Xianglong Han

Biologic response of rapid tooth movement with periodontal ligament distraction

INTRODUCTION Length of treatment is a complaint of many orthodontic patients. The purpose of this study was to evaluate the security and feasibility of rapid tooth movement with periodontal ligament distraction. METHODS Eight male beagles, aged 13 to 16 months, were used in this study. Extraction of the mandibular second premolar and alveolar surgery to reduce the osteal resistance on the mesial side of the extraction socket were performed on the experimental side. Then a device was placed to distract the first premolars distally on the experimental side; on the control side, the first premolars were distalized with nickel-titanium coil springs. The beagles were killed in the first, second, fourth, and eighth weeks after orthodontic force application. RESULTS The first premolar on the experimental side moved more rapidly than that on the control side (P <0.05). Histologic data indicated that more new bone was deposited on tension area of the experimental side than on the control side. Active and extensive bone resorption in the compressive area and bone deposition in the tension area were observed on the experimental side. CONCLUSIONS These results suggest that the periodontal ligament can be rapidly distracted without complications. The rapid orthodontic tooth movement by distracting the periodontal ligament cannot be emulated by current conventional orthodontic concepts and methods.

Nonsurgical correction of a Class III malocclusion in an adult by miniscrew-assisted mandibular dentition distalization.

This article reports the successful use of miniscrews in the mandible to treat a 20-year-old Mongolian woman with a chief complaint of anterior crossbite. The patient had a skeletal Class III malocclusion with a mildly protrusive mandible, an anterior crossbite, and a deviated midline. In light of the advantages for reconstruction of the occlusal plane and distal en-masse movement of the mandibular arch, we used a multiloop edgewise archwire in the initial stage. However, the maxillary incisors were in excessive labioversion accompanied by little retraction of the mandibular incisors; these results were obviously not satisfying after 4 months of multiloop edgewise archwire treatment. Two miniscrews were subsequently implanted vertically in the external oblique ridge areas of the bilateral mandibular ramus as skeletal anchorage for en-masse distalization of the mandibular dentition. During treatment, the mandibular anterior teeth were retracted about 4.0 mm without negative lingual inclinations. The movement of the mandibular first molar was almost bodily translation. The maxillary incisors maintained good inclinations by rotating their brackets 180° along with the outstanding performance of the beta-titanium wire. The patient received a harmonious facial balance, an attractive smile, and ideal occlusal relationships. The outcome was stable after 1 year of retention. Our results suggest that the application of miniscrews in the posterior area of the mandible is an effective approach for Class III camouflage treatment. This technique requires minimal compliance and is particularly useful for correcting Class III patients with mild mandibular protrusion and minor crowding.

Orthodontic mechanical tension effects on the myofibroblast expression of alpha-smooth muscle actin.

OBJECTIVE To detect myofibroblast formation on the tension side during orthodontic tooth movement in vivo and myofibroblast expression of alpha-smooth muscle actin (alpha-SMA) induced by tension both in vivo and in vitro. MATERIALS AND METHODS Fifty 6-week male rats were used in this in vivo study, and the right maxillary first molar was moved mesially, which served as the experimental group, and the left maxillary first molar served as the control. Rats were sacrificed at days 0, 3, 5, 7, and 14 after force loading. Myofibroblasts, identified with alpha-SMA, were examined through immunohistochemistry. For the in vitro study, human periodontal ligament (PDL) fibroblasts were obtained. Cyclic mechanical tension was applied to the fibroblasts for 0, 1, 3, 6, and 12 hours. Transmission electron microscopy was used to detect the ultrastructure of myofibroblasts. alpha-SMA mRNA gene expression was quantified by real-time quantitative PCR. The expression of alpha-SMA was detected by immunofluorescence and quantified by Western blotting. RESULTS In vivo, the myofibroblasts expressing alpha-SMA were identified both in the experimental group and in the control group. The expressions of alpha-SMA were increased in the tension areas of the experimental group over time, and reached the maximum in day 14. In vitro, fibronexus junctions and actin microfilaments in the cells could be found with transmission electron microscopy. Cyclic mechanical tension could significantly induce alpha-SMA expression at 12 hours (P < .01) than the controls. CONCLUSIONS Myofibroblasts existed in the PDL. The expressions of alpha-SMA in the myofibroblasts were significantly up regulated under tension both in vivo and in vitro.

Expression of osteocalcin during surgically assisted rapid orthodontic tooth movement in beagle dogs.

PURPOSE To investigate the expression of osteocalcin during rapid orthodontic tooth movement aided by alveolar surgery in beagle dogs. MATERIALS AND METHODS Eight male beagles were used, and bilateral mandibular second premolars were extracted for distalization of the first premolars against the third premolars by orthodontic NiTi coil spring with a force of 100 gm. Right and left mandibular sides were randomly assigned to experimental and sham sides, and alveolar surgery was performed only on the experimental side to reduce the osteal resistance on the mesial side of the extraction socket. Distance of tooth movement was measured once a week during the first 4 weeks. Two beagles were sacrificed after 1, 2, 4, and 8 weeks of orthodontic force application, and expression of osteocalcin was demonstrated by immunohistochemistry and quantified with computer-aided image analysis. RESULTS The average total movement of the first premolars in 4 weeks on the experimental side (1.868 +/- 0.022 mm) was approximately double that on the sham side (1.008 +/- 0.057 mm). As regards the average total anchorage loss, no significant difference (P > .05) was revealed. Dynamic osteocalcin concentrations presented at 4 time periods (P < .05). The staining intensity of osteocalcin on the experimental sides was higher than the corresponding sham sides, and that on the compression sites higher than the corresponding tension sites (P < .05). CONCLUSIONS The results suggested that alveolar surgery might serve as an effective and safe way to accelerate orthodontic tooth movement, and promote the rate of bone remodeling as revealed by the expression of osteocalcin.

Tooth movement after orthodontic treatment with 4 second premolar extractions

INTRODUCTION This retrospective study was designed to investigate the position changes and movement patterns of incisors and molars after orthodontic treatment with extractions of 4 second premolars in patients with mild crowding, slight dental protrusion, and Angle Class I relationship. METHODS Pretreatment and posttreatment cephalograms of 26 subjects were chosen from patients treated by an experienced orthodontist. The movements of the incisors and the molars as well as tooth tipping were measured. RESULTS Relative to the posttreatment occlusal plane, the mean incisor movements were 3.3 and 2.9 mm lingually in the maxilla and the mandible, respectively. The first molars were moved mesially an average of 3.2 and 3.4 mm in the maxilla and the mandible, respectively. The incisor inclination was under proper control. The extraction space was almost equally taken up by the anterior and posterior segments. CONCLUSIONS These data can be used to estimate the expected position changes and movement patterns of the incisors and molars in patients with mild crowding and slight bialveolar dental protrusion after orthodontic treatment with 4 second premolar extractions.

Dental, skeletal asymmetries and functional characteristics in Class II subdivision malocclusions

Treatment outcomes of Angle Class II subdivision malocclusions may be compromised because of the uncertainty of the aetiology. Previous studies have reported controversial ideas about the origins, but the existence of a primary contributor still remains unknown. Functional factors have been mentioned as a probable cause, but until now, there have been no supporting data. This study was a cross-sectional investigation of the characteristics of Angle Class II subdivision malocclusion, including dental, skeletal and functional factors, by comparison of the subdivision group and the normal occlusion group. The evaluations of dental and skeletal asymmetries of both groups were carried out by cone-beam computed tomography (CBCT) and analysis of dental casts. The functional deviations were evaluated by cast mounting and measuring. In the subdivision group, the asymmetric position of the glenoid fossa was found to be the most significant skeletal asymmetry. No dentoalveolar asymmetry was found in this group. The most important finding was that, in subdivision malocclusions, functional deviation resulting in pseudoasymmetry occurred in 32.86% of the study participants. This deviation is probably related to the disharmonious arch width between maxillary and mandibular dental arches in the premolar section. The origin of Angle Class II subdivision malocclusion is multifactorial, with dental, skeletal and functional factors included. Functional deviation occurs, probably due to dental arch width disharmony. Asymmetric position of the glenoid fossa may account for most of the skeletal asymmetry.

Comparison of arch width, alveolar width and buccolingual inclination of teeth between Class II division 1 malocclusion and Class I occlusion

OBJECTIVE To compare the arch width, alveolar width, and buccolingual inclination of maxillary and mandibular posterior teeth between Class II division 1 malocclusion and Class I occlusion. MATERIALS AND METHODS Forty-five subjects with Class I occlusion and 45 subjects with Class II division 1 malocclusion were selected to measure the maxillary and mandibular arch width and alveolar width of premolars and first molars with digital caliper. Buccolingual inclination of maxillary and mandibular premolars and first molars were measured with a modified universal bevel protractor. RESULTS All of the posterior teeth in both groups were lingually tilted. The maxillary premolars and first molars were significantly more lingually tilted (P < .05) in Class II division 1 malocclusion than in Class I occlusion. Mandibular first premolars were significantly less lingually tilted in Class II division 1 malocclusion than in Class I occlusion. No significant difference of buccolingual inclination was found in mandibular second premolars and first molars between the two groups. No significant difference in maxillary and mandibular arch width and alveolar width was found between the two groups. CONCLUSIONS Buccolingual inclination rather than arch width and alveolar width plays an important role in transverse discrepancy of Class II division 1 malocclusion.

Response of immortalized murine cementoblast cells to hypoxia in vitro

OBJECTIVES The aim of the study was to investigate the impact of hypoxia on proliferation, apoptosis and mineralization of cementoblast-like cells (OCCM-30) in vitro. METHODS The effects of different periods of hypoxia (2% O2) on proliferation, apoptosis, cementoblastic potential and root cementum resorption capability of OCCM-30 were evaluated, by using MTT, flow cytometry, alkaline phosphatase (ALP) activity assay, reverse transcription-polymerase chain reaction measurement, enzyme-linked immunosorbent assay and mineralization nodule formation assay. RESULTS OCCM-30 viability was significantly inhibited by hypoxia while the apoptosis ratio was enhanced in a time-dependent manner; hypoxia inducible factor-1α and vascular endothelial growth factor mRNA were induced by hypoxia in different manners; temporary hypoxia (<24 h) stimulated cementoblastic function of OCCM-30, while long-term hypoxia inhibited it, manifested by decreased mRNA level or release of ALP, osteocalcin, bone sialoprotein, osteopontin and osteoprotegerin. In addition, hypoxia affected mineralized nodule formation of OCCM-30 in a time-dependent fashion; moreover, root cementum resorption function was also induced by hypoxia, manifested by increased receptor activator of nuclear factor kappa B ligand mRNA and protein expression. CONCLUSION Temporary exposure of OCCM-30 to hypoxia inhibited proliferation, promoted apoptosis and mineralization, while longer duration of hypoxia could inhibit the cementoblast function. The findings may provide theoretical basis for developing novel therapeutics to prevent root resorption during orthodontic treatment.

Sclerostin Promotes Bone Remodeling in the Process of Tooth Movement

Tooth movement is a biological process of bone remodeling induced by mechanical force. Sclerostin secreted by osteocytes is mechanosensory and important in bone remodeling. However, little is known regarding the role of sclerostin in tooth movement. In this study, models of experimental tooth movement were established in rats and mice. Sclerostin expression was investigated with immunohistochemistry staining, and osteoclastic activity was analyzed with tartrate-resistant acid phosphatase (TRAP) staining. MLO-Y4 osteocyte-like cells underwent uniaxial compression and tension stress or were cultured in hypoxia conditions. Expression of sclerostin was assessed by RT-qPCR and ELISA. MLO-Y4 cells were cultured with recombinant human sclerostin (rhSCL) interference and then co-cultured with RAW264.7 osteoclast precursor cells. Expressions of RANKL and OPG were analyzed by RT-qPCR, and osteoclastic activity was assessed by TRAP staining. During tooth movement, sclerostin was expressed differently in compression and tension sites. In SOST knock-out mice, there were significantly fewer TRAP-positive cells than in WT mice during tooth movement in compression sites. In-vitro studies showed that the expression of sclerostin in MLO-Y4 osteocyte-like cells was not different under a uniaxial compression and tension force, whereas hypoxia conditions significantly increased sclerostin expression in MLO-Y4 cells. rhSCL interference increased the expression of RANKL and the RANKL/OPG ratio in MLO-Y4 cells and the osteoclastic induction ability of MLO-Y4 cells in experimental osteocyte-osteoclast co-culture. These data suggest that sclerostin plays an important role in the bone remodeling of tooth movement.

Effects of self-ligating brackets on oral hygiene and discomfort: a systematic review and meta-analysis of randomized controlled clinical trials.

Background: Self‐ligating brackets (SLBs) are widely adopted in clinic owing to their claimed superiorities. Here, we collected and analysed all randomized controlled clinical trials (RCTs) comparing SLBs with conventional brackets (CBs) and thereby investigated whether SLBs can relieve discomfort or promote oral hygiene. Methods: Electronic databases including MEDLINE, Cochrane Central Register of Controlled Trials, EMBASE, World Health Organization International Clinical Trials Registry Platform, Chinese BioMedical Literature Database and the China National Knowledge Infrastructure were searched to find out RCTs comparing active or passive SLBs with CBs. Two reviewers extracted the data and assessed risks of bias independently. Any disagreement between them was resolved through discussion with a third reviewer. Meta‐analysis was conducted on Review Manager 5.3. Results: A total of 12 RCTs with 575 participants were included, and eight of the trials were synthesized quantitatively. Two trials were assessed as low risk of bias, whereas others as unclear risk of bias. Passive SLBs and CBs are not significantly different in plaque control. SLBs and CBs are not significantly different in discomfort reduction at any of four time points (4 h, 24 h, 3 days and 7 days). Conclusions: Clinical evidences from existing RCTs suggest that SLBs do not outperform CBs in reliving discomfort or promoting oral health in clinic.