Serial Growth Changes in the Lips

Abstract

This study is based upon annual serial observation of six pairs of like-sexed twins who were observed for various periods between the ages of 9 and 18 years. It is introduced by similar observations at more frequent intervals of a baby between the ages of 3 weeks and 2 years who was then also observed annually until the age of 7 years. The records consist of stereoscopic pairs of photographs recorded with a stereometric camera, which were subsequently used to plot contour maps of the face, including the mouth, with the outline of the vermilion borders of the lips and a contour interval of 2 mm. The landmarks used to study antero-posterior change were the mid points of the upper and lower vermilion borders of the lips relative to a line joining the right and left angles of the mouth. Local changes were measured in terms of lip shape, using the same reference line. The differing growth velocities by which the shape of the mouth changes so much in the first 2 years of life are examined and contrasted with the low rates of growth found later. The long-term changes in the older twins are examined in terms of changes in antero-posterior displacement of one lip relative to the other with any changes of shape, and are related to dental changes, as recorded on study models of the dentition.