Influence of masticating cycles and chewing patterns on inadvertent enamel wear caused by zirconia brackets.

Little information is available about enamel wear caused by zirconia brackets, an inadvertent side effect of orthodontic treatment. The purpose of this study was to examine potential enamel damage induced by contact with zirconia brackets. Sliding and impact wear simulations were performed using bovine enamel specimens positioned at a 25° slant to a zirconium ball to determine wear behaviour. Different chewing patterns, tapping and grinding, were simulated. Specimens were profiled using confocal laser scanning microscopy, and the mean maximum depth and surface roughness were measured. Scanning electron microscopy was also performed. The mean maximum depth of wear values differed according to the number of mastication cycles, with a higher number of cycles producing higher depths of wear. The facet wear depth was significantly greater with the tapping pattern than with the grinding pattern. Scanning electron microscopic observation of the wear facets revealed that surface textures at the edges were rougher than those at the centre of all facets. The results of this study indicated that enamel wear was induced by contact with zirconia brackets during the early period of mastication, and that the patterns and number of cycles of mastication affected the wear progression of enamel.

Age dependence of the maturation of the midpalatal suture in the stability of orthodontic anchoring screws.

INTRODUCTION: Orthodontic anchoring screws (OASs) have been placed around midpalatal sutures in patients of various ages. Our previous study found that OAS placement more than 1.5 mm from midpalatal suture was more successful than placement directly at the suture. This study aimed to investigate the relationship between age and midpalatal suture maturation, considering factors affecting the failure of OASs using cone-beam computed tomography. METHODS: In total, 150 patients who underwent cone-beam computed tomography were selected. The total depth and sutured depth of the midpalatal suture corresponding area to anterior (interpremolar zone) and posterior region (mesial and distal borders of the first molar) were measured, and the ratio of sutured depth to total depth (sutured ratio) was calculated. RESULTS: The mean sutured ratios at interpremolar zone and mesial and distal borders of the first molar according to age were 40%, 60%, and 63% in the younger group (≤17 years), 46%, 76%, and 76% in the middle group (18-25 years), and 47%, 74%, and 76% in the older group (≥26 years), respectively. The sutured ratio of the anterior region was significantly lower than that of the posterior region (P <0.01). Each mean sutured ratio of the middle and older group was significantly higher than that of the younger group on both sides (P <0.01). According to the cervical vertebral maturation, the mean sutured ratio of cervical vertebral stages 5-6 was significantly higher than cervical vertebral stages 1-3 on the distal side (P <0.05). CONCLUSIONS: Incomplete closure of the midpalatal suture was observed frequently, even in the older group. This might be caused by insufficient calcification of the midpalatal suture, including in elder patients. To prevent OAS placement to the unsutured area, the midpalatal suture should be avoided regardless of age.

Acid-electrolyzed functional water-induces Interleukin-1α release from Intracellular Storage Sites in Oral Squamous Cell Carcinoma.

The aim of this study was to examine the acid-electrolyzed functional water (FW)-mediated cytokine release in an oral squamous cell carcinoma-derived cell line (OSCC) following treatment with FW. FW is generated by the electrolysis of a sodium chloride solution and accelerate the burn wound healing. To elucidate the underlying mechanisms, the cytokine/chemokine secretion profile of HSC3 cells was examined using a cytokine array. FW treatment significantly induced interleukin (IL)-1α secretion, which was confirmed by enzyme-linked immunosorbent assay. Subsequently, the HSC3 cells were pre-treated with cycloheximide (CHX) for 1 h prior to FW stimulation to determine whether the augmented IL-1α secretion was due to enhanced protein synthesis. CHX pre-treatment did not affect IL-1α secretion suggesting that the secreted IL-1α might have been derived from intracellular storage sites. The amount of IL-1α in the cell lysate of the FW-treated HSC3 cells was significantly lower than that of the non-treated cells. Immunofluorescence staining using a polyclonal antibody against full-length IL-1α revealed a drastic reduction in IL-1α inside the FW- treated cells. IL-1α is synthesized in its precursor form (pIL-1α) and cleaved to produce pro-piece and mature IL-1α (ppIL-1α and mIL-1α) inside the cells. In the present study, only pIL-1α was detected within the HSC3 cells in its resting state. However, FW stimulation resulted in the release of the 33 kDa and two other smaller forms (about 19 kDa) of the protein. These results indicates that FW treatment induces IL-1α secretion, a typical alarmin, from the intracellular storage in OSCC cells.

Effect of low-intensity pulsed ultrasound on orofacial sensory disturbance following inferior alveolar nerve injury: Role of neurotrophin-3 signaling.

Percutaneous treatment of low-intensity pulsed ultrasound (LIPUS) to the site of inferior alveolar nerve (IAN) transection promotes functional regeneration, but the detailed mechanism is unknown. We examined the involvement of neurotrophin-3 (NT-3), which primarily binds with tropomyosin receptor kinase C (TrkC), in functional transected IAN regeneration following LIPUS treatment in rats. Daily LIPUS treatment to the transected IAN was performed, and the mechanical sensitivity of the facial skin was measured for 14 d. On day 5 after IAN transection, the expression of NT-3 in the transected IAN and TrkC-positive trigeminal ganglion neurons were immunohistochemically examined. Further, the effect of TrkC neutralization on the acceleration of facial mechanosensory disturbance restoration due to LIPUS treatment was analyzed. LIPUS treatment to the site of IAN transection significantly facilitated functional recovery from sensory disturbance on facial skin. Schwann cells in the transected IAN expressed NT-3, and LIPUS treatment increased the amount of NT-3. The facilitated recovery from the mechanosensory disturbance by continuous LIPUS treatment was inhibited by the ongoing TrkC neutralization at the IAN transection site. These results suggest that LIPUS treatment accelerates the recovery of orofacial mechanosensory function following IAN transection through the enhancement of NT-3 signaling in the transected IAN.

Continuous Compressive Force Induces Differentiation of Osteoclasts with High Levels of Inorganic Dissolution.

BACKGROUND Osteoclast precursor cells are constitutively differentiated into mature osteoclasts on bone tissues. We previously reported that the continuous stimulation of RAW264.7 precursor cells with compressive force induces the formation of multinucleated giant cells via receptor activator of nuclear factor kappaB (RANK)-RANK ligand (RANKL) signaling. Here, we examined the bone resorptive function of multinucleated osteoclasts induced by continuous compressive force. MATERIAL AND METHODS Cells were continuously stimulated with 0.3, 0.6, and 1.1 g/cm² compressive force created by increasing the amount of the culture solution in the presence of RANKL. Actin ring organization was evaluated by fluorescence microscopy. mRNA expression of genes encoding osteoclastic bone resorption-related enzymes was examined by quantitative real-time reverse transcription-polymerase chain reaction. Mineral resorption was evaluated using calcium phosphate-coated plates. RESULTS Multinucleated osteoclast-like cells with actin rings were observed for all three magnitudes of compressive force, and the area of actin rings increased as a function of the applied force. Carbonic anhydrase II expression as well as calcium elution from the calcium phosphate plate was markedly higher after stimulation with 0.6 and 1.1 g/cm² force than 0.3 g/cm². Matrix metalloproteinase-9 expression decreased and cathepsin K expression increased slightly by the continuous application of compressive force. CONCLUSIONS Our study demonstrated that multinucleated osteoclast-like cells induced by the stimulation of RAW264.7 cells with continuous compressive force exhibit high dissolution of the inorganic phase of bone by upregulating carbonic anhydrase II expression and actin ring formation. These findings improve our understanding of the role of mechanical load in bone remodeling.

Functional comparison of high and low molecular weight basic fibroblast growth factors.

Acid-electrolyzed functional water (FW) is obtained through the electrolysis of sodium chloride solution. Stimulation of the human fibroblastic cell line HeLa by FW led to the augmented secretion of basic fibroblast growth factor (bFGF). Immunoprecipitation followed by Western blot analysis revealed that both high and low molecular weight isoforms of bFGF were secreted in response to FW treatment. To explore intracellular bFGF localization, a cell fractionation assay was performed. Despite the presence of nuclear localization signals within the N-terminal portion of these proteins, the high molecular weight isoforms (34, 24, 22.5, and 21 kDa) were localized in the cytoplasm. FW stimulation drastically reduced the amount of intracytoplasmically localized isoforms, and the 34-kDa isoform was found to localize in a DNase-sensitive fraction, suggesting a weak nuclear attachment. By contrast, the 24-kDa isoform remained in the nucleus even after FW stimulation. Functional differences between the 34- and 18-kDa isoforms were examined further. Chinese hamster ovary cells were transfected with expression plasmids for each isoform. By treating each transfectant with FW, both isoforms were secreted successfully into the culture supernatants. Stimulation of HeLa cells with these supernatants resulted in the augmented secretion of vascular endothelial growth factor (VEGF). To further confirm the functionality of these isoforms, an in vitro transcription/translation reaction was performed; both of the isoforms induced VEGF secretion from HeLa cells. Taken together, these results indicate that the high molecular weight 34-kDa isoform and low molecular weight 18-kDa mature bFGF isoform have identical roles in VEGF induction.

EMMPRIN Inhibits bFGF-Induced IL-6 Secretion in an Osteoblastic Cell Line, MC3T3-E1.

Background: Electrolytically-generated acid functional water (FW) is obtained by electrolyzing low concentrations of saline. Although it has been widely used in clinical practice with various purposes, the underlying mechanisms of action involved have not been fully elucidated so far. We used the human cervical cancer-derived fibroblastic cell line (HeLa), to examine the cytokine secretion profile following FW treatment in the present study. Results: FW stimulation significantly induced the secretion of basic fibroblast growth factor (bFGF) and extracellular matrix metalloproteinase inducer (EMMPRIN). The effect of both factors on osteoblast-like MC3T3-E1 cells was further examined by stimulating the cells with the conditioned medium of FW-stimulated HeLa cells. However, the conditioned medium failed to induce IL-6 secretion. The MC3T3-E1 cells were further stimulated with recombinant bFGF or EMMPRIN or a combination of both factors. Intriguingly, bFGF-stimulated IL-6 induction was totally inhibited by EMMPRIN. Pretreatment with the specific inhibitor of nuclear factor-kappa B (NF-κB) drastically inhibited IL-6 secretion indicating that bFGF-induced IL-6 expression was dependent on NF-κB activation. The phosphorylation status of NF-κB p65 subunit was further examined. The results indicated that EMMPRIN inhibited bFGF-induced NF-κB p65 phosphorylation. Conclusions: These findings suggest that bFGF can induce IL-6 secretion in MC3T3-E1 cells through NF-κB activation. As EMMPRIN inhibited bFGF-induced IL-6 secretion by reducing the p65 subunit phosphorylation, it might be concluded that bFGF and EMMPRIN crosstalk in their respective signaling pathways.

Low-intensity pulsed ultrasound accelerates nerve regeneration following inferior alveolar nerve transection in rats.

Inferior alveolar nerve (IAN) injury, which is frequently caused by orofacial surgery or trauma, induces sensory loss in orofacial regions innervated by the IAN. However, no effective treatment for orofacial sensory loss currently exists. We determined whether sensory loss in facial skin above the mental foramen following IAN transection was recovered by exposure of the transected IAN to low-intensity pulsed ultrasound (LIPUS). Inferior alveolar nerve transection (IANX) was performed in 7-wk-old male Sprague-Dawley rats. On day 7 after IANX, the effect of daily LIPUS (from day 0) on the transected IAN, in terms of sensitivity to mechanical stimulation of the facial skin above the mental foramen, was examined. Moreover, the number of trigeminal ganglion (TG) neurons innervating the facial skin above the mental foramen of rats with IANX treated daily with LIPUS was counted using the retrograde neurotracing technique. Daily exposure of the transected IAN to LIPUS significantly promoted recovery of the head-withdrawal threshold in response to mechanical stimulation of the facial skin above the mental foramen, and the number of TG neurons innervating the facial skin above mental foramen was significantly increased in rats with IANX treated daily with LIPUS compared with sham or LIPUS-unexposed rats. Daily treatment of stumps of the transected IAN with LIPUS facilitated morphological and functional regeneration, suggesting that LIPUS is an effective and novel therapy for IAN injury.

Are assessments of damping capacity and placement torque useful in estimating root proximity of orthodontic anchor screws?

INTRODUCTION: Placement torque and damping capacity may increase when the orthodontic anchor screws make contact with an adjacent root. If this is the case, root contact can be inferred from the placement torque and damping capacity. The purpose of this study was to verify the detectability of root proximity of the screws by placement torque and damping capacity. For this purpose, we investigated the relationship among placement torque, damping capacity, and screw-root proximity. METHODS: The placement torque, damping capacity, and root proximity of 202 screws (diameter, 1.6 mm; length, 8.0 mm) were evaluated in 110 patients (31 male, 79 female; mean age, 21.3 ± 6.9 years). Placement torque was measured using a digital torque tester, damping capacity was measured with a Periotest device (Medizintechnik Gulden, Modautal, Germany), and root contact was judged using cone-beam computed tomography images. RESULTS: The rate of root contact was 18.3%. Placement torque and damping capacity were 7.8 N·cm and 3.8, respectively. The placement torque of screws with root contact was greater than that of screws with no root contact (P <0.05; effect size, 0.44; power, <0.8). Damping capacity of screws with root contact was significantly greater than that of screws with no root contact (P <0.01; effect size, >0.5; power, >0.95). CONCLUSIONS: It was suggested that the damping capacity is related to root contact.

Effects of tooth root contact on the stability of orthodontic anchor screws in the maxilla: Comparison between self-drilling and self-tapping methods.

INTRODUCTION: We evaluated the effects of screw placement angle on the frequency of root contact and the effects of root contact on screw stability, comparing self-drilling and self-tapping methods. METHODS: In total, 80 patients with 142 screws (diameter, 1.6 mm; length, 8.0 mm) were included. Cone-beam computed tomography images were taken. Cortical bone thickness, interroot distance, shortest distance between the screw and adjacent tooth root, and screw placement angle were measured. RESULTS: The success rates of the screws were 91.5% for the self-drilling method and 94.4% for the self-tapping method (P >0.05). The self-drilling screws tended to contact the distal tooth roots in the right maxilla. In the self-drilling method, the failure rate was significantly higher in the root contact group than in the no-contact group (P <0.05). CONCLUSIONS: The success rate was not significantly different between the self-drilling and the self-tapping methods in the maxilla. Avoidance of tooth root contact may improve the success rate more in the self-drilling method than in the self-tapping method.

Satisfaction with orthognathic surgery of skeletal Class III patients.

INTRODUCTION: Class III relationships can be corrected with single-jaw or bimaxillary surgery. The purpose of this research was to assess patient satisfaction after bimaxillary surgery, compared with setback surgery alone, for Class III corrections. Identifying patients' relative levels of satisfaction will provide guidance for the selection of surgical options. METHODS: The cephalometric outcomes for 25 patients who underwent 2-jaw surgery were compared with the outcomes in 40 patients who had mandibular setback. Soft and hard tissue changes were evaluated using initial and postsurgical lateral cephalograms. The patients were asked to complete self-administered questionnaires after orthognathic treatment. Correlations between cephalometric improvement and patient satisfaction were evaluated. RESULTS: The patients in the 2-jaw group reported significantly higher satisfaction in the appearance of the mouth (P <0.05), smile (P <0.05), and treatment outcome (P <0.001). These item scores and the changes in ANB, ANS-M, and nasolabial angle showed strong correlations in the 2-jaw group and moderate correlations in the 1-jaw group. CONCLUSIONS: ANS-M and nasolabial angle should be considered in the conventional diagnosis of skeletal Class III orthognathic surgery to obtain adequate correction of facial esthetics and patient satisfaction. Esthetic needs contribute to surgical decisions when treating patients with skeletal Class III malocclusions and dentofacial deformities such as maxillary deficiency and long facial height that causes a turned-up upper lip.

Effects of palate depth, modified arm shape, and anchor screw on rapid maxillary expansion: a finite element analysis.

OBJECTIVES: This study examined the effects of palate depth, modifications of the arm shape, and anchor screw placement in the mid-palatal area on rapid maxillary expansion (RME) using finite element (FE) analysis. MATERIALS AND METHODS: Three-dimensional FE models were constructed that included the maxilla (cortical and cancellous bone), maxillary sinus, maxillary first molar and first premolar, periodontal membrane, and an RME appliance with arms, bands, and anchor screws. The expansion screws were activated 0.2mm transversely. RESULTS: The deepest palate model had the smallest lateral displacement of the tooth and expansion of the mid-palatal suture and the greatest strain of the arm among the models with different palate heights. The model with a larger diameter arm had the smallest arm strain among the models with various arm shapes. The model with an anchor screw had the greatest lateral displacement of the tooth and expansion of the mid-palatal suture among all models. CONCLUSIONS: For a deeper palate, the arm strain increased and the effect of RME decreased. Modified arm shapes such as a larger diameter arm, arms connected by a diagonal wire, a straight arm, and a shorter arm efficiently expanded the maxillary dental arch. Anchor screws increased the effect of RME, generated more and closer bodily movement of the tooth, and parallel expansion of the mid-palatal suture. The model with an anchor screw without arms decreased the displacement of the teeth compared to the models with arms, so the arms are necessary for effective RME.

Assessment of damping capacity as an index of root proximity in self-drilling orthodontic mini-implants.

OBJECTIVES: This study aims to investigate orthodontic mini-implant root proximity, placement torque, and damping capacity and to determine whether placement torque and damping capacity (Periotest value (PTV)) are useful indices for the estimation of mini-implant root proximity. MATERIALS AND METHODS: The root proximity of 143 orthodontic mini-implants (1.6 mm diameter, 8 mm screw thread length) was evaluated in 79 patients (24 males, 55 females; mean age, 22.5 ± 8 years) using cone-beam computed tomography. The placement torque and PTV of each implant were determined using a torque tester and the Periotest, respectively. Variability in these values according to root proximity was evaluated. RESULTS: PTVs of mini-implants with multiple (two or more) points of contact between the root and implant were significantly larger than those of mini-implants with no root contact in the self-drilling group. Placement torque did not differ significantly according to root proximity. In the self-drilling group, the odds ratio for root contact was 20.82 (P = 0.000) for a PTV >6. CONCLUSIONS: Placement torque could not be used to estimate root proximity. The PTV was significantly affected by root proximity in the self-drilling group. CLINICAL RELEVANCE: A threshold of PTV >6 could be applied clinically for the estimation of self-drilling mini-implant root proximity.

Comparative study of the primary stability of self-drilling and self-tapping orthodontic miniscrews.

INTRODUCTION: The purpose of this study was to determine the influence of self-tapping and self-drilling placement techniques on the stability of miniscrews. METHODS: We included 70 orthodontic patients who received miniscrews (140 screws). Miniscrews measuring 1.6 mm in diameter and 8 mm in length were placed using the self-tapping (35 patients, 70 screws) and self-drilling (35 patients, 70 screws) methods. We examined the success rates, placement torque values, Periotest (Medizintechnik Gulden, Bensheim, Germany) values, rates of root contact, and influence of root contact on mobility. Cone-beam computed tomography was used to evaluate root contact. Miniscrews that endured an orthodontic force for 6 months or more were considered successful. RESULTS: The success rates of the miniscrews were approximately 96% with either placement technique. The placement torques were 7 and 7.5 N cm in the self-tapping and self-drilling miniscrews, respectively (P >0.05). The Periotest values of the self-drilling method were significantly greater than those of the self-tapping method. The Periotest values of the self-drilling miniscrews with root contact were significantly greater than those with no root contact. CONCLUSIONS: Both placement techniques showed high stability in the maxillary bone, although the self-drilling miniscrews with root contact had greater mobility. Special attention to root contact further improves the stability of the self-drilling miniscrews.

A preliminary study of the effects of low-intensity pulsed ultrasound exposure on the stability of orthodontic miniscrews in growing rats.

BACKGROUND: Orthodontic miniscrews placed in growing subjects often loosen during orthodontic treatment. The ability to place miniscrews, regardless of age, would be clinically beneficial. OBJECTIVES: To assess the effects of low-intensity pulsed ultrasound (LIPUS) on the stability of orthodontic miniscrews in growing rats. MATERIALS/METHODS: The mobility of miniscrews after placement was recorded and the miniscrew-bone interface was examined histomorphometrically using tibiae of seven male Sprague-Dawley rats (aged 6 weeks). Field-emission scanning electron microscopic images were used to evaluate the bone-miniscrew interface, and a mobility test device was used to assess the stiffness of miniscrew placement. Fourteen custom-made miniscrews with 1.4mm diameters and 4.0mm lengths were placed in the right and left tibiae. LIPUS was used to stimulate right tibiae at the sites of miniscrew placement, and left tibiae were left untreated as controls. RESULTS: Significantly lower mobility was observed in the LIPUS-treated group compared with the control group (P < 0.05). Histomorphometric evaluation indicated that bone-miniscrew adhesion was significantly better in the LIPUS-treated group than in the control group (P < 0.05). LIMITATIONS: This in vivo study used tibiae rather than jaw bones because the jaw bones of 6-week-old rats were too small to allow miniscrew placement. CONCLUSIONS: LIPUS was able to increase the bone-miniscrew contact and reduce the mobility of miniscrews in growing subjects. IMPLICATIONS: LIPUS may accelerate the bone healing process after miniscrew placement in growing subjects and can reduce the latent period.

Analysis of the effects of importin α1 on the nuclear translocation of IL-1α in HeLa cells.

Interleukin-1α (IL-1α), a cytokine released by necrotic cells, causes sterile inflammation. On the other hand, IL-1α is present in the nucleus and also regulates the expression of many proteins. A protein substrate containing a classical nuclear localization signal (cNLS) typically forms a substrate/importin α/ß complex, which is subsequently transported to the nucleus. To the best of our knowledge, no study has directly investigated whether IL-1α-which includes cNLS-is imported into the nucleus in an importin α/ß-dependent manner. In this study, we noted that all detected importin α subtypes interacted with IL-1α. In HeLa cells, importin α1-mediated nuclear translocation of IL-1α occurred at steady state and was independent of importin ß1. Importin α1 not only was engaged in IL-1α nuclear transport but also concurrently functioned as a molecule that regulated IL-1α protein level in the cell. Furthermore, we discussed the underlying mechanism of IL-1α nuclear translocation by importin α1 based on our findings.

Changes in enamel hardness, wear resistance, surface texture, and surface crystal structure with glass ionomer cement containing BioUnion fillers.

This study investigated the potential of BioUnion filler containing glass ionomer cement (GIC) to enhance the properties of enamel surrounding restorations, with a specific focus on the effect on hardness. The hardness of the bovine enamel immersed in the cement was measured using Vickers hardness numbers. Following sliding and impact wear simulations, the enamel facets were examined using confocal-laser-scanning microscopy and scanning-electron microscopy. Surface properties were further analyzed using energy-dispersive X-ray spectroscopy and X-ray diffraction (XRD). A significant increase in Vickers hardness numbers was observed in the BioUnion filler GIC after 2 days. Furthermore, the mean depth of enamel facets treated with BioUnion filler GIC was significantly less than that of untreated facets. Characteristic XRD peaks indicating the presence of hydroxyapatite were also observed. Our findings imply that GIC with BioUnion fillers enhances the mechanical properties of the tooth surface adjacent to the cement.

LRP1-deficient leptin receptor-positive cells in periodontal ligament tissue reduce alveolar bone mass by inhibiting bone formation.

OBJECTIVE: Leptin receptor-positive (LepR+) periodontal ligament (PDL) cells play a crucial role in osteogenesis during tooth socket healing and orthodontic tooth movement; however, the factors regulating osteoblast differentiation remain unclear. This study aimed to demonstrate the function of low-density lipoprotein receptor-related protein 1 (LRP1) in alveolar bone formation by examining conditional knockout (cKO) mice lacking LRP1 in LepR+ cells. DESIGN: Bone mass and formation were examined via bone morphometric analysis. Bone formation and resorption activities were determined via histochemical staining. Additionally, PDL cells collected from molars were induced to differentiate into osteoblasts with the addition of BMP2 and to mineralize with the addition of osteogenic medium. Osteoblast differentiation of PDL cells was examined by measuring the expression of osteoblast markers. RESULTS: Bone morphometry analysis revealed decreased mineral apposition rate and alveolar bone mass in cKO mice. Additionally, cKO mice showed a decreased number of osterix-positive cells in the PDL. cKO mice had a large number of osteoclasts around the alveolar bone near the root apex and mesial surface of the tooth. In the PDL cells from cKO mice, inhibition of mineralized matrix formation and decreased expression of alkaline phosphatase, osterix, bone sialoprotein, and osteocalcin were observed even when BMP2 was added to the medium. BMP2, BMP4, and osteoprotegerin expression also decreased, but RANKL expression increased dominantly. CONCLUSION: LRP1 in LepR+ cells promotes bone formation by stimulating osteoblast differentiation. Our findings can contribute to clinical research on bone diseases and help elucidate bone metabolism in the periodontal tissue.

Root proximity and inclination of orthodontic mini-implants after placement: cone-beam computed tomography evaluation.

INTRODUCTION: Root contact by mini-implants should be avoided. Prolonged contact can damage the root and might cause external root resorption. To reduce the proximity of a mini-implant to the root, information about positioning of the implants and the variability of inclination is useful. The purpose of this study was to investigate root proximity and variability of the placement inclination of a mini-implant according to placement position. METHODS: Fifty patients with 147 implants (diameter, 1.6 mm; length, 8 mm) were included. Cone-beam computed tomography images were taken of the area around the implant-placement site. The distances between the root and the mini-implant, and the vertical and horizontal inclinations of the placed implants, were measured. RESULTS: Of 147 implants, approximately 20% were in contact with a root. The vertical inclinations of the mini-implants were 48.3° to 50.4° in the maxilla and 57.5° to 63.3° in the mandible. In the right maxilla, the incidence of root contact with the distal adjacent tooth was significantly greater than that with the mesial tooth. CONCLUSIONS: One fifth of the mini-implants in this study contacted adjacent roots. During placement of mini-implants in the buccal maxillary right alveolar bone, contact with the root of the distal adjacent tooth should be avoided.

Analysis of a force system for upper molar distalization using a trans-palatal arch and mini-implant: a finite element analysis study.

The purpose of this study was to analyse distal movements of molars in a force system using a trans-palatal arch (TPA), fixed to the maxillary first molar, and mini-implants placed at the palatal midline, considering the diagnostic standard for placement site in association with variation in upper molar locations, using finite element (FE) analysis. Three-dimensional FE models, divided by the differing direction of traction force, mesiodistal locations of the left and right molars, and the lateral location of the mini-implant were constructed. (1) When a traction force was fixed from the height of alveolar crest to the mini-implant placed at the middle of palate, the molars underwent bodily movement. (2) When the location of the mini-implant was moved to the left of the midline, the amount of distal movement of the left molar increased. When the mesiodistal locations of the left and right molars differed, the amount of distal movement of the molar located mesially was larger than that of the contralateral molar, even when the mini-implant was located on the midline.