Residual chloroform and plasticity in customized gutta-percha master cones

Drying before use has been recommended for customizedmaster cones prepared with the chloroform dip technique. This was suggested to minimize future shrinkage of the cone. The effect of drying time on residual chloroform in customized gutta-percha master cones and on their plasticity was studied by gravimetric and indirect plasticity assays. Gutta-percha master cones, dipped in chloroform (apical 5 mm) for 1s, absorbed 0.35 mg of the solvent. Most of the solvent (62%) evaporated within the first 3 min of drying. However, after 10 min of drying, 20% of the absorbed chloroform was still present in the cone. Plasticity of the cones was lost more rapidly than the chloroform: within 15 s of drying, most of the plasticity was lost. After 30 s of drying, the cones could no longer be permanently deformed. The discrepancy between loss of plasticity and rate of chloroform evaporation may mislead the clinician to think that most of the chloroform has evaporated within the first 30 s of drying. The results of this study indicate that longer drying time should be recommended. The physical and biological implications of the residual chloroform should also be studied.