Three-Dimensional Analysis of the Cranial Base Structure in Patients with Facial Asymmetry
Yuki HayashiChie TachikiTaiki MorikawaYasuo AiharaSatoru MatsunagaKeisuke SugaharaAkira WatanabeTakakazu KawamataYasushi Nishii
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Abstract:
Facial asymmetry is often seen in patients with skeletal mandibular prognathism and is associated with deformities in the maxillofacial and head regions. The maxillofacial deviation is three-dimensional and affects not only the lateral deviation of the mandible and midface, but also the cranium. This study conducted a three-dimensional morphological evaluation of the cranial base morphology of patients with skeletal mandibular prognathism (ANB < 0°, Wits < 0 mm) with the aim of examining the relationship between deformities of the head region and facial asymmetry. Data obtained from computed tomography conducted during the initial examination of patients with and without skeletal mandibular prognathism with facial asymmetry were used. Differences in the position of structures present in the cranial base were measured, and the association between cranial deformities and mandibular deviation was assessed. The middle cranial base area and the lateral deviation of the mandibular fossa were significantly larger in patients with facial asymmetry compared to those without facial asymmetry. In addition, a correlation between the amount of mandibular deviation and the area of the anterior cranial base was identified in patients with significant cranial deformity (p = 0.012). Given the identified association between the structure of the head region and facial asymmetry, further studies are needed to determine the factors implicated in the growth process.Keywords:
Facial symmetry
Prognathism
Middle cranial fossa
Mandibular prognathism
Mandible (arthropod mouthpart)
Cephalometry
Three major goals of Orthognathic Surgery (OGS) are, of course, beautiful re-creation of the unbalanced and/or unfavorable face, complete rehabilitation of the disturbed stomatognathic function and prolonged maintenance of the stable surgical results.These goals have been remarkably achieved during last five decades in worldwide places-especially in Japan and Korea.However, perfect control of facial asymmetry by OGS still remains as a challenge because of the complex pattern of facial asymmetry due to their various underlying etiology and developmental diversity.Frontal appearance of facial asymmetry seems to be more complex in cases of overgrown mandible compared to undergrowth.Such facial asymmetry does not always follow abnormal growing pattern of the functional developmental units of the mandible.In addition, developmental and growing pattern of the maxilla may not affect the pattern of the mandible.Therefore, patients with facial asymmetry combined with mandibular prognathism present various and complex pattern of appearance, which often develop independently from growing abnormalities of the facial bones.Moreover, soft tissue asymmetry of the face may not originate from hard tissue architecture of the facial bones.There have been brilliant progress last several decades through many trials to find causes of facial asymmetry and to set-up effective diagnostic references.Currently, we employed 3-D images and navigation system for surgery.However, confidential references to clarify the etio-pathogenesis of facial asymmetry and reliable protocols to establishing perfect symmetric face by OGS are still in need.
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The relationship between subjective and objective evaluation of facial asymmetry of mandibular prognathism patients shown by photographs, was investigated. Seven parts of measuring distances and angles representing facial asymmetry were selected in the first experiment and six for the second experiment.The parts of the face include: the distance from the median line of the face to point A, B, Ch and Al of right and left sides, angle ABC of right and left sides, angle OBC of right and left sides, and the right and left sides of the chin (Me) as shown in the diagram of a mandibular prognathism patient. The two results are as follow:1) The evaluation by the oral surgeons in our department, using multiple regression analysis, showed that the more the asymmetry in the region of the mandibular angle was severe, the more the facial asymmetry was felt to be severe. On the other hand, the result obtained from a questionnaire, distributed at the same time to the same subjects showed the chin to be most important for realizing facial symmetry. Therefore oral surgeons are inclined to pay too much attention to asymmetry of the chin region.2) Multiple regression analysis shows, for oral surgeons and the public, that the postoperative improvement of facial asymmetry is most closely related to the improvement of the symmetry of the mandibular angle region. However, 57.5% of oral surgeons, on the questionnaire, regarded the asymmetry of the chin region as most important in evaluating the asymmetry of the face. The percentage indicating the mandibular angle was only 20%. This was remarkably different from the 60% of the public. Together the multiple regression analysis and questionnaire results coincide, and they suggest that the mandibular angle is the most important part in judging the asymmetry of the face.
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Various techniques and modifications have been introduced in the treatment of mandibular prognathism. However, there are still few reports concerning long-term stability, especially using the intraoral vertical ramus osteotomy (IVRO) method. The purpose of this study was to investigate the long-term stability for correction of mandibular prognathism using IVRO. Twenty-five mandibular prognathism patients were treated by bilateral IVRO, and were evaluated cephalometrically by reference to the menton. A set of 3 standardized lateral cephalograms were obtained from each subject preoperatively (T1), immediately postoperatively (T2), and after 2 years postoperatively (T3). Relapse was defined as forward movement of menton after the 2-year follow-up. The mean setback of the menton was 12.8 mm in horizontal direction and 0.9 mm downward in vertical direction. The average follow-up was 33.9 months. The mean relapse was 1.3 mm (10.2% = 1.3 of 12.8) in forward direction and 0.6 mm in upward direction. There was no significant movement in the vertical direction. However, significant relapse was shown in the horizontal direction, even though the amount was small. The long-term stability of our present study suggested that IVRO is useful for correction of mandibular prognathism.
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The present study was designed to three-dimensionally evaluate the morphological asymmetry of maxillofacial complexes such as the maxilla and the mandible, and the state of the maxillary and mandibular deviation in the craniofacial complex of jaw-deformity patients with facial asymmetry. Based upon the results obtained, we tried to classify the states of asymmetry and/or deviation in the cases showing diverted jaw.The subjects comprised 15 patients (10 males and 5 females; 16 years and 6 months old on average) diagnosed as mandibular prognathism with facial asymmetry. All subjects exhibited more than 4-mm deviation of the mandible from the midline on the frontal cephalogram. Pretreatment CT images were taken as data for precise diagnosis in all subjects. Then, sliced CT data were forwarded to 3D reconstruction software Medical Viewer INTAGE 3.1 in order to form the MPR images. After that, 3D-CT images were constructed using the volume rendering (VR) method. After these images were obtained, the three-dimensional ratio of morphological asymmetry of the maxilla and the mandible was analyzed. The three-dimensional ratio of the maxillary and mandibular deviation was also examined.As a result, various types of asymmetry and/or deviation existed and the cases examined were divided into the following eight types: 1. Symmetrical maxilla without deviation in the craniofacial complex, 2. Almost symmetrical maxilla with deviation in the craniofacial complex, 3. Asymmetrical maxilla without deviation, 4. Asymmetrical maxilla with deviation, 5. Asymmetrical maxilla with deviation but complementary to each other, 6. Symmetrical mandible without deviation, and 7. Asymmetrical mandible with deviation, 8. Asymmetrical mandible with deviation but complementary to each other.The present method for three-dimensional evaluation made it possible to classify the state of asymmetry and/or deviation of the maxilla and the mandible in cases with diverted jaw. This VR method may be helpful in determining a more suitable treatment plan for jaw-deformity patients with deviation.
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Data from questionnaires consisting of 36 items which were sent to patients with prognathism were analysed, for self-evaluation on the postoperative release from various troubles that were suffered before surgery.The subjects were 77 patients (14 males and 63 females) out of 147 patients who had undergone sagittal splitting ramus osteotomy in our clinic from 1989 to 1994. The patients were divided into three groups with different facial profile, skeleton, and occlusion: prognathism group (28 patients with mandibular prognathism only), asymmetry group (27 patients with mandibular prognathism with asymmetry), and open bite group (22 patients with mandibular prognathism and open bite).The results were as follows:1) As for the preoperative particular troubles, those concerning occlusion and facial profile were noted in the prognathism group and those concerning mastication in the open bite group. The patients in the asymmetry group had the same troubles as noted in the above two groups, but suffered from multiple troubles, including temporomandibular joint disorder and others. Moreover, they were comparatively younger.2) In the open bite group, only a few patients evaluated the postoperative change in the facial profile, but much more patients evaluated the change in speech after surgery.3) Over 90 per cent of the evaluated patients from the three groups the improvement of occlusion after the operation, but it took more time for patients to eat an ordinary meal satisfacorily in the asymmetry group.4) Preoperative discomforts due to the temporomandibular joint syndrome were most remarkable in the asymmetry group, but less reduced in the prognathism group after surgery.5) As for the change in tongue and the numbness of lip or chin after surgery, there were no significant differences among the three groups.6) The difference between before and after surgery in the open bite group was move noticeable than the others.7) As for the motive of undergoing surgery, although many patients were recommended to undergo surgery by dentists among the three groups, more patients from the prognathism group decided to undergo it by themselves.8) As for the overall evaluation for the result of surgery, most patients in the three groups showed positive response to surgery. As the main reason, aesthetic improvement was evaluated in the prognathism group, that of occlusion and mastication in the open bite group, and that of the psychological aspect in the asymmetory group.
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In order to build a criterion of facial morphology diagnosis, the authors previously proposed the facial form classification chart. This chart was clinically used to diagnose 176 cases of maxillofacial deformity in five institutions, and these were subjected to a statistical study. The results were as follows:1) Facial morphology diagnoses given to 176 cases aggregated 283. The most common diagnosis was mandibular prognathism (123/176, 70%), followed by facial asymmetry (66/176, 38.0%), and maxillary retrognathism (38/176, 21.6%).2) Ninety cases (90/176, 51.1%) were given a single diagnosis and 86 (86/176, 48.9%) were given multiple diagnoses. Mandibular prognathism only was most common (56/176, 31.8%), followed by mandibular prognathism with maxillary retrognathism (33/176, 18.8%), mandibular prognathism with facial asymmetry (29/176, 16.5%), facial asymmetry single (19/176, 10.8%) and so on.3) The facial form classification chart was empirically assumed to systematize a common proress of facial morphology diagnosis, and offers a guide line that could standardize diagnosis of maxillofacial deformities.
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Facial symmetry
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Facial symmetry
Mandibular prognathism
Prognathism
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Bilateral sagittal split ramus osteotomy is considered a standard technique in mandibular orthognathic surgeries to reduce unexpected bilateral stress in the temporomandibular joints. Unilateral sagittal split ramus osteotomy (USSO) was recently introduced to correct facial asymmetry caused by asymmetric mandibular prognathism and has shown favorable outcomes. If unilateral surgery could guarantee long-term postoperative stability as well as favorable results, operation time and the incidence of postoperative complications could be reduced compared to those in bilateral surgery. This report highlights three consecutive cases with long-term follow-up in which USSO was used to correct asymmetric mandibular prognathism. Long-term postoperative changes in the condylar contour and ramus and condylar head length were analyzed using routine radiography and computed tomography. In addition, prior USSO studies were reviewed to outline clear criteria for applying this technique. In conclusion, patients showing functional-type asymmetry with predicted unilateral mandibular movement of less than 7 mm can be considered suitable candidates for USSO-based correction of asymmetric mandibular prognathism with or without maxillary arch surgeries.
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