Dental Caries

The word caries (med.), literally means the decay of bones, etc. XVII. — L., ‘rottenness, decay’, and specifically to the tooth, it is being referred to as dental caries.

Dental caries is defined as the localised destruction of susceptical dental hard tissues such as enamel, dentine, cementum by acidic by-products from bacterial fermentation of carbohydrates in the diet. It is a multifactorial disease which begins with microbiological shifts within the complex biofilm (dental plaque) and is affected by salivary flow and composition, exposure to fluoride, consumption of sugars, as well as hygienic practices (brushing and flossing of teeth).

In addition to factors which directly stimulate the formation of dental caries, there are many external personal factors that lead to the compromise in maintenance of oral health, which then causes the creation of dental caries. The personal factors include, sociodemographic status, financial status, dental insurance coverage, accessibility to information about dental caries, attitudes and behaviour towards oral health.

This video illustrates the formation of dental caries on the occlusal (pits and fissures) and the interproximal (near the gingival margin) surfaces of the tooth. The development of caries is also shown to cause the enamel and dentine changes as caries progresses. It also elaborates on the need to brush and floss the teeth, to remove dental plague accumulated from the consumption of sweet foods such as “sugary snacks, soda pop, and sports drinks”. Once oral hygiene is maintained, the formation of dental caries is prevented.

Dental Caries - An Infectious Disease or a Chronic Disease?

Why Classify?

First before we begin, we need to understand the importance of classifying and defining diseases. Why is there a need to classify dental caries into either category of diseases mentioned above? And is the classification of dental caries into infectious or chronic diseases truly going to help us in preventing them?

It is important to note that defining and categorizing diseases and illnesses is at the heart of medical practice. One must admit that the task is an arduous and time consuming one, however once individual diseases are defined, they can be classified, resulting in the creation of conceptual links that are in essence vital for medical practice and the progression of medical knowledge. The identification of the causative microorganisms of specific infections has also allowed for a much better understanding of their epidemiology, which in turn informed prevention strategies.


Next, before we can properly classify dental caries into these categories (or neither) let us find fully comprehend the true definition of both infectious diseases and chronic diseases.

Infectious Disease: An infectious disease is a clinically evident disease resulting from the presence of pathogenic microbial agents, including pathogenic viruses, pathogenic bacteria, fungi, protozoa, multicellular parasites, and aberrant proteins known as prions. These pathogens are able to cause disease in animals and/or plants. Infectious pathologies are usually qualified as contagious diseases (also called communicable diseases) due to their potential of transmission from one person or species to another. [Wikipedia, 2009a]

Chronic Disease: In medicine, a chronic disease is a disease that is long-lasting or recurrent. The term chronic describes the course of the disease, or its rate of onset and development. A chronic course is distinguished from a recurrent course; recurrent diseases relapse repeatedly, with periods of remission in between. As an adjective, chronic can refer to a persistent and lasting medical condition. Chronicity is usually applied to a condition that lasts more than three months. [Wikipedia, 2009b]

Dental Caries – An Infectious Disease?

Firstly lets evaluate the of requisites and theories associated with the epidemiology of infectious diseases and then compare them to the nature of dental caries and how dental caries can be classified as infectious.

Table 1 illustrating why dental caries may be perceived as an infectious disease [Greenstein G & Lamster I, 1997]

·For an infectious disease to occur, it must have a source or reservoir (person, animal, soil).
In dental caries the source may be the mother who transfers the infection to the infant.

·Potential microorganisms may be transferred directly (by people, insects) or indirectly (through water, air or soil).
In dental caries the transfer agent is through saliva of the mother to the infant.

·Pathogens must survive the transfer and successfully establish within the host.
In dental caries, this will take several attempts and only at specified time periods.

·Colonization (multiplication of the organism) may occur without evoking a tissue or immune response.
In dental caries this occurs. Additionally, colonization and bacterial multiplication in dental caries is dependent upon sugar intake and other local factors.

·Infection indicates that colonization has occurred and the disease process has begun as indicated by damage to the tissue.
In dental caries, there is demineralization of the tooth surface.

·The host response will determine if there is a manifestation of the disease (demineralization). If the host response is adequate, the individual may have the infection without the clinical manifestations of the disease. He/she may thus be a carrier, harbouring the infectious agent which can be spread to others.
In dental caries, the carrier would usually be the mother.

The theory of dental caries being ‘infectious and transmittable’ stemmed from the rodent studies completed mainly by Paul H. Keyes in 1960. Caries were found to only develop in the rodents that were caged with or fed with the fecal pellets of various species of caries-active rodents. Further proof later then emerged from a different study conducted by Robert J. Fitzgerald and Paul H. Keyes in 1960 when certain streptococci isolated from caries lesions in hamsters, unlike other types of streptococci, resulted in the widespread decay in formerly caries-inactive animals.

Studies have also shown that the main pathogen in dental caries formation is S.mutans and early acquirement of this bacterium would result in the key risk factor for early childhood caries. Human dental flora is site-specific; and a child is most readily colonized with normal dental flora after the eruption of the primary dentition, which would normally be from 6 to 30 months of age. However, latest studies have highlighted that colonization takes place prior to teeth eruption. [Greenstein G & Lamster I, 1997] Initial infection that may have occurred early in life for some children will result in an increased risk of developing caries and an increased number of tooth surfaces affected. And the chief source of transmission to infants is their very own parents.

Studies have shown that successful colonization of the infant is related to inoculums dose, inoculation frequency and minimum infective dose. Transmission of S. mutans happens in about 60 percent of infants when maternal salivary concentrations are 105 colony-forming units (CFUs) per milliliter of saliva or greater, compared with only 6 percent transmission when the maternal concentrations were 103 CFUs/mL of saliva or less. [García-Godoy F & Hicks MJ., 2008 ]

Dental Caries - Cariology
Fig .1 Streptococcus mutans[Kenneth Todar, 2009]

Horizontal transmission, (which is the spread of an infectious agent from one person or group to another, usually through contact with contaminated material) from family members, friends, and other children also is a means for colonization of infants. This information has led to the health boards of various countries such as the New York Department of Health to issue guidelines which would lead to the decrease in maternal transmission of S. mutans to infants. Some of the practices that were implemented to help reduce maternal transmission of S. mutans include eradicating active caries and promoting fluoride and chlorhexidine use. Saliva-sharing activities (food tasting before feeding infants, toothbrush sharing) were also discouraged and professional oral health examinations by dentists were also encouraged especially for children before their first birthdays.

Dental Caries Not Infectious?

There are however, opponents to the idea that dental caries are an infectious disease. Firstly if bacteria such as the S.mutans strains that have been aforementioned is truly the sole cause of dental caries, a simple dose of antibiotics treatment would be able to reverse the process. However, this is not true. You cannot stop dental caries using antibiotics, people don’t actually build up antibodies against the disease and antibacterial mouthwashes play a minor role in the reduction of its prevalence in an individual. Furthermore, once you get dental caries you do not develop immunity to it and unless your diet is dramatically changed. In addition, if caries is truly an infectious disease, it can also be prevented by vaccination and based on the very fact that it cannot, it is actually not a classical infectious disease.

In fact, it is the confluence factors that include an ecological shift in the tooth-surface biofilm leading to a mineral disparity between plaque fluid and tooth and the net repletion of tooth mineral that causes this disease. Therefore, caries can actually be categorized into a 'complex' or 'multi-factorial' type of disease or a type of ‘non-classical’ form of infectious disease. [García-Godoy F & Hicks MJ., 2008 ]

Dental Caries – A Chronic Disease?

One of the most outstanding features of dental caries is the extensive amount of time it takes to develop and emerge. This is true not only of the individual lesion of caries, but the succession of lesions throughout the dentition as a whole, making caries a lifelong disease in most individuals who do not become edentulous at an early age.

Epidemiological data have also clearly established that caries is a chronic disease. The percentage of the population with clinically demonstrable evidence of caries is very significant, even in early childhood, and increases with their age. These observations are consistent with the concept of continuing, dynamic interactions among varying degrees of multiple risk factors and protective factors throughout the course of individuals’ life spans.

It is important to understand that the caries incidence rate in a group of individuals appears fairly the same through­out life if no special efforts to control lesion progression are carried out. These new paradigms help to explain the nature of lesion initiation and progression and, accordingly, why dental caries cannot truly be “prevented,” but rather “controlled” by a multitude of interventions. At the individual patient level, we have successfully “controlled” the physiologic balance of the intraoral environment with topical fluorides, dietary monitoring, “plaque control,” but the well-trained clinician will understand that some patients require much more and closer monitoring than others to avoid new lesions. The consequence of the paradigms is to appreciate that the risk of developing new lesions is never 0.

Dental caries is also the most common chronic disease of children:

· Aged 6 to 11 years (25%)

· Adolescents aged 12 to 19 years (59%).

· And tooth decay is four times more common than asthma among adolescents aged 14 to 17 years (59% compared with 15%).
[Centers for disease control and prevention, USA , 2009 ]

Dental Caries - Cariology
Fig. 3 Schematic illustration explains why Dental
Caries has to be controlled lifelong if a functional dentition is to be maintained
[García-Godoy F & Hicks MJ., 2008]

Dental caries fit in to the group of common diseases considered as ‘complex’ or ‘multifactorial’ such as cancer, heart diseases, diabetes, and certain psychiatric illnesses, and we have to realise that there is no simple causation pathway. Complex diseases cannot be ascribed to mutations in a single gene or to a single environmental factor. Rather they stem from the combined act of various genes, environmental features, and risk-conferring behaviours. And the prevention of these types of diseases requires the full comprehension of the various factors that might lead to the prevalence of the disease and the concise eradication of those factors.

Dental Caries - Cariology
[Dan Peterson ,2009 ]


Centers for disease control and prevention, USA (2009). Preventing Dental Caries with Community Programs. Retrieved Oct 23, 2009 from

Dan Peterson (2009). Family gentle dental care. Retrieved Oct 23, 2009 from

Fejerskov O. (2004). Changing paradigms in concepts on dental caries: consequences for oral health care. Caries Res;38(3):182-91.

García-Godoy F, Hicks MJ.(2008). Maintaining the integrity of the enamel surface: the role of dental biofilm, saliva and preventive agents in enamel demineralization and remineralization. J Am Dent Assoc;139 Suppl:25S-34S.

Greenstein, G & Lamster, I. (1997). Bactrerial transmission in periodontal disease: A critical review. J Periodontol;68(5):421-31

Kenneth Todar (2009). The Microbial World. Retrieved Oct 23, 2009 from

Stewart RE, Hale KJ. (2003). The paradigm shift in the etiology, prevention, and management of dental caries: its effect on the practice of clinical dentistry J Calif Dent Assoc. 2003 Mar;31(3):247-51.

Wikipedia(2009a). Infectious disease. Retrieved Oct 20, 2009 from

Wikipedia (2009b). Chronic. Retrieved Oct 20, 2009 from


An Introduction | Tooth Anatomy and Histology | Dental Caries | Dental Caries - An Infectious Disease or a Chronic Disease |

Early Caries and Enamel Changes | Caries Progression and Dentine Changes | Pulpo-dentinal Changes

Root Surface Caries and Changes in the Cementum
| Dental Fluorosis | Erosion of the Teeth | Conclusion


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