Darkening of Third Molar Roots: Panoramic Radiographic Associations With Inferior Alveolar Nerve Exposure

Automatic visualization of the mandibular canal in relation to an impacted mandibular third molar on panoramic radiographs using deep learning segmentation and transfer learning techniques

OBJECTIVE

The aim of this study was to create and assess a deep learning model using segmentation and transfer learning methods to visualize the proximity of the mandibular canal to an impacted third molar on panoramic radiographs.

STUDY DESIGN

The panoramic radiographs containing the mandibular canal and impacted third molar were collected from 2 hospitals (Hospitals A and B). A total of 3200 areas were used for creating and evaluating learning models. A source model was created using the data from Hospital A, simulatively transferred to Hospital B, and trained using various amounts of data from Hospital B to create target models. The same data were then applied to the target models to calculate the Dice coefficient, Jaccard index, and sensitivity.

RESULTS

The performance of target models trained using 200 or more data sets was equivalent to that of the source model tested using data obtained from the same hospital (Hospital A).

CONCLUSIONS

Sufficiently qualified models could delineate the mandibular canal in relation to an impacted third molar on panoramic radiographs using a segmentation technique. Transfer learning appears to be an effective method for creating such models using a relatively small number of data sets.

Pre-eruptive intracoronal resorption in "high-risk" impacted third molars: A report of four cases

Pre-eruptive intracoronal resorption (PEIR) is usually an incidental finding as a radiolucent lesion within the coronal dentin of unerupted teeth. Through the four cases reported here, authors would demonstrate deeply impacted "high-risk" third molars with PEIR defects, showing an increased risk of inferior alveolar nerve (IAN) injury. However, follow-up or coronectomy may eliminate or reduce the risk of neurosensory disturbances, in case of PEIR lesions this can be contradictory due to the unpredictable reactions of the third molar's pulp. Cases show the important role of preoperative imaging in the diagnostics and management of deeply impacted PEIR third molars and highlight the need for investigations regarding coronectomy in such cases.

Comparison of Digital OPG and CBCT in Assessment of Risk Factors Associated with Inferior Nerve Injury during Mandibular Third Molar Surgery

Background: Pre-operative radiographic assessment of the anatomical relationship between the roots of the mandibular third molar and the inferior alveolar nerve (IAN) is a must to minimize the risk of IAN injury during surgery. Objectives: To compare the radiographic signs of digital orthopantomogram (OPG) and cone-beam computed tomography (CBCT). An additional objective was to assess the cortex status between the mandibular canal and third molar on CBCT images in relation to the demographic characteristics, region (right or left side), and angulation of mandibular molar. Methodology: In this retrospective study, a total of 350 impacted mandibular third molars with a close relationship between the inferior alveolar canal (IAC) and impacted mandibular third molars on digital OPG were further referred for CBCT imaging for assessment of the position of the mandibular canal. The study was conducted between August 2018 and February 2020. Digital OPGs were evaluated for radiographic signs like interruption of the mandibular canal wall, darkening of the roots, diversion of the mandibular canal, and narrowing of the mandibular canal. The age and sex of patients, site of impacted third molar, Winter’s classification of mandibular third molar, position of IAC relative to impacted molar, and the radiographic markers of OPG were assessed for cortical integrity using CBCT. Chi square testing was applied to study the values of difference and binomial logistic regression was done to assess the factors associated with cortication. Statistical significance was set at p ≤ 0.05. Results: Among 350 patients, 207 (59.1%) were male and 143 (40.9%) were female with a mean age of 36.8 years. The most common OPG sign was interruption of white line, seen in 179 (51.1%) cases. In total, 246 cases (70.3%) showed an absence of canal cortication between the mandibular canal and the impacted third molar on CBCT images. Cortication was observed in all cases with a combination of panoramic signs which was statistically significant (p = 0.047). Cortication was observed in 85 (50.6%) cases where IAC was positioned on the buccal side, 11 (16.9%) in cases of inferiorly positioned IAC, and just 8 (7.6%) for cases of lingually positioned IAC which was statistically significant (p = 0.003). Statistically insignificant (p > 0.05) results were noted for cortex status in CBCT images with regards to the age, sex, site, and angulation of impacted third molars. Conclusion: CBCT imaging is highly recommended for those cases where diversion of the mandibular canal is observed on OPG and when the roots are present between canals.

Positive Predictive Value of Panoramic Radiography for Assessment of the Relationship of Impacted Mandibular Third Molars with the Mandibular Canal Based on Cone-Beam Computed Tomography: A Cross-Sectional Study

The aim of the present study was to assess the positive predictive value (PPV) of panoramic radiographic signs in the assessment of the relationship between impacted mandibular third molars (IMTMs) and the mandibular canal (MC). This cross-sectional study was conducted by reviewing 102 cone-beam computed tomography (CBCT) and panoramic radiographs of patients with IMTMs and radiographic signs of the contact of the IMTMs with the MC on panoramic radiographs (i.e., root apex darkening and interference with the white line). A positive relationship of the IMTM roots with the MC based on CBCT findings was recorded as the gold standard. The PPV of panoramic radiographic signs was calculated for the detection of the relationship of the IMTM root with the MC. The IMTMs were in contact with the MC on CBCT scans in 90.1% of the cases. The PPV of root apex darkening and the interference with the white line was found to be 89.09% (95% CI: (77.75, 95.88)) and 91.48% (95% CI: (79.62, 97.63)), respectively. The MC had a buccal position in 63.7%, and a lingual position in 35.2%, of the cases. The contact of IMTMs with the MC was more commonly seen in patients with a lingual position (100% of the samples). The IMTM root apex darkening and interference with the white line of the MC on panoramic radiographs had a high PPV for determination of the contact of IMTMs with the MC. Thus, presence of the above-mentioned risk factors indicates the need for subsequent 3D radiographic assessments.

Is it possible to filter third molar cases with panoramic radiography in which roots surround the inferior alveolar canal? A comparison using cone-beam computed tomography

Inferior alveolar nerve (IAN) entrapment in third molar (M3) roots bears a significant risk for nerve injury. The aim of this study was to identify specific panoramic radiographic (PR) signs that can reliably identify IAN entrapment (IANE) root conformations. In a retrospective case-control study, 10 IANE and 218 non-IANE third molar risk cases were examined by PR and CBCT. The collected data included "classic" specific high-risk panoramic signs, number of M3 roots, extent of inferior alveolar canal (IAC)-root tip overlap, rotated position of M3 and impaction pattern. After bivariate analysis, sensitivity, specificity, positive and negative predictive values, positive likelihood ratios (LR+) and accuracy (area under the curve [AUC]) were calculated for the most significant predictive variables. Interruption of both cortical lines (LR⁺: 43.6; AUC: 96.0%) and upward diversion of the IAC (LR⁺: 36.3; AUC: 96.5%) were the most accurate single signs indicating IANE. Upward diversion combined with root darkening and interruption of the IAC (AUC: 97.4%) and the combination of darkening with interruption and with a rotated M3 (LR⁺:130.8; AUC: 97.8%) were the most accurate combinations predicting IANE. IANE may be correctly filtered with PR when focusing on the signs of upward diversion, darkening, interruption and rotated M3 position, especially in cases involving their multiple (≥3) presence. CBCT evaluation is highly recommended in these cases before partial and total tooth removals.

Reliability of Cone Beam Computed Tomography in Comparison with Panoramic Radiography to Predict the Anatomical Relationship of Inferior Alveolar Nerve with Mandibular Third Molar: A Radiological and Clinical Study

Objectives:

The purpose of the study was to assess the precision of cone beam computed tomography (CBCT) in comparison with panoramic radiography in determining the anatomical relationship of inferior alveolar nerve (IAN) with the impacted mandibular third molar.

Materials and Methods:

Twenty patients diagnosed with the following panoramic radiographic markers: darkening of the root, interruption of white line of mandibular canal, diversion of mandibular canal, and narrowing of the roots suggesting a close relationship of roots with the mandibular canal were selected and underwent an additional CBCT to assess the proximity of IAN to mandibular third molar roots. All patients were assessed for loss of sensation or neurosensory deficit in the chin and lower lip during postoperative period by objective and subjective methods.

Results:

Twenty patients with an average age of 25.4 years (21–39 years) with 21 impacted mandibular third molars were included in this sample. It was found that after the removal of impacted third molars, IAN was not visible in any of the cases and postoperative objective and subjective neurosensory tests showed no signs of neurosensory disturbances.

Conclusion:

The study found that CBCT had limited usefulness in neurovascular bundle exposure prediction, prior to surgical removal of impacted mandibular third molars. The accuracy of radiographic markers in conventional panoramic radiography to predict neurovascular exposure was also limited.

Comparison of 3 deep learning neural networks for classifying the relationship between the mandibular third molar and the mandibular canal on panoramic radiographs

OBJECTIVE

The aim of this study was to compare time and storage space requirements, diagnostic performance, and consistency among 3 image recognition convolutional neural networks (CNNs) in the evaluation of the relationships between the mandibular third molar and the mandibular canal on panoramic radiographs.

STUDY DESIGN

Of 600 panoramic radiographs, 300 each were assigned to noncontact and contact groups based on the relationship between the mandibular third molar and the mandibular canal. The CNNs were trained twice by using cropped image patches with sizes of 70 × 70 pixels and 140 × 140 pixels. Time and storage space were measured for each system. Accuracy, sensitivity, specificity, and the area under the receiver operating characteristic curve (AUC) were determined. Intra-CNN and inter-CNN consistency values were calculated.

RESULTS

Time and storage space requirements depended on the depth of CNN layers and number of learned parameters, respectively. The highest AUC values ranged from 0.88 to 0.93 in the CNNs created by 70 × 70 pixel patches, but there were no significant differences in diagnostic performance among any of the models with smaller patches. Intra-CNN and inter-CNN consistency values were good or very good for all CNNs.

CONCLUSIONS

The size of the image patches should be carefully determined to ensure acquisition of high diagnostic performance and consistency.

Identification of Specific Panoramic High-Risk Signs in Impacted Third Molar Cases in Which Cone Beam Computed Tomography Changes the Treatment Decision

PURPOSE

The aim of this study was to investigate the treatment decisions of oral-maxillofacial surgeons in the management of impacted lower third molars (M3s) according to panoramic radiography (PR) and cone beam computed tomography (CBCT) risk analysis.

PATIENTS AND METHODS

Ten surgeons analyzed 40 deliberately selected M3 cases showing 1 or more panoramic high-risk signs: 1) darkening of the root, 2) interruption of the white line, 3) diversion of the inferior alveolar canal (IAC), 4) narrowing of the IAC, and 5) 2 or more signs occurring simultaneously (including darkening and/or interruption of the IAC). After evaluating the PR images, the observers analyzed the patients' CBCT images. The treatment decision (extraction vs coronectomy) and surgical technique (number of planned tooth sections) were recorded.

RESULTS

On the CBCT coronal slices, direct contact between the M3 and IAC, together with narrowing and/or fenestration of the IAC, was observed most frequently when 2 or more panoramic signs were seen simultaneously on the PR images (odds ratio [OR], 7.2; P = .021). CBCT findings led to a significant decrease in the number of coronectomy decisions (23% vs 14.5%, P = .002), which was most prominent in the groups showing panoramic signs of darkening (approximately 50%, P = .007) and narrowing (approximately 66%, P = .044). A significant number of extraction decisions were modified to coronectomy when 2 or more panoramic signs occurred together (OR, 7.9; P < .001). However, there were no significant differences regarding the number of planned hypothetical tooth sections.

CONCLUSIONS

The results showed that the surgeons' confidence in the treatment decision increased after CBCT imaging, resulting in fewer coronectomy decisions. CBCT information that changed a previous coronectomy decision to extraction was most frequently observed in cases showing darkening and narrowing PR signs. The chance of changing an extraction decision to a coronectomy decision after evaluating the patient's CBCT images was the highest when 2 or more PR signs were observed simultaneously.

Tooth sectioning for coronectomy: how to perform?

OBJECTIVES

The aim of this study was to determine the increase in heat production, preparation time, and cutting surface quality of conventional, high-speed rotating instruments and piezoelectric preparation for coronectomy procedures.

MATERIALS AND METHODS

One hundred intact extracted molars were sectioned horizontally, sub-totally, 1 mm under the cemento-enamel line with five methods: (1) tungsten carbide torpedo (TcT), (2) round (TcR) drills using a conventional speed surgical straight handpiece (< 40,000 min^-1), (3) tungsten carbide fissure (TcF), (4) diamond torpedo (DT) drills using a surgical high-speed, contra-angle handpiece (~ 120,000 min^-1), or (5) a saw-like piezoelectric tip (PT). Temperatures, preparation times, and cutting surface irregularities were registered and the differences were analyzed with ANOVA, Tukey's HSD post hoc test (temperature, time) and with chi-square test (irregular surface).

RESULTS

Rotating instruments produced a maximal temperature increase of less than 1 °C. TcF produced the least heat (ΔT = - 3.92 °C to the baseline), while PT produced significantly the highest temperature increases (ΔT = 12.38 °C, p < 0.001). Tungsten carbide drills were the fastest for coronectomy (from 55.9 to 64.3 s), while DT (169.7 s) while PT (146.8 s) were significantly slower. TcT and TcR drills produced an irregular root surface more frequently.

CONCLUSIONS

During coronectomy, rotating instruments produced entirely acceptable heat, while PT produced unacceptable temperatures. Tungsten carbide drills performed coronectomies effectively, but the diamond torpedo and PT seemed clinically questionable. Considering heat, speed, and the cutting surface quality simultaneously, TcF in a surgical high-speed handpiece seems to be the best choice for coronectomy.

CLINICAL RELEVANCE

The correct insert can significantly reduce excessive heat and operation time during coronectomy procedures.

Diagnostic value of cone beam computed tomography and panoramic radiography in predicting mandibular nerve exposure during third molar surgery

The aim of this study was to evaluate the diagnostic accuracies of cone beam computed tomography (CBCT) and panoramic techniques in predicting inferior alveolar nerve (IAN) exposure. The sample size was determined based on a pilot study. This prospective clinical series study included 59 third molar extraction sites with any of seven previously suggested panoramic signs of IAN exposure. The diagnosis of nerve exposure was done on panoramic and CBCT images. Molars were extracted and nerve exposure was evaluated clinically. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of CBCT method, and sensitivity and PPV of panoramic method were estimated). The panoramic and CBCT methods correctly classified 67.7% and 93.3%, respectively, of 60 cases. This difference was statistically significant (χ²=13.333, P=0.000). The sensitivity, specificity, PPV, and NPV for CBCT were 97.4%, 85.7%, 92.7%, and 94.7%, respectively. The sensitivity and PPV of panoramic radiography were 67.8% and 97.6%, respectively. The signs with the highest sensitivity were interruption of the mandibular canal border and abrupt canal narrowing. None of the Pell and Gregory criteria, molar angulations, or three-dimensional canal-apex relationships was significantly associated with clinically confirmed IAN exposure. Panoramic radiography may miss about one-third of exposure cases, but a positive panoramic diagnosis is most likely to be a real exposure and should be taken seriously.

Accuracy of Panoramic Radiograph in Assessment of the Relationship Between Mandibular Canal and Impacted Third Molars

Background:

The relationship between impacted mandibular third molar and mandibular canal is important for removal of this tooth. Panoramic radiography is one of the commonly used diagnostic tools for evaluating the relationship of these two structures.

Objectives:

To evaluate the accuracy of panoramic radiographic findings in predicting direct contact between mandibular canal and impacted third molars on 3D digital images, and to define panoramic criterion in predicting direct contact between the two structures.

Methods:

Two observers examined panoramic radiographs of 178 patients (256 impacted mandibular third molars). Panoramic findings of interruption of mandibular canal wall, isolated or with darkening of third molar root, diversion of mandibular canal and narrowing of third molar root were evaluated for 3D digital radiography. Direct contact between mandibular canal and impacted third molars on 3D digital images was then correlated with panoramic findings. Panoramic criterion was also defined in predicting direct contact between the two structures.

Results:

Panoramic findings of interruption of mandibular canal wall, isolated or with darkening of third molar root were statistically significantly correlated with direct contact between mandibular canal and impacted third molars on 3D digital images (p < 0.005), and were defined as panoramic criteria in predicting direct contact between the two structures.

Conclusion:

Interruption of mandibular canal wall, isolated or with darkening of third molar root observed on panoramic radiographs were effective in predicting direct contact between mandibular canal and impacted third molars on 3D digital images. Panoramic radiography is one of the efficient diagnostic tools for pre-operative assessment of impacted mandibular third molars.

Significance of radiological variables studied on orthopantamogram to pridict post-operative inferior alveoler nerve paresthesia after third molar extraction

CONTEXT

Removal of impacted third molar is a procedure that is often associated with post-operative complications. The rate of complications is somewhat high because of its proximity to the vital structures. Inferior alveolar nerve paresthesia is one of the common complications of impacted their molar surgery. This is due to intimate relationship between roots of mandibular third molar and inferior alveolar canal. To access the proximity of inferior alveolar canal to third molar many diagnostic methods are suggested but in conventional radiography orthopantamogram is considered as the best. There are many findings onorthopantamogram that are suggestive of close proximity of nerve to the canal. In this study authors reviewed seven radiographic findings related to proximity of roots to the inferior alveolar nerve as seen on orthopantamogram and try to find a relationship between these radiographic variables and presence of post-operative paresthesia.

STUDY DESIGN

The study containd 100 impacted third molars need to be removed. Presence of radiographic findings on orthopantamogram were noted and analyzed, to find a relationship with occurrence of post-operative inferior alveolar nerve paresthesia.

MATERIALS AND METHODS

This study comprises of 100 impacted third molar teeth indicated for extraction. Cases were randomly selected from the patients, needs to undergo extraction of impacted mandibular third molar. After extraction cases were evaluated for occurrence of inferior alveolar nerve paresthesia. Stastical Analyisis: Data was transferred to SPss 21 software for frequency calculation, and two tailed p-values were obtained betweens these variables and post-operative paresthesia, by applying Fischer's exact test (GRAPH PAD SOFTWARE).

RESULTS

Out of seven, four radiological findings that are grooving of roots, hooked roots, bifid roots and obliteration of white line are significantly related to post-operative paresthesia while bending of canal, narrow canal and darkening of tooth roots over the canal are not significantly associated with post-operative morbidity of facial nerve.

Panoramic radiography and cone-beam computed tomography findings in preoperative examination of impacted mandibular third molars

BACKGROUND

Preoperative radiographic examination of impacted mandibular third molars (IMTM) is essential to prevent inferior alveolar nerve injury during extraction. The purpose of this study was to evaluate the correlation between cone-beam computed tomography (CBCT) and digital panoramic radiography (DPR) findings in preoperative examination of IMTM.

METHODS

This retrospective study included 298 teeth in 191 individuals. The relationship between the inferior alveolar canal (IAC) and the IMTM (buccal, lingual, interradicular or inferior), the position of the IMTM with respect to the IAC (contact, no contact), the morphologic shape of the mandible in the IMTM region (round, lingual extended, lingual concave), the type of IMTM (vertical, horizontal or angular) and the number of roots of the IMTM were evaluated on CBCT images. DPR images were evaluated for the number of roots of the IMTM and for the most common radiographic findings indicating a relationship between the IAC and the IMTM (darkening of the roots, diversion of the IAC, narrowing of the IAC and interruption of the white line). Data were statistically analyzed with Cramer V coefficient, Kappa statistic, chi-square and Fisher's exact test.

RESULTS

There was a significant difference in number of roots detected on DPR versus CBCT images. There was a significant association between the type of IMTM and the morphologic shape of the mandible on CBCT images. Darkening of the roots and interruption of the white line on DPR images were significantly associated with the presence of contact between the IMTM and the IAC on CBCT images.

CONCLUSIONS

Panoramic radiography is inadequate, whereas CBCT is useful to detect multiple roots of IMTM. When darkening of the roots and interruption of the white line are observed on panoramic images, there is increased likelihood of contact between the IMTM and the IAC. CBCT is required in these cases.

Objectivity and reliability of panoramic radiographic signs of intimate relationship between impacted mandibular third molar and inferior alveolar nerve

INTRODUCTION

The results of prior studies assessing the accuracy of panoramic radiographic signs of intimate relationship between inferior alveolar nerve (IAN) and impacted molars are controversial. This may be partly due to inadequate objectivity and reliability of these radiographic signs, which is evaluated in the present study.

MATERIALS AND METHODS

Three hundred radiographs in which impacted third molar reached the superior border of the inferior alveolar canal or was superimposed by the canal were evaluated by three examiners independently, twice 3 months apart. Inter- and intra-examiner agreements were analyzed using kappa statistics.

RESULTS

The inter-examiner agreement for all radiographic signs was poor (k < 0.2). The intra-examiner agreement for radiographic signs 2, 3, and 6 was poor with mean kappa values of 0.08, 0.00, and 0.09, respectively. Concerning the radiographic signs 4, 5, 7, and 8, the intra-examiner agreement was moderate with mean kappa values of 0.54, 0.49, 0.44, and 0.57, respectively. The mean kappa coefficient for the radiographic sign 1 yielded a good agreement (k = 0.65).

CONCLUSIONS

In the present study, the examiners were unable to reliably assess radiographic signs of intimate relationship between IAN and third molar, indicating that panoramic images should not be relied upon for preoperative prediction of IAN injury.

Factors that are associated with injury to the inferior alveolar nerve in high-risk patients after removal of third molars

Our aim was to answer the question: "Among patients at high risk of injury to the inferior alveolar nerve (IAN) after removal of 3rd molars, what factors are associated with postoperative neurosensory deficits?" We organized a retrospective, two-center study and enrolled a group of subjects who were at increased risk of injury to the IAN after removal of 3rd molars because radiographic findings indicated a risk on panoramic radiography that was high enough to warrant preoperative computed tomography (CT). The primary outcome variable was postoperative injury to the IAN. We used descriptive, bivariate, and multivariate analyses to assess the significance of differences, and probabilities of less than 0.05 were accepted as significant. We studied 149 subjects who had 235 3rd molars removed. Their mean (SD) age was 31 (11) years and 25/235 (11%) of 3rd molars were associated with injury to the IAN. In the multiple logistic regression model, increasing age (odds ratio (OR) 1.05, 95% CI 1.01-1.1, p=0.04), female sex (OR 5.3, 95% CI 1.6-16.9, p=0.005), and the size (mm) of the cortical perforation in the inferior alveolar canal (IAC) viewed on the coronal CT cut (OR 1.3; 95% CI 1.0-1.6, p=0.03) were associated with an increased risk of postoperative injury to the IAN. Age, sex, and the size of the perforation in the IAC on the coronal CT were associated with an increased risk of injury to the IAN. These findings may help to guide recommendations for treatment of patients at high risk of injury to the IAN during removal of 3rd molars.

Quantitative pixel grey measurement of the "high-risk" sign, darkening of third molar roots: a pilot study

OBJECTIVES

Our aim was to examine the panoramic darkening of the root, which is a "high-risk" sign, using quantitative measurements of pixel grey values to determine different aetiological backgrounds, namely inferior alveolar nerve (IAN) exposure with or without groove formation of the third molar roots or thinning/fenestration of the lingual cortex (LCTF).

METHODS

38 impacted third molars that had been surgically removed and had darkened roots on panoramic radiographs were included in this retrospective case-control study. 15 IAN exposure cases were selected for the case group, and 23 cases with proven lingual cortical thinning or fenestration were chosen for the control group. The mean pixel grey values of selected areas in the dark band (D) and control areas within the same roots (R) were determined with the ImageTool (University of Texas Health Science Center, San Antonio, TX) software. The differences in pixel values (R-D) of the IAN and LCTF groups were analysed using the Mann-Whitney U-test and Pearson's χ(2) test.

RESULTS

The medians of the R-D pixel values were 45.7 in the IAN group and 34.3 in the LCTF group, whereas the interquartile ranges were 12.0 (IAN) and 18.3 (LCTF) (p < 0.001). The R-D critical value at which the outcomes differed significantly was 38. If the differences in pixel grey values (R-D) were higher than 38, the chance of IAN exposure was approximately 32 times higher than the chance of LCTF (χ(2) test, p < 0.001; odds ratio, 32.0; 95% confidence interval, 3.5-293.1).

CONCLUSIONS

The pre-operative prediction of IAN exposure or lingual cortical thinning in cases with "darkening" is possible based on pixel grey measurements of digital panoramic radiographs.

Darkening of third molar roots on panoramic radiographs: is it really predominantly thinning of the lingual cortex? Int J Oral Maxillofac Surg. 2013;42:483-488. [PMID: 22835682 DOI: 10.1016/j.ijom.2012.06.018]

This study investigated the exact intra-alveolar aetiology of a panoramic high-risk sign, darkening of the third molar roots. 83 mandibular third molar surgical removals demonstrating dark bands on the third molar roots in preoperative radiographs were included in this prospective study. Exposure of the inferior alveolar nerve (IAN), the root morphology of the third molar (e.g. groove or hook) and the integrity of the mandibular canal or lingual cortical wall were observed. Differences between single (increased radiolucency alone) and multiple darkening cases (increased radiolucency with accompanying 'high risk' signs) and between IAN exposure and groove formation were analysed. In 38 cases (45.8%), the IAN was visible during the operation. Groove was present in 37.4% of cases. 26.5% of the cases showed lingual cortical thinning, while specious root conformation explained the formation of darkening on the radiographic images of an additional 9.6% of the cases. IAN exposure (P<0.001) and groove formation (P<0.001) were significantly more frequent in multiple darkening cases than in single darkening cases. According to these findings, darkening of the third molar roots is more often the result of fenestration of the inferior alveolar canal wall or groove formation of the root than lingual cortical thinning.

Correlation of panoramic radiography and cone beam CT findings in the assessment of the relationship between impacted mandibular third molars and the mandibular canal

OBJECTIVES

The aim of this study was to assess the reliability of four panoramic radiographic findings, both individually and in association, in predicting the absence of corticalization between the mandibular canal and the third molar on cone beam CT (CBCT) images.

METHODS

The sample consisted of 72 individuals (142 mandibular third molars) who underwent pre-operative radiographic evaluation before extraction of impacted mandibular third molars. On panoramic radiographs, the most common signs of corticalization (darkening of roots, diversion of mandibular canal, narrowing of mandibular canal and interruption of white line) and the presence or absence of corticalization between the mandibular third molar and the mandibular canal on CBCT images were evaluated.

RESULTS

Darkening of roots and interruption of white line associated with the absence of corticalization between the mandibular third molar and the mandibular canal on CBCT images were statistically significant, both as isolated findings (p = 0.0001 and p = 0.0006, respectively) and in association (p = 0.002). No statistically significant association was observed for the other panoramic radiographic findings, either individually or in association (p > 0.05).

CONCLUSION

Darkening of roots and interruption of white line observed on panoramic radiographs, both as isolated findings and in association, were effective in determining the risk relationship between the tooth roots and the mandibular canal, requiring three-dimensional evaluation of the case.