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ORIGINAL ARTICLE
Year : 2020  |  Volume : 23  |  Issue : 3  |  Page : 392-397

Third molar agenesis: Prevalence and Association with agenesis of other teeth in a Turkish population


Department of Oral Surgery, Altinbas University, Istanbul, Turkey

Date of Submission27-Sep-2019
Date of Acceptance25-Nov-2019
Date of Web Publication5-Mar-2020

Correspondence Address:
Dr. P Ercal
Department of Oral Surgery, Altinbas University, Bakirkoy 34147, Istanbul
Turkey
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/njcp.njcp_520_19

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   Abstract 


Background: Tooth agenesis is the congenital lack of one or more primary or permanent teeth and it is the most frequently seen dental anomaly. The prevalence of third molar agenesis is significantly higher than the agenesis of other teeth varying from 10% to 40% and shows geographical variance. Aims: The aim of this study was to investigate the prevalence of third molar agenesis and its association with other tooth agenesis of jaws. Subjects and Methods: A total of 594 Turkish subjects with or without agenesis of third molars (M3) were included in the study. Dental records and panoramic radiographs were evaluated for M3 agenesis, hypodontia and hyperdontia. Significant differences in the prevalence rate of M3 agenesis between genders among with evaluation of coexistence of M3 and other tooth agenesis were determined by Fisher's exact test. Results: The prevalence of M3 agenesis was determined as 28.7% with no statistically significant gender or location difference. Most common form of M3 agenesis involved one molar followed by two, four and three molars. Agenesis of other teeth was seen among both patient groups with and without M3 agenesis, without significant difference. Conclusions: Turkish population with M3 agenesis did not show increased prevalence of other tooth agenesis, indicating no association between occurrence of agenesis of other teeth and M3.

Keywords: Dental agenesis, hypodontia, third molar, wisdom tooth


How to cite this article:
Ercal P, Taysi A E. Third molar agenesis: Prevalence and Association with agenesis of other teeth in a Turkish population. Niger J Clin Pract 2020;23:392-7

How to cite this URL:
Ercal P, Taysi A E. Third molar agenesis: Prevalence and Association with agenesis of other teeth in a Turkish population. Niger J Clin Pract [serial online] 2020 [cited 2020 Apr 7];23:392-7. Available from: http://www.njcponline.com/text.asp?2020/23/3/392/280036




   Introduction Top


The most common anomaly in the development of human dentition is tooth agenesis, which is defined as the congenital absence of one or more deciduous or permanent teeth.[1] Hypodontia, agenesis of one or more permanent teeth excluding third molars, is the most frequently seen type of dental anomaly, in which the prevalence varies between 2.3 and 10.1%.[2] Genetic factors play a role in tooth agenesis as suggested by familial occurrence, different prevalence data between populations, strong association with hereditary syndromes and defects found in several genes by molecular studies.[3] Specific gene polymorphisms in Msx 1, Pax 9, TGFA are reported for their association to tooth agenesis.[4] Besides genetic factors, environmental factors, systemic diseases, and dietary habits can play an etiological role in the occurrence of dental anomalies including agenesis.[5]

M3 agenesis is the most common form of agenesis among being the most variable tooth in dentition with its formation time and morphology.[6] Due to great variance in crown and root morphology, and eruption, up to 50% of humans experience problems with their M3, such as impaction, pathologies including caries, inflammation or cysts.[7] M3 agenesis prevalence varies among different populations: 38.4% in a Bangladeshi population,[5] 24.75% in a Chile population,[8] 20.9% in a Greek population,[9] 17.3% in a Turkish population,[10] 15.2% in a New Zealand population,[11] and 12.7% in a British population.[12] The lowest prevalence of agenesis is encountered in Saharan Africa and Australian aboriginal population with the prevalence of 0.5% and 1.8%, respectively.[7] Different underlying causes might be responsible for M3 agenesis as suggested by the variations of M3 agenesis among different populations.

An increased incidence of other absent teeth is more likely to be expected where M3 is missing.[13] Some studies indicate that the prevalence rate of M3 agenesis is significantly increased in orthodontic patients with agenesis of other teeth including second premolars and lateral incisors.[14]

Studies of M3 agenesis and associated dental anomalies have been scarce and inconclusive in recent years. There is still no consensus on the developmental and demographic factors contributing to the occurrence of M3 agenesis. The aim of the present study was to determine patterns of M3 agenesis and identify whether there is any relationship between M3 agenesis and other types of dental agenesis in Turkish population.


   Subjects and Methods Top


The current study was reviewed and approved by the Ethics Committee for Human Research of Istanbul University, Faculty of Dentistry (Approval no. 2019/65). A total of 594 patients (242 males, 352 females) aged between 11 and 24 years were reviewed retrospectively from the patient files of the Oral and Dental Research and Application Center of Altinbas University (Istanbul, Turkey). Agenesis was examined using patient files that included patient history and panoramic radiographs. All panoramic radiographs were acquired with NewTom Vgi evo (CeflaGroup, Verona, Italy) and reviewed with radiographic software (NNT Viewer, CeflaGroup, Verona, Italy).

A tooth was considered developmentally missing when there was no evidence of surgical tooth extraction in the records, when there was no sign of tooth crown mineralization or crypt development with radiolucency on panoramic radiographs. Patients with congenital disorders or craniofacial deformities, and radiographs that show pathologies such as cysts or tumors were excluded from the study. Panoramic images reflecting any movement artifact, and evident surgery or orthodontic treatment in the past were also excluded from the study.

All the radiographs were examined by two investigators. Two weeks after the first evaluation, 10% of the images were randomly selected and reevaluated by both investigators. Patients were divided into six groups according to the presence of third molars: group M (76 males and 95 females), patients with at least 1 M3 agenesis; group 1M (35 males and 41 females), patients with agenesis of 1 M3; group 2M (14 males and 26 females), patients with agenesis of 2 M3; group 3M (11 males and 10 females), patients with agenesis of 3 M3s; group 4M (16 males and 18 females), patients with agenesis of 4 M3s and group C (166 males and 257 females), patients without agenesis of M3s [Table 1].
Table 1: Patient with agenesis of third molars. (Percentage in parenthesis)

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Statistical analysis was performed using the GraphPad Prism 8.0 (GraphPad Software, Inc., San Diego, CA, USA). Fisher's exact test was performed to determine the significant differences in the prevalence rate of M3 agenesis between genders and between other tooth agenesis. The odds ratio (OR) was calculated at the 95% confidence interval (CI) to measure the strength of association between gender and agenesis.


   Results Top


Out of 594 patients included in the study, 171 were found to have absence of at least one M3, suggesting the prevalence of M3 agenesis as 28.7%. [Table 1] represents the distribution and prevalence of M3 agenesis according to gender. The most frequent M3 agenesis involved one tooth followed by four, two and three teeth for males, whereas for females, agenesis of M3s involved one, followed by two, four and three teeth. M3 agenesis was found more frequently in females (36.9%) than in males (31.4%); however, there was no significant difference between genders in the prevalence rate (P = 0.428).

Distribution of M3 agenesis according to jaws and sides are given in [Figure 1]. Higher number of M3 agenesis was determined in maxilla than mandible for both genders without any significant difference. Bilateral agenesis was more common than unilateral agenesis. The incidence of agenesis of M3 was the highest in the right maxillary region (16.6%), followed by right mandibular (14.8%), left mandibular (14.6%), and left maxillary (13.6%) region. Right side involvement of M3 agenesis was more frequent in both genders; however, there was no statistically significant difference between sides or genders.
Figure 1: Distribution of third molar agenesis according to locations

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Investigation of agenesis of other teeth within each group revealed that there was no significant correlation between agenesis of M3 and agenesis of other teeth as determined by a comparison between groups C and M (P = 0.149). Hypodontia was identified in each group; however, hyperdontia was only found in group C [Table 2]. A comparison between genders showed no significant difference for M3 agenesis and its relation to agenesis of other teeth (P > 0.05) [Table 3]. Other than M3s, most commonly seen agenesis was for maxillary lateral incisors followed by mandibular second premolars and maxillary second premolars for both genders [Figure 2]. Further investigation of laterality indicated that agenesis of maxillary lateral incisors is most commonly seen in bilateral agenesis of other teeth for both genders, followed by maxillary second premolars for males; followed by mandibular second premolars for females [Figure 3].
Table 2: Association of third molar agenesis with hypodontia and hyperdontia. (Percentage in parenthesis)

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Table 3: Association of third molar agenesis with agenesis of other teeth according to gender

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Figure 2: Distribution of third molar agenesis according to tooth number

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Figure 3: Laterality of other tooth agenesis according to gender (*indicate absence)

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   Discussion Top


Dental agenesis has a multi-factorial nature displaying a large variation in prevalence according to ethnicity.[14] Genetic, epigenetic, and environmental factors, and their interactions between each other, play a role to cause dental agenesis.[15] Several studies have shown that the M3 is the most frequently affected tooth associated with dental agenesis.[1],[7],[16] This descriptive and retrospective study was performed to set out the relationship of M3 agenesis between gender, location, and its association to the other tooth agenesis.

The commencement of calcification of the M3 is quite variable.[17],[18],[19] M3 tooth germ is usually visible from the age 7 and calcification begins by the age 11 at the latest according to most studies.[7],[20] The eruption time of the M3 begins at 17 and may last up to 21 years of age.[17] In addition, NICE (National Institute for Clinical Excellence) guidelines (2000) report that M3s usually erupt between the ages of 18 and 24 years of age, and they can also erupt many years later.[21] Therefore, patients aged 11 to 24 were included in this study to accurately assess the rate of agenesis of the M3. In order to avoid overestimation of M3 agenesis, upper age limit was set to 24 as the eruption of M3s is expected to be completed by then.

In the current study, the number of the patients with at least one tooth agenesis was 202 (34%; n = 594) whereas the prevalence of M3 agenesis was found to be 28.7%. In a recent meta-analysis, the mean worldwide rate of M3 agenesis was shown to be 22.63%.[7] Evaluation of the few published data regarding Turkish populations showed that the rate of M3 agenesis ranged from 17.3% to 23.8%[10],[22],[23] with the exception of a higher prevalence described by Komerik et al. (2014) as 37%.[24] The difference between described Turkish populations might be due methodological variations between studies such as different sample size, minimum subject age, and the sample type such as including only orthodontic patients. However, genetic and environmental disparities among different regions of Turkey might also be attributed to the heterogeneity noted in the M3 agenesis rate.

In terms of gender, women are reported to be 14% more likely to have a missing M3.[7] The prevalence rate of M3 agenesis was higher in females (36.9%) than in males (31.4%) without indicating a significant difference in the current study. This result is consistent with many other studies suggesting no statistically significant gender specific difference.[22],[25],[26] The cause of female predilection might be attributed to differences in craniofacial morphology as dental arch and jaws are smaller in females; however, there is no consensus on significantly more M3 agenesis seen in women than men.

In the current study, the order of frequency of M3 agenesis indicates a difference between male and female samples as 1 > 4 > 2 > 3 and 1 > 2 > 4 > 3, respectively. The order of frequency of M3 agenesis is reported as 2 > 1 > 4 > 3 with a minor and not significant differences between male and female samples.[12],[25],[27] When the results of frequency orders were evaluated together for both male and female, it was 1 > 2 > 4 > 3, which is in accordance with various studies.[5],[28]

In this study, M3 agenesis had a greater predilection on maxilla than mandible for both genders. Despite the greater predilection of maxilla, there is no significant difference between locations and genders in M3 agenesis. It has been reported that M3 agenesis was more common on the right side of maxilla with a statistically significant difference.[5] This study indicates that right side involvement was more frequent in both genders without any significance. These results tie well with some studies, wherein report that both of jaw and side disparities are not statistically significant.[20],[28]

When two teeth are affected by agenesis, bilaterality is more likely to be observed.[25],[27],[29] In this study, the most common tooth bilaterally affected by agenesis was the M3. While we observed that multiple M3 agenesis was always found as bilaterally, there were no cases in which only maxillary and mandibular M3s on the left side or only on the right side were missing. Reports vary on the second most common bilateral agenesis, differing between mandibular second premolar or maxillary lateral incisors.[10],[14],[15],[25],[30] Although similar results suggest a distinct pattern, variations between populations affect the distribution of agenesis in dentition.

It has long been suggested that agenesis of M3 is associated with a 13-fold increase in the incidence of other absent teeth.[13] A vast majority of studies have pointed out a significant correlation between agenesis of M3 and other dental agenesis.[10],[13],[14],[15],[25] Associations between M3 agenesis and other dental anomalies including microdontia and hypodontia is also suggested.[5] In cases of missing second premolars, M3 agenesis is significantly increased in orthodontic patients.[30],[31] A study among orthodontic patients in a Turkish population showed that the prevalence of patients with agenesis of other teeth was significantly greater in M3 agenesis group compared to control group, especially more commonly observed in patients with agenesis of three to four M3s.[32] Another study among orthodontic patients in a Japanese population supported the previous findings by reporting agenesis of one or more M3s presenting with bilateral agenesis of other teeth.[25] Similarly, another study with a larger patient sample indicated an increased incidence of agenesis of other teeth in M3 agenesis group compared to control group without a significant difference.[6] Findings of this study show no significant correlation between agenesis of M3 and other dental agenesis, and indeed our results are in agreement with Shah and Boyd (1979) who indicated no association between M3 nondevelopment and increased prevalence of agenesis of other teeth.[33]

Evaluation of hypodontia revealed that the prevalence rates of overall agenesis of teeth, excluding M3s, ranged from 4.5% to 20.6% in the M3 agenesis groups, compared to 7.33% in group C. Moreover, hypodontia was slightly higher in the group 4M than the other M3 groups. This finding is in good agreement with the various studies suggesting that hypodontia is frequently observed in patients with multiple version of M3 agenesis.[5],[32],[33] Although agenesis of M3 is not significantly related with agenesis of other teeth, hypodontia is more likely to include agenesis of M3s among other teeth.


   Conclusion Top


According to the results of this study, the prevalence of M3 agenesis is 28.7% in Turkish population. Most common form of M3 agenesis involves absence of one tooth with no significant predilection of location or gender. The prevalence of agenesis of other teeth is not significantly increased in patients with agenesis of M3s.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

Acknowledgement

The authors would like to thank Dr. Soner Sismanoglu for his generous support.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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