Intermittent 8-hour activation in orthodontic molar movement.

The duration of force application is an important factor, together with the magnitude of force, in stimulating osteoclast recruitment in the periodontal ligament. The purpose of this study was to examine the effect of duration of intermittent versus continuous force application on the amount of molar movement in rats. Seventy-six molars of 38 rats were randomly assigned to continuous, intermittent, and sham-operation groups. A calibrated nickel-titanium coil spring exerting 40 g of initial force was suspended between the maxillary first molars and the incisors for 13 days. In the intermittent group, the coil spring was suspended for 8 hours per day. Tooth movement was measured on radiographs. There was no significant difference in the initial tooth displacement between the continuous-force and intermittent-force groups. Tooth movement at day 7 was significantly (P <.05) less in the intermittent group than in the continuous group. Actual mesial tooth movement and total tooth movement in the intermittent group were 65.9% and 73.7%, respectively, of those in the continuous group. Our results suggest that the amount of tooth movement in response to intermittent force is less than that in response to continuous force, but that the amount of tooth movement achieved by intermittent force exceeds the expected value predicted by the duration (33.3%) of force application.     

Intermittent force in orthodontic tooth movement

A single orthodontic activation lasting one hour can initiate tooth movement. The purpose of this study is to examine tooth movement, osteoclasts, and root resorption in rats following several one-hour activations. Rats (n = 144) were randomly assigned to intermittent (multiple activations of 1 hr/day), continuous, and sham appliances. Twelve rats were killed at 3, 5, 7, and 14 days. Tooth movement, osteoclasts, osteoclast %, and root resorption % were quantified. Continuous force moved molars mesially at days 3 and 14 (p < 0.05), but intermittent and sham did not. Intermittent and continuous force increased osteoclast numbers at days 3, 5, and 7 (p < 0.05). Continuous force increased osteoclast surface on days 3 and 14 (p < 0.05). Continuous force increased root resorption at days 5, 7, and 14 (p < 0.05). These results demonstrate that orthodontic force for one hour in 24 stimulates osteoclasts at compression sites but does not stimulate tooth movement or root resorption.     

糖尿病大鼠正畸牙齿移动及组织学变化

目的 探讨糖尿病大鼠正畸牙移动对牙周组织的影响。方法 选用80只雄性SD大鼠，牵引左上颌第一磨牙近中移动。实验组以STZ腹腔注射制备Ⅰ型糖尿病模型，对照组注射柠檬酸缓冲液，3周后开始实验。分别在加力0、3、7、14、21天处死大鼠，记录上颌第一磨牙移动距离，组织HE染色后，观察牙周组织形态学的改变。结果 ①实验组大鼠牙齿移动距离在移动末期明显大于对照组；②实验组骨质疏松；③实验组大鼠压力侧破骨细胞数在骨吸收期少于对照组，3、7、14天有统计学意义；④实验组大鼠在骨形成期张力侧成骨细胞数少于对照组，14、21天有统计学意义。结论 ①糖尿病性骨质疏松导致正畸牙齿移动末期牙齿移动速度加快；②糖尿病骨质反应能力降低，牙齿移动过程中破骨活动和成骨过程均受抑制。     

大鼠正畸牙移动中牙髓iNOS表达的免疫组化研究

目的:建立大鼠正畸牙移动模型,观察牙髓组织中诱导型一氧化氮合酶(iNOS)的表达及分布,探讨正畸牙移动过程中牙髓改建的分子机制。方法:采用免疫组织化学方法对正畸加力后12h、1d、3d、7d和14d大鼠牙髓组织中iNOS进行检测,观察iNOS的时空分布。结果:iNOS阳性反应的产物呈深褐色均质沉淀,主要在血管内皮细胞、成牙本质细胞胞浆核周区颗粒状阳性表达。这种染色在正畸加力后12h、1d、3d天有不同程度的增强,3d达到高峰,加力后7d和14d表达减弱,第14d与对照组无明显差异。结论:正畸牙移动过程中牙髓组织iNOS的表达先升高后逐渐恢复正常,提示iNOS可能在正畸牙移动牙髓组织改建过程中起重要作用。     

拔牙区骨改建对邻牙移动速度的影响

目的　本研究通过对拔牙创的骨改建进程及矫治力对牙齿移动的影响进行研究,为临床医生选择理想的矫治力和牙齿移动时机,缩短矫治时间提供依据。方法　取SD大鼠36只,随机分为3组,全麻下拔除一侧上颌第一磨牙,3月后拔除另一侧上颌第一磨牙。在拔牙后不同的时间制作口内矫治器,分别以0·30、0·60、1·36 N的力牵上颌第二磨牙向拔牙区移动,分别在施力前及施力后的第1、3、5、7、10、14天拍摄X线片,利用图像处理技术, 测量牙齿移动距离,以置入的拔髓针校正放大率。结果　①牙齿向新鲜拔牙区移动的速度明显大于向已愈合拔牙区移动的速度。②无论向新鲜拔牙区移动还是向已经愈合的拔牙区移动,0·30 N力组牙齿移动的距离在各时间点与0·60 N、1·36 N力组牙齿移动的距离之间存在显著的统计学差异;而0·60 N与1·36 N力组牙齿移动的距离之间基本上从第5天开始差别不大。③加力后牙齿移动周期一般包括三个阶段:瞬时运动;迟滞期;后期移动阶段。大约在第14天时,由于矫治力衰减,牙齿停止移动。结论　①牙齿向新鲜拔牙区移动速度快,而向已经愈合的拔牙区移动速度慢。②在矫治过程中,中等力较为合适;即使使用较大的力,也不一定引起较大的牙齿移动。     

Force magnitude and duration effects on amount of tooth movement and root resorption in the rat molar

OBJECTIVE: To test the hypothesis that there is no difference in the effect of different continuous moderate to very heavy forces on root resorption or amount of tooth movement. MATERIALS AND METHODS: In the study, 10, 25, 50 and 100 g mesial force were applied to the maxillary first molars of rat using nickel titanium closed-coil springs for 3 days, 14 days, and 28 days. The molars were extracted and the surface areas of the root resorption craters were measured using scanning electron microscope. The depths of the root resorption craters were measured using a three-dimensional laser scanning microscope. Tooth movement of the maxillary first molar was measured in relation to the maxillary second molar on digitized lateral cephalometric radiographs. RESULTS: Three days after force application, the tooth movement was not proportionally related to force magnitude. However, 14 days of force application resulted in significantly more tooth movement in the 10, 25, and 50 g force groups than in the 100 g force group. A force application of 10 g produced significantly more tooth movement at 28 days than all the other three force applications. The largest and deepest resorption craters were observed in the disto-buccal root followed by disto-palatal, middle-buccal, middle-palatal, and mesial root. Root resorption and tooth movement increased over time from 3 to 28 days. As heavier forces were applied, greater root resorption occurred. CONCLUSION: The hypothesis is rejected. The light mesially oriented forces, as applied in this study, produced more tooth movement and less root resorption compared with heavier forces.     

The monitoring of gingival crevicular fluid volume during orthodontic treatment: a longitudinal randomized split-mouth study

This randomized split-mouth study was aimed at evaluating whether an orthodontic appliance per se or orthodontic tooth movement can induce detectable changes in gingival crevicular fluid (GCF) volume, and thus whether GCF volume is a predictable biomarker for tissue remodelling incident to orthodontic tooth movement. Materials and Methods: Sixteen healthy orthodontic patients (7 females and 9 males; mean age, 17.7 years; range, 13-27 years) with the need for extraction of the first upper premolars were enrolled. One randomly chosen maxillary canine was subjected to a distalizing force by a 0.017 × 0.025 inch titanium-molybdenum alloy archwire and considered as the test tooth (TT). The contralateral canine, which was not subjected to any force but was included in an orthodontic appliance, was used as a control (CT). GCF sampling was performed at both mesial and distal sites of the CTs and TTs at baseline, immediately before applying the orthodontic appliance, and after 1 hour, 24 hours, and 7, 14, and 21 days. A Periotron was used to measure the GCF volume. A modest but significant increase in the GCF volume over time was seen in both the CTs (mesial sites) and the TTs (both mesial and distal sites) with no differences between the experimental teeth. Subclinical tissue inflammation consequent to the placement of the orthodontic appliance might be responsible for these GCF volume changes. The GCF volume does not appear to be a reliable biomarker for tissue remodelling during orthodontic treatment.     

Rapid Palatal Expansion in Mixed Dentition Using a Modified Expander: a Cephalometric Investigation

Abstract

Aim: To investigate light forces for experimental tooth movement.

Method: Light orthodontic forces of 1.2, 3.6, 6.5, and 10 g force (gf) were applied for 14 days to move rat molars, and the effects of the forces on the rate of tooth movement and changes of the periodontium were examined.

Results: In the early period, despite the different levels of force used in each group, there were no significant differences in tooth displacement. From hour 56 to day 14, the tooth displacement in the 1.2 gf group was significantly smaller than that in the other groups and the rate was nearly constant. The rates of tooth displacement in the 3.6, 6.5, and 10 gf groups fluctuated repeatedly, while the orthodontic forces gradually decreased.

Conclusion: Experimental tooth movement in rats, tipping without friction under light forces, were either constant or fluctuated in cycles of several days' duration. This is in contradiction to the three-phases-theory of tooth movement described in previous investigations using heavy forces.     

Duration of orthodontic force affecting initial response of nitric oxide synthase in rat periodontal ligaments

Clinical experience suggests that successful orthodontic tooth movement can be produced with a threshold for force duration at about 6 hours, however, the changes in the periodontal ligaments (PDL) during this period is still unclear. Nitric oxide (NO) is a marker of signal transduction relating to bone remodeling. The aim of this study was to observe the initial response of NO synthase (NOS) when PDL equilibrium would be broken against light continuous orthodontic force. Rat maxillary first molars were moved mesially with 2 gf Titanium-Nickel closed coil springs for 1, 3 and 6 hours. The number of NADPH-diaphorase positive cells in PDL was counted for investigating NOS activity. At the control group, NOS activity in the distal area of the PDL was significantly higher than that of the mesial area (P<0.001). The activity of mesial area increased at 1-hour group (P<0.01), while the activity of distal area dropped down at 3- and 6-hour groups (P 3-hour<0.05, P 6-hour<0.001), compared with the control group. These results suggest that 1-3 hours would be the threshold of force duration for tooth movement with light continuous force.     

Effects of different force magnitudes on corticotomy-assisted orthodontic tooth movement in rats

Objectives:To investigate the effects of light and heavy forces with corticotomy on tooth movement rate, alveolar bone response, and root resorption in a rat model.Materials and Methods:The right and left sides of 40 male Wistar rats were randomly assigned using the split-mouth design to two groups: light force with corticotomy (LF) and heavy force with corticotomy (HF). Tooth movement was performed on the maxillary first molars using a nickel-titanium closed-coil spring delivering either 10 g (light force) or 50 g (heavy force). Tooth movement and alveolar bone response were assessed by micro–computed tomography (micro-CT) at day 0 as the baseline and on days 7, 14, 21, and 28. Root resorption was examined by histomorphometric analysis at day 28.Results:Micro-CT analysis showed a significantly greater tooth movement in the HF group at days 7 and 14 but no difference in bone volume fraction at any of the observed periods. Histomorphometric analysis found no significant difference in root resorption between the LF and HF groups at day 28.Conclusions:Heavy force with corticotomy increased tooth movement at days 7 and 14 but did not show any difference in alveolar bone change or root resorption.     

Evening primrose oil effects on osteoclasts during tooth movement

This study was conducted to investigate the influence of supplemented evening primrose oil (EPO) on osteoclast expression during experimental tooth movement in rats. Forty-eight 10-week-old male Sprague-Dawley rats were divided into experimental and control groups. Animals in the experiment group were fed a 7.25 g/kg daily dose of EPO orally by gastric intubation for 20 days before orthodontic tooth movement. The animals in the control group received an equivalent volume of distilled water by the same method. On day 21, a 40-g mesial tipping force was applied to the maxillary right first molar of each rat. After loading, six animals in each group were sacrificed on days 0, 3, 7, and 14 with the appliance in situ. On day 3, the number of osteoclasts on the appliance side of the experimental group was significantly increased compared with the control group (P < .05). On day 7, the number of osteoclasts on the non-appliance side of the experimental group was significantly increased compared with the control group (P < .05). This study indicates that oral administration of EPO can increase the number of osteoclasts and may accelerate orthodontic tooth movement.     

Levels of interleukin-8 during tooth movement

A host-derived neutrophil-activating cytokine interleukin-8 (IL-8) is secreted mainly by monocytes and is considered to be important in regulating alveolar bone resorption during tooth movement. The aim of this study was to evaluate the levels of IL-8 during mechanical forces on periodontal tissues at different stages of orthodontic therapy. Ten canine teeth of patients having different Angle classifications were selected for the study. After the premolars were extracted, the maxillary/mandibular canines were tipped distally. Gingival crevicular fluid was sampled from mesial and distal gingival crevices of each canine separately at baseline and one hour, 24 hours, six days, 10 days, and 30 days after the application of the force. An enzyme-linked immunosorbent assay for quantitative detection of IL-8 was used. Although there was an increase in the concentration of IL-8 at tension (mesial) sites after one hour, 24 hours, six days, and 10 days, a decrease was observed at 30 days. Pressure (distal) sites did not demonstrate such an increase at any period except at 10 days. However, the concentration of IL-8 at both sites showed a similar decrease and approached each other at day 30. We concluded that local host response toward the orthodontic forces might lead an increase in IL-8 and neutrophil accumulation, and this may be one of the triggers for bone remodeling processes.     

Root resorption and tooth movement in orthodontically treated, calcium-deficient, and lactating rats

Previous studies have shown that chronic dietary deficiency of calcium can result in more rapid orthodontic tooth movement. The purposes of this study were to confirm that finding in a calcium-deficient, lactating rat model and to quantify the degree to which the area of root surface resorption is affected by these conditions. Thirty-five adult female Sprague-Dawley rats were divided into two groups: (1) nonlactating animals on a control diet and (2) lactating animals on a calcium-deficient diet. A 60-gm orthodontic force designed to tip maxillary molars mesially was applied for varying times. At sacrifice, tooth movement was quantified by measuring the space created between maxillary molars; percent bone ash was measured for each humerus, and root surface resorption was estimated by means of a morphometric technique to measure the area of cratering on the mesial roots of first molars. Both groups showed a typical two-phased tooth movement cycle lasting for 10 days, although the magnitude of movement was significantly greater (p less than 0.001) in the test animals. The "humerus" test from animals exhibited a significantly decreased (p less than 0.001) fat-free dry weight, ash, and percent ash weight. The test group also displayed a significantly reduced percent area of root surface resorption (p less than 0.05) by 7 and 10 days following appliance activation. These findings confirm earlier observations that lactation, coupled with calcium deficiency, will produce decreased bone density which is consistent with increased parathyroid hormone secretion.(ABSTRACT TRUNCATED AT 250 WORDS)     

大鼠正畸牙移动过程中牙周膜骨硬化蛋白的表达

目的 观察正畸牙移动过程中大鼠牙周组织中骨硬化蛋白（Sclerostin）的表达及分布,研究Sclerostin在正畸牙移动骨改建中的作用。方法 选取24只Wistar大鼠,安装加力装置,加载50 g力近中移动左侧第一磨牙,分别于安装加力装置后的0、1、3、5、7、14 d处死大鼠,用苏木精-伊红（HE）染色观察第一磨牙牙周组织形态学变化,抗酒石酸酸性磷酸酶（TRAP）染色观察破骨细胞的数量变化,免疫组织化学染色方法探究第一磨牙牙周膜中Sclerostin的表达变化。结果 HE染色显示随加力时间的延长压力侧骨组织破坏逐渐加重,免疫组织化学染色显示Sclerostin的表达逐渐增加,5 d时达到高峰,之后又逐渐降低,压力侧表达多于张力侧。结论 Sclerostin可能通过Wnt信号通路或者直接或间接控制骨形态发生蛋白参与了正畸牙移动骨改建过程。     

The effect of age on tooth movement and mineral density in the alveolar tissues of the rat

A comparison of tooth movement cycles and changes in alveolar tissue mineral densities was made between young (21 to 28 days old) and adult (90 to 100 days old) rats. An initial 60-g mesial tipping force was applied to the maxillary first molars; tooth movement was estimated by measuring the opening between first and second molars, and tissue mineral density by sample ash weight per cubic centimeter. A characteristic three-part tooth movement cycle was found in both groups of rats. This cycle consists of an early "instantaneous" movement that is a function of the viscoelastic properties of the tissues, a delay period during which little tooth movement occurs due to hyalinization and undermining resorption, and a late period during which bone remodeling and tooth movement occur. Compared with the adult group, the amount of "instantaneous" movement in the young rats was greater (P less than 0.001), the delay period was shorter, and the rate of late tooth movement was faster (P less than 0.001). The young rats had significantly lower (P less than 0.05) mineral densities before orthodontic treatment. Both groups experienced a slight but insignificant increase in density followed by rapid declines to a nadir that was not different between the groups. The young rats reached this point by day 5 and the adults by day 7. The point of lowest mineral density occurred in the treated alveolar tissues toward the end of the delay period for each group and was followed by a return to control values at rates that were not significantly different between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

大鼠正畸牙齿移动过程中Wnt3a和DKK1的表达

目的:观察Wnt3a和DKK1在大鼠正畸牙移动时牙周组织中的表达变化。方法:将30只健康雄性SD大鼠随机分为6组,即正畸加力1,3,5,7,10,14 d组。使用镍钛拉簧施加50 g力近中移动左侧上颌第一磨牙,以右侧上颌第一磨牙不加力为自身对照。通过免疫组化方法检测牙周组织中Wnt3a和DKK1蛋白的表达。结果:Wnt3a和DKK1在加力组和未加力组的牙周膜中都有表达。在张力区,Wnt3a和DKK1都先增加后减少,分别在第5天和第10天达到高峰;在压力区,Wnt3a先减少后增加,DKK1先增加后减少,分别在第5天和第10天达峰值。结论:Wnt3a和DKK1参与牙周组织的改建,提示Wnt信号通路可能是正畸牙周改建的调控途径之一。[关键词] Wnt3a DKK1 正畸牙齿移动 牙周组织改建     

局部应用二磷酸盐对鼠正畸牙移动影响的研究

目的 探讨局部注射Zoledronate溶液对鼠正畸牙齿移动距离与牙周组织形态的影响。方法 选用42只雄性Wistar大鼠，牵引其上颌第一磨牙近中移动。实验中分别将Zoledronate溶液及生理盐水注射入实验组（左侧）及对照组大鼠（双侧）上颌第一磨牙腭侧的粘骨膜下。注射于实验前3d开始，共进行9次，每3d一次。分别在加力0、3、7、14、21d后记录上颌第一磨牙移动距离，组织HE染色后，观察牙周组织形态学的改变。结果 ①实验组大鼠牙齿移动距离明显低于对照组。②实验组大鼠压力侧破骨细胞数在实验全过程中均低于对照组，而根分叉区破牙骨质细胞数除加力14d外，2组差异无显著性。③实验过程中Zoledronate溶液对破骨细胞和破牙骨质细胞以外的细胞作用不明显。结论 Zoledronate能有效地抑制支抗牙移动，减少压力侧牙槽骨表面破骨细胞数。     

Effects of different types of tooth movement and force magnitudes on the amount of tooth movement and root resorption in rats

Objective:To investigate differences in the amount of tooth movement and root resorption that occurred after tipping and bodily movement of the maxillary first molar in rats.Materials and Methods:Ten-week-old female Wistar rats were divided into two groups according to type of tooth movement and subdivided into four subgroups according to the magnitude of applied force. Nickel-titanium closed-coil springs exerting forces of 10, 25, 50, or 100 g were applied to the maxillary left first molars to induce mesial tooth movement. We designed a novel orthodontic appliance for bodily tooth movement. Tooth movement distance and root resorption were measured using microcomputed tomography and scanning electron and scanning laser microscopy.Results:The amount of tooth movement in the bodily tooth movement group was less than half that in the tipping tooth movement group. The greatest amount of tooth movement occurred in the 10-g tipping and 50-g bodily tooth movement subgroups, and the amount of tooth movement decreased with the application of an excessive magnitude of force. Conversely, root resorption increased when the heavier orthodontic force was applied in both groups. Root resorption in the tipping tooth movement group was approximately twice that in the bodily tooth movement group.Conclusions:Root resorption in the tipping tooth movement group was more pronounced than that in the bodily tooth movement group. Although the amount of tooth movement decreased when extremely heavy forces were applied, root resorption increased in both the tipping and bodily tooth movement groups in rats.     

Tissue response resulting from different force magnitudes combined with corticotomy in rats

Objectives:To evaluate the amount of hyalinization and root resorption after application of light and heavy forces during corticotomy-assisted tooth movement.Materials and Methods:Forty-eight male Wistar rats were used. Eight animals were the control group (day 0). The other 40 animals were randomly divided into two groups using the split-mouth technique: (1) corticotomy combined light force (CLF) and (2) corticotomy combined heavy force (CHF). Nickel-titanium closed coil springs that generated 10 g (light force) and 50 g (heavy force) were used for maxillary first molar movement. three-dimensional root volume was evaluated at 0, 14, and 28 days. Percent hyalinization was analyzed at 0, 3, 7, 14, 21, and 28 days by histomorphometric analysis.Results:The CHF group showed significantly lower cervical root volume than the CLF group at 28 days. Compared with day 0, the CHF group showed significantly less root volume in both distobuccal and distopalatal roots at 28 days. The hyalinization percentages in the CHF group were significantly higher than the CLF group at days 3 and 21.Conclusions:Heavy force combined with corticotomy produced more periodontal ligament hyalinization and root resorption than the light force combined with corticotomy.