Correlation between insertion torque and peri-implant bone strain during placement of orthodontic mini-implants: A finite element study.

INTRODUCTION: Insertion torque is the amount of torque exerted on the implant to tighten into the bone. We investigated whether insertion torque values could be correlated with the strain level in the peri-implant cortical bone resulting from mini-implant insertion. METHODS: The insertion of a standard size mini-implant (φ 1.4 mm × 7 mm) into maxillary alveolar bone was simulated using the finite element method. A total of 3600 calculation steps were employed to numerically reproduce the mini-implant insertion process and analyze the insertion torque and strain distribution in bone. Special attention was given to the relationship between insertion torque values and strain level in the cortical bone at the final tightening. The strain level was quantified using the following 3 strain parameters: (1) average insertion strain, (2) peak insertion strain recorded near the mini-implant thread tips, and (3) the size of the damage zone in the cortical bone. Correlations between the insertion torque values and these 3 parameters were analyzed using linear regression. RESULTS: Direct proportionality and strong correlation were found between the insertion torque values and each of the 3 strain parameters: average insertion strain (r2 = 0.91), peak insertion strain (r2 = 0.91), and the size of damage zone (r2 = 0.90) in the peri-implant cortical bone. CONCLUSIONS: The results of this finite element method study demonstrated that insertion torque could serve as a reliable indicator of the strain level in the peri-implant cortical bone resulting from mini-implant insertion.

Evaluation of clinical parameters for the stability of 2 types of miniscrews.

INTRODUCTION: The purpose of this research was to compare insertion techniques and effects on mechanical and clinical parameters between 2 types of miniscrews. METHODS: Forty-four consecutive patients whose orthodontic treatment involved the use of miniscrews (miniscrew A [MA] and miniscrew B [MB]) for anchorage were included in this study. Miniscrews were placed with predrilling or self-drilling; peak maximum insertion torque (MIT) and Periotest values were measured. Cone-beam computed tomography was performed after the insertion of miniscrews and root proximity determination; cortical bone thickness was also analyzed. Periotest values were measured after the application of orthodontic force. RESULTS: Self-drilling produced higher Periotest values (P <0.01) for MA and higher MIT (P <0.01) for MB with closer root proximity (P <0.05). MB had higher MIT and Periotest values with drilling compared with MA (P <0.05); MB also showed closer root proximity (P <0.05). Successful miniscrews had lower MIT (P <0.05) for MB and lower Periotest values (P <0.01) for both MA and MB, with significantly more distant root proximity (P <0.01). Self-drilling produced higher Periotest values at the time of placement (P <0.01) and after 4 weeks (P <0.05) in MA. Drilling produced higher Periotest values for MB at the time of placement (P <0.05). MIT had positive correlations with Periotest values for MB with self-drilling (P <0.01) and with root proximity for MA with drilling (P <0.01). Periotest values had negative correlations with root proximity for MA and the MB group with drilling (P <0.01). CONCLUSIONS: For miniscrews with larger diameters, higher MIT may result in more mobility (higher Periotest values). Drilling can avoid root contact and enhance primary stability, thus producing lower Periotest values.

Biomechanical analysis for total mesialization of the maxillary dentition: A finite element study.

INTRODUCTION: The purpose of this study was to analyze and clarify tooth movement during mesialization of the whole maxillary dentition with various force angulations (FAs). METHODS: A finite element method was used to simulate the long-term orthodontic movement of the maxillary dentition by accumulating the initial displacement of teeth produced by elastic deformation of the periodontal ligament. A mesial force of 3 N was applied to the maxillary second molar at 5 different FAs (-30°, -15°, 0°, 15°, and 30°) to the occlusal plane. RESULTS: At an FA of 28°, the line of action of the force passed through the center of resistance of the maxillary whole dentition. With all FAs, the central incisors and molars tipped labially and mesially, respectively. The tipping angles gradually decreased as the FAs shifted from -30° to 30°. The molars tipped lingually with FAs of -30° and -15°, whereas they tipped buccally with FAs of 0°, 15°, and 30°. The molars tended to rotate mesiolingually more as the angle of force increased toward an FA of 30°. The occlusal plane rotated counterclockwise with FAs of -30°, -15°, and 0°, whereas it rotated clockwise with FAs of 15° and 30°. With an FA of 30°, buccal tipping and mesiolingual rotation of the molars, and the change in the occlusal plane angle decreased when the transpalatal arch (TPA) was fixed to the first molars and decreased, even more when the TPA was fixed to the second molars rather than the first molars, when a thicker TPA was used, and when the TPA was fixed to both molars rather than a single molar. CONCLUSIONS: There was a correlation between tooth movement during mesialization of the whole maxillary dentition and the angle at which the force was applied.

Biomechanical analysis for total distalization of the maxillary dentition: A finite element study.

INTRODUCTION: This study aimed to identify the tooth movement patterns relative to various force angulations (FAs) when distalizing the total maxillary dentition. METHODS: Long-term orthodontic movement of the maxillary dentition was simulated by accumulating the initial displacement of teeth produced by elastic deflection of the periodontal ligament using a finite element analysis. Distalization forces of 3 N were applied to the archwire between the maxillary canine and first premolar at 5 different FAs (-30°, -15°, 0°, 15°, and 30°) to the occlusal plane. RESULTS: Maxillary incisors and molars showed lingual and distal tipping at all FAs, respectively. At a force angulation of 30°, almost bodily distalization of the total maxillary dentition occurred, but incisors showed considerable lingual tipping because of the effect of clearance gap (0.003-in, 0.022 × 0.025-in bracket slot, 0.019 × 0.025-in archwire) and elastic deflection of the archwire. Medial displacement of the maxillary anterior teeth occurred because of lingual tipping during distalization. The occlusal plane rotated clockwise at all FAs because of extrusion of the maxillary incisors and intrusion of the maxillary second molars, and the amounts decreased as FA increased. CONCLUSIONS: Tooth movement patterns during distalization of the total maxillary dentition were recognized. With an understanding of the mechanics, a proper treatment plan can be established.

Mechanical and clinical evaluation of the effect of microscrew on root proximity and cortical bone thickness.

BACKGROUND/OBJECTIVES: Primary stability is required for successful use of microscrew. This study investigated correlations among biomechanical, morphological, and clinical values in relationship to root contact and different placement locations. MATERIALS/METHODS: Thirty-three microscrews were placed between the molars (n = 18) or in the body of the mandible (n = 15) in three pigs. Insertion torque, Periotest, resonance frequency analysis (RFA), and static and dynamic stiffness were measured. Cone beam computed tomography was performed before and after the insertion of microscrews. Interproximal microscrews were divided into root contacted microscrews (n = 9) and non-root contact microscrews (n = 9). Factorial analysis of variance was conducted, with significance set at P < 0.05. RESULTS: A significant difference was observed between bodily and root contacted microscrews in Periotest, RFA, static and dynamic stiffness, Tanδ, and bone density (RFA, P = 0.045; all others, P < 0.001). A significant difference was observed between bodily and non-root contact microscrews in Periotest, RFA, and bone density (RFA, P = 0.025; all others, P < 0.001). A significant difference was observed in static (P = 0.01) and dynamic (P = 0.038) stiffness between microscrews with and without contact. Dynamic stiffness (P = 0.02) and Tanδ (P = 0.03) showed significant correlations with Periotest results only in bodily microscrews. LIMITATIONS: Since a pig bone was used, some differences in the quality and quantity of the bone might be observed between humans. CONCLUSIONS/IMPLICATIONS: Stiffness values distinguished between microscrews with and without contact. Periotest and RFA results indicated that bodily microscrews were more stable than interproximal microscrews. Periotest and RFA may be useful with large, microscrews and/or in thick cortical bone, but further investigation is required to determine the stability of interproximal microscrews.

Biomechanical analysis for total mesialization of the mandibular dentition: A finite element study.

OBJECTIVES: To clarify the mechanics of tooth movement in mesialization of the whole mandibular dentition when changing the force angulation. SETTING: A finite element method was used to simulate long-term movements of the whole mandibular dentition. MATERIAL AND METHODS: Tooth movement was simulated by accumulating the initial displacement, which was produced by elastic deformation of the periodontal ligament. Mesial forces of 3 N were applied to the second molar bracket at -30°, -15°, 0°, 15° and 30° to the occlusal plane. RESULTS: The whole dentition and occlusal plane were rotated depending on the direction of the force with respect to the centre of resistance (CR). At a force angulation of -30°, the line of action of the force passed near the CR, and the whole dentition translated without rotation of the occlusal plane. The second molar tipped buccally due to a clearance gap between the archwire and bracket slot. When increasing a force angulation from -30°, the line of action of the force passed above the CR, and thereby, the occlusal plane rotated clockwise. This rotation of the whole dentition induced tipping of the individual teeth. Buccal tipping of the molar due to an elastic deformation of the archwire was prevented by using a lingually pre-bent archwire. CONCLUSIONS: Careful selection of force angulation and biomechanics is essential to obtain proper tooth movement in total mesialization of the mandibular dentition.

Biomechanical analysis for total distalization of the mandibular dentition: A finite element study.

INTRODUCTION: The aim of this finite element study was to analyze and clarify the mechanics of tooth movement patterns for total distalization of the mandibular dentition based on force angulation. METHODS: Long-term orthodontic movement of the mandibular dentition was simulated by accumulating the initial displacement of teeth produced by elastic deformation of the periodontal ligament. RESULTS: Displacement of each tooth was caused by movement of the whole dentition, elastic deflection of the archwire, and clearance gap between the archwire and bracket slot. The whole dentition was rotated clockwise or counterclockwise when the line of action of the force passed below or above the center of resistance. Elastic deflection of the archwire induced a lingual tipping of the anterior teeth. It became larger when increasing the magnitude of angulation. The archwire could be rotated within the clearance gap between the archwire and the bracket slot, and thereby the teeth tipped. CONCLUSIONS: Mechanics of total mandibular distalization was clarified. Selective use of force angulation with a careful biomechanical understanding can achieve proper distalization of the whole mandibular dentition.

Long-term changes of the anterior palatal alveolar bone after treatment with bialveolar protrusion, evaluated with computed tomography.

This case report describes the treatment of a 31-year-old woman with a convex profile, protrusive maxilla, retrusive mandible, and gummy smile. Four premolars were extracted, and micro-implant anchorage was used to retract the anterior teeth. Lip protrusion and the gummy smile were improved, but the computed tomography images showed dehiscence on the palatal alveolar bone of the maxillary incisors. Approximately 10 years after treatment, significant alveolar bone apposition was seen on the palatal surface of the maxillary anterior teeth.

Effect of longitudinal flutes on miniscrew implant stability and 3-dimensional bone formation.

INTRODUCTION: The purpose of this study was to evaluate the effects of longitudinal flutes on miniscrew implant (MSI) stability and bone healing. METHODS: Using 11 skeletally mature New Zealand white rabbits, we placed 31 longitudinally fluted and 31 nonfluted, 3-mm-long MSIs in standardized positions in their calvaria and immediately loaded them with 100 g using nickel-titanium coil springs. Insertion torque values were obtained for each MSI placed; removal torque values were obtained for 28 MSIs that had been in place for 6 weeks and 20 MSIs that had been in place for 2 weeks. The bone volume fractions at 6 to 24, 24 to 42, and 42 to 60 µm from the MSI surfaces were evaluated using microcomputed tomography with an isotropic resolution of 6 µm. RESULTS: The success rate was 97% for both the fluted and nonfluted MSIs. The difference in insertion torque between the fluted and nonfluted MSIs was not statistically significant (P = 0.930). After 2 weeks, there was no statistically significant (P = 0.702) difference in removal torque between the fluted and nonfluted MSIs. After 6 weeks, removal torque values were significantly (P = 0.008) higher for the fluted (3.42 ± 0.26 N.cm) than the nonfluted (2.49 ± 0.20 N.cm) MSIs. Bone volume fractions of the 6-to-24-, 24-to-42-, and 42-to-60-µm layers were significantly (P <0.05) greater for the nonfluted than the fluted MSIs. CONCLUSIONS: Loaded 3-mm-long MSIs with and without flutes have high success rates. Longitudinal flutes placed in 3-mm MSIs increased their removal torque by 37% and decreased the amount of bone immediately surrounding them.

Laser-treated stainless steel mini-screw implants: 3D surface roughness, bone-implant contact, and fracture resistance analysis.

BACKGROUND/OBJECTIVES: This study investigated the biomechanical properties and bone-implant intersurface response of machined and laser surface-treated stainless steel (SS) mini-screw implants (MSIs). MATERIAL AND METHODS: Forty-eight 1.3mm in diameter and 6mm long SS MSIs were divided into two groups. The control (machined surface) group received no surface treatment; the laser-treated group received Nd-YAG laser surface treatment. Half in each group was used for examining surface roughness (Sa and Sq), surface texture, and facture resistance. The remaining MSIs were placed in the maxilla of six skeletally mature male beagle dogs in a randomized split-mouth design. A pair with the same surface treatment was placed on the same side and immediately loaded with 200 g nickel-titanium coil springs for 8 weeks. After killing, the bone-implant contact (BIC) for each MSI was calculated using micro computed tomography. Analysis of variance model and two-sample t test were used for statistical analysis with a significance level of P <0.05. RESULTS: The mean values of Sa and Sq were significantly higher in the laser-treated group compared with the machined group (P <0.05). There were no significant differences in fracture resistance and BIC between the two groups. LIMITATION: animal study CONCLUSIONS/IMPLICATIONS: Laser treatment increased surface roughness without compromising fracture resistance. Despite increasing surface roughness, laser treatment did not improve BIC. Overall, it appears that medical grade SS has the potential to be substituted for titanium alloy MSIs.

Stability of mandibular setback surgery with and without presurgical orthodontics.

PURPOSE: The purpose of this study was to compare stability after mandibular setback surgery in patients with skeletal Class III malocclusion with and without presurgical orthodontics. MATERIALS AND METHODS: This retrospective cohort study included consecutive patients with skeletal Class III malocclusion who underwent only mandibular surgery. Patients treated with the surgery-first approach without presurgical orthodontics (SF group) were compared with a control group (conventional surgery with presurgical orthodontics; CS group) using lateral cephalograms taken preoperatively, immediately postoperatively, and at the time of debonding. Predictor variables (group and timing), outcome variables (cephalometric measurements over time), and other variables, such as baseline characteristics, were evaluated to determine the difference in stability of mandibular positions such as the B point. RESULTS: Sixty-one patients were enrolled in this study (CS group, n = 38; SF group, n = 23). Baseline demographic variables were similar in the 2 groups except for orthodontic treatment period. The mean setback of the mandible at the B point was similar (CS group, 8.7 mm; SF group, 9.1 mm; difference, P > .05), but the horizontal relapse in the SF group (2.4 mm) was significantly greater than in the CS group (1.6 mm; P < .05). Patients with a horizontal relapse greater than 3 mm comprised 39.1% of the SF group compared with 15.8% of the CS group (P < .05). CONCLUSION: Mandibular sagittal split ramus osteotomy without presurgical orthodontic treatment was less stable than conventional orthognathic surgery for mandibular prognathism. Before performing a surgery-first approach, skeletal stability needs to be considered.

Torque ratio as a predictable factor on primary stability of orthodontic miniscrew implants.

OBJECTIVE: To evaluate the torque ratio (TR) as a predictable factor on primary stability of orthodontic miniscrews. DESIGN: Fifty-eight orthodontic patients (17 men, 41 women; mean age, 21.9 years) with a total of 112 titanium miniscrews of 3 different diameters were subjected. Maximum insertion torque (MIT) and maximum removal torque (MRT) were measured by a digital torque checker at the screw placement. Four weeks after the placement, the stable screw was recorded as a success. Multiple logistic regression analysis was performed to estimate the influence of each clinical variable on success. RESULTS: Success rates were 82.1% to 89.5%, and there were no significant differences in the 3 types of miniscrews. MIT and MRT showed a positive correlation but did not affect the success rates of miniscrews directly. On the contrary, TR was significantly higher in the success group than in the failure group. In multiple regression analysis, age, TR, and screw proximity had a significant influence on the miniscrew success. CONCLUSIONS: TR might be related with the miniscrew success rates, and it can be used as a predictable factor on primary stability of orthodontic miniscrew implants. Miniscrew implants should be replaced if MRT is significantly lower than MIT at placement surgery.

Biomechanical effectiveness of cortical bone thickness on orthodontic microimplant stability: an evaluation based on the load share between cortical and cancellous bone.

INTRODUCTION: The aim of this study was to determine the appropriate range of cortical bone thickness (CBT) for supporting an orthodontic microimplant. METHODS: Analysis of an orthodontic microimplant subjected to a horizontal force of 2N was performed using a nonlinear finite element method. The peak stresses in the cortical bone of 6 bone specimens (6 base models) with CBT of 0.5, 0.75, 1.0, 1.5, 2.0, and 3.0 mm, respectively, were analyzed. Assuming that the biomechanical effectiveness of cortical and cancellous bone is determined by the portion of the orthodontic force that each bone component takes up, we defined the ratios of the orthodontic force divided between the cortical and cancellous bone as load share ratios (LSR): ie, LSRcortical and LSRcancellous. Along with the base models, imaginary models created by removal of the cancellous bone from the base model bone specimens were analyzed in parallel; the imaginary models were designed so that the cortical bone alone took up all of the orthodontic force. By comparing the peak stresses in the imaginary and base models, the ratios of orthodontic force taken up by the cancellous and cortical bone (LSRcancellous and LSRcortical) were calculated. RESULTS: The highest stress concentration occurred near the fulcrum where the orthodontic microimplant, undergoing tipping, presses the cortical bone surface in the direction of the force. Overall, the increase in CBT resulted in a decrease of the peak stress in the cortical bone. The decrease of stress, however, was not significant when the CBT was > 2.0 mm. LSR analysis showed that the cancellous bone has a substantial role in resisting the orthodontic force in cases of CBT ≤1.0 mm. Its role, however, declined rapidly with an increase of CBT and virtually disappeared at CBT values > 2.0 mm. LSRcortical was approximately 95% (LSRcancellous was 5%) at CBT = 1.5 mm and almost 100% at CBT = 2.0 mm, indicating that virtually all of the orthodontic force is transmitted to the cortical bone at CBT values of 2.0 mm or above. These results collectively demonstrated that CBT > 2.0 mm is biomechanically redundant. CONCLUSIONS: From the biomechanical perspective, CBT values of 1.0 to 2.0 mm might be appropriate for orthodontic microimplant treatment.

Comparison of stainless steel and titanium alloy orthodontic miniscrew implants: a mechanical and histologic analysis.

INTRODUCTION: The detailed mechanical and histologic properties of stainless steel miniscrew implants used for temporary orthodontic anchorage have not been assessed. Thus, the purpose of this study was to compare them with identically sized titanium alloy miniscrew implants. METHODS: Forty-eight stainless steel and 48 titanium alloy miniscrew implants were inserted into the tibias of 12 rabbits. Insertion torque and primary stability were recorded. One hundred grams of tensile force was applied between half of the implants in each group, resulting in 4 subgroups of 24 specimens each. Fluorochrome labeling was administered at weeks 4 and 5. When the rabbits were euthanized at 6 weeks, stability and removal torque were measured in half (ie, 12 specimens) of each of the 4 subgroups. Microdamage burden and bone-to-implant contact ratio were quantified in the other 12 specimens in each subgroup. Mixed model analysis of variance was used for statistical analysis. RESULTS: All implants were stable at insertion and after 6 weeks. The only significant difference was the higher (9%) insertion torque for stainless steel. No significant differences were found between stainless steel and titanium alloy miniscrew implants in microdamage burden and bone-to-implant contact regardless of loading status. CONCLUSIONS: Stainless steel and titanium alloy miniscrew implants provide the same mechanical stability and similar histologic responses, suggesting that both are suitable for immediate orthodontic clinical loads.

Recombinant human bone morphogenetic protein-2 stimulates bone formation during interfrontal suture expansion in rabbits.

INTRODUCTION: Suture expansion stimulates bone growth to correct craniofacial deficiencies but has a high potential of treatment relapse. The objective of this study was to investigate whether there is a dose-dependent relationship between the recombinant human bone morphogenetic protein-2 (rhBMP-2) and bone formation during suture expansion. METHODS: Fifty 6-week-old male New Zealand white rabbits were randomly assigned to 5 groups to receive 0 (control), 0.01, 0.025, 0.1, or 0.4 mg/mL of rhBMP-2 delivered by absorbable collagen sponge placed over the interfrontal suture. The suture was expanded for 33 days by 200 g of constant force via a spring anchored with 2 miniscrew implants. Distance of suture expansion, suture volume, and cross-sectional area after expansion were measured using radiographs with bone markers and microcomputed tomography. Suture widths and mineralization appositional rates were calculated based on the widths between bone labels under an epifluorescent microscope. Software (Multilevel Win 2.0; University of Bristol, Bristol, United Kingdom) was used to model distance of suture expansion over time as polynomials to compare group differences. Wilcoxon signed rank tests were performed to compare the suture volume and cross-sectional area, mineral apposition rate, and suture width between groups. The significance level was set at P = 0.05. RESULTS: Whereas the sutures were expanded in all groups, sutures were expanded by significantly greater amounts in the control and the 0.01 mg/mL groups without fusing the sutures than in the 0.025, 0.1, and 0.4 mg/mL groups with fusing sutures. Compared with the controls, the 0.01 mg/mL group showed significantly lower suture volumes, cross-sectional areas, and suture widths after expansion. The mineral apposition rate was significantly higher in the 0.01 mg/mL group than in the controls from days 10 to 30. CONCLUSIONS: The 0.01 mg/mL dose of rhBMP-2 delivered by absorbable collagen sponge can stimulate bone formation at the bony edges of the suture during suture expansion; however, higher concentrations cause suture fusion. With an appropriate concentration, rhBMP-2 might facilitate suture expansion for clinical uses.

Dynamic simulation of the self-tapping insertion process of orthodontic microimplants into cortical bone with a 3-dimensional finite element method.

INTRODUCTION: The aim of this study was to evaluate the stress state in the cortical bone around an orthodontic microimplant during and after the insertion surgery. METHODS: The self-tapping insertion of an orthodontic microimplant into 1-mm-thick cortical bone containing a predrilled hole was simulated by using a 3-dimensional finite element method. The entire insertion surgery was replicated by a total of 3601 calculation steps: ie, the first 3600 dynamic steps analyzing the insertion process and an additional static step for analyzing the residual stress state after insertion. Four microimplants were experimentally inserted into rabbit tibiae to measure the insertion torques and compare them with the finite element analysis results. RESULTS: Reasonable agreement was observed between the experimentally measured and the finite element calculated torques, confirming the validity of our finite element simulation, which showed that high stresses can develop in the interfacial bone during microimplant insertion. Hoop stresses above the ultimate tensile strength and radial stresses above the ultimate compressive strength of cortical bone developed in the bone. Furthermore, residual radial stresses higher than the critical threshold stress to trigger pathologic bone resorption were observed after insertion. These high insertion-related stresses implied that it is not the orthodontic force or the timing of its application, but the insertion conditions that can determine the bone's response to the microimplant and its clinical prognosis. CONCLUSIONS: This in-vitro finite element analysis showed that, during the self-tapping insertion of orthodontic microimplants, stresses high enough to fracture cortical bone can develop. After the self-tapping insertion, the radial stresses calculated at the interfacial bone were higher than the threshold value to trigger pathologic bone resorption.

Assessment of pharyngeal airway in Korean adolescents according to skeletal pattern, sex, and cervical vertebral maturation: A cross-sectional CBCT study.

Objective: To investigate airway volumes using cone-beam computed tomography (CBCT) by skeletal patterns, sex, and cervical vertebral maturation (CVM) stages in Korean adolescents. Methods: The sample consisted of pretreatment CBCT and cephalograms of 95 adolescents (aged 12-19) obtained out of 1,611 patients examined for orthodontic treatment from 2018 to 2020 in Kyungpook National University Dental Hospital. The samples were classified into two sex groups; three skeletal pattern groups, four chronological age groups and four CVM stages. Nasopharyngeal volumes (NPV), oropharyngeal volumes (OPV), total pharyngeal airway volume (TAV) and minimum cross-sectional area (MCA) measurements were taken from the CBCT. Multiple linear regression analyses to find out which one of the independent variables are good predictors for airway variables. Significant factors were analyzed by two-way multivariate analysis of variance (MANOVA) then multiple comparisons were analyzed using a t-test, and Fisher least significant difference. Results: Age, sex, CVM, and Sella-Nasion-B point have significant influence on airway variable. Males and females showed similar patterns of change in chronological age groups 1-3; however, males had larger NPV, OPV, and MCA at CVM in group 4. According to CVM stages, males had larger OPV, TAV, and MCA at CVM stage 6 (p-value: 0.019, 0.021, 0.015, respectively) and no sex differences at CVM stages 3, 4, and 5. Conclusions: Skeletal patterns have an effect on airway volume. Sex differences were found in CVM 6.

Alveolar bone thickness and height changes following incisor retraction treatment with microimplants.

OBJECTIVES: To evaluate alveolar bone remodeling following incisor retraction treatment with microimplants and to examine the relationship between crown/root distal movement and thickness/height changes of the alveolus. MATERIALS AND METHODS: A total of 24 patients (mean age, 19.29 ± 4.64 years) with bialveolar protrusion treated by incisor retraction with microimplants were included. The distances of the crown and root tip movements as well as the thickness (alveolar bone thickness [ABT]; labial, lingual, and total) and vertical level (vertical bone level [VBL]; labial and lingual) of the alveolar bone were assessed using cone-beam computed tomography images obtained before treatment (T1) and after treatment (T2). All T1 and T2 variables were compared, and further comparisons of alveolar bone changes were conducted between the two groups based on the distance of the crown (low-crown-movement and high-crown-movement groups) and root movements (low-root-movement and high-root-movement groups). To determine the correlation of the crown or root movement with the variables of alveolar bone changes, Pearson correlation coefficients were calculated. RESULTS: Significant differences were found in all VBL and ABT variables after treatment in both jaws but not in total ABT. Based on the crown and root movements, alveolar bone change significantly differed between the root-movement groups, whereas there was no significant difference between the crown-movement groups. In addition, root movement showed significant correlations with the variables. CONCLUSIONS: Remarkable changes in the height and thickness of alveolar bone were found after microimplant-aided incisor retraction treatment in all groups except for total ABT. Root movement was significantly correlated with the alveolar bone changes.