Vertical components of overbite change: A mathematical model

The purpose of this study was to better understand the multidimensional nat ure of overbite changes that occur during adolescence. The study used longi tudinal cephalograms of 181 untreated children (102 males, 79 females) take n at ages 10 and 15. Four major components that directly affect overbite we re measured: (1) maxillary vertical displacement, (2) mandibular vertical d isplacement, (3) upper incisor vertical change within the bone, (4) lower i ncisor vertical change within the bone. Cranial base, maxillary, and mandib ular superimpositions were performed for each subject to assess the vertica l changes that occurred in these 4 components and to assess overbite, A mul tiple regression analysis was used to develop a mathematical model describi ng the relationships of these components to changes in overbite. The model was validated with an independent subsample and a comparison of subjects wh ose overbites decreased and those whose overbites increased. The results sh owed that overbite changed minimally (0.2 mm) over the 5-year period; varia tion ranged from a 2.4 mm decrease to a 5.6 mm increase. The regression mod el indicated that the mandibular skeletal changes were twice as important a s the mandibular dental changes and about 2.5 times as important as the max illary changes in effecting overbite change. Within the mandibular skeletal component, vertical growth was more important than mandibular rotation in determining overbite change. The model demonstrated that a multivariate app roach is necessary to understand overbite changes. More effective orthodont ic treatment might be achieved by focusing on the primary components effect ing overbite change, especially those with the greatest potential for thera peutic modification.