The dental root system of lower molars in a mesio-distal direction may have different shapes depending on the form and position of both roots. The aim of this study has been to detect the presence of particular characteristics of lower molars. We analyzed 896 orthopan X-ray films of orthodontic patients from Niš, according to Zubov's method. In all the cases, M1 has 2 roots, while M2 has one root in 7.1% of them. In M1, the most frequent root system type is with a distally inclined mesial root (type 5) and it appears in about 32% of the patients, while 22.36% have paralel roots (type 3) and 22.61% have convergent roots in the apical third (type 2). The same percentage of the patients (23%) have M2 of the types 3 and 5. Dominant numbers of M1 and M2 (82% and 88%) have roots of equal length, while the mesial root was shorter in 16% of M1 and in 9.55% of M2. The mesial root form always occurs in normal variants: it appears most frequently in its form I in M1 (74.63%) and in the form II in M2 (55.42%). Asymmetry of the left and right sides is also present: in M1 it is within the limits of 6-10% and in M2 within the limits of 5-15%.
