Effect of pulsed electromagnetic fields on orthodontic tooth movement

The purpose of this study was to determine whether the application of a simple surgically noninvasive, pulsed electromagnetic field could increase both the rate and amount of orthodontic tooth movement observed in guinea pigs. In addition, the objective was to evaluate the electromagnetic field's effects on bony physiology and metabolism and to search for possible systemic side effects. Laterally directed orthodontic force was applied to the maxillary central incisors of a sample of 40 young male, Hartley guinea pigs (20 experimental, 20 control) by means of a standardized intraoral coil spring inserted under constricting pressure into holes drilled in the guinea pigs' two maxillary central incisors. During the experimental period, the guinea pigs were placed in specially constructed, plastic animal holders with their heads positioned in an area of uniform electromagnetic field. Control animals were placed in similar plastic holders that did not carry the electrical apparatus. The application of a pulsed electromagnetic field to the experimental animals significantly increased both the rate and final amount of orthodontic tooth movement observed over the 10-day experimental period. The experimental animals also demonstrated histologic evidence of significantly greater amounts of bone and matrix deposited in the area of tension between the orthodontically moved maxillary incisors. This increase in cellular activity was also reflected by the presence of significantly greater numbers of osteoclasts in the alveolar bone surrounding the maxillary incisors of the experimental animals. After a 10-day exposure to pulsed electromagnetic field, minor changes in serologic parameters relating to protein metabolism and muscle activity were noted. The results of this study suggest that it is possible to increase the rate of orthodontic tooth movement and bone deposition through the application of a noninvasive, pulsed electromagnetic field.     

Condylar cartilage response to continuous passive motion in adult guinea pigs: A pilot study.

This article reports on the development and testing of a continuous passive motion device suitable for experimental animals and on the effect of 1 week of continuous passive motion on the thickness of the condylar cartilage in adult guinea pigs. Continuous passive motion is currently used for postsurgical joint therapy and consists of moving a synovial joint passively and constantly through its normal range of motion. In this study continuous passive motion was applied to the temporomandibular joints of two experimental animals for 7 hours per day for 5 days. Two animals were restrained for the same amount of time that the experimental animals were on the continuous passive motion machines (control group 1), and two animals were allowed normal cage activity (control group 2). Six weeks later all animals were sacrificed. Each mandibular condyle was sectioned sagitally, and routine histologic sections were prepared with hematoxylin-eosin stain. Microscopic examination of the mandibular condylar cartilage of the animals placed on continuous passive motion showed a marked increase in thickness compared with the condylar cartilage found on the control animals. The condylar cartilage of the animals placed on continuous passive motion averaged 345 microm, and the controls averaged 232 microm. These findings demonstrate the application of continuous passive motion in an experimental model and provide interesting information regarding the response of the mandibular condyle to increased motion. More studies are necessary to further investigate the effect of continuous passive motion on the condylar cartilage.     

The effects of samarium-cobalt magnets and pulsed electromagnetic fields on tooth movement

The purpose of this study was to determine whether the application of either samarium cobalt magnets or pulsed electromagnetic fields could increase the rate and amount of orthodontic tooth movement observed in guinea pigs. In addition, the objective was to evaluate the effect of a magnetic field on bony physiology and metabolism and to monitor for possible systemic side effects. Fifteen grams of laterally directed orthodontic force were applied to move the maxillary central incisors of a sample of 18 young male Hartley guinea pigs divided into three groups: group 1, an orthodontic coil spring was used to move the incisors; group 2, a pair of samarium-cobalt magnets provided the tooth moving force; and group 3, a coil spring was used in combination with a pulsed electromagnetic field. The results showed that both the static magnetic field produced by the samarium-cobalt magnets and the pulsed electromagnetic field used in combination with the coil spring were successful in increasing the rate of tooth movement over that produced by the coil springs alone. The mechanism producing this effect appears to have involved a reduction in the “lag” phase often seen in orthodontic tooth movement. Both magnetically stimulated groups also showed increases in both the organization and amount of new bone deposited in the area of tension between the orthodontically moved maxillary incisors. (AM J ORTHOD DENTOFAC ORTHOP 1995;107:578-88.)     

The effect of prenatally increased oxygen tension on the development of the mandibular condyle

Twenty-four Long Evans/Turku rats were used to study the effect of prenatally increased oxygen tension on the mandibular condylar cartilage. Pregnant rats were exposed to increased oxygen tension in an air chamber for 14 days. The animals were returned to normal laboratory conditions after parturition. Three control and three experimental young rats were killed at the ages of 1, 5, 10, and 20 days for microscopic studies. Sagittal sections of the temporomandibular joint showed the cartilagenous condylar process to be narrower anteroposteriorly at 1, 5, 10, and 20 days postnatally, and it seemed to be bent backwards in experimental animals at the age of 1 day, in comparison with controls. The mesenchymal and chondroblast cell layers were thickened at the ages of 1, 5, 10, and 20 days. The findings indicate that prenatally increased oxygen tension increases the postnatal mesenchymal cell population and support the hypothesis that the size of the mandible is partly determined by the number of mesenchymal cells present during the prenatal phase.     

脉冲电磁场和功能矫形对大鼠下颌髁突影响的扫描电镜研究

目的:用扫描电镜研究脉冲电磁场和功能矫形对下颌髁突生长发育的影响.方法:将20只青春期雄性SD大鼠随机等量分为对照组,脉冲电磁场(Pulsating Electromagnetic Fields,PEMF)组,功能矫治器(Functional Appliances,FA)组,二者共同作用(PEMF+FA)组四组,PEMF组大鼠头部每天8小时处于PEMF环境中,FA组大鼠每天戴矫治器10-12小时,10天后用扫描电镜观察大鼠髁突表面和矢状断面.结果:脉冲电磁场和功能矫形能够使髁突表面纤维组织及软骨细胞明显增生,能促进细胞外基质的钙化.结论:脉冲电磁场和功能矫形能够促进髁突的生长发育,并且二者有协同作用.     

Gene therapy to enhance condylar growth using rAAV-VEGF

OBJECTIVE: To test the hypothesis that the introduction of specific vascular growth inducting genes would favorably affect mandibular condylar growth in Sprague-Dawley (SD) rats over a limited experimental period. Therefore, the aim of this study is to examine the effect of gene therapy on condylar growth by means of a morphological assessment. MATERIALS AND METHODS: Ninety 35-day-old female SD rats were randomly divided into three groups, which received any of the injections of recombinant adeno-associated virus mediated vascular endothelial growth factor (rAAV-VEGF), rAAV mediated enhanced green fluorescence protein (rAAV-eGFP), or phosphate-buffered saline (PBS) into both mandibular condyles. Each group of rats was sacrificed on the following experimental days: 7, 14, 21, 30, and 60. Left halves of the mandibles were isolated and digital pictures were obtained in a standardized manner. RESULTS: The length of condylar process (B-F) as well as mandibular length (A-F) significantly increased on day 30 and continued to increase until the end of the experiment. Moreover, the width of condyle (Q-R) had increased significantly from day 30 and lasted to day 60. Condylar length (C-D) was found to be significantly longer on day 60. CONCLUSIONS: Gene therapy with VEGF stimulates condylar growth at will. The rAAV-VEGF is an excellent candidate for future gene therapy to induce mandibular growth.     

Matrix formation in the mandibular condyle of the rat (35S) - sulfate incorporation studies.

The matrix formation activity of the mandibular condylar cartilage was investigated using radioactive sulfate incorporation. The condylar cartilage was studied at various developmental stages; as an autotransplant, in situ and on a chemically defined medium. An initial decrease in the cpm/DNA was followed by an increase, until a maximum was attained for all groups, between the 14th and 17th days. Thereafter, the matrix formation activity decreased. There was a surprising likeness in the patterns of activity for all the samples investigated. This tends to support the hypothesis that cartilagenous growth seem to be regulated, at least to some extent by one or more humoral factors.     

脉冲电磁场和功能矫形对大鼠下颌髁突IGF-I表达影响的研究

将２０只青春期雄性ＳＤ大鼠随机等量分为对照组,脉冲电磁场（ＰＥＭＦ）组,戴功能矫治器（ＦＡ）组及二者共同作用（ＰＥＭＦ＋ＦＡ）组,研究脉冲电磁场和功能矫治器对大鼠下颌髁突胰岛素样生长因子Ｉ（ＩＧＦ—Ｉ）表达变化。经过１０天的实验,结果发现ＰＥＭＦ和功能矫治器都可显著性增加髁突软骨细胞的ＩＧＦ—Ｉ表达,提示二者具有协同作用,为临床联合使用ＰＥＭＦ和ＦＡ进行下颌骨的矫形治疗提供了实验依据。     

静张应力对大鼠髁突软骨细胞增殖效应调节研究

目的　探讨静张应力环境对髁突软骨细胞增殖效应的影响。方法　将第4代大鼠下颌髁突软骨细胞在细胞膜式张应力施加装置上培养,检测不同血清浓度及持续不同的静张应力(5 kPa、10 kPa)在0~12 h内对髁突软骨细胞增殖活性的影响。结果　低血清培养基中,随培养时间的延长,硅胶膜上髁突软骨细胞的增殖活性受到抑制;短期(2h)的静张应力(5 kPa、10 kPa)对髁突软骨细胞细胞周期的调控影响不大;0~10 h内5 kPa静张应力组软骨细胞增殖指数随着张应力作用时间的延长不断上升,增殖指数峰值位于10 h处;0~8 h内10 kPa静张应力组软骨细胞增殖指数随着张应力作用时间的延长不断上升,增殖指数峰值位于8 h处;5 kPa静张应力组较10 kPa静张应力组对髁突软骨细胞具有更大的促增殖作用。结论　静张应力可以调节髁突软骨细胞的增殖活性。     

Effect of pulsed electromagnetic field on orthodontic tooth movement through transmission electromicroscopy

This experiment is to observe the effect of pulsed electromagnetic field (PEMF) on orthodontic tooth movement of guinea pigs through transmission electron microscope (TEM). 14-days observations indicate that PEMF could accelerate the rate of orthodontic tooth movement as a result of the increase in quantity of active cell without changing the ultrastructures of cells and have no unfavorable effects on periodontal tissues.     

Effects of growth hormone and ultrasound on mandibular growth in rats: MicroCT and toxicity analyses

It has been shown by previous studies that mandibular growth can be enhanced by the systemic administration of recombinant growth hormone (rGH) and/or local application of therapeutic low intensity pulsed ultrasound (LIPUS). The purpose of this study was to determine if local injection of rGH and application of LIPUS to the temporomandibular joint (TMJ) would synergistically enhance mandibular growth. In an animal study, the effect of rGH, LIPUS, and combination of rGH and LIPUS on male Sprague–Dawley rats was observed. Mandibular growth was evaluated by measuring total hemimandibular and condylar bone volume and bone surface area as well as condylar bone mineral density (BMD) after 21 days on dissected rats’ mandibles using micro-computed tomography (MicroCT). The expression of c-jun mRNA extracted from the liver of each of these rats was also quantified by real-time polymerase chain reaction to evaluate possible systemic effect of local rGH administration. Significant growth stimulation was observed in the mandibular and condylar bone of the animals treated with rGH, LIPUS, and rGH/LIPUS combined when compared with the control group. Bone volume, surface area, condylar bone mineral density, and c-jun expression were also compared between the treatment groups and the control in the liver. The results suggest that mandibular growth may be enhanced by injection of rGH or LIPUS application. The current study although showed synergetic effect of rGH and LIPUS application in increasing mandibular condylar head length, there was no significant changes in mandibular bone volume using both treatments together when compared to the two individual treatments. Moreover, combined rGH and LIPUS decreased condylar bone mineral density than each treatment separately. Future research could be directed to investigate the effects of different rGH doses and/or different LIPUS exposures parameters on lower jaw growth.     

导下颌向前对生长期大鼠髁突软骨结缔组织生长因子表达的影响

目的:通过建立导下颌向前的Sprague-Dawley (SD)大鼠的动物模型进行免疫组化实验,观察结缔组织生长因子(CTGF)在髁突软骨中分布的变化,探讨CTGF对前伸下颌后的髁突软骨的影响。方法:建立SD大鼠动物模型,选取45只5周龄SD 雌性大鼠,体重约100 g,随机分为对照组(20只)和实验组(25)只,组内再随机平均分为5组(3、7、14、21 和30 d)。实验组动物24 h佩戴改良可摘式上颌斜面导板矫治器,对照组动物不做处理。免疫组化染色标记CTGF,观察髁突软骨各层CTGF的表达变化。对CTGF的阳性表达量进行半定量分析。结果:对照组和实验组中髁突软骨组织中均有CTGF的表达,主要分布于肥大层和增殖层。实验组不同时间点髁突肥大层和增殖层中CTGF的平均光密度值分别高于对照组的平均光密度值(P<0.05 ) 。与对照组相比,实验组7 d后髁突肥大层和增殖层中CTGF的表达开始上升,到第14天达到最高,之后CTGF表达回落,但仍高于对照组(P<0.05 )。实验3 d、30 d,肥大层和增殖层中CTGF实验组与对照组相比无统计学差异。结论:CTGF可能参与了功能负荷改变所导致的髁突软骨适应性改建活动。     

Changes in condylar cartilage after anterior mandibular displacement in juvenile pigs

Adaptive remodelling of the mandibular condyle in response to mandibular advancement is the mechanism exploited by orthodontic forward displacement devices.ObjectiveThis work investigated the expression of collagens, matrix metalloproteinases and vascular endothelial growth factor during this process.DesignTwenty juvenile pigs were randomly divided into two experimental groups, where the treatment group was fitted with mandibular advancement splints, and the control group was not. Changes in the mRNA content of condylar cartilage tissue was then were measured by real-time PCR using specific primers after 4 weeks of treatment.ResultsThe temporal pattern of the expression of Col1 and MMP13 during condylar adaptation coincided with that during natural condylar growth. The amount of the expression of Col10 during condylar adaptation was significantly lower (p < 0.05), whereas the expression of Col2, MMP8 and VEGF was significantly higher compared to natural growth (p < 0.05).ConclusionsIt is suggested that condylar adaptation in growing pigs triggered by mandibular forward positioning results not only from passive adaptation of cartilage, but also involves growth affected processes. Our results showed that mechanical strain produced by mandibular advancement induced remodelling and revascularization in the posteriocranial mandibular condyle. These results are mostly consistent with former published histological and histomorphometrical analyses.     

Effects of experimental defects of the articular disc of the temporomandibular joint in rats

Triangular defects were made in different locations of the disc in rat temporomandibular joints. After 3 months the following effects were observed. Central defects had become rounded without gross changes in the mandibular head. Peripheral defects were enlarged towards the centre, occasionally accompanied by condylar hyperplasia. Microscopically the cartilagenous covering of the mandibular head in all operated cases was characterized by thickening, dispersion of cells normally closely packed in the intermediate zone, and the constant appearance of a tear parallel to the surface.     

下颌持续前导对成年大鼠髁突软骨骨形态发生蛋白表达及超微结构的影响

目的 观察成年期大鼠在下颌持续前导作用下髁突软骨的改建以及超微结构的变化。方法 将30只9周龄SD大鼠随机分为实验组和对照组,实验组佩戴上颌斜面导板,对照组不做任何处理,分别在第3、7、14、21、30天处死动物并取材,免疫组织化学染色检测骨形态发生蛋白2（BMP-2）在髁突中的表达及分布,透射电镜观察髁突软骨细胞的超微结构,Micro CT分析髁突骨质的变化。结果 与对照组相比,实验组髁突中部和后部软骨增生明显,软骨细胞BMP-2阳性细胞率及灰度值在第7天开始增多,随时间延长而增强,髁突软骨细胞的超微结构出现细胞核固缩,核周微丝变少、脂滴变小、内质网腔隙肿胀、细胞外基质增宽变多等。Micro-CT显示实验组的新生骨和骨小梁厚度、骨小梁数量和分离度随时间延长而增加。结论 在下颌持续前导下,成年期大鼠髁突软骨出现增生性改建,并存在BMP-2的高表达。     

Collagenolytic and phosphatase activity in the rat mandible after functional protrusion

The effect of chronic mandibular protrusion on the collagenolytic and phosphatase activity of several mandibular bone sites and the condylar cartilage was evaluated. Ninety-three male Sprague-Dawley rats were equally divided into two experimental and one control group. One experimental group wore a protrusive appliance for 2 weeks, the other for 4 weeks. All animals were killed at 59 days of age. Collagenolytic, alkaline and cid phosphatase activities were determined in the condylar cartilage, the subchondral bone and condylar neck, and in the gonial angle and coronoid process. In the cartilage and subchondral bone, the protrusive appliance caused a reduction in collagenolytic and alkaline phosphatase activity. In the condylar neck, it caused a large increase in collagenolytic activity and a decrease in alkaline phosphatase activity in both experimental groups. In the gonial angle and coronoid process, the appliance increased the collagenolytic activity only in the 2-week group. In the 4-week group, the alkaline phosphatase and collagenolytic activities were not different from the activities in those tissues in the control animals. Thus a protrusive appliance induced quantitative changes in enzyme activities in condylar cartilage and mandibular bone. The increase in collagenolytic activity (representing increased bone resorption) occurred typically in areas of muscle attachment and might have been the result of the neuromuscular changes induced by the protrusive appliance. The recovery to normal values of collagenolytic activity in the coronoid process and gonial angle of the 4-week group suggests that at these sites the muscles (and subperiosteal bone) might have adapted to their new biomechanical environment after the longer period of appliance wear.     

Forward deviation of the mandibular condyle enhances endochondral ossification of condylar cartilage indicated by increased expression of type X collagen

OBJECTIVE: Using type X collagen as a marker, this research was designed to examine the alteration of condylar growth in response to mandibular condylar forward positioning. METHODS: One hundred female Sprague-Dawley rats with 5 weeks of age were randomly divided into five experimental and five control groups. In the experimental groups, bite jumping appliances created forward positioning of the condyle. The experimental rats, together with the age-matched controls, were sacrificed on days 3, 7, 14, 21 and 30, respectively. Tissue sections were cut in the sagittal plane through the mandibular condyle and were processed for in situ hybridization and immunostaining of type X collagen and then for quantitative imaging analyses. RESULTS: (1) Both type X collagen mRNA in situ hybridization signals and type X collagen immunostaining were localized within the hypertrophic zone of the condylar cartilage. (2) With condylar forward positioning, the level of type X collagen mRNA signals (8,541 +/- 74 microm(2) at peak) was 300% higher than that in the controls (2,117 +/- 78 microm(2) at peak); type X collagen immunostaining in condylar advancing groups (54,864 +/- 134 microm(2) at peak) was 254% more than that in the controls (15,470 +/- 121 microm(2) at peak). (3) The amount of type X collagen mRNA signals and immunostaining in experimental and control groups reached the highest levels at day 14 and day 21, respectively, indicating that an increase in endochondral ossification occurred 21 days after condylar forward deviation. CONCLUSION: Condylar forward repositioning provokes an enhanced maturation of condylar chondrocytes resulting in increased synthesis of type X collagen, a extracellular protein that attributes to endochondral ossification.     

The effect of continuous bite-jumping in adult rats: a morphological study

The aim of this study was to determine the mandibular morphology before, during, and after bite-jumping in nongrowing species. Fifty-two adult female Sprague-Dawley rats were divided into four experimental groups and four control groups. The experimental groups were fitted with fixed bite-jumping devices that protruded the mandible. The animals were sacrificed on days 3, 14, 30, and 60. Right halves of the mandible were harvested and freed of soft tissue. Digital pictures were obtained in a standardized manner. Selected linear and angular measurements were made. There were no morphological differences between the controls and experimental group on days 3 and 14. The length of condylar process increased significantly on day 30 and remained so on day 60 in the experimental group. The angulation of the condylar process was significantly affected because of increased apposition of bone in the middle and especially the posterior parts of the condyle. Thus, bite-jumping of the mandible in adult rats affects the size and angulation of the condylar process because of differential apposition of bone on the condylar head.     

机械压力对大鼠下颌髁突软骨细胞增殖活性影响的体外研究

目的:建立体外培养细胞加力装置,在细胞水平探讨机械力作用下大鼠髁突软骨细胞功能代谢的变化。方法:采用流式细胞术检测不同时段、不同力值的机械压力对体外培养的大鼠髁突软骨细胞增殖活性的影响。结果:在一定时间、0～2.03×10-4Pa(0～207g/cm2)力值范围内,随着机械压力的增大,受压的下颌髁突软骨细胞增殖活性增高,以持续压力作用6h最为明显;当持续压力作用于下颌髁突软骨细胞24h后,细胞增殖活性则出现下降。结论:在一定时间、一定力值范围内,随着机械压力的增大,受压的下颌髁突软骨细胞增殖活性有逐渐增高的趋势;当持续压力作用超过一定的范围,细胞增殖活性则出现下降趋势