Double primary teeth and their relationship with the permanent successors: a radiographic study of 376 cases.

Double primary teeth were observed in 367 children and their relationship with the permanent successors was studied with the aid of radiographs. Double primary teeth involving 2 adjacent teeth and those involving the same tooth have different patterns of association with the permanent successors. Double primary teeth involving 2 adjacent teeth are associated more frequently with congenitally missing permanent successors. A combination of factors such as decreased hereditary dependent mitotic potential of the tooth germ and presence of an inhibitory zone around the tooth germ might have been responsible for the formation of these anomalies. It is suggested that double primary teeth probably result from unseparated rather than fused tooth masses. Double tooth is the term frequently used to describe the anomaly of conjoined teeth. 1 Other terms, such as fusion (Livitas 1965; Mader 1979) gemination (Levitas 1965; Mader 1981) connation (Hutchin Morris 1966) linking tooth (Sprinz 1953) synodontia and schizodontia (DeJonge 1955) also have been suggested. In this article, the term double tooth is used because in many instances, it is clinically difficult to decide whether fusion or gemination has occurred. 2 The anomaly occurs more frequently in the primary than in the permanent dentition and has been reported to be more prevalent in Mongoloid (3%: Saito 1959; Niswander and Sujaku 1963) than Caucasian (1.6%) 3 populations. No preference of sex has been apparent. Although double teeth have been reported in premolar and permanent molar areas, the condition Moody and Montgomery 1934; Miles 1954; Grahnen and Granath 1961; Brook and Winter 1970; Itkin and Barr 1975; Weiss 1980; Gellin 1984. Miles 1954; Brook and Winter I970; Itkin and Barr 1975. Grahnen and Granath 1961; Clayton 1956; Ravn 1971. is seen predominantly in the incisor and canine regions. Double primary molars only have been reported as anomalies in the otodental syndrome (Winter 1983). Double teeth can occur unilaterally or bilaterally in either the maxillary or mandibular arch. The simultaneous bilateral occurrence in both arches has not been reported. The association of double primary teeth with variation in tooth number, both in the primary and permanent dentitions, has been documented. 4 In general, congenital absence of a permanent successor often is associated with a double primary tooth if the normal number of teeth exists when the double tooth is counted as 2 teeth (Grahnen and Granath 1961; Gellin 1984). On the other hand, a supernumerary tooth is sometimes present if hyperdontia exists when the double tooth is considered as 2 teeth (Brook and Winter 1970; Ravn 1971). Although esthetic and functional problems created by double primary teeth are relatively transient in the primary dentition, proper monitoring of occlusal development should not be overlooked to prevent deviation of the midline and abnormal delay in eruption of the permanent successors. In cases where permanent successors are congenitally absent or in double tooth formation, esthetic and functional problems in the permanent dentition should be anticipated. Extensive carious involvement on the labial and lingual vertical grooves of the double primary tooth often requires early treatment (Lowell and Solomon 1964). The purpose of this study was to compare the distribution of the different types of double primary teeth and their relationship to the permanent suc~ Grahnen and Granath 1961; Brook and Winter 1970; Gellin 1984; Ravn 1971. 42 DOUBLE PRIMARY TEETH AND PERMANENT SUCCESSORS: Yuen et al. TABLE 1. Distribution of Maxillary Double Primary Teeth as Related to the Permanent Successors I 2M I ] 2M peg21 I peg2 2M1 2M 2MI peg2 peg212M I S Total aa[ 1 1 1 (2.6) ~ 1 1 6 5 4 1 11 7 18 (47.4) ~ 3 1 1 1 5 1 6 (15.8) bb~ 1 1 1 1 2 (5.3) __~bb 2 1 1 4 4 (10.5) cc~ 1 1 1 (2.6) __~cc 1 1 1 (2.6) ab[ab 3 3 3 (7.9) ab ~bM 1 1 1 (2.6) ccIcc 1 1 1 (2.6) Total 6 4 6 5 3 4 1 1 1 3 1 2 1 27 11 38 (100.0) (%) (15.8) (10.5) (15.8) (13.2) (10.5) (2.6) (2.6) (2.6) (7.9) (2.6) (5.3) (2.6) (71.1) (28.9) cessors in a sample of Hong Kong school children. The possible etiology and development of the anomaly are discussed. Methods and Materials The sample consisted of 376 children (186 boys and 190 girls) with ages ranging from 5 to 9 with mean age of 6.8 + 0.7 years. They were all normal and healthy Hong Kong school children participating in the school dental care service. Double primary teeth were found during routine clinical examination. All children were of Chinese ethnic origin and most had not been examined previously by a dentist. Upper and lower anterior occlusal radiographs were obtained from each child. Occasionally periapical and panoramic radiographs also were taken to verify the condition of the permanent successors. Children with a history of trauma to the primary dentition or premature loss of the primary teeth were excluded. The "two-tooth rule" similar to that frequently applied to differentiate between fusion and gemination (Mader 1979) was employed to designate the types of double primary teeth according to their position in the dental arch. If the double tooth was counted as 2 teeth and if the normal number of teeth was present, the condition was designated as double primary tooth involving 2 adjacent teeth. If the double tooth was counted as 2 teeth and if an extra tooth was present, the condition then was designated as double primary tooth involving the same tooth. The clinical findings and corresponding radiographic interpretations were coded into the computer database for analysis. Other dental anomalies such as congenitally missing primary incisors and supernumerary teeth also were recorded. In order to simplify the lengthy descriptions of the types of double primary teeth and their permanent successors, symbols were used to represent their conditions in the clinical observations and radiographic interpretations. In the clinical observations, ’ab’, ’bc’, and ’de’ represented the double primary teeth involving 2 adjacent teeth, while ’aa’, ’bb’, and ’cc’ represented the double primary teeth involving the same tooth. a, b, c, d and e were the primary central incisor, lateral incisor, canine, first and second molars respectively. bM indicated that the primary lateral incisor was congenitally missing. For the radiographic interpretations, the conditions of the permanent successors were represented as: