2.2. Clinical examinations

A calibrated periodontist (coauthor Thomas E. Rams) performed the temperature measurements and clinical evaluations (American Academy of Periodontology, 2000). An electronic temperature probe (PerioTemp Probe System, ABIODENT Inc.) measured absolute subgingival and sublingual site temperatures and determined normalized differential values of subgingival temperature relative to sublingual temperature. The device, cleared for clinical use by the United States Food and Drug Administration, has a computer‐linked thermocouple embedded inside a plastic periodontal probe tip with dimensions and shape similar to a Michigan‐O probe (Kung et al., 1990), a foot‐activated switch, and a print‐out of measured values (Kung et al., 1990). As a proxy for body core temperature, the probe tip placed for 5 s under the most posterior and medial part of the tongue, measured sublingual temperature to the nearest 0.01°C. Subgingival temperature was determined by gently advancing the probe tip to full pocket depth at six sites of each study tooth. The temperature probe provided a normalized subgingival temperature differential by subtracting the patient's sublingual temperature from the subgingival temperature (Kung et al., 1990). The temperature probe designated the subgingival temperature as either “hot” (red light) or “cool” (green light) after taking into account the normal warmer posterior versus cooler anterior teeth and warmer maxillary versus cooler mandibular teeth (Kung et al., 1990) and the variability in subgingival temperature among periodontally healthy individuals (Haffajee et al., 1992a). The tooth‐specific temperature threshold values are published elsewhere (Haffajee et al., 1992a; Kung et al., 1990) and were utilized in prior studies (Haffajee et al., 1992a, 1992b, 1992c;  Kung et al., 1990; Maiden et al., 1998; Niederman et al., 1995; Rams & Slots, 2023) as well as in the present study. The reproducibility of temperature measurements was determined in replicate readings taken 2 min apart at 18 sublingual and 55 subgingival sites. Bleeding on probing was assessed within 30 s after the removal of the temperature probe from subgingival sites. A Michigan‐O probe assessed periodontal pocket depth and a Nabers probe furcation involvement.