Influence of various impression procedures for removable partial denture on displacement of soft mucosal tissue

In the impression-taking procedure for the distal extension removable partial denture, the pressure produced at the interface of the soft mucosal tissue and the impression material is the most important factor for the stability of the saddle under functional load. However, a review of the literature revealed little information about the displacement of the soft tissue caused by the impression pressure. In the present study, to investigate the influence of various impression procedures on the magnitude of the soft tissue displacement more precisely, a new three-dimensional deformation measurement system was devised. Compared to the previous studies, the greatest advantage of the system is that the hardened impression material can be surveyed directly without substituting a dental stone. It was found that, in the investigation using a partially edentulous simulated model, the amount of the subsidence in the soft tissue was increased as the thickness of the spacer of the impression tray was reduced or the seating speed of the tray was fast. Especially in the buccal area, a large amount of vertical displacement was present compared to the midridge and lingual area. Thus it was suggested that many factors are associated with the form of soft tissue under impression loading.