Volume shrinkage mechanism of gutta percha point studied by differential scanning calorimetry and volume dilatometer in vitro

The mechanism of the volume shrinkage of gutta-percha (GP) point was investigated from the viewpoints of crystalline phase transition of GP and thermal expansion and contraction of thermal-conductive filler. Differential scanning calorimetry (DSC) was employed to calculate the volume shrinkage rate (VSR) of GP point indirectly by determining enthalpy changes that were caused by the crystalline phase transition. Volume dilatometer was utilized to determine the VSR directly to verify the result of DSC. The VSR of GP point calculated by DSC was approximately 2%, which was in good consistence with the result of volume dilatometer tested directly. The volume shrinkage of GP point was driven by two factors, one was the crystalline phase transition of GP that contributed to approximately 99% of the VSR of GP point, and the other was the cold contraction of thermal-conductive filler that could be ignored completely because its contribution rate was only approximately 1%. It was valuable to understand the volume shrinkage behavior of GP point materials and decrease the adverse effect of volume shrinkage in clinical therapy.