Vocabulary – Development of a MWCNT-DAO Biosensor for Periodontal Disease

Periodontal Disease: Definition & Impact

Periodontal disease (PD) = bacterially-driven inflammatory destruction of the periodontium.
- Manifests as
- Re-occurring gingival inflammation.
- Gingival bleeding.
- Formation of periodontal pockets.
- Global prevalence: 20\text{–}50\% of adults → 6th most common human disease.
Untreated progression
- Detachment of collagen fibres from root cementum.
- Apical migration of junctional epithelium.
- Deepened pockets + resorption of alveolar bone.
- Final outcome: loss of periodontal ligament, bone destruction, ↑ tooth mobility → tooth loss.
Pain & invasiveness of conventional clinical probing emphasise need for rapid, non-invasive diagnostics.

Anatomy & Microenvironment of the Oral Cavity

Unique, complex gateway for digestive & respiratory tracts.
Juxtaposition of hard & soft tissues continually challenged by external pressures.
Hard tissues
- Teeth lined by gingiva / oral mucosa.
Soft tissues
- Cheeks, hard & soft palate, tongue.
Periodontium = collective tooth-supporting tissues
- Gingiva, root cementum, periodontal ligament, alveolar bone.
Structural diversity → extensive microbial colonisation.

Biofluids: Saliva & Gingival Crevicular Fluid (GCF)

Saliva

Secreted by 3 major glands (≈90\% of flow) + many minor glands (≈10\%).
Functions: protects oral tissues, lubricates mastication & speech.
Composition: electrolytes (Na(^+), bicarbonate, phosphate), immunoglobulins, proteins, mucins.
Continuous bathing shapes oral ecology.

GCF

Inflammatory exudate derived from periodontal tissues; located in sulcus between tooth & gingiva.
Normal flow: 0.43\text{–}1.56\ \text{mL\,h}^{-1}.
Immune stimulation / PD can raise flow to 44\ \text{mL\,h}^{-1}.
Roles: antimicrobial defence, maintain junctional epithelium.
Excess GCF supplies nutrients & niche → positive feedback for periodontal microbes.

Oral Microbiome & Dental Biofilm

Second-largest human microbial community; >700 species (bacteria, fungi, mycoplasma, protozoa).
Composed of
- Core microbiome (common to all).
- Variable microbiome (lifestyle/physiology dependent).
Surfaces for colonisation: hard (teeth) & soft (mucosa).
Initial colonisation → proliferation → biofilm (dental plaque).
Normal microbiota prevents exogenous pathogens; health depends on host–microbe equilibrium.

Periodontopathogens & Bacterial Complexes

Biofilm dysbiosis drives gingivitis → periodontitis.
Anaerobic species associated with PD
- Porphyromonas gingivalis, Tannerella forsythia, Treponema denticola.
Complex classification
- Red complex = most pathogenic, Gram-negative, late colonisers; initiate inflammation → connective tissue & bone loss.

Dysbiosis & Polymicrobial Synergy–Dysbiosis (PSD) Model

Dysbiosis = imbalance in microbiota, altered function/metabolism, shifted distribution.
PSD model: disease emerges from synergistic, metabolically compatible microbes that co-operate, elevate community virulence & disrupt tissue homeostasis.
Periodontal infection opens portal for
- Microbes, metabolites, antigens → systemic dissemination (e.g., Alzheimer’s, CKD).

Systemic Disease Links

Transient bacteraemia + microbial metabolites can provoke systemic inflammation & metastatic infections.
Strong epidemiological correlations: periodontitis with CKD, Alzheimer’s, certain cancers.

Biomarkers: Concepts & Utility

Biomarker = “biochemical, cellular or molecular alteration measurable in tissues, cells or fluids”.
Categories
- Exposure biomarkers (risk assessment).
- Disease biomarkers (screening, diagnosis, monitoring).
Ideal traits: measurable outside body, precise, reproducible, biofluid matrix non-interfering.
Widely used in Alzheimer’s, cancer, TB (to overcome slow, costly traditional diagnostics).

Saliva & GCF as Periodontal Biomarker Sources

Non-invasive, readily collectable.
Molecule transport via passive diffusion, active transport, ultrafiltration.
PD elevates salivary & GCF biomarker concentrations.
Biomolecule classes released by bacteria
- Enzymes, endotoxins, nucleic acids, proteins, carbohydrates, degradation products, immunoglobulins.

Polyamines in Periodontal & Renal Disease

General Bacterial Polyamines

Putrescine, cadaverine, spermidine, spermine.
Roles: metabolism, signalling, differentiation, motility, cell division.

Periodontal Disease

Shift from Gram-positive to Gram-negative microbiota → ↑ polyamine release.
Cadaverine & putrescine up-regulated in PD.
- Restricted oral hygiene raised mean cadaverine from 7.9\ \text{mM} → 11.8\ \text{mM}.
- Up to 10-fold increases align with higher plaque index.
Cadaverine features
- Colourless, foul-smelling liquid; associated with putrefaction.
- Absent from healthy blood; diffuses from biofilm → saliva → tongue biofilms / sulci.
- Pathogenic effects: inhibits leukocytes, reduces phagocytosis → bacterial proliferation.

Chronic Kidney Disease (CKD)

CKD prevalence: ≈10\% worldwide.
Defined by reduced GFR for ≥3 months; progressive nephron loss → renal failure.
Traditional biomarkers (serum creatinine, blood urea nitrogen, urine tests) have low sensitivity/specificity.
- Creatinine influenced by age, weight shifts, assay variability.
- Cystatin C also used but limitations persist.
Polyamines (e.g., putrescine) significantly elevated in chronic renal failure; implicated in anaemia via impaired cell maturation.

Interrelationship: PD ↔ CKD

Periodontitis-induced dysbiosis & transient bacteraemia allow microbial/metabolite translocation → kidney.
Inflammation & bacterial products may exacerbate CKD pathogenesis.
Shared polyamine biomarker profiles suggest dual-disease diagnostic opportunities.

Current Clinical PD Detection Methods

In-clinic periodontal probing, clinical attachment level measurement, bleeding on probing, plaque indices, radiographs.
Limitations: invasive, painful, time-consuming, offer only historical—not real-time—disease status.

Biosensor Objectives for Periodontal Diagnostics

Deliver rapid, high-impact, chair-side tests.
Must be affordable, reproducible, and improve patient outcomes.
Salivary/GCF polyamine sensing fits non-invasive paradigm.

MWCNT-DAO Biosensor Concept

Multi-walled carbon nanotube (MWCNT) electrode functionalised with diamine oxidase (DAO).
- DAO catalyses oxidative deamination of polyamines (e.g., cadaverine) → measurable electrochemical signal.
Targets cadaverine as PD biomarker; potential extension to CKD monitoring.
Design considerations
- Sensitivity within disease-relevant range (≈8\text{–}12\ \text{mM}).
- Selectivity over interfering salivary constituents.
- Minimal matrix effects from saliva or GCF.

Key Pathogen: Porphyromonas gingivalis

Red-complex keystone; most influential due to immune evasion.
Attributes
- Size 1\text{–}2\ \mu\text{m}, Gram-negative, black-pigmented, non-motile, obligate anaerobic coccobacillus.
- Rapid host adhesion → cellular internalisation.
- Produces damaging metabolites incl. cadaverine.

Clinical & Ethical Implications

Early, painless detection reduces disease burden, improves quality of life.
Screening high-risk groups (CKD, diabetics) via salivary biosensor could enable preventative care.
Data privacy & equitable access to low-cost diagnostics essential.

Numerical/Statistical Highlights (LaTeX-formatted)

Normal GCF: 0.43\text{–}1.56\ \text{mL\,h}^{-1}; diseased: 44\ \text{mL\,h}^{-1}.
Polyamine concentration shift: cadaverine 7.9\ \text{mM} \rightarrow 11.8\ \text{mM} after hygiene restriction.
Global PD prevalence: 20\text{–}50\% adults.
CKD global burden: \approx10\% population.
P. gingivalis dimensions: 1\text{–}2\ \mu\text{m}.
Cadaverine increase with high plaque index: up to 10-fold.

Summary Connections

Oral biofilm dysbiosis raises polyamines (notably cadaverine) detectable in saliva/GCF.
Same polyamines implicated in CKD; salivary levels could hint at systemic risk.
MWCNT-DAO biosensor aims to quantify cadaverine rapidly, non-invasively, supporting early intervention for PD and possibly CKD.