Since the identification of periapical lesions typically requires invasive testing that may adversely affect individuals suffering from concomitant disease, the diagnosis of apical periodontitis remains a challenge. This study aimed to determine the effectiveness of infrared thermal imaging for the detection of asymptomatic odontogenic inflammatory response in patients with a high risk of systemic infections. The examinations were performed using the FLIR T1020 thermal camera. The acquired images were analyzed with a ThermaCAM TM Researcher Pro 2.8 SR-3. Statistical analyses were conducted using the Statistica 10 software. The Mann–Whitney U test was used for data that were not normally distributed or did not meet the assumption of homogeneity of variance, while normally distributed data were analyzed with the t-test. The mean temperature difference between the periapical regions of the suspect and contralateral teeth was found to be greatest at 30 s of mouth opening. This is a preliminary study conducted to evaluate the potential of infrared thermal imaging as a diagnostic tool for the identification and elimination of odontogenic infection foci. Thermography seems to facilitate the quantitative assessment of inflammation by displaying temperature differences between the affected and unaffected regions.