Dental Radiographs Dental Assistant Registration Course Click the play (arrow) button to advance to the next slide.

X-Ray Techniques A variety of techniques were discovered in an effort to capture dental x-rays. In 1905, Dr. Howard Robert and A. Cieszykski developed the bisecting technique, in which isometry is employed. The parallel technique, developed by Frank McCormack in 1920, used the right angle technique to expose dental x- rays. The panoramic technique was discovered in 1959 by a team of doctors and Dr. Paatero was credited with developing the first unit to capture an x-ray of the entire dental arch on one film. Currently, mouth structures can be visualized using tomography in which certain planes are selected for view.

Extraoral Radiographs Panoramic Common in general and specialty offices Cephalometric Common with orthodontists Digital Becoming standard Easier for the staff

Panoramic Radiography Tomography shows the imaging of one layer or section of the body while blurring images from other areas. Rotational centers include a tubehead that rotates around the patient while the cassette that holds the x-ray rotates in the opposite direction. Conforms to the dental arches. The focal trough is the three dimensional curved zone in which the dental arches are positioned to achieve the sharpest image possible.

Panoramic Radiography Exposure controls Located outside the x-ray room. Manufacturers determine the exposure time; see manual. Head positioner Lateral head supports or guides, chin rest, notched bite block, and forehead rest. Some have handles for the patient to hold on to. X-ray tubehead Similar to an internal x-ray tubehead, although the collimator is different; narrow verticals slit instead of round/rectangular Patient receives minimum radiation exposure due to small slit Cassette holder Flat, hard containers that open on back or flexible, thin sleeves that open on one end (to prevent light entering) Lined with intensifying screens

Panoramic Technique Lead apron without a thyroid collar because the collar interferes with the image and because the x- ray beam is directed upward, the exposure is minimal. Explaining the procedure to the patient can help with nervousness and not knowing what to expect. The patients must remove jewelry, hair clips, and bulky sweaters. Patient must be still for the machine to accurately reflect data. This procedure is done by the dental assistant at the directions of the dentist.

Cephalometric Radiographs Mainly used by orthodontists to plan treatment for their patients, although some oral maxillofacial surgeons and general practitioners include these radiographs for patient assessment

Film Exposures The periapical radiograph shows the entire tooth and surrounding structures. The bite-wing radiograph shows the crowns, interproximal spaces, and the crest of the alveolar bone. Occlusal radiographs picture large areas of the mandible and maxilla.

Bisecting Technique The bisecting technique is used to expose periapical, bite-wing or occlusal radiographs. To expose a quality film using this technique the patient’s hard must be correctly positioned, the film must be placed as close as possible to the lingual surface, and the vertical angulation must be appropriately set. This is generally not the technique of choice as it may cause distortion and guesswork.

Full Mouth Survey This consists of a number of periapical and bite-wing radiographs to collectively display all teeth and surrounding structures. The dental assistant should form a consistent sequence or routine for exposing these films to avoid double exposure of the patient.

Bite-wing series These are typically used for caries detection and are taken at six to twelve month intervals. The film is usually placed in the horizontal position, but may also be placed vertically if the dentist wants to see more of the root of the tooth.

Special Radiographs Occlusal radiographs are used in children and patients who have difficulty opening the mouth or controlling muscular movement. The two techniques used for obtaining occlusal radiographs are the topographic technique and the cross-section technique. Pediatric radiographs are an important part of maintaining oral health in children and are used to detect caries and various other anomalies. Care must be taken not to overexpose children to radiation.

Special Radiographs Radiographs are taken of edentulous patients to show cysts, impacted teeth, retained root tips, or other pathological conditions. Radiographs may be taken during endodontic procedures to assess the progress of the procedure and to take necessary measurements. The dental assistant must be able to adapt radiographic techniques for patients who have special needs, such as those in wheelchairs, those who may be deaf, or those with physical impairments.

Radiographic Interpretation It is important to be familiar with the terminology used in radiographic interpretation; the dental assistant will be prepared and perform better. Anatomical landmarks – assist in identifying abnormal areas for mounting x-rays so that good communication can exist. Radiopaque/Radiolucent – structures that are dense and do not allow x-rays to pass through them (light gray to white shades). Diagnosis – structures that are not dense (dark gray to black). Interpretation – explain the meaning of something. Superimposition – one structure lying over another.

Tooth and Surrounding Structures Parts of the tooth and surrounding structures: Enamel – radiopaque area on crown. Dentin – area just inferior to the enamel; less radiopaque than enamel. Cementum – radiopaque like dentin; thin covering on the roots. Pulp chamber – radiolucent area surrounded by dentin; pulp horns can be seen.

Tooth and Surrounding Structures Pulp canals or root canals – radiolucent areas in the root; extend from pulp chamber to apex. Periodontal ligament/space – radiolucent area that surrounds the roots. Lamina dura – radiopaque line of cortical bone that surrounds the roots. Cortical plate – dense compact bone that forms the tooth socket.

Mandibular Landmarks Mental foramen – radiolucent area between the roots of the premolar. Mandibular canal – radiolucent but it is outlined by radiopaque lines that extend between foramens. External oblique ridge – oblique line found on the external surface of the mandible from the middle of the rami to beyond molars. Trabucular patterns – spongy/cancellous bone that surrounds the teeth and forms the mandible. Alveolar crest - compact edge of cortical bone that shows as radiopaque between teeth. Mandibular retromolar area – behind the last mandibular molar; shows varying tissues in this triangular space.

Mandibular Landmarks Internal oblique ridge – bone on the mylohyoid ridge internal surface of the mandible that runs from the middle of the rami to third molar region; sometimes continues past molars to cuspids and is known as the mylohyoid ridge and show superimposed over the root area. Mandibular foramen – radiolucent area in the middle of the ramus of the mandible on the interior surface. Condyle – back projection on top of the ramus; shows radiopaque and is articulated in the glenoid fossa. Coronoid process – front projection of tip of ramus; shows radiopaque. Medial sigmoid notch – indented area between condyle and coronoid processes on the ramus; also known as the coronoid notch or the mandibular notch.

Mandibular Landmarks Lingual foramen – radiolucent area on lingual surface of the mandible at midline/symphysis. Genial tubercle – raised areas of bone that surround lingual foramen Ramus – section of each side of mandible that runs vertically. Body of mandible – section that runs horizontally. Border of the mandible – lower edge of body of the mandible that is made of compact bone. Symphysis – “chin” area; anterior portion of the mandible. Hyoid bone – “U” shaped bone suspended by ligaments below the mandible but anterior to the larynx; occasionally seen on dental x-rays. Nutrient canals – radiolucent paths that extend toward the alveolar crest.

Maxillary Landmarks Hard plate – radiopaque structure that forms roof of mouth. Incisive foramen – radiolucent area at midline of palate behind central incisors. Maxillary suture – aka median palatine suture – radiolucent line joining right and left halves of maxillary bone and palatine bones. Zygomatic process – process on external surface beginning around the first molar region. Malar – part of zygomatic bone that forms the cheek. Nasal septum – radiopaque line that divides the nasal fossae. Nasal cavities – two side by side openings of the nose. Nasal conchae – bony, scroll-shaped plates in the lateral walls of the nasal cavity. Maxillary sinuses – left and right cavities above apices of the teeth, can extend from canines to molars.

Maxillary Landmarks Intraorbital foramen – radiolucent area below the inferior border of eye sockets. Maxillary tuberosity – radiopaque area behind most posterior molar on the maxilla. Glenoid fossa – depression on the lower border of temporal bone where the condyloid process of the mandible articulates as temporomandibular joint. Mastoid process – temporal bone that lies in the lower, anterior section just behind the ear canal.

Maxillary Landmarks External auditory meatus – radiolucent area in the temporal bone for auditory canal. Hamular process – slender projection of the bone that lies behind medial to the maxillary tuberosity. Styloid process – projection of bone, larger than hamular process, which comes from the temporal bone and lies behind the glenoid fossa.

Producing Quality Radiographs All appropriate barriers should be placed on the chair and radiographic equipment prior to seating the patient. Materials needed for the exposure should also be set up. DA should be wearing appropriate PPE during exposure. Seat the patient comfortably and place the lead apron and thyroid collar on the patient. Position the tubehead. Place the exposed film into a paper cup. Take the lead apron from the patient and dismiss the patient to the treatment room. Make necessary notations in the patient’s chart, remove barriers and clean the equipment

References Dental Assisting: A Comprehensive Approach, Phinney, D.J., Halstead, J.H. (3rd. Ed.) Thomson /Delmar Learning,2008 Dental Radiography: Principles & Techniques, 3rd Ed; Iannucci & Howerton, Elsevier, St. Louis, 2006