OBJECTIVETo investigate three-dimensional imaging registration and superimposition techniques in measuring the tip and torque change of upper canine, premolar and first molar after orthodontic treatment.

METHODSTwenty-eight subjects (14 extraction cases and 14 non-extraction cases) with full records were randomly selected from the Department of Orthodontics, Peking University School and Hospital of Stomatology. The pre-and post-treatment upper dental casts were digitized with three-dimensional spot laser scanner and superimposed with reverse engineering software. The facial axis of the clinical crown (FACC) was transferred from post-treatment teeth to the pre-treatment teeth using three-dimensional imaging registration. The occlusal plane was constructed on the post-treatment upper digital cast and the tip and torque values were measured.

RESULTSIn the non-extraction group, the tip of the second premolar decreased by 1.5° (P < 0.05). The buccal crown torque of the first and second premolars increased by 5.1° and 4.2° (P < 0.05), respectively. In the extraction group, the lingual crown torque of upper canine increased by 3.8° (P < 0.05).

CONCLUSIONSNon-extraction orthodontic treatment tended to tip the upper second premolar distally and increased the buccal crown torque of the upper premolars while extraction treatment increased the lingual crown torque of the upper canine.