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Combined 3-dimensional and mirror-image analysis for the diagnosis of asymmetry

2011; Elsevier BV; Volume: 140; Issue: 6 Linguagem: Inglês

10.1016/j.ajodo.2010.03.032

1097-6752

Janalt Damstra, Barbara Constance Maria Oosterkamp, J. Jansma, Yijin Ren,

Forensic Anthropology and Bioarchaeology Studies

Three-dimensional imaging techniques have greatly improved our ability to assess asymmetry by means of linear and angular measurements. However, visualizing deformities enables a unique appreciation of the underlying deformity, which might not be possible by looking at quantitative numbers alone. This article describes the method of a mirror-image analysis technique to visualize the asymmetry to assist in diagnosis and treatment planning. Other advantages of a mirror-image analysis, in addition to the quantitative analysis, are also discussed. Three-dimensional imaging techniques have greatly improved our ability to assess asymmetry by means of linear and angular measurements. However, visualizing deformities enables a unique appreciation of the underlying deformity, which might not be possible by looking at quantitative numbers alone. This article describes the method of a mirror-image analysis technique to visualize the asymmetry to assist in diagnosis and treatment planning. Other advantages of a mirror-image analysis, in addition to the quantitative analysis, are also discussed. The development of computerized tomography (CT) has greatly reduced errors of frontal cephalometry and improved our ability to diagnose asymmetry and other craniofacial deformities.1Hwang H.S. Hwang C.H. Lee K.H. Kang B.C. Maxillofacial 3-dimensional image analysis for the diagnosis of facial asymmetry.Am J Orthod Dentofacial Orthop. 2006; 130: 779-785Abstract Full Text Full Text PDF PubMed Scopus (156) Google Scholar, 2Baek S.K. Cho I.S. Chang Y.I. Kim M.J. Skeletodental factors affecting chin point deviation in female patients with Class III malocclusion and facial asymmetry: a three dimensional analysis using computed tomography.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007; 104: 628-639Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar Cone-beam CT (CBCT) was developed for 3-dimensional (3D) imaging of the maxillofacial area and has become popular in dentistry, orthodontics, and maxillofacial surgery.3Jacobson R.L. Three-dimensional cephalometry.in: Jacobson A. Jacobson R.L. Radiographic cephalometry: from basics to 3-D imaging. 2nd ed. Quintessence, Hanover Park, Ill2006: 233-247Google Scholar The advantages of CBCT include less radiation exposure (than conventional CT), less artefact formation, and submillimeter spatial resolution.3Jacobson R.L. Three-dimensional cephalometry.in: Jacobson A. Jacobson R.L. Radiographic cephalometry: from basics to 3-D imaging. 2nd ed. Quintessence, Hanover Park, Ill2006: 233-247Google Scholar CBCT has been shown to produce accurate 3D images of the craniofacial region and a 1-to-1 image-to-reality ratio, which is necessary for accurate detection of the underlying deformities and asymmetries.4Damstra J. Fourie Z. Huddleston Slater J.J.R. Ren Y. Accuracy of linear measurements from cone-beam computed tomography-derived surface models of different voxel sizes.Am J Orthod Dentofacial Orthop. 2010; 137: 16.e1-16.e6Scopus (127) Google Scholar, 5Lagravère M.O. Carey J. Toogood R.W. Major P.W. Three-dimensional accuracy of measurements made with software on cone-beam computed tomography images.Am J Orthod Dentofacial Orthop. 2008; 134: 112-116Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar, 6Hassan B. van der Stelt P. Sanderink G. Accuracy of three-dimensional measurements obtained from cone beam computed tomography surface-rendered images for cephalometric analysis: influence of patient scanning position.Eur J Orthod. 2008; 31: 129-134Crossref PubMed Scopus (135) Google Scholar, 7Brown A.A. Scarfe W.C. Scheetz J.P. Silveira A.M. Farman A.G. Linear accuracy of cone beam CT 3D images.Angle Orthod. 2009; 79: 150-157Crossref PubMed Scopus (133) Google Scholar, 8Mischkowski R.A. Pulsfort R. Ritter L. Neugebauer J. Brochhagen H.G. Keeve E. et al.Geometric accuracy of a newly developed cone-beam device for maxillofacial imaging.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007; 104: 551-559Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar Recent literature has described new quantitative analyses to diagnose asymmetries on 3D CT or CBCT images.1Hwang H.S. Hwang C.H. Lee K.H. Kang B.C. Maxillofacial 3-dimensional image analysis for the diagnosis of facial asymmetry.Am J Orthod Dentofacial Orthop. 2006; 130: 779-785Abstract Full Text Full Text PDF PubMed Scopus (156) Google Scholar, 2Baek S.K. Cho I.S. Chang Y.I. Kim M.J. Skeletodental factors affecting chin point deviation in female patients with Class III malocclusion and facial asymmetry: a three dimensional analysis using computed tomography.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007; 104: 628-639Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar, 3Jacobson R.L. Three-dimensional cephalometry.in: Jacobson A. Jacobson R.L. Radiographic cephalometry: from basics to 3-D imaging. 2nd ed. Quintessence, Hanover Park, Ill2006: 233-247Google Scholar, 9Park S.H. Yu H.S. Kim K.D. Lee K.J. Baik H.S. A proposal for a new analysis of craniofacial morphology by 3-dimensional computed tomography.Am J Orthod Dentofacial Orthop. 2006; 129: 600.e23-600.e34Abstract Full Text Full Text PDF PubMed Scopus (165) Google Scholar, 10Haraguchi S. Takada K. Yasuda Y. Facial asymmetry in patients with skeletal Class III deformity.Angle Orthod. 2002; 72: 28-35PubMed Google Scholar, 11Cho H.J. A three-dimensional cephalometric analysis.J Clin Orthod. 2009; 43: 235-252PubMed Google Scholar, 12Maeda M. Katsumata A. Ariji Y. Maramatsu A. Yoshida K. Goto S. et al.3D-CT evaluation of facial asymmetry in patients with maxillofacial deformities.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006; 101: 652-657Abstract Full Text Full Text PDF PubMed Scopus (112) Google Scholar, 13Tuncer B.B. Atac M.S. Yuksel S. A case report comparing 3-D evaluation in the diagnosis and treatment planning of hemimandibular hyperplasia with conventional radiography.J Craniomaxillofac Surg. 2009; 37: 312-319Abstract Full Text Full Text PDF PubMed Scopus (37) Google Scholar, 14Terajima M. Nakasima A. Aoki Y. Goto T.K. Tokumori K. Mori N. et al.A 3-dimensional method for analyzing the morphology of patients with maxillofacial deformities.Am J Orthod Dentofacial Orthop. 2009; 136: 857-867Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar Because quantitative measurement is a key element in diagnosis of asymmetry, 3D images are best suited for accurate diagnosis. Quantitative measurement provides important information for treatment planning; eg, it determines the target area for operation and the surgical method to be followed. However, by looking at quantitative numbers alone, it might not be possible to appreciate the extent of the underlying deformity. To overcome this limitation, Terajima et al14Terajima M. Nakasima A. Aoki Y. Goto T.K. Tokumori K. Mori N. et al.A 3-dimensional method for analyzing the morphology of patients with maxillofacial deformities.Am J Orthod Dentofacial Orthop. 2009; 136: 857-867Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar described a visual 3D method for analyzing the morphology of patients with maxillofacial deformities. They superimposed a standard 3D Japanese skeletal model on the patient’s 3D CT images to show the underlying deformities. However, these 3D templates only satisfy the Japanese norms; this limits their clinical applications. We use a mirror image for visual analysis of the asymmetry. The mirror-image analysis does not rely on population norms and can therefore be used for the detection of asymmetries in all populations. A mirror image is a reflected duplication that appears identical but in reverse. By superimposition of the mirror image of the anatomically correct part of the anatomy over the deformity, the differences become visual and can also be quantified. The use of mirror images is not new in craniofacial imaging techniques. In maxillofacial surgery, the reverse models of 3D mirror-image templates have been described to correct and reconstruct various craniofacial abnormalities.15Zhou L. He L. Shang H. Lui G. Zhoa J. Lui Y. Correction of hemifacial microsomia with the help of mirror imaging and rapid prototyping technique: a case report.Br J Oral Maxillofac Surg. 2009; 47: 486-488Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar, 16Lee J.W. Fang J.J. Chang L.R. Yu C.K. Mandibular defect reconstruction with the help of mirror imaging coupled with laser stereolithographic modeling technique.J Formos Med Assoc. 2007; 106: 244-250Abstract Full Text PDF PubMed Scopus (36) Google Scholar The aims of this study were to illustrate and discuss the method of mirror-image analysis in addition to the quantitative 3D analysis of asymmetry with a case report. The advantages of the mirror-image analysis will also be discussed. A boy, aged 14 years, was referred to the Department of Orthodontics at the University of Groningen, Groningen, The Netherlands, as part of the multidisciplinary approach for treatment of Parry-Romberg syndrome. His medical history showed that noticeable asymmetry began at the age of 6 years, indicating early onset of the disease. The diagnosis of Parry-Romberg disease was made at the age of 7 years. The extraoral examination showed a marked asymmetry from atrophy of the right side of the face. The chin was deviated to the right, and deviation of the nose to the affected side was noticeable. The intraoral examination showed that the mandibular dental midline was rotated to the right. Delayed eruption of the mandibular premolars and molars was noted on the right side. A CBCT image of the patient was acquired by using a KaVo 3D eXam scanner (KaVo Dental, Bismarckring, Germany). The image was made with a 17-cm field of view at a voxel resolution of 0.4 mm. The CBCT data set was exported in DICOM file format and imported into SimPlant Ortho Pro software (version 2.00; Materialise Dental, Leuven, Belgium). The 3D image was rendered, and surface models of the hard tissues were created with the software (Fig 1). To quantify the osseous changes, a 3D analysis was developed combining linear and angular measurements previously described.1Hwang H.S. Hwang C.H. Lee K.H. Kang B.C. Maxillofacial 3-dimensional image analysis for the diagnosis of facial asymmetry.Am J Orthod Dentofacial Orthop. 2006; 130: 779-785Abstract Full Text Full Text PDF PubMed Scopus (156) Google Scholar, 2Baek S.K. Cho I.S. Chang Y.I. Kim M.J. Skeletodental factors affecting chin point deviation in female patients with Class III malocclusion and facial asymmetry: a three dimensional analysis using computed tomography.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007; 104: 628-639Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar, 3Jacobson R.L. Three-dimensional cephalometry.in: Jacobson A. Jacobson R.L. Radiographic cephalometry: from basics to 3-D imaging. 2nd ed. Quintessence, Hanover Park, Ill2006: 233-247Google Scholar The measurements used for the quantitative 3D analysis are illustrated in Figure 2 and described in Table I. Asymmetry was described by the right-side measurement subtracted from the left-side measurement.1Hwang H.S. Hwang C.H. Lee K.H. Kang B.C. Maxillofacial 3-dimensional image analysis for the diagnosis of facial asymmetry.Am J Orthod Dentofacial Orthop. 2006; 130: 779-785Abstract Full Text Full Text PDF PubMed Scopus (156) Google Scholar, 2Baek S.K. Cho I.S. Chang Y.I. Kim M.J. Skeletodental factors affecting chin point deviation in female patients with Class III malocclusion and facial asymmetry: a three dimensional analysis using computed tomography.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007; 104: 628-639Abstract Full Text Full Text PDF PubMed Scopus (94) Google ScholarFig 2Measurements used for the quantitative analysis of asymmetry: 1, Maxillary rotation; 2, maxillary height; 3, maxillary dental height; 4, maxillary width; 5, maxillary dental width; 6, mandibular rotation; 7, ramus length; 8, mandibular body length; 9, total mandibular length; 10, mandibular width; 11, mandibular dental width; 12, mandibular dental height; 13, gonial angle; 14, lateral ramus inclination; 15, frontal ramus inclination; 16, facial width; 17, occlusal cant; 18, mandibular cant; 19, total maxillary width and total mandibular width; 20, condylar width.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Fig 2Measurements used for the quantitative analysis of asymmetry: 1, Maxillary rotation; 2, maxillary height; 3, maxillary dental height; 4, maxillary width; 5, maxillary dental width; 6, mandibular rotation; 7, ramus length; 8, mandibular body length; 9, total mandibular length; 10, mandibular width; 11, mandibular dental width; 12, mandibular dental height; 13, gonial angle; 14, lateral ramus inclination; 15, frontal ramus inclination; 16, facial width; 17, occlusal cant; 18, mandibular cant; 19, total maxillary width and total mandibular width; 20, condylar width.View Large Image Figure ViewerDownload Hi-res image Download (PPT)Table IReference planes and measurements used for this analysisReference planesDescription1. MidsagittalPlane that passes through nasion and the constructed midpoint between the lateral points of the foramen magnum and the constructed midpoint between the left and right clinoid processes2. Frankfort horizontalPlane that passes through both orbitale landmarks and through the mean of the 2 porion landmarks3. OcclusalPlane that passes through the midpoint of the maxillary incisor tip and mandibular incisor tip landmarks, the midpoint of the maxillary right first molar mesial cusp and the mandibular right first molar mesial cusp and the mean of the maxillary left first molar mesial cusp and the mandibular left first molar mesial cusp4. MandibularPlane that passes through both gonion landmarks and mentonMeasurementsDescription (distance or angle)1. Maxillary rotationPoint A to the midsagittal plane2. Maxillary heightJugulare to the Frankfort horizontal plane3. Maxillary dental heightMesial cusp tip of the maxillary first molar to the Frankfort horizontal plane4. Maxillary widthJugulare to the midsagittal plane5. Maxillary dental widthMesial cusp tip of the maxillary first molar to the midsagittal plane6. Mandibular rotationPogonion to the midsagittal plane7. Ramus lengthCondylion to gonion8. Body lengthGonion to menton9. Total mandibular lengthCondylion to menton10. Mandibular width differenceAntegonion to the midsagittal plane11. Mandibular dental width differenceMesial cusp tip of the mandibular first molar to the midsagittal plane12. Mandibular dental height differenceMesial cusp tip of the mandibular first molar to the mandibular plane13. Gonial angleAngle between a line that connects the landmarks of gonion and condylion and a line that connects gonion and menton14. Lateral ramus inclinationAngle between the Frankfort horizontal plane and a line formed by connecting the landmarks of gonion and condylion from the lateral view15. Frontal ramus inclinationAngle between the Frankfort horizontal plane and a line formed by connecting the landmarks of gonion and condylion from the frontal view16. Facial widthZygion to the midsagittal plane17. Occlusal cantAngle between the Frankfort horizontal plane and a line connecting the maxillary left and right first molar cusps18. Mandibular cantAngle between the Frankfort horizontal plane and a line connecting the left and right antegonion landmarks19. Maxillary total widthJugulare left to jugulare rightMandibular total widthAntegonion left to antegonion right20. Condylar widthMost lateral point of the condylar head to the most medial point of the condylar head Open table in a new tab In addition to the quantitative 3D analysis, a mirror-image analysis was performed to visually analyze the extent of the atrophy and confirm the diagnosis. The method for the mirror image of the maxilla was as follows: the left unaffected side was mirrored along the midsagittal plane. The mirror image was then superimposed over the right affected side (Fig 3, A-C). The software allows for the surface models to become semitransparent and allows for movement of the models in all 3 planes of space. Visual inspection of the anterior and posterior cranial base confirmed the superimposition (Fig 3, D). For the mandible, a vertical plane through the spina mentalis, parallel to the midsagittal plane, was used because of the chin deviation (Fig 4, A). The left side was mirrored and superimposed over the right side (Fig 4, A-C). Visual inspection of the inner contour of the cortical plates of the inferior border of the symphysis confirmed the superimposition (Fig 4, D). For both the maxilla and mandible, the difference in volume was visualized with the software by means of a customized color scale (Figs 3, F, and 4, F). The measurement differences were used as a guide to determine the parameters of the color scales.Fig 4Mirror-image analysis of the mandible: A-C, the left side of the mandible is mirrored (blue) over the right original surface model (pink) along the vertical plane through menton; D, the superimposition is adjusted to best fit along the inner contour of the cortical plates of the inferior border of the symphysis if necessary; E, final superimposition with the surface models is semitransparent to visualize the differences; F, the differences of the mirror image and the original surface model are calculated and expressed with a customized color scale (in millimeters).View Large Image Figure ViewerDownload Hi-res image Download (PPT) The quantitative results of the 3D cephalometric analysis are described in Table II. The smaller measurements indicate that the mandible and the maxilla were affected on the right side. The facial width was 5 mm less on the right side compared with the left side. This indicates restricted growth of the zygomatic arch because of soft-tissue atrophy. The maxilla height was decreased on the right side (1.7 mm). However, there was no difference between the maxillary dental heights of the left and right sides, possibly because of the overeruption of the maxillary dentition from the delayed eruption of the posterior mandibular dentition.Table IIResults of the quantitive 3D analysis, with asymmetry defined as the right side subtracted from the left sideMaxillaRightLeftAsymmetry1. Maxillary rotation (mm)0.22. Maxillary height difference (mm)21.022.51.53. Maxillary dental height difference (mm)42.441.9−0.54. Maxillary width difference (mm)34.133.1−1.05. Maxillary dental width difference (mm)27.126.1−1Mandible6. Mandibular rotation (mm)4.887. Ramus length difference (mm)47.452.34.98. Body length difference (mm)73.984.210.39. Total length difference (mm)108.7115.26.510. Mandibular width difference (mm)42.643.71.111. Mandibular dental width difference (mm)23.422.6−0.812. Mandibular dental height difference (mm)19.224.55.313. Gonion angle difference (°)125.9113.0−12.914. Lateral ramus inclination difference (°)78.082.26.215. Frontal ramus inclination difference (°)85.088.0−3.0Other16. Occlusal cant (°)1.01.017. Mandibular cant (°)13.013.018. Mandibular width-maxillary width (mm)80.067.013.019. Facial width difference (mm)54.459.45.020. Condyle width difference (mm)18.2718.07−0.20 Open table in a new tab The mandible was rotated 4.88 mm to the right. On the affected side, the mandibular body length was 10.3 mm shorter compared with the left side. The ramus was also 4.2 mm shorter on the affected side. The difference in the ramus length explains the significant cant of the mandible (13.0°). The restrictive nature of the disease manifested not only as restriction of the lengths but also the angular development of the mandible. Most noticeable was the underdevelopment of the gonial angle on the right side; it was 113.0° on the left side compared with 125.9° on the right side. The lateral and frontal ramus inclinations were smaller on the right side (6.2° and 3.0°). Delayed eruption caused the underdevelopment of the alveolar process of the mandible (5.3 mm) and resulted in an occlusal cant. Interestingly, although the lower face of the affected side showed significant osseous changes, the condylar width dimensions were not different from the unaffected side. The mirror-image technique visualized the findings of the quantitative 3D analysis regarding the hypoplasia of the zygomatic region and the mandible. The differences between the mirror image and the affected side were calculated and illustrated with color scales in Figures 3, F, and 4, F. Parry-Romberg syndrome (or progressive hemifacial atrophy) is an uncommon degenerative condition characterized by a slow and progressive atrophy of facial tissues, muscles, bones, and skin.17Mazzeo N. Fisher J.G. Mayer M.H. Mathieu G.P. Progressive hemifacial atrophy (Parry-Romberg syndrome). Case Report.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 1995; 79: 30-35Abstract Full Text PDF PubMed Scopus (68) Google Scholar, 18Lakhani P.K. David T.J. Progressive hemifacial atrophy with scleroderma and ipsilateral limb wasting (Parry-Romberg syndrome).J R Soc Med. 1984; 77: 138-139PubMed Google Scholar, 19Gomez-Diez S. Lopez L.G. Escobar M.L. Gutierrez L.J. Oliva N.P. Progressive facial hemiatrophy with associated osseous lesions.Med Oral Patol Oral Cir Bucal. 2007; 12: E602-E604PubMed Google Scholar, 20Miller M.T. Sloane H. Goldberg M.F. Grisolano J. Frenkel M. Mafee M.F. Progressive hemifacial atrophy (Parry-Romberg disease).J Pediatr Ophthalamol Strabismus. 1987; 24: 27-36PubMed Google Scholar, 21Neville B.W. Damm D.D. Allen C.N. Bouquot J.E. Patologica oral e maxilofacial. Guanabara Koogan, Rio de Janeiro, Brazil1998: 85Google Scholar, 22Moore W.H. Wong K.S. Proudman T.W. David D.J. Progressive hemifacial atrophy (Romberg’s disease): skeletal involvement and treatment.Br J Plast Surg. 1993; 46: 39-44Abstract Full Text PDF PubMed Scopus (45) Google Scholar, 23Pinheiro T.P. Silva C.C. Silveira C.S. Botelho P.C. Pinheiro M.G. Pinheiro J.J. Progressive hemifacial atrophy–case report.Med Oral Patol Oral Cir Bucal. 2006; 11: E112-E114PubMed Google Scholar, 24Zafarulla M.Y. Progressive hemifacial atrophy: a case report.Br J Ophthalmol. 1985; 69: 669-676Crossref Scopus (23) Google Scholar, 25Asher S. Berg B.O. Progressive hemifacial atrophy: report of three cases, including one observed over 43 years and computer tomographic findings.Arch Neurol. 1982; 39: 44-46Crossref PubMed Scopus (57) Google Scholar, 26Duymaz A. Karabekmez F.E. Keskin M. Tosun Z. Parry-Romberg syndrome: facial atrophy and its relationship with other regions of the body.Ann Plast Surg. 2009; 63: 457-461Crossref PubMed Scopus (45) Google Scholar The progressive atrophy of the facial tissues is often in stark contrast to the apparently normal contralateral side. The extent of the atrophy is usually limited to 1 side of the face. The osseous lesions described in Parry-Romberg syndrome appear to be related to the age at which the condition appears. With late onset of the condition after the age of 15 years, the lesions appear exclusively in the soft tissues.24Zafarulla M.Y. Progressive hemifacial atrophy: a case report.Br J Ophthalmol. 1985; 69: 669-676Crossref Scopus (23) Google Scholar Restriction of skeletal growth from the soft-tissue atrophy of early-onset Parry-Romberg syndrome has been previously reported. However, Duymaz et al26Duymaz A. Karabekmez F.E. Keskin M. Tosun Z. Parry-Romberg syndrome: facial atrophy and its relationship with other regions of the body.Ann Plast Surg. 2009; 63: 457-461Crossref PubMed Scopus (45) Google Scholar reported no osseous changes of the craniofacial region after 3D CT examination of a patient with early-onset Parry-Romberg syndrome. In our patient, early onset of the atrophy resulted in hypoplasia of the fronto-orbitozygomatic region, mandibular rotation, and underdevelopment of the mandible in all dimensions of space. This is in contrast to the findings of Duymaz et al. It would, however, be incorrect to draw conclusions from 1 case report because the osseous changes might be different from person to person. This is because involvement can stabilize at any stage of growth and development, and patients who manifest atrophy earlier have greater repercussions.24Zafarulla M.Y. Progressive hemifacial atrophy: a case report.Br J Ophthalmol. 1985; 69: 669-676Crossref Scopus (23) Google Scholar Future studies will investigate a larger group of patients with early-onset Parry-Romberg syndrome by means of 3D analysis to fully determine the characteristics of early-onset soft-tissue atrophy on the middle and lower face. The mirror-image analysis performed in addition to the quantitative 3D analysis proved to be valuable. Not only did it confirm the diagnosis derived from quantitative measurements, but it also helped to reduce diagnostic errors when relying on numbers alone. It does not rely on normative values, it creates new appreciation of osseous changes because the differences can be depicted as volumes rather than numbers, it helps in development of treatment strategies, and it improves communications between orthodontists and maxillofacial surgeons. Perhaps the most valuable contribution of the visual analysis is that it has been an excellent tool to explain the extent of the osseous changes to patients to further their understanding of the disease and the possibilities and limitations of the treatment. It is therefore recommended to perform a mirror-image analysis in addition to quantitative analyses in patients with asymmetries to enable a unique appreciation of the underlying deformity that might not be possible by studying quantitative numbers alone. Importantly, where there is unilateral growth of the mandible, it will have a tendency to rotate toward the area of less growth and cause chin deviation. Therefore, it is debatable whether the mandible can be divided into affected and unaffected sides because the unaffected side is always indirectly affected. As a result of rotation, the ramus inclinations on both sides might be affected. The chin deviation also excludes the use of the midsagittal plane, and the mandible should be divided and mirrored with a vertical plane through the spina mentalis. The effect of unilateral growth of the mandible is illustrated in Figure 5. Therefore, it is important to realize that mirror-image analysis is unlikely to give an accurate representation of the ramus inclinations when there is chin deviation. However, the differences in mandibular body length, ramus length, and gonial angle differences can be accurately determined with a mirror-image analysis (Fig 4, E). In the literature, there seem to be great variations concerning the vertical axis or the midsagittal plane for analysis of asymmetry.2Baek S.K. Cho I.S. Chang Y.I. Kim M.J. Skeletodental factors affecting chin point deviation in female patients with Class III malocclusion and facial asymmetry: a three dimensional analysis using computed tomography.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007; 104: 628-639Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar, 3Jacobson R.L. Three-dimensional cephalometry.in: Jacobson A. Jacobson R.L. Radiographic cephalometry: from basics to 3-D imaging. 2nd ed. Quintessence, Hanover Park, Ill2006: 233-247Google Scholar, 11Cho H.J. A three-dimensional cephalometric analysis.J Clin Orthod. 2009; 43: 235-252PubMed Google Scholar, 13Tuncer B.B. Atac M.S. Yuksel S. A case report comparing 3-D evaluation in the diagnosis and treatment planning of hemimandibular hyperplasia with conventional radiography.J Craniomaxillofac Surg. 2009; 37: 312-319Abstract Full Text Full Text PDF PubMed Scopus (37) Google Scholar, 27Grummons D.C. Kappeyne van de Coppello M.A. A frontal asymmetry analysis.J Clin Orthod. 1987; 21: 448-465PubMed Google Scholar Jacobson3Jacobson R.L. Three-dimensional cephalometry.in: Jacobson A. Jacobson R.L. Radiographic cephalometry: from basics to 3-D imaging. 2nd ed. Quintessence, Hanover Park, Ill2006: 233-247Google Scholar defined the midsagittal plane as a midline plane bisecting the head sagittally when viewing the patient from the front. He used nasion, the midpoint of the frontonasal suture, as the reference point. Grummons and Kappeyne van de Coppello27Grummons D.C. Kappeyne van de Coppello M.A. A frontal asymmetry analysis.J Clin Orthod. 1987; 21: 448-465PubMed Google Scholar used a midsagittal line through crista galli and anterior nasal spine. Tuncer et al13Tuncer B.B. Atac M.S. Yuksel S. A case report comparing 3-D evaluation in the diagnosis and treatment planning of hemimandibular hyperplasia with conventional radiography.J Craniomaxillofac Surg. 2009; 37: 312-319Abstract Full Text Full Text PDF PubMed Scopus (37) Google Scholar used a plane through nasion, sella, and anterior nasal spine as the midsagittal plane for their 3D analysis. Harvold28Harvold E. Cleft lip and palate: morphological studies of the facial skeleton.Am J Orthod. 1954; 40: 493-506Abstract Full Text PDF Scopus (65) Google Scholar reported that a line through nasion and anterior nasal spine represented the midsagittal line in more than 90% of patients. Baek et al2Baek S.K. Cho I.S. Chang Y.I. Kim M.J. Skeletodental factors affecting chin point deviation in female patients with Class III malocclusion and facial asymmetry: a three dimensional analysis using computed tomography.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007; 104: 628-639Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar used the most superior edge of the crista galli and the midpoint between the anterior clinoid processes to construct a midsagittal plane perpendicular to the Frankfort horizontal plane. However, the anterior nasal spine and the Frankfort horizontal plane might not be accurate when there is asymmetry of the upper and midfacial regions.14Terajima M. Nakasima A. Aoki Y. Goto T.K. Tokumori K. Mori N. et al.A 3-dimensional method for analyzing the morphology of patients with maxillofacial deformities.Am J Orthod Dentofacial Orthop. 2009; 136: 857-867Abstract Full Text Full Text PDF PubMed Scopus (29) Google Scholar, 29Athanasios A. Van der Meij A.J.W. Posteroanterior (frontal) cephalometry.in: Athanasios A. Orthodontic cephalometry. Times Mirror International Publishers, London, United Kingdom1995: 141-162Google Scholar In addition, we experienced variations in the midsagittal plane due to landmark identification differences of orbitale and porion when using the method of Baek et al.2Baek S.K. Cho I.S. Chang Y.I. Kim M.J. Skeletodental factors affecting chin point deviation in female patients with Class III malocclusion and facial asymmetry: a three dimensional analysis using computed tomography.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2007; 104: 628-639Abstract Full Text Full Text PDF PubMed Scopus (94) Google Scholar The midpoint between the foramina spinosum (ELSA)30Lagravère M.O. Major P.W. Proposed reference point for 3-dimensional cephalometric analysis with cone-beam computerized tomography.Am J Orthod Dentofacial Orthop. 2005; 128: 657-660Abstract Full Text Full Text PDF PubMed Scopus (67) Google Scholar was considered the reference point, but we found that the foramina was not always clear on the CBCT images. To construct the midsagittal plane, we used nasion, the midpoint between the anterior clinoid processes, and the midpoint between the most lateral points on the foramen magnum (Fig 6). The advantages of this method are that the landmarks are easily identifiable on the CBCT images, and the accuracy of the midsagittal plane does not rely on the accuracy of other planes: eg, the Frankfort horizontal plane and the midsagittal plane are not influenced by upper and midfacial deformities. However, recently published literature suggests that a morphometrically determined midsagittal plane that eliminates the problems related to anatomical planes might therefore be more appropriate in describing the midsagittal plane of skeletal asymmetry.31Damstra J. Fourie Z. De Wit M.F. Ren Y. A three-dimensional comparison of a morphometric midsagittal plane to cephalometric midsagittal planes for craniofacial asymmetry.Clin Oral Investig. 2011; https://doi.org/10.1007/s00784-011-0512-4Crossref PubMed Scopus (78) Google Scholar We introduced a new method for visualizing asymmetries. The combined 3D and mirror-image analysis was useful to visualize and better understand the osseous changes. The mirror-image analysis is useful to confirm the diagnosis derived from the quantitative results and assists in 3D treatment planning. The combined analysis showed that early-onset Parry-Romberg syndrome caused rotation of the mandible, hypoplasia of all dimensions of the mandible, and hypoplasia of the zygomatic region and the zygomatic arch.