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P r o x i m i t y o f m a n d i b u l a r f i r s t a n d s e c o n d m o l a r s t o I A C Introduction The inferior alveolar canal (IAC) runs in an S-shaped pattern in the mandible. Factors like age, race, sex and the anatomy of the mandible influence its location. The IAC contains a nerve that, along with the inferior alveolar artery and vein, innervates the posterior teeth through the IAC before splitting into incisive and mental components that innervate the mandibular anterior teeth, lower lip and gingiva. All of these factors have clinical significance with reference to the distance from the first and second molars to the IAC, more so than the distance from the third mandibular molar. These facts are well documented with regard to the proximity of the IAC to the apices of the mandibular first molars. The inferior alveolar nerve (IAN) is the most commonly injured nerve—about 64.4% of inju- ries occur from trauma due to implant place- ment.1 While evaluating the benefits and out- comes of dental treatment, the dentist should be aware of the position of the IAN/IAC with respect to the apices of the mandibular molars.2 Injuries to the IAC are mostly iatrogenic.3 Dental clinical procedures such as endodontics, tooth extraction, implant placement and other surgical procedures in the area of the first and second molars are the major causes of iatrogenic injury to the branches of the trigeminal nerve within the IAC.4 In 40% of the cases, injury is due to dental implants,1 followed by 1–10% due to endodontic procedures (Fig. 1). Other types of injury to the IAN occur through mechanical trauma caused by overinstrumentation, extru- sion of chemical agents such as irrigants, intracanal medicaments, root filling materials, the presence of foreign material or thermal injury during endodontic procedures.1, 5 The con- sequence of injury to the nerve is postoperative paresthesia or anesthesia that may be transient or permanent. The mandibular second molar apices have been reported to be the closest to the IAN compared with the premolars and first molar1 and hence more prone to injury. In order to interpret these problems, clini- cians rely on various methods of radiographic examination. Information regarding teeth and their associated anatomy, including root canal morphology, is commonly obtained from con- ventional imaging modalities such as intraoral radiographs, cephalograms, dental panoramic tomograms and cone beam computed tomog- raphy (CBCT). The conventional signs of prox- imity of the IAN to molars include root narrowing, root deflection and bifid apices, as well as root canals that show diversion, narrow- ing or loss of lamina dura.4 Hence, the newer method of 3-D imaging is considered to be the most reliable aid in assessing the relationship of roots to the IAN because of its accuracy, effi- ciency and effectiveness.5 The objective of this review was to determine the proximity of mandibular first and second molar apices to the IAC and to determine the justification of the use of CBCT of mandibular first and second molars to assess treatment outcome. The results of this review will enable clinicians to estimate the distance between the IAN/IAC and the apices of mandibular first and second molars on the basis of various published studies. The information obtained can be applied during various dental procedures to estimate the potential risk of any injury to the IAN/IAC due to varying dental procedures in the mandib- ular posterior areas. Materials and methods We used secondary data and included studies that considered mandibular first and second molar apices in determining proximity to the IAC using 3-D imaging. We did not include the stud- ies for analysis from 2-D imaging, but considered them to determine the difference between 3-D and 2-D imaging in distances recorded. S e a r c h m e t h o d s a n d i d e n t i f i c a t i o n a n d s e l e c t i o n o f s t u d i e s We carried out a search of the literature using the PubMed, Web of Science and Scopus data- bases. A total of three independent searches were carried out. The study used reports of CBCT scans from 1986 to 2016 that included first and second mandibular molars and their distance to the IAC in different populations and considering age, sex and various other factors. The key terms used for extracting the relevant articles were “cone beam computed tomogra- phy” or “cbct” or “CBCT dental” or “cone beam CT dental” or “cone beam dental” and “inferior alveolar canal” or “IAN canal” or “IAN” and “lower molar” or “lower first molar” or “lower second molar” or “mandibular molar”. The process of article inclusion and exclusion was according to the PRISMA protocol (Fig. 2). The initial search of all three databases yielded 94 articles. Later, after reviewing the Journal of Oral Science & Rehabilitation Volume 3 | Issue 4/2017 49