8. Cephalometric Radiography.pptx

Cephalometric Radiography, a branch of extraoral dental Radiography.

1. Cephalometric Radiography PRESENTED BY GROUP M; Faith surtan Kituzi Mshindi Euro undisa

2. CEPHALOMETRICS Faith Surtan

3. INTRODUCTION A scientific approach to the scrutiny of human craniofacial patterns was first initiated by anthropologists and anatomists who recorded the various dimensions of ancient dry skulls. The measurement of the dry skull from osteological landmarks called craniometry , was then applied to living subjects so that a longitudinal growth study could be undertaken. Since the measurements were taken through skin and soft tissue coverage, their accuracy was questionable. By the discovery of X-rays by Roentgen in 1895, a radiographic head image could be measured in two dimensions, thereby making possible the accurate study of craniofacial growth and development. The credit of bringing the X – rays to the field of dentistry is given to C. Edmund Kells . Soon after Roentgen announced his discovery in December 1895, Kells went to work to make the capabilities of the X-ray available to the dental profession and thereby forever changed the way dentistry would be practiced. The measurement of head from the shadows of bony and soft tissue land marks on the radiographic image became known as roentgenographic cephalometry.

4. Cephalometrics Definition ‘ cephalo ’ means head and ‘metric’ means measurement. Measurement of the shadows of the bony and soft tissue landmark on the radiographic image is known as roentgenographic cephalometry

5. Types of cephalograms Lateral cephalogram ; provides lateral view of skull. Frontal or anteroposterior cephalogram ; provides anteroposterior view of skull. Oblique cephalogram

6. Uses of cephalograms Orthodontic diagnosis to elucidate the skeletal, dental and soft tissue relationships of the craniofacial region. Identification and classification of skeletal and dental anomalies. Estimating the facial type. Quantify the changes brought about by the treatment.

7. Distinguish changes produced by natural growth and orthodonthic treatment. Assessment of growth of facial skeleton through serial cephalograms . Growth prediction. Plan the skeletal repositioning in surgical orthodonthics

8. Advantages of cephalograms Functional analysis. Tangible records that are relatively permanent Relatively non-destructive and non-invasive producing a high yield of information at relatively low physiologic cost. Easy to store, transport and reproduce.

9. Limitation and drawbacks Patient is exposed to ionizing radiation which is harmful. The processes of image acquisition as well as measurement procedures are not well standardized. The difficulty in locating landmarks and surfaces on the X-ray image as the image lacks hard edges and defined outlines. The structures being imaged are three dimensional whereas the radiographic image is two dimensional.

10. Limitation and drawbacks Anatomical structures lying at different planes within the head undergo projective displacement. Patient is positioned with the ear rods in the external acoustic meatus. (The operator assumes that the meatuses are symmetrical. It need not be so.) Patient is made to bite in maximum intercuspation while taking the cephalogram . (There could be a mandibular shift from centric relation.) A cephalometric analysis makes us of means obtained from different population samples .( They have only limited relevance when applied to individual patient.)

11. Equipment Several different types of equipment are available for cephalometric radiography, either as separate units, or as additional attachments to panoramic units. In some equipment the patients are seated, while in others they remain standing. Traditional equipment was designed to use indirect-action radiographic film in an extraoral cassette as the image receptor. The advent of digital imaging, using phosphor plates and solid-state sensors, has seen the development of new dedicated digital equipment. The basic components of these different types of equipment are described below. Traditional film-based equipment This either consists of an additional attachment to a panoramic unit or as a completely separate dedicated unit. The basic components include:

12.   X-ray generating apparatus  that should: – Be in a fixed position relative to the cephalostat and film so that successive radiographs are reproducible and comparable. To minimize the effect of magnification the focus-to-film distance should be greater than 1 m and ideally in the range 1.5–1.8 m . – Include a light beam diaphragm to facilitate the collimation. The beam should be 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 and thyroid gland. – Be capable of producing an X-ray beam that is sufficiently penetrating to reach the film and parallel in nature.

13. •  Cephalostat  (or  craniostat ) comprising: Head positioning and stabilizing apparatus with ear rods to ensure a standardized patient position. Additional positioning guides can include forehead supports and infraorbital guide rods. – Cassette holder. – Optional fixed anti-scatter grid to stop photons scattered within the patient reaching the film and degrading the image. This is not usually included in combined panoramic/ cephalostat units.

14.   Cassette  (usually 18 × 24 cm) containing rare-earth intensifying screens and indirect action film. Aluminium wedge filter  designed to attenuate the X-ray beam selectively in the region of the facial soft tissues to enable the soft tissue profile to be seen on the final radiograph. This is either attached to the tubehead , covering the anterior part of the beam (the preferred position) or it is included as part of the cephalostat and positioned between the patient and the anterior part of the cassette.

15. Broadent bolton type Uses two x ray sources and two film holders. Lateral and AP cephalograms can be taken without moving the subject. More precise results can be obtained..

16. Highleys Type Uses one x ray source and one film holder Patient is repositioned for various projections.. Less reliable results as there is movement of subject.

17. MAIN RADIOGRAPHIC PROJECTIONS These include: True cephalometric lateral skull Cephalometric posteroanterior of the jaws (PA jaws)

18. True cephalometric lateral skull As stated in the previous topic, 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 image receptor is parallel to the sagittal plane of the patient’s head The X-ray beam is perpendicular to image receptor 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 13. It is now an accepted convention to view orthodontic lateral skull radiographs with the patient facing to the right, as shown in Fig. 14.6.

19. 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 image receptor 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 ear rods being inserted gradually into the external auditory meati . 3. The aluminium wedge, if used, is positioned to cover the anterior part of the image receptor. 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. 14.6

20. Cephalometric tracing/digitizing This produces a diagrammatic representation of certain anatomical points or landmarks These points are traced on to an overlying sheet of paper or acetate or digitally recorded. They allow precise measurements to be made. As a basic system these could include: ● The outline and inclination of 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.

21. Main Cephalometric points The definitions of the main cephalometric points (as indicated in a clockwise direction on the tracing shown in Fig. 14.7) 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 fronto -nasal suture. Anterior nasal spine (ANS) . The tip of the anteriornasal 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 centralincisors . Supramentale or point B. The deepest point in the bony outline between the infradentale and the pogonion.

22. Pogonion ( Pog ). The most anterior point of the bony chin. 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 earrods of the cephalostat .

23. Main cephalometric planes and angles The definitions of the main cephalometric planes and angles shown in Fig. 14.8 include: Frankfort plane. A transverse plane through the skull represented by the line joining 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 joining gnathion and gonion ● A line joining menton and gonion. Maxillary plane. A transverse plane through the skull represented by a joining of the anterior and posterior nasal spines.

24. SN plane . A transverse plane through the skull represented by the line joining 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 antero-posterior 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.

25. CEPHALOMETRIC POSTEROANTERIOR OF THE JAWS (PA JAWS) This projection is identical to the PA view of the jaws described in Skull and maxillofacial radiography, except that it is standardized and reproducible. Suitable for the assessment of facial asymmetries and for preoperative and postoperative comparisons in orthognathic surgery involving the mandible.

26. Technique and positioning This can be summarized as follows: The head-stabilizing apparatus of the cephalostat is rotated through 90°. 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. The head is immobilized within the apparatus by inserting the plastic ear rods into the external auditory meatus 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 Figs 14.9 and 14.10).