Inferior alveolar nerve injury and surgical difficulty prediction in third molar surgery: the role of dental panoramic tomography.

OBJECTIVE

The purpose of this study was to evaluate the relationship between preoperative panoramic radiological findings and postoperative inferior alveolar nerve paresthesia following third molar surgery, and to assess the surgical difficulty.

METHODOLOGY

This retrospective study involved two groups of patients who were randomly selected. The first group presented with inferior alveolar nerve (IAN) paresthesia following surgery, and the second group presented with no complications, including IAN paresthesia. Radiological findings were collected from the panoramic radiographs of those patients and compared to postoperative paresthesia. The degree of surgical difficulty was also assessed radiographically.

RESULTS

The application of Chi-square testing on the numbness group and the control group, as well as the numbness group (two years postoperatively) and the control group, showed that parameters like type of impaction (fully impacted), depth of impaction (depth C), ramus/space (class 3), spatial relationship (distoangular and horizontal), number of roots (multiple and incomplete), shape of root (thick and incomplete), shape of the tip of root (curved and incomplete), and relation to IAN (touching, superimposed, or non-specific) are highly significant (p < 0.001) in predicting the incidence of temporary and permanent paresthesia. Logistic regression showed that a patient whose lower third molar is > or = 1 mm from IAC has a 98% probability of no numbness, while if the tooth is touching the IAC the probability of numbness between one week and < two years is 60%. Numbness probability of darkening of the root is 48% for > two years, deflection of the root has a 42% probability of > two years numbness, narrowing of the root has 87% of numbness between > one month and < two years, a dark and bifid root has a 97% of numbness between > six months and < two years, interruption of the IAC has a 54% chance of numbness between > one month and < two years, diversion of the canal has a 60% probability of > six months to > two years numbness, while narrowing of the canal has a probability of 100% of > six months to > two years numbness. By using logistic regression, cases that were recorded as "very difficult," according to the Pederson Difficulty Index, were more likely to develop permanent paresthesia (95%). The application of logistic regression on the radiological findings showed that we can use them in predicting nerve paresthesia following third molar surgery. A classification tree has been developed and found to be very accurate in predicting permanent numbness (95%) and no numbness (100%) in third molar surgery depending on the radiological findings.

CONCLUSION

Surgical difficulty of impacted third molars may be assessed radiographically through seven factors, including spatial relationship, depth of impaction, ramus relationship/space available, type of impaction, number and shape of roots, shape of the tip of the root, and relation of the root to the inferior alveolar nerve. The application of logistic regression on the radiological findings showed that we could use them in predicting nerve paresthesia following third molar surgery. By developing a classification tree, it is easier to predict the possibility of temporary or permanent paresthesia. A full collaboration between clinicians and radiologists may help to uncover more parameters that can lead to a more accurate prediction of temporary and permanent paresthesia.