The Six Keys to Normal Occlusion.

This study aimed to obtain information on the relationship between crown and root in terms of morphology – dimensions and crown-root angles –to be used for orthodontic set-ups without the use of radiological examinations.All the good quality CBCTs of patients obeying the eligibility criteria, from 2000 to 2015, were analysed. All teeth were analysed except for third molars. Six variables were evaluated: crown (CL) and root length (RL), crown width (CW), root width (RW), crown-root angles in both the frontal (CR-frontal) and sagittal plane (CR-sagittal). All teeth were divided into 3 groups according to number of root (single, two, three-rooted). The measurements were assessed with the Invivo professional software and then, subjected to correlation matrices and linear regression statistical analysis in order to find any significant correlations between crown and root measurements (α ≤ 0.05).Seventy-three out of 247 good quality CBCTs were assessed. Correlation matrices statistical analysis showed linear correlations for some variables investigated, especially for CW/RW pairing in all subgroups (r = 0.81, r = 0.70 and r = 0.58 respectively for single-, two- and three-rooted) and CL/RL in the single-rooted subgroup (r = 0.29). Subsequent linear regression analysis allowed to obtain information about roots starting from crown measurements by means of equations [RW = 0.76 + (0.73 × CW) and RL = 10.94 + (0.25 × CL) for single-rooted teeth; RL = 1.11 + (0.73 × CW) and RW = 0.99 + (0.76 × CW), respectively for single- and two-rooted teeth]. No linear correlation was found between crown measurements and C-R angular values.It is possible to obtain root information starting from some crown measurements but these do not fulfil the need of minimal information to guarantee a perfect root position starting from that of crown.