Microbiology of Dental Caries

Oral Microbiome

Unique natural ecology of the mouth is an ecosystem or community of microorganisms that live in symbiosis with one another and with their host, which contribute positively to the individual’s health

Plaque

• Is an adhesive layer comprising colonies of bacteria which deposits on the surface of the tooth

• Tends to stick to the surface of the teeth, facilitating bacteria to have cariogenic effect

Virulence

The ability of a bacterium to cause infection

Koch’s Postulates

• Developed by Robert Koch and Friedrich Loeffler

• Criteria used to establish a causal relationship between a microorganism and a disease

• Are essential in understanding the etiology of oral infection

Dynamic Stage

• Presence of homeostatic mechanisms in the plaque

• Brings the microflora to a stage whereby bacteria and hard tissues remain in stable stage

Acidogenic Stage

• An increase in proteon impermeability of the cell membrane

• When sugar intake is frequent or salivary secretions are less effective

• Subsequently demineralization or remineralization balance is disturbed over an extended period of time leading to initiation or progression of dental caries

Aciduric Stage

• Acidic environment temporarily impairs bacterial growth ability

• Normal flora will be eliminated and replaced by more aciduric bacteria

• Acid induced selection by acid impairment and growth competition are the major reasons for the shift in the composition of the microflora

Steptococcus Mutans

• It is a major etiological agent of human dental caries that resides primarily in biofilms that form on the tooth surfaces

• It is responsible for cases of infective endocarditis with a subset of strains being indirectly implicated with the onset of additional extraoral pathologies

• It is a facultatively anaerobic, gram-positive coccus commonly found in the human oral cavity and is a significant contributor to tooth decay

Acidogenicity

The ability to transport and metabolize a wide range of carbohydrates into organic acids

Aciduricity

The ability to thrive under environmental stress conditions, particularly low pH

Serotype C

75% of S. mutans strains (serological groups)

Serotype E

20% of S. mutans strains (serological groups)

Serotype F & K

5% of S. mutans strains (serological groups)

S. mutans & sobrinus

The most important mutans streptococci isolated from tooth caries samples are?

Mutacins

S. mutans produces this and it is an important factor in the colonization and establishment of S. mutans in the dental biofilm

James Kilian Clarke

He discovered and described Streptococcus mutans in 1924

S. sobrinus

• It is a gram-positive, catalase-negative, non-motile, and anaerobic member of the genus Streptococcus

• They are pathogenic within humans and enhances the formation of caries within the teeth

• Affiliated with early childhood caries

Louis Pasteur

He discovered Streptococcus sobrinus in 1887

Glucosyltransferase

An enzyme of streptococci that uses sucrose to produce glucans (help them accumulate on tooth enamel surfaces)

Glucans

It provides a shelter for bacterial colonization, and the protected environment creates the perfect nesting ground for S. sobrinus and other microorganisms to sustain a stable community in the form of dental plaque

Lactobacilli

• It is a genus of gram-positive, aerotolerant anaerobes or microaerophilic, rod-shaped, non-spore-forming bacteria

• Cause existing carious lesions to PROGRESS, especially those in coronal caries

Homofermentative

• The fermentation process of glucose produce mainly lactic acid

• L. casei & acidophilus

• Convert glucose to two molecules of lactate and use this reaction to perform substrate-level phosphorylation to make two molecules of ATP

Heterofermentative

• Production of acetate, ethanol and carbon dioxide aside from lactice acid

• L. fermentum

• Produce less lactate and less ATP, but produce several other end products

Actinomyces

• Are gram-positive, rod shaped, and facultative anaerobes

• Form fungus like branched network of hyphae

• Primary root caries, secondary enamel caries and periodontal disease

Aggregatibacter actinomycetemcomitans

Has been identified as being of note in periodontal disease

Pit and Fissure Caries

• Have the highest prevalence of microorganism

• Provide excellent mechanical shelters for microorganisms

Smooth Surface Caries

• Most common microorganism in this surface: S. mutans & salivarius

• The proximal enamel surfaces especially immediately gingival to the contact area are the most susceptible to plaque accumulation

Root Caries

• Actinomyces common micororganisms in this area

• Comparatively rapid progression

• Often asymptomatic

• Rapid progress, close to pulp

• Difficult to restore, especially in hidden areas