Morphologic relationship between the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism Sung-Jin Kim, a Kee-Joon Lee, b Sang-Hwy Lee, c and Hyoung-Seon Baik d Seoul, South Korea Introduction: This study was conducted to measure the dimensional changes in the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism, and to examine the morphologic rela- tionship between asymmetries of the cranial base and the mandible. Methods: The patients were 60 adults with mandibular prognathism, divided into a symmetry group (menton deviation, \2 mm; n 5 30) and an asymmetry group (menton deviation, .4 mm; n 5 30) according to the degree of menton deviation. Three-dimensional computed tomography scans were obtained with a spiral scanner. Landmarks were designated on the reconstructed 3-dimensional surface models. Linear, angular, and volumetric measurements of the cranial base and mandibular variables were made. Results: In the asymmetry group, the hemi-base, anterior cranial base, and middle cranial base volumes were significantly larger (P \0.01), and crista galli to sphenoid, sphenoid to petrous ridge, anterior clinoid process to petrous ridge, and vomer to petrous ridge lengths were significantly longer (P \0.05) on the nondeviated side than on the deviated side. Menton deviation was significantly correlated with the difference in hemi-base volume, and ramal volume was significantly correlated with the difference in hemi-base and middle cranial base volumes between the nondeviated and deviated sides (P \0.05). Conclusions: In patients with facial asymmetry and mandibular prognathism, cranial base volume increased on the nondeviated side and was also correlated with mandibular asymmetry. (Am J Orthod Dentofacial Orthop 2013;144:330-40) F acial asymmetry is a complex problem that mani- fests in inconsistent size, form, and arrangement of the facial features on either side of the median sagittal plane. 1 Hereditary and environmental factors during the fetal, infant, or adolescent periods are known to contribute to the expression of craniofacial asymme- try. 2 Various etiologic factors have been proposed con- cerning facial asymmetry, including unilateral condylar hyperactivity, 3 functional disharmony of the masticatory muscles, 4 hemisphere dominance of the brain, 4 plagio- cephaly caused by head posture during early infancy, 5,6 and unilateral craniosynostosis. 7 Severt and Proffit 8 reported that in a group with facial asymmetry, asymmetry of the upper face was seen in only 5% of the patients, whereas 36% showed middle third asymmetry and 75% had deviation of the chin. Cheon and Suhr 9 and Haraguchi et al 10 also reported that asymmetry was found most obviously in the lower part of the face in the posteroanterior cephalometric ra- diographs. For these reasons, most studies regarding facial asymmetry have analyzed mandibular asymmetry using 3-dimensional computed tomography, but there are few studies regarding cranial base asymmetry. 11-15 Facial asymmetry is often accompanied by varying de- grees of cranial base asymmetry as well as mandibular asymmetry, 16 but cranial base asymmetry is also observed in patients with no notable facial asymmetry. 17,18 Additionally, Hayashi 19 reported that the morphology of the cranial base has an effect on the positions of the maxilla and the mandible, and that temporomandibular joint position and mandibular shape can also be altered in those with plagiocephaly and an asymmetric cranial vault and cranial base. 6,7,20 However, most previous studies regarding cranial base asymmetry analyzed plagiocephaly in subjects at early ages, and the effect of cranial base asymmetry on mandibular asymmetry is From the School of Dentistry, Yonsei University, Seoul, South Korea. a Graduate student, Department of Orthodontics. b Associate professor, Department of Orthodontics. c Professor, Department of Oral and Maxillofacial Surgery. d Professor, Department of Orthodontics, Institute of Craniofacial Deformity. All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest, and none were reported. Reprint requests to: Hyoung-Seon Baik, Department of Orthodontics, School of Dentistry, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120- 752, South Korea; e-mail, [email protected]. Submitted, January 2013; revised and accepted, March 2013. 0889-5406/$36.00 Copyright Ó 2013 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.03.024 330 ORIGINAL ARTICLE
Morphologic relationship between the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism
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Morphologic relationship between the cranial base and the mandible in patients with facial asymmetry and mandibular prognathismORIGINAL ARTICLE
Morphologic relationship between the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism
Sung-Jin Kim,a Kee-Joon Lee,b Sang-Hwy Lee,c and Hyoung-Seon Baikd
Seoul, South Korea
From aGrad bAsso cProfe dProfe All au Poten Reprin Denti 752, S Subm 0889- Copyr http:/
330
Introduction: This study was conducted to measure the dimensional changes in the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism, and to examine the morphologic rela- tionship between asymmetries of the cranial base and the mandible.Methods: The patients were 60 adults with mandibular prognathism, divided into a symmetry group (menton deviation,\2 mm; n5 30) and an asymmetry group (menton deviation, .4 mm; n 5 30) according to the degree of menton deviation. Three-dimensional computed tomography scans were obtained with a spiral scanner. Landmarks were designated on the reconstructed 3-dimensional surface models. Linear, angular, and volumetric measurements of the cranial base and mandibular variables were made. Results: In the asymmetry group, the hemi-base, anterior cranial base, and middle cranial base volumes were significantly larger (P \0.01), and crista galli to sphenoid, sphenoid to petrous ridge, anterior clinoid process to petrous ridge, and vomer to petrous ridge lengths were significantly longer (P \0.05) on the nondeviated side than on the deviated side. Menton deviation was significantly correlated with the difference in hemi-base volume, and ramal volume was significantly correlated with the difference in hemi-base and middle cranial base volumes between the nondeviated and deviated sides (P\0.05). Conclusions: In patients with facial asymmetry and mandibular prognathism, cranial base volume increased on the nondeviated side and was also correlated with mandibular asymmetry. (Am J Orthod Dentofacial Orthop 2013;144:330-40)
Facial asymmetry is a complex problem that mani- fests in inconsistent size, form, and arrangement of the facial features on either side of the median
sagittal plane.1 Hereditary and environmental factors during the fetal, infant, or adolescent periods are known to contribute to the expression of craniofacial asymme- try.2 Various etiologic factors have been proposed con- cerning facial asymmetry, including unilateral condylar hyperactivity,3 functional disharmony of the masticatory muscles,4 hemisphere dominance of the brain,4 plagio- cephaly caused by head posture during early infancy,5,6
and unilateral craniosynostosis.7
the School of Dentistry, Yonsei University, Seoul, South Korea. uate student, Department of Orthodontics. ciate professor, Department of Orthodontics. ssor, Department of Oral and Maxillofacial Surgery. ssor, Department of Orthodontics, Institute of Craniofacial Deformity. thors have completed and submitted the ICMJE Form for Disclosure of tial Conflicts of Interest, and none were reported. t requests to: Hyoung-Seon Baik, Department of Orthodontics, School of stry, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120- outh Korea; e-mail, [email protected]. itted, January 2013; revised and accepted, March 2013. 5406/$36.00 ight 2013 by the American Association of Orthodontists. /dx.doi.org/10.1016/j.ajodo.2013.03.024
Severt and Proffit8 reported that in a groupwith facial asymmetry, asymmetry of the upper face was seen in only 5% of the patients, whereas 36% showed middle third asymmetry and 75% had deviation of the chin. Cheon and Suhr9 and Haraguchi et al10 also reported that asymmetry was found most obviously in the lower part of the face in the posteroanterior cephalometric ra- diographs. For these reasons, most studies regarding facial asymmetry have analyzed mandibular asymmetry using 3-dimensional computed tomography, but there are few studies regarding cranial base asymmetry.11-15
Facial asymmetry is often accompanied by varying de- grees of cranial base asymmetry as well as mandibular asymmetry,16 but cranial base asymmetry is also observed in patients with no notable facial asymmetry.17,18
Additionally, Hayashi19 reported that the morphology of the cranial base has an effect on the positions of the maxilla and the mandible, and that temporomandibular joint position and mandibular shape can also be altered in those with plagiocephaly and an asymmetric cranial vault and cranial base.6,7,20 However, most previous studies regarding cranial base asymmetry analyzed plagiocephaly in subjects at early ages, and the effect of cranial base asymmetry on mandibular asymmetry is
Table I. Patient characteristics in the symmetry and asymmetry groups
Variable Mean SD Minimum Maximum Symmetry group Age (y) 20.8 3.4 18.0 29.0 ANB () 3.6 2.5 9.9 0.5 Pog to nasion perpendicular 11.7 6.7 5.1 31.4
Kim et al 331
still uncertain in adults with facial asymmetries.11,12 The purposes of this study were to measure the dimensions of the cranial base and the mandible using 3-dimensional computed tomography images of skeletal Class III adults with mandibular prognathism and to examine the morphologic relationship between asymmetries of the cranial base and the mandible.
(mm) MD (mm) 1.0 0.7 0.2 2.0
Asymmetry group Age (y) 20.9 2.6 18.0 29.0 ANB () 2.6 2.4 8.4 0.1 Pog to nasion perpendicular (mm)
9.7 4.5 5.1 21.7
MATERIAL AND METHODS
Clinical and 2-dimensional radiographic examina- tionswere carried out on patients who visited Yonsei Uni- versity Dental Hospital, Seoul, Korea, between 2005 and 2012. The patients included 60 adults with skeletal Class III malocclusion with mandibular prognathism (ANB,\0 Pog to nasion perpendicular, .5.0 mm), no systemic disease, and no degenerative disease of the temporomandibular joint. Since the chin can greatly influence the perception of facial asymmetry, facial asymmetry was defined as menton deviation (MD) from the midsagittal reference line.10,21 The midsagittal reference line was defined as the line passing through the crista galli and anterior nasal spine, as recommended by Grummons and Kappeyne van de Coppello.22 The symmetry group included 30 adults (15 men, 15 women) with an MD from the midsagittal line less than 2 mm; the asymmetry group included 30 adults (15 men, 15 women) with an MD from the midsagittal line of more than 4 mm (Haraguchi et al10). The patients' characteristics in the 2 groups are shown in Table I.
The 3-dimensional computed tomography scans were obtained before orthognathic surgery using a spiral scan- ner (SOMATOM Sensation 64; Siemens, Erlangen, Germany) with the following settings: gantry angle of 0, 5123 512matrix, 120 kV, 150mA, 1.0mm thickness, and rotation time of 0.5 second. The patients were posi- tioned with the Frankfort horizontal plane perpendicular to the floor and the facial midline coinciding with the long axis of the computed tomographymachine. The dig- ital imaging and communication in medicine (DICOM) images were created in 1.0-mm slice thicknesses after scanning. The DICOM data were reconstructed into 3- dimensional images (176 HU threshold value) using the InVivoDental software program (version 5.1; Anatomage, San Jose, Calif).
According to the method of You et al,13 the mandible was separated from the reconstructed image, and the teeth above the alveolar bone were removed. Then, as outlined by Enlow,23 the frontal, ethmoid, sphenoid, temporal, and occipital bones were all included in the cranial base, which was separated from the recon- structed image by removing the facial bones (maxilla, palatine bone, mandible, nasal bone, vomer, lacrimal
American Journal of Orthodontics and Dentofacial Orthoped
bone, inferior nasal concha, and zygomatic bone) and cervical bones. The nasal bone was separated from the frontal bone at the frontonasal suture, and the zygo- matic bone was separated at the frontozygomatic suture. The maxilla was separated from the sphenoid bone at the pterygomaxillary fissure, and the zygomatic bone was separated at the sphenozygomatic suture. In the case of the ethmoid bone, only the cribriform plate and the perpendicular plate were included while the ethmoid labyrinth was removed. After removal of the facial and cervical bones, the calvaria and the cranial base were separated into a plane connecting the superior point os supraorbitale and both petrous ridge points (Fig 1, Table II).
Landmarks were designated on the reconstructed 3- dimensional surface model, and their positions were verified on the axial, coronal, and sagittal slices. Land- marks of the cranial base were selected by referring to the studies of Captier et al,24 Kwon et al,11 Mulliken et al,25 Moss,26 and Lee et al,27 and mandibular land- marks were selected according to the study of You et al.13 Landmarks and measurements are given in Tables II and III, and Figs 1–3. The data were measured in increments of 0.01 mm for linear, 0.01
for angular, and 1 mm3 for volumetric measurements.
Statistical analysis
To account for intraobserver and interobserver errors, the procedure—removing the facial bones and cervical bones and taking measurements—was repeated twice. The initial assessment and the reassessment were done 2 weeks apart by 3 observers (graduate students). The 2 assessments by each observer were analyzed with the intraclass correlation for intraobserver reliability, and the first and second assessments of the 3 observers were compared for interobserver reliability. The paired t test was conducted on measurements performed twice
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Fig 1. Landmarks for segmentation of the cranial base.
Table II. Description of landmarks
Landmark Description Cranial base Cr (crista galli) The most superior edge of the crista galli Cl (anterior clinoid process) Midpoint between the anterior clinoid processes P (petrous ridge) Junction of the superior ridge of the petrous pyramid of the temporal bone and the inner surface
of the parietal bone S (sphenoid) The most anterior point of the posterior edge of the lesser wing of the sphenoid Op (opisthion) Midpoint of the posterior arch of foramen magnum V (vomer) The most posterior point of the junction of the sphenoid bone and vomer SOr (supraorbitale) The most superior point of the supraorbital foramen SS (superior point of supraorbitale) The point 10 mm superior to the left supraorbitale Fz (frontozygomatic suture) The most anterior point of the frontozygomatic suture Po (porion) The most superior point of the external auditory meatus Eu (euryon) The most lateral point on either side of the greatest transverse diameter of the head CSOr (contralateral point of SOr) The point where the extension line of SOr-Cl meets the contralateral occipital area
Mandible Consup (condylion superius) The most superior point of the condylar head F (fossa of mandibular foramen) The most inferior point of the fossa of the mandibular foramen Jlat The most lateral and deepest point of the curvature formed at the junction of the mandibular
ramus and body Jmed The most medial and deepest point of the curvature formed at the junction of the mandibular
ramus and body Gopost (gonion posterius) The most posterior point of the mandibular angle Gomid (gonion midpoint) The midpoint between Gopost and Goinf on the mandibular angle Goinf (gonion inferius) The most inferior point of the mandibular angle MF (mental foramen) The entrance of the mental foramen Me (menton) The most inferior midpoint of the symphysis Pog (pogonion) The most anterior midpoint of the symphysis B (supramentale) The midpoint of the greatest concavity of the anterior border of the symphysis G (genial tubercle) The midpoint of the genial tubercle
332 Kim et al
with a 2-week interval to examine their reproducibility. The method errors were calculated using Dahlberg's for- mula28 (Se 5 O(d2/2n) (d, difference between measure- ments; n, number of measurement pairs). Because the 2-sample t test showed that the MD and differences in the measurements between the male and female subjects
September 2013 Vol 144 Issue 3 American
were not significantly different, no differentiation was made for sex. The 2-sample t test was used to compare the measurements between the symmetry and asymme- try groups, and the paired t test was also used to compare the measurements between the nondeviated and the deviated sides. The Pearson correlation analysis
Journal of Orthodontics and Dentofacial Orthopedics
Table III. Description of measurements
Measurement Description Cranial base Volume
Hemi-base volume The cranial base volume was divided into 2 hemi-base volumes by the plane connecting Cr-Cl-Op
Anterior cranial, middle cranial, and posterior cranial volumes The hemi-base volume was divided into anterior, middle, and posterior cranial by the planes connecting Cl-S-V and Cl-P-V
Angle Anterior cranial angle The angle formed by the intersection of Cr-Cl and Cl-S (:Cr-Cl-S) Middle cranial angle The angle formed by the intersection of S-Cl and Cl-P (:S-Cl-P) Postcranial angle The angle formed by the intersection of P-Cl and Cl-Op (:P-Cl-Op) Petrous ridge angle The angle formed by the intersection of Cr-Cl and Cl-P (:Cr-Cl-P)
Length Cr-S length Distance between Cr and S S-P length Distance between S and P P-Op length Distance between P and Op Cl-S length Distance between Cl and S Cl-P length Distance between Cl and P V-S length Distance between V and S V-P length Distance between V and P Transverse cranial asymmetry SOr (non)-CSOr (dev) length – SOr (dev)-CSOr (non) length CVA (cranial vault asymmetry) Fz (non)-Eu( dev) length – Fz (dev)-Eu (non) length FOA (fronto-orbital asymmetry) Fz (non)-Po (dev) length – Fz (dev)-Po (non) length
Mandible Volume
Hemi-mandibular volume The mandibular volume was divided into 2 hemi-mandibular volumes by the plane connecting Me-B-G
Ramal volume and body volume The hemi-mandibular volume was divided into ramal and body volumes by the plane connecting Gomid-Jlat-Jmed
Length Condylar unit length Distance between Consup and F Body unit length Distance between F and MF
Non, Nondeviated side; dev, deviated side.
Fig 2. Landmarks and measurements of the mandible.
Kim et al 333
was used to determine correlations between MD and the measurements. Statistical evaluations were performed at the 5% level of significance with SPSS for Windows software (version 18.0; SPSS, Chicago, Ill).
American Journal of Orthodontics and Dentofacial Orthoped
RESULTS
Intraclass correlation coefficients were .908 to .964 for intraobserver reliability and 0.902 to 0.919 for inter- observer reliability, indicating high reliability of these
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Fig 3. Landmarks and measurements of the cranial base.
334 Kim et al
measurements. The paired t test showed no statistically significant difference between the measurements made 2 weeks later. Among the measurements of the cranial base, the method errors were 0.56 to 1.68 mm for linear measurements, 0.85 to 1.95 for angular measure- ments, and 123.57 and 385.25 mm3 for volumetric measurements. Among the mandibular measurements, the method errors were 0.45 to 1.03 mm for linear mea- surements and 56.70 to 130.58 mm3 for volumetric measurements.
The asymmetry group showed significantly greater differences in hemi-base volume (P\0.01), anterior cra- nial base volume (P \0.05), and middle cranial base volume (P \0.05) between the nondeviated and devi- ated sides compared with the symmetry group. There
September 2013 Vol 144 Issue 3 American
was no statistically significant difference in other measurements of the cranial base (Table IV).
In the asymmetry group, the hemi-base, anterior cra- nial base, and middle cranial base volume measurements were significantly greater on the nondeviated side than on the deviated side (P \0.01). The Cr-S, S-P, Cl-P, and V-P lengths were significantly longer on the nonde- viated side than on the deviated side (P\0.05). There was no statistically significant difference in angular measurements of the cranial base (Table V).
The asymmetry group showed significantly greater differences in condylar unit length (P \0.01), body unit length (P \0.01), hemi-mandibular volume (P\0.05), and ramal volume (P\0.01), but there was no statistically significant difference in body volume
Journal of Orthodontics and Dentofacial Orthopedics
Table IV. Comparison of differences in measurements of the cranium between the symmetry and asymmetry groups (2-sample t test)
Measurement
Symmetry group
Asymmetry group
P valueMean SD Mean SD Volume difference (3103 mm3) Hemi-base volume 0.22 2.66 2.50 2.50 0.001y
Anterior cranial base volume
Middle cranial base volume
Posterior cranial base volume
0.07 2.81 0.03 2.44 0.884
Angle difference () Anterior cranial angle 0.13 3.01 1.00 3.30 0.170 Middle cranial angle 0.18 3.22 0.37 3.58 0.534 Posterior cranial angle 0.01 2.17 0.32 2.23 0.596 Petrous ridge angle 0.02 2.74 0.62 3.08 0.400
Length difference (mm) Cr-S length 0.17 2.08 0.92 2.24 0.055 S-P length 0.57 3.24 1.17 2.70 0.441 P-Op length 0.29 2.44 0.31 2.89 0.983 Cl-S length 0.12 1.94 0.65 3.19 0.265 Cl-P length 0.53 3.61 1.56 3.19 0.248 V-S length 0.79 1.22 0.09 2.16 0.130 V-P length 0.73 3.85 1.61 3.19 0.343 Transverse cranial asymmetry
0.90 3.66 0.31 3.98 0.552
CVA 1.33 5.47 2.33 5.98 0.500 FOA 0.80 2.59 0.68 3.70 0.880
Difference, Nondeviated side minus deviated side. *P\0.05; yP\0.01.
Kim et al 335
(Table VI). In the asymmetry group, hemi-mandibular volume and ramal volume were greater on the nondevi- ated side (P\0.01), and condylar unit length and body unit length were longer on the nondeviated side (P\0.01). MD was significantly correlated with the dif- ferences in condylar unit length (P \0.01), body unit length (P\0.01), hemi-mandibular volume (P\0.05), and ramal volume (P\0.01; Table VII).
In the asymmetry group, MD was significantly corre- lated with the difference in hemi-base volume (P\0.05; Table V). The difference in ramal volume was signifi- cantly correlated with the differences in hemi-base volume and middle cranial base volume (P \0.05; Table VIII). The difference in hemi-base volume was significantly correlated with the differences in Cl-P (P \0.01), V-P (P \0.05), and S-P length (P \0.05), whereas the difference in anterior cranial base volume was significantly correlated with the difference in Cr-S length (P\0.05). Furthermore, the difference in middle cranial base volume was significantly correlated with the difference in S-P length (P\0.01; Table IX).
American Journal of Orthodontics and Dentofacial Orthoped
DISCUSSION
Traditionally, the cranial base was a 2-dimensional concept, extending from anterior nasion to posterior basion in lateral cephalograms.29 Furthermore, it is difficult to define the border of the cranial base because it is actually a 3-dimensional structure composed of the frontal, ethmoid, sphenoid, temporal, and occipital bones.23 Hence, in this study, these bones were all included for volumetric measurements of the cranial base. To separate the cranial base from the calvaria, a reproducible plane was needed as close to the floor of the cranial vault as possible. A plane connecting both P points (prominent points on the border of the middle cranial base and posterior cranial base) and supraorbi- tale (located closest to the orbital plate of the frontal bone) resulted in the problem of a portion of the orbital plate of the frontal bone being cut off, so SS point was designated 10 mm above the left supraorbitale to construct the SSL-PL-PR plane. After designating V point, which is easily identifiable and located on the lower surface of the body of sphenoid bone, the cranial base was further divided into anterior, middle, and pos- terior cranial bases using the Cl-S-V and Cl-P-V planes, as reported by Captier et al24 and Kwon et al.11 Finally, the cranial base was divided into nondeviated and devi- ated sides according to the direction of MD using the Cr-Cl-Op plane.11
The asymmetry group showed significantly greater differences in hemi-base, anterior cranial base, and mid- dle cranial base volumes between the nondeviated and deviated sides compared with the symmetry group. Also, when comparing the nondeviated and deviated sides in the asymmetry group, the hemi-base, anterior cranial base, and middle cranial base volumes were all significantly greater on the nondeviated side. Moreover, MD was significantly correlated with the difference in hemi-base volume in the asymmetry group. These results suggest that themorphology of the cranial base is altered in patients with facial asymmetry; this contrasts with the findings of Kwon et al11 and Baek et al,12 who reported that the morphology of the cranial base was not related to MD. They examined angular measurements such as the anterior, middle, and posterior cranial base angles and found no significant difference between the asym- metry and symmetry groups, or between the nondeviated and deviated sides. In this study, there was also no signif- icant difference in the angular and linear measurements between the asymmetry and symmetry groups, but sig- nificant differences were found in hemi-base, anterior cranial base, and middle cranial base volumes, indicating the limitations of 2-dimensional measurements in the evaluation of morphologic changes. Volumetric
ics September 2013 Vol 144 Issue 3
Table V. Comparison of measurements of the cranium between the nondeviated and deviated sides…
Morphologic relationship between the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism
Sung-Jin Kim,a Kee-Joon Lee,b Sang-Hwy Lee,c and Hyoung-Seon Baikd
Seoul, South Korea
From aGrad bAsso cProfe dProfe All au Poten Reprin Denti 752, S Subm 0889- Copyr http:/
330
Introduction: This study was conducted to measure the dimensional changes in the cranial base and the mandible in patients with facial asymmetry and mandibular prognathism, and to examine the morphologic rela- tionship between asymmetries of the cranial base and the mandible.Methods: The patients were 60 adults with mandibular prognathism, divided into a symmetry group (menton deviation,\2 mm; n5 30) and an asymmetry group (menton deviation, .4 mm; n 5 30) according to the degree of menton deviation. Three-dimensional computed tomography scans were obtained with a spiral scanner. Landmarks were designated on the reconstructed 3-dimensional surface models. Linear, angular, and volumetric measurements of the cranial base and mandibular variables were made. Results: In the asymmetry group, the hemi-base, anterior cranial base, and middle cranial base volumes were significantly larger (P \0.01), and crista galli to sphenoid, sphenoid to petrous ridge, anterior clinoid process to petrous ridge, and vomer to petrous ridge lengths were significantly longer (P \0.05) on the nondeviated side than on the deviated side. Menton deviation was significantly correlated with the difference in hemi-base volume, and ramal volume was significantly correlated with the difference in hemi-base and middle cranial base volumes between the nondeviated and deviated sides (P\0.05). Conclusions: In patients with facial asymmetry and mandibular prognathism, cranial base volume increased on the nondeviated side and was also correlated with mandibular asymmetry. (Am J Orthod Dentofacial Orthop 2013;144:330-40)
Facial asymmetry is a complex problem that mani- fests in inconsistent size, form, and arrangement of the facial features on either side of the median
sagittal plane.1 Hereditary and environmental factors during the fetal, infant, or adolescent periods are known to contribute to the expression of craniofacial asymme- try.2 Various etiologic factors have been proposed con- cerning facial asymmetry, including unilateral condylar hyperactivity,3 functional disharmony of the masticatory muscles,4 hemisphere dominance of the brain,4 plagio- cephaly caused by head posture during early infancy,5,6
and unilateral craniosynostosis.7
the School of Dentistry, Yonsei University, Seoul, South Korea. uate student, Department of Orthodontics. ciate professor, Department of Orthodontics. ssor, Department of Oral and Maxillofacial Surgery. ssor, Department of Orthodontics, Institute of Craniofacial Deformity. thors have completed and submitted the ICMJE Form for Disclosure of tial Conflicts of Interest, and none were reported. t requests to: Hyoung-Seon Baik, Department of Orthodontics, School of stry, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul 120- outh Korea; e-mail, [email protected]. itted, January 2013; revised and accepted, March 2013. 5406/$36.00 ight 2013 by the American Association of Orthodontists. /dx.doi.org/10.1016/j.ajodo.2013.03.024
Severt and Proffit8 reported that in a groupwith facial asymmetry, asymmetry of the upper face was seen in only 5% of the patients, whereas 36% showed middle third asymmetry and 75% had deviation of the chin. Cheon and Suhr9 and Haraguchi et al10 also reported that asymmetry was found most obviously in the lower part of the face in the posteroanterior cephalometric ra- diographs. For these reasons, most studies regarding facial asymmetry have analyzed mandibular asymmetry using 3-dimensional computed tomography, but there are few studies regarding cranial base asymmetry.11-15
Facial asymmetry is often accompanied by varying de- grees of cranial base asymmetry as well as mandibular asymmetry,16 but cranial base asymmetry is also observed in patients with no notable facial asymmetry.17,18
Additionally, Hayashi19 reported that the morphology of the cranial base has an effect on the positions of the maxilla and the mandible, and that temporomandibular joint position and mandibular shape can also be altered in those with plagiocephaly and an asymmetric cranial vault and cranial base.6,7,20 However, most previous studies regarding cranial base asymmetry analyzed plagiocephaly in subjects at early ages, and the effect of cranial base asymmetry on mandibular asymmetry is
Table I. Patient characteristics in the symmetry and asymmetry groups
Variable Mean SD Minimum Maximum Symmetry group Age (y) 20.8 3.4 18.0 29.0 ANB () 3.6 2.5 9.9 0.5 Pog to nasion perpendicular 11.7 6.7 5.1 31.4
Kim et al 331
still uncertain in adults with facial asymmetries.11,12 The purposes of this study were to measure the dimensions of the cranial base and the mandible using 3-dimensional computed tomography images of skeletal Class III adults with mandibular prognathism and to examine the morphologic relationship between asymmetries of the cranial base and the mandible.
(mm) MD (mm) 1.0 0.7 0.2 2.0
Asymmetry group Age (y) 20.9 2.6 18.0 29.0 ANB () 2.6 2.4 8.4 0.1 Pog to nasion perpendicular (mm)
9.7 4.5 5.1 21.7
MATERIAL AND METHODS
Clinical and 2-dimensional radiographic examina- tionswere carried out on patients who visited Yonsei Uni- versity Dental Hospital, Seoul, Korea, between 2005 and 2012. The patients included 60 adults with skeletal Class III malocclusion with mandibular prognathism (ANB,\0 Pog to nasion perpendicular, .5.0 mm), no systemic disease, and no degenerative disease of the temporomandibular joint. Since the chin can greatly influence the perception of facial asymmetry, facial asymmetry was defined as menton deviation (MD) from the midsagittal reference line.10,21 The midsagittal reference line was defined as the line passing through the crista galli and anterior nasal spine, as recommended by Grummons and Kappeyne van de Coppello.22 The symmetry group included 30 adults (15 men, 15 women) with an MD from the midsagittal line less than 2 mm; the asymmetry group included 30 adults (15 men, 15 women) with an MD from the midsagittal line of more than 4 mm (Haraguchi et al10). The patients' characteristics in the 2 groups are shown in Table I.
The 3-dimensional computed tomography scans were obtained before orthognathic surgery using a spiral scan- ner (SOMATOM Sensation 64; Siemens, Erlangen, Germany) with the following settings: gantry angle of 0, 5123 512matrix, 120 kV, 150mA, 1.0mm thickness, and rotation time of 0.5 second. The patients were posi- tioned with the Frankfort horizontal plane perpendicular to the floor and the facial midline coinciding with the long axis of the computed tomographymachine. The dig- ital imaging and communication in medicine (DICOM) images were created in 1.0-mm slice thicknesses after scanning. The DICOM data were reconstructed into 3- dimensional images (176 HU threshold value) using the InVivoDental software program (version 5.1; Anatomage, San Jose, Calif).
According to the method of You et al,13 the mandible was separated from the reconstructed image, and the teeth above the alveolar bone were removed. Then, as outlined by Enlow,23 the frontal, ethmoid, sphenoid, temporal, and occipital bones were all included in the cranial base, which was separated from the recon- structed image by removing the facial bones (maxilla, palatine bone, mandible, nasal bone, vomer, lacrimal
American Journal of Orthodontics and Dentofacial Orthoped
bone, inferior nasal concha, and zygomatic bone) and cervical bones. The nasal bone was separated from the frontal bone at the frontonasal suture, and the zygo- matic bone was separated at the frontozygomatic suture. The maxilla was separated from the sphenoid bone at the pterygomaxillary fissure, and the zygomatic bone was separated at the sphenozygomatic suture. In the case of the ethmoid bone, only the cribriform plate and the perpendicular plate were included while the ethmoid labyrinth was removed. After removal of the facial and cervical bones, the calvaria and the cranial base were separated into a plane connecting the superior point os supraorbitale and both petrous ridge points (Fig 1, Table II).
Landmarks were designated on the reconstructed 3- dimensional surface model, and their positions were verified on the axial, coronal, and sagittal slices. Land- marks of the cranial base were selected by referring to the studies of Captier et al,24 Kwon et al,11 Mulliken et al,25 Moss,26 and Lee et al,27 and mandibular land- marks were selected according to the study of You et al.13 Landmarks and measurements are given in Tables II and III, and Figs 1–3. The data were measured in increments of 0.01 mm for linear, 0.01
for angular, and 1 mm3 for volumetric measurements.
Statistical analysis
To account for intraobserver and interobserver errors, the procedure—removing the facial bones and cervical bones and taking measurements—was repeated twice. The initial assessment and the reassessment were done 2 weeks apart by 3 observers (graduate students). The 2 assessments by each observer were analyzed with the intraclass correlation for intraobserver reliability, and the first and second assessments of the 3 observers were compared for interobserver reliability. The paired t test was conducted on measurements performed twice
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Fig 1. Landmarks for segmentation of the cranial base.
Table II. Description of landmarks
Landmark Description Cranial base Cr (crista galli) The most superior edge of the crista galli Cl (anterior clinoid process) Midpoint between the anterior clinoid processes P (petrous ridge) Junction of the superior ridge of the petrous pyramid of the temporal bone and the inner surface
of the parietal bone S (sphenoid) The most anterior point of the posterior edge of the lesser wing of the sphenoid Op (opisthion) Midpoint of the posterior arch of foramen magnum V (vomer) The most posterior point of the junction of the sphenoid bone and vomer SOr (supraorbitale) The most superior point of the supraorbital foramen SS (superior point of supraorbitale) The point 10 mm superior to the left supraorbitale Fz (frontozygomatic suture) The most anterior point of the frontozygomatic suture Po (porion) The most superior point of the external auditory meatus Eu (euryon) The most lateral point on either side of the greatest transverse diameter of the head CSOr (contralateral point of SOr) The point where the extension line of SOr-Cl meets the contralateral occipital area
Mandible Consup (condylion superius) The most superior point of the condylar head F (fossa of mandibular foramen) The most inferior point of the fossa of the mandibular foramen Jlat The most lateral and deepest point of the curvature formed at the junction of the mandibular
ramus and body Jmed The most medial and deepest point of the curvature formed at the junction of the mandibular
ramus and body Gopost (gonion posterius) The most posterior point of the mandibular angle Gomid (gonion midpoint) The midpoint between Gopost and Goinf on the mandibular angle Goinf (gonion inferius) The most inferior point of the mandibular angle MF (mental foramen) The entrance of the mental foramen Me (menton) The most inferior midpoint of the symphysis Pog (pogonion) The most anterior midpoint of the symphysis B (supramentale) The midpoint of the greatest concavity of the anterior border of the symphysis G (genial tubercle) The midpoint of the genial tubercle
332 Kim et al
with a 2-week interval to examine their reproducibility. The method errors were calculated using Dahlberg's for- mula28 (Se 5 O(d2/2n) (d, difference between measure- ments; n, number of measurement pairs). Because the 2-sample t test showed that the MD and differences in the measurements between the male and female subjects
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were not significantly different, no differentiation was made for sex. The 2-sample t test was used to compare the measurements between the symmetry and asymme- try groups, and the paired t test was also used to compare the measurements between the nondeviated and the deviated sides. The Pearson correlation analysis
Journal of Orthodontics and Dentofacial Orthopedics
Table III. Description of measurements
Measurement Description Cranial base Volume
Hemi-base volume The cranial base volume was divided into 2 hemi-base volumes by the plane connecting Cr-Cl-Op
Anterior cranial, middle cranial, and posterior cranial volumes The hemi-base volume was divided into anterior, middle, and posterior cranial by the planes connecting Cl-S-V and Cl-P-V
Angle Anterior cranial angle The angle formed by the intersection of Cr-Cl and Cl-S (:Cr-Cl-S) Middle cranial angle The angle formed by the intersection of S-Cl and Cl-P (:S-Cl-P) Postcranial angle The angle formed by the intersection of P-Cl and Cl-Op (:P-Cl-Op) Petrous ridge angle The angle formed by the intersection of Cr-Cl and Cl-P (:Cr-Cl-P)
Length Cr-S length Distance between Cr and S S-P length Distance between S and P P-Op length Distance between P and Op Cl-S length Distance between Cl and S Cl-P length Distance between Cl and P V-S length Distance between V and S V-P length Distance between V and P Transverse cranial asymmetry SOr (non)-CSOr (dev) length – SOr (dev)-CSOr (non) length CVA (cranial vault asymmetry) Fz (non)-Eu( dev) length – Fz (dev)-Eu (non) length FOA (fronto-orbital asymmetry) Fz (non)-Po (dev) length – Fz (dev)-Po (non) length
Mandible Volume
Hemi-mandibular volume The mandibular volume was divided into 2 hemi-mandibular volumes by the plane connecting Me-B-G
Ramal volume and body volume The hemi-mandibular volume was divided into ramal and body volumes by the plane connecting Gomid-Jlat-Jmed
Length Condylar unit length Distance between Consup and F Body unit length Distance between F and MF
Non, Nondeviated side; dev, deviated side.
Fig 2. Landmarks and measurements of the mandible.
Kim et al 333
was used to determine correlations between MD and the measurements. Statistical evaluations were performed at the 5% level of significance with SPSS for Windows software (version 18.0; SPSS, Chicago, Ill).
American Journal of Orthodontics and Dentofacial Orthoped
RESULTS
Intraclass correlation coefficients were .908 to .964 for intraobserver reliability and 0.902 to 0.919 for inter- observer reliability, indicating high reliability of these
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Fig 3. Landmarks and measurements of the cranial base.
334 Kim et al
measurements. The paired t test showed no statistically significant difference between the measurements made 2 weeks later. Among the measurements of the cranial base, the method errors were 0.56 to 1.68 mm for linear measurements, 0.85 to 1.95 for angular measure- ments, and 123.57 and 385.25 mm3 for volumetric measurements. Among the mandibular measurements, the method errors were 0.45 to 1.03 mm for linear mea- surements and 56.70 to 130.58 mm3 for volumetric measurements.
The asymmetry group showed significantly greater differences in hemi-base volume (P\0.01), anterior cra- nial base volume (P \0.05), and middle cranial base volume (P \0.05) between the nondeviated and devi- ated sides compared with the symmetry group. There
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was no statistically significant difference in other measurements of the cranial base (Table IV).
In the asymmetry group, the hemi-base, anterior cra- nial base, and middle cranial base volume measurements were significantly greater on the nondeviated side than on the deviated side (P \0.01). The Cr-S, S-P, Cl-P, and V-P lengths were significantly longer on the nonde- viated side than on the deviated side (P\0.05). There was no statistically significant difference in angular measurements of the cranial base (Table V).
The asymmetry group showed significantly greater differences in condylar unit length (P \0.01), body unit length (P \0.01), hemi-mandibular volume (P\0.05), and ramal volume (P\0.01), but there was no statistically significant difference in body volume
Journal of Orthodontics and Dentofacial Orthopedics
Table IV. Comparison of differences in measurements of the cranium between the symmetry and asymmetry groups (2-sample t test)
Measurement
Symmetry group
Asymmetry group
P valueMean SD Mean SD Volume difference (3103 mm3) Hemi-base volume 0.22 2.66 2.50 2.50 0.001y
Anterior cranial base volume
Middle cranial base volume
Posterior cranial base volume
0.07 2.81 0.03 2.44 0.884
Angle difference () Anterior cranial angle 0.13 3.01 1.00 3.30 0.170 Middle cranial angle 0.18 3.22 0.37 3.58 0.534 Posterior cranial angle 0.01 2.17 0.32 2.23 0.596 Petrous ridge angle 0.02 2.74 0.62 3.08 0.400
Length difference (mm) Cr-S length 0.17 2.08 0.92 2.24 0.055 S-P length 0.57 3.24 1.17 2.70 0.441 P-Op length 0.29 2.44 0.31 2.89 0.983 Cl-S length 0.12 1.94 0.65 3.19 0.265 Cl-P length 0.53 3.61 1.56 3.19 0.248 V-S length 0.79 1.22 0.09 2.16 0.130 V-P length 0.73 3.85 1.61 3.19 0.343 Transverse cranial asymmetry
0.90 3.66 0.31 3.98 0.552
CVA 1.33 5.47 2.33 5.98 0.500 FOA 0.80 2.59 0.68 3.70 0.880
Difference, Nondeviated side minus deviated side. *P\0.05; yP\0.01.
Kim et al 335
(Table VI). In the asymmetry group, hemi-mandibular volume and ramal volume were greater on the nondevi- ated side (P\0.01), and condylar unit length and body unit length were longer on the nondeviated side (P\0.01). MD was significantly correlated with the dif- ferences in condylar unit length (P \0.01), body unit length (P\0.01), hemi-mandibular volume (P\0.05), and ramal volume (P\0.01; Table VII).
In the asymmetry group, MD was significantly corre- lated with the difference in hemi-base volume (P\0.05; Table V). The difference in ramal volume was signifi- cantly correlated with the differences in hemi-base volume and middle cranial base volume (P \0.05; Table VIII). The difference in hemi-base volume was significantly correlated with the differences in Cl-P (P \0.01), V-P (P \0.05), and S-P length (P \0.05), whereas the difference in anterior cranial base volume was significantly correlated with the difference in Cr-S length (P\0.05). Furthermore, the difference in middle cranial base volume was significantly correlated with the difference in S-P length (P\0.01; Table IX).
American Journal of Orthodontics and Dentofacial Orthoped
DISCUSSION
Traditionally, the cranial base was a 2-dimensional concept, extending from anterior nasion to posterior basion in lateral cephalograms.29 Furthermore, it is difficult to define the border of the cranial base because it is actually a 3-dimensional structure composed of the frontal, ethmoid, sphenoid, temporal, and occipital bones.23 Hence, in this study, these bones were all included for volumetric measurements of the cranial base. To separate the cranial base from the calvaria, a reproducible plane was needed as close to the floor of the cranial vault as possible. A plane connecting both P points (prominent points on the border of the middle cranial base and posterior cranial base) and supraorbi- tale (located closest to the orbital plate of the frontal bone) resulted in the problem of a portion of the orbital plate of the frontal bone being cut off, so SS point was designated 10 mm above the left supraorbitale to construct the SSL-PL-PR plane. After designating V point, which is easily identifiable and located on the lower surface of the body of sphenoid bone, the cranial base was further divided into anterior, middle, and pos- terior cranial bases using the Cl-S-V and Cl-P-V planes, as reported by Captier et al24 and Kwon et al.11 Finally, the cranial base was divided into nondeviated and devi- ated sides according to the direction of MD using the Cr-Cl-Op plane.11
The asymmetry group showed significantly greater differences in hemi-base, anterior cranial base, and mid- dle cranial base volumes between the nondeviated and deviated sides compared with the symmetry group. Also, when comparing the nondeviated and deviated sides in the asymmetry group, the hemi-base, anterior cranial base, and middle cranial base volumes were all significantly greater on the nondeviated side. Moreover, MD was significantly correlated with the difference in hemi-base volume in the asymmetry group. These results suggest that themorphology of the cranial base is altered in patients with facial asymmetry; this contrasts with the findings of Kwon et al11 and Baek et al,12 who reported that the morphology of the cranial base was not related to MD. They examined angular measurements such as the anterior, middle, and posterior cranial base angles and found no significant difference between the asym- metry and symmetry groups, or between the nondeviated and deviated sides. In this study, there was also no signif- icant difference in the angular and linear measurements between the asymmetry and symmetry groups, but sig- nificant differences were found in hemi-base, anterior cranial base, and middle cranial base volumes, indicating the limitations of 2-dimensional measurements in the evaluation of morphologic changes. Volumetric
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Table V. Comparison of measurements of the cranium between the nondeviated and deviated sides…
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