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

A total of 50 permanent mandibular Ist molars of 26 children with Down's sy ndrome (DS) were examined from dental casts and 59 permanent mandibular Ist 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-mi, db- d, db-dl, db-mi, d-dl, d-ml, dl-ml); (b) the db-mb-mi, mb-db-mi, mb-mi-db, d-mb-dl, mb-d-dl, mb-dl-d angles, (c) the area of the pentagon formed by co nnecting 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 suffici ent to discriminate between the teeth of DS and the normal population. The model for tooth 36 for example was as follows: p(DS) = e(30.6-5.6(mb-dl)+25(mb-db))/1+e(30.6-5.6(mb-dl)+25(mb-db)) A similar model for tooth 46 was also created, as well as a model which inc orporated both teeth. With respect to the angles, significant differences b etween DS and normals were found in 3 out of the 6 angles which were measur ed: the d-mb-dl angle was smaller than in normals, the mb-d-dl angle was hi gher, 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 p opulation.