正畸拔除第一前磨牙对第三磨牙萌出角度的影响

目的：研究正畸拔除第一前磨牙对第三磨牙的影响。方法：37例第一前磨牙拔除和33例非拔牙患者作为研究对象,拍摄术前术后的全景片,测量第三磨牙长轴与平面及第三磨牙长轴与第二磨牙长轴的夹角,对治疗前后夹角的变化以U检验进行比较。结果：结果显示,拔除第一前磨牙后,下颌第三磨牙的的萌出角度得到了改善,而对上颌第三磨牙萌出改善并不明显。结论：拔除下颌第一前磨牙后,第三磨牙萌出角度会更加直立,从而可能减少其阻生的可能性。     

正畸拔除第一前磨牙后第三磨牙倾斜度的变化

目的 探讨正畸拔除第一前磨牙对第三磨牙倾斜度的影响。方法 选择37例拔牙和32例非拔牙患者,分别在治疗前和治疗后的曲面断层片上测量第三磨牙长轴与平面的交角以及第二、第三磨牙长轴的交角。用U检验来比较两组患者第三磨牙倾斜度在治疗前后的变化。结果 拔牙组和非拔牙组间治疗前后下颌第三磨牙长轴与平面和第二磨牙长轴交角的差异均具有统计学意义（P<0.05）;拔牙组和非拔牙组治疗前后上颌第三磨牙长轴与平面和第二磨牙交角的差异没有统计学意义（P>0.05）。在拔牙组,治疗后下颌第三磨牙比上颌第三磨牙更直立。结论 拔除前磨牙的正畸治疗能够改善第三磨牙的倾斜角度。     

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目的    评价正畸拔除第二前磨牙对第三磨牙萌出角度和萌出间隙的影响。方法    选择2007年1月至2010年7月在济南市口腔医院正畸科行直丝弓正畸治疗的41例安氏Ⅰ类错牙合青少年患者,所有患者第二前磨牙及第二磨牙完全萌出,第三磨牙牙冠已形成但均未萌出。按治疗方法分为拔牙组（21例,均拔除4个第二前磨牙）和非拔牙组（20例）。在治疗前后分别拍摄全口曲面断层片,测量第三磨牙的倾斜角度和萌出间隙。结果    治疗前后上、下颌第三磨牙萌出间隙的增加值拔牙组大于非拔牙组,差异有统计学意义（P < 0.001）。上颌第三磨牙萌出角度的增加值拔牙组大于非拔牙组,差异有统计学意义（P < 0.05）,而下颌第三磨牙萌出角度的增加值两组间差异无统计学意义（P > 0.05）。结论    正畸拔除第二前磨牙可以增加上、下颌第三磨牙的萌出间隙,并使上颌第三磨牙萌出角度更加直立。     

Radiographic evaluation of mandibular third molar eruption space.

OBJECTIVE: The purpose of this study was to investigate variables in third molar and arch dimensions among subjects with impacted and erupted mandibular third molars. STUDY DESIGN: Standardized panoramic radiographs were taken for 134 subjects (60 males and 74 females with 213 third molars) with an average age of 19.8 years. For the impacted group, only those who had mesioangular inclination of the third molars were recorded. The radiographic features studied were angulation of tooth, level of eruption, development of root, mesiodistal crown width, retromolar space, and gonial angle. RESULTS: Third molar angulation in the impacted group (69 subjects with 101 third molars) averaged 16.28 degrees (SD +/- 11.88 degrees), with no significant gender differences. The retromolar space was significantly smaller in the impacted group than in the erupted group (P < .001). This space was also the only significant variable (P < .05) associated with lateral asymmetry in the eruption/impaction status of third molars. In the impacted group, 83% of subjects had third molar space/crown width ratios less than 1, whereas in the erupted group 69% had ratios of at least 1. The average space/crown width ratios in the impacted and erupted groups were 0.78 and 1.06, respectively (P < .001). The impacted and erupted groups did not differ significantly with respect to mesiodistal crown width and gonial angle. Approximately 76% of impacted third molars had complete root formation, 20% had two thirds root formation, and only 4% displayed one third root formation. Of the impacted third molars, 66% were partially erupted and the rest were unerupted. There was a strong positive relationship between frequency of third molar impaction and degree of angulation (P < .001), but the former was inversely associated with retromolar space (P < .001). CONCLUSIONS: The most significant variable associated with third molar impaction is inadequate space. The vast majority of impacted third molars had space/crown width ratios of less than 1.     

A comparison of the effects of first premolar extractions on third molar angulation.

The effect of third molars on the stability of orthodontic treatment has been studied extensively. Yet the effect of orthodontic treatment, particularly premolar extractions, on third molars has not been substantially studied. The purpose of this investigation was to compare the changes in third molar angulation in patients treated with and without extractions. Records of 45 Class I, nonextraction and 33 Class I, first premolar extraction patients were examined. The pretreatment and posttreatment pantographs were digitized, and the angles between the third molar long axes and the occlusal plane were measured. Changes in third molar angulation from pretreatment to posttreatment for the two groups were compared for statistical differences using a Student's t-test. Statistical analysis revealed there were no significant differences in the change in third molar angulation in either group. On average, the maxillary and mandibular third molars showed an improvement in angulation relative to the occlusal plane. The results suggest that factors other than first premolar extractions may influence third molar angulation.     

An easy way to apply orthodontic extraction for impacted lower third molar compressing to the inferior alveolar nerve

PurposeTo study the results of an easy orthodontic extraction method for impacted lower third molar removal which had roots compressing to the inferior alveolar nerve (IAN).Patients and methodsForty patients were divided into two groups according to their desire. Orthodontic traction group (n = 20) had brackets or mini bone screws on the antagonist maxillary molars as anchorage for orthodontic traction from 3 to 10 weeks until the roots’ tip was away from the IAN, the tooth was then removed. Traditional extraction group (n = 20) had the tooth removed immediately by the same surgeon. Post-operative results were compared between the two groups.ResultsAll 20 patients in the orthodontic extraction group had their lower impacted third molar removed easily without lower lip numbness after surgery, while 5 patients in the traditional extraction group had transient IAN injury and went away 1 week later. There were no anchorage teeth and adjacent mandibular second molar loose or displacement.ConclusionApplication of orthodontic brackets or mini bone screws on the antagonist maxillary molars is an easy way for orthodontic extraction of impacted lower third molar with roots’ tip compressed to the IAN. It is an effective way to avoid IAN injury during tooth extraction.     

Association between mandibular third molar formation and retromolar space

Objective:To assess the association between formation stages of the mandibular third molars and the space distal to the permanent molars (retromolar space).Materials and Methods:The material included pretreatment lateral cephalographs of 96 orthodontic patients (49 males, 47 females; 8–18 years old). The molar formation stage was assessed through the method of Nolla, which rates the degree of calcification on a scale of 10 stages. The retromolar space was measured from the most concave point of the anterior border of the ramus to the distal surface of the first molar (used because the second molars had not yet erupted in the younger patients). Statistical analyses included t-tests and analyses of variance for group differences and the Pearson product moment to gauge associations among variables.Results:The formation stage advanced with age, but wide standard deviations were noted. Similarly, the retromolar distance increased with age and was greatest between 10 and 12 years. The correlation between retromolar space and developmental stage was high (r  =  0.85). On average, an increase of 5 mm of retromolar space corresponds to a 1.8 stage in tooth maturation.Conclusions:The correlation between third molar mineralization and available retromolar space essentially represents the association between one biologic age (dental formation) and another growth-related event (mandibular skeletal growth). The findings do not necessarily reflect successful emergence or nonimpaction of the molars. Longitudinal data are needed to determine such outcomes.     

Factors associated with spontaneous mesialization of impacted mandibular third molars after second molar protraction

Objectives:To investigate factors associated with spontaneous mesialization of impacted third molars after second molar protraction to close the space caused by a missing mandibular first molar (L-6) or retained deciduous mandibular second molars with a missing succedaneous premolar (L-E).Materials and Methods:Panoramic radiographs of patients treated with mandibular second molar protraction to close the space due to missing L-6 or L-E (14 males, 36 females, mean age = 18.6 ± 4.4 years) were analyzed before treatment (T1) and after second molar protraction (T2). Factors associated with the amount of third molar mesialization were investigated using regression analyses.Results:Mandibular second molars were protracted by 5.1 ± 2.1 mm and 5.8 ± 2.7 mm, measured at the crown and root furcation, respectively. After second molar protraction, third molars showed spontaneous mesialization by 4.3 ± 1.6 mm and 3.8 ± 2.6 mm, measured at the crown and root furcation, respectively. Nolla''s stage of the third molar at T1 (B = 0.20, P = .026) and second molar protraction time (B = 0.04, P = .042) were significantly associated with the amount of third molar mesialization.Conclusions:Greater third molar mesialization was observed when Nolla''s stage of the third molar was higher before treatment and when the second molar protraction time was longer.     

正畸治疗中磨牙的拔除和保留(十一)——拔除第二磨牙与拔除第一前磨牙后第三磨牙牙胚位置的对比研究

目的：比较正畸治疗中拔除第二磨牙与拔除第一前磨牙后第三磨牙牙胚位置的不同改变。方法：选择拔除第二磨牙患者18例及拔除第一前磨牙患者20例，对两组治疗前后X线头颅侧位片进行测量分析。观察矫治前后第三磨牙在垂直方向、水平方向及倾斜角度的改变，比较两组间的差异。结果：两组病例上、下颌第三磨牙垂直位置的改变有显著性差异，拔除第二磨牙组比拔除第一前磨牙组第三磨牙向胎方移动快。水平距离的改变两组之间无差异。拔除第二磨牙组的下颌第三磨牙在矫治后明显竖直，与对照组之间存在显著性差异；矫治后两组上颌第三磨牙的角度均有较大改善，但两组之间的改变无差异。结论：拔除第二磨牙比拔除第一前磨牙加速了第三磨牙向骀方的移动，有利于下颌第三磨牙的竖直，为其以后的萌出创造了有利条件，减少了第三磨牙阻生的可能性。     

Vertical eruption patterns of impacted mandibular third molars after the mesialization of second molars using miniscrews

Objective:To investigate (1) whether vertical eruption of impacted third molars improves after mesialization of second molars and (2) what factors affect the vertical eruption of impacted third molars when space caused by missing molars is successfully closed by mesialization of the second molar using miniscrews.Materials and Methods:The treatment group (Group 1) included 52 patients who had (1) missing mandibular first molars (ML-6) or missing deciduous mandibular second molars (ML-E), (2) initially impacted mandibular third molars, and (3) successful space closure of the edentulous area with orthodontics. Panoramic radiographs at start of treatment (T1) and at time of space closure (T2) were collected. The control group (Group 2) included 46 nonedentulous patients with impacted mandibular third molars without molar protraction treatment. Panoramic radiographs with similar T1/T2 treatment times were selected. Nine measurements were obtained regarding horizontal available space, vertical eruption, and third molar angulation.Results:Third molars erupted vertically an average of 2.54 mm in Group 1 compared with 0.41 mm in Group 2. Age, gender, Nolla stage, and angle of the third molars did not show significant correlations with the vertical change of the impacted third molars, whereas the depth of third molar impaction and available space showed significant correlations.Conclusions:Impacted mandibular third molars vertically erupt as a result of uprighting with mesialization of the second molar, and vertical eruption is affected by the initial vertical location of impacted third molars and available space.     

Mandibular third molar space in different antero-posterior skeletal patterns

Retromolar space has long been identified as a major factor in the aetiology of mandibular third molar impaction. The aims of this study were to compare mandibular third molar space between the different antero-posterior (A-P) skeletal patterns, between erupted and impacted third molars in the different A-P skeletal patterns, and to report on the status of third molar eruption/impaction among the studied subjects. A total of 432 mandibular third molars in 270 subjects (132 females and 138 males) were investigated from dental pantomograms (DPTs) and lateral cephalograms (LC). The average age for the total sample was 20.80 ± 2.03 years. The subjects were divided into three groups according to their ANB angle as follows: skeletal Class I (144 third molars in 90 subjects), skeletal Class II (145 third molars in 95 subjects), and skeletal Class III (143 third molars in 85 subjects). Each group was subdivided into impacted and erupted subgroups. DPT and LC were traced and the following variables were measured: retromolar space width, third molar width and angulation, β angle, second molar angulation, mandibular length, and gonial angle. Independent t-test, analysis of variance, and chi-square test were used for statistical analysis. Retromolar space width in the Class III subjects was smaller than in the Class I subjects (P?相似文献   

拔除第一前磨牙对第三磨牙倾角的影响

目的研究正畸治疗中拔除第一前磨牙进行矫治和非拔牙矫治对第二磨牙和第三磨牙倾角的影响。方法选择56例上下颌第三磨牙均存在的青少年正畸患者,按拔牙与否分为拔牙组（30例,拔除4颗第一前磨牙）和非拔牙组（26例）,通过术前术后曲面断层片来测量患者上下颌第三磨牙长轴和平面的交角,第二磨牙与平面的交角以及第二、第三磨牙长轴的交角,并进行统计学分析。结果拔牙与非拔牙组矫治前后第三磨牙倾角均有不同程度的改善。与非拔牙组相比,拔牙组上下颌第三磨牙长轴与平面交角的变化量更大,2组间年平均变化量的差异有统计学意义（P<0.05）;2组矫治前后上下颌第二、第三磨牙长轴交角的变化无统计学差异,但其年平均变化量在2组间则有统计学差异（P<0.05）。2组间上颌第二磨牙与平面交角的年平均变化量无统计学差异（P>0.05）,而下颌第二磨牙与平面交角的年平均变化量则有统计学差异（P<0.05）。结论拔除第一前磨牙进行正畸治疗有利于第三磨牙倾角的改善,对第三磨牙萌出有积极意义。     

The effects of first premolar extractions on third molar angulations

The purpose of this study was to determine the relationship between the inclinations of second and third molars during a two- to 2.5-year period in patients treated orthodontically both with and without premolar extractions. Records of 37 first premolar extraction patients and 33 nonextraction patients were examined. The pretreatment and posttreatment panoramic radiographs were analyzed. The angles were measured between the long axis of the third molar and the occlusal plane and between the long axis of the third molar and the long axis of the second molar. Changes in third molar angulations from pretreatment to posttreatment for two groups were compared by Mann-Whitney U-test. Statistical analysis revealed that mandibular third molars showed an improvement in angulation relative to the occlusal plane in the first premolar extraction group.     

阻生前磨牙的临床研究现状

阻生牙是口腔中较常见的一种发育畸形,以尖牙、第三磨牙、中切牙、前磨牙及第二磨牙的阻生多见,尤以下颌第三磨牙及上颌尖牙阻生的患病率最高。目前国内外学者对阻生牙的研究主要集中在上颌尖牙和第三磨牙方面,对阻生前磨牙的研究甚少。临床上,很大一部分正畸患者需要进行拔牙矫治,且拔牙牙位主要位于前磨牙区,可见阻生前磨牙对正畸矫治设计及预后影响极大。本文对阻生前磨牙现有的研究状况进行综述,对阻生前磨牙的流行病学特点、临床定位和治疗方法进行总结,以期为正畸医生制定正畸矫治计划提供参考。     

Position of lower wisdom teeth and their relation to the alveolar nerve in orthodontic patients treated with and without extraction of premolars: a longitudinal study

Objectives

The present longitudinal study aimed to compare changes in the lower third molar position and nerve involvement in orthodontically treated patients with and without premolar extractions.

Materials and methods

The sample consisted of pretreatment and posttreatment panoramic radiographs of 349 orthodontically treated patients subdivided into a non-extraction group (n?=?263) and an extraction group (n?=?86). Patients did not present dental agenesis in the lower jaw. The mandibular third molar position was assessed by classifying the teeth according to Pell and Gregory, Winter, and two new classifications. The relation between third molars and the mandibular canal was assessed based on Whaites’ classification. The development of third molars was evaluated based on Demirjian’s classification. Data were analyzed using frequency analysis, Mann–Whitney U test, Fisher’s exact test, and chi-square testing.

Results

There was a significant difference (p?p?Conclusions Orthodontic treatment without premolar extractions shows significantly more eruption problems of wisdom teeth than those with premolar extractions. Third molars in the non-extraction group were more frequently found in close relationship to the mandibular nerve compared to the extraction group.

Clinical relevance

Orthodontists should be aware of the effect of orthodontic treatment on the development of the lower third molars.     

Second molar extractions: a review

In this exhaustive review, a number of parameters related to maxillary and mandibular second molar extractions are discussed. The parameters reviewed include the timing of extractions and the effect of extractions on third molar eruption, posterior interdigitation, and incisor imbrication. The advantages and limitations of this procedure are outlined. The available information strongly suggests that the extraction of second molars relieves crowding in the posterior part of the arch, causes faster eruption of third molars, and diminishes the number of unerupted and/or impacted third molars. Consideration of the decrease in the number of impacted third molars after second molar extraction should be balanced with the fact that the extracted teeth are usually sound and are unimpacted. In addition, the third molars that do erupt frequently are poorly angulated and/or in poor contact with the first molars. This will necessitate an additional "late" period of fixed-appliance therapy to bring these teeth into good occlusion.     

Patterns of third molar impaction in a group of volunteers in Turkey

The aim of this study was to investigate the different variables in mesio-vertically positioned impacted or erupted third molars in a group of volunteers in Turkey to determine the angular changes and levels of eruption radiographically using standardised panoramic radiographs. There were 213 volunteers with impacted and erupted third molars included in this study, most of whom were dental students. Standardised panoramic radiographs were taken from all the volunteers. The radiographic parameters included angulation of tooth, level of eruption, development of root, mesiodistal crown width, retromolar space, and gonial angle. Statistical analysis was done using the t-test for independent groups. It was found that the mesiodistal angulation of third molars was significantly greater while the retromolar space of third molars was significantly smaller in the impacted group (P<0.05). There was also a significant difference in retromolar space/third molar crown width ratio (P<0.05).     

正畸牵引术在下颌第三磨牙低位近中阻生拔除中的应用

目的 :研究正畸牵引拔除下颌近中阻生第三磨牙对改善邻牙牙槽骨缺损的作用。方法 :选取2016-07—2018-01期间,我院收治的单侧或双侧有第二磨牙远中牙槽骨缺损的下颌第三磨牙近中阻生患者60例,按照随机数字表法将所有患者分为对照组(30例)和正畸牵引组(30例)。对照组患者常规拔除下颌第三磨牙,正畸牵引组患者经正畸牵引1~6个月后拔除下颌第三磨牙。检测患者正畸牵引治疗前(T0)、拔牙前(T1)、拔牙后3个月(T2)、拔牙后6个月(T3)这几个时间点,下颌第二磨牙近中及远中牙槽嵴顶至釉牙骨质界高度、下颌第二磨牙近中及远中牙槽骨密度、张口受限情况。结果:正畸牵引组患者在T1、T2、T3节点时,下颌第二磨牙近中牙槽嵴顶至釉牙骨质界高度分别为5.16、3.98、2.12 mm,均低于对照组的7.16、4.57、3.16 mm,差异有统计学意义(t/P=12.250/0.001、8.963/0.001、56.680/0.001)。正畸牵引组患者在T1、T2、T3节点时,下颌第二磨牙远中牙槽嵴顶至釉牙骨质界高度分别为5.24、3.15、2.34 mm,低于对照组的8.12、5.49、3.16 mm,差异有统计学意义(t/P=17.670/0.001、43.280/0.001、15.110/0.001)。正畸牵引组患者在T1、T2、T3节点时,张口受限评分分别为2.10、1.25、0.68分,均低于对照组的2.56、2.00、1.69分,差异有统计学意义(t/P=9.690/0.001、30.530/0.001、41.120/0.001)。结论:正畸牵引拔除下颌近中阻生第三磨牙可有效改善邻牙牙槽骨缺损现象,增大牙槽骨密度。     

Investigation of the prevalence of impacted third molars and the effects of eruption level and angulation on caries development by panoramic radiographs

Background This study is aimed to determine the prevalence of impacted third molars and to investigate the effects of their eruption level and angulation on caries formation in the distal of the adjacent tooth.Material and Methods This cross-sectional study was conducted on panoramic radiographs of 38481 patients who were admitted to the Trakya University, Faculty of Dentistry. The panoramic radiographs of 7998 patients with at least one impacted third molar were included. Third molars were classified according to Winter’s classification and Pell and Gregory’s classification. The frequency of caries in partially impacted third molars and adjacent second molars was determined. The chi-square tests were used to determine potential associations between the third molars'' level of eruption, angulation, and caries development.Results The study group consisted of 4423 females (55.3%) and 3575 males (44.7%) with a mean age of 36.3±13.4 years. The prevalence of the third molar impaction rate was 23%. The impaction pattern of partially erupted third molars was characterized by an eruption level of A with the vertical position in both jaws. Partially erupted and vertically placed maxillary third molars in the level of position A caused more caries in the adjacent tooth and mesioangularly located partially erupted mandibular third molars were associated with more caries in the adjacent tooth.Conclusions The angulation and eruption level of partially erupted third molars should be carefully examined. The prophylactic extraction of vertically and mesioangularly located third molars, especially with an eruption level of position A can be suggested to eliminate the related complications and risk of caries. Key words:Dental caries, digital radiography, impacted tooth, panoramic radiography, third molar.