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01 July 2020, Volume 47 Issue 4 Previous Issue    Next Issue

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Spontaneous vertical root fracture: a diagnosis and treatment challenge Li Jiyao, Zheng Guangning Int J Stomatol. 2020, 47 (4):  373-382.  DOI: 10.7518/gjkq.2020056 Abstract ( 4749 )   HTML ( 798 )   PDF（pc） (14283KB) ( 4237 )   Save Vertical root fracture in non-endodontically treated teeth, also known as spontaneous vertical root fracture (SVRF), is an intractable disease for most dental practitioners. Due to the lack of pathognomonic clinical manifestation and radiographic presentation in the early stage, the diagnosis of SVRF is extremely challenging even for experienced dentists. Even if SVRF is determined to be present, it is hard to make decision between treatment options including root resection, repairing the fractured root or tooth extract. Timing and method of restoration after tooth extraction also need to be considered. The aim of this paper was to discuss early diagnosis, differential diagnosis, the principles of treatments and the specific treatment plans of SVRF in the light of literature review and a 3-years clinical study, to help clinician to discern SVRF and to act as a reference for better clinical diagnosis and treatment. Figures and Tables | References | Related Articles | Metrics

Original Articles

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Caries status and relevant factor analysis among children in urban and pasture areas of Tibet Autonomous Region Deng Xiaoyu,Renqing Sege,Huo Yuanyuan,Cui Chen,Qi Wenting,Han Xuan,Huang Ruijie,Zhou Yuan,Zhu Lin,Zou Jing,Danzeng Nianzha Int J Stomatol. 2020, 47 (4):  383-390.  DOI: 10.7518/gjkq.2020075 Abstract ( 1033 )   HTML ( 24 )   PDF（pc） (6752KB) ( 352 )   Save Objective This study aimed to investigate the caries status and the association between the caries status and the living habit and healthcare of children living in urban and pasture areas of Tibet. Methods A total of 280 and 376 children were recruited from Lhasa (urban area) and Nagqu (pasture area), respectively, through stratified cluster random sampling. The children’s caries status and their living habits and healthcare behavior were collected using questionnaires. Data were analyzed by SPSS 21.0 software. Results In Lhasa, 124 children (59 males and 65 females) of primary dentition and 156 children (81 males and 75 females) of mixed dentition were recorded. The overall mean decay-missedfilled-teeth (dmft) was 4.54. The mean dmft of children of primary dentition was 4.59, and the dmft values of males and females were 4.41 and 4.86, respectively. The overall mean dmft was 3.55. The mean dmft of children of mixed dentition was 4.51, and the dmft values of males and females were 4.16 and 4.88, respectively. In Nagqu, 190 children (109 males and 81 females) of primary dentition and 186 children (97 males and 89 females) of mixed dentition were recorded. The overall mean dmft was 3.55. The mean dmft of children of primary dentition was 3.31, and the dmft values of males and females were 3.83 and 2.61, respectively. The mean dmft of children of mixed dentition was 3.79, and the dmft values of males and females were 3.68 and 3.91, respectively. The overall dmft and primary dentition dmft of children in Lhasa were higher than those of children in Nagqu (P<0.05). Primary molars were the teeth with the highest caries rate, whereas mandibular incisors were the teeth with the lowest caries rate in both sampling areas. Gender had no significant contribution to the caries rate. Children who frequently visited doctors for non oral diseases had higher rates of caries in Lhasa and Nagqu, respectively (P<0.01). About 81.4% of children from Lhasa brushed their teeth at least once a day, but only 8.9% of the children used fluoride toothpaste. In addition, 56.1% and 36.4% of the children’s families had never consulted with a dentist. In Nagqu, the results were 59.6%, 18.6%, 73.4%, and 51.3%, respectively. Conclusion The children’s caries status in Tibet is still severe. Further studies should be conducted to strengthen oral healthcare education to control caries among children in Tibet. Figures and Tables | References | Related Articles | Metrics

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Analysis of tooth condition and the effect of the first permanent molar pit and fissure sealant in 7-9-year-old children in Chengdu Zhong Ting,Deng Yalan,Shao Meiying,Lei Lei,Li Xue,Hu Tao Int J Stomatol. 2020, 47 (4):  391-396.  DOI: 10.7518/gjkq.2020072 Abstract ( 1142 )   HTML ( 58 )   PDF（pc） (5579KB) ( 386 )   Save Objective This study aimed to evaluate the health status of children aged 7-9 years in Chengdu City and explore the factors affecting the retention rate of their first permanent molars 1 year after the application of pit and fissure sealants. Methods Detailed examinations were conducted on the first permanent molars of children who participated in the Comprehensive Intervention Program for Children’s Oral Diseases in Central and Western China in 2017. The first permanent molars that met the criteria for pit and fissure sealants were sealed, and the sealant retention and caries were reviewed after 1 year. Results were analysed using chi-square test on SPSS 22.0. Results A total of 1 877 teeth were examined among 629 children. The complete retention rate was 87.75% a year after sealing and caries, detection rate of the first molars was 0.96%. Among these teeth, 46, 36, 16 and 26 had 91.61%, 88.25%, 87.69% and 84.40% retention rates, respectively. The retention rate of 26 teeth was lower than that of 46 teeth, and the difference was statistically significant (P<0.001). When grade of schoolchildren was used as the factor, the retention rate of third grade was 89.34% which was slightly higher than that of second grade at 86.57%, but the difference was not statistically significant (P=0.071). Conclusion The retention rate of 1-year pit and fissure sealants was 87.75%. The 26 teeth showed the lowest retention rate, and 46 teeth had the highest retention rate. Tooth position is one of the main factors affecting the retention rate of pit and fissure sealants. References | Related Articles | Metrics

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Meta-analysis of the association between interferon regulatory factor 6 gene polymorphisms and non-syndromic cleft lip with or without cleft palate in Asian population Hou Yali,Ma Li Int J Stomatol. 2020, 47 (4):  397-405.  DOI: 10.7518/gjkq.2020007 Abstract ( 900 )   HTML ( 13 )   PDF（pc） (11861KB) ( 86 )   Save Objective This Meta-analysis was to investigate the relationship of the interferon regulatory factor 6 (IRF6) gene rs2235371 and rs642961 polymorphism and nonsyndromic cleft lip with or without cleft palate (NSCL/P) in Asian population. Methods Data extraction was independently performed by two reviewers. Odds ratio (OR) and its 95% confidence interval (CI) to estimate the associations between IRF6 genetic polymorphisms and the risk of NSCL/P. Variant effects on NSCL/P were assessed using per-genotype approach. A sensitivity analysis was employed to evaluate the influence of single studies on the overall estimate. Publication bias was assessed using the Egger’s test and funnel plot. Results Significant difference was found between IRF6 rs2235371, rs642961 and cleft lip with or without cleft palate (CL/P) risk in heterozygote comparison. For rs2235371, GA, AA and GA+AA carried respectively, 0.77 (0.73-0.81), 0.53 (0.41-0.70) and 0.77 (0.72-0.81) times lower odds of NSCL/P than GG genotype. For rs642961, GA, AA and GA+AA carried respectively, 1.34 (1.09-1.65), 3.56 (2.14-5.92) and 1.45 (1.19-1.77) times higher odds of NSCL/P than GG genotype. The result of sensitivity analysis indicated that no single study could affect the pooled ORs. In addition, there was not publication bias detected by either the funnel plot or Egger’s test. Conclusion These results suggested that the IRF6 rs642961 polymorphism, but not rs2235371, might increase the risk of NSCL/P in the Asian populations. However, more relevant case-control studies are required to obtain more precise results. Figures and Tables | References | Related Articles | Metrics

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Inhibitory effect of pyrroloquinoline quinone on epithelial-mesenchymal transition in tongue squamous cell carcinoma cells Wu Nan,Li Bin Int J Stomatol. 2020, 47 (4):  406-412.  DOI: 10.7518/gjkq.2020079 Abstract ( 1340 )   HTML ( 12 )   PDF（pc） (13427KB) ( 89 )   Save Objective To study the effect of pyrroloquinoline quinone (PQQ) on epithelial-mesenchymal transition (EMT) and its underlying mechanisms in human tongue squamous cell carcinoma cells. Methods Human tongue squamous cell carcinoma cell line CAL27 was selected. MTT assay was used to determine the effect of PQQ on cell viability. The invasion and migration abilities of CAL27 cells were checked by Transwell assay and wound healing test. Fluorescence microscopy was performed to measure the effect of PQQ on the generation of reactive oxygen species (ROS) in CAL27 cells. The expression levels of EMT-related proteins (E-cadherin, Vimentin, and zinc-finger transcription factor Snail) and nuclear factor-κB (NF-κB) activator protein in CAL27 cells under the treatment of PQQ, N-acetyl-L-cysteine (NAC), and phorbol-12-myristate-13-acetate (PMA) were determined by Western blot. Results PQQ inhibited the proliferation of CAL27 cells in a dose-dependent manner, and the half maximal inhibitory concentration of PQQ after 24 h was 6.69 μmol·L -1. Transwell assay and wound healing test showed that 2 μmol·L -1 PQQ inhibited the invasion and migration abilities of CAL27 cells (P<0.05). Cellular ROS level was signi-ficantly boosted (P<0.001) after treatment with 2 μmol·L -1 PQQ for 24 h. PQQ (2 μmol·L -1) increased the expression level of E-cadherin and inhibited the expression levels of Vimentin, Snail, and NF-κB (P<0.001). The coincubation of PQQ with NAC or PMA yielded the following experimental results: 1) NAC could reduce the regulatory effect of PQQ on EMT-related proteins and NF-κB activator protein (P<0.01) such that the increased expression level of E-cadherin was inhibited and the inhibited expression levels of Vimentin, Snail, and NF-κB were increased; 2) PMA could also reduce the regulatory effect of PQQ on EMT-related proteins (P<0.05). Conclusion PQQ can inhibit the EMT process in tongue squamous cell carcinoma cells, and ROS and the NF-κB signaling pathway may play an important role in this process. Figures and Tables | References | Related Articles | Metrics

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Effect of porcelain layer thickness and substrate on the optical properties of porcelain veneers for tetracycline stained teeth Qian Huifen,Lin Yunhong,Wu Meiying,Dai Zichao,Li Xingxing Int J Stomatol. 2020, 47 (4):  413-417.  DOI: 10.7518/gjkq.2020066 Abstract ( 947 )   HTML ( 19 )   PDF（pc） (4860KB) ( 232 )   Save Objective This study aimed to analyze the color properties and translucency of porcelain veneers with different thicknesses and substrates when used to repair tetracycline stained teeth. Methods Porcelain specimens with different opaque and dentine thicknesses (dentine/opaque: 0.40 mm/0.10 mm, 0.30 mm/0.20 mm, 0.65 mm/0.10 mm, and 0.55 mm/0.20 mm) were fabricated by powder-slurry sintering. L*, a*, and b* parameters were measured under simulated tetracycline and black and white backgrounds by using a spectrophotometer. The ΔE001 and ΔE002 color differences among the specimens on simulated tetracycline backgrounds and normal white background, respectively, were calculated. The translucent parameter (TP values) was also examined. Results 1) The ΔE001 of two groups with a total thickness of 0.75 mm were statistically greater than 0.50 mm groups (P<0.01), except for the yellow background. 2) The ΔE002 of specimens of different thickness under different substrates were all less than 1.25 and there was no significant difference over different substrates (P>0.01). 3) The TP values of all specimens were less than 1, and there was no statistical dif-ference between different thickness groups (P>0.01). Conclusion For yellow, red, and gray tetracycline stained teeth, 0.50 mm-thick IPS d.SIGN porcelain veneers (0.10 mm opaque with 0.40 mm dentine) can obtain good color matching with the target color; however, the translucent property of the porcelain veneers is worse than that of natural teeth. Figures and Tables | References | Related Articles | Metrics

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Effect of opaque-shade resin layer thickness on the color of polyetheretherketone-Crea.lign restoration Zhang Jingting,Pan Xudong,Zhang Wenyun Int J Stomatol. 2020, 47 (4):  418-423.  DOI: 10.7518/gjkq.2020059 Abstract ( 957 )   HTML ( 9 )   PDF（pc） (8620KB) ( 108 )   Save Objective This study aimed to test the effect of different thicknesses of opaque-shade resin layer on the color of detin-shade polyetheretherketone (PEEK)-Crea.lign restoration. Methods PEEK of 0.6 mm thickness was synthesized, and A2 shade Crea.lign of opaque-shade resin layers of 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5 mm and body-shade resin layer of 1.0 mm were bonded on the surface of PEEK. CIE (International Commission on illumination) L*a*b* values for specimens were measured, and color difference among the different thickness groups was calculated. Results For the 0.0 mm body-shade resin layer + 0.1-0.3 mm opaque-shade resin layer and 1.0 mm body-shade resin layer + 0.0-0.2 mm opaque-shade resin layer, the color values showed an upward trend with the increasing thickness of the opaque-shade resin layer. When the thicknesses of PEEK and body-shade resin layer were constant at 0.0 and/or 1.0 mm respectively, the color differences between each group of 0.1-0.5 mm-thick opaque-shade resin layer were within the clinical acceptable range. Beyond clinically acceptable color difference was observed for the detin-shade PEEK. Conclusion In clinical setting, the 0.1-0.5 mm thickness range of opaque-shade resin layers did not influence the color of the detin-shade PEEK-Crea.lign restoration. In addition, 0.1 mm was the minimum thickness that sufficiently covered the detin-shade PEEK background. Figures and Tables | References | Related Articles | Metrics

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Randomized cross-control trial of placebo in the regulation of orthodontic tooth movement pain Yang Hong,Jin Yu,Lai Wenli Int J Stomatol. 2020, 47 (4):  424-430.  DOI: 10.7518/gjkq.2020081 Abstract ( 1362 )   HTML ( 10 )   PDF（pc） (7388KB) ( 109 )   Save Objective This study aims to explore the therapeutic effect of placebo on orthodontic pain and its mechanism. Methods Sixty volunteers were recruited and randomly divided into two groups. Vitamin B tablets were used as placebo. At baseline, orthodontic separators were placed between the left lower molars, and subjects in the placebo group took pla-cebos after half an hour. Only orthodontic separators were placed in the non-placebo group. Pain level (visual analogue scales), anxiety level, and salivary alpha-amylase (sAA) and saliva cortisol of the subjects were measured at baseline and 24 hours after separation. After 1 month of wash-out period, the orthodontic separators were placed between the left lower molars again, and subjects in the two groups were cross-experimented. Results The pain and anxiety levels in the placebo and non-placebo groups increased after placement of orthodontic separators. The pain and anxiety levels in the placebo group were significantly lower than those in the non-placebo group (P<0.05). The levels of cortisol and sAA increased in varying degrees, and the expression of cortisol in the placebo group was lower than that in the non-placebo group (P<0.05). No significant difference was observed in the level of sAA expression between two groups (P>0.05). Conclusion The placement of orthodontic separators can stimulate orthodontic pain. The levels of pain and anxiety increased similar to the levels of cortisol and salivary amylase. Cortisol and sAA can be used as objective biological indicators to evaluate pain intensity and anxiety level, respectively. Placebo can effectively reduce the pain and anxiety caused by orthodontic pain. Figures and Tables | References | Related Articles | Metrics

Reviews

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Research progress on regulation of cyclooxygenase-2/prostaglandin E2 pathway on oral cancer Kong Lixin,Ren Biao,Cheng Lei Int J Stomatol. 2020, 47 (4):  431-438.  DOI: 10.7518/gjkq.2020038 Abstract ( 874 )   HTML ( 19 )   PDF（pc） (7923KB) ( 374 )   Save Oral cancer is the sixth most common tumour worldwide. The 5-year survival rate of oral cancer is lower than 60%, and this disease seriously affects human health and quality of life. The cyclooxygenase (COX)-2/prostaglandin (PG) E2 pathway is significantly elevated in oral tumour tissues. This pathway is thus closely related to oral cancer. The COX-2/PGE2 pathway can upregulate epidermal growth factor receptor to enhance cancer growth, upregulate vascular endothelial growth factor to promote angiogenesis and upregulate Bcl-2 to induce cancer apoptosis. The COX-2/PGE2 pathway is one of the most important regulatory pathways in oral cancer. This article will summarise the latest research progress on this pathway in oral cancer. Figures and Tables | References | Related Articles | Metrics

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Research progress on the preparation of titanium-based implant surface coatings by micro-arc oxidation Wang Huan,Liu Yang,Qi Mengchun,Li Jingyi,Liu Mengnan,Sun Hong Int J Stomatol. 2020, 47 (4):  439-444.  DOI: 10.7518/gjkq.2020037 Abstract ( 850 )   HTML ( 27 )   PDF（pc） (5798KB) ( 352 )   Save Titanium and its alloys are widely used as alternative materials for dental implants and bone tissue repair in orthopaedic surgery due to their superior mechanical properties and biocompatibility. However, the surface of these materials is biologically inert and needs to be modified to improve their osteogenic and antibacterial properties. Micro-arc oxidation (MAO) has become a popular surface modification technology because it can conveniently and effectively modify the surface of implants by element doping and morphology. This method can greatly improve the biological properties of titanium-based implants. TiO2 coatings with different morphologies and chemical compositions can be prepared on the surface of titanium-based implants by adjusting the reaction parameters of MAO and combining with other surface modification techniques. This strategy can improve the osteogenic and antibacterial properties of implants and increase the planting success rate. In this paper, the surface coatings of titanium implants prepared by MAO and their osteogenic and antibacterial properties will be reviewed. References | Related Articles | Metrics

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Treatment options for young permanent teeth with pulp necrosis Li Mei,Wen Ningning,Zhao Yuan Int J Stomatol. 2020, 47 (4):  445-451.  DOI: 10.7518/gjkq.2020078 Abstract ( 3463 )   HTML ( 641 )   PDF（pc） (6604KB) ( 3368 )   Save The retention of young permanent teeth with pulp necrosis is seriously affected because the root is not fully developed. At present, three main treatments used for young permanent teeth with pulp necrosis are apexification, apical barrier techniques, and revascularization. This article reviews the principles, advantages, disadvantages, and selection factors of each treatment to help dentists in choosing possible treatment options. Figures and Tables | References | Related Articles | Metrics

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Application of endoscopic technique to remove the foreign bodies in the maxillary sinus Shi Haitao,Huang Jinxia,Pan Jian Int J Stomatol. 2020, 47 (4):  452-457.  DOI: 10.7518/gjkq.2020074 Abstract ( 1825 )   HTML ( 127 )   PDF（pc） (5970KB) ( 597 )   Save The traditional methods to remove the foreign bodies in the maxillary sinus directly through the alveolar socket or canine fossa bone window have the disadvantages of operation blindness, large amounts of damage, and possible postoperative complications. The endoscopic technique is a minimally invasive procedure. The excellent illumination and the magnification of the monitoring system make the surgery field clearly visible and has the advantages of small surgical trauma, quick recovery, and less complications. Here, we review the types and complications, the advantages and disadvantages, the surgical approach of the endoscopic technique for removing foreign bodies in the maxillary sinus, the use of stuffing hemostasis materials, and postoperative care. References | Related Articles | Metrics

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Progress on the treatment of palatogingival groove Zhang Linlin,Du Yi Int J Stomatol. 2020, 47 (4):  458-462.  DOI: 10.7518/gjkq.2020077 Abstract ( 3789 )   HTML ( 423 )   PDF（pc） (4667KB) ( 2747 )   Save Palatogingival groove (PGG) is an anatomic malformation in the maxillary anterior teeth and is often accompanied by the area of bony destruction adjacent to these teeth. The hidden trap in the tooth can harbor plaque and bacteria, which cause periodontal destruction with or without pulpal pathologic change. The severity and prognosis of diseases related to PGG depend on several factors, including the location, range, depth, and type of the groove. Interdisciplinary therapy has been used to remove and block the inflammatory source and recover the health of surrounding periodontal tissues. Clinicians need a detailed understanding of the characteristics, etiology, treatment, and prognosis of PGG to successfully manage this condition. References | Related Articles | Metrics

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Research progress on drug and laser therapy for peri-implantitis Zhang Min,Wan Haoyuan Int J Stomatol. 2020, 47 (4):  463-470.  DOI: 10.7518/gjkq.2020068 Abstract ( 1260 )   HTML ( 38 )   PDF（pc） (7968KB) ( 594 )   Save Implantation has become one of the main restoration schemes for dentition defect and loss, and peri-implantitis is the main cause of implant failure. After implantation restoration, attention should be provided to the subsequent maintenance, prevention, and treatment of peri-implantitis. Many methods can be used to treat peri-implantitis. These methods can be roughly divided into nonsurgical and surgical treatments. At present, nonsurgical treatment is ineffective and is still preferred for peri-implantitis, and surgical treatment is only selected when bone resorption is severe. Nonsurgical treatment methods mainly include mechanical debridement, drug therapy, laser therapy, and hyperbaric oxygen therapy. Drugs and lasers are currently two widely used clinical methods and effective treatments. This article reviews the research progress on drug and laser therapy treatments for peri-implantitis. References | Related Articles | Metrics

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Research progress on the adjunctive drug therapy of peri-implantitis Wu Qiuyue,Li Zhibang Int J Stomatol. 2020, 47 (4):  471-477.  DOI: 10.7518/gjkq.2020044 Abstract ( 1191 )   HTML ( 27 )   PDF（pc） (6866KB) ( 356 )   Save Many patients suffer from peri-implantitis due to the extensive application of implants in dental practice. The treatment of peri-implantitis can be categorized into non-surgical and surgical treatments. Drug therapy is a non-surgical treatment mostly applied with other techniques to enhance their therapeutic effects. The treatment of peri-implantitis is more difficult than that of periodontitis of natural teeth, and adjuvant drug treatment is highly important. At present, the drug protocols for peri-implantitis treatment vary, and the efficacy is controversial. This paper reviews the research progress on commonly used drugs in clinical practice to facilitate rational drug use and provide ideas for further research. References | Related Articles | Metrics

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Research progress on macrophage polarization involved in the regulation of orthodontic tooth movement Zhao Yujie,Guan Xiaoyan,Li Xiaolan,Chen Qijun,Wang Qian,Liu Jianguo Int J Stomatol. 2020, 47 (4):  478-483.  DOI: 10.7518/gjkq.2020071 Abstract ( 1167 )   HTML ( 17 )   PDF（pc） (5876KB) ( 518 )   Save Teeth move under orthodontic force. The plasticity of jawbone, compressive resistance of cementum, and stability of periodontal membrane environment are the biological bases of orthodontic periodontal tissue reconstruction and tooth movement. Orthodontic force on teeth affects the local periodontal microenvironment, which promotes macrophage polarization. In M1-type macrophages, the orthodontic tooth movement (OTM) secretion of inflammatory factors is conducive to alveolar bone absorption and subsequent OTM. M2-type macrophages play an anti-inflammatory role and promote the repair of periodontal tissues. This article reviews the role of M1-type and M2-type macrophages in OTM and the factors that influence macrophage polarization in orthodontic treatment. This article aims to provide theoretical basis for future research on macrophages in the orthodontic field and to accelerate OTM. Figures and Tables | References | Related Articles | Metrics

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Research progress on maxillary skeletal expander Zhang Kaiwen,Zhao Xuefeng,Shu Rui,Han Xianglong Int J Stomatol. 2020, 47 (4):  484-490.  DOI: 10.7518/gjkq.2020067 Abstract ( 3236 )   HTML ( 219 )   PDF（pc） (6997KB) ( 1401 )   Save Maxillary transverse deficiency (MTD), a common malocclusion in people of all ages, affects gnathostomatic development and functions of patients at different degrees, and its main treatment is maxillary expansion. Traditionally, rapid maxillary and surgically assisted rapid palatal expansions have several disadvantages in the treatment of late adolescence and adult patients. At present, miniscrew assisted rapid palatal expansion (MARPE) has emerged as a new treatment with significant advantages in late adolescence and adult patients with MTD. However, the device design, implant sites, curative effect, and complications of MARPE are also controversial. As a special type of MARPE, maxillary skeletal expander (MSE) is positioned at the posterior palate, with four microimplants engaging the palatal bone bicortically. Such positioning results in significant expansion in late adolescence and adult patients. This article aims to review MSE in terms of biological and biomechanical bases, device design, clinical application, and curative effect. References | Related Articles | Metrics

Methodological Introduction

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Clinical application of a novel torque control auxiliary: crimpable gate spring Zheng Dan,Yi Jianru,Li Yu,Zhao Zhihe Int J Stomatol. 2020, 47 (4):  491-496.  DOI: 10.7518/gjkq.2020069 Abstract ( 8312 )   HTML ( 358 )   PDF（pc） (26174KB) ( 2268 )   Save Torque control is critical for orthodontic treatment. However, current torque control approaches are still unsatisfactory. This article aims to introduce crimpable gate spring, a novel, customizable torquing auxiliary that comprises a U loop and two crimpable clips. According to the height of the U loop, the spring has two types: 6 and 8 mm. The large arm of the force contributes to its high efficiency for torque control, and crimpable clips facilitate easy repair. Force is applied by bending the U loop at a certain angle; the force is substantial when the bending angle is large. Lingual and labial root torques are produced by placing the U loop in the gingival and incisal directions, respectively. The torque of the target tooth can generally be changed two to three months after force application. Figures and Tables | References | Related Articles | Metrics