The purpose of this study was to analyze thermal effects during laser-assisted periodontal treatment. An in vitro model for temperature measurements was developed to investigate different laser settings regarding pulp safety. Additionally, the influence of transmission on pulp temperature elevation was evaluated. Longitudinal root sections were irradiated with a 940-nm diode laser with 1.0 and 1.5 W in continuous wave mode. According to wall thicknesses, irradiation times were adjusted to 20 s for upper and 10 s for lower incisors, respectively. Transmission was relatively low in both upper (4.8% to 8.3% of incident power) and lower incisors (10.2% to 15.0%). Samples were embedded in a polyurethane model and six thermocouples were affixed. Regardless of dentine thickness, the middle third of the root was identified to be the area with the most heat load, where a temperature rise of 7.5°C (1.0 W) and 10.5°C (1.5 W) was registered in upper incisors. A difference of 1.5°C to 3°C was detected in lower incisors compared with uppers. All settings were safe except for 1.5 W, 20 s. Transmission affected heat generation remarkably. The proposed model provides advantages regarding heat transfer and enables for spatially resolved temperature measurements.