Oral Radiology Lecture 4 PDF

ORAL RADIOLOGY - II LECTURE 4 EXTRA ORAL RADIOGRAPHY INTRODUCTION Extra-oral radiography are the techniques used to visualize cranium, face (including maxilla and mandible), cervical spine and those areas not fully...

ORAL RADIOLOGY - II LECTURE 4 EXTRA ORAL RADIOGRAPHY INTRODUCTION Extra-oral radiography are the techniques used to visualize cranium, face (including maxilla and mandible), cervical spine and those areas not fully covered by intraoral radiographs. These include the lateral cephalometric projection of the sagittal or median plane; the submentovertex (SMV) projection of the transverse or horizontal plane; and the Waters, posteroanterior (PA) cephalometric, and reverse-Towne projections of the coronal or frontal plane. In extra oral radiography, both the x-ray source and the image receptor are outside the oral cavity. Uses of extraoral radiographs: 1. To evaluate larger areas of maxillofacial/ craniofacial region. 2. To evaluate growth and development 3. To evaluate impacted teeth 4. To evaluate traumatic injuries to the skull 5. To evaluate TMJ 6. To assess airway and paranasal sinuses 7. In pre and post treatment evaluation. Equipments  Skull Xray Unit – used for conventional extraoral projections  Panoramic xray machine with cephalostat  Film - Conventional film or digital sensors  Extraoral films comes in variety of sizes – 5x7, 8x10.  Radiographic grid - Grids reduce scattered radiation and improve contrast and resolution, but they result in higher patient exposure. These are made of thin lead strips embedded in a plastic material. Grids are placed between patient’s head and film, and effectively remove scatter radiation. Cephalometry does not require the use of grids. Dr. Mohammed Nishan PA SKULL - POSTERO-ANTERIOR CEPHALOMETRIC PROJECTION Indications The main clinical indications include:  Investigation of the frontal sinuses  Evaluation of facial asymmetry Conditions affecting the cranium, particularly: 1. Paget’s disease of bone 2. Multiple myeloma 3. Hyperparathyroidism 4. Intracranial calcification. Technique and positioning 1. The patient is positioned facing the image receptor with the head tipped forwards so that the forehead and tip of the nose touch the image receptor – the so-called forehead–nose position. 2. The X-ray tubehead is positioned with the central ray horizontal (0°) centered through the occiput LATERAL SKULL – LATERAL CEPHALOGRAM PROJECTION Indications Dr. Mohammed Nishan  Orthodontics – initial diagnosis and evaluation of skeletal and soft tissue abnormalities. Treatment planning. Fractures of the cranium and the cranial base Middle third facial fractures Investigation of the frontal, sphenoidal and maxillary sinuses Tumour of the pituitary gland Conditions affecting the skull vault, particularly: Paget’s disease of bone Multiple myeloma Hyperparathyroidism Technique and positioning 1. The patient is positioned with the head turned through 90°, so the side of the face touches the image receptor. In this position, the sagittal plane of the head is parallel to the image receptor. 2. The X-ray tubehead is positioned with the central ray horizontal (0°) and perpendicular to the sagittal plane and the image receptor, centred through the external auditory meatus. SUBMENTOVERTEX PROJECTION Indication Investigation of the sphenoidal sinus Assessment of the thickness (mediolateral) of the posterior part of the mandible before osteotomy Fracture of the zygomatic arches – to show these thin bones the submentovertex is taken with reduced exposure factors Dr. Mohammed Nishan  Investigating the skull base Technique and Positioning 1. The patient is positioned facing away from the image receptor. The head is tipped backwards as far as is possible, so the vertex of the skull touches the image receptor. 2. 2. The X-ray tubehead is aimed upwards from below the chin, with the central ray at 5° to the horizontal, centred on an imaginary line joining the lower first molars Contraindicated in patients with suspected neck injuries WATERS PROJECTION Indication Detecting the following middle third facial fractures:  Le Fort I, Le Fort II and Le Fort III  Zygomatic complex  Naso-ethmoidal complex  Orbital blow-out  Coronoid process fractures  Investigation of the sinuses – maxillary, frontal and ethmoidal sinuses  Investigation of the sphenoidal sinus (projection needs to be taken with the patient’s mouth open) Technique and Positioning 1. The patient is positioned facing the image receptor with the head tipped back so the radiographic baseline is at 45° to the image receptor, the so-called nose–chin position. This positioning drops the dense bones of the base of the skull downwards and raises the facial bones so they can be seen. 2. The X-ray tube head is positioned with the central ray horizontal (0°) centred through the occiput. Dr. Mohammed Nishan REVERSE TOWNE PROJECTION Indications High fractures of the condylar necks. Intracapsular fractures of the temporomandibular joint. Investigation of the quality of the articular surfaces of the condylar heads in temporomandibular joint disorders. Condylar hypoplasia or hyperplasia Technique and Positioning 1. The patient is in the PA position, i.e. the head tipped forwards in the forehead–nose position, but in addition the mouth is open. 2. The X-ray tube head is aimed upwards from below the occiput, with the central ray at 30° to the horizontal, centered through the condyle. OBLIQUE LATERALS Dr. Mohammed Nishan Indications  Assessment of the presence and/or position of unerupted teeth  Detection of fractures of the mandible  Evaluation of lesions or conditions affecting the jaws including cysts, tumors, giant cell lesions, and other bone lesions  As an alternative when intraoral views are unobtainable because of severe gagging or if the patient is unable to open the mouth or is undergoing general anaesthesia  As specific views of the salivary glands or temporomandibular joints. OTHER EXTRA ORAL PROJECTIONS FOR TMJ TRANSCRANIAL PROJECTION – LINDBLOM TECHNIQUE – Useful for central and medial surface of the condyle TRANSPHARYNGEAL PROJECTION – also called Parma / MacQueen – Dell / infracranial projection – was intended for a gross view of the condyle. TRANS-ORBITAL PROJECTION – also called Zimmer/ transmaxillary projection Dr. Mohammed Nishan MAXILLOFACIAL REGION OF INTEREST AND THE CORRESPONDING EXTRA ORAL PROJECTIONS IS SUMMARISED AS UNDER Dr. Mohammed Nishan SUMMARY OF VARIOUS EXTRAORAL PROJECTIONS, TECHNIQUE, POSITION OF THE RECEPTOR AND DIRECTION OF THE XRAY SOURCE Dr. Mohammed Nishan