Korean J Orthod.  2017 Jan;47(1):50-58. 10.4041/kjod.2017.47.1.50.

The genial tubercle: A prospective novel landmark for the diagnosis of mandibular asymmetry

• Lee SY
• Choi DS
• Jang I
• Song GS
• Cha BK

• KMID: 2392196
• DOI: http://doi.org/10.4041/kjod.2017.47.1.50

Abstract

INTRODUCTION
Identifying menton (Me) on posteroanterior cephalograms and three-dimensional (3D) cone-beam computed tomography (CBCT) images is difficult, because the midpoint of the symphyseal area is not identifiable after the mandibular symphysis fuses at an early age. The aim of this study was to evaluate the reliability of the identification of the genial tubercle (GT) in patients with mandibular asymmetry and to compare it with that of the traditional landmark, Me.
METHODS
The samples comprised 20 CBCT images of adults with mandibular asymmetry. Two examiners performed the identifications and measurements. Me and GT were marked, and the anteroposterior, vertical, and transverse distances to the three reference planes were measured on 3D-reconstructed CBCT images. The intra- and inter-examiner reliability of landmark identification of Me and GT were assessed using the intraclass correlation coefficient (ICC) and Bland-Altman plots.
RESULTS
The Me and GT landmarks showed excellent reliability (ICC ≥ 0.993) three-dimensionally. In the transverse evaluation, the ICC values of the GT (range, 0.997-0.999) tended to be slightly higher than those of Me (range, 0.993-0.996). In the Bland-Altman plots for the two separate assessments, Me showed a maximum error of 1.76 mm in the transverse direction, whereas the GT showed a maximum error of 0.96 mm in the 95% limit.
CONCLUSIONS
Our results suggest that both Me and GT are clinically reliable and equally useful landmarks for the evaluation of mandibular asymmetry on CBCT images.

Keyword

Cone-beam computed tomography; Three-dimensional cephalometrics; Genial tubercle; Menton

MeSH Terms

Adult
Cone-Beam Computed Tomography
Diagnosis*
Humans
Prospective Studies*

Figure

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  Figure 1 Identification of the menton (Me) and genial tubercle points on cone-beam computed tomography images.

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  Figure 2 Bland-Altman plots showing the agreement of the transverse position of the menton (Me) and genial tubercle (GT) points between the first and second examinations. A and B, assessed by examiner A; C and D, assessed by examiner B. The thick solid lines indicate the mean, and the dotted lines indicate the 95% limits (± 1.96 standard deviation) of agreement.

• 

  Figure 3 Bland-Altman plots showing the agreement of the transverse position of the menton (Me) and genial tubercle (GT) points between examiners A and B. A and B, first examination; C and D, second examination. The thick solid lines indicate the mean, and the dotted lines indicate the 95% limits (± 1.96 standard deviation) of agreement.

• 

  Figure 4 The genial tubercle observed in 39-year-old female who had Class I malocclusion and no facial asymmetry. The size of genial tubercle was 2.7 mm in height and 6.0 mm in vertical width, and located at 9.5 mm from the mandibular border and 30.0 mm from the lower incisor tip, and was coincident with the facial midline.

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