The Effect of Heat Treatments on the Mechanical Properties of Expired Endodontic Gutta-percha – An in vitro Study

INTRODUCTION: Expired gutta-percha (GP) can lose its mechanical properties. This study aimed to compare the tensile strength values between expired and nonexpired GP-cones and to assess the outcome of different heat temperatures on this strength. MATERIALS AND METHODS: Two-hundred-forty ProTaper points were obtained from nonexpired and 2 years expired pack with two different subgroups (sealed or exposed to air and light). All groups were subjected to the following treatments: control, 90°C water bath and cool either at room temperature or 0°C and 70°C water bath and cool either at room temperature or at 0°C. The strength under the tensile load was calculated using the universal testing machine. RESULTS: The collected data were evaluated by one-way analysis of variance. Tensile strength for all control groups did not show any difference. Significant increase in the tensile strength in groups heated for 1 min in a water bath at 70°C, the tensile strengths were 8.19 ± 2.72 Mpa and 5.94 ± 1.14 Mpa cooled at 25°C and 0°C, respectively, P ≤ 0.001. Two years expiration did not lower the tensile strength of the GP and exposure to air and light did not show any change. Appropriate storage of GP is a key factor to extend its lifespan. CONCLUSION: A clinician may consider using expired GP as long as there are no noticeable changes in their structure and properties. A simple chairside technique using hot water may be helpful in restoring the mechanical properties of expired GP.