Buccal-Radial Radiographic Projections Allow Accurate Detection Of Cortical Bone Defects In Cadaver Mandibles By Practitioners With Different Levels Of Expertise

Introduction
Cone beam computed tomography (CBCT) has been recommended for the “diagnosis of radiographic signs of periapical pathology when there are contradictory (nonspecific) signs and/or symptoms”.1 CBCT provides additional information from three-dimensional images; however, there is a need for the clinician to justify its use because of the increased ionizing radiation, so it should be considered only after assessing appropriate conventional radiographs.1,2

Therefore, intraoral radiographs are still essential to perform an adequate diagnosis and root canal treatment; however, some periradicular bone defects remain undetected unless they have eroded or altered a portion of the cortical bone.3–7 It has been reported that radiographic visualization is not directly related to the loss of volume of hard tissue but to the mineral content in it: the higher the mineral content, the less volume of tissue that needs to be lost for visualization.7

Variations of ortho-radial projections taken from different horizontal angulations have been recommended to achieve better visualization of periapical radiolucent images for more accurate detection and diagnosis.8,9 Vertical angulations (also known as lingual-radial and buccal-radial projections) have also been recommended for this purpose.10

Horizontal angulations allow variations from the ortho-radial projection9 to mesial or distal, while the vertical position is maintained. Therefore, the X-ray beam is directed 20° from the longitudinal axis of the tooth to mesial or distal only in the horizontal axis.9 Two vertical angulations were recommended by Kuttler10, the so-called lingual-radial and buccal-radial. For lingual-radial projections, the angulation of the X-ray beam is increased 20°, resulting in a shortened image with clinical crowns radiographically similar in length to the root. On the other hand, buccal-radial projections obtain larger images by diminishing the vertical angulation 20° from the ortho-radial angulation of the tooth, allowing all buccal structures to move occlusally and therefore permit improved observation of the posterior and apical portions of the teeth. In maxillary molars and premolars, the maxillary sinus cortex and zygoma move coronally. In mandibular premolars and molars, the inferior alveolar nerve moves toward the roots, making this angulation effective for locating, for example, an entomolaris radix present in some mandibular molars.10 By making the teeth appear longer, some structures, such as the pulp chamber, root canals, and periapical zone, are also better observed.10

Previous studies have reported the limitations of intraoral radiography to detect periapical bone defects; however, vertical angulations were not used.3–5,7,9,11

Some authors have confirmed the importance of varying the horizontal angulations (observing a third dimension of the teeth)9 and vertical angulations to observe the pulp chamber and periapical lesions more precisely10 and to differentiate anatomical structures from periradicular alterations by using the Clark buccal object rule.12 Digital images have been more accurate than conventional radiographs in detecting artificial lesions cut into human cadavers13,14, but no difference was noted when the lesion involved cortical bone.13 On the other hand, Ektaspeed Plus film showed superior sensitivity and specificity for detecting simulated periapical lesions than did photo-stimulable, phosphor-based digital images.15 Substraction radiographic images were also better than conventional radiographs and radiovisiograph digital images when detecting 2-4 mm deep artificial bone defects, although no method was effective in detecting 0–1 mm defects. At the same time, experienced observers performed better than those without such experience.16

Therefore, the objective of the present study was to evaluate the accuracy of various vertical and horizontal radiographic angulations in detecting artificial bone defects by practitioners with different levels of expertise.

Materials And Methods
A special device named “angulation locator” was designed to obtain five different standardized radiographic projections (three horizontal and two vertical) with a radiovisograph (TRO-USB-RADIO1 RVG, Trophy, Marne-La-Vallée, France) and a Radiologie X-ray machine (Trophy) to be used at 70 kVp and 8 mA.

The mandibles of two adult human skulls were dissected, measured, and cut between the two central incisors to obtain four mandibular segments.

First Series of X-rays: Pre-operative Images
Each segment was placed in the angulation detector and five different images were obtained with the following angulations before any further sectioning was done: ortho-radial, mesial-radial, distal-radial, lingual-radial, and buccal-radial.

Second Series of X-Rays: Images Taken After Removal of the Buccal Cortical Plate and 3 mm of Cancellous Bone
Each mandibular segment was further sectioned with an HM23L tungsten carbide bur (Meisinger, Rin-Ruhr, Germany) to separate only the buccal cortical plates. First, it was cut vertically from the cervical third of the tooth to the inferior border of the mandible and, later, horizontally from the distal surface of the canine (mesial limit) to 5 mm posterior to the last molar present in the arch (distal limit).

The buccal cortical plate was then separated with bone scalpels and reattached with plastic stripes that permitted repositioning in the original position. The width of the cortical plates was measured before creating artificial bone defects. Later, 3 mm of cancellous bone was removed at the root level of the molars in each section. The cortical plate was then reattached and the second series of radiographs was taken from all five angulations.

Third Series of X-rays: Images Taken After Erosion of Cortical Bone Defect (0.5 mm)
An artificial bone defect (diameter, 3 mm; depth, 0.5 mm) was cut into the cortical bone plates with a round diamond bur, size 6909 (Brasseler, Savannah, Ga) in a high-speed handpiece. The amount of bone removed was measured using a calibrator (Fig. 1).

Figure 1

(A) 0.5 mm and (B) 1 mm bone defects in the cortical plate.

The cortical plate was repositioned and the third series of radiographs with the five radiographic angulations was taken.

Fourth Series of X-rays: Images Taken After Erosion of Cortical Bone Defect (1 mm)
The bone defect created in the previous series was enlarged to 1 mm in depth. Bone plates were again repositioned and the fourth series of radiographs with the five radiographic angulations was taken (Fig 1).

A total of 80 images were obtained and stored. Those from the first and second series were considered not to have a cortical bone defect (n = 40) and were included in the “no cortical bone defect” category. Those from the third and fourth series (n = 40) were determined to have cortical bone defects.

Evaluation of Images
Six blinded examiners with different levels of expertise, who had previously been calibrated, evaluated the images. Three examiners were endodontists with more than 20 years of experience, and the other three were first-year endodontic residents.

All 80 images were projected in a random manner on a 1.5 × 1.5-foot screen with a 5× magnification. Each image was projected for 20 seconds on the screen, which was 3.80 meters from the evaluators. Each evaluator blindly rated each image annotating the following parameters:
–Presence of normal trabeculae or bone defect
– Location of the observation in the case that a bone defect was detected.

Kappa coefficient was calculated to measure the overall level of agreement between observers’ data and the actual data registered from each specific phase of analysis. The interobserver level of agreement was also calculated for specialists and nonspecialist practitioners. The level of agreement between actual mandibular data and those obtained from each evaluator was also calculated for each independent X-ray angulation. Consensus data among experienced endodontists and endodontic residents were used independently to calculate the sensitivity and specificity for the overall data and for each specific angulation. Accuracy between experienced endodontists and residents was compared with the chi-square test.

Results
Overall agreement varied from 0.6-0.8 (good) for the experienced endodontists to 0.5-0.58 (moderate) for the endodontic residents. However, the level of agreement varied considerably for each X-ray angulation, as shown in Tables 1A and 1B. Kappa coefficient values reached k = 1 for two of the three experienced endodontists and one of the three residents when buccal-radial angulations were used (Table 1).

Table 1A

Table 1B

Due to the inclusion of images taken in the first and second series in the “no cortical bone defect” category, all evaluators showed 100% accuracy in no defect detection for all the
angulations (specificity = 100%). However, overall sensitivity varied from 70% for the experienced endodontists to 52.5% for the endodontic residents. Specifically, sensitivity varied significantly (p = .001) from 45% to 60% detection with the 0.5 mm cortical bone defect for trained endodontists and endodontic residents, respectively. On the other hand, there were no significant differences in the accuracy of the 1 mm cortical bone defect detection between groups, although it varied from 80% in the endodontist group to 60% in the resident group.

At the same time, independent analysis for each angulation showed different levels of accuracy for both types of practitioners (Table 1). Buccal-radial angulations allowed 100% detection for the experienced endodontists when cortical bone defects were present, compared with 75% detection when ortho-radial and distal-radial angulations were used (Fig 2). The endodontic residents demonstrated 87.5% accuracy with buccal-radial angulations, followed by 75% with ortho-radial, and a significant decrease in accuracy when distal-radial, mesial-radial, or lingual-radial angulations were used.

Discussion
Radiographic interpretation is one of the most important aspects of diagnosis in endodontic therapy. Some studies have shown that detection of bone defects confined only to cancellous bone and without cortical involvement is not possible with conventional radiographic techniques.3–6,11,17 The present study confirmed this fact because the identification of the bone defects did not vary from the preoperative radiograph series to the one with cancellous bone defects (first and second series).

Barbat and Messer found that artificial defects in the cortical bone were better visualized when the defect was expanded both buccally and lingually to a 1 mm size.11 In the present study, a skull model was used, and mandibles were also sectioned from mesial to distal, but only the buccal bony segment was separated instead of both. In agreement with their findings, we observed 1 mm defects not only in ortho-radial radiographs, but in all angulations; however, accuracy varied depending on the evaluator’s level of expertise.

Besides, in the present study, 0.5 mm defects were also detected with all angulations, especially in the buccal-radial, probably because the defects were less “moved” and hidden in large, cancellous bone spaces. Similar observations were reported by Kuttler10, who observed that bone defects and periapical lesions were not detected when vertical angulation was increased; however, they became more evident when vertical angulation was reduced. Similar results were also obtained when micro-CT imaging was used. Detecting periapical lesions based on digitally reconstructed radiographs depended on lesion size, position, shape, and tooth position. Lesions smaller than 1 mm in incisors, 2 mm in premolars, and 3 mm in molars could not be visualized if these virtual lesions were confined within the cancellous bone. A 4 mm lesion in molars was still not visualized even though it encroached on the cortical bone18. Periapical lesions smaller than 1 mm were not detected with precision with either micro-CT or CBCT.18,19

Many authors have reported that CBCT is superior to intraoral digital images and conventional radiographs to detect periodical lesions17,20–22; however, the larger radiation dosages and higher cost17 need reconsidering. Even if radiation dosage can be reduced by lowering milliamperes23, the ALARA (as low as reasonably achievable) principle needs to be considered in all cases.

When the various vertical angulations were analyzed in the present study, the lingual-radial angulation showed the worst results while buccal-radial projections allowed accurate identification of cortical bone defects, reaching 100% accuracy for experienced clinicians. Following Clark’s rules12, all structures located buccally will move occlusally, causing a super-positioning of hard tissues with bone lesions in the periapical area when a lingual-radial projection is used. In contrast, the buccal-radial angulation moves buccal structures apically, making the bone lesions more easily identifiable (Fig. 2).

Figure 2

Bone defects (0.5 mm) observed from different angulations. (A) ortho-radial, (B) lingual-radial, (C) buccal-radial. Note that the buccal-radial angulation allows the best visualization.

Another important finding in this study was that the level of expertise influenced bone defect detection. Experienced evaluators reached the highest interobserver agreement when evaluating bone defects. At the same time, even the less experienced evaluators were able to identify 87.5% of the defects when using the buccal-radial angulation. This study suggests that the buccal-radial angulation is the best to detect bone defects both for inexperienced and experienced evaluators, who reached 100% detection of the artificial cortical bone defects (Table 1). Therefore, we recommend using this projection to detect periapical lesions either in addition to or instead of using horizontal angulations.

New technology such as digital substraction, computed tomography, microtomography, magnetic resonance, ultrasound, and nuclear techniques allow for more precise diagnosis24–34; however, periapical radiographs with different angulations, especially buccal-radial, are a convenient and relevant method to get proper information in many pre-, trans-, and postoperative situations.10

Under the limitations of the present study, we can conclude that buccal-radial angulations allow accurate identification of small cortical bone defects for practitioners with different levels of expertise. Future investigations are recommended to determine whether smaller cortical-bone lesions can also be accurately detected using this projection. OH

Oral Health welcomes this original article.

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