VERTICAL DIMENSION OF OCCLUSION CHARACTERISTICS IN PATIENTS WITH DIFFERENT TYPES OF MALOCCLUSIONS BY THE SHIMBASHI INDEX IN THE AGE ASPECT
Authors: Makarova O.M. , Kuroiedova V.D. , Rud Y.V. 
Published: March 2020

Occlusal vertical dimension is one of the important parameters, which is significantly related to the functional status of the masticatory complex.

The finding of the optimal occlusal vertical dimension and the method of its determining is a debatable and topical issue in planning of orthodontic correction and orthopedic rehabilitation.

One of the morphometric methods of the occlusion vertical dimension (OVD) is the Shimbashi index or the LVI-index. The Shimbashi index allows us to count out the "perfect" occlusal vertical dimension due to the "golden proportion" principle based on the width of the upper center incisor.

The purpose of the research was to verify the expediency of the Shimbashi index using while examinating orthodontic patients.

The morphometric investigation of control-diagnostic models of jaws of 300 orthodontic patients in different ages was performed. All surveyed patients were divided into the age and the tooth row interrelation type in sagittal and vertical planes.

In the age aspect, the smallest value of the occlusion vertical dimension is determined at the age of 8-9 years, which can be connected with incompleted stages of the bite elevation and morphofunctional formation of the masticatory complex. In the period from 8 to 11 years there is one significant increasing of the OVD, which, obviously, is connected with active growth of the alveolar processes and the realization of bite elevation stages. In the 14-15, 16-17 and 18-19 years, the OVD does not reach to the Shimbashi index value by 5 mm and it doesn’t increase more in the future.

Among the sagittal malocclusions, the greatest vertical dimension of occlusion was observed in patients with III class of dentofacial abnormalities. This can be explained by the fact that the mesial bite is usually accompanied by an increase of vertical parameters. However, the interalveolar height was still less by 3 mm compared to the "ideal" one. In classes I and II of dentofacial abnormalities, OVD was almost the same – 13.55 ± 2.55 mm and 13.56 ± 2.55 mm, which is in average by 5 mm less (p˃0.05) than calculated one by the Shimbashi index.

While dividing patients by the depth of the incisal overlap, we obtained quite logical results. In particular, the lowest occlusion vertical dimension was found in patients with increased depth of the incisal overlap. The most interesting is the fact that even in patients with a depth of incisor overlap less than 1/3 of the crowns of lower incisors, that is a tendency for open bite, the vertical dimension of occlusion was still less than measurement found by the Shimbashi index, although the difference between them was minimal (approximately 1,5 mm) compared to other two study groups.

According to the results of the study, all types of malocclusions are characterized by decrease of the occlusion vertical dimension refers to the Shimbashi index. The obtained data suggest the next idea: either the occlusal vertical dimension calculated by Shimbashi index is a bit exaggerated and needs clarification, in particular by the investigation of skeletal parameters according to the skull X-ray, or, indeed, modern orthodontic patients have a total reduction of the interalveolar height.