The Balance Between Safety and Efficacy

Technological advances continue to impact the way dental hygiene is practiced and nowhere is this more evident than in the area of oral radiography. Whether you are an experienced practitioner, a dental hygienist returning to the work force after an extended absence, or changing your practice setting—a review of radiation safety protocol, coupled with an investigation into the role digital imaging plays, will aid in ensuring quality oral health care for your patients.

RADIATION SAFETY

Dental radiographs comprise a critical piece of patient assessment information and safety is an important consideration for film and digital systems. ALARA (as low as reasonably achievable), the buzzword in radiation safety, is defined as making all reasonable efforts to use the lowest practical dose of ionizing radiation for the patient.¹ Clinicians need to use evidence-based guidelines to determine if a patient needs radiographs and then expose the fewest radiographs to achieve that goal. In 2004, the American Dental Association (ADA) and the United States Food and Drug Administration created guidelines for prescribing dental radiographs, which can be downloaded from www.ada.org/ prof/ resources/ topics/ radiography.asp. Individual prescription based on the ADA guidelines precludes the practice of taking radiographs at predetermined intervals. Risk factors for caries, periodontal diseases, or symptomatic teeth drive the need for radiographs rather than an office policy of taking annual bitewings or a full mouth survey every 3 years.²

Updated cancer prevention strategies dictate the use of a thyroid collar along with a lead or lead-equivalent apron during radiographic exposure for all patients, especially children, women of childbearing age, and pregnant women.^2-4 Non-lead aprons— fabricated from tin, tin-antimony (a similar metal), or composite materials—may be used as a substitute for lead.⁵ Newer lead aprons and thyroid collars, containing the equivalent of 0.25 mm lead, are lighter and easier to maneuver.⁶ They can be purchased in different sizes with attached or separate thyroid collars. All protective aprons should be inspected regularly for cracks and should never be folded, but instead hung for storage.²

Other advances in radiation safety have created a less hazardous environment for the patient and the clinician. For example, the pointed cone is a relic of bygone days. Only open-ended position indicating devices (PID) between 20 cm and 40 cm long are recommended with the longer PID preferred.² The longer PID exposes a smaller area of tissue to the beam.⁷Collimation consists of a lead barrier that further reduces the beam and scatter radiation and is best accomplished with a rectangular PID.⁷ The next best choice includes inserting a rectangular collimator into a round PID since round collimation allows for more scatter radiation than rectangular.²

Increasing the film speed or using digital radiography contributes to reducing the patient’s radiation exposure. F speed film requires 20% to 50% less exposure time than E or D speed film, respectively.⁷ Film slower than E speed should not be used for intraoral radiography.^8,9 When digital images are made the dose reduction ranges from 0% to 50% of the exposure required for F speed film.¹⁰ Although reduced radiation stands out as a major reason to use digital imaging, dental professionals indicate an increase in the number of digital radiographs taken, effectively negating the lower dose. The reasons cited for this phenomenon include the ease and speed with which a new image may be exposed and viewed and the perception that the radiation dose is minute.¹⁰

Standard precautions are in order for infection control during conventional and digital radiography. Film holders may be disposable or sterilizable but digital sensors must be covered with plastic barriers.¹¹ Some manufacturers recommend placing double barriers over the sensors to prevent cross contamination.¹² The practitioner should consult the manufacturer’s recommendations and be careful to protect the sensor and the patient. Finally, attention must be paid to asepsis of the computer hardware by either placing a barrier over the keyboard and mouse or setting up the computer software to automatically advance to the next projection during exposure.¹¹

DIGITAL INTRAORAL TECHNOLOGY

Understanding the basics of radiation safety and exposure techniques will help the clinician make the transition from film-based to digital radiography. There are far more similarities than differences in the technology. The dental hygienist should make the effort to understand and investigate the technology available that will produce high quality diagnoses for the patient while reducing patient risk to ionizing radiation. In fact, informed dental patients will often come into the practice with questions about new technology. What do the clinician and the patient really need to know to be comfortable with the technology? The terminology and options in digital sensors can be confusing, but a few terms and descriptions should arm the dental hygienist with information to satisfy all but the most detail-oriented patient.

Digital radiography essentially replaces the film with a digital sensor. Digital sensors come in two basic types: solid-state systems and photo-stimulable phosphor (PSP) systems.¹³ There are two basic solid state systems based on charged-coupling devices (CCD) and complementary metal oxide semiconductor systems (CMOS).^13,14 The CCD and CMOS sensors capture the ionizing rays on a chip within the sensor and are transferred to computer software via a USB cable attached to the sensor.² The image is transferred to the computer screen within seconds, providing the clinician with immediate feedback. CCD and CMOS sensors record a smaller area of tissue than an intraoral film.¹⁵ The sensors, though they vary in size, are thicker than conventional film packets and manipulation in the oral cavity can be more awkward. Wireless sensors are also available. These sensors use the CMOS system of data collection. The information collected from exposure to radiation is transferred via a radio signal, requiring a signal receiver and a quiet setting for exposure and transfer of data.

PSP sensors capture the image on a phosphor crystal-covered plate that is then placed in a laser scanner which records the image on the software.¹³ The laser scanner should be placed in an area with minimal light exposure because the exposed PSP plates are sensitive to direct normal light.^14,15 The plates are the size and flexibility of a standard intraoral film packet.² This makes placement similar to traditional film.¹⁶ Transferring the data from the plates to the software can take the same amount of time as developing film-based radiographs.¹⁴ Although several digital imaging systems are available—CCD, CMOS, PSP—the diagnostic quality of the images still requires the human factor. Among these factors are proper sensor placement, exposure time, and location for viewing.

SENSOR PLACEMENT

Once the computers are in place, the sensors have been purchased, and the imaging software has been loaded onto the computers, the next step in capturing diagnostic intraoral images is deciding how to best complete this task. Two basic techniques are used to accurately capture the structures of the dentition and supporting alveolar process: paralleling or right-angle and bisecting angle methods.⁶ Digital sensor holders are available for existing parallel guiding systems used in film-based radiography. Compatible sensor holders are available in autoclavable or disposable form, making the transition from film to digital image capturing easier. The purpose of the paralleling technique is to minimize distortion.⁶ It offers a more representative image of the tooth. The clinician places the film parallel to the long axis of the tooth and uses the aiming device to direct the central beam of radiation.⁷ Properly used, this technique with the aiming ring in place can reduce the incidence of cone-cuts and need for retakes.

The bisecting technique is more technique sensitive and requires a visualization of the line that bisects the angle between the long axis of the tooth and the sensor. Though not the preferred method for visualizing a tooth radiographically, clinicians should be familiar with this technique and have access to bisecting angle sensor holding devices.⁶ Bitewing images can be achieved using the paralleling guides or with stick-on tabs or holders as with film-based radiographs. Care still must be taken to open contacts and capture important structures in order to avoid the need for retakes. The manufacturing or dental supply representative will help the staff choose the sensor holders that work with the CCD or PSP sensors chosen for the office.

Introduction of the PSP system to a practice allows for a smooth transition to digital radiography because the images can be captured in the same order in which the clinician took film-based radiographs. Each PSP is used like a film to capture each image.¹⁵ Once scanned, the images are arranged in the virtual “x-ray” mount. One caveat to using PSP technology is that the clinician must be very aware of the exposure time. The plates have a wide exposure latitude, allowing the clinician to miss the obvious signs of an overexposed image.^10,15 Existing radiograph holders can be used to capture images, reducing the prospect of retakes and the resulting increased exposure to radiation.¹⁰

Dental hygienists using CCD sensors guide each image into the proper location in a virtual mount. Commonly, default locations will be set into the computer programs. For instance, when capturing bitewings, the first bitewing image captured in the virtual mount will be right molar view.¹⁶ Full-mouth settings can be programmed by each clinician to allow placement of the images in virtual mount in the order that works best.¹⁶ Again, if the imaging system has been set up to automatically advance to the next projection, it is best to follow that pattern. This reduces the need to touch the keyboard or mouse with contaminated gloves. Clinicians may wish to begin all full mouth surveys with the anterior views. This may allow the patient to get used to the feel of the sensors before they are placed in the molar regions.

VIEWING IMAGES

Although many similarities exist between the fundamentals of film-based and digital radiography, there are several distinct advantages to using digital technology. The ability to enhance and manipulate the images is one of the most widely recognized advantages of digital radiography.¹⁴ These advanced systems capture the intraoral image and, in the case of the CCD and CMOS sensors, instantaneously project it onto a computer screen. The ability to control density, contrast, and magnification provides a more accurate diagnosis when interpreting digital images.¹¹ Manipulating the dental image also allows the clinician to see the subtle changes in bone density and caries activity.¹¹ Digital radiography provides the clinician the ability to alter the density by manipulating the pixels of the image.¹¹ Altering the density and contrast in an under- or overexposed image can reduce the need for clinicians to retake radiographs. It remains essential, however, to consider the influence of exposure time on the diagnostic quality of the radiograph and how to best avoid under- or overexposing images.

Viewing any radiographic images is best done in reduced ambient light.^15,16 Diagnostic ability increases as the ambient light is reduced.² Treatment rooms are generally not ideal for diagnostic viewing since they are welllit areas. Diagnostic viewing can be completed in a dimly lit room and treatment room viewing should be reserved for patient education purposes.¹⁵

PATIENT EXPLANATION

While exposing dental radiographs produces only small amounts of radiation, some patients continue to voice concerns regarding the safety of x-ray exposure.^2,16 A dental office that addresses these issues with high tech digital radiography will be appreciated by its patients. These forward thinking patients will expect information that explains why this technology is an improvement, how the equipment is used, and why it will benefit them.¹⁹ A simple conversation with the patient may sound like this: “Dental x-rays are an important part of your dental visit as they allow us to diagnose problems that are not always visible. We are now using digital technology. I am going to place the digital sensor in your mouth and an image of your teeth will appear on the computer screen. The use of this technology reduces your exposure to radiation and the time you spend in the dental chair.”²⁰ In the office equipped with CD or CMOS sensors, the clinician may add that instantaneous viewing of images eliminates the time required to develop film.

People most often hear the first and last things you say and forget the middle part of your message. The significant points here are minimizing the radiation dose and possibly less time in the dental office.¹⁷ The immediate feedback of the image provides the clinician with an opportunity to review patient education.⁶ While reviewing the images with the patient, the dental hygienist can point out the higher quality image, show how the images can be enlarged for a better view of the tooth structure, and explain that a hard copy of the digital image can be printed.¹⁵ An additional benefit is the ability to transfer images to another professional for evaluation and increase the ease of image transfer to insurance providers.^6,11,13

CONCLUSION

Providing individualized patient care requires dental professionals to think critically about radiographic recommendations, rather than providing a one-size-fits-all approach. Informed dental patients often bring questions about new technology to their appointment. The ease with which the clinician can get results with digital imaging should not cloud the basics of radiology, which include taking the time to properly place the sensor, open the contacts, and produce a diagnostic image, all while following the guidelines of ALARA. By following proper technique, digital radiography can offer a safe and efficient alternative to traditional dental radiographs.

REFERENCES

1. Health Physics Society. ALARA, 2009. Available at http://hps.org/publicinformation/radterms/radfact1.html. Accessed January 20, 2010.
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From Dimensions of Dental Hygiene. February 2010; 8(2): 26-27, 29-30.