Does anchorage loss differ with 0.018-inch and 0.022-inch slot bracket systems?

Objectives: To compare maxillary first molar anchorage loss between 0.018-inch and 0.022-inch slot fixed appliance systems. Materials and Methods: Patients requiring bilateral maxillary premolar extractions (n ¼ 74) within a randomized clinical trial comparing the effectiveness of 0.018-inch and 0.022-inch slot MBT bracket systems (3M-Unitek, Monrovia, Calif) were included. Three-dimensional pre- and posttreatment digital models were landmarked and measured (R700 scanner and OrthoAnalyzer software, 3Shape, Copenhagen, Denmark). Anteroposterior position of the first molars was measured using the third medial rugae point as a reference. Anchorage loss (AL) represented the subtraction of the posttreatment distance from the pretreatment distance for both anchorage loss right (ALR) and left (ALL) sides. The values were then compared using a two-way analysis of variance. Results: There were 41 and 33 cases for the 0.018-inch and 0.022-inch bracket slot systems, respectively. The baseline characteristics were similar between groups, except for the presence or absence of anchorage devices (P ¼ .050). For the total sample: 0.018-inch ALR ¼ 3.86 mm, ALL ¼ 3.30 mm and 0.022-inch ALR ¼ 3.73 mm, ALL ¼ 3.47 mm (P ¼ .970). There was also no significant difference between the 0.018-inch and 0.022-inch groups when subjects with anchorage devices were excluded (P ¼ .383). Conclusions: Bracket slot size does not influence maxillary molar anchorage loss during orthodontic treatment.