Variability and age changes in overjet and overbite: Report from a follow-up study of individuals from 12 to 20 years of age

Abstract

A bite analysis in growing individuals should comprise an estimate of the change in the occlusion which may be expected up to adult stage. A necessary condition hereof is that changes in the bite are known with regard to size and direction for various stages of the development. The present article is confined to an analysis of variability and age changes in sagittal and vertical occlusion during the late developmental period. The age changes in the sagittal and vertical incisal occlusion have been calculated statistically with regard to size and direction in a group of 243 Swedish boys by an examination at the age of 12 and a re-examination at 20 years. The following findings of special importance may be mentioned: 1. 1. The variability in overjet is greater than in overbite, at the ages of both 12 and 20 years. 2. 2. The age changes for both overjet and overbite show pronounced individual difference, with regard to both direction and size. The age changes are greater for overbite than for overjet. 3. 3. The overjet generally changes with advancing age, so that the front teeth of the lower arch show a forward displacement in relation to those of the upper one. These general age changes are comparatively slight. The individual differences, expressed as the dispersion of the age changes, are very great, however. In some individuals the relative forward displacement of the front teeth of the lower jaw is very pronounced, the maximum being 4.8 mm. in the present series of cases. A relative backward displacement of the lower dental arch takes place in other individuals, the maximum is 2.6 mm. in this series. The range of variation for these age changes in the overjet (7.4 mm.) is the best expression for the dynamics in the development of the bite. The calculated standard deviation for these age changes is 1.2 mm. The age change in the sagittal molar occlusion is estimated to be within the limits ± 1 2 cuspal width, with a certain general tendency to a relative forward displacement of the lower arch and with great individual differences. 4. 4. Generally the overbite decreases somewhat with advancing age. Individually, the standard deviation of the age changes also is very great, and different with regard to direction. The range of variation is 10.1 mm. with a standard deviation of 1.4 mm. In the present series the largest opening of the bite with advancing age is 5.1 mm., and the largest deepening of the bite is 5 mm. 5. 5. In two out of three children the change in overjet or overbite exceeds ±1 mm. from 12 to 20 years. 6. 6. The general tendency with age to a forward displacement of the lower incisors in relation to the upper incisors differs as to magnitude in primarily different types of sagittal occlusion. This forward displacement of the lower arch with age in relation to the upper arch is on an average greater in mandibular as well as in extreme maxillary overjet cases than in cases with normal value of overjet. This indicates a relationship of nonlinear type and is explained as an effect of functional modeling during the bite development. 7. 7. Age changes in the overbite also show a certain relationship with the primary type of bite. Deep-bites show a greater tendency to open than normal overbites, whereas open-bites show a tendency to close. Individual differences, however, are pronounced. 8. 8. A calculation of the frequency of different types of malocclusion at different age levels cannot be used to express changes in the occlusion with advancing age. Differences in frequency at different age levels will be indicative only of the general growth tendencies. These are slight in relation to the standard deviation of the growth changes. It is the standard deviation of the age changes which is the actual expression of the dynamics in the growth and development of the bite. This tends in both directions, so that the frequency values become relatively stable with advancing age.