This study investigates the temperature changes on the external root surface during root canal preparation using different rotary systems and assesses the impact of irrigation temperatures. Sixty extracted human maxillary incisors were divided into four groups based on the rotary system used: ProTaper Next (Dentsply Sirona, Ballaigues, Switzerland), Reciproc Blue (VDW GmbH, Munich, Germany), WaveOne Gold (Dentsply Sirona, Ballaigues, Switzerland), and TruNatomy (Dentsply Sirona, Ballaigues, Switzerland). These systems differ in cutting efficiency and design. Temperature measurements during instrumentation and irrigation were recorded using a FLIR E60bx thermal camera (Teledyne FLIR LLC, Hudson, NH, USA). Irrigations were conducted with sodium hypochlorite at room temperature and heated to 60 °C. The ProTaper Next group exhibited the highest average temperature increase during instrumentation (5.2 °C), followed by WaveOne Gold (4.3 °C), Reciproc Blue (3.7 °C), and TruNatomy (2.8 °C). During irrigation with heated sodium hypochlorite, temperature rises recorded were 6.8 °C for ProTaper Next, 5.9 °C for WaveOne Gold, 5.2 °C for Reciproc Blue, and 4.1 °C for TruNatomy. Statistical analysis revealed a significant negative correlation between dentin thickness and temperature rise, with r-values ranging from -0.62 to -0.87 across the groups. No significant correlation was found between canal diameter and temperature change, indicating that the canal's size does not influence the thermal impact as much as the properties of the rotary system and irrigation temperature. Different rotary systems produce varying levels of temperature increases on the external root surface, influenced significantly by the thickness of the dentin and the temperature of the irrigation solution. These variations necessitate careful selection of instrumentation and irrigation protocols to minimize potential thermal damage to surrounding periodontal tissues.