Three-dimensional canine displacement patterns in response to translation and controlled tipping retraction strategies

Abstract

Objective To validate whether applying a well-defined initial three-dimensional (3D) load can create consistently expected tooth movement in patients. Materials and Methods Twenty-one patients who needed bilateral canine retraction to close extraction space were selected for this split-mouth clinical trial. After initial alignment and leveling, two canines in each patient were randomly assigned to receive either translation (TR) or controlled tipping (CT) load. The load was delivered by segmental T-loops designed to give specific initial moment/force ratios to the canines in each treatment interval (TI), verified with an orthodontic force tester. Maxillary dental casts were made before canine retraction and after each TI. The casts were digitized with a 3D laser scanner. The digital models were superimposed on the palatal rugae region. The 3D canine displacements and the displacement patterns in terms of TR, CT, and torque were calculated for each TI. Results The method can reliably detect a TR displacement greater than 0.3 mm and a rotation greater than 1.5°. Ninety-two TIs had displacements that were greater than 0.3 mm and were used for further analysis. Most displacements were oriented within ±45° from the distal direction. The displacement pattern in terms of TR or CT was not uniquely controlled by the initial moment/force ratio. Conclusions The initial load system is not the only key factor controlling tooth movement. Using a segmental T-loop with a well-controlled load system, large variations in canine displacement can be expected clinically.

Root resorptions associated with canine retraction treatment

“…Table 1 shows the calculated root length and volume changes of the canine on the TR and CT sides as well as the apical tooth displacements 43 as functions of subject’s gender, age, treatment duration, and genotype. The incisor root shortenings were all less than 0.5 mm, thus were not included in Table 1.…”

“…The apical tooth displacements were reported previously. 43 The root reduction equal to or greater than 0.5 mm was marked red, which were considered as the definite EARR. The volume changes were less than 75 mm 3 , the resolution due to the voxel size of the CBCT images, thus were considered as non-definite.…”

Hounsfield unit change in root and alveolar bone during canine retraction

“…The canine displacement and its direction at the end of the canine retraction were determined from the CBCTs. 18 …”

“…The calculated tooth displacement included both tooth displacement and direction. 18 The tooth movement direction was used to align the divisions characterizing the locations of HU changes. To study the HU changes, the root was segmented first.…”

Mechanical environment change in root, periodontal ligament, and alveolar bone in response to two canine retraction treatment strategies

“…The average time for canine retraction was 4.9 months which varied depending on the size of the initial space, patients' appliance on appointment, and interpatient variations. The canines displaced on average 2.1 ± 1.5 mm .…”