textbook of preventive and community dentistry, 2/e

CHAPTER

30Dental Caries

CHAPTER OUTLINE

� Introduction

� Early Theories of Caries Aetiology

� Current Concepts of Caries Aetiology

� Classification of Dental Caries

� Clinical Manifestations of Dental Caries Process

� Caries of Enamel

� Dentinal Caries

� Root Caries

� Microbiology of Dental Caries

� Mechanism of Adherence of Microorganisms to Tooth Surface

� Formation of Plaque

� Role of Saliva in Dental Caries

INTRODUCTION

Dental caries the disease of civilization, is affecting the mankind since the dawn of the time. Caries has also been noted in the fossil remains of Pithecanthropus erectus and Homo rhodesiensis, early ancestors of man. Caries seems to have increased considerably in Homo sapiens during Neolithic period when it was perhaps as high as that seen in many contemporary primitive people. In fact, in prehistoric skulls about 5% of the teeth exhib-ited caries.

It is a chronic disease, a process that progresses very slowly in most individuals. The multifactorial aetiology of dental caries nowadays is relatively understood and the disease is therefore not only treatable but also most aspects of it, to an extent preventable infection. The cari-ous lesion should be regarded not as a disease entity but as tissue damage caused by the dental caries.

“Caries without cavitation”—caries should be consid-ered as a process rather than simply as an event at a par-ticular stage, i.e. a cavity requiring restoration. Evidence of frank cavitation was required for the diagnosis. There were two reasons for this; one being that from the public health standpoint there was little interest in lesions, which have no effect on the person in terms of requirements for treatment or restoration. When a caries-free individ-ual is referred, it was found that such an individual had many pre-cavitational lesions approximally. However,

epidemiologically it was of little concern if that person went through life without frank cavitation.

Tooth decay is an infectious disease generally affected by diet and the pattern of its consumption by the host. Its dependency on ingestion of fermentable dietary car-bohydrate is beyond question. However caries does not occur in germ free animals, no matter what their diets are, thus establishing it as a fundamentally microbiological disease. Sound enamel demineralizes, if plaque bacteria are given with carbohydrate substrate and they produce acids, however, the presence of saliva in the mouth can act as a buffering agent which in turn to an extent can inhibit the demineralization process. The progression of carious lesion is not inevitable and disease can be controlled.

Salient Features of Carious Process

Salient features of carious process are listed below:

1. Carious process is spread over time2. Carious process does not have to progress3. The initial lesion can be arrested and reversed4. All ages are susceptible to caries5. Caries is the major cause of tooth loss in all age groups.

Definition

Dental caries is an infectious microbial disease that begins as demineralization of inorganic portion of tooth,

– SS Hiremath

Chapter-30.indd 321Chapter-30.indd 321 6/1/2011 6:17:29 PM6/1/2011 6:17:29 PM

322 PREVENTIVE DENTISTRY

followed by destruction of organic portions, leading to cavity formation.

• The Caries Process occurs as an interaction between the biofilm and the tooth surfaces: the caries lesion is the manifestation of the stage of the process at one point in time.

EARLY THEORIES OF CARIES AETIOLOGY

Worm Theory

According to an ancient Sumerian test, toothache was caused by a worm that drank the blood of the teeth and fed on the roots of the jaws. Guy de Cahuliac, the greatest Surgeon of the middle Ages believed that worming caused dental decay. As a cure he advocated fumigation with seeds of leech, onion and hyoscyamus.

Humour Theory

Ancient Greeks considered that relative proportions of four elementary fluids of the body determined a person’s physical and mental constitution: (i) blood, (ii) phlegm, (iii) black bile, and (iv) yellow bile. These four fluids cor-responds to the four humours: (i) phlegmatic, (ii) choleric (iii) sanguine, and (iv) melancholic (Fig. 30.1). All dis-eases including caries were explained by an imbalance of these humours.

Parasitic or Septic Theory

Parasitic or septic theory was given by Erdl (1843). According to this theory, dental caries was caused by filamentous parasites present in the “surface membrane” (plaque?) of teeth. Later, Ficinus, observed filamentous microorganisms, which he called denticolae in material taken from carious cavities.

Vital Theory

The vital theory regarded dental caries as originating within the tooth itself, analogous to bone gangrene. A clinically well-known type of caries is characterized by extensive penetration into the dentin, and even into the pulp, but with a barely detectable catch in the fissure.

Chemical Theory

Chemical theory was given by Parmly (1819). According to this theory, dental caries was caused by unidentified chemical agent. He stated that caries begin on the enamel surface in locations, where food putrefied and acquired sufficient dissolving power to produce the disease chemically.

Chemoparasitic Theory

Chemoparasitic theory is the most accepted theory for the aetiology of dental caries. This theory was given by

Phlegm Blood

Black bile

Yellow bile

Sanguin

Phlegmatic

Melancholic

Choleric

FIGURE 30-1 Humour theory.


323DENTAL CARIES

Miller in 1890. In a series of experiments it was demon-strated that:

1. Acid was present within the deeper carious lesion, as shown by reaction on litmus paper.

2. Different kinds of foods (breads, sugar, but not meat) when mixed with saliva and incubated at 37°C could decalcify the entire crown of the tooth.

3. Several types of mouth bacteria (at least 30 species are isolated) could produce enough acid to cause dental caries.

4. Lactic acid was an identifiable product in carbohydrate-saliva, incubation mixtures.

5. Different microorganisms (filamentous, long and short bacilli and micrococci) invade carious dentin.

Miller concluded that no single species of microorgan-ism caused caries, but rather the process was mediated by oral microorganisms capable of producing acid and digesting protein.

Critique of Chemoparasitic Theory

1. Miller’s chemoparasitic theory is unable to explain the predilection of specific sites on a tooth to dental caries.

2. The phenomenon of arrested caries is not explained by the chemoparasitic theory.

3. Miller’s theory does not explain why some popula-tions are caries-free.

Proteolytic Theory

Proteolytic theory was given by Gottlieb in 1944. This theory suggested that the initial action was due to pro-teolylic enzymes attacking the lamellae, rod sheaths, tufts and walls of the dentinal tubules. Later a coccus, proba-bly Staphylococcus aureus, was involved because of the yellow pigmentation that he considered pathognomonic of dental caries.

Frisbie (1944) also described caries as a proteolytic process involving depolymerization and liquefaction of the organic matrix of enamel.

Pincus (1949) contended that proteolytic organisms first attacked the protein elements, such as dental cuticle and then destroyed the prism sheaths.

Proteolysis–Chelation Theory

Proteolysis–chelation theory was proposed by Schatz et al (1955). It implies a simultaneous microbial degrada-tion of the organic components (proteolysis), and disso-lution of minerals of the tooth by the process of chelation. The word “chelate” is derived from the Greek “chele”

meaning claw, and refers to compounds that are able to bind metallic ions such as calcium, iron, copper, zinc and other metals, by the secondary valence bonds.

CURRENT CONCEPTS OF CARIES AETIOLOGY

Caries is multifactorial disease mainly consisting of three parameters most commonly contributing for the initia-tion of dental caries namely, host factor (susceptible tooth surface), microorganism (Streptococcus mutans), and diet (sucrose), however the interplay between these factors has to take place in an appropriate time. Thus the fourth factor has been considered either as independent factor or all the three primary factors have been put under time factor (outer ring). This factor has been added to empha-size the importance of time factor in the origin of the disease along with other three primary factors. Hence current concept of the aetiology of dental caries includes these important four factors as described in Keyes circle (Figs 30.2–30.4). There are various subfactors or co-factors contributing directly or indirectly in initiation of dental caries.

Keyes Circles

A carious lesion should be regarded not as a disease entity, but as tissue damage or a wound caused by the disease dental caries.

The interaction of saliva, bacteria and microbial prod-ucts in the production of biofilms on the tooth surface is an important factor to initiate dental caries. The suscep-tible host, cariogenic oral microbial flora and fermenta-ble carbohydrate are important in the development of dental caries and they have been depicted through Keyes circles (Figs 30.3A, B).

Each one of them is of equal importance in aetiology of the disease. However there are many secondary fac-tors that either influence the progression or regression of dental caries (Fig. 30.4).

• Caries progression occurs when the demineralization and remineralization equilibrium is out of balance, leading to net mineral loss.

• Remineralization can arrest or reverse progression of disease and can lead to changes in mineral quality; the understanding of the caries process has progressed far beyond the point of restricting the evidence of dental caries to the caries in enamel only or caries in enamel and dentin or levels of cavitation.

1. Lesion detection: Implies an objective method of determining whether or not disease is present.



2. Lesion assessment: Aims to characterize or moni-tor a lesion, once it has been detected.

3. Caries diagnosis: Implies a human, professional, summation of all available data.

It is now appreciated that caries is initially reversible, chronic, disease process with known multifactorial aetiology.

Dental caries progresses slowly in most of the indi-viduals as chronic disease. The disease is seldom self-limiting and in the absence of treatment, a caries progress until the tooth is destroyed. The localized destruction of the hard tissues, often referred as the lesion, is the sign or symptom of the disease (Fezejerskov et al 2008). Lesion progression is often depicted on a linear scale ranging

from initial loss of mineral at the ultra structural level to total destruction of the tooth. However, caries lesion development is a highly dynamic process with alternat-ing periods of progression and arrest/regression.

Lesion progression may be arrested at any stage of lesion development, even at the stage of frank cavitation, provided the local environmental conditions, e.g. biofilm control and topical fluoride exposure, are favourable. Hence, the clinical stages of caries represent nothing but historical signs of the past caries experience. What may be perceived clinically as an “incipient” or “early“ lesion may in reality turn out to be an age established lesion that has been present in the oral cavity for months or years and also from a biochemical point of view the car-ies process is much more complex. Metabolic processes

Absence ofcariogenic plaque

Microorganisms Carbohydrates Acid production No caries+

Plaque + Sucrose + Cariogenic bacteria

+

Acid production

Subsurface demineralization

Initial lesion

Progression of carious lesion

Cavitation

Continuous sucroseconsumption

Repeated attack ofcariogenic challenge

Destruction oforganic matrixMore of mineral loss

Cariogenic plaque Cariogenic diet

FIGURE 30-2 Flowchart depicting the caries process.


325DENTAL CARIES

are constantly taking place in the dental plaque as a result of microbial activity, and this is reflected by con-tinuous, rapid fluctuations in plaque pH, both when the plaque is starved and fed. Hence, any clinically sound or carious tooth surface that is covered by an undisturbed plaque may experience minute mineral loses and min-eral gains depending on the metabolic status of the microflora. The key point is, when the cumulative result of the de- and remineralization process is loss of mineral, caries lesion develop or progress. Caries lesions may be classified in various ways. Firstly, lesions can be classi-fied according to their anatomical site and location. The lesions may be commonly found in pits and fissures, or

on smooth surfaces of the enamel (enamel caries) or on the exposed root cementum (root caries).

Classification Based on Morphology

This classification is according to anatomical site of the lesions.

Pit and Fissure Caries (Occlusal Caries)

• Most common type of dental caries (Fig. 30.5).• Occurs on the occlusal surfaces of molars and

bicuspids.

FIGURE 30-3 Keye’s Circle—current concept of caries aetiology.

Microorganisms

Substrate

Time

CariesHost

&teeth

NoCaries

NoCaries

NoCaries

NoCaries

Time

TimeTime

Caries

Microorganisms(cariogenic plaque)

Substrate(cariogenic diet)

Host(susceptible

tooth surface)

A B

Microorganisms

Substrate Host

Caries

Oral clearanceOral hygieneDetergency of foodFrequency of eatingCarbohydrate (type,concentration)

Strep. mutans (substrate)Oral hygiene Oral floraFluoride in plaqueDiet & nutritionTransmissibility

Secondaryfactors

Primaryfactors

AgeFluoridesMorphologyNutritionTrace elementsCarbonate

FIGURE 30-4 Diagrammatic representation of interplay between primary and secondary factors in caries aetiology.



Smooth surface caries. There are two variations of smooth surface caries. They are: (i) buccal and lingual sur-face caries, and (ii) proximal surfaces (interproximal).

a. Buccal and lingual surface caries

• Cervical caries (smooth surface caries)—occurring on buccal or lingual surfaces near the cementoenamel junction (Fig. 30.6).

b. Proximal surfaces (interproximal)

• Interproximal caries—occurring at mesial or distal contact points. Interproximal caries usually starts just cervical to the contact area (Fig. 30.7).

Classification based on Severity and Progression

I. Rampant caries II. Early childhood caries (nursing caries) III. Radiation caries (xerostomia induced).

Rampant caries. Rampant caries occurs as a sudden, rapid and almost uncontrollable destruction of teeth,

involving surfaces of teeth that are ordinarily relatively caries free (proximal and cervical surfaces of anterior teeth including the mandibular incisors get affected). A caries increment of 10 or more new lesions over a period of about a year is characteristic of a rampant caries attack (Fig. 30.8).

Early childhood caries Early childhood caries is a spe-cific form of rampant decay of the primary teeth of infants and toddlers. According to American Dental Association (ADA) it is defined as “the presence of one or more decayed, missing or filled tooth surfaces in any primary tooth in a preschool age child between birth and 71 months of age”.

FIGURE 30-5 Pit and fissure caries.

B

A

FIGURE 30-6 Cervical caries.

FIGURE 30-7 Proximal surfaces (interproximal).

A

B


327DENTAL CARIES

ECG is a particularly virulant form of dental caries that is characterized by an overwhelming infections challenge and is associated with unusual dietary practices. It is a unique pattern of dental decay affecting maxillary primary incisors in young children due to prolonged nursing habit espe-cially when the child is sleeping. This is also named as baby bottle tooth decay. The main cause for this type of caries is inappropriate feeding bottle or at will breastfeeding or combination of both and poor oral hygiene (Fig. 30.9).

Radiation caries (xerostomia induced). This is a common complication of radiotherapy of oral cancer lesions and radiation-induced xerostomia (from the Greek, xeros = dry, stoma = mouth).

Such patients develop rampant dental caries (Fig. 30.10). Xerostomia may be caused by factors other than radiation like

– Tumours of salivary glands– Autoimmune diseases (e.g. Sjogren’s syndrome)

– Anti-sialagogue drugs– Prolonged illness

Classification Based upon Part of Tooth Structure Involved

a. Enamel caries• Incipient caries• Linear enamel caries (odontoclasia)

b. Dentinal cariesc. Cemental caries

Enamel Caries

• Incipient lesion: Incipient lesion is also called the early carious lesion. It manifests as a white, opaque region, which is best demarcated when the area is dried (Figs 30.11A, B).

FIGURE 30-8 Rampant caries.

A

B

FIGURE 30-9 Nursing caries.

FIGURE 30-10 Radiation caries.

FIGURE 30-11 Incipient lesion.

Incipientlesion

Incipientlesion

A

B



• Linear enamel caries (Odontoclasia): An atypical form of dental caries, called linear enamel caries, has been observed in the primary dentition of children, in Latin America and Asian countries. The lesions predominate on the labial surfaces of the anterior maxillary teeth, in the region of neonatal line. (The neonatal zone repre-sents the demarcation between pre- and postnatal enamel and is a histologic feature of all primary teeth).

It is thought to result from the metabolic disturbances associated with trauma of birth and transient hypocal-caemia associated with transient hypoparathyroidism.

Dentinal caries. On its way to progression, carious lesion involves dentin and over a period of time when the cariogenic challenge becomes more and more strong and along with other favourable factors, the lesion estab-lishes in dentin. At the same time, outer layer of enamel might breakdown owing to progression of caries and leads to cavitation.

Cemental caries. Recession of gingival margin is an inevitable process as a result of poor oral hygiene and loss of periodontal attachment with age. Subsequently the exposed root surface becomes more vulnerable to plaque accumulation and caries process might initiate involving cementum.

Classification of Caries Based on Activity

a. Primary caries b. Secondary caries (recurrent caries) c. Residual caries d. Arrested caries

Primary caries. Primary caries is used to differentiate lesions, which develop on the healthy enamel surface or on unrestored surfaces from those that develop adjacent to a filling.

Secondary caries. A carious lesion that develops at the interface of restoration and the cavosurface of the enamel is called secondary caries (Fig. 30.12).

This type of caries may result from:

• Poor cavity preparation• Ditching around an amalgam restoration• A defective restoration• Or a combination of these factors.

Residual caries. Residual caries is demineralised tissue that has been left behind before filling is placed (incomplete removal of carious dentin).

Arrested caries. There is clinical evidence that incipi-ent and even more advanced carious lesions may become arrested if there is a significant shift in oral environmen-tal conditions from those that predispose to caries to that tend to slow the caries process (Fig. 30.13).

According to World Health Organization (WHO), the shape and depth of the carious lesions can be scored on a four-point scale (D1 to D4):

• D1—clinically detectable enamel lesions with intact (non-cavitated surfaces)

• D2—clinically detectable cavities limited to the enamel

• D3—clinically detectable lesions in dentin (with and without cavitation of dentin)

• D4—lesions into pulp.

CLINICAL MANIFESTATIONS OF DENTAL CARIES PROCESS

Early Changes

The earliest stage of caries is the first time deminerali-zation of enamel which occurs after the plaque pH depression below the critical pH (5.2–5.5). This amount of demineralization cannot be detected clinically (they go unnoticed), however the repair process, remineraliza-tion and demineralization go hand in hand, and most of the time maintains the homeostasis (Figs 30.14, 30.15).

FIGURE 30-13 Arrested caries.

FIGURE 30-12 Secondary caries.


329DENTAL CARIES

White Spot Lesion

The first visible clinical presentation of dental caries is referred to as white spot lesion. The clinical appearance of white spot lesion is caused by subsurface enamel demineralization, resulting in loss of translucency. Normally white spot lesion being smooth and having intact surface indicates that lesion is not active whereas lesions with rough surfaces because of increased poros-ity suggest that a lesion is active and progressing.

White spot carious lesion does not necessarily progress to frank cavitation. In this stage, the lesion progression could be arrested or reversed by modifying any of the causative factors or application of appropriate preven-tive measures. Arrested lesion may retain the appearance of white spots or acquire the appearance of brown spot. The reversal of the white spot could be due to reminer-alization of the lesion subject to condition that surface layer is intact, and most of the time they may not progress to frank cavitation in the absence of high cariogenic chal-lenge (Fig. 30.16). Therefore white spot can be referred as non-cavitated lesion.

Hidden or Occult Caries

During the cariogenic challenge on account of fall of pH to a critical level, demineralization commences on the subsurface. Calcium and phosphate ions move from

Demineralization

Tooth

Remineralization

FIGURE 30-14 Equilibrium of demineralization and remineralization.

Demineralization

Remineralization

Tooth

Poor oral hygieneFrequent sugar exposureContinuous highcariogenic challenge

FIGURE 30-15 Deranged equilibrium of demineralization and remineralization.

subsurface to the surface and get added to the calcium and phosphate in dental plaque. Later calcium and phosphate along with fluoride from saliva and biofilm helps in the precipitation on the superficial layer on the affected surface enamel. This rapid precipitation of high levels of calcium and phosphate leads to occluding the pores that would further limit demineralization of the surface layer and limits remineralization of the underlying demineralized subsurface. Hence there is an intact surface layer of the enamel, even though caries are progressing at subsurface level, which is not visible.

Caries progressing into dentin with intact surface is not clinically diagnosed but can be detected only in radio-graphs. The prevalence of hidden caries ranges from 0.8 to 3%. These occult lesions are usually seen with low caries rate which is suggestive of increased fluoride exposure. Recently it has been observed that hidden car-ies may have origin as pre-eruptive defects, which are detectable only with the use of radiographs.

Frank Cavitation

As the carious lesion progresses the subsurface lesion increases in dimension, eventually leading to collapse of the surface layer leading to cavitation. At this stage of carious process, tooth destruction progresses more rapidly because cavitation favours plaque accumulation and reduced salivary access.



The progression of the carious lesion is variable, depending on the site of origin and conditions in the mouth. The time for progression from incipient caries to clinical caries (cavitation) on smooth surfaces is esti-mated to be 18 months plus or minus 6 months. The peak rate for the incidence of the new lesions occurs 3 years after the eruption of the tooth. Occlusal pit and fissure lesions develop in less time than smooth surface caries lesion. Both poor oral hygiene and frequent expo-sure to sucrose containing diet can produce incipient lesions in as early as 3 weeks. Radiation-induced xero-stomia (dry mouth) can lead to clinical caries develop-ment as little as 3 months from the onset of the radiation. Thus, caries development and progression in healthy individuals is usually slow in comparison among com-promised persons.

Arrested Caries

Caries lesion can become arrested at any stage of the car-ies process assuming that causal factors are changed or protective factors are increased. Once the open carious lesion becomes self-cleansing, with improved oral hygiene measures, restricted intake of refined sugars and use of fluorides, the carious process is arrested and dentin becomes hard.

The boundaries of caries diagnosis and caries inter-vention are changing dramatically. Using emerging tech-nology we should be able to detect clinically the incipient dental caries lesion earlier. Thus, dental caries is a dam-aging process, which in its early stages is reversible and even in its more advanced stages, can be arrested.

CARIES OF ENAMEL

Macroscopic Changes of Enamel

On smooth surfaces. On smooth enamel surfaces, the earliest visible changes are usually manifested as a loss of translucency, resulting in an opaque chalky white lesion in location where caries progressed most probably are becoming arrested, discoloured pigmentation of the enamel may be seen. Smooth surface lesions when sec-tioned longitudinally are cone shaped with the apex directed towards the dentin (Figs 30.17, 30.18).

Pit and fissure caries. Occlusal fissures are deep invagination of enamel, they can be extremely diverse in shape and size and have been shown as broad or narrow funnels, constricted hour glasses, multiple invaginations with inverted shape.

Classification of fissure morphology is as follows (see Fig. 39.1):

a. ‘Y’-shaped divisions (5–10%). b. ‘V’ type-wide at top and gradually narrowing

towards the bottom (30–35%).c. ‘U’ type, almost the same width from top to bottom

(12–15%). d. ‘I’ type, and extremely narrow slit (18–20%). e. ‘IK’ type, extremely narrow slit with a larger space at

bottom (24–26%). f. Other types (7–9%).

Several morphological variations may be found along the length of the individual occlusal fissure as a result it

Sound enamel

Carious enamel

Cavitation

High cariogenic challenge

Fermentablecarbohydrates

Cariogenic plaque

FluoridesGood oral hygiene

FIGURE 30-16 Schematic presentation of factors affecting sound and carious enamel.


331DENTAL CARIES

is not always possible to classify a tooth as having a par-ticular type occlusal morphology. Frequently, fissures having a broad base give rise to several pits, which when sectioned, look like inverted ‘Ys’. Many teeth have areas at the base of the fissures where a very thin enamel covers underlying dentin.

Carious lesion more often starts at both sides of the fissure wall rather than at the base, penetrating nearly perpendicularly towards the dentinoenamel junction. In newly erupted teeth, brown stain or discoloured lesion is indicative of underlying decay, whereas in older indi-viduals the lesions may be arrested or remineralised areas. This lesion is commonly described as cone shaped with the base directed towards the dentin and apex towards the enamel surface. Later these macroscopic changes of the enamel in initial caries proceed cavitation and occur with-out apparent break in the enamel surface.

Microscopic Changes of Carious Enamel

Under microscope, the enamel caries (initial caries) shows four zones, starting from the inner advancing front of the lesion. The zones are:

1. Translucent zone2. Dark zone3. Body of the lesion4. Surface layer.

There is no sudden or dramatic change from zone to zone but there is a gradual series of changes within the lesion (Figs 30.20A, B). Furthermore, all zones may not be visible by polarized light microscopy.

Zone 1: translucent zone. The translucent zone of enamel caries is not seen in all lesions, but when it is present it lies at the advancing front of the lesion and is

Pulpalinvolvement

Cavitation

Progression

Clinical detectablelevel

Microscopic level

Ultra structural level

Irreversible

Reversible

Min

eral

loss

FIGURE 30-17 Figure depicting progression of mineral loss in relation to time.

FIGURE 30-18 Smooth surface caries.FIGURE 30-19 Longitudinal sectional view of pit and fissure caries.



the first recognizable alteration from the normal enamel. It is more porous than sound enamel, the pores having been created by the demineralization process. Sound enamel has a pore volume of about 0.1%, the translucent zone, however, has a pore volume of approximately 1%. The pores are probably located at junctional sites such as prism borders, cross-striations or along the striae of Retzius.

Once these areas are filled with quinoline, structural markings are lost, due to penetration of the quinoline, which has an identical refractive index to that of enamel apatite giving translucent appearance.

Zone 2: dark zone. The dark zone is the most com-mon feature of the carious lesion and it is the 2nd zone of alteration from normal enamel. It lies just superficial to the translucent zone and appears dark when the ground section is placed in quinoline. This zone is more porous than translucent zone, with a pore volume of 2–4%.

It is shown that in this zone the pores are of varying sizes, large and small. Quinoline is a large molecule and cannot enter the small pores, which remain filled with air, giving a dark appearance.

These small pores could represent areas of repair where mineral has been re-deposited or they may have been created by demineralization that is by an opening up of sites not previously attacked.

Zone 3: body of the lesion. The body of the lesion comprises the largest proportion of carious enamel in the small lesion. This zone lies superficial to dark zone and deep to the relatively unaffected surface layer of the lesion. The maximum amount of mineral loss is found in this zone. In longitudinal section with quinoline in polar-ized light microscopy, the area appears translucent and the stria of Retzius may be well marked. When examined in ground section in water, the water molecules enter the pores in the tissue and since the refractive index of water (1.3) is different to that of enamel (1.62), the area appears dark. The pore volume of this region is 5% at its periphery, increasing to 25% or more in the centre.

Zone 4: surface zone. The surface layer ranges between 30–100 mm thick and it is thinner in active lesions and thicker in inactive carious lesions. This zone is most clearly seen in polarized light microscope when the sec-tion is in water, where it appears as a relatively unaffected area superficial to the body of the lesion. The zone has a pore volume of 1% but if the lesion progresses, the surface layer is eventually destroyed and a cavity forms.

DENTINAL CARIES

Macroscopic Changes of Dentin

Dentin is the hard portion of the tooth that is covered by enamel on the crown and cementum on the root. The development and progression of caries in dentin is dif-ferent from progression in the overlying enamel because of structural differences of dentin. Dentin contains much less mineral and possesses microscopic tubules that pro-vide the pathway for the ingress of acids and egress of mineral. The dentinoenamel junction (DEJ) has the least resistance to caries attack, hence allows for rapid lateral spreading once caries has penetrated the enamel. Because of this characteristics, dentinal caries is ‘V’ shaped or cone shaped in cross-section with a wide base at the DEJ and the apex directed pulpally.

Defence Reactions of Pulp-Dentin Complex

Histopathology. Caries advances more rapidly in den-tin than in enamel because dentin provides much less resis-tance to acid attack because of less mineralized content. Caries in dentin produces variety of responses including sensitivity, pain, demineralization and remineralization.

Episodes of short duration pain may be felt occasion-ally during earlier stages of dentin caries. These pains are due to stimulation of pulp tissue by movement of

FIGURE 30-20 Microscopic changes of initial caries.

A

B

Demineralized zoneDemineralized zone

Plaque

Translucent zone


333DENTAL CARIES

fluid through dentinal tubules that have been exposed to the oral environment by cavitation. Once bacterial inva-sion of dentin is near to the pulp, toxins and few bacteria enter the pulp resulting in inflammation of the pulpal tissue. Initial pulpal inflammation is thought to be evident clinically by production of sharp pain (for few seconds) in response to a thermal stimulus. The degree of inflam-matory response depends on the rapidity of caries. If den-tinal sclerosis occurs, injurious agents will have reduced or no access to the pulp attack.

The pulp-dentin complex reacts to caries attack by attempting to initiate remineralization and blocking off the open tissues. This reaction results from odonto-blastic activity. The dentin can react defensively through repair to low and moderate intensity caries attack as long as pulp remains vital and has an adequate blood supply. In slowly advancing caries vital pulp can repair demineral-ised dentin by remineralization of the intertubular dentin and by opposition of peritubular dentin.

Dentin responds to the stimulus of its caries deminer-alization episode by deposition of crystalline material in both the lumen of tubules and intertubular dentin of affected dentin in front of the infected dentin portion of the lesion. These hypermineralised or repaired areas may be seen as zones of increased porosity in radiographs.

A short painful response to cold suggests reversible pulpitis or pulpal hyperaemia. When the pulp becomes more severely inflamed, thermal stimulus will produce pain even after termination of stimulus typically for longer duration. This suggests irreversible pulpitis and the pulp is unlikely to recover even after removing caries. In such situations, pulp extirpation and root canal treat-ment are necessary.

Tubular Sclerosis within the Dentin

Tubular sclerosis within the dentin is a process in which minerals are deposited within the lumina of the dentinal tubules. It is also called translucent zone. It represents an area of increased mineral content.

Dentin which has more mineral content than normal dentin is termed as ‘sclerotic dentin’ (Fig. 30.21). Sclerotic dentin formation occurs ahead of the demineralization front of a slowly advancing lesion and may be seen under an old restoration. Sclerotic dentin is usually shiny and dis-coloured but feels hard to the explorer’s tip (Fig. 30.20).

More intense caries activity results in bacterial invasion of the dentin. The infected dentin contains a wide variety of pathogenic materials, including high levels of acids, hydrolytic enzymes, bacteria and bacterial cellular debris. This material can cause degeneration and death of the odontoblasts as well as mild inflammation of the pulp. These dead empty tubules are termed as ‘dead tracts’.

The pulp may be irritated sufficiently from high acid levels or bacterial enzyme production to cause the formation of replacement odontoblasts (secondary odontoblasts).

Reactionary Dentin (Reparative Dentin)

Reactionary dentin is a layer of dentin formed at the interference between the dentin and pulp. It is formed in response to stimulus acting further peripherally and its distribution is limited to the area beneath the stimulus. It provides extra protection for the odontoblasts and other cells of the pulp by increasing the distance between them and the injurious stimulus (Figs 30.22A, B).

These cells produce repairable dentin (reactionary dentin) on affected portion of the pulpal wall. Reparative dentin is very effective barrier to diffusion of material through the tubules and is an important step in dentin repair. The success of dentinal reparative responses, either by remineralization of intertubular dentin and opposition of peritubular dentin or by reparative dentin, depends on the severity of caries attack and ability of the pulp to respond. The blood supply of the pulp could be the most important limiting factor to the pulpal responses.

Inflammation of Pulp

The third level of dentinal response is severe irritation, like Acute and rapidly advancing caries with very high levels of acid production, overpowers dentinal responses and results in infection, abscess and death of the pulp. The inflammation of the pulp is called pulpitis. It may be acute or chronic, and it is the vascular response of the pulp tissue to injury.

Zones of Dentinal Caries

Zone 1: Normal dentin. The deepest area is normal dentin, which has tubules with odontoblastic process

FIGURE 30-21 Sclerosis dentin.



that are smooth and no crystals are in the lumen. There are no bacteria in the tubules. Stimulation of dentin by osmotic gradient (from applied sucrose or salt), a bur, a dragging instrument or desiccation from heat or air, produces a sharp pain.

Zone 2: Subtransparent dentin (zone of deminer-alization). Subtransparent zone is seen next to normal dentin. This is the zone of demineralization of the inter-tubular dentin and initial formation of very fine crystals in the tubular lumen at the advancing front. There are no bacterial area found in this zone also. The dentin in this zone is capable of remineralization.

Zone 3: Transparent dentin. This zone of carious dentin is softer than normal dentin and shows further loss of mineral from the intertubular dentin. No bacteria are present in this zone either. Stimulation of this region produces pain. Collagen (organic) content of the dentin is intact, which serves as a template for remineralization

of the intertubular dentin. Thus, this region remains capable of self-repair provided the pulp remains vital.

Zone 4: Turbid dentin. Turbid dentin is the zone of bacterial invasion and is marked by widening and dis-tortion of the dentinal tubules, which are filled with bacteria. Less mineral is present in this zone and colla-gen in this zone will not self-repair. This zone cannot be remineralized and must be removed before restoration.

Zone 5: Infected dentin. The outermost zone, pro-tected dentin, consists of decomposed dentin that is teem-ing with bacteria. There is no recognizable structure to the dentin, and collagen and mineral seem to be absent. Removal of infected dentin is essential to sound, suc-cessful restorative procedures as well as prevention of spreading the infection.

Advanced Carious Lesions

Caries advancement in dentin proceeds through three changes:

I. Weak organic acid demineralizes the dentin II. The organic material of the dentin, particularly col-

lagen, degenerates and dissolves III. The loss of structural integrity is followed by inva-

sion of bacteria.

Increasing frequent demineralization of the body of the enamel lesion over a period of time results in weak-ening and eventual collapse of the surface covering. This results in cavitation and provides an even more protec-tive and retentive zone for the cariogenic plaque, thus helps in accelerating the caries progression.

Affected Dentin: This is softened, demineralised dentin that is not yet invaded by bacteria (zones 2 and 3). It is vital and no need to remove this dentin as it can be repaired.

Infected Dentin: This is both softened and contami-nated with bacteria and dead (zones 4 and 5). It includes the superficial granular necrotic tissue, soft dry and leathery dentin.

The zone of decomposed dentin (outer carious dentin) is soft infected dentin, which cannot be remineralized and must be removed during cavity preparation. There is evi-dence that collagen fibres in the outer layer are irrevers-ibly denatured. In the outer carious dentin, the crosslinks decrease markedly and these biochemical findings sug-gest that remineralization can occur only in the inner carious dentin where the collagen denaturation is revers-ible depending on pH. Collagen fibres are believed to be important in the remineralization of carious dentin.

The inner layer of carious dentin although partially sof-tened by demineralization contains only few bacteria, and should be preserved, because it can be remineralized.

FIGURE 30-22 Reactionary dentin.

A

B

Crack (artefact) Primary dentin

Secondary dentin

Pulp tissue

Reactive dentin


335DENTAL CARIES

ROOT CARIES

Recession of gingival margin is an inevitable reason for poor oral hygiene and loss of periodontal attachment, with age. Gingival recession is a prerequisite for expo-sure of a root surface. It is commonly seen in older peo-ple. Bacteria seem to penetrate into the tissue at an earlier stage in root caries than in coronal caries. The cemento-enamel junction is highly irregular and repre-sents a particular bacterial retention site and majority of root caries lesions develops at this site. It is claimed that root surface caries may occur within a deep periodontal pocket and lesion may be hidden in the pocket. Like enamel lesions, root surface caries lesions may be classi-fied as active or arrested. Root lesions are very vulnera-ble to mechanical damage and probing should be avoided. Early diagnosis of such lesions is important because active lesions may become arrested following improved plaque control, use of fluoride toothpaste, and care with diet.

Risk Factors for Root Caries

The integrity of the periodontium as age advances, on account of degenerative changes, starts declining. And also the efficiency of the oral hygiene exercise by the older people is poor. There are drastic changes in the salivary composition and flow rate this, in turn, affect natural cleansing effect and protective properties of the saliva. This, sometimes, may get influenced and precipitated by medication due to chronic systemic illnesses in older people. Hence all these factors might act as a risk factors directly or indirectly contributing for development of root caries in older people.

The risk factors for root caries are:

1. Age2. Gender3. Fluoride exposure4. Systemic illness5. Medication6. Oral hygiene7. Diet8. Salivary changes.

MICROBIOLOGY OF DENTAL CARIES

Cariogenic Bacteria

Importance of bacteria for the initiation of dental caries was proved in animal experiment by Orland and colleagues in 1954. This was clearly demonstrated that germ free

rats did not develop caries when fed cariogenic diet. The transmissible nature of the disease in humans was dem-onstrated by the experiments of Keye’s, who showed that previously caries inactive hamsters developed caries after contact with caries active animals.

Acidogenic (acid producing) bacteria along with met-abolic acids must be present to develop caries. Dental plaque fulfills both of these functions. Of the 200–300 spe-cies of microorganisms inhabited in the plaque, the great majority are not directly involved in the caries process. Two bacterial genera of special interest in cariogenesis are: (i) mutans streptococci, and (ii) lactobacilli.

Mutans streptococci and caries. The mutans strepto-cocci (MS) are a group of bacterial species previously con-sidered to be serotypes of the single species, Streptococcus mutans.

Main reasons for Streptococcus mutans (MS) to be con-sidered as a causative agent for dental caries are:

1. Ability to stick to tooth surfaces and production of abundant quantity of insoluble extracellular poly-saccharides from sucrose

2. Their ability to produce organic acid (lactic acid) from a number of sugar substrates

3. Ability to resist aciduric and acidogenic environment because of phosphoenolpyruvate- phosphotrans-ferase mechanism

4. Production of intracellular polysaccharide, which acts as a reserve substrate for bacteria.

These cariogenic features help MS to survive even in an unfriendly environment under the condition with or without sugar substrate, i.e. during the cycles of either very low concentration of sugars (between meals) through to periods of excessive concentration of sugars. The by-products of metabolism of sugars, acids are pumped out of the bacterial cells into plaque fluids. The damage caused by MS is mainly due to lactic acid although other acids such as butyric and propionic present within the plaque. Thus, S. mutans is the most common of the human MS and has the greatest evidence implicating it as the most virulent odontopathogen in the aetiology of dental caries.

Other Microbial Agents Responsible for Caries

1. Streptococcus sobrinus: It differs from S. mutans in that it requires sucrose for attachment and growth in the plaque. It differs from S. mutans in that it lacks the adhesin required for sucrose-independent attachment and therefore only accumulates on smooth surfaces in the presence of sucrose rich diet.



2. Lactobacilli: Lactobacillus helps in progression of dental caries and it is aciduric and acidogenic in nature. It is considered as essential acidogenic bacteria causing caries. Lactobacillus species have been shown that their numbers are so low so as to be incapable of producing range of pH values required for caries initiation. They have been shown to colonize white spot lesions before cavitation. Thus, as a general rule, they have been asso-ciated in lesion development. They are also found in greater numbers in the more advanced smooth surface lesions. This is seen following irradiation for head and neck cancers, wherein extensive, multiple carious lesions develop rapidly because of destruction of the salivary glands. During the initial phases of the development of carious lesions, more number of S. mutans appear, only to decrease in number as Lactobacillus population increases. Thus, S. mutans are implicated in the initiation of the lesion and Lactobacillus (specifically L. casei) associated with progression. Other bacteria particularly Actinomyces (A. odontolyticus) have also been associated with lesion progression including root surface caries.

MECHANISM OF ADHERENCE OF MICROORGANISMS TO TOOTH SURFACE

Adherence by S. mutans to the tooth surface is necessary both before and after colonization. At first bacteria must have to establish a strong foothold on the tooth surface and maintain their positions while continuing to colo-nize in protected areas provided by the interproximal space along the gingiva or in the regions of pit and fis-sures. Otherwise, they would be swept away by the sali-vary flow.

Mutans streptococci are able to attach to the tooth surface by two mechanisms:

i. Sucrose-independent adsorption: In this, the bacteria attach to the acquired pellicle through specific extra-cellular proteins (adhering) located on the fimbriae of these organisms.

ii. Sucrose-dependent mechanisms: In this bacteria require the presence of sucrose to produce sticky extracel-lular polysaccharides or glucans, which allow attachment and accumulation.

Sucrose is a disaccharide sugar, consisting of one glu-cose and fructose unit (referred to as moieties) joined by a disaccharide bond. Streptococcus sobrinus differs from S. mutans in that it lacks the adhesion required for sucrose-independent attachment, and therefore it accumulates only on smooth surfaces in the presence of diet with

sucrose. Thus, the presence of insoluble glucans is an important factor in establishing the presence and viru-lence of an organism. One of the key enzymes in conver-sion of glucose moiety of sucrose to glucan is glucosyltransferase. Sometimes the enzyme may be altered resulting in the production of soluble glucan that does not support adherence to the tooth surface. These mutant strains lacking the insoluble glucan are usually non-cariogenic.

The effect of sucrose dependency for production of glucans is seen in several clinical conditions. Children who consume little or no sucrose, because of sucrose or fructose enzyme deficiencies, have a less cariogenic plaque. Similarly those individuals receiving long-term nourishment via stomach tube have less plaque and very fewer S. mutans. The individuals restricting their sucrose intake have a decreased proportion of S. mutans in the plaque. However, S. mutans number increases when sucrose is re-introduced into the diet. At the same time, sugar restriction has an influence to reduce the acido-genicity of dental plaque. And also S. mutans decrease in number, as teeth are lost throughout life and particularly disappear following full mouth extraction.

FORMATION OF PLAQUE

The initial colonization of microorganisms on the tooth surface probably begins with organisms other than Streptococcus mutans. The mechanism of initial coloniza-tion includes (Fig. 30.23):

1. Adherence of bacteria to pellicle or the enamel surface

2. Adhesion between bacteria of the same or different species

3. Subsequent growth of bacteria from small enamel defects and from cells initially attached to the tooth surface.

The plaque formation continues with the formation of extracellular polysaccharide chains via the breakdown of sucrose to glucose and fructose. The chains of glu-cose are called glucans and those of fructose are called fructans. These extracellular polysaccharides are sticky, gelatinous substances that further enhance the bacterial ability to adhere to the tooth and to each other. They also affect the rate at which saliva can enter the plaque to buffer the acids and reverse the demineralization proc-ess. This leads to further accumulation of acids at the tooth-plaque interface and when sufficient amount of acids are produced, there will be a drop in pH of plaque to critical level.


337DENTAL CARIES

The quantity of plaque that forms on clean tooth sur-faces during a given time represents the net result of interactions among aetiologic factors, many internal and external risk factors, and protective factors:

1. The total oral bacterial population2. The quantity of the oral bacterial flora3. The anatomy and surface morphology of the dentition4. The wettability and surface tension of the tooth

surfaces5. The salivary secretion rate and other properties of

saliva6. The intake of fermentable carbohydrates7. The mobility of the tongue and lips8. The exposure to chewing forces and abrasion from

foods9. The eruption stage of the teeth10. The degree of gingival inflammation and volume of

gingival exudate 11. The individual oral hygiene habits 12. The use of fluorides and other preventive products,

such as chemical plaque control agents.

ROLE OF SALIVA IN DENTAL CARIES

Biological Role of Saliva

Saliva is also called ‘liquid enamel’ as it is a rich source of various minerals. Its pH is in the range of 6.9–7.2.

The composition of saliva and velocity of the salivary film can play a significant role in maintaining the integrity of the tooth tissues as teeth are bathed in saliva (direct contact) constantly. Saliva has many functions: cleansing effect, buffering capacity, providing an environment saturated with calcium and phosphate and antibacterial action. These properties and characteristics of saliva influ-ence either progression or halting of carious process. However important role saliva may play in dental caries, it is not a prerequisite for caries initiation in the same sense that microorganisms, substrate (sucrose) and tooth (host) are essential (Fig. 30.24).

Saliva-acquired components in the pellicle include cystatins, histatins, lysozyme, amylase, lactoferrin, lac-toperoxidase, secretory immunoglobulin A and bacteria derived glucosyl transferase (GTF). These saliva-derived components attempt to negate deleterious by products of bacterial metabolism in the dental biofilm.

1. The buffering effect of saliva is based mainly on bicarbonate, carbonic acid and phosphate buffer systems.

2. Lysozyme, a hydrolytic enzyme, lactoperoxidase, hemoprotein enzyme are present in saliva which play a role in the prevention of bacterial colonization on tooth surface.

3. Lysozyme disrupts bacterial cell wall and leads to bacteriolysis. Lactoferrin binds iron, sequestering iron away from bacteria and inhibits bacterial growth by both iron dependent and independent mechanisms.

Bacteria

Receptor on enamal surface

Enamelsurface

Tooth Flora

Saliva

Flow rate

Buffering capacity

Substrate

pH

Com

position

Caries

SalivaSaliva

FIGURE 30-23 Mechanism of initial colonization of plaque.

FIGURE 30-24 Diagrammatic representation of important role of saliva with other primary factors in caries aetiology.



Iron is an essential element for bacterial metabolism. Lactoperoxidase inhibits glucose metabolism. This peroxidase protects salivary glycoprotein from degra-dation due to bacteria.

4. Several of the proteins like statherin, protein rich glycoprotein bind to and protect hydroxyapapatite. (HAP). These proteins also promote supersaturation of calcium phosphate ions in the fluid phase of the dental biofilm.

5. The most prominent antibody found in the saliva is the SIgA, which reflects the lifetime caries experience of the individual and may not have a protective function.

6. Rapid flow of highly buffered, mobile saliva reduces the fall in plaque pH. Thus less caries is associated with the rapid flow of saliva.

7. Low viscosity is also associated with low caries activ-ity due to rapid clearance of sugar from the oral cavity.

Buffering Power of Saliva

Diffusion of inorganic buffers from the saliva into the dental plaque plays an important part in reducing the effect of acids produced by the bacteria. Bicarbonates are the most important buffers of saliva. Phosphates also play some part. Proteins can be disregarded as buffers. Buffers work by converting any highly ionized acids or alkalis, which tend to alter the pH of the solution into more weakly ionized substance. Bicarbonates release the weak carbonic acid when an acid is added and since this acid is rapidly decomposed into water and carbon dioxide, which leave the solution. The result is not the accumula-tion of a weaker acid but complete removal of acid.

Despite these buffering systems, it is clear that acid formation potential of plaque is such that, when con-fronted with sufficient fermentable carbohydrate, the buffers are overcome within minutes. The damage done to the tooth surface is caused by the intense localized production of acids by bacteria, which breakdown the buffers and lead to dissolution of tooth minerals.

Saliva contains considerable amounts of calcium and phosphate and is nearly always supersaturated with respect to enamel mineral and other biological appetites. In parotid secretion, both pH and calcium concentration increase with increasing flow rate, so that the ion activity product increases with increasing flow rate. Most impor-tantly, unstimulated whole saliva is supersaturated with respect to hydroxyapatite and the level increases when the flow rate is stimulated. It is clear that enamel mineral does not dissolve in saliva under normal conditions, pro-vided it is not acidified with dietary, gastric or medicinal acids.

When a relatively soluble calcium phosphate mineral dissolves and equilibrium is attained with that mineral, the solution is often then supersaturated with respect to a less soluble calcium phosphate, which tends to precipitate if suitable site is present. If under the influence of plaque-cariogenic activity, a small amount of high carbonate, low fluoride mineral of enamel dissolves then the enamel fluid at that site will be supersaturated with respect to low carbonate and/or high fluoride hydroxyapatite.

It is likely that hydroxyapatite crystals in the developing lesion will only be partly dissolved, and it may attempt to regrow using the remains of the original crystal as a template. Thus, the repaired section will contain less car-bonate and will be less soluble and therefore much more resistant to future dissolution events. At the same time, fluoride ions in solution (from the saliva) are likely to be incorporated so that repaired section will be not only lower in carbonate but richer in fluoride.

CONCLUSION

Dental caries is a multifactorial disease of bacterial ori-gin. For caries to occur, three factors must be present simultaneously along with time factor. They are suscep-tible tooth surface, cariogenic bacteria, and sucrose con-taining dietary factors. Caries is an infectious disease caused by cariogenic plaque formation on the tooth which causes demineralization of the tooth. Saliva is very important in the caries process. The protective mechanisms of saliva include buffering actions, antimi-crobial actions and remineralization. The development of carious lesion depends on structural factors of the tooth and also environmental factors. Thus, the mecha-nism of caries process is relatively complex either in the enamel, dentin or cementum.

REVIEW QUESTIONS

1. Define dental caries and discuss the early theories of caries aetiology.

2. Classify dental caries. Discuss each type of dental caries.3. Discuss the role of plaque in dental caries.4. Discuss the role of microbial agents responsible for

caries.5. Write short notes on:

a. Keyes circleb. Root cariesc. Buffering capacity of salivad. Rampant cariese. Nursing cariesf. Radiation cariesg. Hidden cariesh. Microbial flora of cariogenic plaque


339DENTAL CARIES

REFERENCES

1. Artrun J, Thylstrup A. Clinical and scanning electron micro-scopic study of surface changes of incipient enamel caries lesions after debonding. Scand J Dent Res 94: 193–210, 1986.

2. Caravalho JC, Ekstrand KR, Thylstrup A. Dental plaque and caries on occlusal surfaces of first permanent molars in relation to stage of eruption. J Dent Res 68: 773–9, 1989.

3. Daculci G, Legerous KZ, Jean A, Kerbel B. Possible physico-chemical process in human dentin caries. J Dent Res 66: 1356–9, 1987.

4. Fejerskov O, Baelum V, Ostergaard ES. Root caries in Scandinavia in the 1980 and future trend to be expected in dental caries experience in adults. Adv Dent Res 7: 4–14, 1993.

5. Holmen L, Thylstrup A, Ogaard B, Kragh F. A scanning electron microscopic study of progressive stages of enamel caries in vivo. Caries Res 19: 355–67, 1985.

6. Johnson NW. Some aspects of the ultra structure of early human enamel caries seen with the electron microscope. Arch Oral Biol 12: 1505–21, 1967.

7. Larsen MJ, Fejerskov O. Chemical and structural challenges in remineralization of the dental enamel lesions. Scan J Dent Res 97: 285–96, 1989.

8. Nyvad B, Fejerskov O. Active and inactive root surface caries—structural entities? In Thylstrup A, Leach SA, Qvist V (eds). Dentine and Dentin Reactions in the Oral Cavity. IRL Press, Oxford 165–79, 1987.

9. Thylstrup A, Fejerskov O. Textbook of Clinical Cariology (2nd edn). Munksgaard, Copenhagen, 1994.


textbook of preventive and community dentistry, 2/e

Health & Medicine