A comparison of accuracy in bracket positioning between two techniques--localizing the centre of the clinical crown and measuring the distance from the incisal edge.

The placement of orthodontic brackets is guided either by localizing the centre of the clinical crown (CC) or by measuring the distance from incisal edge (ME). The purpose of this study was to examine if there are any significant differences in the accuracy of bracket positioning between these two techniques. Typodont models were simulated with a Class I malocclusion with severe crowding. Nineteen experienced orthodontists (12 males, seven females) with a mean age of 40.6 years bonded pre-adjusted straight-wire brackets (Victory MBT) on the typodonts. Each orthodontist was asked to bond 20 brackets on one typodont using the CC method and 20 brackets on another typodont using the ME method. The teeth were removed from the typodont and photographed for imaging analysis. The errors of bracket placement in the vertical, mesiodistal, and angular/tip dimensions were measured and the data were statistically assessed. An overall test of significance, using all the data, rather than the means, demonstrated a significant vertical difference between the CC and ME methods, with the ME method more accurate vertically (mean CC = 1.19, mean ME = 1.10, P = 0.002) but no significant differences for mesiodistal (mean CC = -0.08, mean ME = -0.05, P = 0.28) or for tip (mean CC = -1.61, mean ME = -1.35, P = 0.34) errors. Analysis of the overall means and the arches independently showed that there was no significant difference in bracket accuracy between the two techniques (P > 0.05). Analysis of the teeth individually showed that the ME method was better in the vertical positioning for several upper and lower anterior teeth (P < 0.01) and poorer for the upper first premolars. The mean time taken to bond the 20 brackets showed no significant difference between two methods (CC 28.53 +/- 9.51 versus ME 28.21 +/- 10.43 minutes, P > 0.05). It is suggested that bracket bonding guided by measuring the distance from incisal edge may result in improved placement for anterior teeth. Archwire bending or bracket repositioning is still necessary to compensate for the inaccuracies with both techniques.