Dental radiography(Redirected from Dental radiograph)
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, according to the American Dental Association website), 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 viewsEdit
Placing the radiographic film or sensor inside the mouth produces an intraoral radiographic view.
The periapical (PA) view is taken of both anterior and posterior teeth. The objective of this type of view is to capture the tip of the root on the film. This is often helpful in determining the cause of pain in a specific tooth, because it allows a dentist to visualize the tooth as well as the surrounding bone in their entirety. This view is often used to determine the need for endodontic therapy as well as to visualize the successful progression of endodontic therapy once it is initiated. It can be used in case of detection hyperdontia (supernumerary teeth) & impacted teeth.
The name periapical is derived from the Greek peri, which means "around," and apical, which means "tip."
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.
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.
Full mouth seriesEdit
A full mouth series is a complete set of intraoral X-rays taken of a patients' teeth and adjacent hard tissue. 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
- 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 TechniquesEdit
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
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.
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 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 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.
Bisecting Angle TechniqueEdit
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 900 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.
The many inherent variables can inevitably result in image distortion and reproducible views are not possible with this technique. An incorrect vertical tube head angulation will result in foreshortening or elongation of the image, while an incorrect horizontal tube head angulation will cause overlapping of the crowns and roots of teeth.
Many frequent errors that arise from the bisecting angle technique include: improper film positioning, incorrect vertical angulation, cone-cutting, and incorrect horizontal angulation.
Extraoral radiographic viewsEdit
Placing the photographic film or sensor outside the mouth, on the opposite side of the head from the X-ray source, produces an extra-oral radiographic view.
A lateral cephalogram is used to evaluate dentofacial proportions and clarify the anatomic basis for a malocclusion, and an antero-posterior radiograph provides a face-forward view.
Lateral cephalometric radiographyEdit
Lateral cephalometric radiography (LCR) is a standardized and reproducible form of skull radiography taken from the side of the face with precise positioning. It is used primarily in orthodontics and orthognathic surgery to assess the relationship of the teeth to the jaws, and the jaws to the rest of the facial skeleton. LCR is analyzed using cephalometric tracing or digitizing to obtain maximum clinical information.
Indications of LCR include-
- Diagnosis of skeletal and/or soft tissues abnormalities
- Treatment planning
- Baseline for monitoring treatment progress
- Appraisal of orthodontic treatment and orthognathic surgery results
- Assessment of unerupted, malformed, or misplaced teeth
- Assessment of upper incisor root length
- Clinical teaching and research
Panoramic films are extraoral films, in which the film is exposed while outside the patient's mouth, and they were developed by the United States Army as a quick way to get an overall view of a soldier's oral health. Exposing eighteen films per soldier was very time consuming, and it was felt that a single panoramic film could speed up the process of examining and assessing the dental health of the soldiers; as soldiers with toothache were incapacitated from duty. It was later discovered that while panoramic films can prove very useful in detecting and localizing mandibular fractures and other pathologic entities of the mandible, they were not very good at assessing periodontal bone loss or tooth decay.
There is increasing use of CT (computed tomography) scans in dentistry, particularly to plan dental implants; there may be significant levels of radiation and potential risk. Specially designed CBCT (cone beam CT) scanners can be used instead, which produce adequate imaging with a stated tenfold reduction in radiation. Although computed tomography offers high quality images and accuracy, the radiation dose of the scans is higher than the other conventional radiography views, and its use should be justified. Controversy surrounds the degree of radiation reduction though as the highest quality cone beam scans use radiation doses not dissimilar to modern conventional CT scans.[unreliable medical source?]
Cone beam computed tomography (CBCT)Edit
Cone beam computed tomography (CBCT), also known as digital volume tomography (DVT), is a special type of X-ray technology that generates 3D images. In the recent years, CBCT has been developed specifically for its use in the dental and maxillofacial areas to overcome the limitations of 2D imaging such as buccolingual superimposition. It is becoming the imaging modality of choice in certain clinical scenarios although clinical research justifies its limited use.
- Assessment of unerupted and/or impacted teeth
- Assessment of external resorption
- Assessment of cleft palate
- Treatment planning for complex maxillofacial skeletal abnormalities
Restoration of dentition (if conventional imaging is inadequate)
- Assessment of infra-bony defects and furcation lesions
- Assessment of root canal anatomy in multi-rooted teeth
- Treatment planning of surgical endodontic procedures and complex endodontic treatments
- Assessment of dental trauma
- Assessment of lower third molars where intimate relationship with the inferior dental canal is suspected
- Assessment of unerupted teeth
- Prior to implant placement
- Assessment of pathological lesions of the jaws (cysts, tumors, giant cell lesions, etc.)
- Assessment of facial fractures
- Treatment planning of orthognathic surgery
- Assessment of bony elements of the maxillary antra and TMJ
The concept of parallax was first introduced by Clark in 1909. It is defined as “the apparent displacement or difference in apparent direction of an object as seen from two different points not on a straight line with the object”. It is used to overcome the limitations of the 2D image in the assessment of relationships of structures in a 3D object.
It is mostly used to ascertain the position of an unerupted tooth in relation to the erupted ones (i.e. if the unerupted tooth is buccally / palatally placed / in line of the arch). Other indications for radiographic localization include: separating the multiple roots/canals of teeth in endodontics, assessing the displacement of fractures, or determining the expansion or destruction of bone.
- Horizontal parallax: Involves the taking of two radiographs at different horizontal angles, with the same vertical angulation. (E.g. 2 intra-oral periapical radiographs)
- Based on the rule of parallax, the more distant object will appear to move in the same direction as the tube shift, while the object which is nearer to the tube will appear to move in the opposite direction. (Same Lingual Opposite Buccal - SLOB rule)
- Vertical parallax: Involves the taking of two radiographs at different vertical angulations (E.g. one periapical and one maxillary anterior occlusal; one maxillary anterior occlusal and one panoramic)
- MBD Rule: Commonly employed in endodontics, the MBD rule states that when an exposure is given (about 5-7o) from the Mesial surface, the Buccal root or canal will lie to the Distal of the image
With the rise in 3D radiographic techniques, the use of CBCT can be used to replace the undertaking of parallax radiographs, overcoming the limitations of the 2D radiographic technique. In cases of impacted teeth, the image obtained via CBCT can determine the buccal-palatal position and angulation of the impacted tooth, as well as the proximity of it to the roots of adjacent teeth and the degree of root resorption, if any.
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