Third Molar Development Research Articles

Radiographic evaluation of third molar development in Spanish children and young people

Third molar development was evaluated in 786 young people aged between 4 and 20 years, all patients at the School of Dentistry of the University of Granada. The development of third molars and of mandibular second premolars and second molars was determined according to the stages proposed by Nolla. The onset of mandibular third molar formation was observed at very variable ages in this series, ranging from 5.86 to 14.66 years. The first developmental stages of maxillary third molars are not usually visible radiographically, which can lead to an incorrect diagnosis of agenesis. We found no significant relationship between the gender or age of the patient and the presence or absence of third molars. However, the presence/absence of the third molar can be predicted in 82.82% of cases when there is some degree of calcification of mandibular second molars and second premolars.

The unresolved problem of the third molar: Would people be better off without it?

Third molars are teeth that have little functional value and a relatively high rate of associated pain and disease. Their value as part of the dentition of modern people is dubious. The authors review the evolution, development, morbidity and treatment of third molars. They assess the value of third molars in the 21st century and describe the risks these teeth pose when they develop in the dentition. There is a mandate for the dental profession to improve health outcomes and quality of life. The prevention of third molar-related morbidity should be included in dental research efforts. The authors suggest that novel preventive methodologies be developed to alleviate the problems third molars pose. One potential methodology suggested is intentional therapeutic agenesis of this tooth. Prevention of third molar development early in life, even before tooth bud initiation, could dramatically improve health care outcomes for millions of people.

Influence of orthodontic treatment on development of third molars

We aimed to find out whether extraction of lower premolars and subsequent closure of the space by a fixed appliance influenced the chances of mandibular third molars erupting.We compared angular and linear measurements of lower third molars on dental panoramic tomograms in 30 orthodontic patients with similar measurements from 30 patients with impacted third molars in intact arches.We found that the mesial angulation of lower third molars was reduced from 50° to 43 ° by orthodontic treatment (P< 0.001). Distance to the occlusal plane was reduced from 12mm to 10mm (P< 0.001). The space available increased from 4mm to 11mm (P< 0.001).We conclude that extraction of lower premolars and orthodontic treatment to achieve complete closure of the space allowed the positions of many impacted lower third molars to improve significantly.

Methods of reducing observer variation in age estimation from panoramic radiographs.

To compare inter- and intra-observer variation in age estimation using subjective and objective methods. Fifty-six panoramic radiographs of patients aged 13 to 25 years were assessed subjectively twice by four observers for the stage of root development of the lower third molars on a seven-point scale. Two of the observers were calibrated before the first evaluation, and the other two before the second. The same observers also digitized predefined reference points in a subsample of the third molars ten times by means of a computer-based digitizer system. Observer variation in classifying different root stages and in digitizing coordinates and measuring root lengths were studied. Significant systematic differences existed between two of the observers in the subjective assessment. One non-pre-calibrated observer changed her pattern most. Scattergrams from the digitizer measurements showed a good precision within and between observers with no significant differences in calculating root lengths. When, however, the teeth were analysed separately, some significant differences were found. The overall observer agreement was best using the objective method on several teeth. With only one tooth there were some significant differences. Subjective evaluation was improved by prior calibration.

Study on formation and development of third molars in patients with malocclusion.

Study on formation and development of third molars in patients with malocclusion.

Die entwicklung des weisheitszahnes als kriterium der lebensaltersbestimmung

The study is based on the orthopantomographic evaluation of the formation and the development of the permanent third molar (n = 938 patients with known age between 15 and 25 years). We used a modified method according to Gleiser and Hunt (1955) with 3 stages of crown formation and 7 stages of root formation. The correlation between age and the formation of the third molar is not very close. There is a deviation of +/- 4 years (97% statistical safety). The root is completed at the age of about 23 years (upper jaw: 23 years in males and females, mandible: males 23.2 years, females 23.6 years). There is a slight sexual dimorphism with an accelerated development of the third molar in males. The dentition of the molars runs parallel on both sides of the jaw. Only a small proportion (14%) of all persons has completely formed roots at the age of 21. Retination of the third molars (produced by the second molar and by the ascending branch of the mandible) causes a delay of its development.

Lower third molar development subsequent to second molar extraction

Development and eruption of lower third molars was examined in 63 subjects who were treated by extraction of second molars. Changes in mesiodistal and buccolingual lower third molar angulation were measured on 60 degrees cephalograms taken before extraction and 3 or more years later. The final position of lower third molars was assessed on models at the end of the observation period by using a scoring system. All lower third molars erupted in periods ranging from 3 to 10 years after extraction. Ninety-nine percent of the third molars upright mesiodistally, but few became as upright as the second molars they replaced. Model analysis showed that 96% of the lower third molars erupted in good or acceptable positions.

Expression of the neural cell adhesion molecule (NCAM) during second- and third-molar development in the mouse.

Distribution of the neural cell adhesion molecule (NCAM) during the development of the mandibular second- and third-molars of the mouse was studied by indirect immunofluorescence techniques. At the initial stage, NCAM was intensely expressed by the mesenchymal cells surrounding the dental lamina, and by the cap stage NCAM expression by the mesenchymal cells became restricted to the dental follicle. After that, in addition to the follicular mesenchyme, some cells in the basal part of the dental papilla showed NCAM-immunoreactivity for a while after the hard tissue formation had started. During root formation, the follicular cells lost NCAM first from the level of the cervical root and later from the coronal part, while an additional NCAM positive area appeared deep in the dental papilla. Even after the teeth had erupted, NCAM was expressed in the tissue surrounding the apical root and in the pulp core. During the initial and bud stages, the pattern of NCAM expression in the second and third molars was different from that in the first molar, where NCAM was found only after the late bud stage; while from the cap stage onward, it changed in the same sequence as in the first molar. The different pattern of NCAM expression implies that there is a difference in developmental events between the early stages of the first and the other two molars. On the other hand, the common sequence of NCAM expression in the tooth germs later than the cap stage suggests that NCAM plays an essential role in the formation of the basic structure of the teeth and periodontal tissues.

3 第三大臼歯の発育についての臨床的研究 : オルソパントモグラムによる観察 (第414回 大阪歯科学会例会)

3 第三大臼歯の発育についての臨床的研究 : オルソパントモグラムによる観察 (第414回 大阪歯科学会例会)

Clinical observations on the development of third molars.

In order to investigate the developmental conditions of third molars in Japanese, we studied the panoramic radiographs taken during dental treatment at the Pediatric Outpatient Section of Osaka Dental University Hospital of 9,111 children (4,646 boys and 4,465 girls) between the ages of 7 years 0 months and 16 years 11 months, in addition to 2,769 panoramic radiographs of students of this university (2,312 men 457 women) kept by the Department of Oral Radiology. The following results were obtained. 1. Calcification of the third molars in both boys and girls began as early as 7 years 6 months in the maxilla and 7 years 0 months in the mandible. The average age for initiation of calcification in the maxilla was 9 years 4 months for boys, and 9 years 2 months for girls, while the ages in the mandible were 9 years 1 month and 8 years 9 months, respectively. 2. The average age for completion of the third molar crowns in the maxilla was 11 years 8 months for boys and 11 years 5 months for girls, while in the mandible it was 12 years 4 months and 12 years 3 months, respectively. 3. At greater than 13 years of age, the tooth germ could be found in boys about 70% of the time in the maxilla and 75% of the time in the mandible, while these figures for girls were 65 and 80%, respectively. 4. All four third molars were present in 52.3% of the males and 45.5% of the females, while 9.5% of the males and 12.0% of the females had no third molars at all. 5. The direction of eruption was classified as either vertical, mesial, horizontal, distal, or buccal/lingual type. The rate for the vertical type in males was 70% in the maxilla and 45% in the mandible, while these figures for females were 50 and 40%, respectively. 6. Microdontia of the third molars appeared only in the maxilla. 7. Congenital absence of the third molars was more common in females than males, and occurred more frequently in the maxilla than in the mandible. The results of this study allow a better understanding of the third molars of Japanese and provide an aid to planning in such areas of clinical pediatric practice as guiding occlusal development.

Clinical Research on the Development of Third Molars in Panoramic Radiographs

Clinical Research on the Development of Third Molars in Panoramic Radiographs

Organ culture study of effect of Vitamin- A-deficiency on rat third molar development

A culture procedure for rat third molars suitable for nutritional-developmental studies is described. Urerupted third molars from 12-day-old rats were cultured in BGJ b media containing 20 per cent rat serum and supplemented with 25 mM HEPES buffer, 25 mg ascorbic acid, 20 mg L-glutamine, 12mg penicillin G and 10mg streptomycin sulphate per 100 ml of media. Molars were cultured at the liquid-gas interphase using a 50 per cent O 2, 45 per cent N 2, 5 per cent CO 2 gas mixture at 10 lb-psig (pounds per square inch guage). Molar cultures were maintained successfully for 9–14 days without evidence of necrosis, although they developed at a slower rate than in vivo. Molars cultured in 50 per cent O 2 compared to those cultured in 21 per cent O 2 for periods of 2, 4, 6 and 8 days had higher values for protein, alkaline phosphatase (AP), Ca, P and Ca/P. Vitamin- A-deficiency gave lower values for AP, Ca, P, Ca/P, 45Ca, 35S and [ 14C]-proline uptake. Histologically, A-molars had atrophie ameloblasts, some foci of squamous metaplasia and abnormal keratin formation. Thus, deficiency of vitamin A imposed during in-vitro development of rat third molars retarded dentinogenesis and interfered with early mineralization of enamel and dentine.

Lower third molar development in relation to skeletal maturity and chronological age.

The development of lower third molar anlage was investigated longitudinally and related to chronological age and to skeletal maturation stage as judged by the mineralization of epiphyses in the hand. Strong correlations were found between lower third molar development and both skeletal maturation and chronological age. These results indicate that lower third molar development on the whole seems to be correlated with skeletal maturation. One or two lower third molars were found to be missing in 11% of the subjects.

Sexual dimorphism in the development, emergence, and agenesis of the mandibular third molar: G. Y. Levesque, A. Demirjian, and R. TanguayJ. Dent. Res 60:1735-41, 1981

Sexual dimorphism in the development, emergence, and agenesis of the mandibular third molar: G. Y. Levesque, A. Demirjian, and R. TanguayJ. Dent. Res 60:1735-41, 1981

Sexual Dimorphism in the Development, Emergence, and Agenesis of the Mandibular Third Molar

Bilateral agenesis was encountered in about 9% of the cases, with no significant sexual difference. The right and left mandibular third molars had the same pattern of development and emergence. The slight advance of girls over boys at the crown-completion stage was similar to previous observations on other mandibular teeth, particularly the second molar. The root development course of the third molar was faster in males than in females; this sexual dimorphism was much greater for retarded cases than for advanced cases. At the apex closure, the difference between median ages of males and females was 1.5 yr. Alveolar emergence tended to occur at a lower developmental stage in advanced cases compared with retarded cases.

Late third molar genesis: its significance in orthodontic treatment.

(1) Third molar genesis may occur up to the age of sixteen years, although the possibility of their appearance after the age of twelve years is reduced. (2) When third molar genesis is delayed beyond the age of ten years, the possibility of all four third molars developing is reduced by about fifty percent. (3) The intraindividual variability in stage of development of third molars increase when genesis is delayed beyond ten years of age. (4) There is no significant difference in size of early and late developing third molars.

The effects of aspirin on the development of the mouse third molar. A potential screening system for weak teratogens.

Aspirin is teratogenic at high doses in rodents. A dose related effect is shown at much lower levels in an animal testing system which permits subthreshold effects on development to be measured. This system, which depends on changes in tooth size in the mouse, has advantages in assessing weak or cumulative teratogens.

Predicting angulational development and eruption of the lower third molar.

Abstract No Abstract Available. From the Departments of the Pedodontics, Orthodontics and Roentgenology, Institute of Dentistry, University of Helsinki.

A comparison of permanent mandibular molar formation in Australian Aborigines and Caucasoids

The formation of mandibular third molars, relative to the developmental sequence of second molars, was similar in Caucasoid children of Australian, New Zealand and North American stock. Pre-Caucasoid and living Australian Aborigines were alike also in their pattern of molar development. However, when Australian Aborigines and Caucasoids were compared, differences were found in the timing of third molar formation between these two races of man. These differences comprised a marked retardation in the development of third molars in Caucasoids amounting to approximately 4.3 years, as well as a greater variability in the attainment of all stages of third molar maturation. On the other hand, the development of permanent first molars, relative to second molars, was similar in Caucasoids and Australian Aborigines.

Retarded development of maxillary third molar

Retarded development of maxillary third molar