Cephalometric Radiography 3j3p2i
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Cephalometric radiography
Cephalometric radiography is a standardized and reproducible form of skull radiography used extensively in orthodontics to assess the relationships of the teeth to the jaws and the jaws to the rest of the facial skeleton. Standardization was essential for the development of cephalometry — the measurement and comparison of specific points, distances and lines within the facial skeleton, which is now an integral part of orthodontic assessment. The greatest value is probably obtained from these radiographs if they are traced or digitized and this is essential when they are being used for the monitoring of treatment progress.
Main indications The main clinical indications can be considered under two major headings — orthodontics and orthognathic surgery.
Ch. 6). Indications and selection criteria for Cephalometric radiographs are clearly identified in the Faculty of General Dental Practitioners Selection Criteria in Dental Radiography booklet published in the UK in 1998 and in the British Orthodontic Society's booklet Guidelines for the Use of Radiographs in Clinical Orthodontics, published in the UK in 2001. These guidelines are designed to assist in the justification process so as to avoid the use of unnecessary radiographs. Orthognathic surgery • Preoperative evaluation of skeletal and soft tissue patterns • To assist in treatment planning • Postoperative appraisal of the results of surgery and long-term follow-up studies.
Equipment Orthodontics • Initial diagnosis — confirmation of the underlying skeletal and/or soft tissue abnormalities • Treatment planning • Monitoring treatment progress, e.g. to assess anchorage requirements and incisor inclination • Appraisal of treatment results, e.g. 1 or 2 months before the completion of active treatment to ensure that treatment targets have been met and to allow planning of retention. When considering these indications, it should be ed that all radiographs must be clinically justified under current legislation (see
Several different types of equipment are available for Cephalometric radiography, either as separate units, or as additional attachments to dental panoramic units. In some equipment, the patients are seated, while in others they remain standing. Despite these variables the essential requirements for this type of equipment are the same and include: • Cephalostat (or craniostaf) (see Fi| 13.1) comprising: Head positioning and stabilizing apparatus with ear rods to ensure a standardized patient position (some units also have infraorbital guide rods) 145
146
Essentials of dental radiography and radiology
Fig. 13.1 A typical cephalostat (craniostat) containing a patient with the main features indicated. Note that this design of cephalostat has the aluminium wedge filter positioned between the patient and the anti-scatter grid. The Frankfort plane is marked on the patient's face.
— Fixed anti-scatter grid — to stop photons scattered within the patient reaching the film and degrading the final image (see Ch. 12) — Cassette holder. Cassette (usually 18 x 24 cm) containing intensifying screens and indirect-action film Aluminium wedge filter. This is either part of the cephalostat and positioned between the patient and the anterior part of the cassette, as shown in Figure 13.1, or it is attached to the tubehead, covering the anterior part of the emerging beam. Its function is to attenuate the X-ray beam selectively in the region of the facial soft tissues because these tissues are not dense enough on their own to produce a visible radiographic shadow. This added attenuation enables the soft tissue profile to be seen on the final radiograph.
• X-ray generating apparatus that should be: — In a fixed position relative to the cephalostat (approx. 2 m) and the film (see Fig. 13.2) so that successive radiographs are reproducible and comparable — Capable of producing an X-ray beam that is: * Sufficiently penetrating to reach the film * Parallel in nature to minimize magnification between R and L sides of the mandible and to ensure that the midline points S, N and A are as sharp as possible * Collimated to an approximately triangular shape to restrict the area of the patient irradiated to the required cranial base and facial skeleton, so avoiding the skull vault and cervical spine (see Figs 13.2 and 13.3).
Cephalometric radiography
147
Main radiographic projections These include: • True cephalometric lateral skull • Cephalometric postero-anterior of the jaws (PA jaws).
True cephalometric lateral skull As stated in Chapter 11, the terminology used to describe lateral skull projections is somewhat confusing, the adjective true, as opposed to oblique., being used to describe lateral skull projections when:
• The film is parallel to the sagittal plane of the patient's head • The X-ray beam is perpendicular to film and sagittal plane. In addition, the word cephalometric should be included when describing the true lateral skull radiograph taken in the cephalostat. This enables differentiation from the non-standardized true lateral skull projection taken in a skull unit, as described in Chapter 12. It is now an accepted convention to view orthodontic lateral skull radiographs with the patient facing to the right, as shown in Figure 13.3.
B Fig. 13.2A Positioning for the true cephalometric lateral skull projection. Note the X-ray tubehead and cephalostat are in fixed positions (approximately 2 m apart) and the patient's head is stabilized within the cephalostat with the Frankfort plane horizontal. The triangular collimator (C) is indicated by the arrow. B Diagram of the positioning from the front — the sagittal plane of the head is parallel to the film, and the X-ray beam is horizontal and perpendicular to the sagittal plane and the film.
148
Essentials of dental radiography and radiology
Fig. 13.3 An example of a true cephalometric lateral skull radiograph. Note the images of the ear rods should ideally appear superimposed on one another. The various shadows of the cephalostat equipment and the collimator are indicated.
Technique and positioning
This can be summarized as follows: 1. The patient is positioned within the cephalostat, with the sagittal plane of the head vertical and parallel to the film and with the Frankfort plane horizontal. The teeth should generally be in maximum intercuspation. 2. The head is immobilized carefully within the apparatus with the plastic e-ar rods being inserted gradually into the external auditory meati.
3. The aluminium wedge is positioned to cover the anterior part of the film. 4. The equipment is designed to ensure that when the patient is positioned correctly, the X-ray beam is horizontal and centred on the ear rods (see Fig. 13.2).
Cephalometric radiography
149
Cephalometric tracing /digitizing This produces a diagrammatic representation of certain anatomical points or landmarks evident on the lateral skull radiograph (see Fig. 13.4). These points are traced on to an overlying sheet of paper or acetate or digitally recorded. Either method allows precise measurements to be made. As a basic system these could include: • The outline and inclination of the anterior teeth • The positional relationship of the mandibular and maxillary dental bases to the cranial base • The positional relationship of the dental bases to one another, i.e. the skeletal patterns • The relationship between the bones of the skull and the soft tissues of the face. Main Cephalometric points The definitions of the main Cephalometric points (as indicated in a clockwise direction on the tracing shown in Fig. 13.4) include: Sella (S). The centre of the sella turcica, (determined by inspection). Orbitale (Or). The lowest point on the infraorbital margin. Nasion (N). The most anterior point on the frontonasal suture. Anterior nasal spine (ANS). The tip of the anterior nasal spine. Subspinale or point A. The deepest midline point between the anterior nasal spine and prosthion. Prosthion (Pr). The most anterior point of the alveolar crest in the premaxilla, usually between the upper central incisors. Infradentale (Id). The most anterior point of the alveolar crest, situated between the lower central incisors. Supramentale or point B. The deepest point in the bony outline between the infradentale and the pogonion. Pogonion (Pog). The most anterior point of the bony chin.
Fig. 13.4 A Cephalometric tracing of a lateral skull radiograph showing the main Cephalometric points.
Gnathion (Gn). The most anterior and inferior point on the bony outline of the chin, situated equidistant from pogonion and menton. Menton (Me). The lowest point on the bony outline of the mandibular symphysis. Gonion (Go). The most lateral external point at the junction of the horizontal and ascending rami of the mandible. Note: The gonion is found by bisecting the angle formed by tangents to the posterior and inferior borders of the mandible. Posterior nasal spine (PNS). The tip of the posterior spine of the palatine bone in the hard palate. Articulare (Ar). The point of intersection of the dorsal contours of the posterior border of the mandible and temporal bone. Porion (Po). The uppermost point of the bony external auditory meatus, usually regarded as coincidental with the uppermost point of the ear rods of the cephalostat.
150
Essentials of dental radiography and radiology
Fig. 13.5 A cephalometric tracing of a lateral skull radiograph showing the main cephalometric planes and angles.
Main cephalometric planes and angles The definitions of the main cephalometric planes and angles shown in Figure 13.5 include: Frankfort plane. A transverse plane through the skull represented by the line ing porion and orbitale. Mandibular plane. A transverse plane through the skull representing the lower border of the horizontal ramus of the mandible. There are several definitions: • A tangent to the lower border of the mandible • A line ing gnathion and gonion • A line ing menton and gonion. Maxillary plane. A transverse plane through the skull represented by a ing of the anterior and posterior nasal spines. SNplane. A transverse plane through the skull represented by the line ing sella and nasion.
SNA. Relates the anteroposterior position of the maxilla, as represented by the A point, to the cranial base. SNB. Relates the anteroposterior position of the mandible, as represented by the B point, to the cranial base. ANB. Relates the anteroposterior position of the maxilla to the mandible, i.e. indicates the anteroposterior skeletal pattern — Class I, II or III. Maxillary incisal inclination. The angle between the long axis of the maxillary incisors and the maxillary plane. Mandibular incisal inclination. The angle between the long axis of the mandibular incisors and the mandibular plane. All the definitions are those specified in The British Standards Glossary of Dental (BS4492: 1983).
Cephalometric radiography
151
Cephalometric postero-anterior of the jaws (PA jaws)
Technique and positioning
This projection is identical to the PA view of the jaws described in Chapter 12, except that it is standardized and reproducible. This makes it suitable for the assessment of facial asymmetries and for preoperative and postoperative comparisons in orthognathic surgery involving the mandible.
1. The head-stabilizing apparatus of the cephalostat is rotated through 90°. 2. The patient is positioned in the apparatus with the head tipped forwards and with the radiographic baseline horizontal and perpendicular to the film, i.e. in the forehead-nose position. 3. The head is immobilized within the apparatus by inserting the plastic ear rods into the external auditory meati. 4. The fixed X-ray beam is horizontal with the central ray centred through the cervical spine at the level of the rami of the mandible (see Fig. 13.6).
This can be summarized as follows:
Fig. 13.7 An example of a cephalometric PA jaws radiograph. The arrows indicate the position of the ear rods.
B
Fig. 13.6A Positioning for the cephalometric PA jaws projection. The patient is in the forehead—nose position, with the radiographic baseline (marked on the face) horizontal and perpendicular to the film. B Diagram of the patient positioning and showing the X-ray beam horizontal and centred through the rami.
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Cephalometric radiography
Cephalometric radiography is a standardized and reproducible form of skull radiography used extensively in orthodontics to assess the relationships of the teeth to the jaws and the jaws to the rest of the facial skeleton. Standardization was essential for the development of cephalometry — the measurement and comparison of specific points, distances and lines within the facial skeleton, which is now an integral part of orthodontic assessment. The greatest value is probably obtained from these radiographs if they are traced or digitized and this is essential when they are being used for the monitoring of treatment progress.
Main indications The main clinical indications can be considered under two major headings — orthodontics and orthognathic surgery.
Ch. 6). Indications and selection criteria for Cephalometric radiographs are clearly identified in the Faculty of General Dental Practitioners Selection Criteria in Dental Radiography booklet published in the UK in 1998 and in the British Orthodontic Society's booklet Guidelines for the Use of Radiographs in Clinical Orthodontics, published in the UK in 2001. These guidelines are designed to assist in the justification process so as to avoid the use of unnecessary radiographs. Orthognathic surgery • Preoperative evaluation of skeletal and soft tissue patterns • To assist in treatment planning • Postoperative appraisal of the results of surgery and long-term follow-up studies.
Equipment Orthodontics • Initial diagnosis — confirmation of the underlying skeletal and/or soft tissue abnormalities • Treatment planning • Monitoring treatment progress, e.g. to assess anchorage requirements and incisor inclination • Appraisal of treatment results, e.g. 1 or 2 months before the completion of active treatment to ensure that treatment targets have been met and to allow planning of retention. When considering these indications, it should be ed that all radiographs must be clinically justified under current legislation (see
Several different types of equipment are available for Cephalometric radiography, either as separate units, or as additional attachments to dental panoramic units. In some equipment, the patients are seated, while in others they remain standing. Despite these variables the essential requirements for this type of equipment are the same and include: • Cephalostat (or craniostaf) (see Fi| 13.1) comprising: Head positioning and stabilizing apparatus with ear rods to ensure a standardized patient position (some units also have infraorbital guide rods) 145
146
Essentials of dental radiography and radiology
Fig. 13.1 A typical cephalostat (craniostat) containing a patient with the main features indicated. Note that this design of cephalostat has the aluminium wedge filter positioned between the patient and the anti-scatter grid. The Frankfort plane is marked on the patient's face.
— Fixed anti-scatter grid — to stop photons scattered within the patient reaching the film and degrading the final image (see Ch. 12) — Cassette holder. Cassette (usually 18 x 24 cm) containing intensifying screens and indirect-action film Aluminium wedge filter. This is either part of the cephalostat and positioned between the patient and the anterior part of the cassette, as shown in Figure 13.1, or it is attached to the tubehead, covering the anterior part of the emerging beam. Its function is to attenuate the X-ray beam selectively in the region of the facial soft tissues because these tissues are not dense enough on their own to produce a visible radiographic shadow. This added attenuation enables the soft tissue profile to be seen on the final radiograph.
• X-ray generating apparatus that should be: — In a fixed position relative to the cephalostat (approx. 2 m) and the film (see Fig. 13.2) so that successive radiographs are reproducible and comparable — Capable of producing an X-ray beam that is: * Sufficiently penetrating to reach the film * Parallel in nature to minimize magnification between R and L sides of the mandible and to ensure that the midline points S, N and A are as sharp as possible * Collimated to an approximately triangular shape to restrict the area of the patient irradiated to the required cranial base and facial skeleton, so avoiding the skull vault and cervical spine (see Figs 13.2 and 13.3).
Cephalometric radiography
147
Main radiographic projections These include: • True cephalometric lateral skull • Cephalometric postero-anterior of the jaws (PA jaws).
True cephalometric lateral skull As stated in Chapter 11, the terminology used to describe lateral skull projections is somewhat confusing, the adjective true, as opposed to oblique., being used to describe lateral skull projections when:
• The film is parallel to the sagittal plane of the patient's head • The X-ray beam is perpendicular to film and sagittal plane. In addition, the word cephalometric should be included when describing the true lateral skull radiograph taken in the cephalostat. This enables differentiation from the non-standardized true lateral skull projection taken in a skull unit, as described in Chapter 12. It is now an accepted convention to view orthodontic lateral skull radiographs with the patient facing to the right, as shown in Figure 13.3.
B Fig. 13.2A Positioning for the true cephalometric lateral skull projection. Note the X-ray tubehead and cephalostat are in fixed positions (approximately 2 m apart) and the patient's head is stabilized within the cephalostat with the Frankfort plane horizontal. The triangular collimator (C) is indicated by the arrow. B Diagram of the positioning from the front — the sagittal plane of the head is parallel to the film, and the X-ray beam is horizontal and perpendicular to the sagittal plane and the film.
148
Essentials of dental radiography and radiology
Fig. 13.3 An example of a true cephalometric lateral skull radiograph. Note the images of the ear rods should ideally appear superimposed on one another. The various shadows of the cephalostat equipment and the collimator are indicated.
Technique and positioning
This can be summarized as follows: 1. The patient is positioned within the cephalostat, with the sagittal plane of the head vertical and parallel to the film and with the Frankfort plane horizontal. The teeth should generally be in maximum intercuspation. 2. The head is immobilized carefully within the apparatus with the plastic e-ar rods being inserted gradually into the external auditory meati.
3. The aluminium wedge is positioned to cover the anterior part of the film. 4. The equipment is designed to ensure that when the patient is positioned correctly, the X-ray beam is horizontal and centred on the ear rods (see Fig. 13.2).
Cephalometric radiography
149
Cephalometric tracing /digitizing This produces a diagrammatic representation of certain anatomical points or landmarks evident on the lateral skull radiograph (see Fig. 13.4). These points are traced on to an overlying sheet of paper or acetate or digitally recorded. Either method allows precise measurements to be made. As a basic system these could include: • The outline and inclination of the anterior teeth • The positional relationship of the mandibular and maxillary dental bases to the cranial base • The positional relationship of the dental bases to one another, i.e. the skeletal patterns • The relationship between the bones of the skull and the soft tissues of the face. Main Cephalometric points The definitions of the main Cephalometric points (as indicated in a clockwise direction on the tracing shown in Fig. 13.4) include: Sella (S). The centre of the sella turcica, (determined by inspection). Orbitale (Or). The lowest point on the infraorbital margin. Nasion (N). The most anterior point on the frontonasal suture. Anterior nasal spine (ANS). The tip of the anterior nasal spine. Subspinale or point A. The deepest midline point between the anterior nasal spine and prosthion. Prosthion (Pr). The most anterior point of the alveolar crest in the premaxilla, usually between the upper central incisors. Infradentale (Id). The most anterior point of the alveolar crest, situated between the lower central incisors. Supramentale or point B. The deepest point in the bony outline between the infradentale and the pogonion. Pogonion (Pog). The most anterior point of the bony chin.
Fig. 13.4 A Cephalometric tracing of a lateral skull radiograph showing the main Cephalometric points.
Gnathion (Gn). The most anterior and inferior point on the bony outline of the chin, situated equidistant from pogonion and menton. Menton (Me). The lowest point on the bony outline of the mandibular symphysis. Gonion (Go). The most lateral external point at the junction of the horizontal and ascending rami of the mandible. Note: The gonion is found by bisecting the angle formed by tangents to the posterior and inferior borders of the mandible. Posterior nasal spine (PNS). The tip of the posterior spine of the palatine bone in the hard palate. Articulare (Ar). The point of intersection of the dorsal contours of the posterior border of the mandible and temporal bone. Porion (Po). The uppermost point of the bony external auditory meatus, usually regarded as coincidental with the uppermost point of the ear rods of the cephalostat.
150
Essentials of dental radiography and radiology
Fig. 13.5 A cephalometric tracing of a lateral skull radiograph showing the main cephalometric planes and angles.
Main cephalometric planes and angles The definitions of the main cephalometric planes and angles shown in Figure 13.5 include: Frankfort plane. A transverse plane through the skull represented by the line ing porion and orbitale. Mandibular plane. A transverse plane through the skull representing the lower border of the horizontal ramus of the mandible. There are several definitions: • A tangent to the lower border of the mandible • A line ing gnathion and gonion • A line ing menton and gonion. Maxillary plane. A transverse plane through the skull represented by a ing of the anterior and posterior nasal spines. SNplane. A transverse plane through the skull represented by the line ing sella and nasion.
SNA. Relates the anteroposterior position of the maxilla, as represented by the A point, to the cranial base. SNB. Relates the anteroposterior position of the mandible, as represented by the B point, to the cranial base. ANB. Relates the anteroposterior position of the maxilla to the mandible, i.e. indicates the anteroposterior skeletal pattern — Class I, II or III. Maxillary incisal inclination. The angle between the long axis of the maxillary incisors and the maxillary plane. Mandibular incisal inclination. The angle between the long axis of the mandibular incisors and the mandibular plane. All the definitions are those specified in The British Standards Glossary of Dental (BS4492: 1983).
Cephalometric radiography
151
Cephalometric postero-anterior of the jaws (PA jaws)
Technique and positioning
This projection is identical to the PA view of the jaws described in Chapter 12, except that it is standardized and reproducible. This makes it suitable for the assessment of facial asymmetries and for preoperative and postoperative comparisons in orthognathic surgery involving the mandible.
1. The head-stabilizing apparatus of the cephalostat is rotated through 90°. 2. The patient is positioned in the apparatus with the head tipped forwards and with the radiographic baseline horizontal and perpendicular to the film, i.e. in the forehead-nose position. 3. The head is immobilized within the apparatus by inserting the plastic ear rods into the external auditory meati. 4. The fixed X-ray beam is horizontal with the central ray centred through the cervical spine at the level of the rami of the mandible (see Fig. 13.6).
This can be summarized as follows:
Fig. 13.7 An example of a cephalometric PA jaws radiograph. The arrows indicate the position of the ear rods.
B
Fig. 13.6A Positioning for the cephalometric PA jaws projection. The patient is in the forehead—nose position, with the radiographic baseline (marked on the face) horizontal and perpendicular to the film. B Diagram of the patient positioning and showing the X-ray beam horizontal and centred through the rami.
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