Influence of cyclic heating on physical property and biocompatibility of alpha- and beta-form gutta-percha.

BACKGROUND/PURPOSE: Thermoplasticized techniques with high temperature and repetitive heating in root canal filling may cause degeneration of gutta-percha, producing cytotoxic byproducts and interfering sealing quality. This study was conducted to investigate the influence of cyclic heating on the physical property and biocompatibility of alpha- and beta-form gutta-perchas. METHODS: Both alpha- and beta-form gutta-perchas were submitted to two heating processes: continuous heating and cyclic heating. Continuous heating was carried out by heating the samples up to 300 degrees C and 400 degrees C. The samples were then analyzed by differential scanning calorimetry, differential thermal analysis (DTA), and thermogravimetry. For cyclic heating process, samples were heated from 30 degrees C to 200 degrees C for seven cycles and analyzed with DTA and thermogravimetry. For cell adhesion assay, samples were treated (30 degrees C to 200 degrees C, one and seven cycles), submitted to cell culture and examined by scanning electron microscope. RESULTS: Differential scanning calorimetry and DTA indicated that alpha-form gutta-percha presented a major endothermic peak at 50-57 degrees C, while beta-form gutta-percha showed two major endothermic peaks at 46-50 degrees C and 60-63 degrees C. Total weight loss of beta-form gutta-percha was about 2-fold greater than that of alpha-form gutta-percha after continuous heating up to 300 degrees C, or cyclic heating for seven times. Scanning electron microscopy showed no obvious difference of cell adhesion on alpha- and beta-form samples, even with seven cyclic heating or one heating cycle. However, the attachment of the cells to the culture plate (the control) is better than to the gutta-percha samples. CONCLUSION: The increase of heating cycles for alpha- and beta-form gutta-percha exerts no adverse influence on their biocompatibility. Because the physical property of beta-form gutta-percha becomes unstable when it is heated at over 300 degrees C or subjected to cyclic heating, beta-form gutta-percha may not be recommended for use in thermoplasticized gutta-percha techniques.