Journal of Orofacial Sciences

ORIGINAL ARTICLE
Year
: 2018  |  Volume : 10  |  Issue : 2  |  Page : 101--107

Does Darkening of Roots or Loss of White Line on Panoramic Radiographs Pose a Risk for Inferior Alveolar Nerve Damage? A CBCT Evaluation


Chintan M Savani1, Kishan Panicker2, B. Sarat Ravi Kiran3, Uday Kiran Uppada3,  
1 Happy Dental Clinic, Surat, Gujarat, India
2 Kannur Dental College, Anjarakkandy, Kerala, India
3 Sri Sai College of Dental Surgery, Vikarabad, Telangana, India

Correspondence Address:
Dr. B. Sarat Ravi Kiran
Sri Sai College of Dental Surgery, Vikarabad, Telangana
India

Abstract

Introduction: Surgical removal of impacted mandibular third molars may cause dysesthesia due to damage to the inferior alveolar nerve (IAN), and the risk increases when there is direct contact between the nerve and the tooth root. An accurate preoperative radiographic examination using Cone beam computed tomography (CBCT) provides precise information pertaining the relationship between the third molar roots and the inferior alveolar canal. Aim & Objective: This study was intended to correlate the two panoramic radiographic findings in predicting the absence of corticalization between the mandibular canal and the third molar on cone beam computed tomography (CBCT) images and to evaluate the possibility of inferior alveolar nerve (IAN) injury. Materials and Methods: The study was conducted on 60 patients, who were divided into two groups of 30 each. Group I included 30 patients whose panoramic radiographic findings showed darkening of the root of impacted mandibular third molar. Group II included 30 patients whose panoramic radiographic findings showed interruption of white line of mandibular canal. The patients whose panoramic radiographic findings showed darkening of the root or interruption in the white line of the canal were subjected to CBCT examination. Surgical removal of impacted mandibular third molar in all the patients was performed under local anesthesia (LA). Evaluation for any nerve injury was performed and recorded as presence or absence of paresthesia at regular postoperatively. Results: The results of this study showed that 46.7% patients had absence of cortication in Group I (darkening of roots), whereas it was absent in 33.3% of patients in Group II (loss of white lines). Presence of cortication was seen in 53.3% of patients in Group I when compared to 66.7% in Group II. The difference between the groups was not found to be statistically significant. 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 necessitating CBCT evaluation.



How to cite this article:
Savani CM, Panicker K, Ravi Kiran BS, Uppada UK. Does Darkening of Roots or Loss of White Line on Panoramic Radiographs Pose a Risk for Inferior Alveolar Nerve Damage? A CBCT Evaluation.J Orofac Sci 2018;10:101-107


How to cite this URL:
Savani CM, Panicker K, Ravi Kiran BS, Uppada UK. Does Darkening of Roots or Loss of White Line on Panoramic Radiographs Pose a Risk for Inferior Alveolar Nerve Damage? A CBCT Evaluation. J Orofac Sci [serial online] 2018 [cited 2019 Aug 23 ];10:101-107
Available from: http://www.jofs.in/text.asp?2018/10/2/101/249096


Full Text



 Introduction



Surgical removal of impacted mandibular third molars may cause dysesthesia due to damage to the inferior alveolar nerve (IAN), and the risk increases when there is direct contact between the nerve and the tooth root.[1],[2] An accurate preoperative radiographic examination is considered indispensable before surgical removal of the lower third molars.[3]

Presence or absence of radiographic signs on plain radiographs does not always determine the possibility of injury to the IAN.[1] Cone beam computed tomography (CBCT) provides a precise structural image with high contrast, high diagnostic accuracy, and acceptable radiation exposure.

This study was intended to correlate the two panoramic radiographic findings in predicting the absence of corticalization between the mandibular canal and the third molar on CBCT images and to evaluate the possibility of IAN injury.

 Materials and Methods



This study consisted of 60 patients who had an impacted mandibular third molar and reported to the outpatients wing of our unit.

Ethical clearance

Ethical approval for this study was provided by the Institution of Oxford Dental College & Hospital, Bangalore (Regd No.: 677/ODCHRC/RB-E/2014) on February 12, 2014.

Ethics

An informed consent was obtained from all the patients selected for the study.

A detailed case history was recorded for all patients followed by a thorough clinical examination. Panoramic radiographs were taken for all the patients.

These patients were then divided into two groups of 30 patients each.

Group I had 30 patients whose panoramic radiographic findings showed darkening of the root of impacted mandibular third molar.

Group II had 30 patients whose panoramic radiographic findings showed interruption of white line of mandibular canal.

Inclusion criteria

Individuals with impacted mandibular third molar whose panoramic radiograph showed darkening of the roots or interruption in the white line of the canal.Patient with age group of 18 years and above.

Exclusion criteria

Patient who previously underwent radiation therapy.Patients in whom time interval between imaging and third molar removal exceeded 6 months.Any local pathology, such as cyst or tumor.Patients with systemic diseases and pregnancy.Patient with more number of metal restorations in their mouth.

Technical information

All the patients were subjected to digital panoramic imaging with Kodak 8000C (Banglore, India) system operating at 75 to 80 kVp for 13.9 s at 12 mA. On the panoramic radiographs, the relationship between the mandibular third molar and the mandibular canal was evaluated. In this study, we used most common signs such as darkening of roots or interruption in white line associated with higher risk of IAN injury.

CS 3D imaging software version 4.1.2 was used for the analysis. In the CBCT images, the presence or absence of cortication between the mandibular third molar and the mandibular canal was evaluated using cross-sectional images.

After panoramic radiography and CBCT examination of all patients, comparison of these findings was performed. After radiographic assessment, surgical removal of the impacted tooth was performed under local anesthesia in all the individuals by a single experienced surgeon under aseptic conditions. Regular follow-up was performed on 1st, 7th, 15th, and 21st postoperative day, and after 3 months for evaluation of the IAN injury. Nerve injury was evaluated and recorded for presence or absence of paresthesia.

Evaluation of nerve injury

Light touch test: the lower lip and mental skin were lightly touched with a cotton wisp to check if the touch was perceptible.[4]Two point discrimination test: a sharp millimeter divider was used to measure two points. The test was conducted by beginning with the points closed and progressively opening them in 1-mm increment until the patient could discriminate two points. Distance of 2 mm greater than the preoperative value was considered as abnormal. Nerve injury was recorded for presence or absence of paresthesia.Tactile discrimination (TA) test: TA was measured with a needle. The needle was pressed over the skin of the mental nerve and the lower lip region. Nerve injury was recorded for presence or absence of paresthesia.

These tests were performed on 1st, 7th, 15th, and 21st postoperative days, and at 3 month postoperatively on the lower lip and mental nerve region; these tests were divided into four zones and each zone was measured separately. Each of the four facial zones was tested for nerve injury as shown in [[Figure 1] and [Figure 2]].{Figure 1}{Figure 2}

 Results



Following completion of clinical study on the patients, the measurements and data taken from all patients were tabulated for statistical studies. There were 23 men and 37 women in the age range of 19 to 38 years. [Table 1] shows that there was a small difference in the mean age between Group I (28.53 + 5.02) and Group 2 (29.17 + 5.70); this difference between the groups was not found to be statistically significant (P = 0.65). [Table 2] reveals comparison of gender in both the groups; there was a small difference between male and female ratio. In Group I, male:female was 40.0:60.0, whereas in Group II, male:female was 36.7:63.3. The difference between the groups was not found to be statistically significant (P = 0.79).{Table 1}{Table 2}

[Table 3] reveals comparison of presence or absence of cortication in both the groups; there was small difference between presence or absence of cortication in Group I and Group II. Absence of cortication was found in 46.7% of patients in Group I compared with 33.3% of patients in Group II. Presence of cortication was found in 53.3% of patients in Group I compared with 66.7% of patients in Group II. The difference between the groups was not found to be statistically significant (P = 0.29). [Table 4] reveals comparison of presence or absence of nerve paresthesia on 1st, 7th, 15th, and 21st postoperative day, and at 3 months in both the groups.{Table 3}{Table 4}

On the 1st postoperative day, there was presence of paresthesia in 23.3% of patients and absence of paresthesia in 76.7% in Group I. There was presence of paresthesia in 20.0% of patients and absence of paresthesia in 80.0% in Group II. The difference between the groups was not found to be statistically significant (P = 1.00). On the 7th postoperative day, there was presence of paresthesia in 20.0% of patients and absence of paresthesia in 80.0% in Group I. There was presence of paresthesia in 20.0% of patients and absence of paresthesia in 80.0% in Group II. The difference between the groups was not found to be statistically significant (P = 1.00).

On 15th postoperative day, there was presence of paresthesia in 13.3% of patients and absence of paresthesia in 86.7% in Group I. There was presence of paresthesia in 6.7% patients and absence of paresthesia in 93.3% in Group II. The difference between the groups was not found to be statistically significant (P = 0.67). On the 21st postoperative day, there was presence of paresthesia in 6.7% of patients and absence of paresthesia in 93.3% in Group I. There was presence of paresthesia in 3.3% of patients and absence of paresthesia in 96.7% in Group II. The difference between the groups was not found to be statistically significant (P = 1.00). At 3 months postoperatively, all the patients recovered from the IAN paresthesia in both the groups.

[Table 5] reveals comparison of paresthesia along the time period of 1st, 7th, 15th, and 21st, and at 3 months postoperatively. In Group I, 23.3% patients had paresthesia on 1st postoperative day, which was reduced to 20.0% on 7th day, 13.3% on 15th day, and 6.7% on 21st day; there was no nerve paresthesia in any of the patients 3 months postoperatively. The difference in recovery rate between the time periods was found to be statistically significant (P < 0.001) in Group I. In Group II, 20.0% patients had paresthesia on 1st postoperative day, which was same on 7th postoperative day, reduced to 6.7% on 15th postoperative day, and 3.3% on 21st postoperative day. After 3 months postoperatively, there was no nerve paresthesia in any of the patients in Group II. The difference in recovery rate between the time periods was found to be statistically significant (P < 0.001) in Group II. There was faster recovery in nerve paresthesia in Group II (15th day = 93.3%, 21st day = 96.7%) compared with Group I (15th day = 86.7%, 21st day = 93.3%) [[Figure 3] and [Figure 4]].{Table 5}{Figure 3}{Figure 4}

 Discussion



The frequency and severity of untoward events associated with surgical procedures are influenced by multiple factors that may be related to the procedure, patient, and/or surgeon. Intraoperative complications could be in the form of damage of adjacent teeth, tooth or tooth fragments displacement into soft tissues, bleeding, or mandibular fracture. The most serious and unpleasant iatrogenic complications that arise from third molar surgery are inferior alveolar and/or lingual nerve injury and neurosensory function disturbance.[5]

Etiologic factors associated with nerve injury include experience of the surgeon, age of the patient, traumatic tissue manipulation, postsurgical edema, and, most importantly, the anatomic proximity of the nerve to the impacted tooth root.[6]

Periapical radiographs have been used for many years to evaluate the scenario prior to surgical intervention. The biggest concern of periapical radiographs is that mandibular canal could not be clearly identified in the third molar region. Furthermore, the angulation of the periapical film can affect the perceived location of the canal with respect to the bone crest.[5] The panoramic radiograph is the imaging modality most oral and maxillofacial surgeons use to view impacted mandibular third molars and to assess the risk for IAN injury.[6]

The major drawback of panoramic imaging is the lower image resolution, high distortion, and presence of phantom images. Furthermore, it depicts a two-dimensional view of an intricate three-dimensional anatomic relationship and also fails to accurately project the buccolingual relation between the tooth and the inferior alveolar canal.[5] In a panoramic radiograph, structures that are outside the center of rotation of the radiologic source and detector are not displayed sharply and are distorted overproportionally. Impacted third molars are frequently outside of this center of rotation and therefore can be visualized incorrectly, making diagnosis difficult.[7]

CBCT is proving to be increasingly beneficial in determining the precise relationship between these two structures in those individuals where the panoramic radiograph suggests the relationship to be close.[8] The CBCT images can be reformatted with minimal distortion, allowing the canal and tooth to be viewed in all dimensions. Its use results in patients receiving a greater radiation dose compared to standard radiography; therefore, it is not appropriate for CBCT to be used as the first routine imaging technique and should be applied when the benefits of the additional exposure are likely to be considerable.[8]

Therefore, in this study, we compared panoramic radiographic findings with CBCT findings to assess the relationship between roots of impacted mandibular third molar and mandibular canal. According to the authors, the CBCT should be conducted when darkening of roots, narrowing of the mandibular canal, and interruption of white line are observed on panoramic radiograph.

In this study, we correlated two panoramic radiographic findings darkening of impacted mandibular third molar roots and loss of white line with CBCT findings and evaluated the probability of causing an IAN damage following a surgical intervention.

Few authors distinguished four radiographic indicators observed in the tooth root (darkening, deflection, and narrowing of the root, and a bifid root apex), and the other three in the canal (diversion, narrowing, and interruption in the white line of the canal). Literature suggested that three of the seven signs were more significantly associated with IAN injury. These include root darkening, interruption of the white line of the inferior alveolar canal (IAC), and diversion of the IAC.[5],[8],[9]

Ghaeminia et al.[10] and Szalma et al.[11] observed that three panoramic radiographic signs (interruption of white line, darkening of roots, and diversion of the mandibular canal) were significantly associated with IAN injury. Neves et al.[1] found that the narrowing of the mandibular canal was not associated with higher risk of contact between the tooth roots and the mandibular canal, either as an isolated finding or in association with other panoramic radiographic signs based on CBCT images. Therefore, in this study, we selected two findings (darkening of the roots and loss of white line as isolated findings) to compare with the findings of the CBCT.

Numerous studies have previously attributed darkening across the root to reflect grooving of the root and hence loss of tooth substance. This concept was later evaluated using with CBCT, and it was proposed that the darkening is not due to the loss of calcified substance in the tooth, but the loss of calcified substance of the buccal and/or lingual cortical plates.[12] The results of this study support this conclusion and attribute the darkening not due to loss of tooth substance, but in fact due to thinning of a cortical plate. In 46.7% of the cases in our study, there was absence of cortication among all cases of darkening of roots of impacted mandibular third molars.The interruption of the “radiopaque lines” has been attributed to contact of the roots with the nerve. This study corroborates this finding. One study showed that 100% of the cases exhibiting loss of the radiopaque line on panoramic radiographs also displayed loss of cortication of the canal on CBCT, with the roots in contact with the contents of the canal.[12] In contrast, this study shows that there was absence of cortication in 33.3% cases among all cases of loss of white line. Different studies showed that in the absence of cortication, it seems highly probable that if the teeth were to be extracted, the nerve would be exposed and may be visible in the socket.[8] There is also a risk of IAN injury during extractions to this group of patients as manipulation of the root may inadvertently cause compression of the nerve.

In our study in Group I (darkening of the roots), seven patients (23.3%) were presented with IAN paresthesia, and in Group II (loss of white line), six patients (20.0%) were presented with IAN paresthesia, which was gradually recovered in all the cases in both the groups over the period of 4 weeks as shown in [Table 5].

The results of this study showed that 46.7% of the patients showed absence of cortication in Group I (darkening of roots) and when compared with Group II (loss of white lines), it was absent in 33.3%. A total of 53.3% of the patients in Group I showed presence of cortication and when compared with Group II, it was present in 66.7%. The difference between the groups was not found to be statistically significant (P = 0.29). Further clinical trials with longer duration follow-up with larger sample size should be performed to get more affirmative and conclusive results.

 Conclusion



Panoramic radiography is an effective method for preoperative assessment of mandibular third molars. Darkened roots and interruption of white line observed on panoramic radiographs, as both isolated findings and in association with each other, are effective in determining the risk relationship between the tooth roots and the mandibular canal, thus requiring three-dimensional evaluation (CBCT) of the case for accurate understanding of the position of the IAN in relation to the impacted mandibular third molar. Planning of surgical removal of lower third molars can be effectively and precisely enhanced with the use of CBCT, especially in high-risk cases to reduce the risk of the nerve injury.

Ethical approval

All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Financial support and sponsorship

Self funded.

Conflicts of interest

There are no conflicts of interest.

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