Genetic effect of single nucleotide polymorphisms in growth hormone receptor gene on the risk of non-syndromic mandibular prognathism in the Korean population.

OBJECTIVES: To evaluate the association of three single-nucleotide polymorphisms (SNPs) of growth hormone receptor (GHR) gene with mandibular prognathism (MP) and relationships between mandibular morphology and GHR gene SNPs in the Korean population. MATERIALS AND METHODS: A total of 325 subjects were divided into two groups based on sagittal maxillomandibular relationship by the lateral cephalography: the MP and control groups. From the SNPs in the GHR gene, three SNPs (rs6180, rs6182 and rs6184) were selected. SNP genotyping was performed using direct sequencing. The craniofacial measurements of lateral cephalography were analysed. RESULTS: We found a lack of association between GHR and MP. However, in the analysis according to the values of cephalometric measurements, rs6180 was significantly associated with ANB, SNB, effective mandibular length and SNMP in females. Additionally, rs6182 and rs6184 were significantly associated with ramal height in males. CONCLUSION: Growth hormone receptor SNPs may affect not only the sagittal development of mandible but also the vertical development of ramal height, and GHR SNPs may gender-differently influence mandibular morphology. This finding supports that the GHR might be susceptible on mandibular morphogenesis in the Korean population.

Palatal temporary skeletal anchorage devices (TSADs): What to know and how to do?

OBJECTIVES: Since palatal temporary skeletal anchorage devices (TSADs) have become important tools for orthodontic treatment, this narrative review was aimed to provide an updated and integrated guidelines for the clinical application of palatal TSADs. SETTING AND SAMPLE POPULATION: A narrative review article including researches on palatal TSADs in orthodontics related to anatomy, success rate and clinical application. MATERIALS AND METHODS: The anatomical characteristics, success rate and its consideration factors and clinical application of palatal TSADs based on the direction of tooth movement were evaluated. RESULTS: To improve the stability of TSADs, hard tissue factors such as bone depth, cortical bone thickness, bone density and soft tissue thickness were evaluated. Anatomically risky structures, including the nasopalatine foramen, canal and the greater palatine foramen, nerve, vessel need to be identified before placement. The success rate of palatal TSADs was greater than that of the buccal inter-radicular space. Palatal TSADs have been used for various purposes because they can control tooth movement in all directions and, three-dimensionally; their applications include the retraction of anterior teeth, protraction of posterior teeth, distalization, intrusion, expansion and constriction. They can be applied directly or indirectly to the lingual arch or transpalatal arch. Design modifications using splinted 2 miniscrews have been suggested. CONCLUSION: Palatal TSADs allow clinicians to perform minimally invasive and easy placement with good stability by understanding the anatomical characteristics of the palatal region, and they show good control over 3-dimensional tooth movements in various clinical cases.

Clustering-based characterization of clinical phenotypes in obstructive sleep apnoea using severity, obesity, and craniofacial pattern.

OBJECTIVES: To identify and characterize the phenotypes of adult obstructive sleep apnoea (OSA) patients based on clustering using OSA severity, obesity, and craniofacial pattern. MATERIAL AND METHODS: The samples consisted of 89 adult OSA patients whose polysomnography and lateral cephalogram were available. With cluster analysis using apneahypopnea index (AHI, events/hour), body mass index (BMI, kg/m2), ANB (degree), and mandibular plane angle (MPA, degree), three clusters were identified. Cephalometric variables including craniofacial, soft palate, hyoid bone, and pharyngeal space compartments were compared among clusters by one-way analysis of variance or Kruskal-Wallis test. Multivariable linear regression analysis was performed to find contributing factors to OSA severity within each cluster. RESULTS: Cluster-1 (obesity type; 49.4 per cent) exhibited moderate OSA, obesity, and normal sagittal and vertical skeletal pattern (AHI, 22.4; BMI, 25.5; ANB, 3.2 degrees; MPA, 26.3 degrees) without significant upper airway abnormality. Cluster-2 (skeletal type; 33.7 per cent) was characterized by moderate OSA, severe skeletal Class II hyperdivergent pattern with narrow pharyngeal airway spaces, without obesity (AHI, 27.9; BMI, 23.5; ANB, 7.5 degrees; MPA, 36.6 degrees). Cluster-3 (complex type; 16.8 per cent) included severe OSA, obesity, skeletal Class II hyperdivergent pattern (AHI, 52.8; BMI, 28.0; ANB, 4.5 degrees; MPA, 32.2 degrees), with posteriorly displaced hyoid and retroclined soft palate. The main contributing factors to AHI were obesity in Cluster-1; hyperdivergent vertical pattern with narrow pharyngeal space in Cluster-2; and hyperdivergent pattern, obesity, displaced hyoid, and soft palate in Cluster-3. CONCLUSION: Three OSA phenotypes resulted from this study provide a clinical guideline for differential diagnosis and orthodontic intervention in the interdisciplinary treatment for OSA patients.

Morphologic evaluation of dentoalveolar structures of mandibular anterior teeth during augmented corticotomy-assisted decompensation.

INTRODUCTION: Our aim in this study was to evaluate the effect of augmented corticotomy on the decompensation pattern of mandibular anterior teeth, alveolar bone, and surrounding periodontal tissues during presurgical orthodontic treatment. METHODS: Thirty skeletal Class III adult patients were divided into 2 groups according to the application of augmented corticotomy labial to the anterior mandibular roots: experimental group (with augmented corticotomy, n = 15) and control group (without augmented corticotomy, n = 15). Lateral cephalograms and cone-beam computed tomography images were taken before orthodontic treatment and before surgery. The measurements included the inclination and position of the mandibular incisors, labial alveolar bone area, vertical alveolar bone height, root length, and alveolar bone thickness at 3 levels surrounding the mandibular central incisors, lateral incisors, and canines. RESULTS: The mandibular incisors were significantly proclined in both groups (P <0.001); however, the labial movement of the incisor tip was greater in the experimental group (P <0.05). Significant vertical alveolar bone loss was observed only in the control group (P <0.001). The middle and lower alveolar thicknesses and labial alveolar bone area increased in the experimental group. In the control group, the upper and middle alveolar thicknesses and labial alveolar bone area decreased significantly. There were no significant differences in dentoalveolar changes between the 3 kinds of anterior teeth in each group, except for root length in the experimental group (P <0.05). CONCLUSIONS: Augmented corticotomy provided a favorable decompensation pattern of the mandibular incisors, preserving the periodontal structures surrounding the mandibular anterior teeth for skeletal Class III patients.

Effect of tooth displacement and vibration on frictional force and stick-slip phenomenon in conventional brackets: a preliminary in vitro mechanical analysis.

OBJECTIVE: To evaluate the effects of tooth displacement and vibration on frictional force and stick-slip phenomenon (SSP) when conventional brackets were used with a levelling/alignment wire. MATERIALS AND METHODS: The samples consisted of six groups (n = 10 per group) with combinations of tooth displacement (2mm lingual displacement [LD], 2mm gingival displacement [GD], and no displacement [control]) and vibration conditions (absence and presence at 30 Hz and 0.25 N). A stereolithographically made typodont system was used with conventional brackets and elastomeric ligatures. After application of artificial saliva, static/kinetic frictional forces (SFF/KFF) and frequency/amplitude of SSP were measured while drawing a 0.018-inch copper nickel-titanium (Cu-NiTi) archwire at a speed of 0.5mm/min for 5 minutes at 36.5 degree celsius. Two-way analysis of variance and independent t-test were performed. RESULTS: Tooth displacement increased SFF and KFF (control < LD < GD, all P < 0.001) and reduced SSP frequency (control > [LD, GD], P < 0.01). Vibration reduced SFF, KFF, and SSP amplitude in the control group (P < 0.05, P < 0.05, and P < 0.001, respectively), but not in the LD and GD groups. SSP frequency was increased by vibration in the control, LD, and GD groups (all P < 0.001), and it was lower in the LD and GD groups than in the control group (P < 0.01). CONCLUSIONS: When conventional brackets and a 0.018-inch Cu-NiTi archwire were used in the tooth displacement conditions (LD and GD), vibration did not significantly reduce SFF, KFF, or SSP amplitude.

Effect of self-ligating bracket type and vibration on frictional force and stick-slip phenomenon in diverse tooth displacement conditions: an in vitro mechanical analysis.

OBJECTIVE: To evaluate the effects of self-ligating bracket (SLB) type and vibration on frictional force and stick-slip phenomenon (SSP) in diverse tooth displacement conditions when a levelling/alignment wire was drawn. MATERIALS AND METHODS: A total of 16 groups were tested (n = 10/group): Two types of SLBs [active SLB (ASLB, In-Ovation R) and passive SLB (PSLB, Damon Q)]; vibration (30 Hz and 0.25 N) and non-vibration conditions; and 4 types of displacement [2mm lingual displacement of the maxillary right lateral incisor (LD), 2mm gingival displacement of the maxillary right canine (GD), combination of LD and GD (LGD), and control]. After applying artificial saliva to the typodont system, 0.018 copper nickel-titanium archwire was drawn by Instron with a speed of 0.5mm/min for 5 minutes at 36.5°C. After static/kinetic frictional forces (SFF/KFF), and frequency/amplitude of SSP were measured, statistical analysis was performed. RESULTS: ASLB exhibited higher SFF, KFF, and SSP amplitude (all P < 0.001) and lower SSF frequency (all P < 0.05) than PSLB in all displacement groups. Vibration decreased SFF, KFF, and SSP amplitude and increased SSP frequency in control and all displacement groups (all P < 0.001). ASLB exhibited lower SSP frequency than PSLB only under non-vibration condition (P < 0.05 in LD and GD, P < 0.01 in LGD). However, regardless of vibration conditions, ASLB demonstrated higher SSP amplitude than PSLB in all displacement groups (all P < 0.001 under non-vibration; all P < 0.01 under vibration). CONCLUSION: Even in tooth displacement conditions, vibration significantly reduced SFF, KFF, SSP amplitude, and increased SPP frequency in both PSLB and ASLB. However, in vivo studies would be needed to confirm the clinical significance.

Timing of force application affects the rate of tooth movement into surgical alveolar defects with grafts in beagles.

INTRODUCTION: The purpose of this study was to investigate the influence of the timing of orthodontic force application on the rates of orthodontic tooth movement into surgical alveolar defects with bone grafts in beagle dogs. METHODS: Twelve beagles were randomly divided into 2 groups according to the surgical procedure: alveolar osteotomy alone (control) or osteotomy with bone graft (experimental group). The maxillary second premolars were protracted for 6 weeks into the surgical sites: immediately, at 2 weeks, and at 12 weeks after surgery. The orthodontic tooth movement rates and alveolar remodeling concomitant with surgical defect healing were evaluated by model measurements and histomorphometry as well as microcomputed tomography and histology. One-way analysis of variance and the Scheffé post hoc comparison were performed for investigating the rates of orthodontic tooth movement and mineralized bone formation. RESULTS: Both the orthodontic tooth movement rate and the mean appositional length of mineralized bone in the tension side of teeth were significantly accelerated when force was applied at 2 weeks in the control group and immediately in the experimental group (P <0.001). The 2-week control group showed a dramatic increase in apposition rate during 4 to 6 weeks after force application, whereas the immediate protraction experimental group did within the first 3 weeks (P <0.001). Decreased orthodontic tooth movement rates and reduced bone remodeling activities were apparent in the 12-weeks groups, especially in nongrafted defects. CONCLUSIONS: A bone graft into the surgical defect can not only allow immediate force application for accelerating orthodontic tooth movement with favorable periodontal regeneration, but also decrease the risk of inhibited orthodontic tooth movement in case of delayed force application after surgery.

Orthodontic treatment of an open bite after splint therapy for a patient with idiopathic condylar resorption.

In the treatment of orthodontic patients with idiopathic condylar resorption, symptoms of temporomandibular joint disorders and constantly changing occlusions caused by an instability of mandibular position make it difficult for orthodontists to confirm definitive orthodontic diagnosis and treatment plans. Therefore, these patients' temporomandibular joint (TMJ) structures need to be stabilized with splint therapy before active tooth movement to identify and maintain the true mandibular position. For some idiopathic condylar resorption patients, orthognathic surgery can cause further resorption on the vulnerable condyles of the mandible; thus, effective orthodontic camouflage treatment after joint stabilization should be considered. During the orthodontic camouflage treatment, adverse loads on the TMJ structures, which could change the position of condyles, should be avoided, and TMJ-friendly mechanics must be applied.

Effects of low-intensity laser therapy on periodontal tissue remodeling during relapse and retention of orthodontically moved teeth.

This study was designed to investigate the effects of low-intensity laser therapy (LILT) on periodontal ligament (PDL) remodeling during relapse and retention after the completion of orthodontic movement. The maxillary central incisors (n = 104) of the 52 rats were randomly divided into five groups according to the treatment modality: baseline control group without any intervention (n = 8); relapse group without retainer after tooth movement (n = 24); retention group with fixed retainer after tooth movement (n = 24); lased relapse group without retainer after tooth movement and LILT (n = 24); lased retention group with retainer after tooth movement and LILT (n = 24). LILT was daily performed using a gallium-aluminum-arsenide diode laser in a biostimulation mode: wavelength of 780 nm, continuous waves at 70 mW output power, a preset low intensity of 1.75 W/cm(2) in contact mode, resulting in energy dose of 5 J/cm(2) per irradiation for 3 s. The animals were euthanized on days 1, 3, and 7 after removal of the orthodontic appliance. Real-time RT-PCR was performed for quantitative analysis of matrix metalloproteinases mRNA expression. Immunoreactivities of collagen and tissue inhibitor of metalloproteinase were observed on the compression and tension sides. LILT significantly facilitated the expression of five tested MMP mRNAs in both relapse and retention groups. TIMP-1 immunoreactivity was inhibited by LILT in both groups, whereas Col-I immunoreactivity was increased by LILT only in the retention group. These results indicate that LILT would act differently on the stability after orthodontic treatment according to additional retainer wearing or not. LILT when combined with a retainer on the moved teeth may shorten the retention period by accelerating periodontal remodeling in the new tooth position, whereas, LILT on the moved teeth left without any retainer would rather increase the rate of relapse after treatment.

Effect of piezopuncture on tooth movement and bone remodeling in dogs.

INTRODUCTION: The aim of the study was to elucidate whether a newly developed, minimally invasive procedure, piezopuncture, would be a logical modification for accelerating tooth movement in the maxilla and the mandible. METHODS: Ten beagle dogs were divided into 2 groups. Traditional orthodontic tooth movement was performed in the control group. In the experimental group, a piezotome was used to make cortical punctures penetrating the gingiva around the moving tooth. Measurements were made in weeks 1 through 6. Tooth movement and bone apposition rates from the histomorphometric analyses were evaluated by independent t tests. RESULTS: The cumulative tooth movement distance was greater in the piezopuncture group than in the control group: 3.26-fold in the maxilla and 2.45-fold in the mandible. Piezopuncture significantly accelerated the tooth movements at all observation times, and the acceleration was greatest during the first 2 weeks for the maxilla and the second week for the mandible. Anabolic activity was also increased by piezopuncture: 2.55-fold in the maxilla and 2.35-fold in the mandible. CONCLUSIONS: Based on the different effects of piezopuncture on the maxilla and the mandible, the results of a clinical trial of piezopuncture with optimized protocols might give orthodontists a therapeutic benefit for reducing treatment duration.

Accelerated decompensation of mandibular incisors in surgical skeletal class III patients by using augmented corticotomy: a preliminary study.

INTRODUCTION: Our objectives were to evaluate the amount of decompensation of the mandibular incisors and the change of periodontal support around them after corticotomy with bone augmentation before orthognathic surgery. METHODS: Before orthognathic surgery for 15 skeletal Class III patients, orthodontic treatment was combined with corticotomy and bone augmentation labially to the anterior mandibular roots. Lateral cephalograms were taken before orthodontic treatment and before surgery (completion of preoperative orthodontic treatment). The amounts of mandibular incisor proclination, alveolar bone thickness, and periodontal support (gingival margin levels and augmentation pattern) were evaluated. RESULTS: Significant proclination of the mandibular incisors was shown after decompensation (P <0.001; incisor mandibular plane angle, 10.45°; incisor symphyseal plane angle, 10.74°). The incisor edge moved labially by 3.47 mm. The alveolar bone thickness increased by 1.56 mm at the root apex and 1.98 mm at the level of B-point (P <0.001). There was no gingival recession irrespective of the degree of proclination of the mandibular incisiors. Two types of bone augmentation pattern were evident. One was characterized by alveolar bone proclination proportional to the labial tipping of the mandibular incisors. Buccal alveolar bone at the cervical area was well maintained (60%, 9 subjects). The other showed greater increases in alveolar thickness at B-point than at the cervical area (40%, 6 subjects). CONCLUSIONS: The augmented corticotomy provided effective decompensation of the mandibular incisors in skeletal Class III patients while maintaining labial bone thickness and with no periodontal side effects. This technique reduces or eliminates the risk of moving the roots through the labial plate during decompensation with the associated risk of gingival recession.

Effect of extraction treatment on upper airway dimensions in patients with bimaxillary skeletal protrusion relative to their vertical skeletal pattern.

OBJECTIVE: To investigate dimensional changes in regional pharyngeal airway spaces after premolar extraction in bimaxillary skeletal protrusion (BSP) patients according to vertical skeletal pattern, and to further identify dentoskeletal risk factors to predict posttreatment pharyngeal changes. METHODS: Fifty-five adults showing BSP treated with microimplant anchorage after four premolar extractions were included in this retrospective study. The subjects were divided into two groups according to the mandibular plane steepness: hyperdivergent (Frankfort horizontal plane to mandibular plane [FH-MP] ≥ 30) and nonhyperdivergent groups (FH-MP < 30). The control group consisted of 20 untreated adults with skeletal Class I normodivergent pattern and favorable profile. Treatment changes in cephalometric variables were evaluated and compared. The association between posttreatment changes in the dentoskeletal and upper airway variables were analyzed using linear regression analysis. RESULTS: The BSP patients showed no significant decrease in the pharyngeal dimensions to the lower level in comparison with controls, except for middle airway space (MAS, p < 0.01). The upper airway variable representing greater decrease in the hyperdivergent group than in the nonhyperdivergent group was the MAS (p < 0.01). Posttreatment changes in FH-MP had negative correlation with changes in MAS (ß = -0.42, p < 0.01) and inferior airway space (ß = -0.52, p < 0.01) as a result of multivariable regression analysis adjusted for sagittal skeletal relationship. CONCLUSIONS: Decreased pharyngeal dimensions after treatment in BSP patients showed no significant difference from the normal range of pharyngeal dimensions. However, the glossopharyngeal airway space may be susceptible to treatment when vertical dimension increased in hyperdivergent BSP patients.

Protein kinase C ßII and δ/θ play critical roles in bone morphogenic protein-4-stimulated osteoblastic differentiation of MC3T3-E1 cells.

Bone morphogenic protein-4 (BMP-4), one of TGF-ß superfamily, is involved in bone and cartilage development, specifically tooth and bone fracture repair. In the present study, the role of protein kinase C (PKC) was investigated in BMP-4-induced differentiation of osteoblast-like MC3T3-E1 cells. PKC inhibitor UCN-01 significantly attenuated the synthesis of osteocalcin, a marker of mature osteoblast phenotype, in a dose-dependent manner as well as blocked osteroblastic differentiation and mineralization in BMP-4-treated MC3T3-E1 cells. Also, UCN-01 suppressed vascular endothelial growth factor (VEGF) production in BMP-4-treated MC3T3-E1 cells. In addition, UCN-01 remarkably suppressed BMP-4-activated PKC ßII and PKC δ/θ of PKC family proteins by Western blotting. Consistently, 2-dimensional electrophoresis (2-DE) immunoblotting revealed that UCN-01 inhibited the BMP-4-induced activation of PKC subfamilies in MC3T3-E1 cells. Taken together, our findings suggest that PKC ßII and PKC δ/θ mediate BMP-4-induced osteoblastic differentiation.

Use of rhythmic wire system with miniscrews to correct occlusal-plane canting.

Occlusal-plane canting is a challenging problem for orthodontists because it cannot be solved easily without surgical intervention. Normally, a LeFort I osteotomy and concomitant mandibular surgery is used to correct the problem, even in patients with mild facial asymmetry but with noticeable occlusal-plane canting. Skeletal anchorage can be used in patients with occlusal canting to reduce the need for orthognathic surgery. The purpose of this article was to introduce a biomechanical system-rhythmic wire- to correct occlusal-plane canting. The records of 2 patients treated with this system are shown.

Laser-aided circumferential supracrestal fiberotomy and low-level laser therapy effects on relapse of rotated teeth in beagles.

OBJECTIVE: To investigate the effectiveness and periodontal side effects of laser circumferential supracrestal fiberotomy (CSF) and low-level laser therapy (LLLT) on orthodontically rotated teeth in beagles. MATERIALS AND METHODS: Eighteen mandibular incisors from nine dogs were divided into three groups by treatment (n = 6/group): A, orthodontic couple force application only (control); B, laser CSF following orthodontic couple force application; and C, LLLT following orthodontic couple force application. Both mandibular lateral incisors were rotated for 4 weeks, and the relapse tendency was observed for 4 weeks more without any retainers. The amount of relapse, sulcus depth, and gingival recession were measured at weeks 4 and 8. One-way analysis of variance (ANOVA) and Scheffé's post hoc test were used for data analysis. Tissue specimens were examined at week 8 under light microscopy after hematoxylin-eosin (H&E) and Masson's trichrome staining. RESULTS: The mean percentage of relapse was 41.29% in group A, 14.52% in group B, and 56.80% in group C (P < .001). Four weeks after laser CSF, the sulcus depth increased by 0.67 mm, but no gingival recession was observed. There was no significant difference between groups A and C in terms of sulcus depth and gingival recession. CONCLUSIONS: Laser CSF is an effective procedure to decrease relapse after tooth rotation, causing no apparent damage to the supporting periodontal structures, whereas LLLT on orthodontically rotated teeth without retainers appears to increase the relapse tendency.

Regulation of matrix metalloproteinase-9 expression between gingival fibroblast cells from old and young rats.

Gingival fibroblast cells (rGF) from aged rats have an age-related decline in proliferative capacity compared with young rats. We investigated G1 phase cell cycle regulation and MMP-9 expression in both young and aged rGF. G1 cell cycle protein levels and activity were significantly reduced in response to interleukin-1beta (IL-1beta) stimulation with increasing in vitro age. Tumor necrosis factor-alpha (TNF-alpha)-induced matrix metalloproteinase-9 (MMP-9) expression was also decreased in aged rGF in comparison with young rGF. Mutational analysis and gel shift assays demonstrated that the lower MMP-9 expression in aged rGF is associated with lower activities of transcription factors NF-kappaB and AP-1. These results suggest that cell cycle dysregulation and down-regulation of MMP-9 expression in rGF may play a role in gingival remodeling during in vitro aging.

Effects of low-level laser therapy after Corticision on tooth movement and paradental remodeling.

BACKGROUND AND OBJECTIVE: Both Corticision and low-level laser therapy (LLLT) are known to affect the rate of tooth movement. Our objective was to investigate the combined effects of Corticision and LLLT on the tooth movement rate and paradental remodeling in beagles. STUDY DESIGN/MATERIALS AND METHODS: The maxillary second premolars (n = 24) of 12 beagles were randomly divided into four groups (n = 6 per group) based on the treatment modality: group A, only orthodontic force (control); group B, orthodontic force plus Corticision; group C, orthodontic force plus LLLT; group D, orthodontic force plus Corticision and LLLT. RESULTS: Ratios of second premolar-to-canine movement were greater by 2.23-fold in group B and 2.08-fold in group C, but 0.52-fold lesser in group D than in group A. The peak velocity was observed at an earlier stage of tooth movement in group B but at a later stage in group C during the 8-week treatment period. At week 8, both tartrate-resistant acid phosphatase (TRAP)-positive osteoclasts on the compression side and proliferating cell nuclear antigen (PCNA)-positive osteoblasts on the tension side increased significantly (P<.05) in group C but decreased in group D. Histomorphometric analysis revealed that the mean apposition length of newly formed mineralized bone during the 8 weeks of treatment significantly increased in both group B (2.8-fold) and group C (2.2-fold). In group D, the labeling lines on lamina dura were thin and discontinuous, but intratrabecular remodeling and lamellation were found to be active. CONCLUSION: Periodic LLLT after Corticision around a moving tooth decreased the tooth movement rate and alveolar remodeling activity.

Effects of Corticision on paradental remodeling in orthodontic tooth movement.

OBJECTIVE: To investigate the biologic effects of Corticision on alveolar remodeling in orthodontic tooth movement. MATERIALS AND METHODS: In this study, 16 cats were divided into 3 groups: group A, only orthodontic force (control); group B, orthodontic force plus Corticision; and group C, orthodontic force plus Corticision and periodic mobilization. Histologic and histomorphometric studies were performed on tissue specimens on days 7, 14, 21, and 28. RESULTS: Extensive direct resorption of bundle bone with less hyalinization and more rapid removal of hyalinized tissue were observed in group B. The accumulated mean apposition area of new bone on day 28 was observed to be 3.5-fold higher in group B than in the control group A. CONCLUSIONS: Corticision might be an efficient procedure for accelerating orthodontic tooth movement accompanied with alveolar bone remodeling.

Stability of mini-screws invading the dental roots and their impact on the paradental tissues in beagles.

OBJECTIVE: To examine the stability of mini-screws that invade a dental root by measuring the retention period/failure rate, and to illustrate their effects on paradental tissues. MATERIALS AND METHODS: Three adult male beagle dogs received 48 orthodontic mini-screws. Half of the mini-screws were implanted to invade the roots, and the rest were placed in the middle of the alveolar bone. Half of the mini-screws were loaded immediately. The retention period of the mini-screws was documented. The dogs were euthanized after 8 weeks, and tissue samples were examined histologically. RESULTS: The failure rate of the mini-screws that invaded the roots was 79.2%, and that of the mini-screws in the middle of the alveolar bone was 8.3%. The application of force had little effect on the failed mini-screws. Moderately injured roots were repaired with osteoid and/or cementoid tissues with normal periodontal ligaments, followed by recovery of the original configuration. CONCLUSION: Orthodontic mini-screws had a higher failure rate when placed to invade the dental roots. However, minimally damaged dental roots do not adversely affect the healing process.