Single Root Molars- Prevalence in Modern Population and Its Relation to Dental Evolution

<i>Background and Aim: </i>Anatomic variation in root morphology of permanent molars that have been reported pertain to the presence of additional roots, canals or fused roots and C-shaped canals. The occurrence of a single root in molars (SRM) is rare. The aim of the study was to determine the prevalence of single root molar in a large sample of Israeli population and to correlate the crown size of SRM to dental evolution of <I>HS</I>. <i>Methods: </i>2425 panoramic radiographs of modern healthy patients were examined on a light table and the prevalence of SRM was determined. The crown width (MD) of the mandibular second molars of normal two rooted molars, single root molars and homologue two-rooted molars were measured using a digital caliber on a light table. The results of the crown width were compared to anthropological populations (Early <I>HSS</I> and Neanderthals) and archeological population from excavations in Israel from 3000 BC to 13-19 century AC. <i>Results: </i>The prevalence of single root molars in the modern population was 6.13%. No significant differences were found between males and females. In the upper jaw single root molar was found in both first and second molars while in the lower jaw only second molars showed SRM. In both the Neanderthal and Early <I>HSS</I> groups 1 case with single root molars were found. No single root molars were found in the archeological groups from Israel excavations (3000 years BC till 19<sup>th</sup> century AC). The size of the crown was relatively stable during evolution but during the modern period the MD size of the crown was significantly reduced. The crowns of the molars with single root showed significant reduction in comparison to two-rooted molars and even to homologues molars with two roots and the differences were significant statistically (P value<0.01). The homologue two-rooted second molars showed results between the normal population and single root molars. <i>Discussion: </i>This is the first analysis of the prevalence of single root molar in a large population of Israel. The results showed that the crown size is decreasing during the modern period and this reduction is increasing in single root molars, implicating that an on-going reduction in tooth size is happening, probably due to reduction of jaw size and the major changes in food processing and mastication forces.