Unerupted or Impacted Teeth

In young patients, radiographs help the practitioner determine whether unerupted or impacted teeth are present (Figure 11-1). An impacted tooth is an unerupted or partially erupted tooth that is prevented from erupting further by any structure. Dental radiographs are taken in all patients to evaluate the status of root and tooth when the tooth is missing or partly erupted. The practitioner may discover that the patient is edentulous or has a dilacerated or an embedded tooth. Edentulous is the absence of teeth. A dilaceration is an abnormally shaped root resulting from trauma during tooth development (see Figure 2-16). An embedded tooth is a tooth that is usually covered in bone, has not erupted into the oral cavity, and is not likely to erupt.

FIGURE 11-1 Missing adult canine.

Periodontal Disease

During prophylactic or therapeutic teeth cleaning, radiographs can be used to determine the extent of periodontal disease. Dental radiographs allow the practitioner to evaluate bone loss and select an appropriate method of treatment. In patients with oral stomas (fistulas), radiographs can also be used as a diagnostic tool.

Endodontics

Radiographs allow the practitioner to evaluate the effectiveness of endodontic therapy and to study radicular health and size before, during, and after endodontic therapy (Figure 11-2). Chapter 13 has illustrations of endodontic disease before and after treatment.

FIGURE 11-2 After root canal therapy (RCT).

Exodontics

Dental radiographs are indicated before extractions for diagnosis and evaluation of possible complications. Dental radiographs are obtained during the procedure to determine the presence of retained roots and other complications. Radiographs are indicated after extraction to ensure completeness of the procedure. Figure 11-3 shows a preoperative radiograph of a persistent deciduous tooth. The entire root must be extracted. Figure 11-4 shows multiple retained deciduous teeth. The canine tooth will require elevation to extract. The second, third, and fourth premolar roots have resorbed and are being held in place by attached gingiva. They should be removed for the patient’s comfort.

FIGURE 11-3 Preoperative radiograph of a persistent deciduous tooth.

FIGURE 11-4 Radiograph of multiple retained deciduous teeth.

Routine Dental Procedures

Routine dental radiographs on all patients undergoing anesthesia will result in findings that were undetected during clinical examination 25% of the time in dogs and 40% of the time in cats. This is a very high diagnostic yield.

Veterinary Medical Machines

Dental radiographs can be taken using veterinary medical radiographic units. However, these require considerable effort in positioning the patient. With the stationary radiographic unit, the patient must be moved several times to reorient the head.

Dental Machines

The advantage of the dental radiographic unit is its fairly flexible radiographic head and jointed extension arm. The unit can be angled, which minimizes the need for patient repositioning. Human nature being as it is, practitioners tend to take more radiographs when the unit is easy to use. The greater the number of radiographs, the greater the amount of diagnostic information.

There are two types of current that can be input into dental x-ray machine heads: alternating current (AC) and direct current (DC). In most dental machines, the amount of voltage applied to the tube determines the power of the x-ray. An AC unit (that produces a sine wave) produces impulses of x-ray. In the United States, the rate is 60 pulses every second; in some parts of the world, the rate is 50 pulses per second. The amount is measured at its kilovoltage peak (kVp). DC units are actually more like very high-frequency AC units—they produce a wave in the 70,000 cycle per second range. Thus the high pulse is not perceived and is expressed as kilovolt (kV) and the power is more consistent. Therefore a DC unit is used with less kV than an AC unit’s kVp. Milliamperage (mA) is often fixed in AC dental x-ray units—most typically at 7 mA, but it can be 6 or 8 mA; mA is usually variable in DC x-ray units—typically in a range of 4 to 8 mA.

There are two important criteria in choosing an x-ray unit. The stability of the arm is important, especially if there is a long reach from where the x-ray unit is mounted and the patient. Good arms hardly wobble after they are positioned. The second is the focal spot size inside the x-ray head—the smaller the spot the sharper the image: a 0.4-mm spot will be much sharper than a 0.7-mm spot.

The kVp in most dental radiographic units is fixed and usually does not need to be adjusted. Likewise, the mA is fixed for most units. Time, however, is a variable that may require adjustment according to the thickness of the area to be studied. Some units measure time in portions of a second and others set time in impulses—one impulse equals one-sixtieth of a second, thus 30 impulses would equal 0.5 seconds.

Dental x-ray units may be mounted on the wall (Figure 11-5, A), on stands (Figure 11-5, B and C), or handheld (Figure 11-5, D). The advantage of a wall-mounted unit is that it has a smaller footprint than stand-mounted units. However, wall-mounted units cannot be moved from room to room. Stand-mounted units take space in the dental operatory but can be moved around to different rooms or tables. Handheld units tend to be less powerful than stand-mounted (floor-mounted) units.

FIGURE 11-5 A, Wall-mounted x-ray unit. B and C, Stand x-ray units. D, Handheld x-ray unit.

Intraoral Film

Intraoral radiographic film is inexpensive, small, and flexible. It fits neatly into the oral cavity and conforms to the area in which it is placed. Intraoral film is nonscreen film, which provides greater detail than the screen films used in most veterinary situations. Intraoral film can be processed in 1 to 2 minutes in rapid developer and fixer solutions, with minimal loss of detail. This film allows small areas of interest to be isolated.

Description

Most intraoral film comprises a series of layers. A plastic coating covers the external portion. Between the plastic coating and the radiographic film is a layer of paper. The next layer is the radiographic film, sandwiched by another layer of paper. Finally, a layer of lead is followed by another layer of paper that can be peeled from the plastic coating. Some manufacturers have combined the lead and paper layers (Figure 11-6).

FIGURE 11-6 Inside intraoral film.

Dental Radiographic Film Sizes

Dental radiographic film is available in a number of sizes. DF-58, which is size 2 film, is the most common film used in human dentistry. It is also called periapical film. In veterinary dentistry, this type of film is suitable for small patients. DF-50, or size 4 film, is also called occlusal film and is appropriate for larger patients. For cats, size 0 may be useful for radiographic evaluation of the mandible.

Digital Radiology

Digital veterinary dental radiology (DVDR) for veterinary dentistry has made intraoral radiology possible in all practices. Although it is very easy to learn, there is a learning curve to the process. This learning curve can be cut short by proper training.

There are two basic components to DVDR: the dental x-ray machine and the digital x-ray system. These components are independent and can be purchased from different manufacturers. The dental x-ray machine consists of a control unit, a tube head that produces radiation, a collimator that aims and confines the radiation, and a timer that turns the unit on.

One digital x-ray system, which is known as direct or digital radiology (DR), uses a sensor (Figure 11-7) to capture the image. DR sensors have almost unlimited uses, unless one does bad things to them such as drop them, soak them, or allow animals to bite them. Another digital system has a phosphorous plate (Figure 11-8, A) and processing unit (Figure 11-8, B); this system is known as indirect or computerized radiology (CR). In either case, a laptop or desktop computer is used to process and read the image on a computer screen. While there are differences in appearance, the function is very similar for either of these systems. One of the most important components to the whole system is the computer that is being used to read the image. Both the graphics card and monitor must be high quality and capable of image reproduction.

FIGURE 11-7 Digital sensor for digital or direct radiology (DR).

FIGURE 11-8 Plates (A) and processing unit (B) for computerized radiography (CR).

A unique dental unit is a combination handheld unit, digital sensor, and viewer (Figure 11-9).

FIGURE 11-9 A compact unit that combines an x-ray generator, sensor, and viewer.

Prior to taking any intraoral radiographs, it is important to be concerned with radiation safety. Individual and area radiation monitors should be used. The patient and dental x-ray machine should always be positioned so that radiation is never aimed directly at coworkers. Shields and protective devices should always be used if there is any chance of exposure.

The equipment also must be protected because they are very fragile and subject to damage from being dropped or bit or from water getting inside them. Protective covers should be placed on the unit and secured (Figure 11-10). Another trick is to use Velcro to attach a wire from the sensor to the x-ray arm (Figure 11-11).

FIGURE 11-10 Protective covers should be used at all times.

FIGURE 11-11 The cord may be attached to the Velcro to help prevent dropping.

The protective cover will not protect the sensor from animal bites. The patient must be completely anesthetized. Even the slightest flexing may damage a sensor (Figure 11-12).

FIGURE 11-12 This sensor damage on the outside (red circles) may destroy the electronics inside.

It is important to understand how both the dental x-ray machine and digital x-ray system work. Most dental x-ray machines have fixed kVp and mA. The user only sets the time. Two types of timers measure portions of seconds and pulses. Some timers are in units of 1/100th of a second. Other timers use a “pulse,” which is 1/60th of a second; thus 6 pulses equals 1/10th of a second. The third type of timer uses a chart, which graphically represents areas of the mouth. In this type of timer, the user must select dog or cat, select digital, and indicate which tooth is being radiographed. Also, some units have a sensitivity setting, which must be set to digital.

Since radiation is invisible, practitioners often have a difficult time in understanding positioning. Visual aids can make this easier. A flashlight can be used to visualize the direction of radiation. An extracted tooth or model tooth can be positioned to visualize a shadow on a white card to represent the image cast by radiation.

When it comes to actual application, a live patient is not the place to practice taking radiographs. Skulls (see www.skullsunlimited.com) should be used to perfect the technique. Although children’s play dough is not used in clinical practice, it can be used to position the skull and sensor. In practice, a clean washcloth, laparotomy pad, or gauze can be used to position the sensor.

Protective Measures

Personnel should protect themselves by wearing lead safety aprons and using screens. They should also maintain a safe distance from the beam of radiation emitted by the radiographic unit. A variety of devices may be used to hold the film in place. Placing the film in holders, resting the film against the endotracheal tube, and securing the film with gauze sponges are a few common methods.