Are there any precautions to take pvs impression immediately after build up?
Have a look at this:
Volumetric dimensional change of six direct core materials.
Chutinan S, Platt JA, Cochran MA, Moore BK.
Dent Mater. 2004 May;20(4):345-51.
Yes, more than 50 articles you may find on Google scholar, following just as samples, :
Villalta, P., Lu, H., Okte, Z., Garcia-Godoy, F., & Powers, J. M. (2006). Effects of staining and bleaching on color change of dental composite resins. The Journal of prosthetic dentistry, 95(2), 137-142.
Hirasawa, T., Hirano, S., Hirabayashi, S., Harashima, I., & Aizawa, M. (1983). Materials Science Initial Dimensional Change of Composites in Dry and Wet Conditions. Journal of dental research, 62(1), 28-31.
Martin, N., Jedynakiewicz, N. M., & Fisher, A. C. (2003). Hygroscopic expansion and solubility of composite restoratives. Dental Materials, 19(2), 77-86.
All the dimensional change occurs during polymerization. There is no dimensional change after that. With self-cure, the dimensional change is negligible. With light-cure, each succeeding layer fills in the polymerization contraction of the previous layer, making final dimensional change negligible.
Just to broaden the question into an aspect which also has importance in my experience - is the dimensional changes of composite during function involved with the materials wear (long term) and flexibility charecteristics. This aspect of dimensional change also needs to be considered as it has significant clinical implications.
The initial polymerization contraction is 1.5-3.5%, which causes problems with bulk fillings shrinking away from margins, but has little effect on layered build-ups. Wear resistance and flexibility are built into the composite, but do not necessarily directly relate to polymerization shrinkage.
is this also related to marginal leakage somehow ? which occurs after some time ?
Polymerization is essentially completed within seconds. It is the patency of the adhesive micro-mechanical bond which determines subsequent micro-leakage.
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