Imaging Studies
Clinical photographs are essential for documentation and to allow for photometric analysis. Use soft-tissue landmarks to obtain angular and linear measurements that can help define the problem quantitatively. Standardize frontal and profile photographs. A clear acetate ruler can be placed next to the patient when the photographs are obtained for reference measurement for magnification; otherwise, a proportionate-type analysis without reliance on absolute values can be used. Images with the lips at repose and during animation (smiling) are obtained; the degree of dental display is noted for each.
Skeletal evaluation typically includes radiographic evaluation with ortho–Panorex and cephalometric x-rays.
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Ortho–Panorex x-rays provide an overview of the stage of dental development, the mandibular anatomy, and gross pathology. Specific films such as occlusal and periapical views can be obtained to further assess the dentition, supporting bone, and interdental spaces.
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Cephalometric x-rays provide for standardized skull and/or facial views that allow for comparison over time to assess growth in an individual and for comparison of that individual against standardized population norms.
Skeletal views can be obtained in lateral and frontal views.
Lateral cephalometric x-ray allows for assessment of the elements of the dentofacial skeleton from a sagittal perspective. See the image below.
Analysis of the dentofacial skeleton is based on identifiable radiographic landmarks on a lateral cephalometric x-ray.
With lateral cephalometric x-ray, the maxilla can be related to the mandible and each related to their position in the skull base. Simultaneously, the soft-tissue profile can be related to the facial skeleton. See the image below.
Lateral cephalometric analysis of the facial skeleton based on Steiner analysis. The positions of the maxilla and mandible each are related spatially to the anterior cranial base and to each other. Note that normative values of the facial elements depend on a normal anterior cranial base inclination and length, which typically are altered in craniofacial conditions.
Lateral cephalometric x-ray also allows the dentition to be related to each other, and each can be related to its own skeletal base, the maxilla, and the mandible. See the image below.
Frontal cephalometric x-ray allows for assessment of the degree of facial asymmetry.
Obtain quantitative measurements based on key anatomic landmarks (cephalometric analysis). Numerous cephalometric analyses exist, each emphasizing particular skeletal and dental elements. Common analyses include Steiner, Ricketts, and Delaire and are beyond the scope of this overview. For the surgeon, the analysis must be clinically workable, simple to use, and directly relatable to the skeletal elements that can be repositioned. While the analysis is invaluable, do not focus the treatment plan solely on correcting cephalometric abnormalities.
Additional radiographs include the following:
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Periapical films are obtained to determine if sufficient space exists for interdental osteotomies.
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On occasion, hand wrist films are useful to help determine skeletal age based on the known timing of sequential closure of the epiphyseal growth plates. However, typically facial skeletal maturity is determined by comparison of serial lateral cephalometric films obtained at 6-month intervals.
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Three-dimensional computerized tomography (3DCT) is increasingly being used for surgical evaluation and planning in academic settings. Preoperative planning using 3DCT offers multiple potential advantages, including the ability to easily consider multiple different surgical approaches to a problem and the ability to characterize degree and direction of skeletal movement at any point over the osteotomized segment (as opposed to only the occlusal level). With advancing technology, such 3D visualization of the patient's anatomic deformity is likely to replace today's conventional 2D cephalometric analysis.
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In cleft orthognathic surgery, plain film radiographs (occlusal and periapical) and CT are helpful in preoperatively determining the adequacy of bone across a previously bone-grafted alveolar cleft.
Other Tests
Dental models
Surgical movement of maxilla and mandible inherently alter the maxillary-mandibular dental occlusion, and as such, careful analysis of the dental models with the orthodontist is essential. The maxillary dental and mandibular dental casts can be studied individually and hand manipulated with each other to assess how the arches are coordinated.
Assessment of the models includes space analysis and arch length, transverse width discrepancies, position of the individual tooth within its own arch, and the relationship of the maxillary dentition to the mandibular dentition.
Establish the diagnosis from a working problem list generated from the clinical and photographic evaluation, cephalometric analysis, and study dental models.
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Ideal facial proportions believed to be in aesthetic balance. Such proportions are only guidelines, as ideal proportions change over time, and the ideal result varies with patient expectations.
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Profile analysis illustrating the degree of facial convexity or concavity from an acceptable orthognathic norm.
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An overview of the clinical, radiographic, and dental evaluation used in planning orthognathic surgery.
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Analysis of the dentofacial skeleton is based on identifiable radiographic landmarks on a lateral cephalometric x-ray.
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Lateral cephalometric analysis of the facial skeleton based on Steiner analysis. The positions of the maxilla and mandible each are related spatially to the anterior cranial base and to each other. Note that normative values of the facial elements depend on a normal anterior cranial base inclination and length, which typically are altered in craniofacial conditions.
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Lateral cephalometric analysis of the dentition within the skeletal framework.
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Illustration of 2-dimensional (2D) versus 3-dimensional (3D) planning for orthognathic surgery. All images are of the same patient (with maxillary deficiency and mandibular prognathism). Unlike conventional 2D cephalometric analysis and treatment planning, 3DCT-based analysis provides a more accurate simulation of the surgery and affords analysis in all 3 planes. Note that in the upper images, the osteotomies have been made (left) and then the maxillary and mandibular segments have been moved (right).
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Illustration of the role of presurgical dental decompensation in a patient requiring mandibular advancement. Dental decompensation is necessary to allow for proper degree of mandibular advancement and for postsurgical stability at the occlusal level. Note that the occlusion is made worse until corrected by skeletal advancement.
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Presurgical orthodontic management requires appropriate dental decompensation, alignment of the dentition within the individual arches, leveling of the curve of Spee, and coordination of the maxillary and mandibular dentition for postoperative stability.
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Illustration of the transverse maxillary Le Fort I osteotomy. The osteotomy is made with a reciprocating saw and completed at the pterygopalatine junction with a curved osteotome.
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Variation of midfacial osteotomies to correct differing degrees of midfacial deformities involving the zygoma.
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Illustration of the sagittal split ramal osteotomy. Place the horizontal osteotomy superior to the inferior alveolar nerve foramen and continue partially through the body along the oblique line to the region of the second and first molar to complete the vertical osteotomy. Make the osteotomy through the cortex with a reciprocating saw and complete it with an osteotome along the buccal surface.
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Illustration of mandibular excess. The patient underwent bilateral sagittal split ramal osteotomy and mandibular setback.
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Illustration of mandibular deficiency. The patient underwent bilateral sagittal split ramal osteotomy and advancement.
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Illustration of maxillary deficiency with relative mandibular excess. The patient underwent a modified Le Fort I midfacial advancement that included the body of the zygoma.
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Illustration of vertical maxillary excess, apertognathia, and mandibular retrognathia. The patient underwent Le Fort I anterior-posterior differential maxillary impaction with sagittal split ramal osteotomy and mandibular advancement.
Tables
Deformity |
Clinical Features |
Skeletal Assessment |
Dental Assessment |
Maxilla: Sagittal deficiency |
Concave facial profile Retrusive upper lip Acute nasolabial angle Alar base narrow Lack of dental display |
SNA* decreased SNB† normal ANB‡ decreased |
Class III Maxillary dental crowding Maxillary incisors proclined Mandibular incisors normal or retroclined |
Maxilla: Sagittal excess |
Convex facial profile Obtuse nasolabial angle |
SNA increased SNB normal ANB increased |
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Maxilla: Vertical excess (long face syndrome) |
Convex profile Lower facial height increased Alar base constricted Nasolabial angle obtuse Excessive incisor show Excessive gingival show Lip incompetence Mentalis strain with lip closure Chin vertically long, retruded |
Lower FH§ increased SNA decreased SNB decreased ANB increased Mandibular plane angle steep Palatal-occlusal plane increased |
Class II, Class I Anterior open bite Maxillary arch constricted Curve of Spee, flat-accentuated Dental crowding |
Maxilla: Vertical deficiency (short face syndrome) |
Concave facial profile Lower facial height decreased Acute nasolabial angle Alar base widened Lack of incisor show Edentulous appearance Chin protruded |
Lower FH decreased SNB increased ANB negative Palatal-occlusal plane decreased Mandibular plane angle acute |
Class II, Class I Deep bite Crowding Mandibular dentition Curve of Spee reverse |
Mandible: Deficiency |
Convex profile Retruded chin Everted lower lip Deep labiomental crease Mentalis strain with lip closure |
SNA normal SNB decreased ANB increased Ar-Gn¶ decreased |
Class II Mandibular incisors proclined Maxillary incisors retroclined Curve of Spee accentuated |
Mandible: Excess |
Concave profile Midface appears deficient Lower third broad Lower lip thin |
SNA normal SNB decreased ANB decreased |
Class II Maxillary incisors proclined Mandibular incisors retroclined |
