Presence of third molar germs in orthodontic patients in Japan

Clinical risk factors caused by third molar levelling following extraction of a mandibular second molar

BACKGROUND/OBJECTIVES

Mandibular second molar (MdM2) is often lost, and its space is filled with a bridge or implant. MdM2 extraction followed by orthodontic treatment protracting mandibular third molar (MdM3) towards the MdM2 position may overcome the missing of MdM2. The objectives of our study were to describe the outcome of the procedure and examined clinical risk factors such as external apical root resorption (EARR) and alveolar bone loss (ABL), as the indicators of poor orthodontic treatment outcomes.

MATERIALS/METHODS

This retrospective study included 70 cases in 56 patients who received orthodontic treatment at Tokyo Medical and Dental University Hospital between 2007 and 2018. Multi-bracket appliances were used in all patients for MdM3 protraction. Using linear mixed effects models, EARR and ABL were regressed on various factors, including panoramic and cephalometric variables.

RESULTS

With the mean treatment duration of 1040.4 ± 441.8 days, MdM2 space closure was achieved in 92.8% (65 cases). The ANB angle (P = .023) and the use of temporary anchorage devices (TADs) (P = .021) were significantly associated with the greater EARR, while the mandibular plane angle (P = .033) was associated with the greater ABL. MdM3 protraction using the fixed appliances resulted in the closure of MdM2 space in > 90% of cases without evident root resorption.

LIMITATION

There is a possibility of residual confounding due to the nature of observational study.

CONCLUSION/IMPLICATION

Orthodontic treatment of MdM3 protraction may be a feasible strategy to close the space of the missing MdM2.

Factors associated with the eruption of the impacted maxillary third molars after second molar extraction

INTRODUCTION

In orthodontic treatment, the space left after extracting the maxillary second molar (MxM2) may be filled by the eruption of the impacted third molar (MxM3). However, little is known about the factors associated with the eruption of the impacted MxM3. We aimed to characterize the clinical factors associated with the time taken for MxM3 eruption after MxM2 extraction.

METHODS

We analyzed factors associated with late MxM3 eruption (>500 days after MxM2 extraction) in 84 molars. Prespecified risk factors were entered into logistic regression models to estimate odds ratios (ORs).

RESULTS

The median duration between MxM2 extraction and MxM3 eruption was 302 days (interquartile range, 140-424). Significant factors associated with late MxM3 eruption included the proximity of the MxM3 root to the maxillary sinus floor (OR, 51.72), the distance between the occlusal plane of the MxM3 and the apical third of the MxM2 roots (OR, 16.56), MxM3 angulation and depth of ≥20° (OR, 5.58), ANB angle of <2° (OR, 9.05), and ≥1.5 mm distal movement of the maxillary first molar (MxM1) from its original position at the time of MxM2 extraction and MxM3 eruption (OR, 12.9). The probability of late MxM3 eruption was 0% (0 out of 30) with no risk, 6.9% (2 out of 29) with 1 risk factor, and 52% (13 out of 25) with ≥2 risk factors.

CONCLUSIONS

We identified 5 clinical factors associated with late MxM3 eruption after MxM2 extraction. The probability of late MxM3 eruption increased as the number of present risk factors increased. These findings can be used for risk stratification during orthodontic treatment.

Relationships between skeletal morphology and patterns of bilateral agenesis of third molars in Japanese orthodontic patients

The aim of this study was to reveal the correlations between bilateral agenesis of third molars (M3s) and skeletal morphology in Japanese male and female orthodontic patients. Sixty patients (30 males, 30 females), with bilateral agenesis of maxillary M3s and without agenesis of mandibular M3s (group U), and 60 patients (30 males, 30 females), with bilateral agenesis of mandibular M3s and without agenesis of maxillary M3s (group L), were selected as agenesis groups. Additionally, 60 patients (30 males, 30 females) with all four M3s were selected as the control group (group C). Patients in these three groups had no agenesis of teeth other than M3s. Lateral cephalograms of each patient were used to evaluate skeletal morphology of the maxilla and mandible. Two-way analysis of variance was used for statistical comparisons. Groups U and L had significantly smaller maxillary length and area than group C. Group U exhibited a significantly smaller lower facial height than group C. Males showed significantly larger maxillary length; total mandibular and mandibular body length; mandibular ramus height; SNB angle; maxillary area; and mandibular symphysis, corpus and ramus areas than females. Females had significantly larger lower facial height, gonial angle and ANB angle than males. Smaller maxillary length and area and lower facial height should be considered in planning orthodontic treatment for patients with bilateral agenesis of maxillary and mandibular M3s.

Prevalence and patterns of tooth agenesis among malocclusion classes in a Japanese orthodontic population

The purpose of the present study was to assess, in detail, the association between tooth agenesis (TA) and various sagittal skeletal malocclusion groups in a Japanese orthodontic population. One thousand and twenty patients were divided into skeletal Class I, II, or III malocclusion groups using the A point, nasion, and B point angle. TA was identified in each group using panoramic radiographs. Patients with class III malocclusion exhibited a significantly higher prevalence of third molar (M3) agenesis, bilateral and overall agenesis of the maxillary M3s than those patients with a class II malocclusion. Those with a Class II malocclusion demonstrated a significantly lower prevalence of overall agenesis of the mandibular M3s than those with class I or III malocclusions. There were no significant differences in the prevalence of agenesis of teeth other than the M3s between the skeletal malocclusion groups. In each group, there was significantly more M3 agenesis present in the maxilla than in the mandible, and agenesis of the incisors and second premolars was found more often in the mandible than in the maxilla. Sagittal jaw relationships were significantly associated with M3 agenesis but were not associated with agenesis of the maxillary and mandibular incisors and second premolars.

Comparison of the effect of premolar extraction and non-extraction on the position and developmental changes of the lower third molars

The aim of the present study was to comprehensively assess the posttreatment effect of premolar extraction versus non-extraction on the position and development of the lower third molars. The sample consisted of 227 patient's pre- and posttreatment panoramic radiographs (53 with four premolar extractions, 174 without extractions). The position and developmental stage of the lower third molars were evaluated by using Pell-Gregory's, Winter's, modified Miloro-DaBell's and Demirjian's classifications, respectively. Premolar extraction had a considerably positive influence on the position and development of the lower third molars and therefore could provide better prognosis for their eruption.

Association between skeletal morphology and agenesis of all four third molars in Japanese orthodontic patients

The purpose of this study was to clarify differences in skeletal morphologies between male and female orthodontic patients with and without agenesis of all four third molars. A total of 64 patients (32 males and 32 females) with agenesis of all four third molars without agenesis of other teeth were selected as the third molars agenesis group (group 1). In addition, 64 patients (32 males and 32 females) with all these teeth were selected as controls (group 2). Lateral cephalograms taken between the ages of 14 and 30 years were used to compare skeletal morphology between groups 1 and 2 and between sexes. Maxillary length (P < 0.001), lower facial height (P < 0.05), gonial angle (P < 0.001) and mandibular plane angle (P < 0.001) were significantly smaller in group 1 than in group 2. Irrespective of the presence or absence of all four third molars, males had significantly smaller lower facial height (P < 0.01) and mandibular plane angle (P < 0.001) and significantly greater total mandibular length (P < 0.001), mandibular body length (P < 0.001) and mandibular ramus height (P < 0.001) than females. Japanese orthodontic patients with agenesis of all four third molars had significantly small maxillary length, lower facial height, gonial angle and mandibular plane angle.

Obeservations on association between third molar agenesis and craniofacial morphology

OBJECTIVE

This study was designed to examine the relationship between third molar agenesis and skeletal morphology in the Chinese population.

MATERIALS AND METHODS

A total of 1043 patients' records were analyzed with panoramic radiographs and cephalograms. Congenitally missing third molars were assessed with respect to gender, jaw, and side, and assessed in various types of facial morphology. Linear, angular, and proportional cephalometric measurements were analyzed and compared among the samples. For the evaluation of results, the following statistics were used: the Pearson χ ² test, one-way ANOVA, and the Student-Newman-Keuls method.

RESULTS

The overall prevalence of third molar agenesis was 28.7%. Missing third molars were more common in the maxilla and on the right side, while the difference was not statistically significant (P > 0.05) between genders. Every hypodontia group had a smaller SN-GoGn angle, Y-axis-FH angle, and a larger S-Go/N-Me ratio. The group with third molar agenesis in both jaws had smaller SNA and Wits values. The frequency of third molar agenesis in subjects with a Class II malocclusion was significantly lower than in other types of malocclusion (P < 0.05), and the incidence of third molar agenesis in hypodivergent growth pattern was higher than in other patterns (P < 0.05).

CONCLUSION

The results demonstrate a possible association between third molar agenesis and both sagittal and vertical craniofacial morphology.

Agenesis of Third Molars among Turkish Children between the Ages of 12 and 18 Years: A Retrospective Radiographic Study

PURPOSE

The aim of this study was to investigate the agenesis of third molars (M3) in children with permanent dentition in a limited population in the province of Izmir, Turkey.

STUDY DESIGN

The panoramic radiographs of 773 patients (457 females, 316 males) were evaluated retrospectively at the Dental Hospital of Ministry of Health in İzmir, Turkey. The patients' ages ranged from 12-18 years. The agenesis of M3 teeth was investigated according to maxilla and mandible and right and left distribution.

RESULTS

In 593 of the patients (76.7%), all of the M3 teeth were present in the mouth; while in the other 180 (23.3%) patients, agenesis of a varying number of M3 teeth was identified. In 31 patients (4.0%), total M3 tooth agenesis was observed. A statistically significant relationship was not found between gender and M3 teeth (p=0.091). A statistically significant relationship was found between congenital M3 tooth agenesis and the maxilla (14.3%) and mandible (9.6%) (p<0.001). However, a statistically significant difference was not found between the right-left area of the jaw (p=0.100).

CONCLUSION

As a result, while all M3 teeth were present in 76.71% of the population studied in the province of Izmir, agenesis of one or more than one M3 tooth was found in the other 23.29% of the patients studied.

Multivariate analysis of factors affecting presence and/or agenesis of third molar tooth

To investigate the presence and/or agenesis of third molar (M3) tooth germs in orthodontics patients in Malaysian Malay and Chinese population and evaluate the relationship between presence and/or agenesis of M3 with different skeletal malocclusion patterns and sagittal maxillomandibular jaw dimensions. Pretreatment records of 300 orthodontic patients (140 males and 160 females, 219 Malaysian Malay and 81 Chinese, average age was 16.27±4.59) were used. Third-molar agenesis was calculated with respect to race, genders, number of missing teeth, jaws, skeletal malocclusion patterns and sagittal maxillomandibular jaw dimensions. The Pearson chi-square test and ANOVA was performed to determine potential differences. Associations between various factors and M3 presence/agenesis groups were assessed using logistic regression analysis. The percentages of subjects with 1 or more M3 agenesis were 30%, 33% and 31% in the Malaysian Malay, Chinese and total population, respectively. Overall prevalence of M3 agenesis in male and female was equal (P>0.05). The frequency of the agenesis of M3s is greater in maxilla as well in the right side (P>0.05). The prevalence of M3 agenesis in those with a Class III and Class II malocclusion was relatively higher in Malaysian Malay and Malaysian Chinese population respectively. Using stepwise regression analyses, significant associations were found between Mx (P<0.05) and ANB (P<0.05) and M3 agenesis. This multivariate analysis suggested that Mx and ANB were significantly correlated with the M3 presence/agenesis.

Radiographic evaluation of third molar genesis in Greek orthodontic patients

Objectives

The study reported here investigated the first radiographic evidence of third molar (M3) formation, their incidence and distribution as well as their congenital absence on the right or the left side in either the maxilla or the mandible, in both male and female Greek orthodontic patients.

Materials and methods

A total of 618 panoramic radiographs were initially examined. After the application of inclusion/exclusion criteria, the group finally selected consisted of 428 patients (mean age 11.64 years, range 5–18): 179 males (mean age 11.73 ± 2.46) and 249 females (mean age 11.57 ± 2.45). The collected data were analyzed using SPSS software (IBM, Armonk, New York, NY, USA). The level of significance for all analyses was set to p = 0.05. The chi-square (χ²) test was used to assess the relationships between variables. The Wilcoxon’s signed-rank test and the Mann-Whitney U test were also used for comparisons as well as the Spearman’s rho test for correlations.

Results

M3s were first detected in females at the age of 7 years whereas males followed one year later at the age of 8 years. A strong correlation between age and M3 development was revealed for both sexes (Spearman’s rho = 0.177, p = 0.05). Presence of all four M3s was the most common incidence (present in 70.8% of study subjects), followed by the agenesis of two (12.1%), agenesis of all four (8.4%), one (6.8%), and three (1.9%) M3s. Congenitally missing M3s in all subjects showed a significantly greater predilection for the maxilla over the mandible (19.6% and 15.5%, respectively) (Wilcoxon signed-rank test Z = −2.404, p = 0.016). However, the distribution was found equal between the two sides of the jaws. The difference between the absent frequencies of M3s in the mandible and the maxilla was found statistically significant for the total sample (McNemar’s test, p < 0.001) and for males (p = 0.041) as well.

Conclusion

The study data may provide a reference for the M3 genesis in Greeks.

Association between third molar agenesis patterns and agenesis of other teeth in a Japanese orthodontic population

The purpose of this study was to investigate the patterns of third molar agenesis and incidence of agenesis of other permanent teeth in a Japanese orthodontic patient group. A total of 417 Japanese subjects (134 males and 283 females) with agenesis of one or more third molars were divided into four groups according to the agenesis pattern, and 874 other Japanese subjects (302 males and 572 females) without third molar agenesis were assigned to a control group. Panoramic radiographs and medical and dental records were used to examine for tooth agenesis. The Chi-square test and odds ratio were used to make statistical comparisons. The prevalence of third molar agenesis worked out at 32.3% with no statistically significant gender difference. A high prevalence rate of agenesis of third molars, unilateral or bilateral, could be considered characteristic of the Japanese orthodontic population. Significant increases in occurrence of oligodontia, and unilateral or bilateral agenesis of other teeth, including maxillary lateral incisors and maxillary and mandibular second premolars, were observed in all or almost all of the third molar agenesis groups, compared with the controls. A significantly increased prevalence rate of mandibular lateral incisor agenesis was observed in almost all of the third molar agenesis groups. The Japanese patients with third molar agenesis had a significantly increased occurrence of oligodontia, and unilateral or bilateral agenesis of maxillary and mandibular lateral incisors and second premolars, except for bilateral agenesis of mandibular lateral incisors.

Presence of third molars in orthodontic patients from northern Greece

Objective

The purpose of the present study was to investigate the frequency of presence of third molar teeth and their distribution in each jaw and each side, according to sex, in a group of orthodontic patients with permanent dentition from northern Greece.

Methods

The sample included panoramic radiographs from 220 patients with permanent dentition (mean age 13.62 ± 1.81). The χ² test was used to assess the relationships between the variables, and the Fisher’s exact test was used in cases where the expected frequencies in each cell were <5.

Results

The frequency of third molar presence was 79.1%, and 20.9% was the frequency of third molar agenesis. Intersexual differences in the number of third molars was not statistically significant. There was a correlation between the distribution of third molars on the right and the left side (Fisher’s exact test = 100.788; P = 0). The two sides showed the same tendency toward the presence or absence of third molars. A correlation was also found between the distribution of maxillary and mandibular third molars (Fisher’s exact test = 24.372; P = 0). In each jaw, the presence or absence of third molars was highly related to the number of third molars found in the other jaw.

Conclusion

The present results showed that in this orthodontic group of northern Greek patients, presence accounted for 79.1% and agenesis for 20.9%. No significant difference was found between the frequencies of third molar presence on the left and right sides in either the maxilla or mandible.

Third molar agenesis and craniofacial morphology

OBJECTIVE

To test the null hypothesis that agenesis of wisdom teeth is not related with any particular craniofacial morphology.

MATERIALS AND METHODS

Ninety-seven patients (aged 13-19 years) were selected and divided into three groups: (1) bilateral agenesis of maxillary third molars, (2) bilateral agenesis of mandibular third molars, and (3) control group without agenesis. Presence or absence of third molars was determined using ortopantomographs. Cephalometric analysis was carried out from lateral teleradiographs, which included linear, angular, and proportional measurements. When data obtained were distributed normally it was analyzed by means of single-factor variance analysis and the Scheffé test (P < .05). When data did not show normality, the Kruskal-Wallis test (P < .05) and the Mann-Whitney test were applied using Bonferroni correction (P < .017). Multivariance discrimination analysis was also carried out.

RESULTS

Values obtained for the mandibular plain of Groups 1 and 2 were significantly lower than those of the Control Group (P =.00 and P =.00, respectively). For Group 2 lower face height was significantly less than for the control group (P =.01), whilst the mandibular arch and the articular angle were significantly greater than in the Control Group (P =.000 and P = .02, respectively). Multivariance discrimination analysis obtained a correct classification in 58.8% of cases.

CONCLUSION

The hypothesis is rejected. Agenesis of the maxillary third molars was related to a reduced mandibular plane angle. Patients with agenesis of the mandibular third molars showed a diminished lower third and a mandibular morphology characteristic of the brachyfacial pattern.

Angulation of Mandibular Third Molars as a Predictive Factor for Pericoronitis

Aim

The aims of this study were to investigate the association between pericoronitis and the angular position, state of eruption, and the depth of impaction of mandibular third molars as well as to compare these findings with similar studies.

Methods and Materials

A total of 242 patients ranging in age from 18 to 41 years of age suffering from pericoronitis were examined. Subjective and objective observations were recorded on a checklist that included the name, age, gender, type of pericoronitis and state of eruption, position of the affected tooth for each patient as well as any radiographic changes in the mandibular third molars.

Results

The peak age for the occurrence of pericoronitis was in the 21-25 year-old age group. The soft tissues adjacent to vertically inclined, partially erupted mandibular third molars at the level of or above the occlusal plane were the most commonly affected. There was a statistically significant association between radiographic changes and the mesioangular position of the tooth (p<0.002) and the age group of the subject (p=0.004), but the association was not statistically significant between the gender of the subject, type of pericoronitis, state of eruption, and depth of impaction.

Conclusion

The soft tissues adjacent to vertically inclined, partially erupted mandibular third molars were more frequently affected by pericoronitis than teeth that are soft tissue impacted or erupted. Mesioangular erupted third molars were the teeth most frequently associated with bone loss.

Clinical Significance

The soft tissues at highest risk of developing pericoronitis are those adjacent to mandibular third molars that are partially erupted, in a vertical position, and erupted to the level of or above the occlusal plane.

Citation

Hazza'a A, Bataineh A, Odat A. Angulation of Mandibular Third Molars as a Predictive Factor for Pericoronitis. J Contemp Dent Pract 2009 May; (10)3:051-058.