Figure 1.
A, Landmarks and reference planes. B, Mandibular measurements. Cg, crista galli; Dv, deviated side; FH, Frankfort horizontal; Go, gonion; LM, mandibular first molar; Me, menton; MF, mental foramen; NDv, non-deviated side; Op, opisthion; Or, orbitale; Po, porion.
Table I.
Definitions of landmarks, reference planes, and measurements
| Landmark | Definition |
|---|---|
| Cg | The most superior point on the crista galli |
| Op | The middle point of the posterior border of the foramen magnum |
| Or | The most inferior point of the lower orbital margin |
| Po | The most superior point of the external auditory meatus |
| Me | The most inferior point on the symphyseal outline |
| Go | The most inferior point of gonial angle on the lateral view |
| MF | The most inferior point of the mental foramen |
| PM | The point where the curvature changes from concave to convex on the most anterior symphyseal border |
| Cd | The most superior point of the condyle head |
| LM | The central fossa of the mandibular first molar |
| LI_mid | The midpoint between the mandibular central incisor edges of both sides |
| Reference plane | Definition |
| Frankfort horizontal (FH) plane | The plane passing by bilateral Po and right Or |
| Midsagittal plane | The plane passing by Cg and Op, perpendicular to FH plane |
| Measurement | Definition |
| Skeletal | |
| Menton deviation | The distance between menton and midsagittal plane |
| Body length | The distance between menton and Go |
| Ramus height | The distance between Go and Cd |
| Ramus inclination | The angle between the ramus axial line (Cd-Go) and midsagittal plane |
| Landmark line angulation | |
| Line angulation relative to the x-axis of the mandibular coordinate system | |
| Go line to the x-axis | The angle between the Go line (right-left Go) and the x-axis |
| MF line to the x-axis | The angle between the MF line (right-left MF) and the x-axis |
| Line angulation relative to the FH plane | |
| Go line to the FH plane | The angle between the Go line (right-left Go) and FH plane |
| MF line to the FH plane | The angle between the MF line (right-left MF) and FH plane |
| LM line to the FH plane | The angle between the LM line (right-left LM) and FH plane |
Table II.
Sample distribution (age and sex) and cephalometric measurements
| Symmetry (n=30) | Asymmetry (n=60) | P-value | Roll type (n=30) | Non-roll type (n=30) | P-value | |
|---|---|---|---|---|---|---|
| Sex | 0.077 | 0.371 | ||||
| Male (n) | 17 | 45 | 24 | 21 | ||
| Female (n) | 13 | 15 | 6 | 9 | ||
| Age (y)* | 21.34±2.42 | 22.31±3.71 | 0.200 | 21.02±2.14 | 21.66±2.67 | 0.308 |
| Cephalometric measurement* | ||||||
| SNA (°) | 82.57±3.41 | 81.72±2.91 | 0.219 | 81.36±2.99 | 82.08±2.82 | 0.344 |
| SNB (°) | 85.67±3.39 | 84.24±3.17 | 0.052 | 83.58±3.23 | 84.91±3.01 | 0.104 |
| ANB (°) | –3.10±2.33 | –2.52±2.04 | 0.230 | –2.21±1.62 | –2.83±2.37 | 0.247 |
| FMA (°) | 25.02±1.45 | 25.70±5.49 | 0.368 | 25.88±4.66 | 25.52±6.29 | 0.804 |
1* Values are mean±standard deviation. Roll type, asymmetry patients with >3 mm bilateral ramus height difference; Non-roll type, asymmetry patients with<1.5 mm bilateral ramus height difference. No significant difference was found between the symmetry and asymmetry groups and between the roll and non-roll types.
Figure 2.
Workflow of the best-fit mirroring superimposition of the mandibular body and mandibular co-ordinate system. A, Three-dimensional CBCT image. B, Self-mirroring of the original mandibular body image (original, white; mirrored, blue). C, Best-fit superimposition of the original and mirrored body images (yellow area). D, Go and MF co-ordinates. E, Go line and MF line angulations relative to the x-axis. Dv, deviated side; Go, gonion; Me, menton; MF mental foramen; NDv non-deviated side.
Table III.
Three-dimensional skeletal measurements in the symmetry and asymmetry groups and the roll and non-roll types
| Symmetry group | Asymmetry group | Roll type | Non-roll type | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Dv | NDv | P-value | Dv | NDv | P-value | Dv | NDv | P-value | Dv | NDv | P-value | |
| Me deviation (mm) | 1.06±0.53††† | – | – | 7.90±3.23 | – | – | 8.15±3.74 | – | – | 7.65±2.66 | – | – |
| Body length (mm) | 82.56±4.06 | 82.49±4.28† | 0.865 | 81.72±4.68 | 85.21±5.01 | 0.000*** | 81.57±5.10 | 84.71±5.24 | 0.000*** | 81.87±4.29 | 85.72±4.81 | 0.000*** |
| Ramus height (mm) | 70.99±4.48 | 71.44±4.91 | 0.178 | 68.74±6.03 | 71.52±5.42 | 0.000*** | 66.31±5.76†† | 72.17±5.81 | 0.000*** | 71.17±5.35 | 70.87±5.01 | 0.247 |
| Ramus inclination (°) | 11.46±3.68†† | 12.14±3.29 | 0.074 | 8.20±5.51 | 12.70±4.48 | 0.000*** | 7.67±5.16 | 11.94±3.98 | 0.001 ** | 8.73±5.88 | 13.47±4.88 | 0.000*** |
Figure 3.
Scattergrams of Go and MF positions on the XZ plane of the mandibular co-ordinate system. Dv, deviated side; Go, gonion; MF, mental foramen; NDv, non-deviated side.
Figure 4.
Box plots of the Go line and MF line angulations relative to the x-axis of the mandibular co-ordinate system. Go, gonion; MF, mental foramen; Δ Go–MF line, the difference of the Go line and MF line angulations. Significant differences between the lines at *P<0.05, ***P<0.001. Significant differences between the groups or between the asymmetry types at P<0.05.
Table IV.
Transverse cant of Go and MF lines relative to the x-axis on the mandibular coordinate system
| Symmetry (n=30) | Asymmetry (n=60) | P-value (between the groups) | Roll type (n=30) | Non-roll type (n=30) | P-value(between the types) | |
|---|---|---|---|---|---|---|
| Go line angulation (°) | –0.66±1.11 | –1.14±1.27 | 0.080 | –l.3l±1.36 | –0.97±1.l7 | 0.303 |
| MF line angulation (°) | –0.07±0.64 | –0.09±0.87 | 0.893 | 0.17±0.78 | –0.35±0.89 | 0.019† |
| Δ Go-MF line angulation (°) | –0.59±1.30 | –1.05±1.6l | 0.175 | –1.48±1.61 | –0.62±1.52 | 0.036† |
| P-value (between the line angulations) | 0.020* | 0.000*** | 0.000*** | 0.034* |
1 Go, gonion; MF, mental foramen; Go-line, line of the bilateral Go; MF-line, line of the bilateral MF; Δ Go-MF line, difference in Go and MF line angulations relative to the x-axis.
Table V.
Bilateral difference in landmark position using the coordinate component on the mandibular coordinate system
| Symmetry | Asymmetry | Roll type | Non-roll type | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ΔNDv-Dv | Go | MF | P-value | Go | MF | P-value | Go | MF | P-value | Go | MF | P-value |
| x-componeni | –0.25±1.77 | –0.12±1.10 | 0.741 | 0.53±2.49 | 0.38±1.32 | 0.677 | 0.48±2.40 | –0.01±1.39 | 0.340 | 0.58±2.61 | 0.76±1.15 | 0.726 |
| y-component | 0.29±2.66 | 0.06±1.03 | 0.657 | 2.69±3.10 | 0.54±1.30 | 0.000§§§ | 1.95±2.13 | 0.41±1.30 | 0.002§§ | 3.43±3.72 | 0.67±1.29 | 0.000§§§ |
| z-componeni | 1.13±1.86 | 0.06±0.57 | 0.005§§ | 1.95±2.14 | 0.08±0.76 | 0.000§§§ | 2.30±2.36 | –0.15±0.66 | 0.000§§§ | 1.60±1.87 | 0.31±0.79 | 0.001§§ |
Figure 5.
Box plots of the Go line, MF line, and LM line angulations relative to the FH plane. Dv, deviated side; Go, gonion; FH, Frankfort horizontal; LM, mandibular first molar; MF, mental foramen; NDv, non-deviated side. Significant differences between the lines at **P<0.01. Significant differences between the groups or between the asymmetry types at †††P<0.001.
Table VI.
Transverse cant of Go, MF, and LM lines relative to the Frankfort horizontal plane
| Symmetry | Asymmetry | P-value (between the groups) | Roll | Non-roll | P-value (between the types) | |
|---|---|---|---|---|---|---|
| LM line angulation (°) | 0.44±1.49A | 2.08±2.09AB | 0.000††† | 2.77±2.34A | 1.40±l.57 B | 0.000††† |
| Go line angulation (°) | –0.00±1.10A | 1.35±2.04A | 0.000††† | 2.80±l.56 A | –0.ll±1.27 A | 0.000††† |
| MF line angulation (°) | 0.31±1.l9 A | 2.70±2.90 B | 0.000††† | 4.60±2.46 B | 0.79±l.88 AB | 0.000††† |
1 Values are mean±standard deviation. LM, mandibular first molar; Go, gonion; MF, mental foramen; LM-line, line of the bilateral LM; Go-line, line of the bilateral Go; MF-line, line of the bilateral MF. Repeated-measures one-way analysis of variance with Bonferroni correction was performed to compare the LM line, Go line, and MF line angulations. Independent t-test was performed to compare the symmetry and asymmetry groups or between the roll and non-roll types. The values with different superscript letters in a column are significantly different between the line angulations (P<0.05).