The question asks us to arrange elastomeric impression materials in decreasing order of their linear contraction. The materials in consideration are:
- CS: Condensation Silicone
- PS: Polyether
- PE: Polysulfide
- AS: Addition Silicone
To understand the correct order, let's break down their properties:
- Condensation Silicone (CS): Among elastomeric impression materials, condensation silicones exhibit the highest linear contraction due to the by-product formation of alcohol when the material sets. This leads to dimensional changes.
- Polysulfide (PS): Polysulfides show moderate contraction. Their setting reaction involves the formation of water as a by-product, leading to some dimensional change.
- Polyether (PE): Polyethers tend to have lower contraction rates compared to polysulfides but higher than addition silicones. They are relatively more stable dimensionally, but still, some contraction is observed.
- Addition Silicone (AS): Among the options, addition silicones have the least linear contraction. Their setting reaction produces no by-products, thereby ensuring superior dimensional stability.
Based on the above analysis, the decreasing order of linear contraction is:
CS > PS > PE > AS
This is in line with the characteristics of these materials as used in dental applications. This reasoning leads us to conclude that the correct option is:
CS > PS > PE > AS