CHAPTER 5 Radiographic Techniques
Roentgen’s discovery of the x-ray in 1895 provided one of the most important diagnostic aids in dentistry. Radiographs are essential if we are to treat children successfully. Evidence indicates that, unless carious lesions are discovered early, the primary teeth will not be retained until normal exfoliation.
Early diagnosis of caries prevents the pediatric patient from experiencing dental pain, extraction, and emotional stress. In addition, eruptive or developmental problems can be discovered with the use of radiographic images, and early treatment of these problems may reduce the need for prolonged orthodontic procedures. Some restorative procedures require an accurate registration of the pulpal outline that only a radiograph can reveal.
The selection of appropriate radiographs for the pediatric patient depends on the age of the child, the size of the oral cavity, and the level of patient cooperation. These are determined by a careful clinical examination of the patient before ordering the radiographic survey. The examination determines the need for radiographs and the type to be taken. Ideal technique should expose the patient to a minimum amount of radiation, require as few radiographs as possible, take as little time as possible, and provide a diagnostically accurate examination of the dentition and supporting structures. The child’s cooperation is as essential to radiographic examination as is the selection of correct radiographic technique. Both increase the probability of success and reduce additional radiographic exposure.
Dental radiographic equipment can be threatening or can generate curiosity, depending on the child. It is wise to allow the patient to run a hand over the x-ray machine head and become acquainted with the “camera.” The patient might hold one of the films and be shown where it will be placed. If it is a film that requires biting pressure, the patient should be shown how to bite on the film. Show-and-tell goes a long way in gaining cooperation. Careful wording of the description of the procedure is essential to gain patient cooperation. The potential cooperation of a patient may be lost when the patient hears the phrase “shooting a couple of films.” Imaging the easiest region first may ensure success in other areas. This is particularly important if the child has an exaggerated gag reflex or objects to the placement of the film. The use of topical anesthetic agents may be beneficial in both situations.
The dentist should be patient with the child in obtaining radiographs. Repeated attempts at film placement may be necessary before the actual radiation exposure is made. If the child is uncooperative, firmness, voice control, and tender loving care are often effective. Emotionally, mentally, and physically disabled children require special handling.
One characteristic of x-radiation is its ability to impart some of its energy to the matter it traverses. If that matter is living tissue, then some biologic injury may occur. Much information about high levels of radiation and subsequent damage is available. The effects of low levels of x-radiation (as used in diagnostic radiology) on biologic systems are virtually unknown. Our assumptions of damage are based on extrapolation of data from high levels to lower levels of radiation.
Still, dental health professionals must be concerned about any risk that the patient may encounter during therapy. Concern is focused on three primary biologic effects of low-level radiation: (1) carcinogenesis, (2) teratogenesis (malformations), and (3) mutagenesis. Carcinogenesis and malformations are a response of somatic tissues and in most instances are believed to have a threshold response; that is, a certain amount of radiation is necessary before the response is seen. Mutation may occur as a response of genetic tissue (gonads) to x-radiation and is believed to have no threshold. In general, younger tissues and organs are more sensitive to radiation, with the sensitivity decreasing from the period before birth until maturity. It must also be recognized that far higher doses of radiation can be withstood by localized areas than by the whole body. We know that we live in a world that exposes us to natural background radiation averaging 360 mrem per year (3.60 millisievert) in the United States. Medical and dental radiographic examinations add to that exposure and so must be ordered judiciously.
With regard to patient protection, evidence has shown that there are critical organs vulnerable to possible development of late effects. These organs should be shielded when possible. These critical organs and the associated adverse biologic effects are the following: (1) the skin (cancer), (2) red bone marrow (leukemia), (3) the gonads (mutation, infertility, and fetal malformations), (4) the eyes (cataracts), (5) the thyroid (cancer), (6) the breasts (cancer), and (7) possibly the salivary glands (cancer).
The practitioner and staff can physically protect the patient and indirectly protect themselves from unnecessary exposure to radiation by using correct technique. The most obvious method of protecting the patient is to shield those areas not being evaluated. This is easily accomplished using a lead apron and thyroid collar (Fig. 5-1).
The apron and collar may be incorporated as a single unit or used separately. The apron protects the gonads and chest from the primary beam and scatter radiation whereas the collar shields the thyroid. This method does not provide complete protection, particularly of the thyroid, but it does provide a great reduction in exposure. Aprons used in panoramic radiography have a front and back because the source of radiation is from the side and the rear of the patient.
Faster film speeds have contributed most significantly to the reduction in radiation to the patient. Film speeds of the D and F groups are available for intraoral radiography. Faster film also reduces error from patient movement, a consideration with the pediatric patient. Extraoral (panoramic) radiography uses film-screen combinations that also have reduced exposure times. Recently, there has been an increased use of beam-positioning devices (Fig. 5-2), which virtually eliminate some of the technical errors, particularly film cone cuts. Using different lengths and shapes of the cone (Fig. 5-3) has also aided in the reduction of patient radiation exposure. Use of a long rectangular collimator reduces the area unnecessarily exposed to radiation by almost 4 square inches compared with a round collimator. The use of higher kilovolt peak techniques reduces patient exposure to radiation and lowers contrast, thus increasing the number of shades of gray on the film. An additional benefit of using high kilovolt peak technique is that the exposure time is shortened, which potentially reduces retakes caused by patient movement.
Finally, quality control (and thus patient protection) begins with proper processing. With the shift toward using digital radiography, this concern becomes reduced. However, the majority of dental practices still use traditional film and wet tank chemical processing. If the processing does not function at an optimal level, retakes will be required, necessitating additional patient exposure. The dentist must insist on time-temperature developing and the use of proper-strength chemicals if wet tanks are used. The processing area should be clean and free of white light (light leaks). If automatic processing is used, chemical parameters must be continuously monitored and the unit must be cleaned weekly.
The decision to make radiographs is based on a thorough evaluation and examination of the patient. Radiographs should be made only when there is an expectation that disease is present or when an undetected condition left untreated could adversely affect the patient’s dental health. Therefore the decision to use ionizing radiation is based on professional judgment (Table 5-1).
|Primary Dentition (before eruption of first permanent tooth)||Transitional Dentition (after eruption of first permanent tooth)|
|All new patients to assess dental diseases and growth and development||Posterior bite-wing examination if proximal surfaces of primary teeth cannot be visualized or probed||Individualized radiographic examination consisting of periapical/occlusal views and posterior bite-wings or panoramic examination and posterior bite-wings|
|Clinical caries or high-risk factors for caries†||Posterior bite-wing examination 6-month intervals or until no carious lesions are evident|
|No clinical caries and no high-risk factors for caries†||Posterior bite-wing examination at 12- to 14-month intervals if proximal surfaces of primary teeth cannot be visualized or probed||Posterior bite-wing examination at 12- to 24-month intervals|
|Periodontal disease or a history of periodontal treatment||Individualized radiographic examination consisting of selected periapical and/or bite-wing radiographs for areas where periodontal disease (other than nonspecific gingivitis) can be demonstrated clinically|
|Growth and development assessment||Usually not indicated||Individualized radiographic examination consisting of a periapical/occlusal or panoramic examination|
|Permanent Dentition (before eruption of third molars)||Dentulous||Edentulous|
|Individualized radiographic examination consisting of posterior bite-wings and selected periapicals. A full mouth intraoral radiographic examination is appropriate when the patient presents with clinical evidence of generalized dental disease or a history of extensive dental treatment.||Full mouth intraoral radiographic examination or panoramic examination|
|Posterior bite-wing examination at 6- to 12-month intervals or until no carious lesions are evident||Posterior bite-wing examination at 12- to 18-month intervals||Not applicable|
|Posterior bite-wing examination at 18- to 36-month intervals||Posterior bite-wing examination at 24- to 36-month intervals||Not applicable|
|Individualized radiographic examination consisting of selected periapical and/or bite-wing radiographs for areas where periodontal disease (other than nonspecific gingivitis) can be demonstrated clinically||Not applicable|
|Periapical or panoramic examination to assess developing third molars||Usually not indicated||Usually not indicated|
The recommendations contained in this table were developed by an expert dental panel comprised of representatives from the Academy of General Dentistry, American Academy of Dental Radiology, American Academy of Oral Medicine, American Academy of Pediatric Dentistry, American Academy of Periodontology, and American Dental Association under the sponsorship of the Food and Drug Administration (FDA).
Courtesy Carestream Health, Inc.
Selection criteria are clinical signs or symptoms that allow the practitioner to identify patients who will benefit from a radiographic examination. Two important considerations when deciding whether to perform a radiographic examination for children are (1) the stage of dentition development and (2) the risk of dental caries.
The criteria for exposing radiographs assume that the child is asymptomatic and that the dentist finds no specific clinical indications for radiographic examination. Exceptions to this rule include those conditions in which there is clinical evidence of injury, disease such as caries, pulpal pathosis, delayed or accelerated eruption or exfoliation of teeth, swelling, hemorrhage, pain, or ulceration, or those conditions in which there is a need to evaluate treatment. In such cases, taking appropriate radiographs is indicated to confirm the diagnosis and facilitate and evaluate treatment.
If the proximal surfaces of the primary teeth cannot be visually and tactilely inspected, and the child can be expected to cooperate, then dental radiographs should be made to determine the presence of interproximal caries. If all surfaces of all primary teeth can be examined clinically because of open contact, then radiographs are not indicated.