Abstract Introduction The apical thirds of the roots and their cone-shaped parts are neglected into dental literature and education. Apical foramen is the only anatomical structure in the internal part of the root conus with construction described in textbooks, atlases and monographs. Aim The aim of the study is to measure the size and proportion of the longitudinal part of the conic shape of the roots into different groups of teeth for maximum saving of dentine and sound active root surface for prevention of fractures and cracks. Materials and Methods 158 upper and lower front teeth are included in the study. Lengths were measured twice for each tooth with endodontic files and disks as follows: the whole tooth, the root from neck to apex and the conical part of the root. Exclusion criteria consisted of: teeth with broken cusps, roots, or incisal ridges, large apical resorptions higher than 1.5 mm, fluorotic teeth, teeth with abrasion, and lateral root resorptions larger than 1 mm. Results The null hypothesis for a smaller deviation of the length of the cone part from the roots compared with the whole root in the total longitudinal size of the roots was proved. This cone part was measured to be between 4.3-6.3 mm distance from the apex in upper and lower front teeth and premolars. The proportion to the whole length of the roots varies from 25% to 48.8% (p<0.05). The statistics were performed with the more sensible Levene’s test for mean differences. Conclusions Active rotary machine root canal preparations in the apical zone, even at 1-2 mm away from the apex can decrease significantly the amount of apical dentine and can lead to cracks in this area. Bigger sizes of posts can overload the roots in this zone and their safe placement is essential.
Boteva et al. (Sun,) studied this question.