Thermafil retreatment using a new "System B" technique or a solvent

The solid plastic carrier in the Thermafil obturation system must be removed to facilitate retreatment. The purpose of this study was to compare the efficacy and time required to retreat canals obturated with Thermafil with plastic carriers using a new technique based on the System B HeatSource or a solvent. Fifty-two extracted human mandibular premolars with single canals were instrumented and then obturated with Thermafil with plastic carriers. After 2 wk storage at 22 degrees C and 100% humidity, they were randomly divided into 2 groups of 26 teeth each. Group 1 teeth were retreated using chloroform and hand files, whereas teeth in group 2 were retreated with a new technique using the System B HeatSource. The end point of retreatment was defined as complete removal of the plastic carrier. The time required for retreatment was recorded. Then, the apical 5 mm segment of each root was sectioned horizontally at 1 mm intervals and each section digitally imaged. The total area of the canal and the area of the canal occupied by gutta-percha and sealer were measured using NIH image software. Data were analyzed using an unpaired t test. The mean time for retrieval of the plastic carrier was significantly less for the System B technique (1.8 min) than for the solvent technique (3.6 min) (p < 0.001). The difference between the two groups in the amount of filling material (carrier, gutta-percha, and sealer) removed was not significant (p > 0.05).