Administration of osteocalcin accelerates orthodontic tooth movement induced by a closed coil spring in rats.

The effect of local administration of osteocalcin (OC) on experimental tooth movement was examined in the rat. The maxillary first molar was first moved mesially with an initial tipping force of 30 g with a closed-coil spring anchored to the incisor for 10 days (n = 48). Three experimental groups (n = 8) were injected with purified rat OC at doses of 0.1, 1, and 10 micrograms, respectively. The injection into the palatal bifurcation site of the first molar was repeated daily. The control groups (n = 8) were injected with rat serum albumin (10 micrograms), phosphate buffered saline (PBS), or were not injected. Tooth movement was evaluated daily by measuring the inter-cuspal distance between the first and the second molars on a precise plaster model. The cumulative tooth movement (mm) in the 1-microgram OC-injected groups was significantly more than that in all of the control groups on day 9. The rate of tooth movement (mm/day) showed periodical elevation, with high values on days 1, 4, 7, and 9. Acceleration of tooth movement by OC was significant in the early experimental period. Subsequently, acceleration of early tooth movement by OC was histologically evaluated (n = 40). Each of four animals from the control (PBS, n = 20) and the experimental (1 microgram OC, n = 20) groups was killed daily up to 5 days. A significantly larger number of osteoclasts accumulated on the mesial alveolar bone surface in the 1-microgram OC-injected group on day 3 than that observed in control group. These results suggest that administration of OC accelerates orthodontic tooth movement due to enhancement of osteoclastogenesis on the pressure side, primarily in the early experimental period.     

The effect of thyroid hormone on orthodontic tooth movement in rats

The major goals of this study were to determine the effects of different doses of thyroxin on the rate of orthodontic tooth movement and the force-induced root resorption. In this study fifty male Sprague--Dawley rats were divided into five groups: a normal group with no intervention; a control group in which appliances were placed and 10 ml/kg i.p./day normal saline was injected; and three thyroxin groups in which appliances were placed and 5, 10 and 20/microgram/kg i.p./day L-thyroxin were administered, respectively. A fixed orthodontic appliance consisting of a 5 mm closed-coil spring was ligated between the maxillary incisor and maxillary first molar to deliver an initial force of 60 gm. The results showed that administration of 20/microgram/kg i.p./day L-thyroxin significantly increased the amount of orthodontic tooth movement (p < 0.001). The extent of root resorption as seen from scanning electron micrographs decreased with thyroxin administration.     

Effect of misoprostol, a prostaglandin E1 analog, on orthodontic tooth movement in rats.

The purpose of this study was to investigate the effects of oral administration of misoprostol, a prostaglandin E1 analog, on orthodontic tooth movement and root resorption in rats. Sixty-four male Sprague-Dawley rats that initially weighed 250 +/- 20 g were used in this study. The animals were randomly assigned to 1 of 6 experimental and 2 control (nonappliance and appliance) groups. The experimental groups received 2.5, 5.0, 10.0, 25.0, 50.0, and 100.0 microg/kg misoprostol by gastric lavage every 24 hours for 2 weeks. A fixed orthodontic appliance consisting of a nickel-titanium closed-coil spring, 5.0 mm long was ligated between the maxillary right incisor and the maxillary right first molar. The initial activating force was 60 g. For analysis of root resorption, 99 maxillary right and left first molars from 61 animals were chosen. Serial histologic sections of the mesial root of the maxillary first molars were made, and histologic analysis of root resorption on the mesial and distal surfaces was performed. The results showed that oral misoprostol did increase the amount of orthodontic tooth movement in all the experimental groups compared with the appliance control group. This increase was statistically significant in doses of 10.0, 25.0, 50.0, and 100.0 microg/kg (P <.001). However, there were no statistically significant differences among these 4 different doses. There were no statistically significant differences in the amount of root resorption among the groups. However, a trend toward more root resorption was registered. On the basis of these findings, oral misoprostol can be used to enhance orthodontic tooth movement with minimal root resorption.     

PDGF-BB与IGF-I联合应用对大鼠正畸牙移动的影响

目的:观察血小板衍生生长因子-BB(PDGF-BB)与胰岛素样生长因子-I(IGF-I)联合应用对大鼠正畸牙移动的影响,为正畸临床治疗加快正畸牙移动.缩短正畸治疗时间进行探索.方法:在32只SD雄性大鼠上颌安装施加50 g力正畸装置牵引上颌第一磨牙近中移动,隔日在正畸牙颊侧牙龈黏膜下分别或联合注射200 ng rIfl...     

Effect of Reveromycin A on experimental tooth movement in OPG-/- mice

In osteoprotegerin-deficient (OPG-/-) mice, osteoclast activity causes bone resorption to outpace bone formation, leading to the development of severe osteoporosis. Such mice are therefore useful for investigating the alveolar bone of patients with osteoporosis. Reveromycin A (RM-A) was recently identified as the unique agent acting on osteoclast activation. This study aimed to analyze the effect of RM-A on the orthodontic treatment of OPG-/- mice (a model of osteoporosis patients with high levels of bone turnover). We examined alveolar bone remodeling in OPG-/- and wild-type (WT) mice during continuous tooth movement. The orthodontic force was induced by means of a Ni-Ti closed-coil spring to move the maxillary first molar for 14 days. RM-A sodium salt (1 mg/kg) was administered intraperitoneally twice daily. In OPG-/- mice, the tooth movement distance was longer, alveolar bone resorption was enhanced, the osteoclast count was greater, and serum alkaline phosphatase and tartrate-resistant acid phosphatase levels were higher relative to those in WT mice. However, the administration of RM-A in OPG-/- mice reduced these parameters. We conclude that RM-A normalizes bone metabolism and loss of alveolar bone during continuous tooth movement in OPG-/- mice.     

The effect of chronic renal insufficiency on orthodontic tooth movement in rats.

The purpose of this study was to determine the effects of impaired renal function on the amount of orthodontic tooth movement (OTM) in a rat model of renal insufficiency (RI). The animals were divided into three groups: a control unoperated group in which only OTM was done, a sham-operated group, and an RI group. OTM was done two weeks after performance of the sham operation or the surgery to induce RI. Renal failure was induced by electrocoagulation of one kidney cortex followed by contralateral nephrectomy. A fixed orthodontic appliance consisting of a 5 mm length of nickel-titanium closed-coil spring was ligated between the maxillary right incisor and first molar to deliver an initial mesial force of 60 g. Four weeks after RI induction, the amount of tooth movement was estimated by measuring the space created between the first and second molars on a stone cast. Bone density was measured by optical densitometry on radiographs and serum parathyroid hormone (PTH) was measured with a radioimmunoassay method. The results showed that induction of RI significantly increased both OTM (P < .05) and PTH levels (P < .01), although there was no significant difference in bone density by optical densitometry between the unoperated, sham-operated, and RI groups four weeks after RI induction. The results suggest that an increase of bone-remodeling activities, as evident from a significantly higher level of PTH, may be responsible for increase in tooth movement.     

局部注射阿仑膦酸钠对大鼠正畸牙移动的影响

目的观察局部注射阿仑膦酸钠对大鼠正畸牙移动及牙周组织的影响。方法32只Wistar大鼠分为对照组和低剂量、中剂量、高剂量三个实验组,使用40g力牵其左侧上颌第一磨牙近中移动,实验中分别将生理盐水、0.02mmol/L、0.1mmol/L、0.5mmol/L的阿仑膦酸钠溶液注射入各组大鼠上颌第一磨牙近中腭侧的粘骨膜下,注射于实验前3d开始,每3天一次,每次50μl。分别在0、1、3、7、14、17、21d时取模法测量大鼠牙移动量。第21天取上颌组织块经固定、脱钙、脱水、包埋后切片,HE染色观察牙周组织变化,TRAP染色观察压力区破骨细胞数、破牙骨质细胞数,比较各组间是否有差异。结果①各实验组大鼠第一磨牙移动距离显著低于对照组,并随药物浓度增高其抑制效果增强。②实验组压力区破骨细胞数和破牙骨质细胞数显著低于对照组。结论局部注射不同浓度阿仑膦酸钠能获得不同的抑制牙齿移动的效果,可应用于临床中作为一种增强支抗的手段。     

Low dose propranolol decreases orthodontic movement

ObjectiveLow dose propranolol has previously been demonstrated to suppress bone remodelling. Therefore, its effect on orthodontic movement was tested.DesignRats were assigned as follows (n = 5): animals with no orthodontic appliance (G1); the remaining groups were fitted with a Ni-Ti closed-coil spring ligated to the upper left first molar and connected to the incisors using metal and resin and received vehicle only (G2), 0.1 mg/kg (G3) or 20 mg/kg (G4) of propranolol orally. Cone Beam Computed Tomography was performed using high resolution for image capture. The distance between the first and second upper molars, both with and without the orthodontic appliance, was measured in millimetres. Gingival tissue was harvested and assessed for IL-1β and IL-6 using ELISA and for ICAM-1 and RANKL by Western blotting.ResultsThe orthodontic appliance induced a significant tooth movement in G2 when compared to the animals without an orthodontic appliance (G1) (p < 0.05). The animals from G3 showed a significantly reduction in tooth movement (p < 0.05) when compared with rats from G2. Animals treated with 20 mg/kg of propranolol (G4) showed tooth movement similar to that of G2. The reduced tooth movement observed in the animals treated with 0.1 mg/kg of propranolol (G3) occurred due to decreased amounts of IL-1β and IL-6, in addition to lower ICAM-1 and RANKL expression.ConclusionsLow dose propranolol inhibits bone remodelling and orthodontic movement.     

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.     

局部注射重组人转化生长因子对大鼠正畸牙移动的影响

目的:探讨局部注射重组人转化生长因子 (rhTGF -β1)对大鼠正畸牙移动速度的影响。方法:80只模型大鼠随机分为实验组和对照组,每组又按1、4、7、10和14 d再分为5个小组,每小组8只。实验组从加力的第1天开始,每2 d在大鼠加力侧上颌第一磨牙颊侧黏膜下注射rhTGF-β1 0.1 mL(5 ng/mL),对照组注射相同容量的PBS。加力后依实验设计时间分别处死每1小组大鼠。体视显微镜观察并采集图像,运用计算机图像分析软件测量牙移动的距离,同时应用TRAP组织化学染色观察不同时段压力侧破骨细胞数量的变化,采用SPSS 17.0 软件包对数据进行统计学分析。结果:局部注射rhTGF-β1的牙移动速度较对照组快,在加力后第7天,牙移动距离差异显著(P<0.05);第10天和第14天相比,差异显著(P<0.01)。实验组压力侧破骨细胞的TRAP阳性细胞数较对照组显著增多(P<0.01)。结论:局部注射rhTGF-β1增强了大鼠正畸牙破骨细胞的活性,促进了破骨细胞的骨吸收功能,加速了正畸牙移动。     

大鼠动情周期不同阶段加力对正畸牙移动的影响

目的　探讨在雌性大鼠动情周期不同阶段加力对正畸牙移动的影响,以期为正畸临床女性患者的治疗选择最佳介入时间提供参考。方法　选取3月龄Wistar雌性大鼠80只,随机分为对照组、加力组。各组又根据所处动情周期的不同阶段分为4个亚组(动情前期、动情期、动情后期和动情间期)。加力组分别在动情周期的特定阶段给予重复的间断力4次,而后测量大鼠的左侧上颌切牙远中邻面和同侧第一磨牙近中邻面间的距离。单因素方差分析、S-N-K法进行统计分析处理。结果　动情周期的不同阶段加力组的牙移动总量的差异有统计学意义(P< 0·01)。组间两两比较显示:动情前期加力组和动情期加力组牙移动量的差异有统计学意义(P<0·05);动情后期加力组和动情间期加力组的差异无统计学意义(P>0·05),但它们与前两组的差异有统计学意义(P<0·05)。在动情前期加力进行牙移动,牙移动量最小;在动情期加力,则牙移动量最大。结论　选择在动情周期的不同阶段进行正畸加力,所获得的牙移动效果不同。     

Ⅱ类1分类错[牙合]正畸治疗前后牙齿移动与软组织侧貌变化的线性相关分析

目的通过对Ⅱ类1分类错[牙合]患者正畸治疗前后的头影测量指标进行相关性分析,探讨影响面部软组织侧貌变化的相关因素。方法选取2012年6月至2017年11月于上海交通大学医学院附属第九人民医院口腔颅颌面科就诊的42例已完成正畸治疗的Ⅱ类1分类错[牙合]患者[男性10例,女性32例,年龄(23.8±6.3)岁,平均矫治时间1.9年],拔除4颗第一前磨牙或2颗上颌第一前磨牙后进行正畸治疗纠正磨牙关系,测量矫治前后硬组织及软组织相关头影测量指标30个,包括上下唇突点、颏唇沟点、软硬组织颏前点及颏顶点的矢状向及垂直向距离、鼻唇角及颏唇角等。对矫治前后各指标变化量进行线性回归分析,根据标准化回归系数(Beta)分析影响上下唇、鼻唇角、颏唇角等面部软组织的主要相关因素。结果30个头影测量指标中18个矫治前后差异均有统计学意义(P<0.05),与矫治前相比,矫治后上中切牙点矢状向距离[(63.87±7.14)mm]、上唇突点矢状向距离[(77.73±7.60)mm]显著减小(P<0.05)。14对头影测量指标变化量间存在线性关系,其中上唇突点矢状向变化量与上中切牙点矢状向变化量强正相关(r=0.649,P<0.01),上唇突点垂直向变化量与上中切牙点垂直向变化量中度正相关(r=0.544,P<0.01),软组织颏顶点矢状向变化量与Y轴角变化量中度负相关(r=0.537,P<0.01)。多元逐步后退回归分析显示,上唇突点内收量与上中切牙点内收量、平面角增大量以及上中切牙角增大量均相关,且与上中切牙点内收量相关性最大(Beta=0.79);上唇突点下移量与上中切牙点下移量、上中切牙角减小量、上颌第一磨牙面中点到腭平面距离减小量以及平面角增大量相关,且与上中切牙点下移量及平面角增大量的相关性最大(Beta均为0.59);下唇突点下移量与上、下中切牙点下移量相关,且与上中切牙点下移量相关性更大(Beta=0.36)。结论Ⅱ类1分类错[牙合]矫治后鼻唇颏关系得到一定改善,切牙的矢状向变化对唇突度的影响最大,且下唇矢状向与垂直向移动与上中切牙的位置关系更密切,牙齿移动对颏部的影响有限。     

锥形束CT在切牙区唇侧牙槽骨开窗及开裂诊断中的应用研究

目的:应用锥形束CT研究错牙合畸形切牙区唇侧牙槽骨开窗及开裂的发生率等分布情况。方法:选择2010年7月~2015年9月期间在汉中市口腔医院正畸科进行锥形束CT扫描的患者421例,统计在上下颌切牙区唇侧牙槽骨开窗及开裂的发生率和分布情况,并进行统计学分析。结果:在统计的421例患者中,骨开窗及骨开裂的发生率分别为38.95%和20.43%。骨开窗以骨性Ⅰ类错牙合最多39.49%,骨性Ⅱ类次之。骨开裂以骨性Ⅱ类错牙合33.82%最多,骨性Ⅰ类次之。骨开窗牙位以左上侧切牙最高20.43%,骨开裂牙位以左下侧切牙最高6.65%。结论:正畸治疗患者中,骨开窗及骨开裂的发生率分别为38.95%和20.43%,无性别差异,骨性Ⅰ类错牙合切牙区骨开窗的发生率最高,以上侧切牙为主,骨性Ⅱ类错牙合切牙区骨开裂的发生率最高,以下中切牙为主。     

The role of nitric oxide in orthodontic tooth movement in rats

Nitric oxide (NO) is involved in second messenger formation, osteoblast and osteoclast function, and pulpal blood flow. This raises the question of whether or not altered NO production interferes with orthodontic tooth movement (OTM) by influencing the bone remodeling cycle. To investigate the role of NO in OTM, a rat model was established and 48 rats were divided into four study groups of 12 rats each. A 5 mm nickel-titanium closed-coil spring was ligated between the right maxillary incisor and first molar of each rat to deliver an initial force of 60 g. A saline group received subperiosteal injections of normal saline (50 microL/kg), an L-arginine (L-arg) group received L-arginine (NO precursor) injections (200 mg/kg), and a, L-NAME group received N(G)-nitro-L-arginine methyl ester (nitric oxide synthase inhibitor)(10 mg/kg) injections. All injections were given in the upper right first molar mucosa from the first through the 11th day of force application at 48-hour intervals. A control group received no injections. Tooth movement measurements were done at the time of injections. Animals were sacrificed 13 days after appliance insertion and final OTMs were measured at the time of sacrifice. From the third day till the end of the experiment, the L-arg group showed a significant increase in tooth movements, whereas the L-NAME group showed a significant decrease in tooth movements compared to the control and saline group (P < .001). Histopathologic studies revealed that the number of osteoclasts was significantly higher in the L-arg group smears, while the number of osteoclasts in the L-NAME group was significantly lower as compared to the control group (P < .001). Scanning electron microscope analysis showed that the force-induced root resorption in the L-arg group was less than the control group. This study suggests a role for NO in the bone remodeling cycle.     

Surgical and orthodontic treatment of an impacted permanent incisor: case report

Abstract –  This case report presented a combined surgical/orthodontic treatment of an impacted permanent incisor of a 10-year-old boy. Trauma to the primary dentition caused the impaction of the maxillary left permanent central incisor. Application of push coil spring between the adjacent teeth created space for the impacted tooth. A button with an extension of ligature wire was bonded to the maxillary left permanent central incisor to bring it into the arch. The maxillary left permanent central incisor was brought to its proper position after 16 months of active orthodontic treatment.     

Dynamics of tissue changes found after mechanical loading of the rat incisor. I. A three-dimensional longitudinal study of the morphologic aspects

A three-dimensional morphometric method was used to evaluate progressive changes in shape and size of recovering dental and periodontal tissues after orthodontic loading. In 35 female rats weighing 212 +/- 4 gm, loads of 19.7 +/- 1.6 gm generated by closed-coil springs were applied for 2 weeks to the shortened lower left incisor. The rats were killed in groups of five at 0, 1, 3, 5, 7, 9, and 10 weeks (groups 0-w to 10-w) after the springs were removed. A group of rats with normal incisors (group C-1) and one with five incisors that had been continually shortened for 10 weeks (group C-2) served as controls for groups 0-w and 10-w, respectively. Width, area, and volume of the tooth and enamel-bordering periodontal ligament (e-PDL) and cementum-bordering PDL (c-PDL) were measured. After 2 weeks of loading (group 0-w), the volume of the compressed e-PDL had decreased by 22%, and the volume of the stretched c-PDL had increased by 72%, suggesting that bone apposition lags behind the rate of tooth movement. During the recovery period, the dental and periodontal parameters tended toward a gradual return to control (C-2) values, although at the end of 10 weeks many still lagged significantly behind the controls. Recovery was slowed by repeated reversals at different sites in the various groups. The ability of the preloaded incisor to adjust to changes in occlusal function was lastingly impaired.     

Effects of calcitonin on orthodontic tooth movement and associated root resorption in rats

Objectives: Our main aim was to evaluate the effects of calcitonin (CT) on orthodontic tooth movement (OTM) and orthodontic root resorption in a rat model.

Material and methods: Eighty male Wistar rats were randomly divided into five groups. Rats in the negative control group were not given any appliances or injections. All the remaining rats were used to establish a model of OTM. The positive control group were then injected with normal saline, while rats in the three experimental groups were injected with 0.2?IU, 1?IU or 5?IU/kg/day CT. Nickel-titanium closed-coil springs were used to deliver an initial 50?g mesial force to the left maxillary first molar for 14 days in rats in the positive control group and the experimental groups. Each group was randomly subdivided into two groups, one for analysis of tooth movement, tissue changes and tartrate-resistant acid phosphatase (TRAP)-positive cells in alveolar bone, the other to examine root resorption by scanning electron microscopy.

Results: The OTM distance, the number of force-induced osteoclasts and root resorption areas were significantly decreased in CT-injected rats in a dose-dependent manner.

Conclusions: Administration of CT reduces the root resorption area and may therefore be effective as a novel adjunctive orthodontic approach to diminish undesired tooth movement via enhancing anchorage or preventing relapse after OTM.     

骨皮质切开术对大鼠牙移动影响的实验研究

目的建立骨皮质切开术正畸牙移动实验动物模型,观察移动速率和对牙周组织改建的影响。方法 75只SD大鼠,实验组35只行上颌双侧中切牙骨皮质切开术,1周后与对照组35只同时进行正畸加力,空白对照组5只不进行加力。按不同加力时间处死,测量牙齿移动的距离,观察组织学改变。结果实验组2周时牙齿移动距离(3.471±0.359)mm,对照组为(1.247±0.198)mm,具有显著性差异;HE染色结果表明,实验组牙周膜内玻璃样变组织的形成相对于对照组来说,范围缩小,时间缩短。结论骨皮质切开术能够加速正畸牙移动。     

丹参联合电动牙刷对大鼠正畸牙移动过程的影响

目的：研究中药丹参联合电动牙刷对大鼠正畸牙齿移动及移动过程中牙槽骨密度的影响。方法：选取72只SD雄性大鼠,建立大鼠正畸牙齿移动实验模型,随机分为丹参联合电动牙刷+加力组（A组）丹参+加力组（B组）和对照组单纯加力组（C组）,每组24只。 A组每天于左上第一磨牙颊黏膜处注射丹参,并间歇进行15 min电动牙刷颤动,B组注射丹参,C组为对照组。3组动物于正畸加力1、3、7、14 d分批次处死,每批处死6只,分离大鼠上颌骨,HE染色观察牙周组织变化并测量牙齿移动的距离及牙槽骨骨密度。使用SPSS 19.0软件进行数据分析。结果：A组和B组较C组的牙周组织中更早更多出现破骨细胞;A、B组除第1 d外牙齿移动距离均明显高于C组（P<0.01）,且A组明显高于B组（P<0.01）;第7d,A组牙槽骨密度明显高于C组（P<0.05）,第14 d,A组明显高于B组（P<0.05）,且A、B组均高于C组（P<0.05）,差异有统计学意义。结论：丹参联合电动牙刷在加速牙齿移动的同时能有效地降低牙槽骨骨密度的减少。     

Volumetric evaluation of root resorption on the upper incisors using cone beam computed tomography after 1 year of orthodontic treatment in adult patients with marginal bone loss

Objectives:To determine upper incisor root resorption, volume loss, and the relationship between root volume loss and tooth movement after 1 year of orthodontic treatment in patients with marginal bone loss.Materials and Methods:A total of 30 women (46.3 ± 5.4 years old) with moderate upper incisor bone loss who required intrusion during orthodontic treatment were recruited. Pre- and post-treatment cone beam computed tomography images were reconstructed. Upper incisors at pre- and post-treatment were superimposed; labio- and palato-apical, middle, and coronal third root volumes were assessed. Tooth movement and alveolar bone height were measured from lateral cephalometric radiographs and cone beam computed tomography. Changes in root volume/alveolar bone height were compared using paired-sample t-tests, percentage root volume loss for each tooth/segment was evaluated by one-way analysis of variance, and the relationship between percentage root loss and degree of tooth movement was assessed by linear regression.Results:Mean root volume significantly decreased on the labio- and palato-apical aspects of 12 and labio-apical aspects of 21 and 22 (P ≤ .024). Palato-apical segment volume loss was greater on lateral than central incisors (P ≤ .016). Two-dimensional root length and cementoenamel junction-bone crest distance did not change between T0 and T1, with no significant relationship between tooth movement amount and percentage root volume loss.Conclusions:Delivery of 40 g intrusive force to the four upper incisors using a T-loop and the leveling phase lead to more apical root volume loss on lateral than central incisors. There was no relationship between extent of tooth movement and upper incisor root volume loss.