microbiology of dental caries

Dr. Ali Yaldrum SEGi UC, KD

Dental Caries Microbiology

Learning Outcomes

At the end of this session students should be !   Describe rela4onship between plaque and oral diseases !   Describe role of plaque in development of caries !   Define Dental Caries !   Describe the ae4ology and the role different factors play in ini4a4on and progression of the disease

!   Describe the role played by different microorganisms

Plaque bacteria to Caries

Relationship of

Plaque & Caries

Historically for any microbe to be considered responsible for a given condi4on, Koch’s postulate was applied

Koch’s Postulate

1.  The microbes should be found in all cases of the disease with a distribu4on corresponding to the observed lesions

2.  The microbes should be grown on laboratory media for several subcultures

3.  A pure subculture should produce the disease in the suscep4ble animal

4.  A high an4body 4ter to the microbe should be detected during infec4on; this may provide protec4on on subsequent reinfec4on

Koch’s Postulate

1.  A microbe should be present in sufficient numbers to ini4ate disease

2.  The microbe should generate high levels of specific an4bodies 3.  The microbe should produce relevant virulence factors 4.  The microbes should cause disease in an appropriate animal

model 5.  Elimina4on of the microbe should result in clinical improvement

Role of Plaque

!  The ‘Specific Plaque Hypothesis’ (fig.1) !  The ‘Non-‐Specific Plaque Hypothesis’ (fig.2) !  The ‘Ecological Plaque Hypothesis’ (fig.3)

Specific Plaque Hypothesis

Plaque

Disease

( ) X problem disease can stil l occur in absence of these organisms

few species out of diverse resident flora are actively involved in disease {

fig.1

Non-Specific Plaque Hypothesis

Plaque

Disease

( ) problem plaque mediated diseases are polymicrobial but one specif ic organism predominate

out come of the overall activity of the total plaque microflora {

fig.2

Ecological Plaque Hypothesis

Plaque

Disease ( ) disease only initiates as a result of shift in the balance of resident microf lora

organisms associated with disease are already present on teeth but very low to detect {

fig.3

Dental Caries

Dental Caries

!   It is bacterial disease of calcified 4ssue of the teeth characterized

by demineraliza4on of the inorganic and destruc4on of the organic substance of the tooth.

‘Dental Caries is known as disease of civilization’

The Early theories

!   The legend of Worms !   Endogenous Theory !   Chemical Theory !   Parasitic Theory !  Chemoparasitic Theory

Dental Caries

!   Chemoparasitic theory Miller in 1890 suggested that oral bacteria converted dietary carbohydrates into acid which solubilized the calcium phosphate of enamel to produce a caries lesion

Dental Caries

Aetiology of Dental Caries

Saliva

Saliva

Saliva

Saliva Time P laque Bacteria

Susceptible Surface

Sugar

Caries

aetiology of caries fig.4

Role of Saliva

Saliva plays a vital role in the maintenance of oral health and the integrity of oral 4ssues Saliva contains:

• exfoliated epithelial cells • oral microorganisms • food residues (carbohydrates) • an4microbial factors • minerals

Role of Saliva

!  Mechanical washing ac4on of saliva is very effec4ve for cleaning of teeth

!  high buffering capacity neutralizes acid !   supersaturated with Calcium and phosphorus helps in remineraliza4on

Salivary flow rate: 0.8 mm /min on upper labial surface

5.0 -‐ 8.0 mm/min on lower lingual surface

Role of Saliva

Susceptible Surface

Susceptible Surface

Some areas of the tooth are more suscep4ble to developing caries

than others, known as ‘susceptible areas’ Suscep4bility is related to several factors !  Mineral & Fluoride Content !  Structure of that par4cular area

Susceptible Surface

Susceptible tooth surfaces includes !  Pits & Fissures (fig.5) !  Approximal Enamel cervical to contact point (fig.6) !  Exposed root surface (fig.7 & 8) !  Margins of Restora4on (fig.6 & 9) !  Cervical margins of tooth (fig.10)

pits & fissures caries

fig.5

Approximal Caries Caries under restoration

fig.6

Root surface Caries

fig.7

fig.8

Root Surface Caries

Caries under restoration Amalgam restoration

fig.9

white spot lesions

fig.9

white spot lesion Cavitation

From white spot to cavity formation

earliest clinical evidence (reversible) Later clinical stage (irreversible)

Sugar Substrate Time &

!  Direct rela4onship between intake of Carbohydrates (sugar) & Caries

!  Glucose, Fructose & Sucrose are cariogenic ! Sucrose is the most cariogenic sugar

•  fermentable • easily penetrates plaque

Sugar Substrate

There is a direct rela4onship between caries and: !  Frequency of sucrose consump4on !  s4ckiness of the sucrose

Both affects the amount of 4me sugar stays into contact with the teeth surface

Time & Sugar Substrate

Plaque Bacteria

Dental Caries does not occur in vivo if microorganisms in the form of dental plaque are absent; making it clear that dental caries is a plaque mediated disease

Plaque Bacteria

‘ ‘

!  Streptococcus mutans !   Lactobacillus species !  Ac4nomyces Species !  Veillonella species

Plaque Bacteria

The term mutans streptococci refers to a group of 7 different species, but two species are most commonly found in humans !  S. mutans (serotypes c/e/f) !  S. sobrinus (serotypes d/g)

Streptococcus species

Factors related to Cariogenicity of S. mutans ! S.mutans counts in saliva and at site of lesion !   Isolated from site before the development of caries !  Efficient sugar metabolism & transport capability ! Acidogenic & acidouric !   Liele effect of pH on growth and metabolism !  Produc4on of EPS & IPS


S. mutans been implicated in !  Pits & fissure caries (strong evidence) !  Root surface caries !  All forms of caries !  Some strains are more pathogenic than others


!  S. Sobrinus role is uncertain !  Frequently isolated from plaque but in lesser numbers !  Shares the same cariogenic proper4es as S.mutans


Lactobacilli can be divided into two groups !  Homofermenta4ve species !  Heterofermenta4ve species

Lactobacillus species

Homofermentative species !   L. acidophilus & L. casei !  Mainly produce lac4c acid from glucose fermenta4on

Heterofermentative species !   L. fermentum !  Produce lac4c acid and significant amounts of acetate


Most commonly isolated species from oral cavity are !   L. casei !   L. fermentum !   L. acidophilus


Factors related to Cariogenicity of Lactobacillus species !   Increased number in carious cavi4es affec4ng enamel & root surface

!  Number in saliva reflect caries ac4vity ! Acidogenic and acidouric !  Few strains can produce EPS


!  Have a low affinity for tooth surface !   Low in numbers at healthy site !   Implicated in progression of caries deeper into den4ne rather than ini4a4on

!   Implicated in ae4ology of root surface caries


Ac8nomyces spp. form a major and complex part of the oral microflora, par4cularly at the approximal site and gingival crevice

Actinomyces species

! Ac8nomyces odontoly8cus been associated with very early stages of tooth demineraliza4on

! Ac8nomyces naeslundii been associated with development of root surface caries

Actinomyces species

CariesVaccination

In rats , experimental dental caries have been reduced by immunizing with cell-‐wall associated an4gens or glucosyltransferase from S.mutans

Caries Vaccination

The following mechanism have been suggested ! Inhib4on by secretory IgA of bacterial coloniza4on of teeth

!   Interference with bacterial metabolism !  Enhancement of phagocy4c ac4vity in gingival crevices

Caries Vaccination

!  Dental Caries is a mul4factorial disease, strongly associated with the dental plaque

!  Ecological Plaque Hypothesis caries forms as a result of disturbance in the normal balance of Oral Biota

!  The main factors involved are suscep4ble tooth surfaces, 4me, sugar substrate and plaque bacteria

!  Pits & fissure are the most suscep4ble areas !  Frequency of sugar intake is more decisive than total consump4on

Summary

!  Sucrose is the most cariogenic sugar ! Mutans streptococci are implicated in ini4a4on of pits & fissure and root caries

!   Lactobacillus spp are associated with progression of caries

Summary

!  Philip D. Marsh, Michael V Mar4n, “Plaque mediated diseases-‐ Dental Caries and Periodontal diseases” in Oral Microbiology, 5th Edi4on, Churchil Livingstone, 2009, pp 104-‐117

!   J. Bagg, T. W. Macfarlane, I. R. Poxton and A. J. Smith, “Dental Caries” in Essen4als of Microbiology for Dental Students, 2nd Edi4on, Oxford University Press, 2006 pp238-‐248

References

microbiology of dental caries

Education