Abstract of the thesis submitted by Pinpinut Wanichsaithong for the Degree of Doctor of Philosophy entitled âDevelopment and use of an oral health literacy tool for older adultsâ, May 2019. Oral health literacy (OHL) is emerging as an important element in the prediction of the oral health status of individuals. The application of health literacy instruments has largely been targeted at younger adults and parents. While lower OHL has been associated with poor oral health, these associations are unproven in older adult populations. Therefore, this work aimed to develop an oral health literacy tool for older adults, and then use it to assess OHL in older adults and explore associations with oral health status and other factors. A mixed methods approach was utilised including; a literature review, the development of an OHL test, validation studies of the tool, a single cross-sectional study, a qualitative interview, and a protocol for a future study. Each method was used to establish a newly developed tool, explore associated factors, and develop a deeper understanding regarding OHL in older adults. A Test of Functional Health Literacy in Dentistry for Older Adults (OA-TOFHLiD) was developed in two languages (Thai and English) and validated in Thai and American populations. The tool presented good validity and reliability, and the cut-off scores were established in order to classify older adults into Adequate or Inadequate OHL. Further utilisation of the OA-TOFHLiD was explored to assess OHL and identify associations with oral health status. The results indicated that older adults with Adequate OHL had significantly better oral health statuses and less treatment need. In addition, OHL levels classified by OA-TOFHLiD scores presented acceptable sensitivity and specificity to predict oral health status, therefore, the researcher proposed a protocol to use this tool as a screening tool for dental care need in primary care settings with Thai community-living older adults, who were found to have a high prevalence of dental diseases but low dental service utilisation. These results suggest that the implementation of an OHL test as a screening tool at the community level is needed. Further investigation is also recommended regarding the possibility of using this tool as rapid non-professional screening of older adults for oral health needs.