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).
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| Figures 3a and 3b. Standard bite-wing (BW) radiographs duplicate images and are difficult for patients to understand. |
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| Figure 4. Extraoral BWs show much more anatomy, including tooth roots and surrounding structures. |
Panoramic Radiograph
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.
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| 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
Initial Diagnosis
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.
Endodontics
Usually, PAs are sufficient for diagnosis and treatment. Occasionally, clinicians may choose a PAN, additional adjacent PAs, BWs, and/or CBCT images.
Periodontics
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.
Implant Placement
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.
Extractions
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.
Orthodontics
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.
Software Advances
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 Imaging
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.
Extraoral Imaging
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.
CLOSING COMMENTS
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.