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 pulsating electromagnetic fields on condylar growth in guinea pigs

The purpose of this study was to determine if a simple, noninvasive method could be developed for the application of pulsed electromagnetic fields that would lend itself to future clinical applications. Specifically, the modulation and control of condylar cellular metabolism and the stimulation of cellular proliferation were attempted in order to increase the amount of mandibular condylar growth. A pulsed electromagnetic field with a frequency of 100 hertz was applied for 8 hours per day to the mandibular condylar area of rapidly growing, male, Hartley guinea pigs. Ten guinea pigs were exposed for 10 days and a second group of 10 guinea pigs was exposed for 30 days. In addition, 5 guinea pigs were used as controls for each experimental period. During the experimental period the guinea pigs were placed in specially constructed, plastic animal holders with their heads positioned in an area of uniform magnetic field. After 10 days of pulsed electromagnetic field exposure, there were increases in vascularity, secretion of cartilagenous intercellular matrix, and woven-bone formation in the guinea pig condyle. After 30 days, there were continued but attenuated vascular and calcification responses with an increase noted in marrow hemopoietic elements. An increase in the number of osteoclasts was also noted after 10 days. This effect was transient and was not present at the end of the 30-day experimental period. The application of the pulsed electromagnetic field did not result in a significant increase in the overall anteroposterior or vertical size of the guinea pig mandible compared to controls. The results of this study suggest that it is possible to affect condylar cartilagenous and bony metabolism through the application of a noninvasive, pulsed electromagnetic field.     

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.     

张力作用下牙周组织破骨细胞分化因子、破骨细胞发生抑制因子表达变化的研究

目的:运用原位杂交的方法,观察破骨细胞分化因子(ODF)、破骨细胞发生抑制因子(OCIF)在正畸大鼠牙周组织改建过程中张力侧的表达变化,探讨ODF、OCIF与正畸牙周组织改建的关系。方法:8周龄成年健康雄性SD大鼠30只,随机分为对照组、牙齿移动1d组、3d组、5d组、7d组,共5组,每组6只。在大鼠上颌右侧第一磨牙与上颌切牙之间安置正畸矫治器装置,施力50g。在相应时间段处死实验动物,取材固定,进行原位杂交染色、图像分析。结果:在牙齿移动3d后,OCIF原位杂交染色在张力侧逐渐深染,OCIF mR-NA阳性细胞数量逐渐增多,OCIF阳性表达在5d时达到最高,并可见到有新骨形成;7d时OCIF阳性表达及分布情况与3d时相类似。张力侧牙周膜细胞、成骨细胞的ODF原位杂交染色阳性反应随天数的增加有逐渐增强趋势,并可观察到有ODFmRNA阳性破骨细胞出现,但表达变化并不明显。结论:ODF及OCIF参与了正畸牙周组织改建过程,OCIFmRNA在张力区随正畸牙齿移动表达升高具有时间依赖性。     

The effect of indomethacin (an aspirin-like drug) on the rate of orthodontic tooth movement

Prostaglandins (PGs) have been suggested as mediators of bone resorption. In addition, their presence in the periodontal tissues has also been demonstrated. To characterize the involvement of PGs in orthodontic tooth movement, indomethacin, an aspirin-like drug and a potent inhibitor of PG synthesis, was administered orally to six mongrel cats; another group of six animals served as controls. These animals were fitted with orthodontic appliances that consisted of coil springs stretching between the right side maxillary and mandibular canines and third premolars. The data for tooth-movement measurements were analyzed by repeated measures factorial analysis of variance. At the end of the 21-day experimental period, the rate of tooth movement in experimental animals was approximately one half of controls (P less than 0.01). Findings of this study imply a significant role for PGs in bone resorption during orthodontic therapy. It is recommended that aspirin-like drugs not be administered to patients undergoing orthodontic tooth movement as it may extend the treatment time.     

The effect of pregnancy on orthodontic tooth movement in rats

Introduction: The purpose of this study was to investigate the effect of pregnancy on orthodontic tooth movement in Wistar rats. Material and Methods: Forty eight female three-month old Wistar rats with an average weight of 250±25 gr were selected and randomly divided into two experimental (pregnant) and control groups (non-pregnant). Maxillary central incisors were tipped distally by insertion of springs exerting 30g force. Two, seven and fourteen days after spring insertion animals were sacrificed. Then the mesioincisal distance between maxillary incisors were measured. Subsequently, histological sections were prepared to count osteoclasts under a light microscope. The data on the extent of orthodontic tooth movement, and the number of osteoclasts were analyzed by independent sample t-test. Results: The results indicated that 2,7 and 14 days after force application there was no significant difference in orthodontic tooth movement between experimental and control groups (p>0.05). The number of osteoclasts were significantly lower in the experimental group 7 and 14 days after spring insertion (p<0.05). Conclusion: Pregnancy may decrease the amount of tooth movement in the linear phase but it is not statistically significant. The number of osteoclasts is significantly decreased during pregnancy. Key words:Pregnancy, rat, orthodontic tooth movement, osteoclast.     

HSP70在大鼠牙移动过程中的表达及其生物学意义

目的:研究大鼠磨牙移动过程中诱导型热休克蛋白70(HSP70)在牙周组织中的动态表达特点,推测其在牙周组织改建中的生物学意义。方法:建立大鼠牙移动的动物模型,采用免疫组织化学方法观察大鼠磨牙移动1、3、5、7、14d内诱导型HSP70在牙周组织中的动态表达及定位情况。结果:HSP70的表达在牙周膜受力早期呈强阳性,随后表达逐渐减弱,至14d为弱阳性;同一时期牙周膜的张力侧和压力侧诱导型HSP70的表达存在差异。结论:HSP70在大鼠磨牙受外力移动过程中呈现由强到弱的动态变化及区域性变化,这可能与牙周组织损伤的应激保护和改建过程中蛋白合成的需要有关。     

Effects of pulsed electromagnetic field vibration on tooth movement induced by magnetic and mechanical forces: a preliminary study

BACKGROUND: This study was designed to determine whether or not high-frequency and low-magnitude vibration affects orthodontic tooth movement caused by magnetic or/and mechanical forces. METHODS: Forty-four 7-week-old Wistar rats were randomly divided into four groups, with each group further divided into experimental and control subgroups. Neodymium-Iron-Boron (Nd-Fe-B) magnets and Sentalloy closed coil springs were placed between maxillary or mandibular first molars and incisors to activate tooth movement. The animals of experimental subgroups were exposed to the vibration induced by pulsed electromagnetic fields (PEMF) whilst the control subgroups were under normal atmosphere. The experiment lasted for 14 days and all of the animals were sacrificed for examination. The changes in the space between the molar and incisor were measured to indicate the amount of tooth movement. RESULTS: The coil springs, either with sham or active magnets, move molar much more than magnets alone, regardless of absence or presence of PEMF (p < 0.001). Under PEMF, the coil spring moved significantly more amount of tooth movement than that of coil-magnet combination (p < 0.01), as did the magnets compared to sham magnets (p < 0.019). Under a non-PEMF scenario, there was no significant difference in tooth movement between coil spring and coil-magnets combination, nor was there difference between magnets and sham magnets. CONCLUSIONS: It is suggested that the PEMF-induced vibration may enhance the effect of mechanical and magnetic forces on tooth movement.     

正畸牙齿移动过程中iNOS的表达及意义

目的:观察诱导型一氧化氮合酶(induc ib le n itric oxide synthase,iNOS)在大鼠正畸牙齿移动引发牙周组织改建过程中的表达,探讨NO/iNOS在正畸牙齿移动中的作用机制。方法:56只雄性SD大鼠随机分为8组。分别在正畸加力1,3,5,7,14,21,28 d后进行免疫组化染色和图像分析。结果:正畸加力3 d后,牙周组织细胞iNOS表达增强,7 d iNOS表达达到高峰(P<0.01),以后iNOS表达下降。结论:NO/iNOS参与了正畸牙周组织改建过程。     

正畸牙齿移动过程中内皮素的表达

目的:观察内皮素在大鼠正畸牙齿移动过程中牙周组织改建过程中的表达,探讨内皮素在正畸牙齿移动中的作用机制。方法:64只雄性SD大鼠随机分为8组。正畸加力1、3、5、7、14、21、28d组和对照组,牙周组织分别进行免疫组化染色、图像分析。结果:牙齿移动1d后内皮素表达开始增强,5d达到高峰(P<0.01),以后表达降低。结论:内皮素参与了正畸牙周组织改建过程。     

MMP-3及TIMP-1在正畸牙周组织改建过程中的表达

目的：探讨大鼠正畸牙周组织改建过程中基质金属蛋白酶－３（ＭＭＰ－３）和金属蛋白酶组织抑制因子－１（ＴＩＭＰ－１）与正畸牙齿移动的关系。方法：在ＳＤ成年大鼠上颌左侧第一磨牙上颌切牙之间安置正畸装置,建立大鼠上移动实验模型。于牙齿移动１、３、５、７、１４ｄ后取材分别进行免疫组化染色,图像分析,观察ＭＭＰ－３和ＴＩＭＰ－１表达的变化。结果：牙齿移动１ｄ后,牙周组织细胞ＭＭＰ－３表达增强,５ｄ后ＭＭＰ－３     

The effect of gingival fiberotomy on the rate of tooth movement

This study was designed to assess the gingival tissue resistance to remodeling in determining the rate of orthodontic tooth movement. Closed coil spring orthodontic appliances were stretched bilaterally between the first molars and incisors in the maxillary arches of 18 adult rats. The resistance of gingival tissues was eliminated around the randomly chosen first molars by a circumferential fiberotomy procedure. Movements of teeth were measured on submental vertex radiographs against the metallic implants that were placed in zygomatic processes. The data were analyzed by randomized block design analysis of variance. During the 30-day experimental period, the teeth that underwent the fiberotomy procedure moved faster (0.63 mm versus 0.51 mm, P less than 0.05), indicating that the resistance of gingival tissues may be a rate-limiting factor in orthodontic tooth movement.     

The effect of oral contraceptives on orthodontic tooth movement in rat

Introduction: The purpose of this study was to investigate the effect of ethinyl estradiol/norgestrel � used in some oral contraceptives- on orthodontic tooth movement in Wistar rats. Material and Methods: Forty eight female three-month old Wistar rats with an average weight of 250�25gr were divided into two experimental and control groups. One week prior to appliance insertion and during the appliance therapy period, 100 mcg/kg/day of ethinyl estradiol and 1mg/kg/days of norgestrel were administered to the experimental group by gavage; meanwhile the control group received an equivalent volume of Sodium Chloride 0.9 % (Saline). Maxillary central incisors were tipped distally by insertion of springs exerting 30g force. Two, seven and fourteen days after spring insertion animals were sacrificed. The mesioincisal distance between maxillary incisors were measured. Subsequently, histological sections were prepared for histomorphometric studies. Results: 14 days after force application the orthodontic tooth movement was significantly lower in the experimental group (p<0.05). The number of osteoclasts were significantly lower in the experimental group 2, 7 and 14 days after spring insertion (p<0.05). Conclusion: Ethinyl estradiol/norgestrel (oral contraceptives) can significantly decrease the amount of tooth movement in the linear phase. Key words:Oral contraceptives, orthodontic tooth movement, ethinyl estradiol, norgestrel.     

Alveolar bone loss induced by the orthodontic tooth movement under hypofunctional conditions in rats

PurposeTo examine the effect of occlusal hypofunctional conditions on orthodontic tooth movement and its relation to the structure and quality of alveolar bone using the rat model.Materials and methodsTwelve-week-old male Sprague-Dawley rats were divided into 4 groups of 8 animals each: normal occlusion (N) group, normal occlusion with tooth movement (M) group, occlusal hypofunction (H) group, and occlusal hypofunction with tooth movement (HM) group. In H and HM groups, the anterior bite plate and metal cap were attached to the maxillary and mandibular incisors using a light-curing composite resin to induce the occlusal hypofunctional condition. In M and HM groups, an orthodontic force was applied in a palatal direction to the buccal surface of the maxillary first molar (M1) using a nickel–titanium alloy wire. Micro-CT imaging and histomorphometric analysis using fluorescent bone labeling of the alveolar bone surrounding the M1s were performed in each group.ResultsTooth movement of M1 in HM group, was rather accelerated with enhanced tipping than in M group. Micro-CT analysis revealed significant decrease in bone volume fraction, bone mineral density and trabecular thickness of the interradicular bone in HM group among the experimental groups. The fluorescent labeling lines in the interradicular bone were decreased in number in H and M groups compared with N group. A few discontinuous irregular dotted lines-like labeling was observed in HM group.ConclusionThe occlusal hypofunctional condition accelerates orthodontic tooth movement of the respective teeth, while it results in severe bone loss in the surrounding alveolar bone.     

The Expression of MMP—3 and TIMP—1 During Orthodontic Periodontium Remodeling in Rats

目的：观察大鼠正畸牙周组织改建过程中基质金属蛋白酶—3(MMP—3)和金属蛋白酶组织抑制因子—1(TIMP—1)表达的变化，探讨MMP—3及TIMP—1与正畸牙齿移动的关系。方法：在SD成年大鼠上颌右侧第一磨牙与上颌切牙之间安置正畸装置，建立大鼠磨牙移动实验模型。于牙齿移动1、3、5、7、14d后取材分别进行免疫组化染色、图像分析。结果：牙齿移动1d后，牙周组织细胞MMP—3表达增强，5d后MMP—3表达达到高峰，此时破骨细胞脑浆亦呈强阳性表达。以后MMP—3表达有所下降，但仍高于对照组。而TIMP—1于牙齿移动3d后表达开始增强，7d后显著表达。结论：MMP—3及TIMP—1参与了正畸牙周组织改建过程，MMP—3在破骨细胞性骨吸收中起着重要作用。     

Ⅲ型胶原和基质金属蛋白酶-1在大鼠移动牙齿牙周组织中的表达

目的观察正畸移动大鼠牙齿过程中Ⅲ型胶原和基质金属蛋白酶(MMP)-1在上颌第一磨牙牙周组织中的表达和变化。方法建立大鼠磨牙移动模型,分为对照组和术后13、、57、、101、4 d组,用免疫组化方法观察各组中Ⅲ型胶原和MMP-1表达的变化。结果Ⅲ型胶原和MMP-1在移动牙牙周组织中的阳性表达强于对照组,且有时间依赖性。结论MMP-1参与了正畸牙周组织细胞外基质的代谢过程;Ⅲ型胶原在牙周组织改建中有重要作用。     

超声波加速正畸牙移动的实验动物研究

目的:在大鼠正畸模型中,对第一磨牙牙周组织施加超声波振动,观察超声波是否能加速正畸牙移动。方法:选用30只SD大鼠,建立以中切牙为支抗,移动单侧第一磨牙的正畸模型,分为常规正畸组和超声波振动组。于加力第7、14、28天测量牙移动距离,HE染色,trap染色破骨细胞计数,Masson染色观察第一磨牙牙周组织的变化。结果:牙周组织接受超声波振动刺激后,大鼠第一磨牙在第7、14、28天移动速率显著高于常规正畸组(P<0.05);同时可观察到超声波振动组中TRAP阳性的破骨细胞显著多于常规正畸组(P<0.05)。而Masson染色则显示,在加力第7天,常规正畸组和超声波振动组中,皆出现新生骨;但第14天时,前者新骨形成更加明显;直到第28天超声波后者出现更大规模的成骨反应。结论:超声波显著、并持续地增加牙周组织内破骨细胞形成数量,此效应可能导致了大鼠正畸模型的牙齿移动的加速,成功建立超声波加速正畸牙移动的实验动物模型。     

Local and chronic application of PTH accelerates tooth movement in rats

We previously reported that whereas systemic continuous infusion of parathyroid hormone (PTH) accelerated orthodontic tooth movement, systemic but intermittent injection of PTH did not increase the rate of tooth movement. Analysis of these data suggested that continuous administration of PTH could be applicable for orthodontic therapy. In the present study, we investigated whether local and chronic application of PTH(1-34) would accelerate orthodontic tooth movement. To increase the residence time of PTH in the injected area, we used methylcellulose (MC) gel (2% W/V) for a slow-release formulation of PTH. MC gel containing PTH (PTH-MC) continuously released biologically active PTH into the acceptor medium for more than 72 hrs in vitro. When male rats received a local injection of PTH-MC into the subperiosteum in the mesio-palatal region of the maxillary first molar (M1) every other day, M1 movement, which was mesially drawn by an orthodontic coil spring attached to the maxillary incisors, was accelerated in a dose-dependent manner. PTH-MC injection at 1 microg/400 g body weight caused a 1.6-fold increase in the rate of tooth movement. The acceleration of tooth movement by PTH-MC injection was marked on days 6, 9, and 12. Local injection of PTH dissolved in saline without MC did not significantly accelerate tooth movement on day 6 or later. Histological examination revealed active osteoclastic bone resorption and a widened periodontal space on the compression side of the periodontal tissue in the PTH-MC-injected rats. These results suggest that local injection of PTH in a slow-release formulation is applicable to orthodontic therapy.     

Changes in alveolar bone thickness due to retraction of anterior teeth.

In cases of bimaxillary protrusion, extraction of 4 premolars and orthodontic treatment with retraction of the anterior teeth is a widely used approach. However, there is controversy over whether the changes that occur in the anterior alveolar bone always follow the direction and quantity of tooth movement. Nineteen patients with dentoalveolar bimaxillary protrusion treated by extracting the 4 first premolars were evaluated with lateral cephalograms and computed tomography (CT). Cephalograms and CT scans were made before treatment and 3 months after retraction of the incisors. The measurements of the cephalograms showed that maxillary and mandibular incisors were retracted primarily by controlled tipping of the teeth. For all maxillary and mandibular incisors, we assessed the labial and the lingual alveolar plates at crest level (S1), midroot level (S2), and apical level (S3) for bone-thickness changes during retraction of the maxillary and mandibular anterior segments. In the mandibular arch, the labial bone maintained its original thickness, except the S1 measurements, which showed a significant decrease in bone thickness (P <.001). In the maxillary arch, the labial bone thickness remained unchanged. There were statistically significant decreases in lingual bone width in both arches after retracting the incisors. Some of the patients demonstrated bone dehiscence that was not visible macroscopically or cephalometrically. When tooth movement is limited, forcing the tooth against the cortical bone may cause adverse sequelae. This type of approach must be carefully monitored to avoid negative iatrogenic effects.     

Temporal and spatial mRNA expression of bone sialoprotein and type I collagen during rodent tooth movement.

To investigate the mechanism of bone formation during tooth movement, in situ hybridization was performed with digoxigenin-labelled RNA probes to detect bone sialoprotein (BSP) and type I collagen mRNAs in the dentoalveolar tissue of 72 Sprague-Dawley rats. An elastic band was inserted between the first and second right maxillary molars, and the teeth experimentally moved for 1, 3, and 7 days. The left first maxillary molar was used as the control. For the untreated molars, osteoblasts and osteocytes near the distal surface of the interradicular septum (IRS) expressed a high level of both BSP and type I collagen mRNAs, while cells on the mesial side of the IRS showed a low level of these mRNAs. For the first molars subjected to experimental tooth movement, a high level of type I collagen mRNA expression was found in the osteoblasts on the tension side of the IRS after 1 day of experimental tooth movement. A high level of BSP mRNA was detected after 3 days of experimental tooth movement. However, a negligible amount of both mRNAs was found in cells on the compression side. These results support the hypothesis that BSP may be involved in mineralization during physiological bone remodelling. On application of orthodontic force, osteoblasts were activated and induced to express BSP mRNA, which is involved in bone remodelling due to orthodontic force. In addition, response to the orthodontic force was observed in osteocytes.