INTRODUCTION
Third molars are the last teeth to erupt in theoral cavity and are something of an enigma for adentist. Agenesis is the congenital absence of at leastone permanent tooth. The eruption or impaction ofthird molars is most often associated with pain, swelling and many other problems for the patient. In these conditions the problematic third molar isextracted and sometimes the procedure may beaccompanied by post-extraction complications suchas bleeding and dry socket. Third molars are theteeth that are most associated with impaction. Thestudy on third molars not only interest dentalprofessionals but also specialists in anthropology, genetics etc. this is because third molars are foundto be important in understanding the process ofevolution. Many times third molars are not involvedin occlusion and mastication. As a continuousprocess of evolution, the number of cases of missingthird molars is seemed to be increasing.
Updating the knowledge on the status of thirdmolars would be helpful in clinical practice. Thisstudy is aimed at understanding the incidence ofagenesis of third molars in Tamil Nadu populationand the probable causes of the same.
MATERIALS AND METHODS
A total of 100 patients between the age of 15and 35 years who reported to clinic 5 of SaveethaDental Hospital were chosen randomly for the study. The patients came from different places of TamilNadu. Hence the sample size can be considered tobe representing Tamil Nadu population. Those whohad the history of previous extraction of third molarsand all who refused to give consent were excludedfrom the study.
At first the third molars were examinedvisually. All subjects were examined clinically forthe status of third molar and were classified intocompletely erupted and unerupted. Group Acontained people with completely erupted 4 thirdmolars. Group B contained subjects who had at leastone unerupted third molar. Those with uneruptedteeth were subjected to radiographic examination. An OPG was taken for all the subjects in group B.
All the subjects were handed a questionnaire. The patients were questioned for their dietary habitsand the frequency in which they consume non-vegetarian food, fibre rich food and soft food. Subjects were also questioned on the presence offthird molars in their parents.
RESULTS
Out of 100 subjects, 68 were male and 32 werefemale. There were 37 subjects in group A and 63subjects in group B. 42.1% of the subjects in groupB had at least 1 unerupted maxillary third molar. Whereas the percentage of subjects with at least oneunerupted mandibular third molar in group B wasfound to be 93.75%. The graph 1 shows the group Bsubjects based on the number of unerupted thirdmolars in upper and lower arch separately.
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Graph 1: Graph 1 shows group B subjects based on thenumber of unerupted third molars in upper and lowerarch separately.
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31.25% of the subjects in group B had oneunerupted third molar. 43.75% had two uneruptedthird molars. The percentage of subjects in group Bwith three and four unerupted third molars was 14%and 9.3% respectively.
Upon analysing OPG, it was found that 9.4 %(n=6) of the subjects in group B had at least onecongenitally missing third molar. Out of 6 subjects, one had two congenitally absent maxillary thirdmolars. Five subjects had single congenitally missingmaxillary third molar. Two subjects had missingsingle mandibular third molar. All the subjects whohad congenital absence of third molars were female.
When questioned on the prevalence of thirdmolar unration among their parents, four of thesubjects with congenital absence of third molarsreported that their mothers had congenitallymissing third molar. Two of the subjects were notsure about the status of third molars in parents.
When questioned on the dietary habits of theindividuals. Four of the subjects with congenitalabsence of third molars are frequent non-vegetarians, one of them is occasional non-vegetarian and another person is a pure vegetarian.
DISCUSSION
Third molars which are commonly called aswisdom teeth are the last set of teeth to erupt in theoral cavity. The average age of eruption of thirdmolars is 17-20 years. For some individuals thiseruption happens at a much later stage and in manycases eruption does not happen at all. The pain, swelling and complications associated with theeruption and extraction of third molars has made ita subject of interest to dentists. Diet, extend of usageof masticatory system, genetic and racialpredilection are all factors that influence the jawand tooth size and structure.
In the present study 100 random subjectsbetween the age of 15 and 35 were chosen fromamong the patients who reported to Saveetha dentalhospital. 63% of the subjects had at least oneunerupted third molar. It was found that 6% of thesubjects had at least one congenitally missing thirdmolar. All the subjects who had congenitally missingthird molars were found to be female. This issuggestive of a female predilection to the same. 5%of the subjects had at least one congenitally absentmaxillary third molar which shows the maxillarypredilection of agenesis. Dietary influence was foundto be negligible. Four percent of the subjects hadparents who also had unerupted third molars. Theincidence of agenesis in those parents could not beanalysed through OPGs. If they have agenesis, thenit is suggestive of hereditary factors playing a rolein agenesis.
A study conducted in Haryana showed thatthere is 35.4% incidence of third molar agenesis. Agenesis of maxillary third molar was found to bemore significant in the study.1 A study on thepatterns of third molar agenesis and associateddental anomalies in an orthodontic population foundthat permanent tooth agenesis is frequentlyassociated with third molar agenesis.2 A studyconducted among Libyan students showed that thereis maxillary as well as female predilection foragenesis of third molars.3 A study conducted inPunjab showed that 26% of the subjects had missingthird molars.4 Agenesis of third molars aresometimes associated with congenital absence ofother permanent teeth also. Lateral incisors, secondpremolars, central incisors, second permanentmolars, canines and first premolars are the teethwhich show associated agenesis in the order of theirprevalence. The male to female ratio of third molaragenesis was proposed as 3:2.5 A study conductedin Belgaum, Karnataka showed that 3.3% of thesubjects had agenesis of all the third molar.6 In astudy conducted in Nepal the prevalence of thirdmolar agenesis was found to be 50.34%.7 Studyconducted in Czech population showed that theagenesis of third molars is 22.5% and there is malepredilection for agenesis.8
CONCLUSION
Third molar agenesis is prevalent among thepopulation today. It shows maxillary predilectionand also female predilection. There seems to befamilial inheritance of agenesis. In some people whoreported with congenitally absent third molars, agenesis of other permeant teeth were also seen. Further study is required to find out if there areany associated genes which may be responsible foragenesis.