Demineralization and Remineralization in Dental Caries

Introduction

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, p. 701

1. Demineralization

Definition

Mechanism

1. Dental plaque contains cariogenic organisms, chiefly:
   • Streptococcus mutans
   • Lactobacilli
   • Actinomyces species
2. Following intake of fermentable carbohydrates, especially sucrose, plaque bacteria metabolize them to organic acids, mainly:
   • Lactic acid
   • Acetic acid
   • Formic acid
   • Propionic acid
3. The plaque pH falls rapidly. When pH falls below the critical pH, enamel begins to dissolve:
   • Enamel critical pH: approximately 5.5
   • Root surface/cementum critical pH: approximately 6.2-6.7
4. Hydrogen ions diffuse into enamel and dissolve hydroxyapatite crystals:

1. Calcium and phosphate diffuse out of enamel into plaque fluid and saliva.

Features of Demineralization

• It is initially subsurface, while the enamel surface may remain relatively intact.
• Repeated acid attacks produce increased porosity in enamel.
• Clinically, the earliest visible lesion is a white spot lesion, due to altered light reflection from porous enamel.
• Continued mineral loss causes enamel breakdown, cavitation, dentinal involvement, and eventually pulpal infection.

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, p. 701

Factors Promoting Demineralization

• Frequent sugar intake, particularly sucrose
• Sticky retentive foods
• Poor oral hygiene and mature plaque
• Reduced salivary flow or xerostomia
• Low salivary buffering capacity
• Deep pits and fissures, proximal contacts, faulty restorations
• Lack of fluoride exposure
• High counts of acidogenic and aciduric bacteria

2. Remineralization

Definition

Mechanism

1. Salivary flow increases and plaque acids are cleared.
2. Salivary bicarbonate, phosphate, and proteins buffer the acid.
3. Plaque pH rises above the critical pH.
4. Saliva, which is supersaturated with calcium and phosphate, supplies minerals to the porous enamel lesion.
5. Calcium and phosphate reprecipitate within enamel crystals.
6. In the presence of fluoride, fluoridated apatite forms, which is less soluble in acid.

Role of Saliva in Remineralization

• Diluting and clearing carbohydrates and acids
• Buffering plaque acids, mainly through bicarbonate
• Supplying calcium, phosphate, and fluoride
• Maintaining supersaturation of oral fluid with respect to enamel minerals
• Providing antimicrobial factors such as IgA, lysozyme, lactoferrin, and peroxidase

• Cummings Otolaryngology Head and Neck Surgery, section “Maintenance of Tooth Integrity”

3. Role of Fluoride

Actions of fluoride

1. Inhibits demineralization
   Fluoride adsorbed on enamel crystals reduces their dissolution during acid challenge.
2. Promotes remineralization
   It attracts calcium and phosphate ions into demineralized enamel.
3. Forms acid-resistant crystals
   Fluoride substitutes for hydroxyl ions in hydroxyapatite to form fluorapatite or fluorhydroxyapatite, which is less soluble in acid.
4. Antibacterial effect
   At higher concentrations, fluoride inhibits bacterial enzymes and reduces acid production by plaque bacteria.

• Histology: A Text and Atlas with Correlated Cell and Molecular Biology, p. 1469

Sources of fluoride

• Fluoridated toothpaste
• Fluoridated water
• Fluoride mouth rinses
• Professional topical fluoride varnish, gel, or foam
• Fluoride-releasing restorative materials such as glass ionomer cement

4. Demineralization-Remineralization Cycle

Frequent sugar intake
        ↓
Bacterial acid production in plaque
        ↓
Plaque pH falls below critical pH
        ↓
Loss of Ca2+ and PO43− from enamel
        ↓
DEMINERALIZATION
        ↓
White spot lesion → cavitation if repeated

Between meals:
Saliva + calcium + phosphate + fluoride
        ↓
Plaque pH rises
        ↓
REMINERALIZATION
        ↓
Repair and arrest of early non-cavitated lesion

5. Clinical Significance

• The white spot lesion is the earliest clinical manifestation of enamel demineralization.
• It is potentially reversible if the lesion is non-cavitated.
• Caries control should aim to shift the balance in favour of remineralization by:
  • Reducing frequency of sugar consumption
  • Plaque control
  • Regular use of fluoridated toothpaste
  • Increasing salivary flow where possible
  • Applying topical fluoride for high-risk individuals
  • Use of calcium-phosphate remineralizing agents when indicated
• Once cavitation occurs, natural remineralization is inadequate because the lesion retains plaque. Restorative treatment may then be required.

• Scott-Brown's Otorhinolaryngology Head & Neck Surgery, p. 701

Conclusion