Material and methods

The methodology described for this case-control retrospective study was approved by the University of CES Ethics Committee (Ae-209). The study sample consisted of before treatment (T0) and after treatment (T1) CBCT scans and digital dental models (DDMs) of 36 consecutive patients that were prospectively collected in a previous study. Within that study, the patient allocation to the groups was done by a randomized draw. Based on the mean values and standard deviations of previous reports, ^, and the expected difference between the piezocision and control groups, the sample size of the present study allows us to achieve an 80% power with an α = 0.05.

The patients were aged between 18-40 years, with Angle’s Class I and mild Class II or III malocclusion, with moderate mandibular anterior crowding and healthy periodontium, who underwent orthodontic treatment with passive self-ligating bracket system (Damon SL; Ormco, Orange, Calif) for 13.86 ± 5.46 months (control group, 14.95 ± 6.023; experimental group, 12.65 ± 4.649). The experimental group consisted of 17 patients who received mandibular piezocision at the beginning of treatment with the goal of accelerating tooth movement. The surgical procedure was performed under local anesthesia. Vertical and interradicular gingival incisions were performed on the buccal surface of the mandibular arch from the right to the left first molar. The incisions were started 2-3 mm below the interdental papilla and with sufficient depth to the periosteum to allow the scalpel to reach the alveolar bone. Then, through the incision, using a piezoelectric scalpel (piezotome), several bone cuts were performed. One corticotomy per incision was performed for a total of 11 mandibular corticotomies per patient. The piezo surgical tip only penetrated the buccal cortex thickness (1-2 mm). The control group consisted of 19 patients who did not receive mandibular piezocision. The piezocision group was followed up every 2 weeks, and the control group was followed up every 4 weeks. Mandibular archwire sequence for both groups was as follows: copper-nickel-titanium, 0.014, 0.018, or 0.014 × 0.025-in; copper-nickel-titanium, 0.018 × 0.025-in; TMA, 0.17 × 0.25-in; and stainless steel, 0.017 × 0.025-in and were only changed when they were no longer active.

The mandibular CBCT scans were acquired, using the Veraviewepocs 3D R100 (J Morita Corp, Tokyo, Japan) following the acquisition protocol: 90 kV; 3-5 mA; 0.16-mm ³ voxel size; scan time, 9.3 seconds; and field of view of 100 × 80 mm. The DDMs were acquired with the TRIOS 3D intraoral scanner (version 1.3.4.5; 3Shape, Copenhagen, Denmark) with an accuracy of 6.9 ± 0.9 μm. Dehiscences and fenestrations were quantified in T0 and T1 for each tooth in the mandibular lateral segments (mandibular canines, first and second premolars, and first molars), using 3D Slicer (version 4.10.1; https://www.slicer.org ), following the method validated by Sun et al: (1) the digital imaging and communications in medicine files of the CBCT scans were imported into the 3D Slicer software; (2) all measurements were performed in the largest labiolingual section of each tooth (measurement plane), displayed in the sagittal view. The measurement plane of each tooth was located using 3 red, yellow, and green guidelines that were respectively representing the axial, sagittal, and coronal planes. The axial plane was adjusted, bypassing the red guideline through the cement enamel junction of each tooth in the coronal and sagittal views. Then, the yellow guideline was rotated until it passed through the widest part of the root canal in the axial view, and the yellow and green guidelines were rotated until they passed through the midpoint of the cusp and the root apex in the coronal and sagittal views respectively; (3) the buccal bone defects were measured using the ruler tool in the 3D Slicer. The mesial and distal roots of the first mandibular molars were evaluated individually. The variables and landmarks were described according to Sun et al : (1) dehiscence: alveolar bone defect involving an alveolar margin 2 mm or greater and concurrent with a v-shaped bone margin of the alveolar crest; (2) fenestration: a circumscribed defect on the alveolar bone exposing the root, not involving the alveolar crest; (3) Dh: the distance between A (cementoenamel junction at the buccal side) and B (alveolar crest at the buccal side); (4) Fn: the distance between C (coronal border of a fenestration and D (apical border of a fenestration).

We also set the critical point for dehiscence and fenestration according to Sun et al : the critical point for dehiscence on the CBCT was set at 2 mm and for fenestrations at 2.2 mm, meaning that when Dh was greater than 2 mm, it was classified as dehiscence, and when Fn was greater than 2.2 mm it was classified as fenestration. The flow chart of this image analysis procedure is shown in Figure 1 .

Flow chart: Assessment of buccal bone defects.

Two open-source software, ITK-SNAP (version 2.4.0; Cognitica, Philadelphia, Pa) and 3D Slicer, were used to measure the changes in the buccolingual inclination of each tooth in the mandibular lateral segments, based on the following procedures: (1) Construction of 3-dimensional (3D) volumetric label maps (segmentation) of the T0 mandibles from de-identified “gipl.gz” files. (2) From the T0 3D volumetric label maps, T0 3D surface models (CBCT models) were generated for a standardized common orientation, using the transforms tool in slicer software (mandible orientation). Model orientation was achieved by (2.1) aligning the lower border of the mandible with the horizontal plane in the sagittal view; (2.2) aligning the mesial surface of mandibular first molars with the coronal axis; (2.3) aligning the midline with the sagittal axis. Steps 2.2 and 2.3 were done in the axial view having as reference a standardized fixed coordinate system. The matrix generated from the orientation was applied to the T0 scan and segmentation. (3) Approximation of T0 and T1 CBCT scans was achieved having as a reference the mesial-buccal cusp of the second molars, the buccal cusp of the second premolars, and the cusp of the canines using the surface registration tool. (4) Voxel-based CBCT registration of T1 CBCT scans in relation to the oriented T0 CBCT file was achieved using a nongrowing registration module. (5) Prelabeling: 16 3D dots were placed on the oriented (T0) and registered (T1) segmentations. The dots were positioned at the mandibular canines (midpoint of the cusp and the root apex), first and second premolars (midpoint of the buccal cusp and the root apex), and first molars (a midpoint of the mesiobuccal cusp and central point at the apex of the mesial root). After prelabeling, the T0 and T1 mandibular 3D surface models were generated (Visualization Toolkit files). (6) Measurements of the buccolingual inclination were made using the Quantification of 3D Components tool in 3D Slicer software. Landmarks were placed following the prelabeled 3D dots made to determine the long axis of each tooth. The flow chart of this image analysis procedure is shown in Figure 2 .

Flow chart: Assessment of buccolingual inclination.

The arch width and Little’s Irregularity Index ( LII) were measured on the DDM using Ortho Insight (version 7.0.7096; Motion View Software, Hixson, Tenn). The arch width was measured between the occlusal cusp of left and right canines, buccal cusps of first and second premolars, and mesiobuccal cusps of first molars. The LII was calculated by measuring the linear displacement of the anatomic contact points of each mandibular incisor from the adjacent tooth anatomic point. The flow chart of this image analysis procedure is shown in Figure 3 .

Assessment of arch width and LII.

Results

All variables had excellent intraobserver repeatability and interobserver reproducibility. The intraobserver and interobserver ICCs for bone defects were respectively 0.98 and 0.97. The intraobserver ICCs for inclination and transversal width measurements were 0.96 and 0.99, respectively. The Wilcoxon test showed no statistically significant difference when comparing the left and right sides in the mandibular lateral segments, so right and left data were pooled together for subsequent analyses.

At T0, no statistically significant differences in age, treatment time, LII, cephalometric variables, bone defects, inclination, and arch width were found between the 2 groups; the study variables at T0 are summarized in Table I . Means and standard deviations for Dh, Fn, and Arch width at T0, T1, and T1−T0 are summarized in Tables II and III . Means and standard deviations for buccolingual inclination are summarized in Table IV .

Table II

Treatment outcome comparison of Dh, Fn, and width in the mandibular lateral segments at T0, T1, T1−T0 for groups 1 (control) and 2 (piezocision)

Variables (mm)	Group 1 (n = 19)									Group 2 (n = 17)									T1−T0 (Group 1 vs 2)
	T0		T1		T1−T0		95% CI		Wilcoxon test	T0		T1		T1−T0		95% CI		Wilcoxon test	Mann-Whitney test
	Mean	SD	Mean	SD	Mean	SD	Lower	Upper	P value	Mean	SD	Mean	SD	Mean	SD	Lower	Upper	P value	P value
Dh canine	2.20	1.41	4	2.13	1.80	2.00	0.84	2.77	0.001	1.56	0.83	3.41	2.47	1.84	2.39	0.61	3.07	0.002	0.716
Dh first premolar	2.39	1.03	3.79	1.82	1.40	1.70	0.58	2.23	0.004	2.18	0.88	3.32	1.69	1.14	1.93	0.15	2.13	0.039	0.438
Dh second premolar	1.73	0.70	2.39	1.41	0.66	1.39	−0.01	1.33	0.053	1.43	0.53	2.32	1.15	0.88	1.10	0.32	1.46	0.002	0.274
Dh first molar mesial root	1.39	0.41	2.19	1.03	0.79	1.08	0.27	1.32	0.001	1.28	0.59	1.81	0.79	0.53	0.73	0.15	0.91	0.003	0.366
Dh first molar distal root	1.54	0.69	1.75	0.66	0.21	0.69	−0.12	0.55	0.295	1.41	0.43	2.38	2.59	0.96	2.52	−0.33	2.26	0.006	0.178
Fn canine	0.13	0.56	0.29	1.03	0.16	1.08	−0.37	0.55	0.655	0.22	0.43	0.58	0.72	0.36	0.49	0.11	0.62	0.012	0.006
Fn first premolar	0	0	0	0	0	0	0	0	NA	0.28	0.71	0.10	0.28	−0.18	0.76	−0.57	0.21	0.465	NA
Fn Second premolar	0	0	0	0	0	0	0	0	NA	0.29	1.01	0.12	0.36	−0.17	1.05	−0.71	0.37	>0.999	NA
Fn first molar mesial root	0	0	0	0	0	0	0	0	NA	0	0	0.27	0.66	0.27	0.65	−0.07	0.61	0.109	NA
Fn first molar distal root	0	0	0	0	0	0	0	0	NA	0	0	0.99	0.28	0.09	0.28	−0.05	0.24	0.180	NA
3-3 width	25.29	2.16	27.57	1.23	2.28	1.74	1.45	3.12	<0.001	25.88	2.98	27.25	1.52	1.36	2.13	0.27	2.46	0.019	0.350
4-4 width	32.80	2.08	35.33	1.35	2.53	2.24	1.45	3.61	0.002	33.40	3.10	35.50	1.88	2.16	1.72	1.27	3.05	0.001	0.350
5-5 width	38.21	2.33	41.13	1.38	2.90	2.49	1.72	4.12	0.002	38.44	4.02	41.63	2.25	3.19	2.18	2.08	4.32	<0.001	0.987
6-6 width	44.48	2.26	45.43	2.05	0.95	2.25	−0.14	2.03	0.006	44.93	3.18	46.20	2.50	1.27	1.26	0.62	1.92	0.002	0.476

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