During the years, many efforts have been made in order to systematize and clarify the root canal anatomy of permanent teeth, but even today we face difficult endodontic situations.

 An understanding of the architecture of root canal system is essential for successful endodontic treatment.  Excellent knowledge of root canal anatomy is very important, because missed canals is a significant factor in treatment failure.

The aim of our study is to present some rare morphological aspects encountered during the endodontic treatment of permanent teeth, which we consider that are important for every day dental practice.

 We conducted a retrospective radiographic study based on endodontic treatments provided by undergraduate students and postgraduate dentists at Faculty of Dental Medicine Tg.Mure, between  Anatomical variations related to unusual radicular form, number of roots and root canals were recorded for each group of teeth and the frequency of such alterations was calculated.

 We examined a total of 346 teeth; 72 upper front teeth (42 incisors and 27 cuspids), 134 maxillary lateral teeth, ( 83 premolars and 51 molars),

 78 lower front teeth (43 incisors and 35 cuspids) and 62 mandibular lateral teeth (28 premolars and 34 molars).

 The upper front teeth- unusual anatomy in 17% of the cases.  We examined 72 upper front teeth, 42 incisors and 27 canines;  Anatomic variations were recorded in 1 central incisor, 8 lateral incisors and 3 canines.

 These variations were represented by curved canals and root length (upper canines with length over 30 mm reported in literature in 13% of cases).

 Upper premolars - 3 roots in 3% and the first molars - 4 canals in 39% of the cases.

 For the lower front teeth we found double canals in 32 % of the cases.

 First and second premolars with double canals in 6 cases ( 15%, type II and III Vertucci );  Molars with radix entomolaris 1 case (3%), double canals in distal root 4 cases (18%, type II, IVVertucci).

 For upper front teeth - single root with one canal, curvatures in the middle and apical third(Type I Vertucci); No double roots were found;  Upper premolars – 3 roots in 3%, compared to 6%in other studies (Beer 2008);  First upper molar – double canals in MB root in 39% (Type I and II Vertucci), compared to 60% in vivo and 95% in vitro studies (Kulild 2006).

 Lower front teeth – 1 root with 2 canals in 32 % (Type II Vertucci), compared 25-42% in other studies (Beer 2008);  Lower premolars - double canals in 15% of the cases, compared to 24% (Cantatore, 2009)  Lower molars – radix entomolaris in 1 case (3%) compared to 3-30% Kottoor, Distal roots with 2 canals in 23% of cases, compared to 31-35% in other studies (Cantatore 2009).

 Angled radiographs allow a better assessment of the root anatomy; at least two views must be taken before attempting endodontic treatment.  The use of cone beam computed tomography (CBCT) helps accurate diagnosis and avoid complications.

 A surgical operating microscope is highly recommended as it shows in great detail the pulp chamber and root canal orifices; it makes endodontic therapy less stressful to the operator.  In todays endodontic specialist practice we must always look for unusual anatomy, as successful outcome of any case depends on the complete debridement and disinfection of all canals.

 Cantatore G, Berutti E, Castelucci A : Missed anatomy: frequency and clinical impact. Endod Topics 2009, 15:  Castelucci A. Endodontic radiography. In: Castelucci A, ed. Endodontics vol I, 2nd Ed. Florence, Tridente, 2006:  Cleghorn BM, Christie WH, Dong CCS : Root and root canal morphology of the human permanent maxillary first molar: a literature review. J Endod 2006; 32:  Cleghorn BM, Christie WH, Dong CCS : Root and root canal morphology of the human mandibular first premolar: a literature review. J Endod 2007: 33:  Vertucci FJ. Root canal morphology and its relationship to endodontic procedures. Endod Topics 2005: 10: 2-29.

 Demoor A, Deroose KL, Calberson J. The radix endomolaris in mandibular first molars: an endodontic challange. Int Endod J. 2004, 37 (11):  Seo MS, Park DS. C-shaped root canals of mandibular second molars in a Korean population: clinical observation and in vitro analysis. Int Endod J, 2004; 37 (2):  Rambabu T. Endodontic management of radix entomolaris. Two case reports. Annals and Essences of Dentistry, Vol. II, Issue 3, 2010: