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]

Risk factors for impacted lower third molar root perforation through the undercut-shaped lingual plate: preoperative insights from panoramic radiography

This study aimed to identify risk factors associated with perforation of the undercut (U)-shaped lingual plate (LP) by the lower third molar (LM3) root using panoramic radiography (PAN). We retrospectively examined 468 impacted LM3s from 468 individuals, categorizing LM3-LP associations and LP morphology in the coronal section of cone-beam computed tomography as perforation or nonperforation and U-type or non-U-type, respectively. The outcome was the combination of perforation and U-type, and study variables included patient demographics (age and sex) and PAN-associated features (Winter's classification, Pell-Gregory classification, and two major Rood signs). Multivariate logistic regression methods were used for analysis. Perforated and U-type LPs were observed in 205 (43.8%) and 212 (45.3%) cases, respectively. The double-positive outcome was observed in 126 LM3s (26.9%). In the multivariate model, age ≥ 26 years [odds ratio (OR), 2.66; p = 0.002], men (OR, 2.01; p = 0.002), mesioangular (OR, 2.74; p = 0.038) and horizontal impaction (OR, 3.05; p = 0.019), and root darkening (OR, 1.73; p = 0.039) were independently associated with the risk. Class III impaction (OR, 0.35; p = 0.021) and interruption of the white line (OR, 0.55; p = 0.017) were negatively correlated with the risk. In conclusion, this study highlights the importance of identifying the higher probability of U-type LP perforation by the LM3 root in men aged over their midtwenties with Class I/II impaction and mesioangularly or horizontally impacted LM3s, along with root darkening and no interruption of the white line on PAN.

Proximity of mandibular third molar root(s) to surrounding cortical bone: cone beam computed tomography (CBCT) and panoramic findings

PURPOSE

We evaluated the relationship between mandibular third molar roots (M3Ms) and surrounding cortical bone using cone beam computed tomography (CBCT) and panoramic findings. We studied (a) the location of mandibular third molar roots in relation with cortical bone in terms of contact, penetration, and perforation on CBCT; (b) the relationship between characteristics of a root in panoramic findings and the CBCT image (entire and segmentally); and (c) the relationship of the root plane in panoramic findings vs. CBCT.

MATERIAL AND METHODS

One hundred five teeth with 224 roots of mandibular third molar from 73 patients were evaluated by using cone beam computed tomography and panoramic image.

RESULT

The relationships were assessed using 105 images of impacted M3Ms: 104/105 (99%) showed cortical bone involvement (30.4% penetration and 68.6% perforation). The more apical the segment, the higher the proportion of perforation. Most (79.9%) of the M3M roots involved a lingual cortex with 46.9% penetration and 49.2% perforation. The panoramic signs of segmental root images-viz. clear and blurred-were not associated with cortical penetration or perforation. Panoramic signs of individual root images-in the same and different planes-could be used to predict root plane M3M roots. The same appearance in the panoramic image was significantly related to the same plane of the root in CBCT (p-value 0.048).

CONCLUSION

These findings could contribute to enhanced radiological assessment and surgical planning.

Correlation of Panoramic Radiological and Intra-Operative Findings of Impacted Mandibular 3rd Molar in Relation to Inferior Alveolar Canal: A Prospective Study

Aim

The objective of this study was to correlate the preoperative radiological findings and intraoperative surgical findings during removal of impacted mandibular 3rd molar with respect to the inferior alveolar canal.

Materials and Method

The prospective study design included 100 patients between the age group of 20 years and 50 years who visited the Department of Oral and Maxillofacial Surgery at Vydehi Institute of Dental Sciences and Research Centre, Whitefield, Bengaluru. A preoperative panoramic radiograph was taken and the parameters were assessed and a normal surgical protocol was followed to extract the impacted mandibular 3rd molar with intra-operative assessment as well.

Results

Out of the 100 patients with definitive radiological signs showing close relation of the third molar to the mandibular canal who underwent surgical removal, only 12 patients presented with definitive clinical findings of the association.

Conclusion

A true close relationship between the third molars and mandibular canal increases the risk of inferior alveolar nerve injury, and accurate evaluation of the relationship is essential to avoid the risk of surgery. The accuracy of the plain radiographs to diagnose an intimate relationship between the neurovascular bundle and the third molar root has its limitations, since only 12 of the 100 patients with positive radiological signs showed clinical evidence of involvement. Surgeons should be aware of the limitations of the radiographic markers of panoramic radiography and should consider more detailed imaging in more specific cases in which one or more radiographic marker is present.

Anatomical Risk Factors of Inferior Alveolar Nerve Injury Association with Surgical Extraction of Mandibular Third Molar in Korean Population

The purpose of this study was to analyze the incidence and risk factors of possible inferior alveolar nerve (IAN) injury after extraction of the mandibular third molars. A total of 6182 patients were examined for 10,310 mandibular third molar teeth. Panoramic radiography and patients’ medical records were used to analyze age, gender, and impaction pattern of the mandibular third molar. Cone beam computed tomography (CBCT) was used to investigate the detailed pathway of the inferior alveolar nerve and evaluated the presence of symptoms of nerve damage after tooth extraction. In CBCT, 6283 cases (61%) of the inferior alveolar nerve were actually in contact with the root of the mandibular third molar. The correlation with the panoramic signs of root darkening (p < 0.001), root deflection (p < 0.001), interruption of the IAN (p < 0.001), diversion of the IAN (p < 0.001), and narrowing of the IAN (p < 0.001) had statistical significance. Of the 4708 patients who underwent surgical extraction, 31 (0.658%) complained of nerve damage. Among them, 30 patients (0.637%) complained of symptoms of inferior alveolar nerve damage, and 1 patient (0.02%) complained of symptoms of lingual nerve damage. There was a significant correlation with IAN injury in cases where the roots became dark at the IAN area (p = 0.018) and there was diversion of the IAN at the root area (p = 0.041). When the narrowing of the IAN and the lingual driving pathway of the inferior alveolar nerve appeared simultaneously in CBCT, the risk of IAN injury was high.

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.

Assessment of the reliability of radiographic signs on panoramic radiographs to determine the relationship between mandibular third molars and the inferior alveolar canal

OBJECTIVE

To assess the reliability of radiographic signs of the relationship between impacted mandibular third molars (IMTMs) and the inferior alveolar canal (IAC), and the vertical relationship between IMTM and IAC on panoramic radiographs (PRs) as risk indicators for IAC exposure during extraction.

STUDY DESIGN

Seven radiographic signs regarding the appearance of roots and the IAC were assessed as present or absent on PRs. The vertical relationship between IMTM and the IAC was divided into 3 levels. The correlation between radiographic data and IAC exposure during extraction was analyzed by using χ² statistics and logistic regression analysis.

RESULTS

In total, 198 IMTMs were examined. In 46 cases (23.2%), the IAC was exposed during extraction. Four radiographic signs-darkening of the root, narrowing of the root, narrowing of the IAC, and diversion of the IAC-were associated with IAC exposure (P < .05). Concurrence of 2 or more of 7 radiographic signs increased the risk of IAC exposure (P < .001). The vertical relationship between IMTM and the IAC was found to be a risk indicator for IAC exposure (P < .001). No significant correlation was found between IAC exposure and inferior alveolar nerve damage (P = .148).

CONCLUSIONS

Panoramic radiography is useful for assessing the risk of IAC exposure during IMTM extraction.

Orthopantomography and Cone-Beam Computed Tomography for the Relation of Inferior Alveolar Nerve to the Impacted Mandibular Third Molars

Context:

Relation of inferior alveolar nerve to the impacted mandibular third molars (IMTMs).

Aims:

The aim of this study was to assess the reliability of seven specific radiographic signs of mandibular third molar root that are observed on orthopantomography (OPG) and to predict the proximity and the absence of corticalization between the mandibular canal and IMTM root on cone-beam computed tomography (CBCT) images.

Settings and Design:

The present study was conducted in the Department of Oral and Maxillofacial Surgery, Raja Rajeswari Dental College and Hospital.

Subjects and Methods:

Data set of 30 panoramic images was retrieved between the year of 2015 and 2016 indicated for extraction of lower third molars. The sample consisted of 30 individuals, who underwent preoperative radiographic evaluation before the extraction of impacted mandibular third molars (IMTM). Patients aged above 18 years with any of the seven specific signs observed on the panoramic radiograph which includes darkening, deflection, narrowing of roots, bifid root apex, diversion, narrowing of canal and interruption in the white line of the canal were included in the study. If any of the above mentioned seven specific sign were present, the patient was subjected to CBCT. On the CBCT images, the canal was traced in three planes. The acquired images were assessed for the presence or absence of corticalization.

Statistical Analysis Used:

Descriptive and inferential statistical analyses were used. Proportions were compared using the Chi-square test and Student's t-test.

Results:

Among the 4 subjects, diagnosed with an absence of corticalization, patients with isolated darkening of root P = 0.001 and patients with isolated interruption in white line P = 0.69. Patients with darkening of root in association with interruption in white lines on OPG showed the absence of corticalization on CBCT findings P = 0.001, respectively.

Conclusions:

This study showed the poor reliability of radiographic signs seen on OPG on predicting the proximity of third mandibular root with mandibular canal related to CBCT finding. Four were diagnosed with the absence of corticalization in CBCT findings.

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.

Topographic relationship between root apex of mesially and horizontally impacted mandibular third molar and lingual plate: cross-sectional analysis using CBCT

The present study was aimed to determine the topographic relationship between root apex of the mesially and horizontally impacted mandibular third molar and lingual plate of mandible. The original cone beam computed tomography (CBCT) data of 364 teeth from 223 patients were retrospectively collected and analyzed. The topographic relationship between root apex and lingual plate on cross-sectional CBCT images was classified as non-contact (99), contact (145) and perforation (120). The cross-sectional morphology of lingual plate at the level of root apex was defined as parallel (28), undercut (38), slanted (29) and round (4). The distribution of topographic relationship between root apex and lingual plate significantly associated with gender, impaction depth, root number and lingual plate morphology. Moreover, the average bone thickness of lingual cortex and distance between root apex and the outer surface of lingual plate were 1.02 and 1.39 mm, respectively. Furthermore, multivariate regression analyses identified impaction depth and lingual plate morphology as the risk factors for the contact and perforation subtypes between root apex and lingual plate. Collectively, our findings reveal the topographic proximity of root apex of impacted mandibular third molar to the lingual plate, which might be associated with intraoperative and postoperative complications during tooth extraction.

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.

Clinical significance of computed tomography assessment for third molar surgery

Surgical extraction of the third molar is the most commonly performed surgical procedure in the clinical practice of oral surgery. Third molar surgery is warranted when there is inadequate space for eruption, malpositioning, or risk for cyst or odontogenic tumor formation. Preoperative assessment should include a detailed morphologic analysis of the third molar and its relationship to adjacent structures and surrounding tissues. Due to developments in medical engineering technology, computed tomography (CT) now plays a critical role in providing the clear images required for adequate assessment prior to third molar surgery. Removal of the maxillary third molar is associated with a risk for maxillary sinus perforation, whereas removal of the mandibular third molar can put patients at risk for a neurosensory deficit from damage to the lingual nerve or inferior alveolar nerve. Multiple factors, including demographic, anatomic, and treatment-related factors, influence the incidence of nerve injury during or following removal of the third molar. CT assessment of the third molar prior to surgery can identify some of these risk factors, such as the absence of cortication between the mandibular third molar and the inferior alveolar canal, prior to surgery to reduce the risk for nerve damage. This topic highlight presents an overview of the clinical significance of CT assessment in third molar surgery.

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.

Assessment of the shape of the inferior alveolar canal as a marker for increased risk of injury to the inferior alveolar nerve at third molar surgery: a prospective study

PURPOSE

Morphologic evaluation of computed tomographic images is an important assessment tool before surgical removal of the lower third molar (LM3). The aim of this study was to ascertain whether the shape of the inferior alveolar canal (IAC) is a reliable predictor for inferior alveolar nerve (IAN) injury during M3 surgery.

MATERIALS AND METHODS

This prospective study assessed samples with a high risk of IAN injury during M3 surgery based on orthopantomographic examination. The predictor variables were demographic factors (patient's age and gender), anatomic factors (angulation of the tooth), and radiographic factors (cortication status, buccolingual position, shape of the IAC, number of roots, and root shape). The outcome variable was IAN injury. The relation between predictor and outcome variables was analyzed using the Fisher exact test and a logistic regression model.

RESULTS

One hundred sixty-nine LM3s (115 patients) were analyzed. IAN injury was observed in 12 of 115 patients and 13 of 169 LM3s (7.7%). All 13 cases with IAN injury exhibited absence of cortication. A dumb-bell-shaped IAC was considered a useful predictor for IAN injury (sensitivity, 69.2%; specificity, 84.6%). In cases with absence of cortication, logistic regression analysis indicated that a dumb-bell-shaped IAC was closely related to IAN injury (P = .005).

CONCLUSION

The cortication status and shape of the IAC are reliable predictors for IAN injury at M3 surgery. Cases exhibiting absence of cortication and a dumb-bell-shaped IAC should be recognized as presenting a high risk of IAN injury at M3 surgery.

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.