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.     

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.     

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.     

Correlation Between Height and Impacted Third Molars and Genetics Role in Third Molar Impaction

AimThis study sought to evaluate the relationship between height of an individual and the presence of impaction of maxillary and mandibular third molars, and to determine the role of genetics in third molar impaction. Materials and MethodsThis was a case–control study, with cases consisted of 200 subjects with third molar impactions; and 200 controls without third molar impactions. Height of subjects was measured, and saliva samples were collected from all the subjects. DNA was extracted from saliva samples. To investigate the role of selected genes in the etiology of third molar impactions, Taqman Genotyping using SNPs identified for jaw growth, height and tooth agenesis was employed. Five candidate genes were investigated using 11 markers (SNPs). ResultsThe mean height of cases was significantly lower than that of the control subjects (p = 0.04). No difference was found in allele frequency between cases and controls for 10 of the 11 SNPs. However, for rs6504591 the p value was near significance (p = 0.07) with odd ratio of 2.131. Subjects with lower third molar impactions were significantly shorter than those who have fully erupted third molars.ConclusionsSubjects with lower third molar impactions were significantly shorter than those who have fully erupted third molars. We observed that individuals with third molar impaction tend to have T allele at the locus, suggesting that the T allele at the locus may increase the risk for having an impacted third molar. The rs6504591 G/T variation on human chromosome 17 (WNT9B gene) appears to increase risk by twofolds for impaction albeit with inability to detect significance due to small sample size.     

Third molar tooth agenesis and pattern of impaction in patients with palatally displaced canines

Objectives:To investigate the association between third molar agenesis and pattern of impaction, missing teeth, and peg-shaped lateral incisor with palatal canine displacement (PDC).Materials and Methods:The pretreatment orthodontic orthopantomograms of 438 patients (122 males and 316 females) diagnosed with PDC were included. A total of 338 patients with normally erupted canines who had a preexisting radiograph as part of their orthodontic treatment (125 males and 313 females) served as controls. Orthopantomograms were evaluated for missing third molars, third molar eruption status, and type of impaction, third molar spaces, third molar width, and angulation.Results:In the PDC group, at least one third molar was missing in 48% and 19% in the upper and lower arches, respectively. Also, 38% and 67% of PDC patients had at least one third molar impaction in the upper and lower arches, respectively. The difference between the PDC and control groups was significant for both missing and impacted third molars (P < .001 for each). The most common type of third molar impaction in the upper arch was vertical and distoangular in the PDC and control groups, respectively. Upper and lower third molar width and spaces were reduced in PDC patients when compared with the control group (P < .001). In PDC patients, missing teeth and peg-shaped lateral incisors were recorded in 5.6% and 9.1%, respectively.Conclusions:PDC patients showed a high prevalence of third molar agenesis and impaction. Upper and lower third molar width and space were reduced in the PDC patients. There were no significant associations between tooth agenesis (other than third molars) and the PDC anomaly.     

正畸治疗中磨牙的拔除和保留(二十一)——应用全颌曲面断层片对下颌磨牙冠根形态的比较研究

目的：统计分析下颌第一、第二、第三磨牙牙冠近远中宽度、牙体长度、分根情况以及相关因素。方法：选择下颌无缺失牙,下颌第三磨牙牙根发育已完成的全颌曲面断层X线片249张进行测量分析。结果：牙体长度下颌第一磨牙至第三磨牙依次递减;牙冠近远中宽度下颌第一磨牙最大,第二、第三磨牙无差别;分根率下颌第一磨牙至第三磨牙依次递减,根分叉程度下颌第一磨牙最大,第二、第三磨牙无差别;下颌第三磨牙萌出组牙体长度大于第三磨牙阻生组,并且与其牙冠近远中宽度成正相关,分根率也偏大;下颌第三磨牙相对宽度在单根、双根组间有差别;下颌第三磨牙牙冠宽度/磨牙后间隙长度比值与下颌第三磨牙相对长度比成负相关关系。结论：下颌第一磨牙冠根形态最好;第二、第三磨牙冠根形态有较大的相似性,只要有足够的空间,下颌第三磨牙牙根就能得到良好的发育。     

Radiographic assessment of lower third molar eruption in different anteroposterior skeletal patterns and age-related groups

Objective:To analyze radiographic predictors for lower third molar eruption among subjects with different anteroposterior skeletal relations and of different age groups.Materials and Methods:In total, 300 lower third molars were recorded on diagnostic digital orthopantomograms (DPTs) and lateral cephalograms (LCs). The radiographs were grouped according to sagittal intermaxillary angle (ANB), subject age, and level of lower third molar eruption. The DPT was used to analyze retromolar space, mesiodistal crown width, space/width ratio, third and second molar angulation (α, γ), third molar inclination (β), and gonion angle. The LC was used to determine ANB, angles of maxillar and mandibular prognathism (SNA, SNB), mandibular plane angle (SN/MP), and mandibular lengths. A logistic regression model was created using the statistically significant predictors.Results:The logistic regression analysis revealed a statistically significant impact of β angle and distance between gonion and gnathion (Go-Gn) on the level of lower third molar eruption (P < .001 and P < .015, respectively). The retromolar space was significantly increased in the adult subgroup for all skeletal classes. The lower third molar impaction rate was significantly higher in the adult subgroup with the Class II (62.3%) compared with Class III subjects (31.7%; P < .013).Conclusion:The most favorable values of linear and angular predictors of mandibular third molar eruption were measured in Class III subjects. For valid estimation of mandibular third molar eruption, certain linear and angular measures (β angle, Go-Gn), as well as the size of the retromolar space, need to be considered.     

Factors affecting spontaneous eruption of impacted mandibular first molars after surgical exposure

Objectives

The purpose of this study was to investigate factors, such as the status of impaction, root developmental stage, depth of impaction, tooth angulation and eruption space, which can influence the spontaneous eruption of impacted mandibular first molars after surgical exposure.

Arrested eruption of the permanent lower second molar

The incidence of retention/impaction of the permanent lower second molar (M2inf) lies between 0.6/1000 and 3/1000. Therefore, the purpose of the present study was to investigate the craniofacial morphology, the frequency of dental anomalies and the inclination of the affected M2inf and the adjacent first molar in patients with arrested eruption of M2inf. The overall goal was to elucidate the aetiology of arrested tooth eruption and to present the characteristics of these patients in order to improve diagnosis and treatment planning. Radiographic material (profile radiographs and orthopantomograms) from 19 patients (nine females and 10 males; 13-19 years of age at the time of referral) were analysed. The ages of the patients when profile radiographs were taken for cephalometric analysis varied from 8 to 16 years. The study shows that this group of patients, compared with a reference group, had an increased sagittal jaw relationship (Class II). Specifically, the mandibular prognathism was less, the mandibular gonial angle smaller, the mandibular alveolar prognathism enlarged and the maxillary incisor inclination less than in the reference group. Furthermore, this group of patients had a more frequent occurrence of morphological tooth anomalies, such as root deflections, invaginations, and taurodontism. However, none of the patients with arrested eruption of M2inf had agenesis of the lower third molar. The study did not reveal an association between the degree of inclination of the M2inf and that of the first molar in the same region. The results of this investigation show that conditions such as the craniofacial morphology and deviations in the dentition are associated with arrested eruption of M2inf. Therefore, it is important to evaluate these conditions in future diagnosis and treatment planning of patients with arrested eruption of M2inf.     

Risk factors for lingual plate fracture during mandibular third molar extraction

Objective

The aim of this study was to predict the risk of lingual plate fracture during mandibular third molar (M3) extraction.

Materials and methods

Cone beam computed tomography (CBCT) data from 264 mandibular M3s (erupted and impacted) from 264 patients (104 males and 160 females; age range, 17–75 years) were retrospectively analyzed. Lingual plate thicknesses at the levels of the mid-root and root apex of the M3s were measured and defined as “thicker” (bone thicker than 1 mm), “thinner” (bone thinner than 1 mm), or “perforated” (bone perforated by the M3 root). These measurements were correlated with potential risk factors for thinner and perforated lingual plates: tooth position of the mandibular M3, morphology of the lingual plate, and patient characteristics (age and sex).

Results

The mean thickness of the lingual plate was 1.49 ± 1.38 mm at the mid-root of the M3s, and 2.35 ± 2.03 mm at the root apex. Multivariate regression analyses revealed that mesioangularly and horizontally impacted M3s were significantly associated with thinner and perforated lingual plates at the mid-root (P < 0.001), whereas the M3s in infra-occlusion positions (in infra-occlusion when compared with the adjacent second molar) had thinner lingual bone at the root apex (P = 0.022 and P = 0.027, depending on the level of impaction). Female patients were less likely to have lingual plate perforation (P = 0.036).

Conclusions

Mesioangulation, infra-occlusion, and male sex were risk factors for lingual plate fracture.

Clinical relevance

When the risk of lingual plate fracture is high, a sufficiently large flap, osteotomy, and tooth section by bur or piezosurgery are recommended to create a good operative field and avoid excessive pressure on the lingual plate.

     

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   

汉族下颌第三磨牙牙尖与牙根的关系

本文对342颗下颌第三磨牙(牙合)面牙尖与牙根的关系以及阻生的临床类型与牙根数目之间的关系进行了探讨。结果表明:(牙合)面牙尖呈四型,分别是四尖型、五尖型、六尖型和八尖型。牙根呈三型,分别是融合根型、双根型和三根型。(牙合)面牙尖为四尖型,其融合根比例高达71.01％,五尖型融合根比例降为27.97％,双根比例升为61.91％。六尖型没有融合根,双根约占3/4(74.19％),三根约占1/4(25.81％)。八尖型都是三根。 阻生类型中水平位和颊向位融合根的比例大,分别为85.714％和56.43％。近中位、舌向位和垂直位则双根的比例高,分别为60.417％、58.334％和47.619％。以垂直位和远中位三根比例最高,分别为25.397％和25.0％,其余各类型中三根的比例均不足9％。     

磨牙倾斜角度和萌出间隙对第三磨牙萌出的影响

目的研究影响第三磨牙阻生或萌出的一些客观因素。方法选择86例(男37例,女49例)平均年龄25.4岁,上下颌第三磨牙均存在的患者,将其分为萌出组和阻生组,利用曲面断层片对患者上下颌第三磨牙的近中倾斜角、牙冠近远中径、磨牙后间隙、磨牙后间隙和牙冠近远中径的比值进行测量分析。结果上颌萌出组萌出间隙较阻生组大1.95mm,第二磨牙和第三磨牙长轴交角相差12.53°,萌出组第三磨牙近远中径比阻生组小0.69mm,有统计学差异。下颌萌出组萌出间隙L-ES(R)较阻生组平均值大3.33mm;第三磨牙与牙合平面交角阻生组较萌出组大32.48°;萌出组与阻生组的磨牙后间隙/牙冠近远中径平均值分别为1.05、0.85,3项指标差异均有显著性(P<0.01)。下颌第三磨牙近远中径相差0.3mm,无统计学意义。结论第三磨牙萌出受萌出间隙和磨牙间交角的影响,对于上颌第三磨牙,磨牙交角影响更大,对于下颌第三磨牙无足够的间隙萌出,是导致下颌第三磨牙阻生的重要原因。     

Positional changes and eruption of impacted mandibular third molars in young adults: A radiographic 4-year follow-up study

Objective. To measure changes in angular position and eruption status of mesially impacted mandibular third molars (M3) during 4-year follow-up period.Study design. Standardized panoramic radiographs were taken at the start of the study (the average age of the subjects was 19.7 years) and 4 years later. Angulation and degree of impaction of M3 were determined by their sagittal relationships to the adjacent second molars. The impacted M3 were either partially erupted or unerupted.Results. Initial examination showed that among a total of 59 mesioangular M3, 49 (83%) had inclination between 5 and 30 degrees. The proportion of M3 that became upright (zero tilt) was 76% (13/17) with initial angulations of 5 to 10 degrees, 61% (11/18) with initial angulations of 15 to 20 degrees, and 14% (2/14) with initial angulations of 25 to 30 degrees. None of the M3 originally presented at 35 degrees or more became upright, but an average decrease of 12 degrees in angulation was registered. In total, 26 M3 of 59 (44%) became upright during the follow-up period. Initial examination of levels of eruption showed that among 59 M3, 13 (22%) were partially erupted and the rest were unerupted. Of the 46 M3 initially unerupted, 17 (37%) became fully erupted and 7(15%) erupted partially during the 4-year follow-up. Of the total sample, 25 (42%) had erupted to full occlusion during the observation period.Conclusion. A significant proportion of mesially impacted mandibular M3 had changed their angulation and became fully erupted by the time the individual reached 24 years of age. Positional changes and eruption of impacted M3 are unpredictable phenomena.     

Effect of premolar extraction on mandibular third molar impaction in young adults

Objective:To test the null hypothesis that orthodontic therapy with or without premolar extraction does not result in any difference in third molar impaction.Materials and Methods:Two groups were formed: 22 patients in one group with first premolar extractions and 22 patients in the other group without extractions. All patients were nongrowing subjects who had normal gonial angles and were skeletal Class I at the beginning of treatment. The available space for third molars, inclination of second and third molars, and angle between the second and third molars were evaluated. Also, the correlation of measured parameters and type of orthodontic therapy with the eruption of third molars was evaluated.Results:Of the third molars, 81.8% were impacted in the nonextraction group and 63.6% were impacted in the extraction group. Impaction of mandibular third molars was significantly correlated to the pretreatment and posttreatment inclination of third molars and the angle between the second and third molars. In the extraction therapy group, the retromolar distance increased significantly with a mean of 1.30 ± 1.25 mm.Conclusions:When the inclination of the third molar is inconvenient, the tooth may remain impacted even if there is enough retromolar space.     

Eruption Status of Third Molar and Its Possible Influence on the Location of Mandibular Angle Fracture: A Retrospective Analysis

Introduction

This study was designed to evaluate the influence of eruption status of mandibular third molars on the location of mandibular angle fracture. We also aimed to evaluate the incidence of damage to mandibular third molar teeth (M3) and its roots.

Materials and Methods

Medical records and panoramic radiographs of 142 patient cohorts with mandibular angle fractures with third molars present were retrospectively reviewed.

Results

Revealed that incidence of angle fracture were high in patients with fully erupted M3 when compared to unerupted group. Out of 142 patients, 108 fractures were found involving the M3 socket and 14.1 % had damage to M3.

Conclusion

The presence of erupted mandibular third molar increases the chances of angle fracture when compared to impacted M3. Involvement of the M3 socket often resulted in increased operative time and complexity of the surgical procedure with possible removal of the damaged M3.     

Mandibular cephalometric characteristics of a Saudi sample of patients having impacted third molars

Objective

To evaluate the cephalometric characteristics of mandibles of Saudi patients having impacted third molars and to compare them to those of patients having normally erupted third molars.

Material and methods

One hundred and twenty-one Saudi adult subjects (59 females and 62 males; age: 20–40 years) were divided into two groups based on the status of the mandibular third molars: (1) impaction group and (2) normal group. Means and standard deviations of 21 cephalometric measurements related to mandibular geometry were measured and compared between the two groups using the unpaired t-test. Males and females in the impaction group were also compared with their equivalent subgroups in the normal group using the unpaired t-test.

Results

Anteroposteriorly, space distal to second molar, ramal width and mandibular body length were significantly less in the impaction group than in the control group. In addition, posterior teeth were more upright in the impaction group. Vertically, posterior alveolar height was significantly less in the impaction group. The Y-axis was significantly increased in the impaction group.The significance of these measurements was variable between males and females.

Conclusions

Third-molar impactions in the Saudis living in the Western region of Saudi Arabia were more likely to occur when inadequate retromolar space is present. This can be attributed to certain mandibular skeletal and dental features, among which the increased width of mandibular ramus and backward inclination of posterior teeth seem to be the most influencing factors in both sexes.     

下颌第三靡牙牙尖、阻生类型与牙根的相关关系

目的：本文对1090颗下颌阻生第三磨牙H面牙尖、阻生类型与牙根的相互关系进行了探讨。结果：He面牙尖呈六型，分别是三尖型（0．55％）、四尖型（26．42％）、五尖型（53．58％）、六尖型（18．16％）、七尖型（0．83％）和八尖型（0．46％）。牙根呈四型，分别是融合根型（35．14％）、双根型（57．34％）、三根型（7．34％）和四根型（0．18％）。He面牙尖数目少，融合根比例高，三尖主要是融合根型；牙尖根数目增加，双根和三根比例上升。七尖型、八尖型没有融合根型。阻生尖型以近中位最多见（31．62％），垂直位（29．085），颊向位（16．88％），远中位、舌向位和水平位均不足9％，远中位融合根比例高达47．06％；近中位、垂直位水平位双根比例高，分别为64．35％、58．04％和57．73％；颊向位垂直位三根比例高，分别达13．04％和11．35％，其余各类型中三根的比例均不足9．5％，结论：各阻生类型均符合He面牙尖数少数少融合根比例高，He面牙尖数多，双根和三根的比例高的规律。     

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.     

近中阻生的下颌第三磨牙萌出情况与其倾斜角度的关系研究

目的:3年随防观察近中阻生的下颌第三磨牙萌出情况与其倾斜角度的关系。方法:72名在校本科生,年龄18~20岁,共108颗近中阻生的下颌第三磨牙,研究开始和观察3年后分别拍摄全颌曲面断层片,检查下颌第三磨牙倾斜程度和萌出水平。结果:在3年观察结束时,71.4%(30/42)最初倾斜角度在5°~10°之间的下颌第三磨牙变为直立。33.3%(6/18)最初倾斜角度在15°~20°之间的下颌第三磨牙变为直立。25%(3/12)最初倾斜角度在25°~30°之间的下颌第三磨牙变为直立。最初倾斜角度在35°及以上的下颌第三磨牙没有一颗变为直立的。结论:在一定程度上,可以根据阻生的下颌第三磨牙近中倾斜的角度来预测第三磨牙日后的萌出状况。有些近中阻生,倾斜角度小于35°的下颌第三磨牙经过一定时间是有可能完全萌出而不必预防性拔除的。