The reliability of crown-root ratio, linear and angular measurements on panoramic radiographs.

The aim of this study was to evaluate the reliability of crown and root length, crown-root ratio and angular measurements of teeth relative to constructed reference lines and to other teeth in the same region on consecutive (T1 and T2) panoramic radiographs (OPGs). This retrospective study employed 20 cases; ten with five implants in each jaw (age range between 20 and 60 years) and ten with a full permanent dentition (age range between 12 and 16 years). The consecutive pairs of OPGs ranged from 6 months to 3 years apart. Four variables were measured and compared: 1) the crown or coronal segment length and the root or apical segment length; 2) the crown-root ratio; 3) the angulations of teeth and implants relative to specific reference lines in each jaw; 4) the angle between teeth and implants in the same sextant. The results revealed that comparisons of measurements taken of the same structures at T1 and T2, there were no statistically significant differences (p>0.05) between vertical linear measurements. The crown-root ratios and coronal-apical segment ratios too, showed no significant differences (p>0.05). Whereas, angulations of teeth or implants relative to respective reference lines showed significant differences (p=0.001) for some of the teeth. These differences, however, were less than 5 degrees; a clinically acceptable range. Angles measured between teeth or implants in the same sextant showed no significant differences (p>0.05). These results seem to support the hypothesis, therefore, that the linear vertical measurements, ratio calculations and angular measurements can be used to compare crown and root lengths, crown-root ratios and tooth angulations on OPGs taken of the same patient at different times with consistent accuracy.

Accuracy of linear and angular measurements on panoramic radiographs taken at various positions in vitro.

The accuracy of measurement of tooth length and angulation on dental panoramic tomograms (DPTs) is thought to be highly dependent on head positioning technique. A model representing the dentition and the functional occlusal plane was designed using an acrylic framework and stainless steel wires. The aim was to investigate whether varying the position of the model affects the linear and angular measurements on DPTs. Four different positions were investigated: initial position representing natural head posture (NHP) (T1); lateral right cant of the occlusal plane (T2); lateral left cant of the occlusal plane (T3); and tilting the occlusal plane up anteriorly (T4). On each DPT, four sets of measurements were recorded: (1) Vertical linear measurements of the stainless steel pins and ratio calculations of the 'crown' and 'root' segments (represented by the wire above and below the occlusal plane, respectively); (2) angular measurements of the pins relative to the occlusal plane; (3) angular measurements of the pins relative to a constructed reference line; and (4) angular measurements of pins relative to each other in the same segment. The results showed a significant error (P < 0.05) in all measurements when the occlusal plane was tilted up anteriorly by 8 degrees. A lateral cant of the occlusal plane by less than 10 degrees without an upward anterior rotation showed no significant effect on the measurements. This would suggest that there is some tolerance of variation in head position.