Modification of tooth size and shape in Down's syndrome.

Individuals with Down's syndrome (DS) tend to display a reduction in size of permanent teeth, and reduced intercuspal distances in molars. A total of 51 permanent maxillary 1st molars of 26 DS children were examined from dental casts, 65 permanent maxillary 1st molars of normal children were examined from dental casts of 33 individuals. The following measurements were performed on both right and left molars (teeth 16 and 26 respectively): (1) all intercusp distance (distobuccal, db; distolingual, dl; mesiobuccal, mb; mesiolingual, ml); (2) the db-mb-ml, mb-db-ml, db-ml-mb, dl-mb-db, mb-dl-db, and dl-db-mb angles; (3) the area of the quadrangle shaped by connecting the cusp tips. All the intercusp distances were significantly smaller in the DS group. Stepwise logistic regression, applied to all the intercusp distances, was used to build a multivariate probability model for DS and normals. The mb-dl and mb-ml distances of the upper right molar (tooth 16) were sufficient to discriminate between DS and normal teeth: [table: see text] The probability for DS is higher when mb-ml is relatively higher in the mb-ml/mb-dl ratio. Another logistic analysis based on groups of angles revealed a combination of 3 angles which gave highly statistically significant discrimination between both groups: the mb-db-dl angle was higher in DS, the mb-dl-db angle was slightly smaller in DS, and the mb-ml-db angle was slightly smaller in DS. 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 DS population. Our probability model for DS teeth is simple and practical because it requires only 2 intercusp distances to be put into the formula.