Thermal stability and setting dynamics of nanozinc oxide and AH Plus sealers: An in vitro study

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Abstract Introduction: Despite the widespread use of warm vertical compaction, the effects of transient high temperatures on the setting kinetics and chemical stability of the majority of sealers remain uncharacterized. This study aimed to evaluate the effect of heat application on the setting time and chemical properties of AH Plus (epoxy resin-based) and nanozinc oxide (NZO) sealers. Materials and Methods: AH Plus and NZO sealers were assigned to five temperature groups (37°C control, 65°C, 97°C, 150°C, 250°C for 1 min), yielding 10 groups with 9 discs per group (90 discs total). Sealers were placed in 10 mm diameter, 2 mm height stainless-steel molds. Control samples were kept at 37°C, and intervention groups were heated as specified, then all were incubated at 37°C. The setting time was checked periodically using a standard probe. Then, samples were ground for Fourier transform infrared (FTIR) spectroscopy, and differential thermal analysis (DTA). Procedures followed the ISO 6876 specifications. Data were analyzed using ANOVA with Tukey post hoc tests ( P = 0.05). Results: Heat exposure significantly reduced AH Plus setting time ( P < 0.001). NZO was largely unaffected ( P > 0.05), except at 65°C, where setting time was significantly reduced ( P < 0.001). FTIR showed minor, temporary changes in both sealers. DTA revealed that heat decreased the reaction rate between NZO and eugenol but enhanced the reaction between calcium tungstate and zirconium oxide in AH Plus. Conclusions: Both sealers exhibit minimal chemical changes at 250°C, making them suitable for vertical compaction techniques with stable chemical properties.

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