PATHOPHYSIOLOGY OF CARIES

• Dental caries is not simply a continual, cumulative loss of mineral, but rather a dynamic process, characterized by alternating periods of demineralization and remineralization.

• Demineralization – is the dissolution of the calcium and phosphate ions from the hydroxyapatite crystals, which are lost into the plaque and saliva.

• Remineralization – calcium, phosphate, and other ions in the saliva and plaque are redeposited in previously demineralized areas.

Interaction of aetiological factors in the oral cavity

Bacterial plaque+

Refined carbohydrate

demineralization

Saliva + hygiene + fluoride

+Natural protective

factors

remineralizarion

pH below 5.5 – tooth mineral is dissolved; the tooth mineral acts as buffer and loses calcium and phosphate ions into the plaque

pH 3.0 or 4.0 – the surface of the enamel is etched or roughened.

pH 5.0 – the surface remains intact while the subsurface mineral is lost.

Clinical sites for caries initiation1. Pits and fissures – found

mainly on the occlusal surfaces of the teeth as well as in lingual pits of the maxillary incisors

2. Smooth enamel surfaces – arises on intact enamel surfaces

3. Root surface – involve any surface of the root

The incipient lesion• First attack on a tooth surface• Macroscopically evidenced by the appearance of an area

of opacity – white spot lesion• Intact surface and subsurface porosity – clinical

characteristics• Maybe reversed by remineralization• Mutans Streptococci – initiation of enamel caries• Actinomyces viscosus – organism to initiate root caries.• Lactobacilli – progression of dentinal caries

CLINICAL CHARACTERISTICS OF ENAMEL CARIESIncipient Smooth-Surface Lesion

• Earliest evidence of caries on the smooth enamel surface – white spot

• White spot are usually found on the facial and lingual surfaces of the teeth.

• Chalky white, opaque areas revealed when the tooth surface is desiccated – incipient caries

• Incipient caries will partially or totally disappear when the enamel is hydrated while hypocalcified enamel is relatively unaffected by drying or wetting

• Softened chalky enamel is a sign of active caries• Incipient caries of enamel can remineralize

Zones of incipient lesion

1. Translucent zone

2. Dark zone

3. Body of the lesion

4. Surface zone

     

1. Translucent zone • Deepest zone;

advancing front of the enamel lesion

• Structureless appearance

• Pores or voids form along the enamel prism boundaries

• Pore volume is 1%, 10 times greater than normal enamel

2. Dark zone• Does not transit

polarized light• Total pore volume is 2 to

4 %

3. Body of the lesion• Largest portion of the

incipient lesion while in a demineralizing phase

• Has largest pore volume varying from 5% at the periphery to 25% at the center.

4. Surface zone• Unaffected by caries• Lower pore volume than

the body of the lesion

Body of the lesion

Translucent zone

Dark zone

Surface zone

Dentinal caries• Dentin contains much less mineral and possesses

microscopic tubules that provide a pathway for the ingress of acids and egress of mineral

• DEJ has the least resistance to caries attack and allows rapid lateral spreading once caries has penetrated the enamel

• V shaped in cross section with a wide base at the DEJ and the apex directed pulpally.

• Caries advance more rapidly in dentin than enamel because dentin provides much less resistance to acid attack because of less mineralized content.

Zones of Dentinal CariesZone 1: Normal Dentin

• Deepest area which has tubules with odontoblastic processes that are smooth and no crystals are in the lumens

• Intertubular dentin has normal cross-banded collagen and normal dense apatite crystals

• No bacteria are in the tubules• Stimulation produces pain

Zone 2: Subtransparent Dentin• Zone of demineralization of the intertubular dentin and initial

formation of very fine crystals in the tubule lumen at the advancing front

• Damage to the odontoblastic process; no bacteria are found in this zone

• Stimulation produces pain; capable of remineralization

Zone 3: Transparent Dentin• Zone of carious • Stimulation produces pain• No bacteria are present

Zone 4: Turbid Dentin• Zone of bacterial invasion• Very little mineral present• Cannot be remineralized

Zone 5: Infected Dentin• Outermost zone• Consists of decomposed dentin that is teeming with bacteria• No recognizable structure to the dentin and collagen and mineral

seem to be absent• Great numbers of bacteria• Removal of infected dentin is essential

Dentin CariesThis is a photomicrograph of dentinal caries. Observe the five bands usually seen in carious dentin. From the outside (1), we see a zone of necrotic dentin, a zone of infected dentinal tubules, a zone of transparent dentin or sclerotic dentin, a zone of fatty degeneration of tubules and an area of intact dentin.

CARIES TERMINOLOGY

A. Location of caries1. Caries of pit and

fissure origin

- form in the regions of pits and fissures

- two cones, base to base, with the apex of the enamel cone at the point of origin and the apex of the dentin cone directed toward the pulp

pulp

• In x- section gross appearance of a pit and fissure in an inverted V with a narrow entrance and a progressively wider area of involvement closer to the DEJ

2. Caries of enamel-smooth surface origin- form in a smooth area of the enamel surface that is habitually unclean.- apex of the cone of caries in the enamel contacts the base of the cone of caries in the dentin.

enamel

dentin

• X- section shows a V shape with wide area of origin and the apex of the V directed toward the DEJ.

3. Backward caries

- when the spread of caries along the DEJ exceeds the caries in the contiguous enamel

4. Forward caries

- caries cone in enamel is larger or at least the same size as that in dentin. (pit and fissure caries

5. Residual caries

- caries that is not removed during a restorative procedure, either by accident, neglect or intention.

6. Root-Surface caries or senile carious lesion• associated with aging process• may occur on the tooth root

that has been both exposed to the oral environment and habitually covered with plaque

• Have less well defined margins tend to be U shaped in cross section and progress more rapidly because of the lack of protection from an enamel covering

7. Secondary (recurrent) caries

- occurs at the junction of a restoration and the tooth and may progress under the restoration

B. Extent of Caries

A. Incipient caries (reversible)

- first evidence of caries activity in the enamel

B. Cavitated caries (non reversible)

- the enamel surface is broken and usually the lesion has advanced into dentin.

C. Rate (speed) of caries

1. Acute (rampant caries)-is when the disease is rapid in damaging the tooth.- it is usually in the form of many, soft, light –colored lesions in a mouth and is infectious.

2. Chronic (slow or arrested) caries- is slow or it may be arrested following several active phases- lesion is discolored and fairly hard- an arrested enamel lesion is brown-to-black, hard, and as a result of fluoride, may be more caries-resistant than contiguous, unaffected- an arrested dentinal lesion is dark and hard this is termed as sclerotic or eburnated dentin

Frame A: This frame illustrates the very earliest stage of tooth decay that will show up on a dental x-ray.

Frame B: Once a dental x-ray shows that the tooth decay has penetrated through the tooth's enamel and into its dentin layer a dentist will recommend the placement of a filling

Frame C: As discussed previously, the dentin portion of a tooth is less mineralized ("hard") than a enamel layer. This means that dentin will decay at a faster rate than tooth enamel. Notice how in Frame C the size of the lesion in the enamel layer has only slightly increased in size while the tooth decay present in the tooth's dentin has advanced significantly.

Frame D: Frame D illustrates a worst-case scenario situation. If decay is left unchecked it can advance all the way to the tooth's nerve. If it does, not only must the decay be removed and the damaged tooth structure repaired but additionally the tooth's nerve will require root canal treatment

caries