Criteria for early diagnosis of mandibular third molar agenesis based on the developmental stages of mandibular canine, first and second premolars, and second molar: a retrospective cohort study
BMC Oral Health volume 23, Article number: 650 (2023)
Permanent first molars with severe dental caries, developmental defects, or involved in oral pathologies are at risk of poor prognosis in children. Accordingly, using the third molar to replace the first molar can be a good treatment option when third molar agenesis is predicted early. Thus, this retrospective cohort study aimed to develop criteria for early detection of mandibular third molar (L8) agenesis based on the developmental stages of mandibular canine (L3), first premolar (L4), second premolar (L5), and second molar (L7).
Overall, 1,044 and 919 panoramic radiographs of 343 males and 317 females, respectively, taken between the ages of 6 and 12 years were included. All developmental stages of L3, L4, L5, L7, and L8 were analyzed based on the dental age, as suggested by Demirjian et al. The independent t-test was used to assess age differences between males and females. The rank correlation coefficients were examined using Kendall’s tau with bootstrap analysis and Bonferroni’s correction to confirm the teeth showing developmental stages most similar to those of L8s. Finally, a survival analysis was performed to determine the criteria for the early diagnosis of mandibular third molar agenesis.
Some age differences were found in dental developmental stages between males and females. Correlation coefficients between all stages of L3, L4, L5, and L7 and L8 were high. In particular, the correlation coefficient between L7 and L8 was the highest, whereas that between L3 and L8 was the lowest.
If at least two of the following criteria (F stage of L3, F stage of L4, F stage of L5, and E stage of L7) are met in the absence of L8 crypt, agenesis of L8 can be confirmed.
Tooth development is a very sophisticated and systematic process regulated by more than 300 genes and environmental factors . However, abnormalities in tooth development may occur due to genetic or environmental issues during tooth development . The first molar is usually the first permanent tooth to start developing , and it erupts into the oral cavity at approximately 6 years of age . This tooth exhibits a low degree of calcification immediately after eruption. And it is covered by a gingival plate and its vertical occlusal relationship remains unestablished for a long period. Thus, it is vulnerable to severe dental caries , possibly leading to its loss at a young age.
Notably, hard tissue deposition on the first molar begins around the time of birth. If there are some negative factors influencing tooth development during this time, the first molar can have developmental defects such as molar incisor hypomineralization (MIH) and molar root incisor malformation (MRIM). MIH is a relatively common condition and is characterized by defective enamel of the permanent incisors and first molars, with an incidence of 4-25%. Teeth affected by this condition have demarcated opacities of a different color, and owing to the soft and porous enamel of these teeth, they are prone to posteruptive breakdown and dental caries . Therefore, early treatment is required for the affected first molars. However, MIH is often detected after extensive tooth destruction because patients with MIH are sensitive to stimuli, making it difficult to achieve adequate depth of local anesthesia and thereby leading to failure of behavioral control. Meanwhile, MRIM has only been identified relatively recently, and its prevalence remains unknown. The crowns of the first molars affected by MRIM are usually normal, but the roots are dysplastic, with narrowing pulp canals. Further, although the teeth affected by MRIM are susceptible to pulpal and periodontal disease, endodontic and periodontal treatment may be ineffective in severe cases . Both MIH and MRIM are believed to be associated with systemic problems occurring from late pregnancy to early parturition; however, their etiologies are remains unknown.
Previous studies have reported that oral and maxillofacial pathologies occurred in approximately 10% of children and adolescents, and among these pathologies, odontogenic tumors and cysts had a prevalence of 5% and 10%, respectively . The most commonly affected site by these pathologies was the mandible, followed by the maxilla, and they occurred more commonly in the posterior region than in the anterior region . Further, these pathologies are known to cause resorption, displacement or mobility of the affected teeth and malocclusion; thus, their surgical removal is required despite the fact that most of them are benign. During surgery, a considerable number of affected teeth were extracted together [10, 11].
In contrast, the third molar is the last tooth to develop. According to previous studies, its development begins around the age of 9 years, and root growth is completed around the age of 20 years . Notably, it is the only tooth that continues to grow beyond puberty. Given that the accuracy of sexual and skeletal maturity indices decreases with age , developmental stages of the third molar are widely used in forensic odontology for dental age estimation in adolescents [13, 14]. Furthermore, the third molar is the most commonly impacted tooth, and occasionally, it is necessary to extract this tooth because of follicular space enlargement, pericoronitis, and severe dental caries . However, if the first molars with severe dental caries or developmental defects does not respond to palliative treatment, the long-term prognosis of the teeth remains uncertain, and extraction of affected teeth may be required. Moreover, in cases of oral pathologies such as odontogenic cysts or tumors, first molars can be affected by the pathology or need to be extracted during the procedure. In such cases, using the third molar to replace the missing first molar can be a good treatment option [16, 17]. In addition, extraction of the first molar facilitates the mesial drift of the second permanent molar. Further, more mesial movement of the second permanent molars can be expected if hopeless first molars are extracted in a timely manner . Accordingly, it is especially noteworthy that early detection of third molar development or agenesis is beneficial for comprehensive orthodontic treatment planning.
Owing to the wide variability in third molar development, it is difficult to directly compare dental developmental stages with chronological age [19, 20]. Previous research, on the other hand, claims that the developmental stages of adjacent teeth are closely related to each other, and tooth agenesis can be predicted with high accuracy if the developmental stages of adjacent teeth are used together in the analysis [21, 22]. Further, canines, first and second premolars and second molars retain considerable developmental potency at the time of initiation of third molar development. Therefore, the goal of this study is to identify criteria for early diagnosis of mandibular third molar agenesis using the developmental stages of mandibular canine, first and second premolars, and second molars.
This retrospective cohort study was conducted with the approval of the Institutional Review Board of Seoul National University School of Dentistry, Seoul, Korea (IRB No: S-D20210002) and in accordance with the principles of the Declaration of Helsinki. The requirement for obtaining informed consent to use retrospective data was waived by the Institutional Review Board of Seoul National University School of Dentistry. The data of the present study were accessible only to H Kim (first author) and JS Song (corresponding author), and these data were stored in encrypted files by the research manager. The statistician performed statistical analysis using anonymous data.
A total of 9,715 Korean children and adolescents under the age of 20 who had undergone at least one digital panoramic radiographic examination for diagnosis and treatment from January 2020 to December 2020 at Seoul National University Dental Hospital were screened. The inclusion criteria were as follows: patients who had at least two consecutive panoramic radiographs, one of which showed third molar development and the other did not, and those whose final radiographs revealed no missing teeth, including third molars. The exclusion criteria were as follows: any patient with dental pathology caused by genetic syndromes, maxillofacial deformities, lesions in the mandible, abnormal teeth angulation, or dental development disorders such as amelogenesis or dentinogenesis imperfecta and poor image quality on panoramic radiographs. Panoramic radiographs were included if they met the criteria regardless of when they were taken. Further, given that third molar development was not observed before the age of 6 years, and most root developments were completed by the age of 12 years in the present study, panoramic radiographs taken between the ages of 6 and 12 were included in the study. All panoramic radiographs were acquired using OP-100® (Instrumentarium Dental, Tuusula, Finland) and Rayscan α-P® (Ray, Gyeonggi, Korea).
Dental age assessment
Developmental stages of mandibular canine (L3), mandibular first premolar (L4), mandibular second premolar (L5), mandibular second molar (L7), and mandibular third molar (L8) were analyzed on panoramic radiographs based on the dental age, as suggested by Demirjian et al. . They classified developing teeth into eight stages based on the degree of calcification, from stage A (during which the calcification begins at the superior level of the crypt) to stage H (during which the apex of the root is completely closed and the width of periodontal ligament space is uniform). In addition, stage “−1” was defined by no sign of follicle formation, and stage “0” was defined by the presence of only bony crypts without calcification. All abbreviations are shown in Table 1.
The developmental stages were evaluated by two independent pediatric dental specialists: H Kim and JS Song. Intra- and interobserver agreements were calculated using 100 randomly selected panoramic radiographs. In cases of disagreements between the two observers, a consensus was reached by discussion. The mean age at stages 0 and A of L8, where L8 began to develop and appear on panoramic radiographs, were investigated. And the age distribution according to developmental stages of L3, L4, L5, and L7 in males and females was identified.
The intra- and interobserver agreements were evaluated using Cohen’s weighted kappa. The Wilcoxon signed-rank test was used to compare the developmental stages between the left and right teeth, and the independent t-test was used to assess age differences between males and females according to the dental developmental stage.
To identify which teeth among L3, L4, L5, and L7 could be included in the subsequent survival analysis, the correlation between each tooth L3, L4, L5, and L7 and L8 was confirmed using Kendall’s tau, based on the order of the developmental stages. To evaluate differences between each correlation coefficient and present confidence intervals, the bootstrap method and Bonferroni’s correction were used. The confidence interval was estimated using population sampling, which was repeated 1,000 times.
Finally, the survival analysis was performed to establish criteria for diagnosing the development of L8 [21, 22]. Xt was defined by the developmental stage of each tooth (L3, L4, L5, and L7) identified at the particular time t, and Yt was defined by the developmental stage of L8 identified at the particular time t. The value of Xt when each tooth (L3, L4, L5, and L7) developed the most while L8 did not reach stage 0 was defined as follows.
Consequently, according to the abovementioned definition of Z, the relation (Xt, Yt) = (x, − 1) ⇒ Z ≥ x was established. Given that Z is a value between the time when L8 was not observed at all and the time when L8 began to be observed, it can be considered an interval-censored value. P (Z ≥ x) can be nonparametrically estimated using the ic-np function of the icenReg package in the R software. In this study, P (Z ≥ x) was set as a threshold value, and when each tooth’s developmental stage precedes this threshold, we considered that L8 had already developed. Further, this univariate analysis was repeated for the teeth showing developmental stages similar to those of L8, and finally, the decision was made with majority to evaluate the agenesis of L8.
A final study sample included 660 patients, with 343 males (1,044 panoramic radiographs) and 317 females (919 panoramic radiographs) (Table 2). The average number of panoramic radiographs obtained per patient was 3.2 ± 1.0, and the average time between two radiographic examinations was 19.6 ± 12.9 months.
The Cohen’s weighted kappa values for intra- and interobserver reproducibility were all greater than 0.94 (p < 0.001). The number of panoramic radiographs obtained when the stage of L8 was 0 was 338 and 316 in males and females, respectively. At this time, the average age of males was 9.8 ± 1.6 years, whereas the average age of females was 9.9 ± 1.8 years, and L8 developed earlier in males than in females (p = 0.003). The number of panoramic radiographs showing stage A of L8 in males and females was 315 and 296, respectively. At this time, the average age of males and females were 10.2 ± 1.5 and 10.4 ± 1.7 years, respectively. Similarly, regarding L8, compared with females, males transitioned from stage 0 to A at a younger age (p = 0.029).
Because there were no differences between the left and right teeth in terms of the developmental stages (p = 0.75, 0.95, 0.81, and 0.54 for L3, L4, L5, and L7, respectively), they were analyzed together. The development of L3, L4, L5, and L7 was faster in females than in males at stage D, E, F, and G; stage E, F, and G; stage E and F; and stage D, E, and G, respectively (Table 3). Therefore, the analysis for diagnosing L8 agenesis was conducted in terms of sex.
The results of correlations using Kendall’s tau, bootstrap method, and Bonferroni’s correction are as follows. In both males and females, the correlation coefficient between L7 and L8 (ρ7) was the highest, followed by that between L5 and L8 (ρ5) and between L4 and L8 (ρ4); conversely, the correlation coefficient between L3 and L8 (ρ3) was the lowest (Table 4). The likelihood of the order of “ρ7 > ρ5 > ρ4 > ρ3” was identical in 1,000 bootstrap samples, and its possibility was very high (1.000 and 0.999 in males and females, respectively). However, because the differences in correlation coefficients were so small (Table 5), and the value of the correlation coefficient is not proportional to the explanatory power, all teeth were used together to diagnose L8 agenesis regardless of the value of the coefficient values.
The results of the estimation using the survival function are shown in Table 6; Fig. 1, and Fig. 2. Stages in which the probability of L8 development decreased abruptly were as follows: Demirjian stage E in L3, L4, and L5 and Demirjian stage D in L7. As a result, agenesis of L8 can be confirmed if at least two of the following four criteria are met without L8 crypt: F stage of L3, F stage of L4, F stage of L5, and E stage of L7. The accuracy of these diagnostic criteria was 85.71% in males and 84.43% in females. The rate of false positives (L8 was not observed in actual data, but the presence of L8 was diagnosed according to the diagnostic criteria) were 6.53% in males and 11.71% in females, and false negatives (L8 was observed in actual data, but L8 was diagnosed as missing according to the diagnostic criteria) were 7.76% in males and 3.85% in females.
The third molar provides unique information about tooth development because it is the only tooth whose entire developmental stages can be seen in panoramic radiographs . However, when compared with other teeth in the permanent dentition, the development of the third molar has the greatest variation in terms of the morphology and timing of development, ranging from the age of 7 to 16 years . Third molar impaction is a common dental problem caused by a lack of space in the retromolar area, ectopic eruption path, and shape of the mandible and third molars are usually removed surgically . Meanwhile, permanent first molars are the most important teeth that play a key role in occlusion and mastication, so healthy survival of permanent first molars is critical from functional and developmental perspectives . However, the first molars, which are expected to have a poor prognosis in early mixed dentition, can be extracted due to severe dental caries, developmental defects such as MIH and MRIM, and oral pathologies. In such cases, loss of the first molar may be followed by successful eruption of the second molar and, eventually, eruption of the third molar to complete the molar occlusion, though this is not always guaranteed . Accordingly, if pediatric dentists and orthodontists can predict the agenesis of third molar development early, the best treatment plans, including first molar extraction, can be devised .
The mean ages at stage 0 of L8, when the crypt of L8 was first observed, were 9.8 ± 1.6 and 9.9 ± 1.8 years for males and females, respectively. When it came to stage A of L8, when calcification of the crown was first initiated, the mean ages for males and females were 10.2 ± 1.5 and 10.4 ± 1.7 years, respectively. These findings differ from those of other studies reporting that L8 development begins before the age of 9 years [28, 29]. Nonetheless, they are consistent with the results of a previous study on Korean population , suggesting that it may be due to racial differences. Concerning the beginning of L8 development, no observation was found before the age of 6 years in the present study. Meanwhile, L8s were first observed at the age of 6 years only in six males and four females, suggesting that L8 development begins later in the Korean population than in other racial groups.
Unlike first molars and incisors, which mature at a young age, the development of lateral segment teeth such as canines, premolars, and second molars was not completed during the early development of third molars. As a result, the development stages of L3, L4, L5, and L7 were analyzed in this study to evaluate L8 agenesis. And it revealed a strong correlation between L3, L4, L5, and L7 and L8. This can be attributed to the fact that these teeth begin to develop at a similar time and in a relatively late period , so all four teeth, L3, L4, L5, and L7 were used to evaluate L8 agenesis. Given this background, agenesis of L8 can be diagnosed if at least two of the following criteria are met without the presence of L8 on panoramic radiographs: F stage of L3, F stage of L4, F stage of L5, and E stage of L7. The accuracy of these diagnostic criteria was 85.71% for males and 84.43% for females. This rate was lower than that in previous studies that reported higher accuracy for predicting agenesis in the maxillary and mandibular second premolars [21, 22]. This difference could be due to the large variation in the developmental period of third molars between studies [24, 25].
Previous research supported that if the maxillary first molar is extracted before the eruption of the maxillary second molar, the maxillary second molar can erupt to the position of the missing first molar, forming an appropriate occlusion . However, in the mandible, the mesial movement of the second molar may not be enough to create an ideal contact relation . As a result, early extraction of the first molar is critical for achieving the ideal arrangement of the second molar. In general, it is recommended to extract the first molar around the age of 8–10 years, when the second molar is at Demirjian stage E or lower, where calcification of furcation area has just initiated . In the present study, the average age of L8 at stage 0 was 9.8 years for males and 9.9 years for females. Furthermore, as shown in Table 3, the average ages of L3, L4, and L5 at F stage were over 9.7 years in males and over 8.9 years in females. The average ages of L7 at stage E were over 9.3 years. So, the presence of L8 can be confirmed after the age of 9 years. If the mandibular first molar is extracted around the age of 9 years, significant mesial movement of the mandibular second molar can be expected. As a result, the extraction of the first molar at an appropriate time facilitates the eruption of the second molar to the original position of the first molar, followed by the eruption of the third molar into the oral cavity by securing space for the eruption of the third molar; this will finally help to establish proper posterior occlusion [27, 33].
Even if the mandibular first molar is extracted early, L7 may exhibit a mesial inclination or L5 may exhibit a distal inclination, resulting in poor vertical occlusal contact. Further, if too much space remains in the lateral segment area, overbite may worsen due to the lingual tilting of the mandibular incisors . Moreover, removal of the first molar can lead to skeletal changes such as mandibular asymmetry and rotation of the occlusal plane [35, 36]. In addition, it is important to consider the pre-existing malocclusion together. Based on these findings, if the first molar needs to be replaced by the third molar, comprehensive orthodontic treatment planning and the developmental stage of the second molar should be considered. In such cases, dentists should consider long-term orthodontic treatment if the first molar extraction space remains .
This study has several limitations. First, the study sample was limited to Korean children and adolescents; thus, it is difficult to generalize the findings of this study to other racial groups . Second, although third molar agenesis is known to be common [37, 38], less than 5% of all patients screened in the present study exhibited L8 agenesis. Hence, it is hard to compare the developmental stages with L8 agenesis samples. The very low L8 agenesis was attributed to the fact that the frequency of third molar agenesis generally increases in patients with other tooth agenesis or genetic syndrome, who were excluded from this study . Third, it has been reported that the rate of agenesis of the maxillary third molar is at least 1.5 times higher than that of the mandibular third molar [38, 40], but only the mandibular teeth were examined in this study. Lastly, the results of this study cannot be extrapolated to the patients with agenesis of teeth other than the third molars.
This study reported some age differences between males and females in dental developmental stages. Correlation coefficients between all stages of L3, L4, L5, and L7 and L8 were high. ρ7 was the highest, followed by ρ5 and ρ4, and ρ4 was the lowest. Finally, L8 agenesis can be confirmed if at least two of the following criteria are met in the absence of the L8 crypt: F stage of L3, F stage of L4, F stage of L5, and E stage of L7 are met in the absence of the L8 crypt.
The datasets analyzed during the current study are available from the corresponding author upon reasonable request.
Mandibular first premolar
Mandibular second premolar
Mandibular second molar
Mandibular third molar
Correlation coefficients between L8 and L3
Correlation coefficients between L8 and L4
Correlation coefficients between L8 and L5
Correlation coefficients between L8 and L7
Thesleff I. The genetic basis of tooth development and dental defects. Am J Med Genet A. 2006;140A:2530–5.
Brook AH. Multilevel complex interactions between genetic, epigenetic and environmental factors in the aetiology of anomalies of dental development. Arch Oral Biol. 2009;54(Suppl 1):3–17.
Logan WHG, Kronfeld R. Development of the human jaws and surrounding structures from birth to the age of fifteen years. J Am Dent Assoc. 1922;20:379–428.
Ekstrand KR, Christiansen J, Christiansen MEC. Time and duration of eruption of first and second permanent molars: a longitudinal investigation. Community Dent Oral Epidemiol. 2003;31:344–50.
Lynch RJ. The primary and mixed dentition, post-eruptive enamel maturation and dental caries: a review. Int Dent J. 2013;63(Suppl 2):3–13.
William V, Messer LB, Burrow MF. Molar incisor hypomineralization: review and recommendations for clinical management. Pediatr Dent. 2006;28:224–32.
Wright JT, Curran A, Kim KJ, Yang YM, Nam SH, Shin TJ, et al. Molar root-incisor malformation: considerations of diverse developmental and etiologic factors. Oral Surg Oral Med Oral Pathol Oral Radiol. 2016;121:164–72.
Jones AV, Franklin CD. An analysis of oral and maxillofacial pathology found in children over a 30-year period. Int J Paediatr Dent. 2006;16:19–30.
Gohel A, Villa A, Sakai O. Benign jaw lesions. Dent Clin North Am. 2016;60:125–41.
Mehta V, Sarode GS, Obulareddy VT, Sharma T, Kokane S, Cicciù M, et al. Clinicopathologic profile, management and outcome of sinonasal ameloblastoma - a systematic review. J Clin Med. 2023;12:381.
Manor E, Kachko L, Puterman MB, Szabo G, Bodner L. Cystic lesions of the jaws - a clinicopathological study of 322 cases and review of the literature. Int J Med Sci. 2012;9:20–6.
Zandi M, Shokri A, Malekzadeh H, Amini P, Shafiey P. Evaluation of third molar development and its relation to chronological age: a panoramic radiographic study. Oral Maxillofac Surg. 2015;19:183–9.
Lewis JM, Senn DR. Dental age estimation utilizing third molar development: a review of principles, methods, and population studies used in the United States. Forensic Sci Int. 2010;201:79–83.
Santiago BM, Almeida L, Cavalcanti YW, Magno MB, Maia LC. Accuracy of the third molar maturity index in assessing the legal age of 18 years: a systematic review and meta-analysis. Int J Legal Med. 2018;132:1167–84.
Juodzbalys G, Daugela P. Mandibular third molar impaction: a review of literature and a proposal of a classification. J Oral Maxillofac Res. 2013;4:e1.
Neo HLL, Watt EN, Acharya P. Molar-incisor malformation: a case report and clinical considerations. J Orthod. 2019;46:343–8.
Song JS, Yang YM, Kim YJ, Kim JW. Management of severely aberrant permanent first molars in molar root-incisor malformation patients: case series and a guideline. Children. 2021;8:904.
Dean JA. Mcdonald and Avery’s dentistry for the child and adolescent. 10th ed. New York: Mosby; 2016.
Harris EF. Mineralization of the mandibular third molar: a study of american blacks and whites. Am J Phys Anthropol. 2007;132:98–109.
Jung YH, Cho BH. Radiographic evaluation of third molar development in 6- to 24-year-olds. Imaging Sci Dent. 2014;44:185–91.
Song JS, Shin TJ, Kim YJ, Kim JW, Jang KT, Lee SH, et al. Prediction of agenesis of the mandibular second premolar using the developmental stages of the mandibular canine, first premolar, and second molar. Arch Oral Biol. 2018;87:110–4.
Song JS, Shin TJ, Kim YJ, Kim JW, Jang KT, Lee SH, et al. Prediction of agenesis of the maxillary second premolar based on the developmental stages of the maxillary canine, first premolar, and second molar. Arch Oral Biol. 2020;111:104629.
Demirjian A, Goldstein H, Tanner JM. A new system of dental age assessment. Hum Biol. 1973;45:211–27.
Liversidge HM. Timing of human mandibular third molar formation. Ann Hum Biol. 2008;35:294–321.
Richardson M. Late third molar genesis: its significance in orthodontic treatment. Angle Orthod. 1980;50:121–8.
Andrews LF. The six keys to normal occlusion. Am J Orthod. 1972;62:296–309.
Cobourne MT, Williams A, Harrison M. National clinical guidelines for the extraction of first permanent molars in children. Br Dent J. 2014;217:643–8.
Andrews SE, Roberts G, Set P, Warburton F, Gilbert FJ. Third molar development in a London population of White British and Black British or other black ethnicity. J Forensic Sci. 2022;67:229–42.
Thevissen PW, Fieuws S, Willems G. Human third molars development: comparison of 9 country specific populations. Forensic Sci Int. 2010;201:102–5.
Lee SS, Byun YS, Park MJ, Choi JH, Yoon CL, Shin KJ. The chronology of second and third molar development in Koreans and its application to forensic age estimation. Int J Legal Med. 2010;124:659–65.
Langer LJ, Pandis N, de la Rosa MR, Jost-Brinkman P, Bartzela TN. Eruption pattern of third molars in orthodontic patients treated with first permanent molar extraction: a longitudinal retrospective evaluation. J Clin Med. 2023;12:1060.
Teo TK, Ashley PF, Parekh S, Noar J. The evaluation of spontaneous space closure after the extraction of first permanent molars. Eur Arch Paediatr Dent. 2013;14:207–12.
Bayram M, Özer M, Arici S. Effects of first molar extraction on third molar angulation and eruption space. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2009;107:e14–e20.
Cardoso PC, Mecenas P, Normando D. The impact of the loss of first permanent molars on the duration of treatment in patients treated with orthodontic space closure and without skeletal anchorage. Prog Orthod. 2022;23:32.
Cağlaroğlu M, Kilic N, Erdem A. Effects of early unilateral first molar extraction on skeletal asymmetry. Am J Orthod Dentofacial Orthop. 2008;134:270–5.
Saber AM, Altoukhi DH, Horaib MF, El-Housseiny AA, Alamoudi NM, Sabbagh HJ. Consequences of early extraction of compromised first permanent molar: a systematic review. BMC Oral Health. 2018;18:59.
Chung C, Han JH, Kim KH. The pattern and prevalence of hypodontia in Koreans. Oral Dis. 2008;14:620–5.
Sujon MK, Alam MK, Rahman SA. Prevalence of third molar agenesis: associated dental anomalies in non-syndromic 5923 patients. PLoS ONE. 2016;11:e0162070.
Endo S, Sanpei S, Ishida R, Sanpei S, Abe R, Endo T. Association between third molar agenesis patterns and agenesis of other teeth in a japanese orthodontic population. Odontology. 2015;103:89–96.
Trakinienė G, Šidlauskas A, Andriuškevičiūtė I, Šalomskienė L, Švalkauskienė V, Smailienė D. Impact of genetics on third molar agenesis. Sci Rep. 2018;8:8307.
This study was statistically reviewed by Statistical Research Institute, Seoul National University.
This study was supported by grant no 02-2021-0137 from the Seoul National University Dental Hospital Research Fund, Seoul, Republic of Korea.
The authors declare that they have no competing interests.
Ethics approval and consent to participate
This retrospective study was conducted with the approval of the Institutional Review Board of Seoul National University School of Dentistry, Seoul, Korea (IRB No: S-D20210002), and performed in accordance with the Declaration of Helsinki. The Institutional Review Board of Seoul National University School of Dentistry waived the requirement of informed consent for the use of retrospective data, so written or verbal informed consent was not obtained from any participants. The data were accessible only to the first the corresponding authors and were stored in encrypted files protected by the research manager. The statistician performed statistical analysis using anonymous data.
Consent for publication
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
About this article
Cite this article
Kim, H., Hyun, HK., Shin, T.J. et al. Criteria for early diagnosis of mandibular third molar agenesis based on the developmental stages of mandibular canine, first and second premolars, and second molar: a retrospective cohort study. BMC Oral Health 23, 650 (2023). https://doi.org/10.1186/s12903-023-03349-5
- Diagnostic criteria
- Tooth agenesis
- Mandibular third molar
- Dental developmental stage
- Survival analysis