Sodium bicarbonate (NaHCO3) is used as an anti-plaque agent in a variety of dental formulations. The aim of this study was to understand the active ingredient-excipient type of interactions in the solid state using thermal analysis. A simple formulation such as a the dental formulation was chosen as an example. Equivalent-ratio w/w binary, tertiary and quaternary mixtures of commercially obtained NaHCO3 were prepared with solid excipients used in dental formulations. The thermal decomposition of NaHCO3 was studied in the presence of these excipients, using thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Apart from kinetic analysis, two other methods were developed during the course of this project to assess the solid state reactivity of NaHCO3. The reactivity of NaHCO3 changed in the presence of other solid excipients. The methods developed during this project were successfully used in assessing the solid state reactivity of NaHCO3 in the presence of other substances. It was concluded that these thermal analysis methods could also be applied to other substances for similar solid state studies.