New insights and scientific advances over the years have resulted in significant improvements in the treatment, prevention and diagnosis of periodontitis. Apart from improvements in image quality and reductions in radiation exposure, very few other significant advancements or improvements in radiology, as they relate to periodontics, has occurred in recent years.
Radiographs are considered an important source of information which complement the clinical information obtained during the initial examination of a periodontal patient.1 Together this information allows an informed diagnosis and treatment plan to be developed. One of the main purposes of radiographs in a periodontal examination is to assess the level and pattern (angular, horizontal) of alveolar bone destruction which can be measured as linear distances from the cemento-enamel junction (CEJ) to the alveolar crest. Furthermore information can be obtained regarding the lamina dura, periodontal ligament space, furcations, impacted/unerupted teeth, restoration overhangs, calculus, root shape and periapical tissues.2
A major limitation when using radiographs in periodontics is that they provide a two-dimensional image of a three-dimensional object and this leads to problems in terms of validity, accuracy and precision.3 Thus, at best, radiographs can be considered an adjunct to diagnosis. Radiographs should not be used in isolation but must be used in association with a clinical examination looking at parameters such as probing pocket dept, tooth mobility and furcation involvement.4
It is with these limitations in mind and recent technological advances that volumetric cone beam computed tomography (CBCT) has become increasingly popular. The purpose of this review is to assess the background and clinical requirements that have led to developments in these areas, as well as explore whether CBCT can ‘value add’ to traditional radiographic assessment in periodontology.
Digital versus conventional (analogue) radiographs
The benefit of using digital radiographs instead of analogue X-rays in periodontics is not as apparent as it might seem. Digital sensors have been available on the market for about 20 years and with advances in technology have become a mainstream alternative to film based radiographs. The main benefits of digital radiographs are related more to practical issues than diagnostic benefits. Some such practical benefits include the elimination of chemical processing, shorter exposure times, less radiation exposure and integration with practice administration and patient care software. Furthermore, the associated software with most digital radiographic packages allows adjustment of image contrast and magnification, as well as provides a variety of measurement tools.2
Whether or not digital radiographs improve diagnostics is unclear. Several studies have reported that unenhanced digital radiographs are superior in visualizing angular bony defects5 and interproximal bone loss6 compared to traditional film based X-ray images. Furthermore, it has been reported that using software manipulation higher diagnostic efficacy can be achieved using digital radiographs.7,8 Nonetheless, others have reported that digital radiographs are inferior to, or of equivalence to conventional films in detecting caries, with the differences in diagnostics depending on operator experience.9–11 Recently, a systematic review on the topic concluded that there was not enough evidence to support or negate the claimed diagnostic improvements of digital X-rays.12 In general, it seems that provided traditional films are handled and processed correctly there is little diagnostic difference between the traditional and digital methods.
Limitations of traditional radiography in periodontics
Distance of cemento-enamel junction to alveolar bone crest
Bone loss can be measured as the distance from the CEJ to the alveolar crest and is used by many as an indicator of periodontal disease. This measurement has been used for both the management of individual patients,13 as well as in epidemiological studies.14
The effect of radiographic technique for assessment and measurement of bone loss using periapical radiographs has been evaluated in several in vitro studies. One study has reported that the distance from the CEJ to the alveolar crest on radiographs of molars may vary by up to 2.35 mm if the first radiograph is taken at a 90° angle and the second radiograph at a 70° angle, although in the anterior and the bicuspid regions a deviation in angulation of up to 20° was less critical.15 Additionally, considerable differences arise due to both inter- and intra-examiner variability in the examination of alveolar bone levels.16 When intraoral radiographs were assessed by different examiners, the identified variation differed for specific tooth groups and for different levels of periodontal bone loss. Adding to this, a total of 32–48% tooth surfaces could not be assessed by two examiners due to problems in determining bone/root length and bone/tooth interrelationships.16 Therefore, there is significant variation in operator assessment of crestal bone levels when using conventional radiographs.
Vertical bony defects around teeth are considered to be a diagnostic marker of more advanced and active forms of periodontitis.17–19 The importance of identifying vertical defects relates to the possibility of these defects deteriorating if left untreated, leading to further alveolar bone loss.20 Many different treatment options for vertical defects are available, depending on size, shape and defect angle. Therefore, it is important to correctly identify and classify vertical defects in order to choose the most appropriate treatment. However, when compared to surgical measurements, conventional intra and extraoral radiographs have a low ability to image defects as a significant number of anatomical vertical defects may fail to be detected radiographically,21 especially for defects of small depth or small buccolingual width.22
Radiographically determined defect angles have been used to determine the prognosis for regenerative therapy. For example, infrabony defects with a defect angle of ≤22° healed better than defects ≥36°.23 Similar results have been reported for periodontal regenerative procedures using barrier membranes, whereby narrow defects gain more bone compared to wide defects.24–26 Different thresholds have been used to define narrow and wide defects ranging from ≤26°25 to ≤37°.24 Thus, the shallower and wider a bony pocket is, the more it resembles horizontal bone resorbtion, which cannot be easily regenerated with current methods. Therefore, it is important to accurately image and determine the radiographic appearance of infrabony defects in order to determine which treatment option will provide the best outcome.
The diagnosis and classification of furcation defects is an important aspect of a periodontal examination, both for treatment planning and prognosis of teeth. Due to limitations arising from the two-dimensional imaging obtained using conventional radiography, as well as the fact that considerable bone loss must occur prior to furcations being visible on radiographs, there are significant problems in determining the degree of furcation involvement.27 One method which has been tried is the assessment of the furcation arrow.28 This was tested by exposing radiographs in dry human skulls with and without proximal furcation involvement in maxillary first or second molars. The furcation arrow was identifiable on the X-rays in 40 out of 96 furcations diagnosed as degree II or III (42% sensitivity). On the other hand, of 186 furcations with no or incipient involvement, the arrow was absent in 159 (85% specificity). More recently, similar results have shown that the sensitivity of the furcation arrow image as a diagnostic marker was 38.7% and the specificity was 92.2%.29 Therefore, the furcation arrow approach seems to be a poor indicator of furcation involvement, although when present it is very specific.
Panoramic radiographs in periodontics
Panoramic radiographs are commonly taken as an adjunct in periodontal diagnosis and treatment planning, especially in conjunction with intraoral radiographs.30 The advantages of panoramic radiographs are that they produce an image which can be used to assess teeth, alveolar bone and surrounding structures2 at a lower radiation dose compared to the alternative full mouth survey.31 However, due to the nature of the projection geometry used, artefacts such as ghost and superimposed images as well as image magnification commonly occur. The technique sensitivity in patient positioning also makes replication of images at different time points extremely difficult.2
The amount of bony destruction which is imaged by both periapical as well as panoramic radiographs has been found to underestimate the actual amount of destruction, although the degree of underestimation varies between different studies.22,32,33 The inaccuracy in imaging is also dependent on the disease severity as it has been found that representation of bony destruction was underestimated in initial periodontal disease, relatively accurate in moderate disease and overestimated in severe disease.33 Generally, intraoral radiographs are more accurate for imaging periodontal destruction than panoramic radiographs, which is especially true for smaller areas, as these are detected 4.7 times more frequently by periapical radiographs.22,23 However, when compared to surgical findings, the radiographic detection of any of these sites was very low (less than 4% for periapical views). Similarly, it has been found that periapical radiographs are more accurate in imaging angular defects and furcation defects34 when compared to panoramic radiographs. As such, periapical radiographs are more accurate in imaging bony destruction, although the degree of discrepancy between the two radiographic techniques is relatively small.35
The true value of panoramic and periapical radiographs in periodontal diagnosis is still unclear. Nevertheless, it was concluded that the highest radiographic detectability was achieved when intraoral and panoramic radiographs were used in combination.34 Consequently, panoramic radiograph may be supplemented with periapical films in regions where image quality is poor32,36 or localized defects are observed.
The use of CBCT in the field of periodontics
Due to the limitations associated with traditional imaging techniques there is need for more accurate imaging techniques. This is particularly relevant with regards to the imaging of three-dimensional structures such as furcation defects and infrabony defects, root anatomy and assessment of buccal and lingual bone loss. All of these impact significantly on periodontal treatment and prognosis, and improved imaging to assist in their assessment would be of great benefit to the clinician.
Tomographic imaging in periodontics
The use of conventional CT in determining periodontal destruction has been evaluated in vitro and found to be very accurate in demonstrating periodontal defects. For example, 100% of buccal and lingual defects could be identified employing CT, as opposed to 0% using conventional radiographs.37 Similarly, conventional CT has been shown to be far superior to conventional radiographs in identifying and classifying furcation defects (21% for conventional radiographs vs. 100% for CT),38 as well as interproximal bony defects (60% for conventional radiographs vs. 100% for CT).39 However, due to factors such as cost, accessibility and radiation dosages, CT imaging for these purposes is not routinely performed in dentistry. Nonetheless, with the advancement in volumetric imaging technology, which represents a cheaper, faster and dose sparing alternative, at least some of these issues have been overcome.
At present, the applications of CBCT in periodontics are limited. Indeed, assessment of the current literature indicates that around 3% of papers published on dental applications of CBCT have dealt with its applications in periodontology, with most papers being published relating to oral and maxillofacial surgery (OMFS). CBCT has also been investigated in the field of orthodontics, but this represents only 13% of the volume compared to OMFS. Interestingly, the implantology field accounts for only 11% of the research published on CBCT.40
CBCT for the assessment of horizontal bone loss
To date, no studies have evaluated the clinical relevance of CBCT imaging in relation to horizontal bone loss. However, in terms of linear measurement of alveolar bone loss, CBCT has been found useful in several studies.41 A study comparing the accuracy of CBCT, conventional CT and calliper determined measurements found that both conventional CT and CBCT were able to image to the submillimetre level with no statistically significant differences between the two.42 Similar results were reported from a study which found that CBCT had better diagnostic accuracy detecting the ligament space with a width of 0.19 mm (100%) compared to conventional radiographs (70–81%).43 The CBCT image that was used in this study had a voxel size of 0.15 mm and was thus sufficient to image the space, which translated in the better-quality images. However, with decreasing size in the gap to below 0.15 mm (which is less than the voxel size), imaging and thus detection of the gap by examiners decreased (although it remained higher than for conventional radiographs, irrespective of the size of the gap). Similarly, CBCT with a voxel size of 0.38 mm can be used to measure the distance from the CEJ to alveolar crest, a radiographic measurement often used to assess periodontal destruction, with an accuracy of 0.2 ± 1 mm44 which is substantially more accurate than values for intraoral radiographs.15,16 Although CBCT clearly has the potential to be used to accurately assess horizontal bone loss, the clinical relevance remains unclear. As such it is currently not recommended to use CBCT for this purpose.45
CBCT in assessment of periodontal defects
One of the first studies of the application of CBCT in periodontics compared intraoral radiographs, panoramic radiographs (OPGs), conventional CT and CBCT to histological measurements done by means of reflecting stereomicroscopy.46 The study evaluated dehiscences, fenestrations, two- and three-walled defects as well as Class I and II furcations. It was found that both conventional CT and CBCT were very accurate in terms of imaging infrabony defects, deviating only 0.16 ± 0.1 mm for CT and 0.19 ± 0.11 mm for CBCT scans. This was significantly better when compared to the accuracy of conventional X-rays (0.33 ± 0.18 mm) and OPGs (1.07 ± 0.62 mm). Furthermore, all infrabony defects could be measured in three dimensions using both the CBCT as well as conventional CT scans. In comparison, the intraoral radiographs and OPGs showed defects in only mesial, distal and craniocaudal plains. It was concluded that on a subjective level, CBCT images had the highest quality.
When CBCT has been compared to both conventional analogue X-rays using F-speed films as well as clinical probing, CBCT performed equally well to bone sounding using the probe for detecting defects, although measurements of defect dimensions were statistically more accurate for CBCT.47 In addition, there were differences in the detection of interproximal defects between the methods, but conventional X-rays were found to be very poor for imaging buccal and lingual defects. In this study, CBCT was able to detect all intraosseous defects, compared to only 67% that were detected using conventional intraoral radiographs. Hence, it was concluded that CBCT was superior to the other techniques as it allowed periodontal defects to be observed in all three dimensions. Similar findings have been reported when CBCT was compared to traditional two-dimensional intraoral radiographs employing a digital CCD sensor.48,49 CBCT imaging was superior for the imaging of defect shape, lingual or buccal furcation defects and furcation involvement although more bone detail (bone quality, contrast and lamina dura) was present on the CCD images. Crater and furcation visualization were not significantly different between the conventional two-dimensional images using digital intraoral radiographs used and CBCT panoramic images reconstruction (which is also a two-dimensional image).
Similar results were obtained in a study on cadaver specimens. When comparing CBCT to a series of full mouth radiographs used to image periodontal bone defects on five cadaver skulls, it was reported that cone beam was significantly superior compared to the intraoral radiographs in the posterior dentition.50 However, diagnostic accuracy for CBCT decreased progressively towards the anterior region. Therefore, it was concluded that although CBCT was superior in imaging posterior areas, and especially three-dimensional bone changes, it was of limited use in the anterior regions.50
CBCT and periodontal regeneration
CBCT has also been used to assess the amount of bone fill following periodontal regenerative procedures. This may be of particular significance because conventional radiographs tend to underestimate the amount of bone fill following such procedures.51,52 CBCT may be a valuable tool for periodontal regeneration imaging and assessment, both preoperatively and postoperatively.53,54
To date, there has been only one randomized controlled trial reported concerning the role of CBCT in periodontal regeneration.55 This study investigated the value of CBCT to image infrabony defects that had been treated with bone grafting. The measurements obtained by CBCT were closer to the surgical re-entry measurements than those obtained using conventional digital intraoral periapical radiographs. However, the measurements obtained showed that cone beam only outperformed intraoral radiographs with regards to defect resolution. It was proposed that more research is needed to determine the true value of CBCT in assessment of bone fill following periodontal regenerative techniques.
CBCT and furcation defects
As detailed above, CBCT imaging is superior to intraoral radiographs for the detection, classification and localization (i.e. determining if the furcation is buccal or lingual) of furcations. For example, 100% of furcation defects can be detected and correctly classified with CBCT compared to only 56% of furcations detected when using digital radiographs.49 In other studies the diagnostic certainty of CBVCT has not been as high with CBCT, having a diagnostic accuracy of 83% compared to 73% for digital periapical radiographs.56 While it has been reported that CBCT imaging, compared to surgical re-entry evaluation, can be as high as 84% accurate in determining maxillary molar furcation defects, CBCT may underestimate the extent of the furcation in around 15% of defects and overestimate the defect in only around 1% of defects.57 Furthermore, CBCT was found to be most accurate for assessing disto-palatal furcations, followed by buccal and mesio-palatal defects.57 When using clinical measurements and conventional radiographs, furcation involvement may be accurately predicted for 27% of sites, with 29% overestimating the furcation and 44% underestimating the defect compared to CBCT.58
It may be that CBCT proves to be a valuable tool in determining the furcation involvement of teeth, which could be advantageous in treatment planning and preoperative surgical assessment. Nonetheless, to date, exactly what role CBCT can play in this relation remains to be determined.
Is there a need for CBCT in periodontology?
The current available information suggests that the applications of CBCT in periodontics are limited. CBCT may play a role in the assessment of three-dimensional defects, especially furcations and infrabony defects, in which defect morphology directly influences treatment planning and prognosis of teeth. When used for this purpose it should be recommended that the field of view is limited to the area of interest to avoid unnecessary exposure of the patient to radiation. With advances in technology it may be that the radiation dose needed for imaging may decrease and with new algorithms less noise and artefacts may be produced, which would significantly increase the indications and applications for CBCT imaging. However, it should be noted that unless there is a sound clinical indication, CBCT imaging should not routinely be performed for the evaluation of patients with periodontal disease. At present, it can be seen as an additional imaging technique in situations where insufficient or unreliable information is obtained from traditional X-ray techniques such as intraoral radiographs or OPGs.