An experimental study of increased vertical dimension in the growing face.

Five juvenile rhesus monkeys were used in an experiment designed to study the structural adaptations in the craniofacial complex that resulted from increases in vertical dimension. The bite was opened 2,3,10, or 15 mm. by means of cast bite splints cemented on the maxillary arch. Adaptations were monitored in these animals by means of serial cephalometric radiography with metallic implants. The results of this study indicate that any change in the vertical dimension of the face results in specific structural adaptations throughout the craniofacial complex. The most significant adaptation occurred in the maxillary region, in which the normal downward displacement of this region was decrease and the anterior displacement was increased. Adaptation were less evident in the mandible, except in those animals in which a severe bite opening was produced; resorption in the region of the gonial angle was evident. Dentitional adaptations were of secondary importance. This study demonstrates that the maxillary complex is a very plastic structure which responds to changes in bite opening and altered muscle length. The clinician should be aware of the changes that result from various alterations of vertical dimension to make sure that these changes are not antagonistic to his over-all treatment goal. He may also take advantage of these changes when designing treatment strategies for certain clinical cases.