Modified cuspal relationships of mandibular molar teeth in children with Down s syndrome

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1 J. Anat. (1998) 193, pp , with 3 figures Printed in the United Kingdom 529 Modified cuspal relationships of mandibular molar teeth in children with Down s syndrome BENJAMIN PERETZ, 1 JOSEPH SHAPIRA, 1 HANNA FARBSTEIN, 2 ELIAHU ARIELI 3 AND PATRICIA SMITH 4 Department of Pediatric Dentistry, Division of Anatomy and Embryology, The Hebrew University-Hadassah School of Dental Medicine, Jerusalem, Institute of Advanced Dental Education, Haifa, and Department of Biostatistics, Mor Research Applications, Givat Shmuel, Israel (Accepted 13 July 1998) ABSTRACT A total of 50 permanent mandibular 1st molars of 26 children with Down s syndrome (DS) were examined from dental casts and 59 permanent mandibular 1st molars of normal children were examined from 33 individuals. The following measurements were performed on both right and left molars (teeth 46 and 36 respectively): (a) the intercusp distances (mb-db, mb-d, mb-dl, db-ml, db-d, db-dl, db-ml, d-dl, d-ml, dl-ml); (b) the db-mb-ml, mb-db-ml, mb-ml-db, d-mb-dl, mb-d-dl, mb-dl-d angles; (c) the area of the pentagon formed by connecting the cusp tips. All intercusp distances were significantly smaller in the DS group. Stepwise logistic regression, applied to all the intercusp distances, was used to design a multivariate probability model for DS and normals. A model based on 2 distances only, mb-dl and mb-db, proved sufficient to discriminate between the teeth of DS and the normal population. The model for tooth 36 for example was as follows: p(ds) e (mb-dl)+ (mb-db) 1 e (mb-dl)+ (mb-db) A similar model for tooth 46 was also created, as well as a model which incorporated both teeth. With respect to the angles, significant differences between DS and normals were found in 3 out of the 6 angles which were measured: the d-mb-dl angle was smaller than in normals, the mb-d-dl angle was higher, and the mb-dl-d angle was smaller. The dl cusp was located closer to the centre of the tooth. The change in size occurs at an early stage, while the change in shape occurs in a later stage of tooth formation in the DS population. Key words: Molar teeth; intercuspal distance. INTRODUCTION Tooth development is a complex process involving various tissue components at staggered intervals (Kraus & Jordan, 1965; Butler, 1967; Smith et al. 1997; Peretz et al. 1998). Dental development is modified in people with various diseases (Garn et al. 1979; Townsend, 1983; Peretz et al. 1988). Researchers have considered the changes in crown size as expressions of general systemic problems (Bailit et al. 1970). Previous studies have shown changes in size and shape from their initiation in utero to birth (Kraus & Jordan, 1965; Butler, 1967). Individuals with Down s syndrome (DS) tend to display a reduction in size of permanent teeth, and reduced intercuspal distances in molars (McMillan & Kargashian, 1961; Cohen et al. 1970; Geciauskas & Cohen, 1970; Townsend, 1983; Brown & Townsend, 1984; Prahl-Anderson & Oerlemans, 1976). A recent study demonstrated that in the permanent maxillary 1st molar of DS children, all intercuspal distances were significantly smaller than in normal children, as Correspondence to Dr Benny Peretz, Department of Pediatric Dentistry, Hadassah School of Dental Medicine, P.O. Box 12272, Jerusalem, Israel. Tel: ; fax: ; benny cc.huji.ac.il

2 530 B. Peretz and others well as the area of the quadrangle shaped by connecting the cusp tips (Peretz et al. 1996). This study also provided a simple probability model for DS which was based on stepwise logistic regression and included the distances between the mesiobuccal and distolingual cusps (mb-dl), and the distance between the mesiobuccal and mesiolingual cusps (mb-ml). In addition, a change in shape was shown as well as a change in size, where the distolingual cusp was located closer to the centre of the tooth. The change in the shape was considered to occur in a late stage of crown formation and to reflect different growth of the distolingual cusp. The purpose of the present study was to measure the intercusp distances and angles of mandibular 1st molars in individuals with DS, and in a control group, to compare the measurements of both groups, and to define the parameters that distinguish between the groups, as was found with respect to the upper molar. MATERIAL AND METHODS Fifty permanent mandibular 1st molar teeth of DS children were examined from 26 dental casts of 14 boys and 12 girls aged 7 14 y, obtained from 2 centres for DS, in Jerusalem and in Haifa. The diagnosis of the condition was based on clinical and chromosomal studies. The medical records of the patients with DS were reviewed and confirmed by chromosomal analysis for karyotyping. In addition, distinctive facial features were observed, such as a large tongue, a flattened nose bridge, slanting palpebral fissures and a brachycephalic head with a flattened occiput. Fifty-nine permanent maxillary 1st permanent molars of normal children were examined from dental casts of 33 individuals, 15 boys and 18 girls, taken for routine orthodontic evaluation. The teeth were examined from existing casts. No casts were taken exclusively for the purpose of this study. Care was taken to use only attrition-free teeth, on which cusp tips could be accurately located. On the mandibular left 1st molar (tooth 36), and right 1st molar (tooth 46), the following measurements were performed: (a) The distances (mm) between: (1) the mesiobuccal and the distobuccal cusps (mb-db); (2) the mesiobuccal and distal cusps (mb-d); (3) the mesiobuccal and distolingual cusps (mb-dl); (4) the distobuccal and mesiolingual cusps (db-ml); (5) the distobuccal and distal cusps (db-d); (6) the distobuccal and distolingual cusps (db-dl); (7) the distobuccal and mesiolingual cusps (db-ml); (8) the distal and distolingual cusps (d-dl); (9) the distal and mesiolingual cusps (dml); (10) the distolingual and mesiolingual cusps (dlml); (b) the angles: (1) db-mb-ml; (2) mb-db-ml; (3) mb-ml-db; (4) d-mb-dl; (5) mb-d-dl; (6) mb-dl-d; (c) the area of the pentagon formed by connecting the cusp tips. A video camera, monitor, and a computer with an image analyser program (CUE 4, Galai Co., Migdal HaEmek, Israel) were used to measure all variables. The method was successfully used in previous studies (Peretz & Smith, 1993; Peretz et al. 1996, 1998). Each tooth was analysed separately. The casts were put on a wooden plate and adjusted so that the cusps were on the same height, parallel to the plate and perpendicular to the camera. The cusp tips, reflected by the highest points, were then marked with a graphite pencil. The camera transferred the occlusal view of the teeth to the monitor on which the variables were measured with the image analyser program. All measurements were carried out by a single observer (B. P.). In order to determine intraobserver variation, the intercusp distances of 20 teeth were measured 3 times. The mean error of measurement was 0 03 mm. Since sample sizes were small, the Wilcoxon nonparametric test was used for univariate comparisons of the groups (Sokal & Rohlf, 1981). Multivariate models, based on a stepwise logistic regression of all intercusp distances and angles were designed to assess the changes in size and shape between the teeth in the 2 groups (Breslow & Day, 1980). Significance level was chosen at P RESULTS The Table shows the means and S.D. of all the examined variables in the DS and control groups. Preliminary analyses showed no significant differences between the intercusp distances of males and females either in the DS or the normal children. Thus in each group the data for males and females were combined for analysis. All teeth in both groups displayed 5 cusps (Fig. 1). No significant differences were found between the teeth on both sides of the jaw. The results indicate that all intercusp distances and areas of the pentagon of teeth 36 and 46 were smaller in the DS group. Statistically significant differences between the angles in both groups were found in the d-mb-dl, mb-d-dl and the mb-dl-d angles. Stepwise logistic regression, applied to all the intercusp distances separately for teeth 36 and 46, was used to build a multivariate probability model for DS and normals. A model based on 2 distances only, mb-dl and mb-db, proved sufficient to discriminate between the teeth of DS and the normal population (P for mb-dl and for mb-db of tooth 36, and P for mb-

3 Modification of molar teeth in Down s syndrome 531 Table 1. Means and S.D. of the examined variables (mm for intercusp distances) Tooth 36 Tooth 46 DS (n 25) Normals (n 30) DS (n 25) Normals (n 29) Distance mb-db * mb-d * * mb-dl * * mb-ml * db-d * db-dl * * db-ml * d-dl * * d-ml * * dl-ml * * Angle db-mb-ml mb-db-ml mb-ml-db d-mb-dl * * mb-d-dl * * mb-dl-d * * Area * * * P mb-dl Fig. 1. Crown morphology displaying the cusps of tooth 36. The black dots represent the cusp tips: mb, mesiobuccal; db, distobuccal; d, distal; ml, mesiolingual; dl, distolingual. dl, and for mb-db of tooth 46). The model for tooth 36 was: e (mb-dl)+ (mb-db) 1 e (mb-dl)+ (mb-db) The model for tooth 46 (e 2 71) was: e (mb-dl)+ (mb-db) 1 e (mb-dl)+ (mb-db) A model for both tooth 36 and tooth 46 was computed as follows: e (mb-dl)[ ]+ (mb-db)[ ] (mb-dl)[ ]+ (mb-db)[ ] 1 e (mb-dl)[ ]+ (mb-db)[ ] (mb-dl)[ ]+ (mb-db)[ ]. Fig. 2. The probability of Down s syndrome as a function of mb-dl and mb-db distances for tooth 36. For low values of mb-dl, the probability is high, while for high values of mb-dl is lower. The opposite signs of the coefficients implicate differences in size as well of shape between the DS and the control groups. The graph in Figure 2 illustrates the model for tooth 36. It can be seen that for low values of mb-dl ( 7 0 mm), the probability for DS is high. For values of mb-dl ( 7 7 mm), the probability of DS is very low. In the grey zone (mb-dl distances between 7 2 and 7 6 mm), the probability for DS is proportional to the mb-db distance. In summary the probability for

4 532 B. Peretz and others DS is higher when mb-db is relatively higher in the mb-db mb-dl ratio. With respect to the angles, significant differences between DS and normals were found in 3 out of the 6 angles which were measured: the d-mb-dl angle was smaller than in normals, the mb-d-dl angle was higher in DS, and the mb-dl-d angle was smaller in DS. DISCUSSION The data in our study strongly support the previous findings that the intercusp distances of DS teeth are shorter and that the cusp tips of DS molars are arranged in a somewhat different pattern from teeth of the normal population. (Geciauskas & Cohen 1970; Prahl-Anderson & Oerleman, 1976; Townsend, 1983; Brown & Townsend, 1984; Peretz et al. 1996). Our multivariate probability model used stepwise logistic regression analysis and took into account all the intercusp distances. The moderate sample size led us to consider only nonparametric methods in our statistical analysis. The logistic procedure fits linear logistic regression models for binary response data by the method of maximum likelihood. The results of the logistic approach were obtained by linear discriminant methods that assume normality (an expected result when data are approximately normally distributed). Principal component analysis (not shown in this paper) revealed that the first 2 components accounted for most of the variation in the data, with the first component reflecting an overall size (an expected result due to the positive correlations between all distance pairs). The principal component analysis thus incorporated variables both for size and shape. The model in our article provides a tool for predicting the probability for Down s syndrome from mandibular molars. This model adds to our previous model for predicting the probability for Down s syndrome from maxillary molars (Peretz et al. 1996). Since asymmetry in crown size is more pronounced in children with syndromes such as Down s or fragile X (Bailit et al. 1970; Garn et al. 1970a, Peretz et al. 1988), we tested for differences between DS and normal teeth on tooth 36 and tooth 46 separately, although in this study no significant differences were found between the 2 sides. The best model comprised 2 intercusp distances only (the mb-dl and mb-db). The validity of the model was similar for right and left teeth, and for the 2 teeth together. This demonstrates the strength of the model. In our previous report, the model worked best on tooth 16 (Peretz et al. 1996). The opposite signs of the coefficients in all the Fig. 3. Schematic superimposition of the cusp tip pattern of tooth 36 of the DS and normal groups, using the mb-ml and mb-db lines as anchors. The heavier lines forming the inner pentagon represent the DS group. formulae ( [mb-dl] and [mb-db] distances) suggest that the models contain aspects of size and shape. As seen in Figure 2, the probability for DS is higher when mb-db is relatively higher in the mb-db mb-dl ratio. With regard to the angles, no significant differences were found between the angles of the triangle formed by the mb, db and ml cusps, suggesting that this triangle does not change in shape in DS teeth, but only in size, namely, smaller distances in the DS teeth. The significantly smaller d-mb-dl, and mb-dl-d angles, and the higher mb-d-dl in DS point toward the following changes in the shape of DS teeth: the distal and distolingual cusps are located closer to the centre of the tooth with the distal cusp being closer to the centre. These changes are demonstrated schematically in Figure 3, where thick lines represent the DS tooth. Our findings regarding the lack of significant differences between the intercusp distances of males and females in either DS or normal children reflect the variability of sex dimorphism. Our findings are supported by Kieser et al. (1985) who found sex dimorphism of lower first permanent molars in largetoothed Amerindians to be of less than 5% (P 0 05). Prahl Andersen & Oerlemans (1976) did not examine sex dimorphism and pooled scores of males and females with DS. Brown & Townsend (1984) examined only male DS individuals and compared the findings with normal males. Jensen et al. (1973) and Black (1978) did not find dimorphism in primary teeth, and Garn et al. (1979) did not mention sex as a prenatal factor influencing tooth dimensions. Although the precise timing and sequence of early tooth development in DS are unknown, the sequence is likely to be similar to that in normal teeth, despite a generalised delay (Garn et al. 1970b). The mb cusp is the first cusp to calcify, and the mb-db and mb-ml are bridged first (Kraus & Jordan, 1965). Thus a reduction

5 Modification of molar teeth in Down s syndrome 533 in these distances suggests an early insult to odontogenesis. This pattern was found in the mandibular 1st molar in our present study, and in the maxillary 1st molar in our previous report (Peretz et al. 1996). Nery et al. (1975) proposed that the critical period of tooth formation is the time between initial formation of the enamel organ and the initial period of mineralisation of the dental crown. In the mandibular and maxillary 1st molars, the former occurs between 3 5 and 4 mo in utero, and the latter approximately 6 mo after birth. Some variations may exist between males and females as to the rate of the mineralisation (Moorrees et al. 1963). The growth insult can be explained by a general slowing down of the mitotic cycle and rate of cell proliferation, resulting in growth retardation in the cells of the inner enamel epithelium of DS tooth germs (Mitwoch, 1972). It seems that in DS individuals, the change in size both in the mandibular and the maxillary 1st molars occurs at an early stage, while the change in shape occurs in a later stage of tooth formation reflecting the accumulated effects of continued growth retardation. Our general concept for probability models for DS maxillary and mandibular molars are simple and practical because they require only 2 intercusp distances to put into each formula. Further applications of these models to a larger number of teeth of DS individuals are planned. ACKNOWLEDGEMENTS The authors would like to thank Dr Z. Borochovitz, Head of the Genetics Department, Bnei Zion Medical Center, for his assistance in access to casts and for helpful discussion in the course of this study. 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