Cortical Bone Remodelling Response to Maxillary Incisor Retraction in Orthodontic Extraction Patients: A Cone Beam Computed Tomography Study

AIM:

To explore the labial and palatal cortical bone remodelling and tooth movement measured at different root levels of retracted maxillary incisors.

7 OBJECTIVES:

1)     To check the cortical bone remodelling after retraction of maxillary central incisors in orthodontic treatment.

2)     To check the cortical bone remodelling after retraction of maxillary lateral incisors in orthodontic treatment.

3)     To check the cortical bone remodelling after retraction of maxillary canine in orthodontic treatment.

4)     To evaluate the efficacy of CBCT in detection of bone remodelling and tooth movement in pre-retraction and post retraction.

Materials:

In this study, following armamentarium will be required

·       CBCT scans (Vatech A-9 machine).

m   METHODLOGY

Apart from routine radiographs, pretreatment CBCT scan will be taken for all subjects. All the selected subjects will require bilateral extraction of premolars.

Orthodontic treatment protocol for all the patients will be bonding with metal MBT(Leone) prescription of 0.022- 0.028 inch and transbond XT. All the indicated first premolars will be extracted and alignment and levelling will be performed using 0.014-0.016-inch NiTi arch wires.  This will progress to 0.019-0.025-inch stainless steel wires and en-masse retraction of maxillary anterior teeth will be performed using sliding mechanics. The six maxillary anterior teeth will be consolidated by the figure of 8 ligatures and NiTi closed coil springs of either 9 or12 mm length will be used from canine to molar to retract the maxillary anterior with a constant force of 150 g on both sides.

Post retraction CBCT (T1) scan will be taken for maxillary anterior (including canines) of all the subjects.

The T0 and T1 CBCT scans will be opened in WinRAR Software version 6.24; Vatech A-9 machine and the slices (T0) will be used to outline the buccolingual border of the alveolar bone and incisor edge. The sketch and slice (T1) will be merged into 1 CBCT image, and the crestal (S1), midroot (S2), and apical (S3) level reference lines will be marked and saved in jpeg format

To measure the position changes in the labial and palatal root and alveolar bone in the CBCT images, each tooth will be measured at S1, S2, and S3 levels from the cementoenamel junction every 3mm along the axis of the incisor. The following measurements will be obtained (1) alveolar BR, which is the horizontal distance between labial or palatal alveolar bone on T0 and T1 scans; (2) TM, defined as the horizontal distance the labial or palatal borders of the incisor root on T0 and T1 scans; (3) the BT ratio, defined as BR divided by TM; and (4) incisor movement pattern (IMP) representing the retraction type of incisors, which is defined as TM(S3)/ TM (S1).demonstrate the features of palatal BR more clearly, all patients will be classified according to whether the root penetrated the original cortical bone border and whether BR will be detected.