Dental radiographs, commonly known as X-rays, are radiographs used to diagnose hidden dental structures, malignant or benign masses, bone loss, and cavities.
A radiographic image is formed by a controlled burst of X-ray radiation which penetrates oral structures at different levels, depending on varying anatomical densities, before striking the film or sensor. Teeth appear lighter because less radiation penetrates them to reach the film. Dental caries, infections and other changes in the bone density, and the periodontal ligament, appear darker because X-rays readily penetrate these less dense structures. Dental restorations (fillings, crowns) may appear lighter or darker, depending on the density of the material.
The dosage of X-ray radiation received by a dental patient is typically small (around 0.150 mSv for a full mouth series), equivalent to a few days' worth of background environmental radiation exposure, or similar to the dose received during a cross-country airplane flight (concentrated into one short burst aimed at a small area). Incidental exposure is further reduced by the use of a lead shield, lead apron, sometimes with a lead thyroid collar. Technician exposure is reduced by stepping out of the room, or behind adequate shielding material, when the X-ray source is activated.
Once photographic film has been exposed to X-ray radiation, it needs to be developed, traditionally using a process where the film is exposed to a series of chemicals in a dark room, as the films are sensitive to normal light. This can be a time-consuming process, and incorrect exposures or mistakes in the development process can necessitate retakes, exposing the patient to additional radiation. Digital X-rays, which replace the film with an electronic sensor, address some of these issues, and are becoming widely used in dentistry as the technology evolves. They may require less radiation and are processed much more quickly than conventional radiographic films, often instantly viewable on a computer. However digital sensors are extremely costly and have historically had poor resolution, though this is much improved in modern sensors.
It is possible for both tooth decay and periodontal disease to be missed during a clinical exam, and radiographic evaluation of the dental and periodontal tissues is a critical segment of the comprehensive oral examination. The photographic montage at right depicts a situation in which extensive decay had been overlooked by a number of dentists prior to radiographic evaluation.
Intraoral radiographic views Placing the radiographic film or sensor inside the mouth produces an intraoral radiographic view.
Periapical view Periapical radiographs are taken to evaluate the periapical area of the tooth and surrounding bone
For periapical radiographs, the film or digital receptor should be placed parallel vertically to the full length of the teeth being imaged.
The main indications for periapical radiography are
Detect apical inflammation/ infection including cystic changes Assess periodontal problems Trauma-fractures to tooth and/or surrounding bone Pre/ post apical surgery/extraction. Pre extraction planning for any developmental anomalies and root morphology. Post extraction radiographs for any root fragments any other co-lateral damages. Detect any presence or position of unerupted teeth Endodontics. For any endodontic treatment, a pre-treatment radiograph is taken to measure the working length of the canals and this measurement is confirmed with electronic apex locator. A 'cone fit' radiograph is used when Master Apical Cone is placed in wet canal to correct working length to achieve frictional fit apically. Next, obturation verification radiograph is indicated after the canal space is fully filled with master cone, sealer and accessory cones. In the end, a final radiograph is taken after a definitive restoration is placed to check the final outcome of root canal treatment. Evaluation of implants.
Intraoral periapical radiographs are widely used for the preoperative due to its simple technique, low cost and less radiation exposure and widely available in clinical settings.
Bitewing view The bitewing view is taken to visualize the crowns of the posterior teeth and the height of the alveolar bone in relation to the cementoenamel junctions, which are the demarcation lines on the teeth which separate tooth crown from tooth root. Routine bitewing radiographs are commonly used to examine for interdental caries and recurrent caries under existing restorations. When there is extensive bone loss, the films may be situated with their longer dimension in the vertical axis so as to better visualize their levels in relation to the teeth. Because bitewing views are taken from a more or less perpendicular angle to the buccal surface of the teeth, they more accurately exhibit the bone levels than do periapical views. Bitewings of the anterior teeth are not routinely taken.
The name bitewing refers to a little tab of paper or plastic situated in the center of the X-ray film, which when bitten on, allows the film to hover so that it captures an even amount of maxillary and mandibular information.
Occlusal view The occlusal view reveals the skeletal or pathologic anatomy of either the floor of the mouth or the palate. The occlusal film, which is about three to four times the size of the film used to take a periapical or bitewing, is inserted into the mouth so as to entirely separate the maxillary and mandibular teeth, and the film is exposed either from under the chin or angled down from the top of the nose. Sometimes, it is placed in the inside of the cheek to confirm the presence of a sialolith in Stenson's duct, which carries saliva from the parotid gland. The occlusal view is not included in the standard full mouth series.
1. Anterior oblique occlusal mandible – 45°
Technique: the collimator is positioned in the midline, thru the chin aiming an angle of 45° to the image receptor which is placed centrally into the mouth, on to the occlusal surface of the lower arch.
Indications:
1) Periapical status of lower incisor teeth for patients who cannot tolerate periapical radiographs.
2) Assess the size of lesions such as cyst or tumours at anterior area of mandible
2. Lateral oblique occlusal mandible – 45°
Technique: The collimator is positioned from below and behind the angle of mandible and parallel to the lingual surface of the mandible, aiming upwards and forwards at the image receptors which is placed centrally into the mouth, on to the occlusal surface of lower arch. Patients must turn their head away from the side of investigation.
Indications:
1) Detection of any sialoliths in submandibular salivary glands
2) Used to demonstrate unerupted lower 8's
3) Assess the size of lesions such as cyst or tumours in the posterior of body and angle of mandible
Full mouth series A full mouth series is a complete set of intraoral X-rays taken of a patients' teeth and adjacent hard tissue.Carranza's Clinical Periodontology, 9th Ed., W.B. Saunders 2002, page 435. This is often abbreviated as either FMS or FMX (or CMRS, meaning Complete Mouth Radiographic Series). The full mouth series is composed of 18 films, taken the same day: four bitewings two molar bitewings (left and right) two premolar bitewings (left and right) eight posterior periapicals two maxillary molar periapicals (left and right) two maxillary premolar periapicals (left and right) two mandibular molar periapicals (left and right) two mandibular premolar periapicals (left and right) six anterior periapicals two maxillary canine-lateral incisor periapicals (left and right) two mandibular canine-lateral incisor periapicals (left and right) two central incisor periapicals (maxillary and mandibular)
The Faculty of General Dental Practice of the Royal College of Surgeons of England publication Selection Criteria in Dental Radiography holds that given current evidence full mouth series are to be discouraged due to the large numbers of radiographs involved, many of which will not be necessary for the patient's treatment. An alternative approach using bitewing screening with selected periapical views is suggested as a method of minimising radiation dose to the patient while maximizing diagnostic yield. Contrary to advice that emphasises only conducting radiographs when in the patient's interest, recent evidence suggests that they are used more frequently when dentists are paid under fee-for-service
Intra-oral radiographic techniques Accurate positioning is of utmost importance to produce diagnostic radiographs and to avoid retakes, hence minimizing the radiation exposure of the patient. The requirements for ideal positioning include:
Tooth and image receptor (film packet or digital sensor) should be parallel to one another The long axis of the image receptor is vertical for incisors and canines, and horizontal for premolars and molars. There should be enough receptor beyond the apices of the teeth for record of the apical tissues. The X-ray beam from the tube-head should meet the tooth and the image receptor at right angles in both the vertical and horizontal planes Positioning should be reproducible The tooth under investigation and image receptor should be in contact, or as close together as possible
However, the anatomy of the oral cavity makes it challenging to satisfy the ideal positioning requirements. Two different techniques have hence been developed to be utilised in the undertaking of an intra-oral radiograph – Paralleling technique and Bisected angle technique. It is generally accepted that the paralleling technique offers more advantages than disadvantages, and gives a more reflective image, as compared to the bisecting angle technique.
Paralleling Technique This can be used for both periapical and bitewing radiographs. The image receptor is placed in a holder and positioned parallel to the long axis of the tooth being imaged. The X-ray tube head is aimed at right angles, both vertically and horizontally, to both the tooth and the image receptor. This positioning has the potential to satisfy four out of the five above requirements – the tooth and image receptor cannot be in contact whilst they are parallel. Because of this separation, a long focus-to-skin distance is required to prevent magnification.
This technique is advantageous as the teeth are viewed exactly parallel with the central ray and therefore there are minimal levels of object distortion. With the use of this technique, the positioning can be duplicated with the use of film holders. This makes the recreation of the image is possible, which allows for future comparison. There is some evidence that the use of the paralleling technique reduces the radiation hazard to the thyroid gland, as compared to the use of the bisecting angle technique. This technique, however, may be impossible in some patients due to their anatomy, e.g. a shallow/flat palate.
Bisecting Angle Technique The bisecting angle technique is an older method for periapical radiography. It can be a useful alternative technique when the ideal receptor placement using the paralleling technique cannot be achieved, for reasons such as anatomical obstacles e.g. tori, shallow palate, shallow floor of mouth, or narrow arch width.
This technique is based on the principle of aiming the central ray of the X-ray beam at 90° to an imaginary line which bisects the angle formed by the long axis of the tooth and the plane of the receptor. The image receptor is placed as close as possible to the tooth under investigation, without bending the packet. Applying the geometrical principle of similar triangles, the length of the tooth on the image will be the same as that of the actual length of the tooth in the mouth.