MODIFICATION OF TOOTH SIZE AND SHAPE IN DOWNS-SYNDROME

Individuals with Down's syndrome (DS) tend to display a reduction in s ize of permanent teeth, and reduced intercuspal distances in molars. A total of 51 permanent maxillary Ist molars of 26 DS children were exa mined from dental casts, 65 permanent maxillary Ist molars of normal c hildren were examined from dental casts of 33 individuals. The followi ng measurements were performed on both right and left molars (teeth 16 and 26 respectively): (1) all intercusp distances (distobuccal, db, d istolingual, 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 int ercusp 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-d l and mb-ml distances of the upper right molar (tooth 16) were suffici ent to discriminate between DS and normal teeth: P(DS) = l)+2.98(mb-ml ))/1+e(20.15-4.53(mb-dl)+2.98(mb-ml)) The probability for DS is higher when mb-ml is relatively higher in the mb-ml/mb-dl ratio. Another log istic analysis based on groups of angles revealed a combination of 3 a ngles which gave highly statistically significant discrimination betwe en both groups: the mb-db-dl angle was higher in DS, the mb-dl-db angl e was slightly smaller in DS, and the mb-ml-db angle was slightly smal ler 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 prob ability model for DS teeth is simple and practical because it requires only 2 intercusp distances to be put into the formula.