This study aimed to compare the extent of buccal bone defects (dehiscences and fenestrations) and transversal tooth movement of mandibular lateral segments in patients after orthodontic treatment with and without piezocision in cone-beam computed tomography and digital dental models.
The study sample of this study consisted of cone-beam computed tomography scans and digital dental models taken before (T0) and after (T1) orthodontic treatment of 36 patients with moderate mandibular anterior crowding. The experimental group consisted of 17 patients that had piezocision performed at the beginning of treatment with the goal of accelerating tooth movement, which was compared with 19 patients who did not receive piezocision. The measurement of bone defects, buccolingual inclination, and transversal distances of the tooth in the mandibular lateral segments (mandibular canines, premolars, and first molars) were evaluated at baseline and at the end of the orthodontic treatment.
Overall, an increase in dehiscences, buccal inclination, and arch width from T0 to T1 was observed in both groups, but no statistically significant difference was found between groups. A significant increase in fenestrations from T0 to T1 was observed only for the canines in the experimental group. No statistically significant association was found between the increase of dehiscences and the amount of buccolingual inclination or transversal width changes. However, the changes in transversal width were statistically significantly associated with the increase in buccal inclination at the canines, first and second premolars.
No significant differences were found in buccal dehiscences and transversal tooth movement (buccolingual inclination and arch width) of mandibular lateral segments between patients after orthodontic treatment with and without piezocision. Dehiscences, buccal inclination, and arch width significantly increased from T0 to T1 in both groups.
Mandibular buccal bone levels are significantly decreased immediately after debonding.
Piezocision does not affect buccal bone defects after accelerated orthodontic treatment.
Piezocision has no significant influence on the amount and type of tooth movement.
Superimposed cone-beam computed tomography scans were used to measure buccolingual inclination.
The duration of orthodontic treatment has become one of the most frequent concerns in patients because of the esthetic demands of society, which makes them request a shorter duration of orthodontic treatment. Thus, accelerating orthodontic tooth movement and reducing treatment time has become one of the main research areas in orthodontics. Surgical interventions to accelerate the rate of tooth movement aim to accelerate bone remodeling by cutting the cortical layer of alveolar bone to induce the regional acceleratory phenomenon. The regional acceleratory phenomenon is a localized reaction of soft and hard tissues adjacent to the corticotomy, resulting in increased bone remodeling and a temporary decrease in bone density, which along with conventional orthodontic forces allow an increased rate of orthodontic movement.
Piezocision is a minimally invasive procedure combining gingival microincisions followed by minimal piezoelectric osseous cuts to the buccal cortex to accelerate orthodontic tooth movement, and bone or soft-tissue grafting concomitant with a tunnel approach to enhance periodontium if needed. Recently, several articles have evaluated the effectiveness of piezocision in accelerating orthodontic tooth movement with contradictory results. The relationship between piezocision and periodontal health remains unknown. The region where the osteotomy cuts are made with the piezoelectric knife, usually without bone graft, is a susceptible area for bone defects such as dehiscences and fenestrations even before orthodontic treatment , as well as after conventional orthodontic treatment, owing to the transverse expansive tendency during the alignment of the arches. Charavet et al reported that dehiscences and fenestrations were similar with or without piezocision; however, no standardization of the methods to evaluate dehiscences and fenestrations, nor transverse dimensions or changes in the buccolingual inclination of the mandibular lateral segments were described. Recently, Raj et al, employing cone-beam computed tomography (CBCT) scans in a randomized clinical trial with and without piezocision, evaluated the marginal crestal bone when retracting canines; they demonstrated that with piezocision, there was a statistically significant gain in bone level in buccal and mesial alveolar bone level.
Little is known regarding the use of piezocision to accelerate orthodontic tooth movement and how it influences the risk of alveolar bone defects. Furthermore, the piezocision relationship with the type and amount of transverse tooth movement that occurs during orthodontic alignment is still unknown. Specifically, this study compared the extent of buccal bone defects (dehiscences and fenestrations) and transversal tooth movements of mandibular lateral segments in patients before and after orthodontic treatment with and without piezocision.
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 188.8.131.52; 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; 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 .
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 .
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 .
Before performing the measurements of bone defects, 2 observers were calibrated by a radiologist, who repeated measurements for 10 randomly selected CBCT scans 3 times with a 1-week interval in between scans. To assess intraobserver repeatability for inclination and transversal width, we made repeated measurements for 10 CBCT scans and 8 DDM with an interval of 1 week. To assess intraobserver repeatability and interobserver reproducibility, we used the intraclass correlation coefficient (ICC).
Kolmogorov-Smirnov and Shapiro-Wilk tests revealed that the variables of the study did not have a normal distribution. Therefore, nonparametric tests were used. Wilcoxon test was used to compare the right and left teeth measurements, and the intragroup changes from T0 to T1 (T1−T0). Mann-Whitney test was used to compare the differences at T0 between the 2 groups and the T0 to T1 changes between the 2 groups. Pearson correlation coefficient was used to assess the association between buccolingual inclination with dehiscences, transversal width with dehiscences, and buccolingual inclination with transversal width. All statistical analyses were conducted using SPSS Statistics for Mac (version 25.0; SPSS, Chicago, Ill).
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 .
|Variables||Group 1 (n = 19)||Group 2 (n =17)||Mann-Whitney test|
|Treatment time (mo)||14.95||6.02||12.65||4.65||0.176|
|Wits appraisal (mm)||1.86||3.14||2.09||2.57||0.634|
|Gonial angle (°)||115.88||6.45||117.38||7.33||0.274|
|Molar relation (mm)||−0.82||2.18||−0.55||1.55||0.210|
|Dh canine (mm)||2.20||1.41||1.56||0.83||0.199|
|Dh first premolar (mm)||2.39||1.03||2.18||0.88||0.623|
|Dh second premolar (mm)||1.73||0.70||1.43||0.53||0.358|
|Dh first molar mesial root (mm)||1.39||0.41||1.28||0.59||0.326|
|Dh first molar distal root (mm)||1.54||0.69||1.41||0.43||0.601|
|Fn canine (mm)||0.13||0.56||0.22||0.43||0.147|
|Fn first premolar (mm)||0||0||0.28||0.71||0.060|
|Fn second premolar (mm)||0||0||0.29||1.01||0.129|
|Fn first molar mesial root (mm)||0||0||0||0||>0.999|
|Fn first molar distal root (mm)||0||0||0||0||>0.999|
|3-3 width (mm)||25.29||2.16||25.88||2.98||0.350|
|4-4 width (mm)||32.80||2.08||33.40||3.1||0.350|
|5-5 width (mm)||38.21||2.33||38.44||4.02||0.987|
|6-6 width (mm)||44.48||2.26||44.93||3.18||0.476|
|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 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 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|