Nutrition, Biochemistry, and Oral Health

Core Review

Macronutrients and Oral Health

Carbohydrates

Carbohydrates are the most directly relevant macronutrient for dental caries. They are classified as:

Simple carbohydrates (sugars):

• Monosaccharides: Glucose, fructose, galactose
• Disaccharides: Sucrose (glucose + fructose), lactose (glucose + galactose), maltose (glucose + glucose)

Complex carbohydrates (polysaccharides):

• Starch (amylose + amylopectin — digestible)
• Dietary fiber (cellulose, hemicellulose — non-digestible)

Cariogenicity of carbohydrates:

• Sucrose is the MOST cariogenic sugar because it serves as a substrate for BOTH:
  1. Acid production (fermentation by oral bacteria → lactic acid)
  2. Extracellular polysaccharide (glucan) synthesis by glucosyltransferases (Gtfs) from S. mutans → water-insoluble glucans that form the plaque biofilm matrix
• Frequency of intake is more important than total quantity — each sugar exposure produces an acid challenge. Sipping a sugary beverage over hours is far more cariogenic than drinking it quickly.
• Physical form matters: Sticky/retentive carbohydrates (caramel, dried fruit, crackers) adhere to teeth and are slowly cleared → prolonged acid challenge
• Non-fermentable sugar alcohols (polyols): Xylitol, sorbitol, mannitol, erythritol. Cannot be fermented by oral bacteria to produce significant acid → NON-CARIOGENIC. Xylitol may have additional anti-caries effects (reduces S. mutans colonization and transmission).
• Non-nutritive sweeteners: Aspartame, saccharin, sucralose, stevia, acesulfame-K. Non-cariogenic.

The Stephan Curve and dietary counseling: After sugar consumption, plaque pH drops rapidly (within 2-5 minutes), reaches a minimum (pH 4.0-4.5) in 5-20 minutes, and recovers to resting pH over 30-120 minutes. Each drop below the critical pH (~5.5) contributes to net mineral loss. The key counseling message: LIMIT FREQUENCY of sugar intake — allow sufficient time between sugar exposures for salivary pH recovery and remineralization to occur.

Proteins

• Essential for tissue growth, maintenance, and repair
• Amino acids are the building blocks of collagen (periodontal ligament, gingival connective tissue, dentin matrix), keratin (oral epithelium), and salivary proteins
• Protein deficiency (protein-calorie malnutrition): Impaired wound healing, decreased salivary function, enamel hypoplasia (if during tooth development), increased susceptibility to infection, delayed tooth eruption

Lipids (Fats)

• Essential fatty acids (linoleic acid, alpha-linolenic acid) required for cell membrane integrity and eicosanoid (prostaglandin, leukotriene) synthesis
• Dietary fat is not directly cariogenic (bacteria do not ferment lipids to acid)
• Fat in a meal may have a protective effect: fatty foods stimulate salivary flow and may form a protective film on teeth; cheese consumption after a meal raises plaque pH
• Excessive dietary fat contributes to obesity and cardiovascular disease (indirect dental relevance)

Vitamins: Oral Manifestations of Deficiency

Vitamin C (Ascorbic Acid)

Function: Essential cofactor for prolyl hydroxylase and lysyl hydroxylase in collagen synthesis. Required for hydroxylation of proline and lysine residues in procollagen → stable collagen triple helix. Without vitamin C, collagen is under-hydroxylated, unstable, and rapidly degraded → defective connective tissue, blood vessels, bone, and dentin.

Deficiency (scurvy):

• ORAL MANIFESTATIONS (classic NBDHE material):
  • Gingivae: Swollen, boggy, spongy, hemorrhagic (bleed easily on probing or spontaneously)
  • Purplish-red color
  • Periodontal ligament: Defective collagen → tooth mobility, tooth loss
  • Delayed wound healing (collagen-dependent)
  • Increased susceptibility to infection (impaired neutrophil function)
• Systemic: Petechiae, ecchymoses, perifollicular hemorrhages, coiled (corkscrew) hairs, impaired wound healing, anemia

Risk factors: Poor diet (lack of fresh fruits/vegetables), alcoholism, elderly with poor nutrition, smoking (increases vitamin C turnover)

Dental note: The gingival changes of scurvy are due to a COLLAGEN DEFECT, not simple inflammation. Plaque removal is not curative; vitamin C replacement is required.

Vitamin D

Function: Regulates calcium and phosphate homeostasis → essential for bone and tooth mineralization. Promotes intestinal absorption of calcium and phosphate, renal reabsorption, and bone remodeling.

Deficiency:

• Childhood (rickets): Defective mineralization of bone and teeth. Enamel hypoplasia, delayed tooth eruption, increased caries susceptibility (defective enamel structure), malocclusion.
• Adulthood (osteomalacia): Bone pain, muscle weakness. Possible association with periodontitis (vitamin D has immunomodulatory and anti-inflammatory effects; deficiency may increase periodontal disease risk). Alveolar bone loss, tooth loss.
• Vitamin D sufficiency is important for implant osseointegration and periodontal health.

Vitamin A

Function: Essential for epithelial differentiation and integrity, immune function, vision, and tooth morphogenesis.

Deficiency: Impaired epithelial differentiation → keratinizing metaplasia of salivary glands (reduced salivary flow), enamel hypoplasia (ameloblasts are affected), increased susceptibility to infection. Rare in developed countries.

B-Complex Vitamins

Vitamin B1 (Thiamine): Deficiency (beriberi) — no specific oral manifestations, but may cause glossitis in severe cases.

Vitamin B2 (Riboflavin):

• Deficiency:
  • Angular cheilitis (inflammation/fissuring at corners of mouth)
  • Glossitis: Magenta-colored tongue (atrophic, smooth, purplish-red)
  • Cheilosis (dry, cracked lips)

Vitamin B3 (Niacin, Nicotinic Acid):

• Deficiency (pellagra — the "4 Ds"):
  • Dermatitis (photosensitive), Diarrhea, Dementia, Death (if untreated)
  • Oral manifestations: Glossitis (beefy-red, swollen, painful tongue), stomatitis, burning mouth

Vitamin B6 (Pyridoxine):

• Deficiency: Glossitis, angular cheilitis, peripheral neuropathy
• Drug interaction: Isoniazid (TB treatment) can cause B6 deficiency → peripheral neuropathy

Vitamin B9 (Folate/Folic Acid):

• Deficiency: Megaloblastic anemia, atrophic glossitis, angular cheilitis, aphthous-like ulcers
• Critical during pregnancy (neural tube defects — supplemental folic acid recommended)

Vitamin B12 (Cobalamin):

• Deficiency (pernicious anemia — autoimmune destruction of parietal cells → lack of intrinsic factor → B12 malabsorption):
  • Hunter glossitis (atrophic glossitis): Fiery-red, smooth, depapillated, painful tongue
  • Burning mouth, dysgeusia (altered taste)
  • Angular cheilitis
  • Neurological symptoms: Peripheral neuropathy, paresthesia, ataxia, cognitive changes
  • NBDHE high-yield association: Smooth, red, painful tongue + neurological symptoms → think B12 deficiency

Minerals and Oral Health

Iron

Deficiency (iron deficiency anemia):

• Plummer-Vinson syndrome (Paterson-Brown-Kelly syndrome): Classic triad —
  1. Iron deficiency anemia (microcytic, hypochromic)
  2. Dysphagia (upper esophageal web)
  3. Atrophic glossitis (smooth, painful tongue)
• Angular cheilitis
• Aphthous ulcers
• Burning mouth
• Increased risk of oral and esophageal squamous cell carcinoma
• Koilonychia (spoon-shaped nails)

Calcium and Phosphorus

• Hydroxyapatite: Ca₁₀(PO₄)₆(OH)₂ — the mineral component of enamel (96%), dentin (70%), cementum (50%), and bone (65%)
• Demineralization: Low pH → H⁺ ions protonate phosphate (PO₄³⁻ → HPO₄²⁻) and hydroxide (OH⁻ → H₂O) → hydroxyapatite dissolves → Ca²⁺ and PO₄³⁻ ions released into solution
• Remineralization: When pH returns to neutral and saliva provides Ca²⁺ and PO₄³⁻, mineral redeposits onto the tooth surface; fluoride enhances this dramatically by forming fluorapatite (Ca₁₀(PO₄)₆F₂) which is less soluble and has a lower critical pH (~4.5 vs. ~5.5)
• Saliva is supersaturated with respect to hydroxyapatite → promotes remineralization

Fluoride

Three mechanisms of caries prevention:

1. Promotes remineralization: Fluoride incorporates into the crystal lattice → forms fluorapatite → lower solubility, lower critical pH (~4.5)
2. Inhibits demineralization: Fluorapatite is more resistant to acid dissolution
3. Inhibits bacterial metabolism: Fluoride inhibits enolase in the glycolytic pathway → reduced acid production by bacteria (minor effect)

Salivary Buffering Systems

Saliva contains three major buffer systems to neutralize acids and maintain oral pH:

1. Bicarbonate (HCO₃⁻): THE PRIMARY salivary buffer.

• Concentration increases with salivary flow rate (stimulated saliva has higher HCO₃⁻)
• Reaction: H⁺ + HCO₃⁻ → H₂CO₃ → CO₂ + H₂O
• Key feature: CO₂ diffuses out of the mouth → drives equilibrium to the right → acid is effectively eliminated
• This is the most important buffer for neutralizing acid challenges after meals

2. Phosphate (HPO₄²⁻):

• Important at lower flow rates (unstimulated saliva — where HCO₃⁻ concentration is low)
• Reaction: H⁺ + HPO₄²⁻ → H₂PO₄⁻
• Less capacity than bicarbonate but important at rest

3. Proteins (histidine-rich proteins, sialin):

• Minor contribution to buffering
• Also serve other functions (antimicrobial, pellicle formation)

Demineralization and Remineralization: The Dynamic Balance

The caries process is a DYNAMIC equilibrium between mineral loss and gain at the tooth surface (NOT a linear, unidirectional process):

Demineralization:

• Cariogenic bacteria ferment dietary carbohydrates → organic acids (primarily lactic acid)
• When plaque pH falls below the CRITICAL pH (~5.5 for enamel, ~6.0-6.5 for dentin/cementum, ~4.5 for fluorapatite), the plaque fluid becomes UNDERSATURATED with respect to hydroxyapatite → mineral dissolves
• Net demineralization → white spot lesion (subsurface enamel porosity without cavitation)

Remineralization:

• Saliva neutralizes acid (bicarbonate buffer) → pH rises above critical pH
• Saliva supplies Ca²⁺, PO₄³⁻, and F⁻ → plaque fluid becomes SUPERSATURATED with respect to hydroxyapatite/fluorapatite → mineral redeposits
• Fluoride dramatically enhances this process
• Remineralization can arrest or REVERSE early (non-cavitated) lesions — but once the surface cavitates, remineralization alone is insufficient; restoration is needed

Variables affecting the balance:

• Frequency of fermentable carbohydrate intake (more attacks per day)
• Salivary flow rate and buffering capacity
• Fluoride exposure (water, toothpaste, varnish, rinses)
• Oral hygiene (biofilm disruption, removal of plaque reservoirs)
• Tooth anatomy (deep pits and fissures trap biofilm, limit salivary access)

Acid-Base Chemistry Relevant to Dental Materials

• pH = -log[H⁺]: The logarithmic scale — a change of 1 pH unit = 10-fold change in [H⁺]
• Acidic: pH < 7.0. Acidic beverages (soda pH 2.5-3.5, fruit juice pH 3.0-4.0) can cause dental EROSION (direct chemical dissolution of enamel, not bacterial)
• Neutral: pH ~7.0
• Alkaline: pH > 7.0
• Buffers: Solutions that resist pH change when acid or base is added (saliva is a biological buffer)

Erosion vs. Caries

Erosion: Direct chemical dissolution of enamel/dentin by acids NOT of bacterial origin. Sources: dietary (citrus, soda, sports drinks, wine), gastric (GERD, bulimia, morning sickness), environmental (swimming pool chlorine). Smooth, polished, cupped lesions. Typically affects facial and palatal surfaces. NO bacteria involved.

Caries: Acid dissolution caused by BACTERIAL fermentation of dietary carbohydrates. Subsurface demineralization (white spot), rough, chalky surface.

Attrition/Abrasion/Abfraction: Mechanical, not chemical, loss of tooth structure.

Clinical Application

The dental hygienist integrates nutrition and biochemistry knowledge in multiple ways:

1. Dietary counseling: Identify and reduce frequency of cariogenic carbohydrate intake
2. Caries risk assessment: Consider nutritional status, xerostomia (medications), and fluoride exposure
3. Erosion assessment: Distinguish erosion from caries; identify the acid source (dietary? gastric?)
4. Recognition of deficiency states: Glossitis, angular cheilitis, gingival changes → consider nutritional deficiencies and refer for medical evaluation
5. Fluoride therapy: Prescription fluoride toothpaste, varnish applications to promote remineralization
6. Remineralization strategies: Casein phosphopeptide-amorphous calcium phosphate (CPP-ACP, Recaldent), fluoride, xylitol

Common Traps

• Thinking the gingival changes of scurvy are simply gingivitis — they're a collagen synthesis defect, not just inflammation
• Forgetting that dentin/cementum demineralize at a HIGHER pH (~6.0-6.5) than enamel (~5.5) — root surfaces are more susceptible
• Confusing erosion (chemical, no bacteria, smooth surfaces) with caries (bacterial, subsurface, chalky)
• Thinking fluoride's main effect is systemic/pre-eruptive — the primary caries-preventive effect of fluoride is TOPICAL (post-eruptive)
• Overlooking nutritional deficiencies as a cause for glossitis, angular cheilitis, or aphthous ulcers in an otherwise healthy-appearing patient