Molar Agenesis Research Articles

Presence of third molars in orthodontic patients from northern Greece

ObjectiveThe 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.MethodsThe 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.ResultsThe 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.ConclusionThe 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.

Prevalence of eruption status of third molars in Libyan students.

The aim of the present study is to determine the number of third molars per person, angulation, level, amount of space for eruption of third molar between ramus of mandible and second molar and the eruption status of third molar in a group of Libyan students, with different impaction patterns and agenesis of third molars. In this descriptive retrospective study, a total of 200 students (100 male and 100 female students of bachelor of dental surgery, Faculty of Dentistry, Garyounis University, Benghazi, Libya) were enrolled. Students who had complete complement of teeth within the age group 17-26 years were selected for this study, while those cases who had history of extraction of any of the teeth or who refused to give consent were excluded. Before starting the study, ethical concern from the ethical committee, IRB and informed consent from each student who underwent radiography were obtained. The results showed that 5% of third molars were congenitally missing. Approximately 93.5% of the subjects had all four third molars, 1% had two third molars and 0.5% had one third molars with 2.5% having agenesis of all third molars. Third molar agenesis showed predilection for maxilla with higher proportion in females (3%) than males (2.1%). Angular position was maximum with vertical position (5.83%), with least being horizontal impactions. Level of occlusal plane of third molar similar to that of adjacent tooth was seen in 44.74%, below the occlusal plane in 24.76%, totally impacted noted in 30%. The present study showed that 33% of the teeth were fully erupted and 66% were in various stages of eruption and 5% were congenitally missing in these students.

Radiographic study of mandibular angular cortical thickness in relation to the presence and eruption status of mandibular third molar

Background: Mandible is one of the largest and strongest facial bones but there are some areas which are physically weak and fractured easily, i.e., angle and condyle. Recent studies demonstrated the correlation of the risk of mandibular angle fractures to the presence of the mandibular third molars. The aim of the present study was to evaluate the mandibular angular cortical thickness in relation to the presence and eruption status of mandibular third molar to verify if the mandibular third molar represent a risk factor for angle fracture or not. Materials and methods: The angular cortical thickness was measured using tracing elements and panoramic radiograph of 160 Iraqi subjects aged from (20-28) years, they were divided equally into four groups according to the status of mandibular third molar which were: Subjects with agenesis of mandibular third molar, subjects with completely erupted mandibular third molar, subjects with complete bony impacted mandibular third molar and subjects with extracted mandibular third molar. Results: Subjects with agenesis registered the greatest value in the mean angular cortical thickness followed by subjects with extracted, completely erupted and complete bony impacted mandibular third molar respectively. Extraction of mandibular third molar improved the angular cortical thickness and this effect had a strong positive linear correlation with the extraction duration. Conclusion: The measurement of the angular cortical thickness was greatly affected by the presence and eruption status of mandibular third molar, such measurements registered its highest values in subjects with third molar agenesis and its lowest values in subjects with complete bony impacted third molar.

Eruption Status of Third Molars in South Indian City

Aim : The aim of the present study is to determine the number of third molars per person, angulation, level, amount of space for eruption of third molar between ramus of mandible and second molar status of root and also to study the difficulty index. Objective: To study the eruption status of third molar in South Indian population. Materials and methods: The study conducted at Department of Oral Medicine and Radiology. Maratha Mandals NG Halgekar College of Dental Sciences and Research Centre. Belgaum, Karnataka, India A total of 150 patients (54 females and 96 males) visiting outpatient department between the age group of 17 and 30 with a mean age of 23.5 years were selected- Before starting the study, ethical concern taken from the ethical committee and informed consent from each patent who underwent radiographic examination. Results: The results showed approximately 94.66% of the subjects had all four third molars, 8.6% had three third molars, 4.6% had two third molars and 2% had one third molars with 3.3% having agenesis of all third molars. Third molar agenesis showed predilection for upper jaw with higher proportion in females (5 5%) than males (2%). Angular position seen maximum with vertical position (66.16%) with least being horizontal impactions. Level of occlusal plane of third molar similar to that of adjacent tooth seen in 52.65%. Below the occlusal plane in 19.61 %, totally impacted teeth noted in 27.73%. More than 75% of the teeth had complete root formation. Among total number of teeth, 518 (91.51 %) teeth were easy to extract and remaining 33 (5.8%) were difficult to extract. Conclusion: Radiological and clinical findings have correlated to assess whether teeth were easy to extract or difficult. Because of the increasing incidence of unerupted third molars and the association of numerous complications with these retained teeth, assessment of germ position and prognosis of third molar eruption is necessary for better patient management.

Transposition of a maxillary canine and a lateral incisor and use of cone-beam computed tomography for treatment planning

This report describes the orthodontic treatment of a 12-year-old girl with transposition of the maxillary left canine and the lateral incisor. Cone-beam computed tomography was used during treatment planning. The transposed tooth positions were corrected with an unconventional orthodontic approach. Treatment alternatives and their clinical concerns are presented.

Prevalence and patterns of permanent tooth agenesis in Down syndrome and their association with craniofacial morphology

To (1) document the prevalence and patterns of hypodontia (permanent tooth agenesis) in Down syndrome (DS) and (2) explore whether maxillary or mandibular hypodontia or simultaneous agenesis of all third molars was associated with differential alterations of the craniofacial morphology. Longitudinal panoramic radiographs of 25 white patients with DS (12 male, 13 female; mean age, 15.1 years) treated at The Hospital for Sick Children, Toronto, Ontario, Canada, were evaluated to document hypodontia. Cephalometric measurements of subjects with maxillary or mandibular hypodontia or agenesis of all third molars were compared with those of subjects without hypodontia in these regions using analysis of covariance adjusted for age, gender, and proportion of other missing teeth in the total number of missing teeth. Hypodontia was seen in 92% of the sample when third molars were considered and in 56% when third molars were not considered. Hypodontia was more prevalent and severe in females. The most frequently agenetic teeth were maxillary and mandibular third molars > maxillary lateral incisors > mandibular second premolars > mandibular incisors > maxillary second premolars > maxillary second molars. Simultaneous agenesis of all third molars was seen in 52% of the sample. Maxillary hypodontia was not associated with significant regional craniofacial differences, while mandibular hypodontia was associated with decreased mandibular length and increased ramus∶body ratio. Agenesis of all third molars was not associated with significant craniofacial differences. Hypodontia is widely prevalent in DS. The effect of the syndrome appears to be stronger than that of regional hypodontia in differentially altering the craniofacial morphology.

Familial agenesis of mandibular first molars in Japanese macaques (Macaca fuscata)

We report in this paper two unusual cases of M1 agenesis recently discovered in Japanese macaques (Macaca fuscata). Molar agenesis is the congenital absence of molars. In general, molar agenesis occurs from the posterior molars. In most cases, missing teeth are third molars. Second molars may occasionally be absent in addition to the third molars. However, the congenital absence of first molars is hardly observed in humans, and to our knowledge, no case has been reported in other primates. In addition to the rareness of first molar agenesis, the present cases in M. fuscata are also quite unusual, because the posterior molars (M2 and M3) were completely preserved in contrast to the ordinary pattern of molar reduction. Interestingly, the two cases of the present study were observed in a single maternal lineage (a mother and her son), suggesting that M1 agenesis in these Japanese macaques is genetically inherited.

Unilateral segmental odontomaxillary hypoplasia: an unusual case report

Facial asymmetry is not an uncommon occurrence in day to day dental practice. It can be caused by various etiologic factors ranging from facial trauma to serious hereditary conditions. Here, we report a rare case of non-syndromic facial asymmetry in a young female, who was born with this condition but was not aware of the progression of asymmetry. No relevant family history was recognized. She was also deficient in both deciduous and permanent teeth in the corresponding region of maxilla. Hence, the cause of this asymmetry was believed to be a segmental odontomaxillary hypoplasia of left maxilla accompanied by agenesis of left maxillary premolars and molars and disuse atrophy of corresponding facial musculature. This report briefly discussed the comparative features of segmental odontomaxillary hypoplasia, hemimaxillofacial dysplasia, and segmental odontomaxillary dysplasia and justified the differences between segmental odontomaxillary hypoplasia and the other two conditions.

Maxillary first molar agenesis and other dental anomalies

To explore the association of maxillary first molar agenesis with other dental anomalies in Japanese orthodontic patients. A total of 32 subjects with one or two congenitally missing maxillary first molars (group M) were selected and divided into group 1M (12 subjects with one maxillary first molar missing) and group 2M (20 subjects with two maxillary first molars missing). As controls, 32 sex-matched subjects without agenesis of maxillary first molars were collected (group C). Panoramic and periapical radiographs, cephalograms, study models, intraoral photographs, and anamnestic data were used to identify anomalies of permanent teeth. Chi-square, Fisher's exact, Kruskal-Wallis, and Steel-Dwass tests were used to make statistical comparisons. The prevalence rates of tooth agenesis other than the maxillary first molars and advanced tooth agenesis, with third molars excluded, were significantly higher in group 2M than in group C. The absence of second premolars was most common. The prevalence rate of third molar agenesis was significantly higher in groups 1M and 2M than in group C. The occurrence of symmetrical agenesis of the mandibular third molars was particularly notable in group 2M as compared to group 1M, in which maxillary third molar agenesis was predominant. There was no significant association between maxillary first molar agenesis and other dental anomalies, except for agenesis of teeth other than maxillary first molars. Agenesis of maxillary first molars is associated with a higher prevalence of other permanent tooth agenesis and advanced tooth agenesis.

Phenotypic Classification of 90 Dentitions With Arrested Eruption of First Permanent Mandibular or Maxillary Molars

The purpose of the present study was to subclassify by phenotype those patients who had retained first molars. Radiographs from 53 male and 37 female patients (7 years, 10 months to 17 years, 8 months) comprised the study sample. Subdivision of material according to primary retention (arrested eruption of the first molar occurred before the tooth penetrates the oral mucosa) or secondary retention (continued eruption of a molar arrests after the tooth has penetrated the oral mucosa) revealed that the average age at first diagnosis of primary retention was 9.2 years and of secondary retention 13.8 years of age. The study indicated that primary retention was more frequent than secondary retention and that male and female patients were affected with equal frequency. Primary retention occurred more often in the maxilla than in the mandible, whereas the opposite was found in secondary retention. Primary retention can occur in dentitions that have normal development of the second molar with or without generalized malocclusion, as well as in dentitions with abnormal eruption patterns in the second molar region (late development and second molar agenesis), with or without generalized malocclusion. Secondary retention can occur in dentitions with normal development of the second molar with or without generalized malocclusion. The phenotypic differences noted between the primary and secondary retention was that variations of normal eruption of the second molar were seen in the cases with primary retention. This observation indicates that primary retention can be an acquired condition.

In the absence of dental records, do we need forensic odontologists at mass grave sites?

With the exception of exhumations of mass graves in Latin America, forensic dentists and odontologists are rarely involved in the examination of mortal remains recovered from mass graves. The cited reason is often that “there are no dental records-so what is the point”? In this presentation we review the published accounts of examination of remains arising from the conflict in the former Yugoslavia between 1991 and 1999 in which dental examinations are reported. There are roughly 30,000 missing persons of which more than 15,000 mortal remains have been identified, mostly based on DNA. There are 9 sources which describe postmortem dental examinations of 3919 sets of remains; of these, 23% were purported to have been identified specifically from dental information. Of the 8100 listed missing persons from the Srebrenica mass killings in 1995, we located 600 dental records. A sample of 263 charts was examined for information about first molar treatment as we are concerned that dental charting of individuals who lose their first molars may be incorrectly done if allowance is not made for mesial drift of the remaining molars. We found that of all the first molar extractions that are ever going to occur according to these dental charts, 63% have taken place by age 18. The majority of extracted first molars have a functional age of 17 years. We observe that an adult's remains from Srebrenica usually have only second and third molars, which have often drifted forward to occupy the position of the first molar creating the appearance of third molar agenesis. We conclude: that, since dental identifications of victims in mass graves and mass disasters is the exception rather than the rule, even in the absence of DNA-based identifications, international forensic odontologists have an ethical obligation to become more involved in examination of mass grave victims, that there must be more determined searches for antemortem dental records; that local dentists should be approached to participate in the examination of remains and lastly that dental examination and charting by anthropologists and pathologists may be grossly inaccurate. Furthermore, even in the absence of dental records, there is significant information about the individual to be obtained by an oral biologist since many families have useful memories about the oral status of their loved ones who went missing.

Frequency of Agenesis, Impaction, Angulation, and Related Pathologic Changes of Third Molar Teeth in Orthodontic Patients

The objectives of the present study were to investigate the frequency of impaction, agenesis, angular position, and related pathologic changes of third molar teeth in a group of orthodontic patients. Our sample included the panoramic radiographs of 351 orthodontic patients aged 20 to 26 years (mean 22.8). The descriptive characteristics of agenesis, impaction, angular position, and pathologic changes of third molars were recorded. The chi(2) test was used for analysis. The proportion of third molar agenesis was 17.3% with no statistically significant gender differences (18.4% for women and 15.8% for men). The frequency of impacted third molars (ITMs) was 35.9% (24.2% in men and 45.0% in women; P < .05). The frequency of maxillary ITMs was 43.2% (192 of 444 teeth), and the frequency of mandibular ITMs was 56.8% (252 of 444 teeth). The position observed most often was mesioangular inclination, with a frequency of 50.0%. Only 10.4% of the ITM teeth were affected by any pathologic changes, and most of these changes were associated with the horizontal position. The present results showed that agenesis accounted for 17.3% and impaction for 35.9% of the pathologic features in this group of Turkish orthodontic patients aged 20 to 26 years of age. Mesioangular inclination was seen in 50.0%, and a small proportion (10.4%) had pathologic changes of the ITMs.

Hypohyperdontia: Agenesis of three third molars and mandibular centrals associated with midline supernumerary tooth in mandible

Agenesis of teeth in a patient who also presents with a supernumerary tooth is one of the rare numerical anomalies in human dentition. Agenesis of third molars was shown to be associated with other missing permanent teeth. A review of literature on hypodontia including third molar agenesis, hyperdontia and a concomitant presence of these two conditions which is termed as hypohyperdontia is presented along with a case showing agenesis of three third molars, both mandibular central incisors and a midline supernumerary tooth.

L’oligodontie : stratégie thérapeutique à partir de 30 cas

Hypodontia is defined as the absence of at least six permanent teeth due to the hypodevelopment of tooth germs. The prevalence is weak and varies according to the ethnic origin. This familial abnormality is due to various mutations or polymorphisms of genes. It may be associated with other dental abnormalities. In children, it is responsible for growth, mastication, and phonation disorders, hypo-alveolia and lingual interposition in the toothless sites. We report the management of 30 patients presenting with oligodontia. The diagnosis was made on clinical and paraclinical data. The vertical and transversal facial dimensions, the three facial proportions, labial morphology, the number and localization of teeth, and occlusion were analyzed for future orthognathic and implant rehabilitation. The occlusion was studied transversally and vertically on dental casts. Rehabilitation with implant supported dental prostheses was chosen when conditions were met. The therapeutic protocol could include up to four chronological phases: the early prosthetic phase, the orthodontic phase, the surgical phase, and the implant and prosthetic phase. The 30 patients' age (13 male and 17 female patients) ranged from six to 20 years. An average of 15 dents were missing (6 to 28). Except for one case, all the third molars were missing. In 66% of the cases, the second molar was missing, in 33% for the first molar. In 66% of the cases, two lateral maxillary incisors were missing. There were no premolars in 50% of the patients. Agenesis of premolars and molars induced posterior bone insufficiency in the mandibula. Dysmorphosis was always present with vertical growth disorders. Six patients were not given orthodontic treatment because they did not have enough teeth. Orthognathic surgery was used in 14 cases (46.7%). Seventeen patients (56.7%) underwent apposition graft. In three patients, a high position of the alveolar nerve required nerve derivation. Implants were inserted in 14 patients (46.7%). The total number of implants was 155. Rehabilitation with implant supported dental prostheses is a good treatment for oligodontia. It requires an interdisciplinary approach (including a maxillo-facial surgeon, an orthodontist, a dentist, and a prosthesis specialist). The patient's motivation as well as that of his family is crucial.

The Relationship Between Third Molar Agenesis And Reduction In Tooth Number

The Relationship Between Third Molar Agenesis And Reduction In Tooth Number

The LIM homeodomain transcription factors Lhx6 and Lhx7 are key regulators of mammalian dentition

Genes encoding LIM homeodomain transcription factors are implicated in cell type specification and differentiation during embryogenesis. Two closely related members of this family, Lhx6 and Lhx7, are expressed in the ectomesenchyme of the maxillary and mandibular processes and have been suggested to control patterning of the first branchial arch (BA1) and odontogenesis. However, mice homozygous for single mutations either have no cranial defects (Lhx6) or show only cleft palate (Lhx7). To reveal the potential redundant activities of Lhx6 and Lhx7 in cranial morphogenesis, we generated mice with all combinations of wild-type and mutant alleles. Double homozygous mice have characteristic defects of the cranial skeleton and die shortly after birth, most likely because of cleft palate. In addition, Lhx6/7 deficient embryos lack molar teeth. The absence of molars in double mutants is not due to patterning defects of BA1 but results from failure of specification of the molar mesenchyme. Despite molar agenesis, Lhx6/7-deficient animals have normal incisors which, in the maxilla, are flanked by a supernumerary pair of incisor-like teeth. Our experiments demonstrate that the redundant activities of the LIM homeodomain proteins Lhx6 and Lhx7 are critical for craniofacial development and patterning of mammalian dentition.

Genetic basis of tooth agenesis

Tooth agenesis or hypodontia, failure to develop all normally developing teeth, is one of the most common developmental anomalies in man. Common forms, including third molar agenesis and hypodontia of one or more of the incisors and premolars, constitute the great majority of cases. They typically affect those teeth that develop latest in each tooth class and these teeth are also most commonly affected in more severe and rare types of tooth agenesis. Specific vulnerability of the last developing teeth suggests that agenesis reflects quantitative defects during dental development. So far molecular genetics has revealed the genetic background of only rare forms of tooth agenesis. Mutations in MSX1, PAX9, AXIN2 and EDA have been identified in familial severe agenesis (oligodontia) and mutations in many other genes have been identified in syndromes in which tooth agenesis is a regular feature. Heterozygous loss of function mutations in many genes reduce the gene dose, whereas e.g. in hypohidrotic ectodermal dysplasia (EDA) the complete inactivation of the partially redundant signaling pathway reduces the signaling centers. Although these mechanisms involve quantitative disturbances, the phenotypes associated with mutations in different genes indicate that in addition to an overall reduction of odontogenic potential, tooth class-specific and more complex mechanisms are also involved. Although several of the genes so far identified in rare forms of tooth agenesis are being studied as candidate genes of common third molar agenesis and incisor and premolar hypodontia, it is plausible that novel genes that contribute to these phenotypes will also become identified.

Agenesis of maxillary permanent first molars: Literature review and two case reports

Congenital absence of teeth is the most commonly known developmental dental anomaly in humans. Agenesis of the permanent first molars has the least frequency of all the tooth types and when present, usually occurs in association with oligodontia or anodontia. Generally, it is easy to diagnose agenesis of the permanent first molars retrospectively, based on the clinical morphology and x-ray photographic features of the permanent second molars; while it is often debatable when made prospectively. Several hypotheses have been promulgated to explain the etiology of hypodontia with evolutionary and anatomic models. Nevertheless, clinical epidemiology does not completely support these hypotheses and therefore clinicians should be cautious; while speculating the missing tooth type based on these hypotheses. We encompass a comprehensive review of the literature on missing permanent first molars and illustrate two cases of missing maxillary permanent first molars to emphasize the complexity involved in their diagnosis.

Agenesis of maxillary permanent first molars: Literature review and two case reports

Agenesis of maxillary permanent first molars: Literature review and two case reports

Mouse models of tooth abnormalities

Tooth number is abnormal in about 20% of the human population. The most common defect is agenesis of the third molars, followed by loss of the lateral incisors and loss of the second premolars. Tooth loss appears as both a feature of multi-organ syndromes and as a non-syndromic isolated character. Apart from tooth number, abnormalities are also observed in tooth size, shape, and structure. Many of the genes that underlie dental defects have been identified, and several mouse models have been created to allow functional studies to understand, in greater detail, the role of particular genes in tooth development. The ability to manipulate the mouse embryo using explant culture and genome targeting provides a wealth of information that ultimately may pave the way for better diagnostics, treatment or even cures for human dental disorders. This review aims to summarize recent knowledge obtained in mouse models, which can be used to gain a better understanding of the molecular basis of human dental abnormalities.