Similarly impacted second and third maxillary and mandibular molars in a pair of monozygotic twins v. Oikarinen, o. Gfiven and H. Silaste Department of Oral and Maxillofacial Surgery, Helsinki University, Helsinki, Finland

Received 23 January 1990 and in final form 20 February 1990 Disturbances of eruption of second and third permanent molars in a monozygotic twin pair are reported. Similarly impacted teeth occurred bilaterally in the maxilla and mandible, with only minor differences between twins. The findings suggest the possibility of a genetic influence. Keywords: Molar; molar, third; genetics; twins, monozygotic

Similarity in tooth formation and timing of tooth development in monozygotic twins suggests a degree of genetic control 1-4. The formation of mandibular posterior teeth, in particular, has been found to show greater similarities compared with dizygotic twins", Coincident ectopic eruption of the first molars in monozygotic twins has been reported by AshleyMontague'' and by Jarvinen and Vaataja", There are very few observations in the literature relating to twins exhibiting abnormalities in the eruption of permanent teeth 7 . The following case report records similar dentitions and impacted second and third molars in a monozygotic twin pair.

Case report Male monozygotic twins (P.A. and P.E.), aged 16 years and 4 months, were referred for examination because of delayed eruption of their second permanent molars. Oral examination revealed good dental hygiene

and no sign of gingivitis. The anterior occlusal surface of the left second lower molar was partly erupted in P.A. Panoramic radiographs (Figures 1, 2) showed almost identical unerupted and impacted second and third molars on both sides of the upper and lower jaws. More detailed comparisons were based on stereoradiographs and the corresponding findings during third molar surgery. In one of the twins (P.A.), a supernumerary tooth germ was found distal to wisdom tooth 28. There were slight dissimilarities in the locations of teeth 37 and 48. The stereoradiographs showed that tooth 47 in both twins and tooth 37 in P .A. were displaced lingually in the alveolar crest. The findings are summarized in Table I. Histopathological examination of the third molar follicles revealed no cystic or other pathological changes. Ten months postoperatively the disimpacted second molars were erupting at the same rate in both

Figure] Twin P.A.: panoramic radiograph

© 1990 Butterworth-Heinemann for IADMFR 0252-832 x 90/020133-02

Dentomaxillofac. Radiol., 1990, Vol. 19, August

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Impacted molars in twins: V. Oikarinen et al.

Figure 2 Twin P.E.: panoramic radiograph Table I Similarities (+) and dissimilarities (-) in the positions and development of impacted second and third molars in 16-year-old monozygotic twins (P.A. and P.E.) Impacted tooth

Inferosuperior position Anteroposterior position Angular position Buccolingual position Root development stage Root form

37 38

47 48

18 17

27 28

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those of Efstratiadis et al. 3, who noticed that third molar inclination in two pairs of identical twins exhibited remarkable parallelism in relation to progressive changes in angulation, with close agreement within twin pairs at each stage. Occasionally, values in both the sagittal and frontal planes were identical, suggesting a genetic influence on the normal course of mandibular third molar development. It is hoped that this report will act as a stimulus to further objective and quantitative studies of several monozygotic and dizygotic twin pairs in order to confirm this hypothesis.

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twins. Tooth 28, which was autotransplanted into the socket of 47, is mesially impacted.

Discussion Previous investigations have indicated the significance of genetic factors in the diagnosis and treatment of dental patients'v!''. It has been assumed that monozygotic twins have identical occlusions, as manifested by similar Angle molar classifications, tooth size, crowding patterns and arch shapes and sizes, but individual rotations, overjet and overbite do not reflect a comparable level of similarity'?'!'. Lobb'" compared the occlusions of monozygotic twin pairs. Identical molar relationship and arch form were found within all these twin pairs while Helpin and Duncan'f reported almost similar dentitions and ankylosis in monozygotic twins. The similarities in the disturbance in tooth eruption we report here are consistent with a hereditary influence. The inclinations and inferosuperior positions of teeth 18, 17, 27 and 47 were fairly symmetrical (nearly identical) in the twins. On the other hand, the supernumerary tooth germ in the upper left maxilla in one twin and some minor differences in angulation of the right mandibular wisdom tooth show that potential for expression of environmental influences also exists. Our findings supplement 134 Dentomaxillofac. Radiol., 1990, Vol. 19, August

1. Gam SM, Lewis AB, Polachek DL. Sibling similarities in dental development. J Dent Res 1960; 39: 170-5. 2. Green U, Aszkler SE. Intra-alveolar dental development in twins. J Dent Res 1970; 49: 631-4. 3. Efstratiadis SS, Kent RL, Lebret LML, Moorrees CFA. Spatial position of mandibular third molars in monozygotic twins. Angle Orthod 1984; 54: 271-82. 4. Nystrom M, Ranta R. Dental age and assymmetry in the formation of mandibular teeth in twins concordant for oral clefts. Scand J Dent Res 1988; 96: 393-8. 5. Ashley-Montague MF. The dentition of identical twins with particular reference to an identical pathological condition. Hum Bioi 1933; 5: 629-45. 6. Jarvinen S, Vaataja P. Ectopic eruption of maxillary first permanent molar in twins. Proc Finn Dent Soc 1980; 76: 175-8. 7. Nakata M. Twin studies in craniofacial genetics: a review. Acta Genet Med Gemellol1985; 34: 1-14. 8. Harris JE, Kowalski CJ, Watnick SS. Genetic factors in the shape of craniofacial complex. Angle Orthod 1973; 43: 107-11. 9. Harris JE, Kowalski CJ. All in the family: use of familial information in orthodontic diagnosis, case assessment and treatment planning. Am J Orthod 1976; 69: 493-510. 10. Lobb WK. Craniofacial morphology and occlusal variation in monozygous and dizygous twins. Angle Orthod 1987; 57: 219-33. 11. Potter RHG, Nance WE. A twin study of dental dimension. 1. Discordance, assymmetry, and mirror imagery. Am J Phys Anthropol1976; 44:.391-6. 12. Helpin ML, Duncan WK. Ankylosis in monozygotic twins. J Dent Child 1986; 53: 135-9. Address: Dr Valle J. Oikarinen, Department of Oral and Maxillofacial Surgery, University of Helsinki, Mannerheimintie 172, SF-00300 Helsinki, Finland.

Similarly impacted second and third maxillary and mandibular molars in a pair of monozygotic twins.

Disturbances of eruption of second and third permanent molars in a monozygotic twin pair are reported. Similarly impacted teeth occurred bilaterally i...
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