Inclusion Criteria:  Subjects can communicate in Cantonese, Mandarin or English; Subjects who wear either or both removable partial dentures (RPDs); Subjects meet either one of the following criteria for extensive RPD: a. the corresponding arch has no posterior teeth (residual root will not be counted in) on one side or both sides; b. the corresponding arch has over half of the natural teeth missing (remaining teeth ≤ 8); Participants with both upper and lower dentures meeting the requirement of "extensive RPD" will be included in "both dentures group", and participants with either upper or lower denture eligible will be included in "single denture group".  Exclusion Criteria:  Individuals who are unable to communicate clearly or having dementia; Patients who are mostly bed-ridden, or suffering from infectious or life-threatening disease; Individuals who are currently using denture adhesive; Individuals who are allergic to denture adhesive; Individuals whose denture is implant-supported or contraindicated for application of denture adhesive.