Objectives: The present study was undertaken to clarify the nature of sampling results with dental questionnaires between random sampling of subjects and of patients of dental clinics in the same city.
Methods: The first group comprised 900 subjects selected using the stratified random sampling based on different age groups. The sampling rate was set at 6.46% of the population database and the approach was a mail survey with random sampling. The second group comprised 240 subjects who were patients of 12 dental clinics. The questionnaire had a list of questions about oral health conditions, daily oral habits, daily activities and common eating habits.
Results: The response rates with the mailing method in the first group were 41.0% for male and 49.0% for female residents. The percentages who answered "Yes" to the questions, "Do you have gum swelling?" and "Have you ever received any instructions on tooth brushing from a professional?", were significantly (P < 0.05) lower than for patients from dental clinics.
Conclusions: Dental patients had poor oral health habits and more oral diseases than residents, who visited dentists less frequently. It can be concluded that patients from dental clinics are inappropriate to use as samples to set a baseline for the general population in research evaluation of oral health.