Despite the many advantages of digital radiography, many practitioners in North America still have not made the switch from conventional, film-based radiography. From our observations and discussions with thousands of dentists, the reasons for not transitioning to digital radiography include high cost, no other forms of digital in the office (ie, computers in the operatories, practice management software, etc), unwillingness to endure the hassle of conversion and staff training, and for some, the complete disbelief that digital radiography is an improvement over conventional forms. Many of the objections are valid; however, the overall benefits of digital radiography far surpass the limitations.
This article includes a discussion of the advantages and limitations of digital radiography, the diagnostic quality of digital radiography versus conventional film-based, the various types of digital radiography available based on image size, the types of digital radiography best suited for specific clinical indications, and anticipated future advances in digital radiography.
Advantages of Digital Radiography
The following list of advantages is not all-inclusive, but it highlights the factors that have driven most of the conversion to digital radiography in other developed nations. The same factors should continue to influence the conversion to digital radiography in North America.
Immediate Viewing of Images
This is highly desirable during most procedures but especially during implant procedures, endodontic root canal therapy and post placement, crown and bridge restoration seating, and patient education.
Enhancement of Images
Most digital radiography systems include intuitive software that is easy to use for image enhancement. In fact, most have one button to press that enhances the image for easier reading and diagnosis. Some of the optional enhancements include magnification; changes in contrast; changes in brightness/darkness; coloring of image areas based on density, measurements; and many more. Although all of these image “manipulations” enhance the original image, they may or may not improve the ability to diagnose lesions, as discussed below.
Retake of Images
Digital radiography usually results in fewer retakes due to under- or overexposure, cut-offs, positioning errors, etc. This results in less radiation to the patient.
Conversion to digital radiography also includes incorporation of several computers for image taking and digital storage of the images. For practitioners not wanting to go “all digital,” this incorporation of computers is a feasible first-step option, and it improves overall patient flow and efficiency. The storage and electronic distribution of digital images allows better communication with other practitioners and third-party benefit companies while eliminating the frustration of having to find films in paper charts for comparison and subsequent viewing.
Taking a digital radiograph and immediately explaining the findings as the patient views the condition on an operatory monitor is extremely useful and practical, and it improves acceptance of treatment options and plans. Use of the enhancement features mentioned above also improves the patient’s ability to understand the images.
Based on the type of radiograph being taken, radiation can be reduced by as much as 3 to 4 or more times as conventional (see cone beam computed tomography [CBCT] section). This advantage should not encourage clinicians to take more images. They should only take the minimum images necessary for complete diagnosis and planning.
Elimination of Chemicals and Dark Rooms
Maintenance of developing and fixing solutions, developers, odors, dark rooms, and the frustration of determining why an image is poor can be eliminated on conversion to digital radiography.
Limitations of Digital Radiography
Although advances continue to be made in digital radiography, the following limitations seem to be those most encountered, and a significant emphasis by digital radiography manufacturers is needed to resolve them.
The cost of a single intraoral sensor can be as high as $10,000 (in addition to computers, software, and additional sensors) while the average cost of a CBCT system is in excess of $150,000. The cost of conversion to digital can be offset somewhat by elimination of the film-based equipment and improvement in office efficiency and patient education. However, the other advantages of digital radiography outweigh the potential small savings observed when eliminating film.
Use of the rigid intraoral sensors for periapical (PA) images can be very uncomfortable for patients, especially if they have a shallow palate, narrow palate, tori, or an exaggerated gag reflex. Designs have been implemented that decrease this limitation. However, the problem is still present, and the sensors are still too rigid and much thicker than film. Future advances should be focused toward elimination of intraoral sensors.
Rapid adoption of digital radiography is usually related to the user’s skill with a computer. Taking the digital image is relatively simple, and most assistants and office staff quickly implement the new technology. However, some dentists struggle with basic computer features and image enhancement for better diagnosis, and they do not fully incorporate the features due to their lack of computer experience. Time and continued practice overcome this challenge.
Are Digital Images Superior to Film-Based Conventional Images for Diagnostic Quality?
There are many companies and users that claim the superiority of digital imaging compared to conventional film-based radiography, on an overall basis. However, most research concludes that there is no significant difference in diagnostic image quality between digital and conventional images.
Figure 1. Digital radiograph of apparently small interproximal carious lesions. Figure 2. Actual extent of the carious lesions is usually at least twice the observable radiographic extent of the lesions.
The ability of clinicians to identify and diagnose the actual extent of small carious lesions on digital or film-based images is minimal, and both methods produce potentially misleading images that do not show the full extent of the lesions (Figures 1 and 2). With the current professional emphasis on minimally invasive dental procedures, the ability to accurately diagnose and identify the extent of small lesions is more important than ever.
We have experienced similar difficulties in diagnosing incipient proximal lesions, occlusal lesions, and minor recurrent decay (that could best be treated while small before pulpal involvement). Even when image enhancements are used, the diagnostic quality of current digital images is still lacking in these areas. Assuming that the diagnostic quality of digital and conventional radiographs is the same, we must look to the other advantages and limitations when considering the use of digital images. It is our opinion that the above stated advantages of digital radiography outweigh the limitations, especially considering that an image of the same diagnostic quality can be obtained at a lower radiation dose.
TYPES OF DIGITAL RADIOGRAPHY
Periapical and Bite-Wing Radiographs
For practitioners converting to digital radiography, these radiographs are usually the first ones to be used. Intraoral sensors of varying sizes can be obtained and used in numerous operatories. Images are made in a similar method as conventional, but they can be read immediately on a computer monitor. These types of images are generally of good quality and can be very helpful in diagnosis. The radiation reduction is around 75% or more, in comparison to film-based conventional radiography. Some companies, including Planmeca and Sirona, now offer extraoral bite-wing (BW) radiographs as an addition to their panoramic devices (Figures 3a to 4).
Figures 3a and 3b. Standard bite-wing (BW) radiographs duplicate images and are difficult for patients to understand.
Figure 4. Extraoral BWs show much more anatomy, including tooth roots and surrounding structures.
Although investing in a panoramic (PAN) radiograph system requires space and a significant financial outlay, PANs can assist in planning many dental procedures, and can help determine if further radiographic images, such as PAs, are needed. Clinicians know that the diagnostic quality is not as good as that provided by PAs or BWs when considering single teeth. Many newer digital PAN systems include an extraoral BW option that aligns the posterior quadrants and obtains better images without overlapping interproximal areas. The radiation reduction can be 4 to 10 times less than that of a full-mouth radiographic exam with film-based conventional D-speed, round collimation.
Cephalometric, Tomographic,and Other Skull Images
Many digital PAN systems can be upgraded for a fee to include digital cephalometric images that can be uploaded into orthodontic software for quick analyses and comparisons. In addition, digital tomography can be used to view available bone in a facial-lingual view for implant planning.
Cone Beam Computed Tomography
This is one of the newest and most expensive types of digital radiography available, yet is quickly becoming one of the most useful. A scan similar to a PAN is taken in the area of interest, and the resulting image is displayed as image slices and/or 3-dimensional (3-D) images of the area. Images are displayed in a 1:1 ratio for accurate measurements. Some systems include an optional separate digital PAN to augment or determine the need for a CBCT image. This is useful for those patients who require a PAN image but not a CBCT.
Figure 5. An enhanced cone beam (CB) radiograph with nerve identification for implant planning. Figure 6. The CB radiograph is used for implant planning and removal of third molars.
The major indications for 3-D imaging is implant placement, oral surgery, and orthodontics (Figures 5 and 6). However, practitioners in endodontics, periodontics, and other specialties are discovering its potential. It has yet to be successfully used for diagnosis of small incipient enamel lesion detection, but research is being conducted in this area and improvements should be forthcoming. The radiation reduction is 10 to 30 times less than that of a conventional CT radiograph; however, it is 3 to 10 times more than a digital PAN, requiring judicial use with all patients.
DIGITAL RADIOGRAPHY RELATED TO CLINICAL INDICATIONS
This is based on the number of remaining teeth in the mouth. Many clinicians are taking a digital PAN and BWs, and only taking PAs if they are necessary.
Usually, PAs are sufficient for diagnosis and treatment. Occasionally, clinicians may choose a PAN, additional adjacent PAs, BWs, and/or CBCT images.
BWs and individual PAs are necessary for diagnosis of generalized periodontitis throughout the mouth. A PAN is an excellent addition for viewing the remaining bone and arches. CBCT is being used to diagnose and plan treatment for bone lesions in relation to the bone remaining on all dimensions and supporting walls of specific teeth.
Complete or Partial Edentulism
Digital PANs are necessary to view the arches, remaining bone structure, potential implant sites, and nerve location. PAs are taken to view individual sites as necessary. CBCT is readily being used to plan for extractions and implants.
An initial PA of the site or area in question is taken, and often a PAN as well. Tomography can be used to view the available bone in a sagittal slice. However, CBCT is rapidly becoming the choice for accurate diagnosis and treatment planning.
For third molar extraction, a PAN is required and a PA is useful. However, many surgeons are using CBCT to visualize the nerve and vital structures in proximity to the molar or tooth being extracted.
Digital PANs and cephalometric radiographs are used to diagnose and treatment plan for orthodontic therapy. Use of CBCT is increasing as software designed for these types of images is becoming available and practical.
FUTURE ADVANCES IN DIGITAL RADIOGRAPHY
As more practitioners adopt digital radiography, a higher demand for more intuitive software, better diagnostic capabilities, and improved outcomes will result. The limitations listed above still need to be overcome for future and current generations of digital radiography users. In addition, the failure to detect small carious lesions is still an unsolved problem for any form of digital radiography. Despite these challenges, advances are being made, and they will gradually overcome the current problems. Listed below are a variety of different advances being implemented or researched.
Many new imaging systems and software applications have been developed that enhance the ability to diagnose carious lesions. Examples are Logicon (PracticeWorks) and Spectra (Air Techniques).
Optical Coherence Tomography
Optical coherence tomography is being researched and explored by several groups, including D4D Technologies. This technology of optical coherence tomography allows the user to take an image measuring a few millimeters in depth to create a sliced image of the tooth or structure. It could be used for potential caries diagnosis, tooth crack location, CAD/CAM imaging, subgingival margin location, periodontal diagnosis, soft tissue analysis, and more. Optical coherence tomography is still in the developmental stages, but it could result in improvements on the current ability to image oral structures.
Ultrasound has been used in medicine for decades. An example is imaging a fetus in utero. However, many attempts have been made without success to use ultrasound in dentistry. This technology is being used to make images through hard tissue, even metal restorations and crowns, for early detection of dental pathology, carious lesions, and cracks in teeth. S-Ray Corporation has discovered a method to implement ultrasound technology for dentistry and is working to deliver it on a cost-effective basis.
The continued movement to make extraoral images will provide many benefits for both clinicians and patients. Systems are being developed in dentistry and in other medical applications that will have improved resolution and accuracy. It is anticipated that all film-based systems will soon be obsolete and a new generation of users will be using only extraoral imaging.
Any new concept requires time to be accepted by the practicing profession, especially when apparently adequate current techniques are available to accomplish the same tasks as the new concept. Digital radiography has slowly been introduced into US practices during the past 10-plus years in spite of its near universal use in many other developed countries. The numerous advantages of digital radiography have been noted in this article and are well known to users. However, the limitations of cost of the devices, inadequacy to allow adequate diagnosis of initial carious lesions, thick rigid sensors, and often-complicated software programs have limited acceptance. It is anticipated that continued practitioner acceptance of digital radiography, including slow but continual growth of cone beam, will be present in the next few years, and that the discussed new exciting devices and innovative radiographic techniques will be forthcoming soon.
Written by Paul L. Child, Jr, DMD, CDT, and Gordon J. Christensen, DDS, MSD, PhD