Alzheimer’s disease (AD) is characterized by progressive cognition and behavior impairments. Diagnosing AD early is important for clinicians to slow down AD progression and preserve brain function. Biomarkers such as tau protein and amyloid-β peptide (Aβ) are used to aid diagnosis as clinical diagnosis often lags. Additionally, biomarkers can be used to monitor AD status and evaluate AD treatment. Clinicians detect these AD biomarkers in the brain using positron emission tomography/computed tomography or in the cerebrospinal fluid using a lumbar puncture. However, these methods are expensive and invasive. In contrast, saliva collection is simple, inexpensive, non-invasive, stress-free, and repeatable. Moreover, damage to the brain parenchyma can impact the oral cavity and some pathogenic molecules could travel back and forth from the brain to the mouth. This has prompted researchers to explore biomarkers in the saliva. Therefore, this study provides an overview of the main finding of salivary biomarkers for AD diagnosis. Based on these available studies, Aβ, tau, cholinesterase enzyme activity, lactoferrin, melatonin, cortisol, proteomics, metabolomics, exosomes, and the microbiome were changed in AD patients’ saliva when compared to controls. However, well-designed studies are essential to confirm the reliability and validity of these biomarkers in diagnosing and monitoring AD.

Background and Objective: People living with dementia typically have poor oral health. However, studies of caries status in this population have revealed different results. This systematic review aimed to assess caries status in old adults with dementia. Method: The PubMed, Web of Science, Embase, and Scopus databases were searched from inception to 13 February 2025. The Newcastle–Ottawa Scale (NOS) was used to assess the risk of bias in case–control studies, and the Joanna Briggs Institute (JBI) Critical Appraisal Checklist was used to assess the risk of bias in cross-sectional studies. Caries status was measured by the decayed, missing, filled teeth (DMFT) index, decayed, missing, filled surfaces (DMFS) index, or the component of DMFT/S. A random effects model was used to pool the included data. The weighted mean difference (WMD) and 95% confidence interval (CI) were calculated to analyze the effect of dementia on caries. Results: A total of 5363 studies were retrieved, and 20 studies were included in this study. Meta-analysis showed the DMFT index (WMD: 3.76, p < 0.0001; 13 studies), decayed teeth (DT) index (WMD: 0.40, p < 0.0001; 10 studies), and missing teeth (MT) index (WMD: 3.67, p = 0.04; 7 studies) values were higher in the dementia group than the control group. There were no differences in the filled teeth (FT) index (WMD: −0.66, p = 0.09; 9 studies) between the dementia group and the control group. Conclusions: Caries status was poorer in people with dementia than the controls. These findings suggest that medical staff and caregivers need to pay more attention to the oral health of dementia patients.