Orthodontist's Bracket Placement Repeatability

Orthodontist's Bracket Placement Repeatability

Objective: Bracket placement accuracy is crucial for optimal orthodontic treatment results using the “straight wire” methodology.  This paper describes the bracket placement repeatability in 6-degrees-of-freedom.  Five orthodontists participated in the study.

Method:  One pair of upper and lower maloccluded arches were digitized and then 6 replica models were printed from an Eden 500 rapid prototyping machine.  Five orthodontists placed 3M Unitek Victory Series MBT LP metal brackets 5-5 to their own definitions of ideal positions on 3 pairs of arches directly in a dental mannequin.  The 5 orthodontists also placed brackets on the other 3 pairs of arches without the dental mannequin to simulate an indirect bonding process.  A proprietary lab process using the same digitized models with additional bracket placement guides was also applied to indirectly place brackets.  Bonding trays were made to transfer the brackets to a different arch and the total variations were measured and compared to the orthodontists' direct bond data. The bracket placement variations of all arches were measured using a 3D optical measurement system (SmartScope ZIP 250, Optical Gaging Products, Rochester, NY).

Results:  Pooled standard deviations (PSTDEV) of the bracket placement repeatability were measured for each doctor and the lab process.  Measurements of 3 translational (M-D=medial-distal, O-G=occlusal-gingival, L-L=labial-lingual) variations and 3 angular variations were taken (Figs. 1a-d).

(a)	(b)
(c)	(d)

Figs.  1a-d  Bracket Placement Variations

Conclusions:  It may be concluded that when those orthodontists use their own direct and indirect bond techniques to place the bracket for each tooth, 95% (2 PSTDEV's) of the brackets may be repeatedly placed within ±0.5 mm and ±6.2 degrees versus the lab process of within ±0.2 mm and ±4.9 degrees respectively.