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Problem 1.3: Monica’s Project
Topic: Dental Caries
Problem 1.3: Monica’s Project
Topic: Dental Caries
Prepared by: Joseph Mak
1) Dental Caries
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Dental Caries can be defined as progressive, irreversible bacterial damage to teeth
exposed to the oral environment
Ultimate effect of caries:
i)
To breakdown enamel and dentine
ii)
Open a path for bacteria to reach the underlying tissues, which causes
infection and inflammation of the pulp, and of apical periodontal tissues
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Prerequisities for tooth decay: (Fig 1.3-1)
i)
Teeth
ii)
Saliva
iii)
Bacteria in plaque
iv)
Dietary sugars
v)
Sufficient time
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Caries is dependent on a narrow range of micro-organisms
Streptococcus mutans is the most important one causing tooth decay
Other bacteria are also found in oral cavity, such as lactobacilli / Streptococci,
lactic acid are formed when carbohydrates are broken down by organisms in
saliva
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Ability of Strep. Mutans to cause caries appears to be related to its ability to
adhere to enamel surfaces to form adhesive polysaccharides
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Made of polymerized sucrose to high molecular weight polysaccharides dextrans
important in initiating attachment of organisms to teeth.
Helps building up a large mass of plaque.
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Problem 1.3: Monica’s Project
Topic: Dental Caries
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Micro-organisms can metabolize them when there is depletion of carbohydrates.
Sticky dextrans contribute to the bulk and adhesion of dental plaque to teeth
surface.
1.1 Dental Plaque
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a soft, thin film of food debris, mucin and dead epithelial cells deposited on tooth.
Providing a medium for growth of bacteria
1.1.1 Formation:
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After teeth have been thoroughly washed, dental plaque forms rapidly
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A cell- free mucinous layer (mucin like, chief ingredient of mucous) is deposited
on teeth within a short time
It does not appear to be due to bacterial action. Derived from deposition of
salivary mucinous substances such as glycoproteins.
After ~12 hours, the mucnious layer is colonized by microorganisms, eg.
Strep.Mutans, lactobacilli… etc
These micro-organisms metabolize ingested carbohydrates, producing acid as by
products, thus lowering pH
Produce intracellular polysaccharides such as glycogen-like polymers, eg. Glucans
and fructans (polymer consists of glucose and fructose respectively)
Sticky dextrans contribute to bulk and adhesion of dental plaque to tooth surface.
Dental plaque is cariogenic only in stagnation areas where it can form sufficiently
thicky
Even in the presence of suitable organisms and substrate, plaque appears to need
to form in a critical thickness of laque is probably necessary to maintain the
concentration of acid at the tooth surface, to resitst salivary buffering and to form
reserve carbohydrate stores if caries is to develop.
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1.1.2 Properties of cariogenic plaque:
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Provide a major contribution to its bulk, adhesiveness
Reserve carbohydrate stores
Retention of acid at tooth surface
Resistance to salivary buffering
Resist the escape of ionized molecules, particularly acids
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Plaque is important in the aetiology of caries because acid is generated within this
substance to such extent that enamel may be dissolved.
Dietary sugars diffuse rapidly through plaque where they are converted to acids
(mainly lactic acid but also acetic and propionic acids) by bacterial metabolism
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Problem 1.3: Monica’s Project
Topic: Dental Caries
pH of plaque may fall by as much as 2 units within 10 mins after ingestion of
sugar, the high density of bacteria in the plaque contributing to this rapid fall of
pH. Rapidity the fall in pH is a reflection of speed which sugar can diffuse into
plaque and activity of enzymes produced by the great no. of bacteria in the plaque.
Some 30 to 60 minutes later the pH value of plaque slowly rises to its original
value, due to diffusion of the sugar and some of the acid out of plaque, and the
diffusion into the plaque of buffered saliva which helps to dilute and neutralize the
acid. (fig1.3-2)
Slow reversion to resting pH probably include continued metabolism of
i)
residual sugar absorbed by the plaque
ii)
breakdown of reserve polysaccharides in plaque
iii)
Retention of sticky foods may delay the rise in pH until the food is
dissolved or removed.
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around neutral pH the plaque is supersaturated with mineral ions because of extra
ions from the enamel and some of the excess ions in the plaque may be
redeposited on the enamel crystal surfaces.
However, mineral ions may be lost from the system by diffusion out of the plaque
and into the saliva during the acid phase , and repeated episodes lead to an overall
demineralization and the initiation of enamel caries. Obviously the frequency and
duration of the acid phase of plaque will affect the rate of development of caries.
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Problem 1.3: Monica’s Project
Topic: Dental Caries
1.2 Mineralization and demineraliztion
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Bacterial plaque causes fermentation of carbohydrates from food and beverages
leading to production of acid ions at the tooth surface.
Effectiveness of salivary buffering of this acid is inversely proportional to plaque
thickness
Thick plaque is hold in deep fissures and grooves, between interproximal surfaces,
particularly in relation to those areas where teeth contact each other and around
rough or overcontoured restorations.
Mechanical oral hygeine measures are not very effective in removing plaque form
these sites, hence they are the common areas for caries infection.
Initial enamel lesion results when pH level at the tooth surface exceeds that which
can be conterbalanced by remineralization, but is not low enough to inhibit suface
remineralization. Tooth surface may remain intact through remineralization which
occurs perferentially at the surface due to increased levels of Ca 2+ , PO4 3- , F- and
buffering by salivary products.
Demineralization
- The mineral component of enamel, dentine and cementum is hydroxyapatite,
Ca10(PO4)6(OH)2 . In a neutral environment, hydroxyapatite is in equilibrium with
the local aqueous environment, which is saturated with Ca 2+ and PO4 3- ions.
- Hydroxyapatite is reactive to hydrogen ions at pH 5.5 (the critical pH for
hydroxyapatite) and below. H+ reacts preferentially with the phosphate groups in
the aqueous environment immediately adjacent to the crystal surface.
- The process can be thought of as conversion of PO4 3- to HPO4 3- by the addition
of H+ and the H+ being buffered at the same time. The hydroxyapatie crystal
therefore dissolves. This is termed deminerlization.
- Frequency and duration of acid phrase of plaque will affect the rate of
development of caries.
Remineralization
- The demineralization process can be revered if the pH is neutral and there are
sufficient Ca2+ and PO4 3- ions in the immediate environment.
- Either the apatite dissolution products can reach neutrality by buffering or the
Ca2+ and PO4 3- ions in saliva can inhibit the process of dissolution through the
common ion effect. This enables rebuilding of partially dissolved apatite crystals
and is termed remineralization.
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Problem 1.3: Monica’s Project
Topic: Dental Caries
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This interaction can be greatly enhanced by the presence of fluoride ion at the
reaction site. The overall reaction, which may be characterized as the
“deminearlization- remineralization” process, can be symbolized in general terms
as in fig 1.3-3.
1.3 How fluoride helps prevent tooth decay
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Reprecipitation of mineral is aided by F- ions. It substitutes –OH groups resulting
in deposition of fluoroapatite.
When fluoride content of water is 1 ppm or more the incidence of caries is
reduced substantially.
F- concentrated in bacterial plaque where in high levels inhibit bacterial enzymatic
activity or may affect caries in other ways.
Fluoride facours the precipitation of Ca 2+, PO4 3- ions form solution, encourage
deposition of ions as fluorapatite, inhibiting demineralization process and
enhancing the normal remineralization process by preferentially reacting with
hydroxyapatite breakdown products to form fluoroapatite.
Fluoroapatite is less soluble in water that hydroxyapatite:
Unable to be dissolved by acid ions above pH 4.5 (the critical pH for
fluoroapatite) the mineral is more resistant to acid dissolution.
Hydroxyapatite is reactive to hydrogen ions at pH 5.5 (critical pH for
hydroxyapatite) and below.
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Problem 1.3: Monica’s Project
Topic: Dental Caries
2) Cariology
2.1 Types of cavities
fig 1.3-4 to 8
Class I : Cavities occur in grooves, pits and fissures, found in occlusal pits and
fissures of molars and premolars.
Class II: Occur on approximal surfaces of molars and premolars
Class III: Occur on approximal surfaces of incisors and canines, but do no involve the
incisal angle.
Class IV: Occur on approximal surface of incisors and canines and involving incisal
angle.
Class V: Occurs on facial or lingual surfaces of cervical one-third of all teeth.
Class VI: Occur on incisal edge of anterior teeth or cusp tips of posterior teeth.
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Problem 1.3: Monica’s Project
Topic: Dental Caries
2.2 Sites and micromorphology
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Three different sites where cariogenic plaque may originate:
a) pits and fissures in crowns of teeth
b) Smooth surface of crown
c) Root surface
And also places which dental plaque can easily accumulates, such as approximal
surfaces of all teeth, gingival thirds of all teeth, both on facial and lingual
surfaces.
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Lesions on enamel smooth surface have a board areas of origin and a conical
extension toward the dentinoenameal junction, with the aped of V directed toward
the tip.
Lesions on pits and fissures develop from attack on the walls of enamel defects.
The appearance of a pit and fissure lesion is an inverted V with a base at the
dentinoenamel junction. (fig 1.3-9)
2.3 Histological structure of carious enamel
(fig 1.3-10)
2.3.1 Translucent zone
- Advancing front of lesion. (The naem refers to its structureless apearance when
perfused (applied) quinoline solution and examined with polarized light.
- More porous than normal enamel
- Contains 1 per cent by volume of spaces, the pore volume, comparied with 0.1 per
cent pore volume in normal enamel
- Pores are greater than that in enamel, which only permits H+ and water molecules
- Fall in magnesium and carbonate than enamel, which shows magnesiumcarbonate rich mineral is perferentially dissolved in this zone.
2.3.2 Dark zone
- This zone does not transmit polarized light
- Total pore volume, 2-4%
- Some remineralization has occurred due to precipitation of mineral lost from the
translucent zone
2.3.3 Body of lesion
- Largest portion of caries
- Largest pore volume, varying from 5% (periphery) to 25% (centre)
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Problem 1.3: Monica’s Project
Topic: Dental Caries
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Contains larger crystals result from the reprecipitation of mineral dissolved from
deeper zones.
2.3.4 Surface zone
- 40m thick
- Show little change in early caries
- Highly mineralized and having a higher fluoride level and low magnesium level
- An intact surface, since reprecipitation of minerals derived from plaque and from
that dissolved from deeper areas of lesion.
2.4 Development of enamel caries
1. Dissolution of mineral salts of tooth (hydroxyapatite)
Ca10(PO4)6(OH)2 + 8H+  10 Ca2+ + 6HPO4 2- + 2H2O
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At normal levels of pH at tooth surface the levels of calcium of phosphate ions
around the teeth such that no demineralization occurs.
Favours passage of ions into the surface.
As pH falls, equilibrium point is reached, where minerals will be lost
Presence of fluoride ions facour remineralization
2. Development of a subsurface translucent zone, which is unrecognizable clinically
and radiographically.
3. The subsurface translucent zone enlarges and a dark zone develops in its centre.
4. As the lesion enlarges more mineral is lost, the centre of dark zone becomes the
body of lesion, which is now clinically recognizable as a white spot.
5. Breakdown of the surface zone with the formation of cavity. (fig 1.3-11)
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Problem 1.3: Monica’s Project
Topic: Dental Caries
2.5 Development of dentinal caries
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Dentine differs from enamel in that it is a living tissue and as such can respond to
caries attack. (pain, scelerosis subjacent to lesion)
High organic content, approximately 20% by weight, mainly collagen.
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Four zones are detectable in the carious dentine:
1) Zone of destruction:
Dentine is denatured and infected
2) Zone of bacterial penetration
Dentine is demineralized while tubules are enlarged and full of microorganisms
3) Zone of demineralization
Uninfected, this zone, sometimes referred to as affected dentine, is
remineralizable.
4) Translucent or sclerotic zone
Separates the affected dentine from the underlying normal dentine.
Higher mineral content.
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Reparative dentine is formed on the pulpal ends of dentinal tubules, which seals
off dead tracts.
Chronic inflammatory changes:
- Signs of acute inflammation of the pulp become evident
- Blood capillaries being engorged (vasodilation)
- In some cases, rapartative dentine are formed and the pulp becomes partially
calcified
- Pain in inflammed pulp
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Problem 1.3: Monica’s Project
Topic: Dental Caries
Reference
1) E.S. Akapata: A textbook of Operative Dentistry, London: Class Pub., 1997.
D 617.62 A31
2) J.V. Soames and J.C. Southam: Oral Pathology 2nd Ed., Oxford Medical
Publications. D 617.61 S6
3) Graham J. Mount: Preservation and restoration of tooth structure, London, Mosby,
D 617.62 M92
4) Oral health—diet and other factors: the report of the British Nutrition
Foundation’s Task Force; Amsterdam: Elsevier D 617.654 O6
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