Real‐Time Analysis of Changes in Internal and External Root Temperatures Using Different Systems for Activating the Irrigation Solution

<b>Introduction:</b> There is a concern regarding the heating transfer to the periodontal tissues after irrigating solution activation. Therefore, this study analyzed the real-time changes in internal and external root temperatures using different systems for activating the irrigant. <b>Methods:</b> Two single-rooted mandibular premolars were chemomechanically prepared. Three orifices were drilled on the root surface at 3, 6, and 9 mm from the apical foramen with a spherical diamond bur. In one tooth, drilling was restricted to the cementum. In another tooth, drilling was performed close to canal dentin. Thermocouple sensors were coupled to the orifices and fixed with resin for temperature measurement. Irrigation was performed with 2.5% NaOCl at 25°C or 45°C. The irrigant was activated for 20-, 30- and 60 s using 3 different systems: passive ultrasonic irrigation (PUI), Ultra X (UX), and endoactivator (EA). For each initial irrigant temperature, time, and activation system, the tests were repeated 8 times, resulting in a total of 96 evaluations for the external and internal root temperatures (<i>n</i> = 48 for each). <b>Results:</b> Data was statistically analyzed with a multilevel linear regression model and intraclass correlation coefficients (ICCs) were calculated. Then, four-way ANOVA with Bonferroni's post hoc tests performed intergroup and intragroup comparisons. EA promoted lower temperature increase than PUI and UX (<i>p</i> < 0.05). PUI and UX induced similar internal and external temperature changes when irrigated with NaOCl at 25°C.. <b>Conclusion:</b> The initial temperatures (25°C or 45°C) and the activation systems of the irrigant had influence on the internal and external radicular temperatures. The activation period had little influence on root temperature changes, which may be deemed clinically safe.