The objective of this research was to study the variation in the number of roots of mandibular teeth and to compare them with data from available literature. The retrospective study was conducted at the Department of Maxillo-facial Surgery at the University Hospital Centre Split by analysing Cone-Beam Computed Tomography (CBCT) scans of patients' lower jaws. Out of 145 CBCT scans of the lower jaws, 114 were valid and entered in the Excel table for statistical analysis. Three hypotheses have been put forward: (1) lower incisors, canines and premolars have one root; (2) lower molars have two roots; (3) supernumerary root is the most common variation in lower molars. Data collected from 114 participants, i.e. CBCT scans, were analysed in the STATISTICA 11.0 programme package and every side of a group of teeth was analysed separately. Lower incisors, canines and premolars are, in the largest percentage, single-rooted teeth (two-rooted teeth vary from 0 to 4 per cent), whereas molars are, the most, two-rooted teeth (one-rooted teeth vary from 2 to 5 per cent, while three-rooted teeth stand at about 3 to 6 per cent). The most frequent anatomical variation observed was the presence of a supernumerary root in the mandibular third molar. This research confirmed the hypotheses and obtained data on the number of dental roots in all teeth of the lower jaw, in accordance with data from the literature.