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Year : 2017  |  Volume : 35  |  Issue : 1  |  Page : 51-55

Patterns of incisor-premolar agenesis combinations: A retrospective study

1 Department of Pedodontics, Faculty of Dentistry, Bulent Ecevit University, Zonguldak, Turkey
2 Department of Biostatistics, Faculty of Medicine, Bulent Ecevit University, Zonguldak, Turkey

Date of Web Publication31-Jan-2017

Correspondence Address:
Levent Demiriz
Department of Pedodontics, Faculty of Dentistry, Bulent Ecevit University, 67600 Kozlu, Zonguldak
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-4388.199230

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Background: Tooth agenesis is the most common dental anomaly which causes serious problems in humans. Many theories were asserted to explain the main etiologic factor of this anomaly, and genetic factors were considered as primary reasons. Aims: The aim of the present study was to evaluate the relationship between incisor and premolar tooth agenesis and to reveal a considerable data about combinations of incisor-premolar agenesis and their frequency. Settings and Design: According to inclusion and exclusion criterion, archived panoramic radiographs of nonsyndromic 6535 patients (4077 females and 2058 males) ranging in age from 7 to 18 years old were retrospectively examined to find the presence of tooth agenesis. Panoramic radiographs showing at least one tooth agenesis were recorded, and the missing tooth or teeth excluding third molars were noted. Methods: Combinations of incisor-premolar tooth agenesis were listed, and the most affected teeth groups were noted. Statistical Analysis Used: Collected data were statistically analyzed using Chi-square test or Fisher exact's Chi-square test. Results: Three hundred and eight patients (4.7%) who had at least one tooth agenesis and 648 missing permanent tooth, excluding third molars, were detected. Although the sample size of females was bigger than males in all examined patients, tooth agenesis was detected significantly more in males than females (P = 0.021). Thirty-two patients (10.4%) had both incisor and premolar agenesis, and of all patients, twenty patients (6, 5%) were found to have both maxillary lateral incisor and mandibular second premolar agenesis. Conclusions: Combinations of tooth agenesis are an issue which has begun to take attention recently. The results of the present study may provide empirical data for further genetic studies.

Keywords: Frequency, incisor, premolar, tooth agenesis

How to cite this article:
Demiriz L, Bodrumlu EH, Kokturk F. Patterns of incisor-premolar agenesis combinations: A retrospective study. J Indian Soc Pedod Prev Dent 2017;35:51-5

How to cite this URL:
Demiriz L, Bodrumlu EH, Kokturk F. Patterns of incisor-premolar agenesis combinations: A retrospective study. J Indian Soc Pedod Prev Dent [serial online] 2017 [cited 2022 Dec 3];35:51-5. Available from: http://www.jisppd.com/text.asp?2017/35/1/51/199230

   Introduction Top

Tooth agenesis is the most common developmental anomaly of the dental arch, and it causes serious complications, such as malocclusion, malposition, functional and masticatory dysfunction, reduction in alveolar bone height, speech alteration, and esthetic consequences.[1],[2] The prevalence of tooth agenesis, excluding third molars, varies in different ethnic groups, ranging from 0.03% to 11.3%,[2],[3],[4],[5],[6],[7] and the average prevalence rate in the Turkish population is between 6.2% and 7%.[2],[5],[6] Various reasons, such as evolutive, local, systemic, and genetic factors, were considered as the etiology of this anomaly.[8] However, previous studies [1],[9],[10],[11],[12] suggested that genetic factors may play an important role in tooth agenesis, and certain genetic syndromes are well-known to be associated with tooth agenesis.[13] However, this anomaly also appears in healthy individuals.[2]

Many studies were performed on the topic of tooth agenesis, but they commonly focused on identifying which type of tooth was most often missing in a population. This focus has its limitations in that it elaborates on one tooth at a time, not combinations of missing teeth.[1] In recent years, combinations of tooth agenesis have gained importance among the researched issues, and it is suggested that mutations in some genes may affect the agenesis of premolars and incisors.[9] In addition, the majority of previous studies [2],[3],[6],[9],[10],[14],[15] reports that second premolars and/or upper lateral incisors are the most frequently missing teeth when third molars are excluded. Although evidence shows that the agenesis of incisors and premolars may be together,[9],[11],[14] there are limited data about missing teeth groups, relationships, and combinations in incisor-premolar agenesis. Furthermore, there are no reported data about the frequency of incisor-premolar agenesis combinations in the Turkish population.

The aim of the present study was to evaluate the relationship between incisor and premolar tooth agenesis and reveal considerable data about combinations of incisor-premolar agenesis for future genetic studies.

   Methods Top

This retrospective study was performed on the archived panoramic radiographs of nonsyndromic children and adolescent patients having no surgical extraction stories, ranging in age from 7 to 18 years, who had applied to Bulent Ecevit University Faculty of Dentistry between 2010 and 2015 for dental reasons, such as toothaches, tooth caries, or orthodontic problems. In this period, no panoramic radiographs were taken for the study purpose. According to clinical examination records, panoramic radiographs of patients with any syndrome or developmental anomalies – such as cleft lip and/or palate and ectodermal dysplasia – were excluded from the study. In addition, panoramic radiographs of bad quality with unclear images were not taken into consideration.

The prevalence of tooth agenesis was evaluated based on the chronological age of the patient, calcification level, follicle formation, and eruption time of the teeth. Dental calcification usually begins between the ages of 2 and 3 years in premolars and permanent second molars. However, the mineralization of second premolars can appear even later, and tooth agenesis cannot be decided before the age of 6 years in permanent dentition if the third molars are not taken into account.[10] Thus, panoramic radiographs of patients under the age of 7 years were excluded from the study to avoid any misleading positive result. However, patients over the age of 6 years whose panoramic radiographs showed a lack of follicle formation or mineralization of the tooth crown were included in the study. Developmentally, missing permanent teeth (excluding third molars) and incisor-premolar agenesis combinations were classified and recorded. For each patient, the demographic variables, including age and gender, were noted, and all data were recorded in software (Excel, Office 365, Microsoft, USA) on a personal computer.

Statistical analyses were performed with SPSS 19.0 software (SPSS Inc., Chicago, IL, USA). Continuous variables were expressed as mean ± standard deviation and categorical variables as frequency and percent. The Chi-square test or Fisher exact's Chi-square test was used to determine the difference between groups, and a P < 0.05 was considered statistically significant for all tests.

   Results Top

According to inclusion and exclusion criteria, the panoramic radiographs of 6535 (4077 females and 2458 males) patients were evaluated, and 308 patients (4.7%) who had at least one tooth agenesis were detected in the present study. Of all detected patients, 173 were female and 135 were male, with a 1.28:1 female/male ratio. However, tooth agenesis was significantly higher in males than females (P = 0.021) [Table 1]. In these 308 patients, 648 missing teeth were reported, excluding third molars [Table 2]. The mandibular second premolar was found to be the most affected tooth (n = 245, 37.8%), followed by the maxillary lateral incisor (n = 175, 27%), maxillary second premolar (n = 89, 13.7%), and mandibular lateral incisor (n = 44, 6.8%). Right mandibular central incisor tooth agenesis was significantly higher in males than in females (P = 0.006). Conversely, no first molars were missing in any case. In fifty patients (16.2%), only mandibular second premolars were missing [Figure 1]a, whereas 33 patients (10.7%) had only missing maxillary lateral incisors [Figure 1]b, and eight patients (2.6%) had only missing mandibular lateral incisors [Figure 1]c.
Table 1: Prevalence of tooth agenesis according to gender

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Table 2: Frequency of teeth affected by agenesis (teeth were numbered using universal system)

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Figure 1: Schematic views of some tooth agenesis situations. (a) View of fifty patients who had only the agenesis of all mandibular second premolars. (b) View of 33 patients who had only the agenesis of all maxillary lateral incisors. (c) View of eight patients who had only the agenesis of all mandibular lateral incisors. (d) View of ten patients who had agenesis of all maxillary lateral incisors and mandibular second premolars

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In 32 patients (10.4%), not only they were incisor and premolar agenesis determined but also 20 of them (62, 5%) were also found to have maxillary lateral incisor and mandibular second premolar incisor agenesis combinations [Table 3]. In ten patients (3.2%), all maxillary lateral incisors and mandibular second premolars were missing when all incisor-premolar agenesis combinations were evaluated [Figure 1]d. There was no significant difference between males (n = 17) and females (n = 15) who had both incisor and premolar agenesis (n = 15).
Table 3: Patterns of incisor.premolar tooth agenesis combinations (missing teeth were numbered using universal system)

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   Discussion Top

Tooth agenesis is an important dental problem that causes reduction of chewing ability, inarticulation of pronunciation, and an unfavorable esthetic appearance.[16],[17],[18] In addition, the treatment of cases with tooth agenesis creates an interdisciplinary challenge that includes specialists from various departments, such as pediatric dentistry, orthodontics, and oral and maxillofacial surgery.[6] Therefore, focusing on this issue and finding the exact etiologic factor is important for decreasing the rate of the appearance of this problem. Conversely, the majority of studies has been performed to reveal the prevalence of tooth agenesis in different populations, but the etiology of tooth agenesis still remains largely unclear.[15]

Until today, many etiologic factors have been suggested for tooth agenesis, but these suggestions are still at the hypothesis level.[3],[4] These hypothesized etiologies include chemotherapy or radiotherapy, trauma, drugs, severe infection, physiological obstruction, limitation of space, disruption of the dental lamina, dental epithelium abnormalities, systemic conditions, and genetic factors.[4] Conversely, several studies [12],[19],[20],[21] have already shown that tooth agenesis is probably caused by mutations in different genes. According to these studies, mutation in the MSX1 gene was identified in affected members with missing second premolars and third molars,[12] and mutation of the PAX9 gene was associated with oligodontia affecting most molars.[19],[20],[21] In addition, mutations in transforming growth factor alpha (TGFα) have been suggested as being responsible for isolated incisor hypodontia.[22],[23] According to this evidence, searching the mutations in MSX1, PAX9, and TGFα in different and wide populations may address the exact reason for tooth agenesis. In this stage, targeting and selection of individuals or families gains importance, and understanding which tooth groups have the most missing teeth may help with the selection of individuals for genetic studies.[14] Thus, the aim of the present study was to emphasize the most affected tooth groups and their combinations by tooth agenesis.

One of the aims of the present study was to evaluate cases of hypodontia and oligodontia. In the literature, different terms were used for tooth agenesis.[3] Hypodontia is a term used for the absence of one or more teeth (up to five), and until now, many authors [4], 7, [24],[25],[26] evaluated hypodontia, excluding third molars, in different populations. Commonly, in previous studies on hypodontia, the prevalence of tooth agenesis and the most affected tooth type were investigated. Conversely, some authors [1],[14] evaluated the missing tooth groups and combinations in oligodontia (or severe hypodontia) cases involving six or more missing teeth.[6] However, any research that evaluates the most common combinations or tooth groups of agenesis for both terms (hypodontia and oligodontia) cannot be found in the literature.

The majority of studies on the prevalence of tooth agenesis has been performed on Caucasians, with a reported prevalence range of 4%–7%.[2],[6],[24],[27],[28],[29] In the present study, it was observed that 308 nonsyndromic patients out of 6535 were affected with a frequency of 4.7%, and this result is also compatible with previous studies performed in Caucasians. However, this frequency value is lower than the study of Topkara and Sari,[2] which was about the prevalence of tooth agenesis in the orthodontic patient population in Turkey (excluding third molars), which reported (6.77%). Conversely, in another prevalence study of tooth agenesis in the Turkish population, Celikoglu et al.[24] had almost the same frequency result (4.6%) as the present study, and their examined samples were also orthodontic patients. In a similar study, in the Turkish orthodontic population, Gökkaya et al.[5] found the frequency of tooth agenesis to be 7%. When these different findings are considered, it is well understood that prevalence studies regarding tooth agenesis show various results, and this situation depends on the differences in the methods sampling and examination and in the distribution of the participants' age, sex, and racial origin.[18],[19] In terms of gender, the proportion of tooth agenesis was significantly more prevalent in the male population although the sample size of females was bigger than that of males in all examined patients. This result was different from the results of previous studies [2],[6],[24] reporting that females are more affected than males in permanent dentition, excluding third molars, in the Turkish population, and it shows that prevalence results according to gender may vary between different regions in the same population. In addition, in terms of gender, population differences affect and change these results. In the study of Chung et al.,[4] there was no significant difference in the prevalence between males and females in the Korean orthodontic population. In Mexican [8] and Brazilian [15] populations, the same results, based on gender, were obtained. On the other hand, Kirkham et al.[28] found a high prevalence of tooth agenesis among males in the British population, and these results are similar to the findings of our study.

Although the general results vary in many prevalence studies, second premolars and/or lateral incisors were found as the most commonly affected teeth by agenesis.[2],[4],[6],[7],[9],[10],[15],[24],[25],[26] Polder et al.[27] stated that the mandibular second premolars and the maxillary lateral incisors are the most frequently affected teeth among Caucasian people. In the present study, the most affected teeth by agenesis are the mandibular second premolars (37.8%), followed by the maxillary lateral incisors (27%); these results are compatible with statements of Polder et al.[27] In 2001, Arte et al.[11] stated that second premolars and lateral incisors are the most frequently missing teeth, and they named this trait “incisor-premolar hypodontia.” Garib et al.[9] revealed that the prevalence of agenesis of other permanent teeth was significantly increased in the group of patients characterized by agenesis of second premolars. In addition, patients with agenesis of second premolars presented a significantly higher prevalence of microdontia of maxillary lateral incisors.[9] In another study, Tan et al.[14] focused on severe hypodontia cases, and they reported that the most common patterns included the agenesis of the maxillary lateral incisor and both premolars. These findings create a suspicion that tooth groups, especially incisors and premolars, may be affected together by agenesis. For this reason, individuals with incisor-premolar agenesis were evaluated in this study.

In the present study, at least one incisor and one premolar tooth were missing together in 32 patients when all 308 patients affected by agenesis were evaluated. According to these results, the rate of the individuals with incisor and premolar tooth agenesis is considerable, with a prevalence of 10.4%, and this means that almost one in every ten patients who has had teeth agenesis has come to the clinic with both incisor and premolar tooth agenesis. These findings are compatible with the revealed results of Tan et al.,[14] who highlighted the rate of the appearance of incisor-premolar agenesis. Furthermore, among these 32 patients, the combination of the maxillary lateral incisor and mandibular second premolar incisor agenesis was observed in twenty patients, with 62.5% of all incisor premolar agenesis cases showing the pattern of at least one maxillary lateral and one mandibular second premolar tooth agenesis. This relationship was also emphasized by Tan et al.,[14] and it was qualified as the most common pattern of tooth agenesis. Eventually, individuals with incisor-premolar agenesis, especially those having the pattern of a maxillary lateral and mandibular second premolar, may address the target samples for genetic studies when all compatible results are considered. Conversely, Tan et al.[14] emphasized that it is unclear exactly how genetic mutations are related to specific tooth agenesis patterns, and focusing on them and analyzing the patterns may help clarify which of them are related to genetic mutations and which are not.

   Conclusion Top

Consequently, in the present study, patterns of incisor-premolar agenesis in the Turkish population were analyzed since being the most affected teeth by agenesis,[2],[3],[6],[9],[10],[14],[15] and the results of the present study may be remarkable and may provide empirical data for the future genetic studies to understand the exact role of genetic factors on tooth agenesis. Moreover, increasing the frequency of incisor-premolar agenesis in time is another important issue that should be evaluated by researchers, and further periodical analysis studies focusing on this issue are necessary in different populations to reveal useful and considerable data.

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Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1]

  [Table 1], [Table 2], [Table 3]

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