背景：目前已有許多研究探討口腔衛生與失智症之間的關聯，而口腔衛生可以有效地透過牙齒喪失程度進行判斷，亦有文獻指出牙齒喪失是認知功能下降的危險因子，不過配戴義齒是否能減緩恆齒喪失帶來的認知功能受損之不利影響這類研究相對較少；然而，口腔衛生與失智症可能存在著雙向關係，因此，確定兩者的時序性將有助於相關性分析結果的正確解釋。目前台灣相關文獻多關注於牙周病與失智症的關聯，對於牙齒喪失或義齒配戴與失智症風險的影響之獨立與交互作用證據較為有限。另外，也尚未有研究針對缺少牙齒的長者是否可以透過配戴足量義齒而降低失智症風險的問題進行探討。
目的：本研究目的包含：（一）探討台灣65歲以上長者牙齒喪失與失智症發生風險之相關性，以及牙齒喪失與配戴義齒之間是否具有交互作用；（二）探討台灣65歲以上牙齒喪失長者中，是否可以透過配戴義齒增加總牙齒數而降低失智症之發生風險。
方法：本研究採用回溯性世代追蹤研究，並以2009年國民健康訪問暨藥物濫用調查及2008-2017年全民健康保險申報資料作為資料來源。研究世代是透過選取於2009年國民健康訪問暨藥物濫用調查，樣本為65歲以上且在2008-2009年間無失智症就醫紀錄，且有完整恆齒與義齒數目者（n=2,247），並追蹤後續失智症發生事件至2017年。參考日本牙科協會提出厚生省核定的8020標準，本研究以20顆牙齒作為分界點，以下列兩種暴露分組方法來進行前述兩個研究目的的探討：（1）恆齒數≥20顆且有配戴義齒（參考組）、恆齒數≥20顆但沒有配戴義齒、恆齒數<20顆但有配戴義齒、恆齒數<20顆且沒有配戴義齒；以及（2）恆齒數≥20顆，無論是否有配戴義齒（參考組）、恆齒數<20顆但總牙齒數（指恆齒與義齒數量的總和）≥20顆、與總牙齒數<20顆。本研究透過繪製有向無環圖選取潛在干擾因子後，利用Cox比例風險模型並考量競爭死因，計算危害對比值進行以上的分析。
結果：（一）在迴歸模式納入年齡、性別、教育程度、婚姻狀況、吸菸習慣、飲酒習慣、糖尿病史、牙周病、恆齒數是否≥20顆、以及義齒配戴後發現，恆齒數<20顆組發生失智症之校正危害比為恆齒數≥20顆組的1.299倍（95% CI=0.986-1.710）；未戴義齒組之校正危害比為有戴義齒組的1.199倍（95% CI=0.945-1.521）。（二）以恆齒數≥20顆且有戴義齒組為對照組，恆齒數≥20顆但未戴義齒組、恆齒數<20顆但有戴義齒組、以及恆齒數<20顆但有戴義齒組樣本的校正危害比分別為1.234倍（95% CI=0.814-1.870）、1.324倍（95% CI=0.923-1.900）、及1.569倍（95% CI=1.038-2.370）。（三）以恆齒數≥20顆之樣本為對照組，恆齒數<20顆但總牙齒數≥20顆、以及總牙齒數<20顆之樣本其校正危害比分別為1.226倍（95% CI=0.923-1.627）與1.279倍（95% CI=0.926-1.766）。進一步的分層分析發現，年齡與總牙齒數具統計顯著之交互作用（P for interaction=0.0049），配戴義齒以降低失智風險的效果於65-74歲長者中最為明顯。
結論：本研究發現在台灣65歲以上長者中，牙齒喪失（<20顆）與未戴義齒都可能會些許增加失智的風險，兩者對失智症發生風險也具有些許的交互作用效果，但未達統計顯著意義。另外，本研究發現配戴足量義齒者傾向有較低的失智症風險。進一步分層分析顯示：透過配戴義齒以維持足夠的總牙齒數可以降低失智症風險的現象只出現在65-74歲年輕長者、女性以及未吸菸者中。

Most previous studies in Taiwan focused on the correlation between periodontal disease and dementia. Limited information available regarding the associations of dementia with both tooth loss and denture use. This study had two aims: Firstly, to investigate whether tooth loss and denture usage showed independent and interactive effects on dementia incidence. Secondly, determine if older people with tooth loss can reduce dementia risk by wearing sufficient denture teeth. This is a retrospective cohort study involving 2,247 adults aged over 65 years, using data from the 2009 National Health Interview Survey (NHIS) and National Health Insurance (NHI) claims. Participants were categorized into groups based on their baseline number of natural teeth and denture use, and followed until the end of 2017, death or dementia diagnosed which were identified from the NHI claims. Cox proportional hazard models were used to calculate hazard ratios (HR) for dementia risk in different exposure groups. The findings indicated that with <20 remaining natural teeth and without denture teeth was associated with significantly increased covariate adjusted HR of dementia. Additionally, waering enough denture teeth tended to compromise the risk of dementia among older adults with <20 remaining natural teeth, which was especially evident in those aged 65-74, females, and non-smokers.

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