摘要
牙根吸收是正畸临床工作中常见的并发症。一旦发生牙根吸收,往往患者难以接受。为了能够更好的保证正畸治疗的安全性,正畸医生就必须研究牙根吸收的发生机制和防治措施。本实验通过对成年雄性杂种犬上颌切牙施加持续性压低重力,建立出在X线影像片上肉眼可见牙根吸收的动物模型,并通过比较不同修复时间下的牙根情况,研究了发生变短性吸收的牙根的自行修复情况。
目的:
1.持续性压低重力加力作用装置的设定。
2.以持续性压低重力作用方式建立出在X线影像片上有明显牙根吸收变短指证的动物模型。
3.观察发生吸收的牙根的自行修复情况。
方法:
1.持续性压低重力作用装置的设定:选取结扎皮圈、含四个圈的长间隔、短间隔和无间隔橡皮链。随机分为2组,一组拉伸1倍,一组拉伸0.5倍。观察其力值随时间的变化规律,以探讨其是否能够产生持续性的恒力作用。采用spss12.0统计软件进行数据处理分析。
2.牙根吸收动物模型的建立:选用成年杂种雄性犬6只,以种植钉为支抗,对其上颌切牙施加压低性重力300g,持续作用6周。观察X线根尖片、受力牙的大体形态和组织病理切片。
3.牙根吸收自行修复性研究:选用成年杂种雄性犬6只,以种植钉为支抗,对其上颌切牙施加持续性压低重力300g。作用6周后,去除加力装置,使其自行修复。分别于2,4,6周后处死动物。通过X线根尖片和组织病理切片,比较不同时间的牙根修复状况。
结果:
1.持续压低重力作用装置的设定:在不同的拉伸状态下,四种研究对象的力值随时间衰减的规律基本相同。在加力后的第一个小时内,弹力衰减最快,其衰减率为20-35%。此后,力值衰减逐渐变小。两周后,弹力力值基本稳定。在第四周结束时,弹力基本保持在初始力值的40%-55%。
2.牙根吸收动物模型的建立:①X线观察:加力2周后牙齿根尖周出现阴影聚集区;6周后根尖区出现牙根组织缺损性吸收。②牙根大体形态观察:牙根形态不完整,根尖区吸收后呈不规则形态截面。③组织切片观察:根尖吸收区有大量单核、多核细胞聚集。④通过X线影像片比较冠根比例:冠根比平均每周增加约3-4%。
3.牙根吸收自行修复性研究:去除加力装置2周后,根尖周仍存在明显阴影区,根尖圆钝,切片显示有明显的吸收陷窝存在,陷窝区有大量单核、多核细胞聚集;4周后,吸收陷窝变少变浅;6周后,根尖周阴影区基本消失,根尖形态基本正常,细胞排列整齐。冠根比平均每周增加约1.5-2.5%。
结论:
1.弹性加力装置在拉伸一个小时后,基本进入力值衰减很低的状态。这提示如果应用弹性橡皮圈作为加力装置,需要按衰减1小时后的力值为300g的状态设定初始力值,可以达到牙根吸收动物模型制作所需的持续性重力作用效果。
2.通过施加持续性压低重力,可建立起X线影像片上肉眼可见的进展性牙根吸收动物模型;同时也提示持续性过大压低重力可造成正畸过程中牙根变短性吸收。
3.牙根的吸收并不随着作用力的停止而立即停止。发生变短性吸收的牙根随着修复时间的延长逐渐停止吸收,但已发生变短性吸收的牙根部分结构则无法恢复,牙根无法恢复原有长度。
综上所述,本研究成功的建立出X线影像片上有明显变短性牙根吸收指证、并且能够用于牙根吸收进程研究的动物模型。通过对发生了牙根吸收的动物模型去除矫治力作用后吸收牙根的修复情况观察,我们发现牙根的变短性吸收并不随着矫治力的去除立即停止。这一结果提示,对于发生了变短性牙根吸收的牙齿仅仅采取停止矫治力作用的处理是不够的,为了减少牙根的吸收量,有研究能够促进牙根修复作用发生的措施的必要性。
Root resorption is a common complication during the orthodontic tooth movement. Usually, it is not an easy thing for the patient to accept the orthodontic treatment with root resorption. For safety of orthodontic treatment, orthodontists must study on the mechanism of the resorption and the prevention for it. In this study, the root resorption model was established on adult male hybrid dogs’maxillary incisors by the way of continuous intrusive heave force engagement. The resorption on the model can be seen on X-ray periapical films. And the characteristic of the selt-repair after resorption was investigated by the observation of the process on the models.
Objective:
1. To develop the way of continuous heave intrusive force to be engaged on the dog’s maxillary incisors.
2. To establish the root resorption model on the dogs’maxillary incisors by the way of continuous intrusive heave force engagement. The resorption could be detected on the the X-ray periapical films with shortened root. 3. To investigate the characteristics of root self-repair after the resorption.
Method:
1. The development of the continuous heave intrusive force engagement way: Some orthodontic elastic appliances were chosen for this study, such as elastomeric ligatures and four-loop elastomeric chains with long, short, and no intervals respectively. They were randomly divided into two groups. One group was at 1 time stretched length, and the other group was at 0.5 time stretched length. The regularity of time-dependant force decay was analyzed in order to investigate whether the unvarying force could be engaged by the appliances. Spss12.0 statistical software was used for data processing and analysis.
2. The establishment of the animal model of root resorption: In six adult hybrid male dog, continuous heave intrusive force 300g was imposed to the maxillary incisor teeth with mini-implant as anchorage. Then the occurrence and development of the resorption were observed by X-ray periapical films、gross anatomy and histological morphology.
3. The study on the characteristics of root self-repair after resorping: In six adult hybrid male dog, continuous heave intrusive force 300g was imposed to the maxillary incisor teeth with mini-implant as anchorage. After 6 weeks, the force was removed and the process of selt-repair began. The animals were killed after 2, 4, 6 weeks’self-repair respectively. The repair in different time was compared on the the X-ray periapical films and histological sections.
Results:
1. The development of the continuous heave intrusive force engagement way: For all kinds of elastic appliances, there was no significant difference in the regularity of time-dependant force decay between the two different tension conditions. During the first hour after the engagement, force decay was the fastest with the decaying rate 20%-35%.Then, the force degradation decreased. Two weeks after the engagement, the elastic force was nearly stable. At the end of the fourth week, elastic force remained at 40% - 55% of the initial force.
2. The establishment of the animal model of root resorption:①observation on the X-ray periapical film: Two weeks later, the periapical radiolucent areas appeared; Six weeks later, defective root resorption was found around root tip.②observation on the anatomy morphology: It was found that the root was incomplete with irregular absorbed section in the apex area.③observation on the histological sections: It was found that a large number of cells with monocytes or polyocytes focused in the area of root resorption.④the crown-root ratio in X-ray periapical film: It was found that the crown-root ratio increased about 3-4% per week.
3. The study on the characteristics of root self-repair after resorping: After removing the force two weeks, the periapical radiolucent areas still existed and the root tip was blunt. There were obvious absorption lacunas and a large number of cells with monocytes or polyocytes in the area of root resorption; Four weeks later, the absorption lacunas were less and shallow; Six weeks later, the absorption lacunas were disappeared basically and the morphology of root tip was normal, cells arranging regularly. The crown-root ratio increased about 1.5-2.5% per week.
Conclusion:
1. The elastic force of orthodontic elastic appliances was with low decayi- -ng rate since one hour after the engagement. It was suggested that if the appliance would be applied for the continuous heave force engagement in our study, the initial force of the elastic appliance should be set according to the condition (300g) of the appliances after one hour’s degradation.
2. By the way of continuous heave intrusive force engagement, the animal model of root resorption can be established and the resorption can be found on X-ray film. It was suggested that the continuous heave intrusive force engagement can induce shorter root resorption during the orthodontic treatment.
3. The absorption of root tip will not stop as soon as the force engagement was removed. As time going, the absorption of shortened root would stop gradually. However, the resorped part of the root could not be rehabilitated and the original root length could not be restored.
Therefore, in this study, the animal model of root resorption was established successfully, on which the resorption could be detected with shortened root on X-ray periapical films. The study on the developing process of the resorption could be studied on the models. Through observing the self-repair after resorption, it was showed that the absorption of shortened root would not stop as soon as the force engagement was removed. It was suggested that it was not effective enough only to remove force engagement when the clinical root resorption was detected. To decrease the amount of root resorption, it is necessary to find a way to promote root restoration.
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