Early Caries and Enamel Changes

Enamel material

  • Made up of carbonated hydroxyapatite with a complex crystal structure that is readily dissolved in acid (95-96% by weight).
  • Many impurities and inclusions of other ions, substitution of phosphate ion with carbonate ion makes the enamel and dentine more soluble than pure hydroxyapatite and fluoroapatite
  • Protein layers, and/or lipids on surface of enamel can slow down loss of mineral ions through the enamel surface
  • Porous, presence of millions of enamel rods, surrounded by a matrix containing inorganic material, small amounts of protein, water and lipids.
  • Fundamental unit of enamel is an enamel rod, there are about 5-12 million rods per crown
  • Rods project outwards from the enamel-dentin junction (not really at a right angle). (university of Illinois at Chicago, 2009a).
  • Each enamel rod (about the width of a human hair): made up of millions of extremely fine crystals, composed primarily of phosphate and calcium.

Something interesting!
Tooth enamel holds clues to future aircraft design (Indo-Asian News Service, 2009)

  • Professor Chai said: ‘Teeth are made from an extremely sophisticated composite material which reacts in an extraordinary way under pressure.
  • ‘Teeth exhibit graded mechanical properties ..., and over time they develop a network of micro-cracks which help diffuse stress. ...The tooth's built-in ability to heal the micro-cracks over time, prevents it from fracturing into large pieces when we eat hard food, like nuts.'
  • If engineers can incorporate tooth enamel's wavy hierarchy, micro-cracking mechanism, and capacity to heal, lighter and stronger aircraft and space vehicles can be developed.
  • Tooth fractures ‘have a hard time deciding which way to go,' making the tooth more resistant to cracking apart. Harnessing this property could lead to a new generation of much stronger composites for planes.

The approximal white spot lesion

  • White spot lesion: areas of decalcified enamel on tooth on the occlusal surface and along the cervical margin which lead to the detoriation of the teeth

Early Caries and Enamel Changes - Cariology

fig1: white spot lesion indicated by arrows
(Featherstone JD, 2008)

Early Caries and Enamel Changes - Cariology
fig2: white spot lesion indicated by arrows
(Featherstone JD, 2008).
  • earliest clinical sign that dental caries is in progress in the enamel ·
  • due to small areas of subsurface demineralisation beneath the dental plaque and build up of dental plaque
  • wearing of orthodontic bands can cause white spot lesions
  • remineralisation can prevent caries from occurring at this stage

Early Caries and Enamel Changes - Cariology
fig 3: polarized light image (thin section) of an early enamel lesion
(Featherstone JD, 2008)

Early Caries and Enamel Changes - Cariology
fig 4 (a,d): microscopic imaging of enamel changes
(Chen SY, 2008)

Note the difference in structures in areas 1,2 and 3.
Area 1: hollow structures
Area 2: half filled structures
Area 3: fully filled structures

(Areas 1 and 2 are both due to demineralisation and thus show optical non-homogenity.)

Arrested Lesions

Early Caries and Enamel Changes - Cariology
fig 6: different zones on enamel
( Nurul Islam, 2009)
  • Show widening of dark zones, indicating reprecipation of minerals at the site of demineralization
  • Surface lesion may be hard and shiny, white spot becomes less obvious
  • Shape of lesion determined by distribution of biofilms and direction of enamel prisms

If lesion is on:
  1. approximal surface - (kidney-shaped between the contact facet and gingival margin)
  2. smooth surface- (conical, due to variations in dissolution along enamel prisms)
  3. within enamel- (along enamel prisms)
  4. central traverse- (most active portion of lesion)
When lesion is visible on:
  1. dry tooth surface incdicates lesion is on outer enamel
  2. wet tooth surface indicates lesion has penetrated most of the way through the enamel and maybe dentine

  • white tooth lesion looks white because of the difference in refractive indexes between enamel and water, makes lesion look opaque
  • worsening of white spot lesion leads to cavities (Featherstone JD, 2008).

Demineralisation leading to enamel loss (figures 7-10)

Graphic representation of a block of enamel showing the surface and sub-surface enamel morphological changes in various stages of demineralization leading to white spot formation and finally to cavitation. (University of Illinois at Chicago, 2009b )

Early Caries and Enamel Changes - Cariology
Fig 7. Intact block showing enamel surface and subsurface

Early Caries and Enamel Changes - Cariology
Fig 8. Start of demineralization creates spaces in the enamel called pore spaces which extend from the surface into the subsurface area. These are the initial signs of the white spot lesion creating the surface roughness and loss of shine.

Early Caries and Enamel Changes - Cariology
Fig 9. Demineralisation progresses.
Number of surface pores and pore size increases. As long as a relatively intact surface layer is present no bacterial invasion into the subsurface areas appears to occur, no cavities formed yet. Pore space increases and with remineralisation the pore space decreases.

Early Caries and Enamel Changes - Cariology
Fig 10. Enamel matrix has been lost resulting in the inward collapse of the remaining surface layer. At this stage restorative procedures are indicated. Caries are formed.

Demineralisation and demineralisation

Demineralisation: A tooth’s loss of materials, such as calcium and hydroxyapatite from the tooth matrix, caused by acidic exposure

Early Caries and Enamel Changes - Cariology
Early Caries and Enamel Changes - Cariology
fig 11: High resolution electron micrograph- calcium atoms(black), demineralised regions(white)
(Featherstone JD, 2008)

  1. Carbohydrate metabolism by bacteria produces organic acids that diffuse onto and into the enamel via intercrystalline spaces

  1. Calcium and phosphate in enamel rods and dentine crystals are dissolved (atomic level: high resolution electron micrograph shows white patches corresponding to calcium deficiency, pores in enamel, surface roughness and loss of shine)

  1. when the pores in the enamel enlarge, the white spot lesion will lose its ability to remineralise, giving rise to cavities

Zones seen before complete disintegration of enamel: ( Nurul Islam, 2009)

Early Caries and Enamel Changes - Cariology

fig 12: different zones superimposed on tooth structure
( Nurul Islam, 2009)

  1. Translucent Zone (TZ)
  • not always present, lies at advancing front of the lesion, slightly more porous than healthy enamel, loss of 1-2% minerals
  1. Dark Zone (DZ)
  • formed due to demineralisation (5-10% porosity)
  1. Body of Lesion
  • area of greatest demineralisation (25-50% porosity)
  1. Surface Zone (S)
  • relatively unaffected area due to greater degree of mineralisation and greater fluoride concentration present in the area (1-2% porosity)

Early Caries and Enamel Changes - Cariology
fig 13, 14: micrograph pictures showing demineralisation of tooth
( Nurul Islam, 2009)
Remineralisation: process of restoring minerals in the form of mineral ions to the lattice structure of the hydroxyapatite

  • Natural repair process by body for non-cavitated lesions
  • Saliva promotes remineralisation by providing saturated environment of calcium, phosphate, antibacterial components, restores pH levels

Process of Remineralisation

CO2 + H2O --> H2CO3 --> HCO3- + H+

Carbonate-bicarbonate buffer in saliva - acid produced by bacteria increases H+ concetration
  • equation shifts left, favouring production of carbon dioxide and water.

Remineralisation – Role of Fluoride Ions
  • Strongly adsorbed and high electronegativity protects against demineralisation by acid.

Early Caries and Enamel Changes - Cariology

fig 15: schematic enhancement of remineralisation by fluoride
(Featherstone JD, 2008)

  1. Fluoride ions attract calcium and phosphate ions (from saliva) which builds on existing affected crystal remnants
  2. Formation of fluoroapatite-like remineralised veener on repaired crystal surface
  3. Crystal surface less soluble than before, less susceptible to acid-attacks.

How to increase remineralisation:
  • 1. maintain oral hygiene
  • 2. maintain normal salivary flow
  • 3. have good lifestyle habits
  • 4. usage of supplementary fluoride products such as: mouthrinse, toothpaste, gels, varnishes, chewing gums, lozenges


  • Balance between processes of demineralisation and remineralisation determine progress of dental caries.
  • Illustrated by Stephan Curve
Early Caries and Enamel Changes - Cariology
Fig 16: The Stephen Curve
(Newcastle University, 2009a)

  • Fall in pH levels due to metabolisation of carbohydrates by plaque bacteria, which leads to demineralisation.
  • Rise in pH levels due to remineralisation of tooth, with salivary buffer coming into play.

Occlusal caries

  • Bacteria (mutans streptococci, lactobacilli species) live on teeth in microcolonies encapsulated to protect themselves against host defences, antimicrobial agents
  • Bacteria in contact with food particles in the mouth produces organic acids (lactic, acetic, formic, propanic), forms dental plaque
  • Local pH falls below critical value (pH 5.5)
  • Acid dissolves in all directions, through pores of enamel, dentine and underlying tissues.
  • Dissolves acid-soluble material in the tooth

  • After months, years = cavities/dental caries

Overview of plaque
  • A firmly adherent microbial biofilm attached to teeth
  • they can interact with other bacteria in cooperative manner to maximise their potential.

Major Areas of Plaque Accumulation (Newcastle University, 2009b)

  1. margin between tooth and gum
  2. fissures in occlusal surfaces of molars
  3. the approximal areas

Early Caries and Enamel Changes - Cariology
fig 17: different areas of plaque accumulation
(Newcastle University, 2009b)

Early Caries and Enamel Changes - Cariology
fig 18: sections of smooth surface caries and caries in a groove
( Nurul Islam, 2009)

  • Method of examination of caries on occlusal surfaces of enamel and dentin through use of dental probes highly controversial.
  • Grooves, pits, fissures on occlusal surfaces allow for food stagnation
  • Dental biofilm tends to form and accumulate notably on occlusal surfaces, due to protection against functional wear
  • Enamel in pits and fissures is very thin, therefore caries reaches dentin quickly leading to a greater rate of cavity formation than smooth surface caries


Chen SY, Hsu CY, Sun CK. (2008). Epi-third and second harmonic generation microscopic imaging of abnormal enamel. Opt Express. 2008 Jul 21;16(15):11670-9.

Featherstone JD (2008). Dental caries: a dynamic disease process. Aust Dent J;53(3):286-91

Indo-Asian News Service (2009). Tooth enamel can inspire lighter, stronger aircraft. Retrieved Oct 29, 2009 from http://www.thaindian.com/newsportal/sci-tech/tooth-enamel-can-inspire-lighter-stronger-aircraft_100235293.html

Newcastle University. (2009a). Stephen curves: the basics. Retrieved Oct 29, 2009 from http://www.ncl.ac.uk/dental/oralbiol/oralenv/tutorials/stephancurves1.htm

Newcastle University. (2009b). Why Plaque Forms at Specific Sites. Retrieved Oct 29, 2009 from http://www.ncl.ac.uk/dental/oralbiol/oralenv/tutorials/plaquesites.htm

Nurul Islam (2009). Histopathology of Dental Caries. Retrieved Oct 29, 2009 from http://www.kck.usm.my/ppsg/histology/Histopathology_of_dental_Dental_caries_1.ppt

University of Illinois at Chicago (2009 a). Biology of the human dentition II. Retrieved Oct 29, 2009 from http://www.uic.edu/classes/orla/orla312/BHDTwo.html

University of Illinois at Chicago (2009 b). White Spot Carious Lesions 2. Retrieved Oct 29, 2009 from http://www.uic.edu/classes/peri/peri343/WhiteSpt/whitspt2.htm

  • Links

    An Introduction | Tooth Anatomy and Histology | Dental Caries | Dental Caries - An Infectious Disease or a Chronic Disease |

    Early Caries and Enamel Changes | Caries Progression and Dentine Changes | Pulpo-dentinal Changes

    Root Surface Caries and Changes in the Cementum
    | Dental Fluorosis | Erosion of the Teeth | Conclusion

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