The Root and Root Canal Morphology of the Human Mandibular Second Premolar: A Literature Review Blaine M. Cleghorn, DMD, MS,* William H. Christie, DMD, MS † and Cecilia C.S. Dong, DMD, BSc, MS ‡ Abstract The objective was to review thoroughly the literature of the root and root canal morphology of the human mandibular second premolar and compare the results with the mandibular first premolar. Published studies cite the anatomy and morphology of the mandibular second premolar tooth for more than 7700 teeth. These studies were divided into anatomic studies reporting the number of roots, number of canals, and apical anatomy. Differences caused by gender and ethnicity have also been reported. Individual case reports of anomalies were included to demonstrate the extreme range of variation. Almost all of the teeth in the ana- tomic studies were single-rooted (99.6%). The inci- dence of 2 roots (0.3%) and 3 roots (0.1%) was ex- tremely rare. Anatomic studies of the internal canal morphology found that a single canal was present in 91.0% of the teeth. A single apical foramen was found in 91.8% of the teeth. The incidence of more than 1 root (0.4%), more than 1 canal system (9.9%), and more than 1 foramen (8.2%) is lower than that of the mandibular first premolar tooth (2.0%, 24.2%, and 21.1%, respectively). However, the root and root canal morphology of the mandibular second premolar can be extremely complex and requires careful assessment. (J Endod 2007;33:1031–1037) Key Words Abnormal morphology, anomalies, mandibular second premolar, number of canals, number of roots, root canal morphology K nowledge of both basic root and root canal morphology as well as possible variation in anatomy of the root canal system is important in achieving successful nonsurgical root canal treatment (NSRCT). This is followed by negotiation, cleaning and shaping, and obturation of the entire canal system in 3 dimensions (1–3). Ingle (1) has reported that the most significant cause for endodontic failures was incomplete canal instrumentation, followed by incorrect canal obturation. Slowey (4) has indicated that probably because of the variations in canal anatomy, the mandibular premolars are the most difficult teeth to treat endodontically. Variation in root canal morphology was suggested as the most likely reason for the high frequency of endodon- tic flare-ups and failures (Figs. 1–3)(4–6). The mandibular second premolar is typically described in textbooks as a single- rooted tooth with a single root canal system (5, 7–12). The ovoid-shaped root in cross section normally has developmental grooves or depressions on the mesial and distal surfaces (Fig. 4). Woelfel and Scheid (12) have described the depression on the distal surface as being the deeper of the two. There are also numerous case reports and anatomic studies that have reported variations. The incidence of the number of roots (13–20) and of the number of canals (13–17, 19, 21–28) reported in anatomic studies varies greatly in the literature. The root morphology and canal morphology of the mandibular second premolar can be extremely complex and highly variable (Figs. 1–3)(3, 7, 9, 29, 30). The factors that can contribute to differences observed in the various anatomic studies have been reported previously (30), and these factors include ethnicity (17, 29, 31–55), age (24, 56 – 61), gender (44, 60, 62), unintentional bias in the selection of clinical examples of patients or teeth (specialty endodontic practice versus general dental practice) (30), as well as study design (in vitro versus in vivo) (63– 65). Normal root and root canal anatomy of the mandibular second premolar is well- documented in numerous textbooks, but there is a great deal of variation in the report- ing of the incidence of anomalies (2, 3, 5, 7–12, 66, 67). As a result, there is no consensus on the range of variation or possible anomalies. The purpose of this article was to review the literature and conduct an analysis of the variations found in studies that reported on root and root canal morphology of the human mandibular second premolar. These results were compared with a recent study on the mandibular first premolar (68). Materials and Methods A review of the literature was performed for the human mandibular second pre- molar with respect to the number and type of roots and the root canal morphology. Key words used in the search included “mandibular second premolar,” “mandibular sec- ond bicuspid,” “number of roots,” “number of canals,” “root canal morphology,” “extra roots,” “anomalies,” and “abnormal morphology.” Peer-reviewed studies of the mandibular second premolar were identified first through PubMed, and then other related articles were added by hand searching of bibliographies and internet articles pre-1966 that might be missed in a PubMed search and articles in which key words do not match the subject of the search. Pooled data from teeth identified only as “premo- lars” or “mandibular premolars” were avoided. Significant non-English language stud- ies were included when they could be accessed and translated. More than 7700 per- manent mandibular second premolar teeth were analyzed in the studies contained in this review. Case studies were included to illustrate anomalies and genetic variation not From the *Department of Dental Clinical Sciences, Dal- housie University, Halifax, Nova Scotia, Canada; † Division of Endodontics, Department of Restorative Dentistry, University of Manitoba, Winnipeg, Manitoba, and ‡ Department of Re- storative Dentistry, University of Manitoba, Winnipeg, Mani- toba, Canada. Address requests for reprints to Blaine M. Cleghorn, DMD, MS, Dalhousie University, Faculty of Dentistry, 1210-5981 University Ave, Halifax, Nova Scotia, B3H 3J5 Canada. E-mail address: blaine.cleghorn@dal.ca 0099-2399/$0 - see front matter Copyright © 2007 by the American Association of Endodontists. doi:10.1016/j.joen.2007.03.020 Review Article JOE — Volume 33, Number 9, September 2007 Root and Root Canal Morphology of Human Mandibular Second Premolar 1031