In this study, we evaluated the presence of JAR and its relationship with the presence of paresthesia in CBCT images. Also, thinning of the lingual cortical plate, JAR position relative to IAN, and proximity of JAR to the mandibular canal were evaluated in the case and control groups. There was a significant association between JAR and the presence of temporary paresthesia (P = 0.034), whereas no cases of permanent paresthesia were detected three months after surgery in either of the groups.
Seven radiological signs are considered to be indicative of a close relationship between the impacted mandibular third molars and the inferior alveolar canal. Only three of these signs seem to be significantly related to the inferior alveolar nerve injury, including the canal diversion, darkening of the root, and interruption in the white line of IAN . Moreover, JAR and deviation of the canal were significantly associated with nerve injury . In the present study, the main risk factor for injury was the presence of JAR in CBCT images.
Recently, it has been hypothesized that JAR is the initial area of focal osseous dysplasia . In this regard, Umar et al.  reported that JAR originates from the superimposition of a large cancellous bone on the mandibular canal. Also, Gilvetti et al.  studied 50 cases of JAR in panoramic images and found no temporary or permanent paresthesia after at least 18 months. Yalcin and Artas  confirmed this result, as they found no significant relationship between JAR and the mandibular canal. In a study by Nascimento et al., in most JAR cases, the mandibular canal is positioned lingual to the third molar and contacts the JAR . In our study population, 18.37% of the patients had JAR signs in CBCT images. In two studies by Nascimento et al. [12, 14], 15.9% and 32.6% of patients showed JAR in CBCT images. Also, in the study by Yalcin and Artas, 33% of patients showed JAR in CBCT images. In our study, the number of female patients was significantly higher in the JAR group than the control group (P = 0.037). As reported by Nascimento et al., the probability of JAR identification in female patients is almost twice as high as male patients .
In the present study, the majority of JARs (90.7%) were in contact with IAN, with or without cortical boarder preservation. This finding is in line with the results reported by Nascimento et al., which revealed that only 6.4% of cases were located distant from the mandibular canal, while most cases were in contact with the canal . In contrast, a study by Kapila et al. showed that 28.57% of JAR cases were in contact with the mandibular canal in CBCT images . Similarly, Yalcin and Artas found that JAR was mostly distant from the mandibular canal (76.3%) .
Overall, determining the position of the JAR is important, considering the possible need for special attention during surgery . In this regard, Ghaeminia reported that the lingual side of the mandibular canal in the third molar region is more susceptible to unfavorable forces during surgery . Regarding the JAR position, different outcomes have been reported in the literature. Nascimento et al. found that JAR was in the lingual position relative to IAN (59.6%) , while in a study by Kapila et al., the most frequent positions were buccal and superior to IAN . Also, Yalcin and Artas showed that JAR was mostly in the superior position . In our study, lingual and buccal positions were the most common ones, and most JARs with paresthesia were on the lingual side of the mandibular canal.
Moreover, Yalcin and Artas found cortical thinning in 67% of cases in their study. Also, Kapila et al. reported that thinning of cortical plates was significantly more common in JAR cases than the controls (70% vs. 37%). They postulated that cortical plate thinning could be responsible for postoperative paresthesia following the extraction of third molars. In the present study, 84% of JAR cases showed at least some degree of lingual cortical plate thinning, and even 16% of cases were perforated. However, we found no significant relationship between the presence of JAR and thinning of the cortical plate (P = 0.626), although most cases of JAR with paresthesia (95.7%) showed some degree of cortical thinning.
In the current study, most cases of JAR (54.7%) were detected in teeth with a mesioangular position; however, there was no significant difference between the groups (P = 0.346). In this regard, Kapila et al. found the mesioangular position to be the most common one ; however, they did not include a control group to analyze the significance of their findings. On the other hand, in the study by Nascimento et al., JAR was related to vertically positioned teeth , although panoramic images were examined in their study. Yalcin and Artas also found that the vertical position was the most common angulation related to JAR in CBCT images; however, they did not include a control group in their study .
Loescher et al. postulated that the patient’s subjective report is the most sensitive indicator of abnormal sensation and that tests cannot detect minor sensory disturbances . Therefore, we did not use any quantitative tests in our study and identified the patients qualitatively by asking them about any tingling sensation or numbness of the lips or the chin. In their study, the patient follow-up was conducted via phone calls, as such follow-ups can increase the number of participants in the research and is more cost-effective .
Overall, the current study revealed that temporary paresthesia is more common in patients with JAR (on CBCT images) than the control group. However, no permanent paresthesia was detected in the three-month follow-up. Consistent with our findings, a study by Alling et al. showed that 96% of inferior alveolar nerve injuries recovered within 4–8 weeks after surgery . There is only another study investigating the relationship between paresthesia and JAR in panoramic images, which indicated no significant relationship . However, our study was based on CBCT images, as JAR detection is more accurate in CBCT images than panoramic images .