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Clinical research status of premolars

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发表于 2018-9-16 15:44:04 | 显示全部楼层 |阅读模式
Impacted teeth are teeth that can only erupt partially or completely due to obstruction of adjacent teeth, bones or soft tissues. In general, teeth erupted when the roots formed 1/2~3/4. In mild impacted teeth, delayed eruption and dislocation eruption occur; in severe impacted teeth, completely embedded in the bone or submucosa is called impacted teeth. Teeth in any position can be impacted. At present, scholars at home and abroad mainly focus on maxillary canine and third molar impacted teeth, mainly on its epidemiological characteristics, diagnosis and treatment methods. With the increasing number of orthodontic patients, the number of impacted premolars in clinic is increasing. However, there are few literatures on impacted premolars. This article reviews the epidemiological characteristics, etiology, location and treatment of impacted premolars in order to provide a reference for orthodontists to make a comprehensive treatment plan.
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 楼主| 发表于 2018-9-16 15:44:46 | 显示全部楼层
Epidemiological characteristics of 1. premolars

1.1 prevalence rate

There are few special studies on premolars. Mustafa, Xianim ek-Kaya, Tian Jun and other scholars studied the epidemiological characteristics of impacted premolars; Chu, Yang Zaibo, Pang Yunnai, Grover, Chen Min and other scholars involved impacted premolars in the study of impacted teeth, and reported the epidemiological characteristics of impacted premolars. By analyzing these studies, we can see that the incidence of impacted premolars varies with the subjects, methods and criteria reported. The prevalence of impacted premolars was 1.2%, 1.03%, 8.59%, 1.85%, 2.83%, 1.98% and 1.3% respectively. Several other scholars have concluded that the prevalence of premolar impacted is 0.53%~3.2%.

As far as the research object is concerned, Mustafa, imek-Kaya and other scholars take the patients in oral and maxillofacial surgery as the research object, while the others take the patients in orthodontic department as the research object. As far as research methods are concerned, Yang Zaibao and others are based on multi-level reconstruction of image volume information collected by 64-slice spiral CT, while the rest of the scholars are based on panoramic analysis. As far as the criteria are concerned, the criteria used in the studies such as Jaim ek-Kaya and Pang Yunnai are age-specific. However, other scholars did not mention age-specific criteria in their studies, but based on the development of root or the height of tooth eruption.

Xu Lu et al. showed that the eruption time of permanent teeth ranged from 7 to 14 years old and 6 to 14 years old respectively, and the peak period was 9 to 10 years old; the eruption age ranged from 7 to 14 years old and 7 to 15 years old respectively, and the peak period was 10 to 11 years old. The prevalence of premolars will be affected to some extent. Mustafa's and Yang's studies were compared with the eruption of other teeth in the mouth as a criterion for judging impacted premolars. Mustafa took the height of premolar eruption not up to the height of other teeth in the upper or lower dental arch as the criterion of impacted teeth. Yang Zaibo and others compared the eruption of premolar with that of the contralateral homonymous teeth. The criterion for judging bilateral impacted teeth was not specified, but the patient's age was not taken as the criterion. One of them.

Chen Min, et al. And Deng Xiaoli studied the criteria for judging that the root had not been sprouted. The authors believe that it is more accurate to estimate the growth potential of premolars by age than by age. Therefore, it is more appropriate to judge the root development of premolars with 2/3 or more roots, which can only erupt partially or completely because of the obstruction of adjacent teeth, bone or soft tissue. At the same time, the subjects selected in the above studies are patients, so there is no study on the incidence of the general population.
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 楼主| 发表于 2018-9-16 15:45:11 | 显示全部楼层
1.2 gender differences

In most studies, premolars were more common in females than in females. Walker and others believe that the gender difference in the prevalence of impacted teeth is due to differences in craniomaxillofacial growth and development between men and women. In addition, because these studies are based on patients, and women have a higher demand for beauty, so female patients have a higher rate of visits, which is one of the reasons why impacted premolars are more common in women.

1.3 feature of tooth position

The results of Mustafa, imek-Kaya and Grover all showed that the impacted rate of mandibular premolars was higher than that of maxilla. In the reports of Deng Xiaoli and Chen Min, the incidence of maxillary second premolar was the highest, and that of mandibular first premolar was the lowest. These studies did not explain the difference in tooth position characteristics. The author believes that the difference may be related to the order of tooth eruption, age and other factors.
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 楼主| 发表于 2018-9-16 15:45:27 | 显示全部楼层
1.2 gender differences

In most studies, premolars were more common in females than in females. Walker and others believe that the gender difference in the prevalence of impacted teeth is due to differences in craniomaxillofacial growth and development between men and women. In addition, because these studies are based on patients, and women have a higher demand for beauty, so female patients have a higher rate of visits, which is one of the reasons why impacted premolars are more common in women.

1.3 feature of tooth position

The results of Mustafa, imek-Kaya and Grover all showed that the impacted rate of mandibular premolars was higher than that of maxilla. In the reports of Deng Xiaoli and Chen Min, the incidence of maxillary second premolar was the highest, and that of mandibular first premolar was the lowest. These studies did not explain the difference in tooth position characteristics. The author believes that the difference may be related to the order of tooth eruption, age and other factors.
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 楼主| 发表于 2018-9-16 15:45:32 | 显示全部楼层
2. the cause of impaction of premolars

The etiology of premolar impaction is complex, including systemic factors and local factors. Systemic factors include endocrine defects, fibrous diseases and genetic diseases. Local factors are the main factors of premolar impaction. The most common local factors leading to premolar impaction are premature loss of deciduous molars and abnormal location of tooth germs, and retention of deciduous molars is also one of the important factors leading to premolar impaction. In addition, pathological changes in the development of premolar germs, such as inflammation or dental cysts, supernumerary teeth or odontoma, are all causes of premolar impaction. Reasons for impaction.
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 楼主| 发表于 2018-9-16 15:45:59 | 显示全部楼层
Localization of 3. premolars

Correctly locating the premolars is a very important step, and is also the basis for making accurate corrective plans. How to locate impacted premolars correctly is a complicated process. The locating methods mainly include clinical examination and X-ray examination. Orthodontists need to combine them for comprehensive analysis. Clinical examination includes visual inspection and palpation. X-ray location includes two dimensional observation mode and three dimensional observation mode. For impacted premolars with superficial submucosal location, local protrusion and hard palpation can be seen in clinical examination. It is easy to determine the presence of impacted teeth, but it is not accurate to determine the shape and direction of impacted teeth. The deep impacted premolars and the shape and position of impacted teeth need to be judged accurately by X-ray.

Two-dimensional X-ray film includes apical film, curved tomography, lateral cephalometric film and so on. The three-dimensional X-ray observation mode is mainly cone beam computed tomography (CBCT). This method can provide multi-plane reconstruction images of sagittal plane, coronal plane and axial plane, and has high accuracy, and no distortion of random amplification and rotation. Tian Jun and his colleagues studied the location of impacted premolars on a curved section. The first reference line was the connection between the first premolar plane and the first molar plane. The second reference line was the connection between the enamel-cementum boundary of the first premolar and the enamel-cementum boundary of the first molar. The clinical characteristics of impacted second premolars were analyzed. In this two-dimensional study, the impacted teeth can only be roughly measured in the near-far and vertical directions, and the impacted situation on the buccal-lingual side and the exact location relationship with adjacent teeth can not be measured.

CBCT can observe the shape and number of impacted teeth, the location of lip and palate and the relationship between impacted teeth and adjacent teeth. There is no literature on CBCT positioning of impacted premolars, but it can refer to other methods in the study of impacted teeth. CBCT was used to study the impacted maxillary palatal canines and the root resorption of adjacent teeth. The study can provide reference for the location of impacted premolars. In this study, the vertical distances and angles between the cusp and the long axis of the impacted canine and the corresponding reference plane were measured on three planes. The horizontal plane is the orbital ear plane, which is a plane composed of the bilateral ear points and the right orbital points; the median sagittal plane is the plane which passes through the nasal root point and the middle point of the anterior margin of the foramen magnum and is perpendicular to the horizontal plane; the coronal plane is the plane perpendicular to the horizontal plane and the sagittal plane; and the plane is defined as the plane passing through the mesiobuccal cusp of the bilateral maxillary first molars and the maxilla. The plane formed by the midpoint of the central incisor.

The three-dimensional positioning methods are: the angle between the long axis and sagittal plane of the impacted teeth, the distance and angle between the long axis and the plane of the impacted teeth, the distance and angle between the long axis and the sagittal plane, the distance and angle between the long axis and the plane of the impacted teeth and the long axis of the impacted teeth. According to this study, the authors believe that this method can also be used to locate impacted premolars in three-dimensional direction. The vertical distances and angles between the midpoint and the long axis of the impacted premolars and the corresponding reference plane can be measured on three planes.
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 楼主| 发表于 2018-9-16 15:46:21 | 显示全部楼层
4. methods of treating premolars.

The treatment methods of impacted premolars can be summarized as observation, blocking treatment, autogenous tooth replantation, extraction and germination induction.

4.1 observation

If the impacted premolar is located deep and distant from the root of other teeth, it will not damage the surrounding tissues or adjacent teeth, nor affect the movement of teeth during orthodontic treatment. However, if the operation of sprouting and traction is traumatic, the success rate is low, or even can not be tracted, it can be temporarily carried out. Bed observation is not done. Because impacted teeth have an increased risk of cystic tumors, these patients need regular X-ray reexamination.

4.2 blocking therapy

Early prophylactic treatment is very important in the presence of risk factors for impacted premolars, such as retained deciduous molars. In order to provide enough space for eruption of permanent premolars, it is necessary to select the right time for preventive extraction of deciduous molars and maintain the extraction space with space retainer. When the second premolar is impacted due to the premature loss of the second deciduous molar, the movable appliance should be used unilaterally or bilaterally to remove the first permanent molar and the straight wire appliance should be used to treat the impacted second premolar. Ma Qiaoling and other researchers found that distal movement of maxillary first molars in the late stage of unerupted second molars can promote the normal eruption of maxillary second premolars and effectively prevent the impacted or ectopic eruption of the second premolar. Li Xiaobing and others reported the diagnosis and treatment of a case of left mandibular first deciduous molar with horizontal impaction of left mandibular first premolar. Therefore, early diagnosis and prompt treatment are very necessary.

4.3 replantation of autogenous teeth

Autogenous tooth replantation is the complete removal of impacted autogenous teeth, transplanted to the corresponding or other parts of the missing teeth, which is one of the methods of orthodontic clinical treatment of missing teeth, successfully achieved the transfer of teeth from crowded parts to missing parts. Teeth with immature teeth can have higher survival rate by autologous transplantation. Bokelund believes that the survival rate of transplanted root is the highest when 3/4 is the root length. Andreasen et al. showed that the survival rate of premolars with incomplete root formation was 95%, and that of premolars with incomplete root formation was 98% after root canal therapy within 4 weeks. Other studies have shown that young patients with maxillary anterior teeth loss due to trauma are often difficult to accept removable dentures. Fixed dentures and implant dentures are not good indications. At this time autologous premolar transplantation instead of maxillary anterior teeth is one of the feasible options. This method can give the alveolar bone appropriate stimulation, not only maintain the integrity of the arch shape and ensure the normal growth of the arch, in line with the normal growth and development of the law.
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 楼主| 发表于 2018-9-16 15:49:18 | 显示全部楼层
4.4 removal

Impacted premolars can be removed if there are no gaps in the arch, and the occlusal relationship between the remaining teeth is still acceptable; 2) Impacted premolars are malformed, or have short or curved roots, or accompanied by odontogenic lesions or infections, and can not be replanted; 3) Patients insist on extraction. For cases of impacted premolars caused by odontogenic cysts, it is not recommended to remove impacted teeth easily. Minimally invasive cyst fenestration and decompression can be performed at this time, which is conducive to the spontaneous eruption of permanent teeth.

4.5 surgical orthodontic guided eruption

The best treatment for impacted premolars is surgical orthodontic guided eruption. This method is suitable for those impacted teeth with well-developed crown and root, appropriate crown-root ratio, abundant dental space in the arch, or abundant dental space can be obtained by early orthodontic treatment, and the space can accommodate the impacted teeth and establish a good occlusal relationship. Accurate three-dimensional localization can provide a reference for surgical exposure and orthodontic guidance device.

Surgical exposure is divided into two types. 1) Open technique: removing the mucosa and bone covering the crown surface of impacted teeth; 2) Closed technique: Retaining the complete mucoperiosteal flap by flap flipping technique; after removing the bone and revealing the impacted crown, bonding bracket and rubber chain, and then restoring and suturing the mucoperiosteal flap. After exposing impacted teeth, lingual buckles are bonded to the exposed teeth for traction. The traction force should be light. The main arch wire should be lifted 2 mm to prevent root resorption. Once a month, the impacted teeth are pulled in place, then the square arch or straight arch brackets are bonded to fine adjust the tooth position.
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 楼主| 发表于 2018-9-16 15:49:39 | 显示全部楼层
5. summary

In summary, because of the low prevalence of impacted premolars, the comprehensive treatment of impacted premolars is rarely studied. The choice of treatment options requires a comprehensive assessment and, if necessary, multidisciplinary consultation. If there is enough space in the arch and the germ eruption position is normal, the impacted teeth can still erupt to the normal position by conservative method, even if the anterior molars with deeply embedded bone are evaluated comprehensively. If the impacted premolar can not erupt to the normal position by itself and the near and far dislocation is not serious, orthodontic traction or combined surgical-orthodontic treatment is needed. If only orthodontic treatment can not remove the impacted premolars eruption barrier, then the use of orthodontic and surgical traction to guide the eruption of impacted premolars, at this time through CBCT to accurately locate the impacted premolars, determine the surgical window location and the direction of orthodontic traction.

Removal of impacted premolars should be considered only when they are severely deformed, with short curvature of the root, or with odontogenic lesions or infections, and can not be transplanted. The risk of pulp necrosis, root adhesion and resorption exists in the treatment of either assisted or guided eruption. Patients and parents should be informed before treatment. When the palatal hindrance premolar moves in the labial direction, the crown should be moved as far as possible to prevent the crown from falling. In a word, when making orthodontic treatment plan in orthodontic clinic, the orthodontic method with the least damage should be chosen to obtain the best tooth position.
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