Korean J Orthod.  2013 Jun;43(3):134-140. 10.4041/kjod.2013.43.3.134.

Alveolar bone thickness and lower incisor position in skeletal Class I and Class II malocclusions assessed with cone-beam computed tomography

• Baysal A
• Ucar FI
• Buyuk SK
• Ozer T
• Uysal T

• KMID: 1975128
• DOI: http://doi.org/10.4041/kjod.2013.43.3.134

Abstract

OBJECTIVE
To evaluate lower incisor position and bony support between patients with Class II average- and high-angle malocclusions and compare with the patients presenting Class I malocclusions.
METHODS
CBCT records of 79 patients were divided into 2 groups according to sagittal jaw relationships: Class I and II. Each group was further divided into average- and high-angle subgroups. Six angular and 6 linear measurements were performed. Independent samples t-test, Kruskal-Wallis, and Dunn post-hoc tests were performed for statistical comparisons.
RESULTS
Labial alveolar bone thickness was significantly higher in Class I group compared to Class II group (p = 0.003). Lingual alveolar bone angle (p = 0.004), lower incisor protrusion (p = 0.007) and proclination (p = 0.046) were greatest in Class II average-angle patients. Spongious bone was thinner (p = 0.016) and root apex was closer to the labial cortex in high-angle subgroups when compared to the Class II average-angle subgroup (p = 0.004).
CONCLUSIONS
Mandibular anterior bony support and lower incisor position were different between average- and high-angle Class II patients. Clinicians should be aware that the range of lower incisor movement in high-angle Class II patients is limited compared to average- angle Class II patients.

Keyword

3 Dimensional diagnosis and treatment planning; Class II

MeSH Terms

Cone-Beam Computed Tomography
Humans
Incisor
Jaw
Malocclusion
Malocclusion, Angle Class II
Overbite

Figure

• 

  Figure 1 Landmark points at the symphysis and mandibular incisor. L1a, Lower central incisor apex; point A, the most anterior-superior point of mandibular alveolar bone; point B, the most posterior-superior point of the mandibular alveolar bone; point C, the most anterior point of the mandibular alveolar bone; point F, the most posterior point of the mandibular alveolar bone; point D, the inner contour of the anterior cortical plate; point E, the inner contour of the posterior cortical plate (points C, D, E, and F were defined on the trajectory of the hypothetical tipping movement of the mandibular central incisor root around the center of rotation); labial cortical bone thickness (D-C), the length of the arc between points D and C; lingual cortical bone thickness (F-E), the length of the arc between points F and E; alveolar spongious bone thickness (E-D), the length of the arc between points E and D; alveolar spongious and cortical bone thickness (F-C), the length of the arc between points F and C; L1a-D, the length of the arc between points L1a and D; L1a-E, the length of the arc between points L1a and E.

• 

  Figure 2 Definition of angular measurements. Abbreviations were given in Figure 1 in detail. The description of the measurements were as follows: Incisor mandibular plane angle, the angle between the central incisor axis and the mandibular plane; labial alveolar bone angle, the angle between line A-C and the mandibular plane; lingual alveolar bone angle; the angle between line B-F and the mandibular line.

• 

  Figure 3 Arch length measurements.

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