The CDC and American Academy of Periodontology (AAP) updated case definitions for periodontitis to include mild periodontitis, allowing for a more accurate assessment of overall prevalence. Previously, definitions for moderate and severe periodontitis were used, but they did not account for mild cases, leading to underestimation of total prevalence. The new definition for mild periodontitis includes ≥2 interproximal sites with AL ≥3 mm and ≥2 interproximal sites with PD ≥4 mm (not on the same tooth), or one site with PD ≥5 mm. This definition was developed through consensus to capture early cases of periodontitis before it progresses to moderate disease. In a study of 456 adults aged 35–82 years, the addition of mild periodontitis increased the total prevalence of periodontitis by approximately 31% compared to severe and moderate disease alone. The CDC–AAP definitions detected 29.4% of periodontitis cases, while the European definitions detected 46.5%, with higher sensitivity for incipient cases. However, the European definition had lower specificity, misclassifying more cases. Both definitions detected 4.8% of severe periodontitis cases with high agreement. The study highlights the importance of including mild periodontitis in surveillance to accurately assess the burden of the disease. The CDC–AAP and European definitions differ in their thresholds and sites used for measurement, affecting prevalence estimates. The European definition uses a lower threshold for incipient cases, capturing more cases but with potential misclassification. The CDC–AAP definition is more conservative, requiring additional consideration of PD measurements. The study concludes that total periodontitis should be based on the sum of mild, moderate, and severe cases. Further research is needed to validate these definitions across different populations. The findings suggest that while both definitions have limitations, they can complement each other in surveillance and research, particularly for severe periodontitis. The study also notes that the sample used was not representative of the general population, and third molars were excluded, which may affect prevalence estimates. Overall, the updated case definitions aim to improve the accuracy and consistency of periodontitis surveillance.The CDC and American Academy of Periodontology (AAP) updated case definitions for periodontitis to include mild periodontitis, allowing for a more accurate assessment of overall prevalence. Previously, definitions for moderate and severe periodontitis were used, but they did not account for mild cases, leading to underestimation of total prevalence. The new definition for mild periodontitis includes ≥2 interproximal sites with AL ≥3 mm and ≥2 interproximal sites with PD ≥4 mm (not on the same tooth), or one site with PD ≥5 mm. This definition was developed through consensus to capture early cases of periodontitis before it progresses to moderate disease. In a study of 456 adults aged 35–82 years, the addition of mild periodontitis increased the total prevalence of periodontitis by approximately 31% compared to severe and moderate disease alone. The CDC–AAP definitions detected 29.4% of periodontitis cases, while the European definitions detected 46.5%, with higher sensitivity for incipient cases. However, the European definition had lower specificity, misclassifying more cases. Both definitions detected 4.8% of severe periodontitis cases with high agreement. The study highlights the importance of including mild periodontitis in surveillance to accurately assess the burden of the disease. The CDC–AAP and European definitions differ in their thresholds and sites used for measurement, affecting prevalence estimates. The European definition uses a lower threshold for incipient cases, capturing more cases but with potential misclassification. The CDC–AAP definition is more conservative, requiring additional consideration of PD measurements. The study concludes that total periodontitis should be based on the sum of mild, moderate, and severe cases. Further research is needed to validate these definitions across different populations. The findings suggest that while both definitions have limitations, they can complement each other in surveillance and research, particularly for severe periodontitis. The study also notes that the sample used was not representative of the general population, and third molars were excluded, which may affect prevalence estimates. Overall, the updated case definitions aim to improve the accuracy and consistency of periodontitis surveillance.