The Periodontal Inflamed Surface Area (PISA) is a novel parameter which quantifies the extent of periodontal inflammation. This cross-sectional study aimed to explore the association between the PISA value and conventional
parameters, including mean probing pocket depth (PPD) and mean clinical attachment level (CAL). Additionally, the PISA value was compared across severity levels of periodontitis, as classified by the CPITN and CDC/AAP definitions in the Electricity Generating Authority of Thailand (EGAT) workers. PISA was calculated using full-mouth periodontal parameters including PPD, CAL, and bleeding on probing. Periodontitis, as defined by CPITN and CDC/AAP, was classified into no/mild, moderate, or severe periodontitis. The reliability of PISA compared with severity types of periodontitis defining by CPITN and CDC/AAP was explored by the Kruskal-Wallis test. Among a total of 2,643 participants aged 34-74 years, the median of PISA value was 319.4 mm2 with a range of 2.2 to 3624.4 mm2, and the mean of PISA value was 440.68±415.40 mm2. When defining periodontitis according to CPITN and CDC/AAP, the prevalence of severe periodontitis were 28.7% and 26.3%, respectively. Pearson’s correlation indicated that the correlation between PISA and mean PPD, as well as between PISA and mean CAL, was significant (p <0.001) with coefficients of 0.78 and 0.52, respectively. When comparing PISA values across severity levels, there were statistically significant (p <0.001) differences in PISA values among severity levels of periodontitis classified by CPITN and CDC/AAP. A dose-response relationship was also observed. Therefore, periodontal parameter represented by PISA had the significant association with conventional periodontal case definitions.