additionally, a more posteriorly inclined ramus in the lower region was correlated with a Class II pattern and flat mandibular plane.
Conclusions
The width, height, and inclination of the ramus were correlated with facial shape changes in the vertical and sagittal planes.

Keyword

Mandibular ramus; Face; Morphometrics; Covariance

Figure

• 

  Figure 1 Lateral cephalogram presenting 15 landmarks, 51 semi-landmarks, and five curves organized in three datasets: ramus (green), rest of the face (blue), and whole configuration (green and blue). Fixed landmarks are denoted with squares: Nasion; Rhinion; the most posterior point of the frontonasal suture; the most inferior and posterior points on the alveolar portion of the premaxilla; posterior nasal spine; anterior nasal spine; Supradentale; the most superior and posterior points on the alveolar lingual portion; Infradentale; Menton; Antegonial notch; Gonion; the most posterior point of the condyle; the most inferior point on the anterior margin of ramus posterior to second molars, and Coronion. The semi-landmarks are denoted with circles.

• 

  Figure 2 On the left, plots of PC1 and PC2 colored by sex; yellow dots represent females, and blue dots represent males. On the right, the shape changes from the average configuration of all individuals. The average configuration is colored black, and changes are represented in blue. Scaling in the positive and negative directions corresponds to the extreme values of the respective principal axes. PC, principal component.

• 

  Figure 3 Plots of PLS scores for ramus (Block 1) and rest of the face (Block 2) explaining 45.5% and 25.5% of the total covariance for PLS 1 and PLS 2, respectively. Blue dots represent males, and yellow dots represent females. The associated outline drawings depict the covariance pattern between the aforementioned structures at a scale of 0.12 for Block 1 and 0.1 for Block 2. The average outline shape is depicted in black and shape changes in blue. PLS, partial least squares.

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