Introduction Lower third molar surgery is a common and relatively uncomplicated procedure. Commonly indicated where there is infection, bony pathology, soft tissue pathology or damage to the adjacent tooth. Difficult surgical challenges and unpredictable surgical outcomes can be caused by wide variations in the position and anatomy of the mandibular third molar roots, and relationship of these roots to the mandibular canal containing the Inferior Alveolar Nerve (IAN) may at times present the surgeon with inadvertent crush injury, stretch injury or even severing of the inferior alveolar nerve. Appropriate imaging and treatment planning results in predictable surgical outcome. The relative relationship and proximidity of the mandibular third molar roots to the inferior alveolar canal can be predicted by several radiographic signs displayed on an orthopantomograph (OPG), including darkening of the roots, deflection of the roots, narrowing of the roots, dark and bifid roots, interruption of white line(s), diversion of the inferior alveolar canal and narrowing of the inferior alveolar canal. An OPG is however limited by depth of view, superimposed structures and distorted structures with positioning errors. Cone-Beam Computed Tomography (CBCT) is a radiographic imaging method which may provide the ability to predict more accurately the relationship of the root(s) to the inferior alveolar canal, and therefore a more predictable and favourable outcome. CBCT has been in use at Sydney’s Westmead Centre for Oral Health (WCOH) since 2006. The purpose of this study is to evaluate whether OPG alone or utilisation of OPG and CBCT together provides the more predictable outcome following surgery where there has been a close relationship of the roots to the inferior alveolar canal. Methods A retrospective study was performed of lower third molar cases that were managed at Westmead Centre for Oral Health, Westmead NSW, between November 2005 to August 2006 prior to CBCT (Group one) and November 2010 to August 2011 following CBCT (Group two). The study involved examination of de-identified pre-operative, operative and post-operative written records, as well as the OPG and relevant CBCT records. Relevant data was tabulated along with any associated complications in an excel spreadsheet. The variables within the data and the two groups were crosstabulated and analysed with a statistic software (SPSS). Results Total of 590 surgical cases were included in the study, with 265 in group one and 325 in group two. Post-operative complications totalled 9, where group one had 6 and group two had 3. Numbers with no post-operative complications totalled 581, with 259 for group one and 322 for group two. Discussion A two by two risk calculation demonstrated reduction of IAN complication by 50% with CBCT, with a risk ratio of 2.45 and risk difference of 0.0134. The numbers needed to be treated were calculated from there as 75. With CBCT, the superimposed structures can be eliminated and distortions minimised, via the mode of image scanning and digital software manipulation of the DICOM data set, so providing more depth of view and allowing a more accurate measurement of relative position between the roots of lower third molar teeth and inferior alveolar nerve. Coronal, sagittal, axial and panoramic views obtained from CBCT allow three-dimensional evaluation of the relationship between the roots of lower third molar teeth and inferior alveolar nerve. This may influence surgical techniques to provide more accurate and safer surgery or influence an alternative treatment plan such as coronectomy or leaving the impacted tooth in-situ. Safer outcome would not only benefit the patient and the surgeon, but may reduce costs to the institution, the community and the profession in terms of medico-legal liability and indemnity. One disadvantage of CBCT include the higher radiation dosage that the patient is exposed to when compared to OPG, but relatively lower radiation dosage than helical beam CT. Another disadvantage of CBCT is the high initial cost, as well as maintenance and replacement cost of each unit, whilst that of OPG remains relatively low. The cost effectiveness of CBCT needs to be considered, whereby an institution such as WCOH receives high numbers of external and internal referrals, which may justify these associated costs when weighted against the benefits to the patient and the surgeon by the 50% reduction in complications. Conclusion It can be concluded from the results that seventy five lower third molar surgeries are needed to be performed utilising CBCT as pre-operative diagnostic tools in order to reduce the incidence of inferior alveolar nerve complication by one. This study has been a retrospective study. A randomised prospective study would be the next step to verify the accuracy and demonstrate the benefits of CBCT
