Dental Radiography-A Mandatory Service For Modern Practices

Gregg DuPont, DVM, Fellow AVD, Diplomate AVDC



Summary

Dental radiography benefits the practitioner, the client, and the patient; a true win-win-win service. It is not possible to diagnose, stage, plan, and perform quality treatment for many oral diseases and problems without good oral radiographs. This lecture presentation will address the equipment, supplies, techniques, and indications for taking oral films, in addition to reading films and identifying lesions.

Oral radiology is vital for diagnosis, treatment planning, procedural decision making, follow-up evaluation and medical record keeping. The veterinary dentist needs an adequate number of quality radiographs to evaluate the need for, quality of, and success of treatment. Clients know the value of dental x-rays, and they expect to have dental radiographs taken when they visit their dentist. Pet owners want and expect the same high level of care for their pets that they know is available for themselves.

Some indications for dental and oral radiographs include:

  •  - Dental resorptive lesions – to determine type and best treatment option
  •  - Super-erupted teeth – to evaluate alveolar health and best treatment option
  •  - Fractured teeth – to look for endodontic disease (peri-apical rarefying lesion, internal resorption, immature pulp)
  •  - Discolored teeth – to look for endodontic disease from prior pulp hemorrhage
  •  - Worn teeth – to look for endodontic disease
  •  - Prior to most extractions – to look for root fractures, complex root anatomy, thin cortical bone
  •  - Missing teeth – to find submerged or impacted teeth or retained root fragments
  •  - Anomalous or malformed teeth – to determine nature and severity of anomaly
  •  - Areas of periodontitis – to evaluate bone loss, perio-endo lesions
  •  - Sneezing or nasal discharge – to look for intranasal masses or foreign bodies
  •  - Oral trauma – for mandibular fractures, temporomandibular joint injuries
  •  - Routine full mouth (?) – for identifying unapparent lesions and for baseline data

POSITIONING.

Oral radiographs can be exposed with the film placed either intra- or extra-oral. Most commonly, dental film (small sized non-screen film) is placed inside the mouth using either parallel technique (best quality but possible only on mandibular films) or a bisecting angle technique. The bisecting angle technique involves placing the tube head at an angle which is perpendicular to a line which bisects the angle made by the radiograph film and the long axis of the tooth. By creating an isosceles triangle with the image as one side and the subject as the opposite-but-equal side, it creates a relatively accurate image. Another way of thinking about this is to place the tube head in a position that is mid-way between perpendicular to the subject and perpendicular to the film. When performed properly, it prevents either elongation or foreshortening of the root image, although some degree of distortion (apical magnification) is unavoidable. A dental X-ray machine tremendously facilitates positioning, and simplifies taking oral radiographs by allowing the tube head to be easily positioned at any angle. When extra-oral radiography is used with a full size X-ray machine, positioning is more difficult and time consuming, making it less attractive to the operator as a diagnostic tool. This may result in fewer dental x-rays and more missed diagnoses.

TECHNIQUE.

Older human dental X-ray machines often have settings of description, i.e. “pediatric”, or “endodontic” etc. Newer dental units allow the operator to choose the exposure speed. Some also allow variable MA and kvP settings. You may need to experiment to find the best setting for your machine. Generally, a typical 70 kvP 8 MA machine will take good exposures at 0.3- 0.4 seconds for large dogs, and 0.16 - 0.2 sec for smaller dogs and cats. For digital radiography, exposure times of .02 to .05 seconds at 70 kvP are used.

Radiographic Equipment and Supplies

Many companies provide a wide selection of dental X-ray units. The veterinary vendors offer units that are convenient and simple. They have a small and easily positioned head that can be placed at any angle needed for exposing a film. A movable arm holds the head and allows it to swing out of the way when not in use.

Chair side developers provide instant developing of films in a convenient chairside location. Eliminating the need to walk back and forth to the darkroom adds significantly to the convenience of dental radiology. Of the available models, helpful features include: 1) fluid cups large enough to accept and submerge size 4 occlusal film without having to bend the film, 2) hinged or easily removed and replaced air-tight container lids to reduce fluid oxidization, 3) be sure to get the correct light filter; most include a filter cover appropriate for Ultraspeed film.  If you plan to use Ektaspeed, then a special filter should be used. Automatic processors designed for dental sized films add convenience and may stimulate some practitioners to expose more radiographs. They are somewhat limited in that many cannot handle size 4 (“occlusal”) film and they do not speed up the time-to-view.

Automatic processors specialized for dental sized films add convenience and may stimulate some practitioners to expose more radiographs. They are somewhat limited in that they can not handle size 4 (“occlusal”) film.

Rapid processing fluids allow viewing radiographs in one minute. A number of manufacturers supply these, and some tend to last longer than others. 

The most useful dental x-ray films are sizes 0 (i.e. DF54, 22 X 35mm), 2 (i.e. DF58, “Periapical”, 31 X 41mm), or 4 (i.e. DF50, “Occlusal”, 57X76mm). For our purposes, most projections can fit nicely on either a size 2 or size 4 film. DUP films have two films per packet. Generally, Ultraspeed film has been recommended over Ektaspeed due to its increased resolution, but the new Ektaspeed plus has improved resolution.  Ektaspeed allows lower radiation doses, but the light filter top routinely supplied with chairside developers does not completely protect the more  sensitive film from fogging due to ambient light.

Computed dental radiography uses charge coupled devices instead of film, allowing far less radiation for exposure, and instant computer images that can be stored and manipulated. 

Stainless steel film hangars hold the film during developing and drying.  Their added convenience, long life, and decreased film artifact make them well worth their very modest cost.

Film positioners used in human dentistry rarely help much but can occasionally be handy.  A veterinary gadget consisting of a variety of sizes of malleable cylinders is quite useful, as is a wadded up bit of paper towel, to hold films in position. Avoid bending the film during positioning.

SAFETY CONCERNS.

Radiology has improved dramatically since the first known dental radiograph in 1896 of a lower premolar tooth that required an exposure time of 25 minutes. Improvements in the tubes that produce radiation and in film sensitivity have combined to allow dramatically decreased exposure times. However, patient and operator safety is still a vital concern.  X-radiation used for diagnostic radiographs has a relatively short wavelength (between 0.1Å and 0.3Å) that allows them to penetrate tissues where their energy can ionize atoms. X-ray images are produced when the radiation that has not been absorbed by tissues travels completely through the subject and acts on the photographic emulsion surface of an acetate film. Although any single diagnostic exposure presents very little hazard, tissue damage from ionizing radiation is cumulative throughout a person or animal’s life. The veterinarian or technician is exposed to repeated doses if equipment or procedural precautions are not followed.  Although the patient, with very few exposures, is at minimal risk, the patient’s owners are increasingly concerned about the “dangers” of radiation. We must also remain diligent to minimize our exposure to radiation.

Routine veterinary radiographs frequently use intensifying screens and a focal film distance (FFD) of approximately 40 inches (100 cm). Dental radiographic film has no intensifying screen and therefore needs a larger dose of radiation for diagnostic films. Further, veterinary dental radiographs are generally exposed with a FFD of 8 inches or less.  The inverse square law tells us that the intensity of radiation varies with the inverse of the square of this distance. It therefore follows that dental units expose the film (and patient and careless operator) to over 30 times more radiation at 8 inches FFD than a conventional X-ray machine at similar exposure settings. Although the beams are well-collimated, one must keep in mind the high exposure settings used and maintain vigilance against inadvertent exposure to direct beam or indirect scatter radiation.