Dental Caries: Aetiology and Prevention

Aetiology of Dental Caries

• The presentation covers the causes and prevention of dental caries

GDC Learning Outcomes

• The presentation aims to explain aetiology and pathogenesis of oral disease
• Psychological and sociological factors are recognized if they contribute to poor oral health, disease progression and how they effect treatment success
• The presentation discusses components of the patient assessment process
• The role of a dental therapist in tooth restoration is covered

Intended Learning Outcomes

• The session will help define dental caries and explain its aetiology
• Four aetiological factors that lead to dental caries are to be described
• Evidence supporting the proposed aetiologies is to be listed

Causes of Tooth Loss

• Periodontal disease
• Trauma
• Elective reasons
• Caries

Cost of Dental Caries

• The average hospital cost for tooth extraction in a child 5 and under is £836
• £50.5 million was spent on tooth extractions in those under 19 between 2015 to 2016
• £7.8 million was spent on tooth extractions for children under 5

Caries Prevention

• It is necessary to prevent and treat dental caries to reduce tooth loss
• Prevention and treatment are not possible without understanding dental caries

Definition of Carious process

• Carious process is a localised, chemical dissolution of the surface of a tooth
• Dissolution is caused by metabolic activity in a dental biofilm covering the tooth
• Dental caries refers to the signs and symptoms of a localized chemical dissolution of the tooth surface caused by metabolic events in a biofilm (dental plaque) covering the affected area
• Dental caries is reversible in its initial stages
• It is a progressive disease of dental hard tissues like enamel, dentine, and cementum
• Caries caused by bacteria acting on fermentable carbohydrates in the plaque biofilm on tooth surfaces
• The carious process involves chemicals, microbes and their metabolites
• It involves dissolution and reversible reactions and affects hard tissue and fermentable carbohydrates, and is often localized

Aetiological Agents for Caries

• Susceptible tooth surface
• Plaque bacteria
• Fermentable carbohydrates
• Time

Definition of Caries

• Caries is localized, chemical dissolution of a susceptible tooth surface
• It occurs over time due to metabolic activity on fermentable carbohydrates, in a microbial deposit (dental biofilm) covering a tooth surface

Factors Influencing Caries

• Social class, income, education, attitudes and knowledge
• Factors such as fluoride, diet composition, frequency, microbial species, behavior, saliva flow rate, saliva composition, microbial deposit pH, time, sugar clearance rate, and buffer capacity all factor into caries development

Susceptible Tooth Surface

• All dental hard tissues are susceptible to some degree
• Some teeth are more susceptible than others
• Tooth areas with factors that promote plaque biofilm accumulation are more susceptible to dental caries

Susceptible Areas of Teeth

• Pits and fissures
• Smooth surfaces
• Proximal areas
• Defective margins/ledges/overhangs

Fermentable Carbohydrates

• Bacteria within plaque biofilm need food to survive
• Sugars present in the diet are metabolized by oral commensal bacteria, producing lactic acid
• Not all carbohydrates are equally cariogenic
• Sucrose is rapidly metabolized to produce extracellular polysaccharides
• Simple sugars diffuse quicker into plaque and hence are more cariogenic than complex ones
• Starch is not completely digested in the mouth
• Intrinsic sugars include naturally occurring sugars packaged intracellularly, and present in fruits and vegetables
• They become available when processed; Lactose is an example not contained within a cell
• Extrinsic sugars are not bound within a cellular structure
• Examples include glucose, fructose, and sucrose
• Bacteria + Simple sugars = Acid

Critical pH

• Critical pH means that when pH becomes acidic, saliva draws out ions from the hydroxyapatite
• Saliva becomes supersaturated with phosphate & hydroxide ions
• Critical pH is when tooth tissues begin to lose mineral to saliva/plaque
• An acidic pH causes demineralisation of the enamel and dentine
• Demineralisation occurs if the pH is less than critical, and caries will develop
• Critical pH is 5 - 5.5 for enamel
• Critical pH is 6 - 6.5 for dentine
• Remineralisation occurs when the pH is higher than the critical one

Chemical Equation for Hydroxyapatite

• Ca5(PO4)3OH converts into 5 Ca(2+) + 3 PO4(3-) + OH(-)

Influence of time

• Time is a factor in the carious process
• Caries will not occur if all other factors occur for a short duration
• Need to consider frequency of acid attack; grazing, snacking, and suckling
• Aim to reduce acid attacks to 4 times a day or less with at least 2 - 3 hours between each attack
• Regular frequency makes for = increased time!
• Diet analysis to reduce the frequency of intake
• Infrequent attacks mean that there will be a reduced time below the critical pH and hence lower caries risk

Stephan Curve

• Stefen showed in studies that dental plaque had a resting PH of 6.5-7
• When exposed to fermentable sugars such as sucrose, fructose or glucose, pH fell rapidly to a pH below 5
• PH takes up to an hour to return to normal after exposure
• This plotting has become known as the Stephan Curve
• More frequent attacks mean more time below the critical PH and hence more demineralisation = higher caries risk

Plaque Bacteria

• Plaque bacteria is needed for caries development
• When pH drops, bacteria such as lactobacillus and strep mutans cause the biofilm microbial population to shift
• As biofilm thickens, there is less oxygen favoring anaerobic bacteria, also causing a microbial population shift
• Anaerobic bacteria produce more lactic acid, which causes a further drop in PH and more demineralisation

Caries Development Summary

• Caries develops on a susceptible tooth surface normally covered in plaque biofilm
• Sugar in the diet provides the substrate for oral commensal bacteria to metabolize and produce lactic acid
• The acid demineralises the enamel surface, causing calcium ions to pass into the surrounding plaque
• Mutans streptococci are the bacteria commonly associated with enamel caries
• A remineralisation/demineralisation "see-saw" favors remineralisation if frequency of intake is more than every 2-3 hours
• Calcium ions in the plaque will move back into the tooth if sugar consumption is infrequent
• Enamel becomes porous leading to white spot lesions if sugar consumption is more frequent and the calcium ions will pass into the plaque than are re-added because they are lost though swallowing of saliva

Studies that demonstrate caries

• Orland 1954 – Experiments with germ free rats, bacteria need for caries to exist, specifically plaque biofilm
• Orland – Experiments with non germ free rats fed a sugar free diet shows sugar substate is needed for caries, specifically fermentable carbohydrates
• Vipeholm study 1952 – Demonstates sugar type and frequency is associated with caries, specifically time
• Tristan de Cunha – South Atlantic Island was caries free until Americans imported cariogenic food and drink, specifically fermentable carbohydrate

Vipeholm Study (1945-1952)

• The study was conducted patients in a Swedish mental hospital without informed consent
• Patients were divided into groups to vary the amounts of sugar and frequencies of sugar consumption
• The subjects that were given most cariogenic food with greatest frequency developed the most caries
• The subjects that were given less cariogenic food with the lowest frequencies developed the least caries
• The subjects given food with increased frequency developed more caries
• The study demonstrated that caries depends on the substrate and time