When comparing the two groups between ACF vs ACS and ECF vs ECS, 18 common proteins with lower relative abundances in both caries-susceptible young adults and the elderly were identified, such as mucin-5B, histatin-1, BPI fold-containing family B member 1, protein S100-A9, protein S100-A8 and lipocalin-1, indicating their potential protective effects on dental caries. The gene discussed is S100A9; the disease is dental caries.