[Pressures produced in a tray during impression procedures. Maxillary edentulous impressions].

It was previously reported that pressures produced during compression of impression materials between parallel disks were affected by several factors, and that hydrodynamical analyses well characterized the results of experiments. The present study was undertaken to measure and theoretically demonstrate pressure distributions during mechanical impression making of a maxillary edentulous cast and intraoral impression procedures. The highest pressures were recorded over the anterior palate and pressures decreased with approaching to the posterior end when an unmodified tray was used. Little difference in pressures was found in right-angled direction to the median line of the palate, and small pressures were recorded even on the borders. Such distributions were caused by differences in width of the paths where impression materials flowed. Addition of relief or an escape hole to the tray brought identical effects as shown in the previous experiments using parallel disks, that is, the pressures distributed rather evenly in the relieved area, while pressures remarkably decreased beneath the escape hole. The pressure distributions occurred during intraoral impression makig showed same tendencies as those of mechanical impressions of the cast, but some variations were considered according to the manner in which the tray was manually seated.