ABSTRACT
BACKGROUND: To evaluate and compare the distribution of stress and displacement of teeth during mandibular arch distalization using buccal shelf screws. MATERIALS AND METHODS: Three three-dimensional finite element models of mandibular arch were constructed with third molars extracted. Models 1, 2, and 3 were constructed on the basis of the lever arm heights of 0 mm, 3 mm, and 6 mm, respectively, between the lateral incisor and canine. A buccal shelf screw was placed at the area in the second molar region with the initial point of insertion being inter-dental between the first and second molars and 2 mm below the mucogingival junction. MBT pre-adjusted brackets (slot size 0.022 × 0.028") were placed over the clinical crown's center with a 0.019 × 0.025" stainless-steel archwire on three models. A retraction force of 300 g was applied with buccal shelf screws and a lever arm bilaterally using nickel-titanium closed coil springs. The displacement of each tooth was calculated on X, Y, and Z axes, and the von Mises stress distribution was visualized using color-coded scales using ANSYS 12.1 software. RESULT: The maximum von Mises stress in the cortical and cancellous bones was observed in model 1. The maximum von Mises stress in the buccal shelf screw and the cortical bone decreased as the height of the lever arm increased. Applying orthodontic forces at the level of 6 mm lever arm height resulted in greater biomechanical bodily movement in distalization of the mandibular molars compared to when the orthodontic forces were applied at the level of 0 mm lever arm height. CONCLUSION: Displacement of the entire arch may be dictated by a direct relationship between the center of resistance of the whole arch and the line of action generated between the buccal shelf screw and force application points at the archwire, which makes the total arch movement highly predictable.
ABSTRACT
OBJECTIVE: To evaluate the effectiveness of micro-osteoperforation (MOP) over a 56-day period and to determine the influence of number of perforations on the rate of canine retraction. In addition, the amount of pain and discomfort caused by the MOP was evaluated. TRIAL DESIGN: A single-center, split-mouth, triple-blind, randomized, controlled trial. METHODS: 22 patients (18-30 years) who need fixed orthodontic treatment were recruited and randomly assigned to MOP1 and MOP2 groups. The recruited patients were divided into two groups with 1:1 allocation ratio. Randomization for the determination of experimental side and number of perforations was done using sealed envelopes. On each patient, the other side of mouth worked as control side with no MOPs. 4 months after first premolar extraction, patients in MOP1 received 3MOPs on the buccal surface of alveolar bone, whereas patients in MOP2 received three buccal and three palatal MOPs in the experimental side. The amount of canine retraction was measured every 28 days at two intervals on both sides of mouth. Pain perception was measured after 1 hr, 24 hr, 72 hr, 7 days, and 28 days of procedure. RESULTS: Result of the intra-examiner reliability using ICC is more than 0.97 (P < 0.001), indicating excellent repeatability and reliability of the measurements. The baseline characteristics between groups were similar (P > 0.05). A statistically significant difference in the rate of canine retraction on the MOP side was observed at the end of 56 days, amounting to two folds more than that of the control side. No significant difference was seen between MOP1 and MOP2 groups (P > 0.05). Mild-to-moderate pain was experienced only in first 72 hours of procedure. CONCLUSION: The study recommends that MOP procedure has substantial potential to be used as an adjunct to the routine mechanotherapy for accelerating tooth movement, as it may reduce treatment time by half in the first four weeks after the MOP procedure. TRIAL REGISTRATION: Clinical trial registry of India (CTRI/2022/12/048181).
