Saliva biomarkers in oral disease

Supramolecular oral delivery technologies for polypeptide-based drugs

Oral supramolecular drug delivery systems (SDDSs) have shown promising potential, along with a rapid increase in the development of polypeptide-based drugs. Biofriendly, biocompatible, and multistimulation-responsive SDDSs achieve their unique deliverability via noncovalent bonds, which can encapsulate drugs and release them at the target site along the oral tract. In this review, we analyze the oral tract from an anatomical perspective and explain the potential physical, microenvironmental, and systematic barriers, as well as the properties of drug delivery. After understanding the specific environment at different oral sites, the application of SDDSs to the mouth, stomach, small intestine, and cell targeting is summarized. Finally, this review summarizes the application of SDDSs for the successful delivery of drugs and describes how to overcome the barriers of SDDSs in drug delivery using a more biofriendly approach.

Potential changes in microorganisms and metabolites associated with oral cancer: a preliminary study

BACKGROUND

Oral squamous cell carcinoma is a malignant tumor with high morbidity and mortality, and changes in microflora have a close relationship with tumor development. In this study, we tried to identify the changes in oral microbial characteristics and metabolite levels in OSCC patients.

METHODS

In this study, saliva samples were collected from 40 oral cancer cases and 39 healthy controls. The microbiome was analysed by 16 S rDNA gene sequencing, and the metabolome was detected by Liquid Chromatography-Mass Spectrometry (LC-MS) with metabolite traceability using the Metorigin platform. Correlations between the microbiome and metabolome were analysed using the Spearman correlation method.

RESULTS

The study found a significant difference in the β diversity of oral microbiota between the oral cancer group and healthy controls, while α diversity showed no significant difference. At the phylum level, Deferribacterota significantly increased, and Cyanobacteria significantly decreased in the oral cancer group. At the genus level, Vibrio and Lactococcus were significantly elevated, while Bifidobacterium and Faecalibacterium were significantly reduced. Metabolomic analysis identified 36 differentially abundant metabolites; 13(S)-HOTrE and 13-HODE were significantly downregulated, while docosanamide was significantly upregulated in the oral cancer group. Six bacteria-specific metabolites, including Indole, were also downregulated. Correlation analysis showed that N-Acetylneuraminic acid had a significant negative correlation with Pseudoalteromonas and Vibrio (r < -0.4).

CONCLUSION

This study found large differences in microbiome levels at the portal level, at the genus level, and significant differences in the levels of a variety of metabolites labeled by indoles, providing a new and potentially valuable direction for the diagnosis and treatment of oral squamous carcinoma.

Salivary Extracellular Vesicles in Detection of Cancers Other than Head and Neck: A Systematic Review

Cancer is one of the leading causes of death worldwide. Evidence indicates that extracellular vesicles are involved in cancer development and may be used as promising biomarkers in cancer detection. Concomitantly, saliva constitutes a non-invasive and inexpensive source of biomarkers. This systematic review investigates the use of salivary extracellular vesicles in detecting cancers located outside of the head and neck. PubMed, Web of Science, Scopus, and Embase were thoroughly searched from database inception to 16 July 2024. Data from sixteen eligible studies were analyzed, including glioblastoma, lung, esophageal, gastric, prostate, hepatocellular, breast, and pancreatobiliary tract cancers. The findings highlight strong diagnostic potential for lung and esophageal cancers, where specific exosomal RNAs and proteins demonstrated high accuracy in distinguishing cancer patients from healthy individuals. Additionally, biomarkers in glioblastoma showed prognostic value, while those in hepatocellular and pancreatobiliary cancers exhibited potential for early detection. However, gastric and prostate cancer biomarkers showed limited reliability, and breast cancer biomarkers require further validation. In conclusion, salivary extracellular vesicles present potential in non-invasive detection across multiple cancer types; however, their diagnostic power needs further research, including standardization and large-scale validation.

Salivary Lactoferrin Levels and Polymorphisms in Down Syndrome Individuals with Periodontitis

Background/Objectives: Lactoferrin, a protein involved in the immune response, plays a significant role in the etiopathogenesis of periodontitis in the general population. This cross-sectional study aims to determine the salivary concentration of lactoferrin in Down syndrome individuals with periodontitis. Methods: A convenience cohort of 76 Down syndrome individuals was established, including 34 with periodontitis, 29 with gingivitis, and 13 with healthy gums. Unstimulated saliva samples were collected and processed to quantify the lactoferrin concentration using the Human Lactoferrin ELISA kit, the total protein concentration (bicinchoninic acid assay [BCA]) using the BCA Protein Assay Kit (Pierce, Rockford, IL, USA), and the lactoferrin/BCA ratio. Additionally, the Lf rs1126478 (140A/G in exon 2, Lys/Arg) genotypes were determined via PCR with restriction fragment length polymorphism (RFLP) analysis using the Earl enzyme. Results: The lactoferrin levels were comparable across patients with periodontitis, gingivitis, and healthy gums (median = 8.20, 6.57, and 7.61 µg/mL, respectively). There were no differences in the BCA levels between the three groups (median = 2.21, 3.17, and 2.08 µg/µL, respectively) nor in the lactoferrin/BCA ratios. The distribution of the Lf 140A/G polymorphism did not show differences concerning periodontal health status. Conclusions: In Down syndrome individuals, salivary lactoferrin and BCA levels are not influenced by the periodontal health condition. Additionally, no significant genetic associations were found with the rs1126478 polymorphism in Down syndrome individuals with and without periodontitis. Lactoferrin production in Down syndrome may not be upregulated in response to periodontal pathogens, which could be indicative of an immune system dysregulation contributing to the early onset and severity of periodontitis in this population.

Deep Saliva Proteomics Elucidating the Pathogenesis of Early Childhood Caries and Identifying Biomarkers for Early Prediction

Early childhood caries (ECC) significantly impacts the physical and mental health of children. Saliva stands as a critical model for investigating the pathogenesis of caries disease since it reflects both host and microbial dynamics. However, the specific contributions of salivary host factors to ECC have not been fully understood. In this study, we monitored a prospective cohort of 3-4 year-old healthy children for 12 months, who either stayed caries-free or developed caries. Deep quantitative proteomics analysis of saliva was conducted at both recruitment and end point of the cohort to investigate the molecular mechanisms underlying ECC etiology and identify potential biomarkers for caries prediction. Proteomics analysis identified a total of 2873 proteins and revealed involvement of immune response, dental structure repair, and regeneration, as well as interactions with microorganisms during caries pathogenesis. Characteristic salivary proteins were identified in caries-susceptible children prior to caries development. An ECC prediction panel of proteins keratin 3 (KRT3) and mucin 21 (MUC21) was established and further validated through another independent cohort. This study illuminated the role of the complex salivary microenvironment in caries etiology and offered a prognostic tool for early ECC prediction, thus facilitating the precise prevention and control of ECC to ultimately reduce its incidence.

Diagnostic Accuracy of Novel Protein Biomarkers in Saliva to Detect Periodontitis Using Untargeted 'SWATH' Mass Spectrometry

AIM

To discover new salivary biomarkers to diagnose periodontitis and evaluate the impact of age and smoking on predictive capacity.

MATERIAL AND METHODS

Saliva samples were collected from 44 healthy periodontal individuals and 41 with periodontitis. Samples were analysed by sequential window acquisition of all theoretical mass spectra (SWATH-MS), and proteins were identified by employing the UniProt database. The diagnostic capacity of the molecules was determined with generalized additive models. The models obtained were single-protein unadjusted and adjusted for age and smoking status, besides two-protein combinations.

RESULTS

Eight single salivary proteins had a bias-corrected accuracy (bc-ACC) of 78.8%-86.8% (bc-sensitivity/bc-specificity of 62.5%-86.9%/60.9%-98.1%) to diagnose periodontitis. Predictive capacity increased more by adjusting for age (bc-ACC: 94.1%-98.2%; bc-sensitivity/bc-specificity: 90.2%-98.6%/93.6%-97.2%) than smoking (bc-ACC: 83.9%-90.4%; bc-sensitivity/bc-specificity: 73.6%-89.9%/76.2%-96.4%). These proteins were keratin, type II cytoskeletal 1, protein S100-A8, β-2-microglobulin, neutrophil defensin 1, lysozyme C, ubiquitin-60S ribosomal protein L40, isoform 2 of tropomyosin α-3 chain and resistin. Two dual combinations showed bc-sensitivity/bc-specificity of > 90%: β-2-microglobulin with profilin-1, and lysozyme C with zymogen granule protein 16 homologue B.

CONCLUSIONS

New salivary biomarkers show good or excellent ability to diagnose periodontitis. Age has a more significant influence on the accuracy of the single biomarkers than smoking, with results comparable to two-protein combinations.

Noninvasive Detection of Alpha-Amylase in Saliva Using Screen-Printed Carbon Electrodes: A Promising Biomarker for Clinical Oral Diagnostics

Background

Biomarkers are essential tools for diagnosing diseases. Saliva, as a human fluid, effectively reflects the body's condition due to its rich composition. Analyzing saliva components allows for noninvasive, cost-effective, and time-efficient screening and diagnosis. Alpha-amylase, a key biomarker present in saliva, has been linked to oral diseases. This study introduces an innovative method for the noninvasive detection of alpha-amylase using screen-printed electrodes (SPEs), enabling easy and efficient screening and diagnosis.

Methods

The proposed method involves measuring varying concentrations of alpha-amylase using Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV). Saliva samples are applied directly onto electrodes pre-coated with biomarkers and a conditioning agent, allowing for precise detection and analysis.

Results

The screen-printed carbon electrode demonstrated excellent performance in detecting alpha-amylase, with clear voltammogram results, achieving a limit of detection (LOD) of 104.252 units and a limit of quantification (LOQ) of 315.915 units.

Conclusion

A gold nanoparticle-modified screen-printed electrode (SPE) was developed to measure alpha-amylase quantitatively. Despite sensitivity to external interference, notably temperature, pH, and the duration of incubation, While the sensor showed sensitivity to external factors such as pH and temperature variations, it maintained a strong linear response, reinforcing its potential for reliable diagnostics with linear regression score (R² = 0.9513) across alpha-amylase concentrations of 100-500 units. This study underscores the sensor's effectiveness as a non-invasive tool for early detection using saliva as a biomarker, enhancing patient comfort and compliance. However, further research is needed for medical applications.

Evaluation of salivary melatonin and MMP-9 levels in periodontal diseases

OBJECTIVE

The aim of this study was to evaluate salivary matrix metalloproteinase-9 (MMP-9) and melatonin levels in individuals with periodontal health, gingivitis, and periodontitis.

DESIGN

A total of 170 participants were enrolled in this study. They included 57 periodontally healthy individuals, 58 gingivitis patients, and 55 periodontitis patients. Saliva samples were collected by passive drool technique. The levels of MMP-9 and melatonin in saliva were measured biochemically using the ELISA method.

RESULTS

Salivary MMP-9 levels in the periodontitis group were significantly higher than those in the gingivitis and periodontally healthy groups, while salivary melatonin levels were significantly lower (p<0.001). A positive correlation was observed between clinical periodontal parameters and salivary MMP-9 levels, while salivary melatonin levels were negatively correlated (p<0.001). A negative correlation was also observed between salivary MMP-9 levels and salivary melatonin levels (p<0.001).

CONCLUSION

This study shows that the level of melatonin in saliva is associated with periodontal disease and with the level of MMP-9 in saliva, which plays a role in this disease.

The Emergence of Saliva as a Diagnostic and Prognostic Tool for Viral Infections

Saliva has emerged as a promising diagnostic fluid for viral infections, enabling the direct analysis of viral genetic material and the detection of infection markers such as proteins, metabolites, microRNAs, and immunoglobulins. This comprehensive review aimed to explore the use of saliva as a diagnostic tool for viral infections, emphasizing its advantages and limitations. Saliva stands out due to its simplicity and safety in collection, along with the convenience of self-collection without the need for healthcare supervision, while potentially being comparable to urine and blood in terms of effectiveness. Herein, we highlighted the significant potential of saliva in assessing viral loads and diagnosing viral infections, such as herpesviruses, HPV, PyV, TTV, SARS-CoV-2, and MPXV. The detection of viral shedding in saliva underscores its utility in early diagnosis, the monitoring of infection progression, and evaluating treatment responses. The non-invasive nature of saliva collection makes it an appealing alternative to more invasive methods, promoting better patient compliance and facilitating large-scale screening and surveillance. As such, we further highlight current evidence on the use of saliva as a prognostic tool. Although a significant amount of data is already available, further investigations are warranted to more comprehensively assess the added benefit from the utilization of salivary biomarkers in the clinics. Salivary biomarkers show great promise for the early detection and prevention of viral infection complications, potentially improving disease management and control at the population level. Integrating these non-invasive tools into routine clinical practice could enhance personalized healthcare strategies and patient outcomes. Future studies should focus on establishing standardization protocols, validating the accuracy of salivary diagnostics, and expanding clinical research to enhance the diagnostic and monitoring capabilities of salivary biomarkers.

Oral and Gingival Crevicular Fluid Biomarkers for Jawbone Turnover Diseases: A Scoping Review

Gingival crevicular fluid (GCF) and oral fluid have emerged as promising diagnostic tools for detecting biomarkers. This review aimed to evaluate the existing literature on using oral fluids as a source of biomarkers for bone turnover diseases affecting the jawbone. A comprehensive search strategy was executed between August 2014 and August 2024 across five major databases (Web of Science, EBSCOhost Dentistry & Oral Sciences Source, Cochrane Library, Scopus, and PubMed) and grey literature sources. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) was applied. The screening was facilitated using Rayyan at rayyan.ai and Endnote X20 software tools, culminating in the evaluation of 14,965 citations from databases and 34 from grey literature. Following rigorous scrutiny, 37 articles were selected for inclusion in this review, encompassing diseases such as periodontitis, medication-related osteonecrosis of the jaw (MRONJ), and osteoporosis. The quality of the included observational studies was assessed using the Revised Risk of Bias Assessment Tool for Non-Randomized Studies (RoBANS 2). Interleukin-1 beta (IL-1β), sclerostin, osteoprotegerin (OPG), and interleukin-34 (IL-34) emerged as significant biomarkers in GCF, and they were mainly from periodontitis and osteoporosis. Osteocalcin (OC), IL-1β, tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), OPG, and matrix metalloproteinase-9 (MMP-9) were significant in oral fluid or saliva, and they were from periodontitis, MRONJ, and osteoporosis. These findings underscore the potential use of oral fluids, which are regarded as non-invasive tools for biomarker identification in bone turnover. Many biomarkers overlap, and it is important to identify other specific biomarkers to enable accurate diagnosis of these conditions.

A review: early detection of oral cancer biomarkers using microfluidic colorimetric point-of-care devices

Oral squamous cell carcinoma (OSCC) is the most common type of head and neck cancers. OSCC constitutes 90% of the head and neck malignancies. The delayed identification of oral cancer is the primary cause of ineffective medical treatment. To address this issue, low-cost, reliable point-of-care devices that can be utilized for large-scale screening, even in low-resource settings, including rural areas and primary healthcare centers, are of great interest. Herein, a comprehensive analysis of numerous salivary biomarkers that exhibit significant variations in concentration between individuals with oral cancer and those without is given. Furthermore, the article explores several point-of-care devices that exhibit potential in the realm of oral cancer detection. The biomarkers are discussed with a focus on their structural characteristics and role in oral cancer progression. The devices based on colorimetry and microfluidics are discussed in detail, considering their compliance with the 'REASSURED' criteria given by the World Health Organization (WHO) and suitability for mass screening in low-resource settings. Finally, the discourse revolves around the fundamental aspects pertaining to the advancement of multiplex, cost-effective point-of-care devices designed for widespread screening purposes.

Salivary 8-hydroxy-2'-deoxyguanosine levels in patients with oral cancer: a systematic review and meta-analysis

BACKGROUND

DNA is an important target for oxidative attack and its modification may increase the risk of mutagenesis. The aim of this study was to evaluate and compare salivary levels of the oxidative stress biomarker 8-hydroxy-2'-deoxyguanosine (8-OHdG) in patients with oral cancer (OC) compared to the control group by a comprehensive search of the available literature.

METHODS

The present systematic review and meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines and was registered in Open Science Framework (OSF): https://doi.org/10.17605/OSF.IO/X3YMR. Four electronic databases were used to identify studies for this systematic review: PubMed, Scopus, ScienceDirect, and Web of Science from January 15, 2005, to April 15, 2021. The Joanna Briggs Institute (JBI) tool was used to assess article quality.

RESULTS

Of the 166 articles identified, 130 articles were excluded on the basis of title and abstract screening (duplicates, reviews, etc.). Thirty-six articles were evaluated at full text and 7 articles met the inclusion criteria. Of these, only 5 studies had compatible data for quantitative analysis. An increase in salivary 8-OHdG levels was found in patients with OC compared to healthy subjects, but without statistical significance. 8-OHdG: SMD = 2,72 (95%CI= -0.25-5.70); *p = 0.07.

CONCLUSIONS

This systematic review and meta-analysis suggests a clear trend of increased 8-OHdG levels in saliva of OC patients compared to the control group. However, further studies are required to clarify and understand the altered levels of this oxidative stress marker.

Relationship between oral hypofunction and salivary biomarkers in older adults: a cross-sectional study

BACKGROUND

Oral health problems have increased among older adults. Oral hypofunction is characterized by seven signs and symptoms: oral uncleanness, oral dryness, decline in occlusal force, decline in the movement function of the tongue and lips, decline in tongue pressure, decline in masticatory function, and decline in swallowing function, the latter being a significant risk factors for oral frailty. Recent research has suggested that salivary biomarkers can be used to assess not only oral diseases, including dental caries and periodontitis, but also systemic diseases, such as cancer and diabetes mellitus. This cross-sectional study investigated the relationship between oral hypofunction and the levels of salivary biomarkers.

METHODS

In total, 116 patients, aged 65 years or older, were included in this cross-sectional study. If three or more signs or symptoms in seven kinds of tests met the criteria of each test, oral hypofunction was diagnosed. The levels of biomarkers in the saliva collected from the patients were analyzed using an enzyme-linked immunosorbent assay.

RESULTS

In total, 63.8% of patients were diagnosed with oral hypofunction. Multivariable linear regression analysis showed that calprotectin levels in the saliva were significantly related to oral moisture and masticatory function. Furthermore, 8-OHdG levels in saliva were associated with the movement function of the tongue and lips and oral hygiene level, and salivary AGE correlated only with the movement function of the tongue and lips. Multiple logistic regression analysis revealed that calprotectin levels in the saliva were significantly correlated with the prevalence of oral hypofunction, even after adjusting for age, sex, and periodontal status. However, none of the biomarker levels in the saliva had a significant relationship with the number of examinations outside the reference range.

CONCLUSIONS

Calprotectin, 8-OHdG, and AGE levels are associated with oral hypofunction in older adults.

A Roadmap for the Rational Use of Biomarkers in Oral Disease Screening

Oral health has witnessed a significant transformation with the integration of biomarkers in early-diagnostic processes. This article briefly reviews the types of biomarkers used in the screening and early detection of oral diseases, particularly oral cancer, periodontal diseases, and dental caries, with an emphasis on molecular biomarkers. While the advent of these biomarkers may represent a leap forward in oral healthcare, it also opens the door to potential overtesting, overdiagnosis, and overtreatment. To inform the selection of novel biomarkers and ensure their rational use in screening tests, it is imperative to consider some key characteristics, which are specific to the biomarker (e.g., surrogate biomarkers should reliably reflect the primary health outcome), to the test (e.g., sensitivity and specificity must be balanced based on the disease of interest), and to the disease (e.g., the efficacy of treatment should improve when the condition is diagnosed earlier). For systemic conditions associated with oral diseases, researchers should be extremely cautious when determining who is "at risk", particularly when such risk is small, non-existent, or inconsequent. This framework aims to ensure that advancements in oral health diagnostics translate into genuine improvements in patient care and well-being.

Realizing the clinical utility of saliva for monitoring oral diseases

In the era of personalized/precision health care, additional effort is being expended to understand the biology and molecular mechanisms of disease processes. How these mechanisms are affected by individual genetics, environmental exposures, and behavioral choices will encompass an expanding role in the future of optimally preventing and treating diseases. Considering saliva as an important biological fluid for analysis to inform oral disease detection/description continues to expand. This review provides an overview of saliva as a diagnostic fluid and the features of various biomarkers that have been reported. We emphasize the use of salivary biomarkers in periodontitis and transport the reader through extant literature, gaps in knowledge, and a structured approach toward validating and determine the utility of biomarkers in periodontitis. A summation of the findings support the likelihood that a panel of biomarkers including both host molecules and specific microorganisms will be required to most effectively identify risk for early transition to disease, ongoing disease activity, progression, and likelihood of response to standard periodontal therapy. The goals would be to develop predictive algorithms that serve as adjunctive diagnostic tools which provide the clinician and patient important information for making informed clinical decisions.

New frontiers in salivary extracellular vesicles: transforming diagnostics, monitoring, and therapeutics in oral and systemic diseases

Salivary extracellular vesicles (EVs) have emerged as key tools for non-invasive diagnostics, playing a crucial role in the early detection and monitoring of diseases. These EVs surpass whole saliva in biomarker detection due to their enhanced stability, which minimizes contamination and enzymatic degradation. The review comprehensively discusses methods for isolating, enriching, quantifying, and characterizing salivary EVs. It highlights their importance as biomarkers in oral diseases like periodontitis and oral cancer, and underscores their potential in monitoring systemic conditions. Furthermore, the review explores the therapeutic possibilities of salivary EVs, particularly in personalized medicine through engineered EVs for targeted drug delivery. The discussion also covers the current challenges and future prospects in the field, emphasizing the potential of salivary EVs in advancing clinical practice and disease management.

MicroRNA expression as a prognostic biomarker of tongue squamous cell carcinoma (TSCC): a systematic review and meta-analysis

BACKGROUND

Recent studies have indicated that microRNA (miRNA) expression in tumour tissues has prognostic significance in Tongue squamous cell carcinoma (TSCC) patients. This study explored the possible prognostic value of miRNAs for TSCC based on published research.

METHODS

A comprehensive literature search of multiple databases was conducted according to predefined eligibility criteria. Data were extracted from the included studies by two researchers, and HR results were determined based on Kaplan‒Meier curves according to the Tierney method. The Newcastle‒Ottawa Scale (NOS) and GRADE (Grading of Recommendations Assessment, Development, and Evaluation) pro-GDT were applied to assess the quality of all studies. Publication bias was estimated by funnel plot, Egger's rank correlation test and sensitivity analysis.

RESULTS

Eleven studies (891patients) were included, of which 6 reported up-regulated miRNAs and 7 mentioned down-regulated miRNAs. The pooled hazard ratio (HR) from the prognostic indicator overall survival (OS) was 1.34 (1.25-1.44), p < 0.00001, indicating a significant difference in miRNA expression between TSCC patients with better or worse prognosis.

CONCLUSION

MiRNAs may have high prognostic value and could be used as prognostic biomarkers of TSCC.

Variability of salivary analytes under daily conditions and their implications for periodontitis biomarkers

Introduction

Recent studies have identified inflammatory mediators as potential biomarkers for monitoring or diagnosing periodontitis. However, the brief half-life of these mediators, coupled with their variability among different individuals and across different stages of periodontal disease, may limit their reliability as biomarkers.

Methods

In this study, we assessed the concentration profile of salivary biomarkers (IL-6, IL-8, and total protein) through repeated measurements within the same day and across different days in 79 patients exhibiting various states of periodontal health: intact periodontium, stable periodontitis, and active periodontitis. Additionally, we explored how daily variations, such as the interval between toothbrushing and eating, impact the levels of these salivary biomarkers and their diagnostic efficacy for periodontitis activity.

Results

Our results showed high salivary levels of IL-6 and total proteins in periodontitis patients (p < 0.001), with detection ability reflected by an Area Under the Receiver Operating Characteristic Curve (AUC-ROC) ranging between 0.709 and 0.852. Conversely, IL-8 levels were higher in patients with intact periodontium (p < 0.001), with an AUC-ROC for periodontitis detection between 0.671 and 0.815. Daily activities such as toothbrushing and eating influenced the levels of specific analytes, particularly total proteins (p < 0.001), but this did not affect their ability to detect periodontal disease activity. The highest measurement agreement, assessed by Intraclass Correlation Coefficients (ICC), was found for IL-6, with no significant differences in agreement between same-day and different-day measurements.

Conclusions

Our study demonstrated consistency in the repeated measurements of salivary analytes, both within the same day and across different days, except for salivary total protein levels. These analytes exhibited variability within a range that did not undermine their effectiveness as biomarkers for periodontal disease.