Vertical Displacement of Distal Extension Ridges by Different Impression Techniques

Objective: To compare the vertical displacement of distal extension ridges of three impression techniques using polyvinyl siloxane (PVS) regular body impression material with irreversible hydrocolloid impression as control.

Method: Eleven subjects participated in the study. Cast produced of the irreversible hydrocolloid impression taken with special tray of each patient was used as a control (A). The second impression technique (M) and third impression technique(C) were taken with PVS regular body using special tray, which used modeling wax and casting wax as spacer at edentulous area respectively.  The fourth impression was altered cast technique (ACT).  Three standardized areas were identified on each ridge, the left (L) and right (R) side; 5mm distal to the last abutment tooth (1), midway between L1 and the centre of the retromolar pad (2), and central of the retromolar pad (3). Three standardized points of each area were measured using the Digimatic indicator (Mitutoyo, Japan) on the casts and comparisons on the displacement were made with the control cast (the measurements were in millimetres). Data were analysed with paired t-test and Wilcoxon signed-rank test. 

Results: The mean differences (MDs) of the mucosal vertical displacement between impressions were:

The greatest MD for each area was in M1, M2, M3 for both L and R. However, they were not significant (P>0.05).

Conclusion: Even though there were differences in the displacement of the mucosa using different impression techniques, they were small and not significant. This may indicate that the control is comparable to the M, C and ACT according to the mucosal vertical displacement. (Supported by vote P0213/2007A, University of Malaya).