Long Term Linear Dimensional Stability of Impression Materials

Objective: The aim of this study was to evaluate the long-term linear dimensional stability of vinylpolysiloxane (VPS), polysulfide and polyether impression materials. Methods: Three dental impression materials: a VPS-based alginate alternative-AlgiNot (ALG, Kerr), a polysulfide-Permlastic Regular (PER, Kerr), and a polyether-Impregum Garant Soft LB (IMP, 3M/ESPE) were investigated. The linear dimensional change was measured using a Titan Zoomatic Measuring Microscope (Model TM-II). Three specimens per product were prepared according to ISO Standard No. 4823. Each material was mixed and placed to the stainless steel ring mold (30mmX3mm).  The specimen was cured in the water bath at 35±1°C and was demolded after the setting time. Two points on the specimen corresponding to the two known marks on the mold were marked with a permanent marker for easy identification. Measurement was made initially and then at predetermined time intervals (24 hours, 10 months, 27 months, 34 months) after the specimen was stored at room temperature. The linear dimensional change of the sample as compared to the ruled test block was calculated and reported in percent (%). Three measurements on each material were made and the dimensional change was averaged. Results: The mean linear dimensional changes were reported in the following table. Statistical analysis (ANOVA, p<0.05) showed that there were not significant differences in linear dimensional change for ALG and PER after 34 months. There were significant differences in linear dimensional change for IMP after 10 months.

	ALG(%)	PER(%)	IMP(%)
24hr	0.996±0.032a	1.342±0.736b	1.350±0.034c
10mo	1.071±0.073a	1.543±0.368b	0.783±0.048d
27mo	0.938±0.212a	1.557±0.328b	melted
34mo	1.020±0.181a	1.423±0.232b	melted

*Means with the same letter within the same column are not statistical different at p<0.05

Conclusion: The vinylpolysiloxane and polysulfide impression materials have a better long term dimensional stability than the polyether impression material when storage at ambient conditions.