Biomechanical study on orthodontic tooth movement by means of numerical simulation. Effects of principal stresses in periodontal membrane

The effect of biomechanical factors on tooth movement has not been clarified in a quantitative manner. This study was designed to investigate the stresses affecting tooth movement, using a numerical simulation. The influence of decrease in Young's modulus of the periodontal membrane on canine retraction was also examined through the simulation. A two-dimensional finite element model was constructed based on the average anatomic morphology of Japanese canine. A numerical simulation program based on the finite element method was developed for the orthodontic tooth movement. The stresses in the periodontal membrane were evaluated. The principal stress of which absolute is larger was selected as a reference stress. Each nodal point at the alveolar bone-periodontal membrane interface was repositioned in the direction of reference stresses, in response to discrepancy between assumed thresholds and the reference stresses. Moment to force (M/F) ratios at the bracket position of this model were examined for evaluating force conditions. Simulation of tooth movement were executed under three force conditions with different M/F ratios for distal movements and two force conditions for vertical movements. Three types of canine retraction, tipping movement, bodily movement and root movement, were displayed with the numerical simulation. Extrusion and intrusion were also displayed. Analytic movements of the canine were close to the actual tooth movements that have been reported, utilizing the principal stresses with the thresholds of the maximum and minimum principal stresses being about +0.4 gf/mm2 and -0.4 gf/mm2. The decrease in the Young's modulus of the periodontal membrane changed bodily movement to tipping movement under the same force conditions. These results indicate that the value and the direction of the principal stress in the periodontal membrane are key determinants of tooth movement and this numerical simulation is useful for investigating the influence of the biomechanical factors on tooth movement.     

Effects of gradually increasing force generated by permanent rare earth magnets for orthodontic tooth movement

OBJECTIVE: To examine the effects of gradually increasing force generated by permanent rare earth magnets for orthodontic tooth movement by using a novel experimental rat model and computer simulation. MATERIALS AND METHODS: Fifty-five male rats (age 18 weeks) were used as animal experiments. Magnetic (experimental groups) or titanium (control group) cuboids (1.5 x 1.5 x 0.7 mm) were bonded to the lingual surface of the maxillary first molars. The initial distance between materials was 1.0 mm, generating 4.96 gf (experimental group I), or 1.5 mm, generating 2.26 gf (experimental group II). Tooth movement was measured and periodontal structures were observed with microfocus x-ray computed tomography radiographs. RESULTS: The distance between the magnets decreased with time in experimental groups I and II (P < .001), whereas there was no tooth displacement in the control group. Experimental group I showed rapid tooth movement in the initial phase followed by slower tooth movement. Experimental group II showed gradual tooth movement. Horizontal sections on microfocus computed tomgraphy radiographs revealed no pathological changes, such as root resorption, on the compressed side in the experimental groups. CONCLUSIONS: The initial light force and gradual increasing force in magnetic attractive force induced effective tooth movement in rats without inducing any pathological changes.     

Human tooth movement in response to continuous stress of low magnitude.

Conventional orthodontic therapy often uses force magnitudes in excess of 100 g to retract canine teeth. Typically, this results in a lag phase of approximately 21 days before tooth movement occurs. The current project was undertaken to demonstrate that by using lower force magnitudes, tooth translation can start without a lag phase and can occur at velocities that are clinically significant. Seven subjects participated in the 84-day study. A continuous retraction force averaging 18 g was applied to 1 of the maxillary canines, whereas a continuous retraction force averaging 60 g was applied to the other. The magnitude was adjusted for each canine to produce equivalent compressive stresses between subjects. Estimated average compressive stress on the distal aspect of the canine teeth was 4 kPa or 13 kPa. The moment-to-force ratios were between 9 and 13 mm. Tooth movement in 3 linear and 3 rotational dimensions was measured with a 3-axis measuring microscope and a series of dental casts made at 1- to 14-day intervals. The results showed a statistical difference in the velocity of distal movement of the canines produced by the 2 stresses (P =.02). The lag phase was eliminated and average velocities were 0.87 and 1.27 mm/month for 18 and 60 g of average retraction force. Interindividual velocities varied as much as 3 to 1 for equivalent stress conditions. It was concluded that effective tooth movement can be produced with lower forces and that because loading conditions were controlled, cell biology must account for the variability in tooth velocities measured in these subjects.     

An evaluation of the biomechanical response of the tooth and periodontium to orthodontic forces in adolescent and adult subjects.

Abstract

This study was designed to quantify the magnitude of tooth mobility in adolescents and adults, and to investigate the differences in the biomechanical response of tooth and periodontium to orthodontic forces. The initial displacement of the maxillary central incisor was measured in 50 adolescent and fifty adult patients and the biomechanical properties of the periodontium were examined using the finite element method (FEM) and supporting experimental data. The magnitude of tooth mobility was significantly greater in the adolescent group than in the adult group. By integrating the differences in tooth mobility in both subject groups with analytical tooth displacements, the Young's modulus of the periodontal ligament (PDL) was demonstrated to be greater in the adults than in the adolescent subjects. The differing biomechanical properties of the PDL in adults were demonstrated to result in almost equivalent or somewhat increased stress levels in the PDL in adult subjects. It is suggested that this might produce a reduction in the biological response of the PDL and thus lead to a delay in tooth movement in adults.     

Human interleukin-1 beta and interleukin-1 receptor antagonist secretion and velocity of tooth movement

The cytokines interleukin-1 beta (IL-1 beta) and IL-1 receptor antagonist (IL-1RA) probably play a part in orthodontic tooth movement. Here, the force magnitudes and the area of force application in the compressed periodontal ligament (PDL) were controlled and the velocity of tooth movement correlated with concentrations of IL-1 beta and IL-1RA in the gingival crevicular fluid (GCF). Seven individuals undergoing orthodontic treatment involving maxillary first premolar extractions and distal movement (bodily retraction) of the maxillary canines participated in the 84-day study. For each participant, continuous retraction forces were applied so that they received equivalent PDL stresses of 13 kPa for one canine and 4 kPa for the other. GCF cytokine concentrations from experimental and control teeth were expressed relative to total protein in the GCF and compared using an 'Activity Index' (AI)=Experimental (IL-1 beta/IL-1RA)/Control (IL-1 beta/IL-1RA). The results showed that the velocity of tooth movement in an individual was related to their AI. The correlation between AI and tooth movement was stronger from the distal (R(d)=0.78) than from the mesial (R(m)=0.65) of retracted teeth. The results demonstrate that equivalent force systems produce individual differences in cytokine production, which correlate with interindividual differences in the velocity of canine retraction.     

Three-dimensional analysis of orthodontic tooth movement based on XYZ and finite helical axis systems

The purpose of this study was to demonstrate the advantage of the finite helical axis (FHA) system in the biomechanical analysis of orthodontic tooth movement by comparing it with the rectangular coordinate (XYZ) system. Ten patients (6 females and 4 males, mean age 23 years 7 months) were selected. Maxillary canine retraction using light continuous forces of two different magnitudes (0.5 and 1 N) was used to retract the right and left maxillary canines in subjects who required maximum posterior anchorage. The findings were compared based on midpalatal implants that provided a fixed reference for measurement. The significance of the difference between the results with the two different force magnitudes was determined using Wilcoxon's signed-rank test. With both the XYZ and the FHA system, no significant differences in the amount of distal movement of the canines over 2 months were found between the two force magnitudes. However, the results showed that the canine was likely to incline distally during tooth retraction with a force of 1 N compared with a force of 0.5 N (P < 0.05). With the FHA system, the result indicated that the canine was likely to incline palatally during tooth retraction with a force of 0.5 N compared with a force of 1 N (P < 0.05). In this study, the combination of these two different approaches for describing tooth movement clearly showed a difference between light continuous forces of 0.5 and 1 N.     

Age effect on orthodontic tooth movement in rats

Orthodontic procedures seem to be more time-consuming in adults than in juveniles. This might be related to delay in the initial tissue response or to a slower turnover of the bone and periodontal ligament in adults. To study this problem, we studied orthodontic tooth movement in two groups of 30 rats, aged 6 wks and 9-12 mos, respectively. At one side of the maxilla, 3 molars together were moved mesially with a standardized orthodontic appliance delivering a force of 10 cN. The other side served as a control. The results showed a faster initial tooth movement in juvenile than in adult animals. However, once tooth movement had reached the linear phase, the rate of tooth movement was the same in both groups. The results indicate that, besides a delay in the onset of tooth movement in adult animals, tooth movement could be equally efficient in adults once it had started.     

消炎痛对正畸牙齿移动中牙周组织超微结构的影响

目的：在细胞水平上进一步研究消炎痛影响正畸牙周组织改建与牙齿移动的机理。方法：通过扫描和透射电子显微镜（ＳＥＭ和ＴＥＭ），观察牙周组织细胞超微结构的改变。结果：ＳＥＭ和ＴＥＭ观察表明，２５ｇ力可引起兔切牙牙周组织细胞超微结构发生改变，在压力和张力侧均出现损伤和修复性反应，消炎痛对正畸牙周组织细胞超微结构变化的影响包括两方面，一方面抑制了牙周组织的炎症反应和损伤，另一方面也抑制了组织的修复过程，从而抑制了正畸牙周组织改建和牙齿移动。结论：消炎痛可以抑制牙周组织对正畸力的反应，使牙齿移动速度减慢，在临床治疗中，对长期服用消炎痛类药物的患者，可能因此影响矫治效果，应引起足够重视。     

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。     

The effect of cortical activation on orthodontic tooth movement

OBJECTIVE: Cortical activation is one of the procedures to accelerate tooth movement by manipulating the cortical bone. In this study, the effect of cortical activation on orthodontic tooth movement was investigated clinically and histologically in the surrounding bony tissue. MATERIALS AND METHODS: In the lower and upper jaws of two beagle dogs, cortical activation was applied to the buccal and lingual side of the alveolar bone in the right jaw where 12 holes were made on each cortical plate 4 weeks after the extraction of all the second bicuspids while under deep anesthesia. All third bicuspids on both jaws were forced to move forward by a 150-g force using NiTi coil spring with/without guiding wire. The tooth movement was measured and the animals were killed after tooth movement. RESULTS: Rapid initial tooth movement was apparent after cortical activation. However, after 6 months of cortical activation, the cell number and cellular activity of the surrounding periodontal tissue were decreased. CONCLUSIONS: This experiment showed that rapid initial tooth movement was apparent following the application of orthodontic force after cortical activation but the cellular activity and fibroblast structure were abnormal in the surrounding periodontal tissue.     

增龄性因素对正畸牙齿移动过程中牙周组织细胞凋亡的影响

目的 探讨增龄性因素对大鼠正畸牙齿移动过程中牙周组织细胞凋亡的影响.方法 建立不同年龄组的正畸牙齿移动动物模型,在实验加力1d、3d、7d、14d及28d后,采用TUNEL方法检测牙齿移动过程中牙周组织细胞凋亡情况.结果 青少年组实验侧加力3d时,压力区细胞凋亡率显著增高,7d开始呈下降趋势,28d时细胞凋亡率基本同对照侧;成年组加力3d开始压力区细胞凋亡率逐渐增加,28d时细胞凋亡率开始降低.在牙齿移动过程中,成年组实验侧牙周组织细胞凋亡率明显高于青少年组.结论 细胞凋亡可能参与了正畸牙齿移动,但是增龄性因素使得成年组牙周组织细胞凋亡增加,进而影响各类细胞比例,改变牙周组织改建的速度和效果,使得牙齿移动速度减慢.     

大鼠正畸牙移动过程中牙周组织内转化生长因子β1的变化

目的 了解大鼠正畸牙移动过程中转化生长因子β１（ｔｒａｎｓｆｏｒｍｉｎｇ ｇｒｏｗｔｈ ｆａｃｔｏｒβ１,ＴＧＦ－β１）在牙周组织内的变化,探讨ＴＧＦ－β１在正畸牙移动过程中的作用。方法 对大习正畸牙移动不同阶段的牙及牙周组织联合切片,进行免疫组织化学研究。结果 正畸牙移动过程中,牙周膜内ＴＧＦ－β１表达增加。强力第５～１０天,张力区ＴＧＦ－β１表达增加的幅度明显大于压力区。结论 ＴＧＦ－β１在正     

大鼠正畸牙移动过程中牙周组织NGF的表达变化

目的了解大鼠正畸牙移动过程中牙周组织内神经生长因子(nerve growth factor,NGF)的变化,探讨NGF在正畸牙移动过程中的作用。方法将85只雄性SD大鼠随机分为17组,其中空白对照组(0d组)、实验加力和对照不加力组各6h、12h、24h、3d、5d、7d、14d、21d组。选择左上第一磨牙作为实验牙,制备大鼠正畸牙移动不同时间牙周组织切片,进行免疫组织化学研究。结果正畸牙移动过程中,牙周组织内NGF表达发生改变。NGF表达量在正畸模型加载后迅速上调,实验组和对照组分别于5d、1d时表达水平达到最高,所有观察区域牙周膜内NGF表达显著增加,且实验组明显高于对照组。结论NGF在正畸牙移动过程中牙周组织改建的多个阶段起作用,参与了牙周膜早期的炎症反应及修复和晚期的改建。     

偏侧咀嚼对正畸牙移动影响的实验研究

目的通过建立偏侧咀嚼大鼠模型,探讨偏侧咀嚼对正畸牙移动过程的影响。方法选择30只6～8周龄,（250±10）g,雄性SD大鼠,随机分为实验组与对照组,每组各15只。通过拔除实验组大鼠右下颌所有磨牙使右上颌第一磨牙丧失咬合接触建立大鼠偏侧咀嚼动物模型,同时,在两组大鼠双侧上颌切牙和第一磨牙间放置镍钛拉簧,初始力值为50g,近中移动磨牙。分别于第0、3、7、10、14天测量大鼠上颌第一磨牙近中移动的距离并通过HE染色观察大鼠上颌第一磨牙牙周组织形态学变化。结果各时间点代偿性咀嚼增强侧牙移动速率均小于对照组（P〈0.05）,牙周组织变化与对照组相似;失咬合侧牙移动速率大于对照组（P〈0.05）,牙周组织出现退行性改变;但三种咬合状态下牙齿移动速率曲线均表现为瞬时运动、迟滞期及后期移动三个阶段。结论动物实验证实偏侧咀嚼引起正畸牙牙周组织发生相应改变最终影响牙移动速率,但无论牙移动速率快慢,牙移动均符合正畸性牙移动的一般规律。     

弓丝形变对微种植体舌侧内收上前牙影响的三维有限元分析

目的:对舌侧矫治系统中,内收弓丝形变及微种植体植入位置对上前牙三维方向移动的影响进行生物力学评价。方法:建立舌侧矫治三维有限元模型,当弓丝为可变形体及刚性体滑动法内收时,微种植体的植入位置设置为距离第二前磨牙与第一磨牙之间的牙槽嵴顶0、3、5、7 mm,分析上前牙的初始位移和牙周膜静水压的大小。结果:舌侧矫治系统中,使用可变形体弓丝内收上前牙,加力瞬间弓丝发生形变,牙初始位移受弓丝形变的作用发生舌向倾斜移动;随着微种植体高度的增加,上颌侧切牙牙冠的初始位移増大。弓丝为刚性体内收时,上前牙发生冠舌向倾斜移动;随着微种植体高度的增加,其位移趋势未发生明显变化。弓丝为可变形体时,上前牙的牙周膜静水压值超过毛细血管压的上限值。弓丝为刚性体时,上前牙的牙周膜静水压值小于毛细血管压的上限值。结论:弓丝形变对牙初始位移及牙周膜静水压影响较大。临床上可考虑使用刚性高的内收弓丝并减小内收力值,以降低牙根吸收风险。     

正畸牙齿移动时骨形成蛋白变化的实验研究

目的：探讨正畸虎齿移动过程中骨形成蛋白（bone morphogenetic protein BMP)的分布，表面的变化，方法：采用MBP单克隆抗体免疫 化染色及计算机图像分析的方法对实验性兔正畸牙齿移动牙周组织中BMP的表达变化进行了定性，定量分析，结果：正畸牙齿移动过程中，张力区牙周膜BMP达高峰出现早于牙槽骨表面，与张力区比较，压力区BMP表达高峰出现较迟，结论：BMP参与正畸牙齿移动时的骨吸收和骨增生的骨改建过程，并发挥着重要的作用。     

正畸牙移动过程中高迁移率族蛋白B1的改变

目的:研究高迁移率族蛋白B1(High Mobility Group Box-1,HMGB1)在正畸牙移动过程中的表达,以指导正畸临床加力。方法:30只Wistar大鼠,分为0、1、3、5和7 d组,每组6只;左侧施加0.6 N以近中移动上颌第一磨牙,右侧放置正畸装置但不加力作为对照;HE染色观察正畸牙移动过程中牙周组织的变化,免疫组织化学染色观察牙周支持组织中HMGB1的变化,以平均光密度法检测组织中HMGB1的表达量。结果:HE染色显示,加力1 d~7 d,大鼠第一磨牙牙周组织呈现正畸牙移动的典型变化:压力侧牙周膜变窄,呈现纤维排列紊乱,破骨细胞数目逐渐增多;张力侧牙周膜增宽,纤维排列整齐,成骨细胞数目逐渐增多。免疫组织化学染色显示,压力侧1 d时HMGB1表达量最低(0.0012 ± 0.0009),显著低于1 d对照组(0.0239 ± 0.011),从1~7 d,压力侧HMGB1逐渐增加,到7 d时到达加力后最高值(0.0127 ± 0.0014);张力侧1 d时HMGB1表达量(0.0193 ± 0.0012)低于1 d对照组(0.0284 ± 0.009),到5 d时,张力侧HMGB1达到最高值(0.0324 ± 0.0014),但与5 d对照组(0.0289 ± 0.0012)无显著差别。结论:过大的正畸矫治力减少压力侧牙周组织内HMGB1的表达,减慢透明样组织清除和正畸牙移动。     

增龄因素对鼠正畸牙牙周组织骨保护素及其配体表达的影响

目的:比较幼年鼠和成年鼠在正畸牙移动中牙周组织骨保护素(OPG)及其配体(OPGL)表达的不同比值,探讨增龄因素对正畸骨改建影响的分子机制。方法:制备大鼠正畸牙齿移动模型,于牙齿移动1d、3d、5d、7d、10d、14d及14d后去除正畸力1周后取材,免疫组化检测牙周组织OPG和OPGL的表达。结果:①.牙齿移动3d时,幼年鼠压力侧OPGL的表达明显增强;而成年鼠此时OPGL的表达没有幼年鼠明显。②.牙齿移动5d和7d时,幼年鼠和成年鼠OPGL的表达均成强阳性,破骨细胞多。③.牙齿移动10d、14d时,幼年鼠和成年鼠OPGL的表达逐渐减弱。④.14d时去除正畸力至21d时发现幼年鼠和成年鼠OPGL均已成弱阳性表达,幼年鼠可见部分成骨细胞。结论:在正畸力的作用下,OPGL与OPG的表达比值与年龄关系密切,增龄因素引起的牙周组织内OPGL/OPG表达变化可能是导致成年正畸特点的分子机制之一。     

持续力和间歇力对牙移动骨改建的影响

正畸矫治力的作用时间对牙移动和牙槽骨改建的速度有直接影响,国内外许多学者对此进行了研究。该文就持续力和间歇力对牙移动速度、牙周膜牙槽骨改建和牙体应力反应的影响作一简要综述。选择合适的正畸加力方式,有助于临床医师有效控制牙移动,缩短正畸疗程。     

下颌骨牵引成骨区即刻牙移动的实验研究

目的：研究下颌骨牵引成骨后在新骨区即刻牙移动时牙周组织的改建行为及牙移动规律。方法：选择4只牙列完整的Beagle犬,其中2只犬建立双侧下颌骨牵引成骨动物模型,牵引完成后,即刻以30g力远中移动下颌第三前磨牙进入牵引成骨区;另外2只犬拔除双侧下颌第四前磨牙后3个月,以30g力远中移动下颌第三前磨牙。实验中,每周加力1次拍摄X线片,并记录牙移动速率。牙移动8周后,观察实验牙及其牙周组织特点。测量数据采用SPSS12.0软件包进行t检验。结果：实验牙借助自制的持续加力装置移动进入牵引成骨区,实验牙未产生倾斜,牙无明显松动,牙根未见明显吸收。实验组牙移动速度显著快于对照组,P〈0.01。组组织学观察发现,牙槽骨和牙周膜未出现不可逆性损伤。结论：牵引成骨区的新生骨质中,牙可以快速而平稳地移动。