New Approaches to the Problem of Third Molar

The authors review most important characteristics in the development of the third molar. They include the time of foundation, course and the duration of individual stages of development, dynamism in the development of the third molar if upper and lower jaw, the occurrence of agenesis and its microsymptoms and the relation of the development of third molar to the dental and chronological age.The analysis of panoramic radiograms from 1700 probands at the age of 5 and 21 years provided a general view of the development of the third molar from its foundation to the end of the root development. This picture may be considered as specific for the Czech population. The obtained values represent decisive indices for individual evaluation. The span of foundation of the third molar is 8 years (from 6 to 13 years of age). The foundation occurred most frequently at the age of 9 years. The last term was established at 13 years of age. These results are valid for the population, which is not burdened by the hypodontia syndrome.Based on the calculation of the duration of individual developmental stages it has become possible to establish the mean period of development of the third molar. We have also determined differences in the course of development of third molars between the upper and lower jaw.Intra-individual differences in the development of the third molar were encountered in about 50 % of our group. This rarely observed phenomenon is of considerable importance for the determination of dental age as well as the symptom of the hypodontia syndrome.A significant relationship was observed between the degree of development of third molars and dental age. The important knowledge also includes the observed fact that the agenesis of 1-3 molar is accompanied by significantly delayed development of founded third molars.All partial results were evaluated separately for boys and girls. No significant sex-related differences were established in other indices except the agenesis of third molars.The time differences in key events in the development of the third molar should give more precision and certainty to planning of orthodontic therapy and should provide indices for optimal planning of extractions of third molars with unfavorable prognosis.The described knowledge will contribute to the practice of anthropology and forensic medicine in the determination of age of adolescent individuals, if there is no other available biological method for the evaluation of chronological age

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Abstract: The aim of this study is to evaluate the incidence of third molars agenesis in the Czech population. One thousand patient's panoramic radiographs of the pedostomatological department of Second Stomatological Clinic of The First Faculty of Medicine, Charles University, has been analyzed. The age of probands was ranging between 12 to 21 years inclusive. Patients were divided into 10 groups according to age. In each age group were 100 individuals -50 boys and 50 girls. Agenesis of 1-4 third molars was present in 22.5 % (25.6 % in boys and 19.4 % in girls). Intersexual difference is significant. Further, the incidence of third molars agenesis in individual dentition quadrants, upper and lower jaw and right and left side of dentition was examined. Neither in boys nor in girls were detected significant differences in these values. Agenesis of just one, any third molar occurs in 10.9 % (12.0 % in boys and 9.9 % in girls). For one individual it is mean 1.9 congenitally missing third molars in boys and 2.0 congenitally missing third molars in girls. These intersexual differences are not significant. In boys, the most frequent agenesis was of one, next of two, then of three and at last of four third molars. In girls, agenesis of two was on the first place, then that of one and lastly and equally of three and of four third molars. The results were compared with literature data. Key words: Hypodontia -Agenesis of third molars -Incidence of third molars agenesis in population -Intersexual difference