The importance of humidity in the in vitro study of the cranium with regard to initial bone displacement after force application.

The aim of this pilot study was to find a suitable model for simulating in vivo initial displacements of the maxilla after force application. Force was exerted on the maxillae of four dogs by means of a dental splint. To register the bone displacement, speckle interferometry was used as the measurement technique. The initial orthopaedic effect as a result of force application in vivo was registered by the construction of rotation centres around which the maxilla rotated. The orthopaedic effect after force application in vivo was compared with different in vitro situations of the laboratory animal. After the animal had been killed and its maxilla macerated, the cranium was placed in a sealed conditioned box. Only three skulls were found to be suitable for this experiment. The environment thus created can be influenced by changes in relative humidity. Various forces were applied in various directions on the maxilla of three Alsatians. By changing the relative humidity, an attempt was made to create a situation in which the initial bone displacements after force application were comparable to the in vivo situation. None of the laboratory animals used showed a comparable condition for the in vivo situation through manipulation of relative humidity. As only three dogs were experimented on, these findings are tentative. This experiment will be extended to three more dogs from the same litter.