A modulated differential scanning calorimetric (MDSC) study was performed to investigate melting and glass transitions in vinyl polysiloxane, polyether and polysulfide dental elastomeric impression materials. The MDSC analyses were performed from -150 to 200 degreesC, using heating-only modulation conditions and sufficient modulations to define the transitions. The two vinyl polysiloxane materials had a single melting peak near -50 degreesC, whereas the polyether material had two melting peaks near -20 and 50 degreesC. The polysulfide material had a small apparent melting peak near 70 degreesC and an endothermic peak near 190 degreesC that requires further investigation. Apparent crystallization peaks were observed on the nonreversing heat flow curves for the vinyl polysiloxane materials. These two silicones had glass transitions near -125 degreesC that were very weak because of their high filler content. The polyether material had a glass transition near -80 degreesC, and the polysulfide material had a glass transition near -55 degreesC. More research is needed to elucidate the nature of the melting peaks in these elastomers and the relationships between polymer structural transformations and clinically relevant properties.