Dentistry dates back to as far as 5000 BC when the thinking was that the cause of dental caries was a “tooth worm.” The term “dental caries” first reported in the literature approximately around 1634, and it originates from the Latin word “caries,” which stands for decay. The term was initially used to describe holes in the teeth. Dental caries is reported to be one of the oldest and most common diseases found in humans. Dental caries is a prevalent chronic infectious, transmissible disease resulting from tooth-adherent specific bacteria, primarily Streptococcus mutans that metabolize sugars to produce acid, which over time, demineralizes tooth structure.
Dental caries is a multifactorial disease, dynamics of which depend on various factors predominantly on the presence of fermentable sugar, host factors, presence of cariogenic microbial flora, and other associated environmental factors. In the context of dental caries, researchers have proposed numerous theories. One such theory, proposed by W.D Miller in 1881, and is accepted universally with modification, is “chemo-parasitic theory.” This theory explains the combined effect of acid and acid-producing bacteria in the oral cavity. Considering this theory as the backbone, several models have been proposed to discuss the possible etiology of dental caries such as J.L Williams concept of dental plaque-causing dental caries, Keyes and Fitzgerald model to explain the potential causal relationship of presence of specific microorganism like streptococci, lactobacilli in dental plaque and incidence of dental caries.
After summarizing all the observations, the etiology of dental caries can be explained by a simple Venn’s diagram, which consists of three circles and the interaction of these circles. Two circles depict diet, dental plaque, or microbial load, and the third one depicts the host. The intersection of all these three circles represents caries. Recently, a fourth circle “time” has been added, which describes the duration of the interaction of the above circles. Plaque and dietary factors are interdependent upon each other in the causation of dental caries. In contrast, the third circle, which represents host, acts as a platform for the interaction of these factors.  Specific microorganisms are associated with the initiation and progressions of dental caries. Streptococcus mutans (S. mutans) primarily has links with dental caries initiation, and Lactobacilli has links with the progression of dental caries. The substrates for these bacteria are fermentable carbohydrates and the bacterial-generated carbohydrate reserve in the biofilm.
As the bacteria metabolize these substrates, they form lactic and other acids. Formation of lactic acid, along with host factors, lowers down the oxygen coefficient locally, which fosters the rate and progression of dental caries. Repeated cycles of acid generation result in the microscopic dissolution of calcified tissue in tooth and eventually into cavitation. Studies have shown that enamel demineralization occurs at a pH of 5.5 and below.
Dental caries is a widely prevalent disease problem globally. According to a recent survey by Global Oral Health Data Bank, the prevalence of dental caries varies in the range of 49% to 83%. Irrespective of the age, dental caries negatively impacts almost all the age groups. Data gathered from various surveys have shown that adolescents aged 12 to 19 years had the highest number of dental caries followed by children and then adults. Infants are prone to “rampant caries” or “nursing bottle caries” that affects primarily one or more decayed teeth in any primary tooth between the period of birth and 71 months of age.
The initial source of S. mutans in infants is usually from the mother, most likely via free-floating organisms in saliva. Most studies indicate that infants become colonized before the eruption of the first primary tooth. Infants with mothers who have high levels of S. mutans have a greater risk of acquiring S. mutans earlier than children whose mothers have low levels. Horizontal transmission also occurs.
Dental biofilm is an aggregate of microorganisms in which cells adhere to each other and/or to a surface. This aggregate of cells is encapsulated in a self-produced organic matrix of polysaccharides, proteins, and DNA. The significance of the dental biofilm is that it enhances the cariogenicity of acid-producing bacteria by protecting these bacteria from host defense.
The oral cavity is a unique microbiological habitat; it allows for distinct ecological niches. There are shedding surfaces (soft tissue), non-shedding surfaces (teeth), saliva, and others; each of these is a separate ecological niche. Colonization of these locations is dependent upon the characteristics of the specific organism and microbiological niche. The saliva is a medium for free-floating or planktonic bacteria.
A carious tissue consists of four different zones histologically, among which three zones are visible clinically. The outer layer consists of the necrotic zone and contaminated zone containing microbial biofilm, which can be appreciated clinically as soft mineralized tissue of the tooth. This necrotic zone has a very high microbial load in the range of 10to 10per milligram. The next zone is the zone of demineralization characterized by very few microorganisms, minimal nutrients, and anaerobic atmosphere. This zone can be correlated clinically as leathery dentine. Finally, the innermost zone located near the pulp is the translucent zone of firm softer dentine. Demineralization and the absence of microorganisms characterize this zone because microbial flora cannot penetrate till this depth.
History: The patients with dental caries present with various symptoms depending on the extent of carious involvement. For the initial lesion, which represents a white spot on the tooth surface, the patients complain of a surface discoloration on the particular teeth. Some of the patients present with food lodged in the area affected, which may be due to cavitation of the tooth. If caries has progressed close to the pulp, the patients may report with complain of pain. The severity of pain may differ based on the stage of involvement, extent, loss of hard structure, and host reparative response.
Physical: The most common method used for physical evaluation of dental caries is the use of dental mouth mirror and explorer. If there is a presence of a “catch” on the tooth surface along with the loss of some tooth structure, caries may be suspected.
Evaluation of dental caries involves the use of various techniques like visual-tactile method, radiographs, chemical methods that include the use of caries detecting dyes, and most recent techniques like the use of fiberoptic illumination (FOTI), digital fiberoptic illumination (DIFOTI) and electric caries monitor. The most common and easiest method is the conventional visual-tactile method in which the examiner uses a dental mouth mirror and straight explorer along with clinical judgment. To detect caries radiographically, several radiographic techniques are effective, such as intraoral periapical radiograph, bitewing radiograph for occluso-proximal caries, and radiovisiography, based on the density of sound and carious hard tooth structure. Digital techniques include fiber-optic transillumination (FOTI), digital imaging fiber-optic transillumination (DIFOTI), which works on the principle of optical transillumination. Chemical methods include the use of various dyes that are used to stain the collagenous part of the carious tooth structure, thereby delineating affected and non affected tooth structure. The most recent method is a caries meter, based on the principle that as the carious process progress, there is an increase in pore volume and porosity at the microstructure level, which increases the electrical conductance.
Management of carious lesions depends on the extent, severity, and stage of dental caries. If the lesion is in the initial stage and remineralization is possible, preventive treatment should be considered, such as the application of fluoride gel, varnishes and pit, and fissure sealant. If caries has a marked involvement of hard tissues but is asymptomatic with no pulpal involvement, caries excavation and restoration of the involved tooth surfaces is an option with the different restorative materials based on location in the dental arch. For example, if the carious lesion is in the esthetic segment, tooth-colored restoration should be done. If it is in the posterior portion where it has to bear the heavy masticatory load, restoration can use silver amalgam. If the lesion is active and has involved both enamel and dentin with a close approximation to pulpal tissue, indirect pulp capping is optimal. If the lesion is progressive and has involved the enamel, dentin, and pulpal tissue, root canal treatment merits consideration, followed by extra-coronal restoration.
Differential diagnosis of dental caries includes dental fluorosis, developmental disorders encompassing hypomineralization and hypoplasia of the tooth, white spot lesion or periapical pathology, and pigmented lesion of the tooth.
A malignant tumor of the salivary gland often requires surgical treatment. Surgery could involve removing a portion and/or the entire major salivary gland; this reduces salivary flow and may increase the risk of dental caries, as saliva serves the purpose of flushing the oral cavity and also imparts host immunity.
Radiation therapy affects the tissues of oral tissues in several manners. The early changes following radiation therapy include mucositis, atrophy, and thinning of the oral mucosa, fibrotic changes, and taste disorders following atrophy of taste buds. The significant changes involve radiation caries. The term “radiation caries” represents a severe form of rampant caries. Dental caries following radiation therapy mostly results from hyposalivation, which is due to fibrotic changes in major salivary glands. Most characteristic features of radiation caries are the involvement of tooth at gum level and cusp tip in contrast to normal cavitation, which mostly affects smooth surfaces. The rate of progression of radiation caries is much faster than normal cavitation.
Dental caries have received extensive study. Several studies have sought to find the initiating cause and halt the process. Recently, more sophisticated studies like genomic studies, molecular dynamics studies of polysaccharide carriers based on starch in dental caries, an association of risk factors of dental caries, and polymorphism of the MBL2 gene in S. mutans and human clinical trials on dental caries vaccine are a focus of current research. The most recent study looked at bisphenol A glycidyl methacrylate (bis-GMA), which is released into the oral environment from leaching of dental composite and can lead to secondary caries at a margin of restoration.
Treatment planning for a disease to be treated is a step by step process of decision making or formation of a protocol. Levels of prevention can classify treatment for dental caries. A widely used taxonomy of prevention describes primary, secondary, and tertiary prevention. These terms can be applied to the disease process of dental caries and can help providers to understand where in the process, they can intervene and how they can do so. Primary prevention is the prevention of the disease process before it begins. Primary prevention would encompass assessing the risk for dental caries and instituting efforts to decrease or remove that risk. Secondary prevention refers to detecting the presence of the disease early in the disease process and intervening to prevent further development of the disease. For the dentist, this would involve recognizing the signs of the early stages of dental caries, intervening, or referring for intervention. Tertiary prevention refers to alleviating the effects of the disease and lies primarily within the surgical realm of the dental professional in rehabilitating the damaged tooth. For proper treatment, the International Caries Classification and Management System (ICCMS) has been given, which is a set of clinical protocols such as diagnostic, preventive, and restorative decisions that are necessary to rebuild and restore the tooth structure only when necessary.
To decide on the treatment of any particular disease, knowledge of the progression and staging of the disease plays an important role. To decide whether or not to intervene in a specific stage in the progress of dental caries, the dentist should know the course of the disease. Various systems have been introduced to determine the stage of dental caries. The most common is the International Caries Detection and Assessment System (ICDAS), and it is associated with the International Caries Classification and Management System (ICCMS). ICDAS describes and classifies dental caries based on their clinical visual appearance, and it integrates with ICCMS to plan, manage, and review caries. There are various keystones which have been given by ICCMS. The first keystone describes the caries staging and lesion activity based on whether the lesion is active or inactive. The second keystone includes assessment of the patient’s caries risk status at the lesion level and patient level. The third keystone provides for the synthesis of all the risk factors and arriving at the diagnosis. The fourth keystone includes a comprehensive caries care plan based on whether the lesion is progressive or not. According to the risk factor category of low, moderate, and high, and if the sound tooth structure is present, risk factor management and prevention strategies apply. The initial stage considers non-operative treatment. If the lesion falls under the active category or extensive caries category, the clinician can consider a tooth preserving operative treatment. The last keystone by ICCMS advocates continuous recall, monitoring, and review of the patients and measurement of the outcomes.
Dental caries prognosis depends on the health of the patient, maintenance of oral hygiene, and the extent and severity of dental caries. If the individual reports with early signs of dental caries, a lesion may be reversed with a preventive method and minor dental intervention like remineralization of the initial lesion. If dental caries progresses to the moderate stage with loss of specific tooth structure, the tooth must be filled and rebuilt. Prognosis is also crucial for decision making regarding whether ordinary restoration or extensive restorative treatment should take place. Extensive restoration should not occur when there is a chance that prognosis will be poor for salvaging the tooth.
If dental caries is left untreated for a more extended period, it may lead to several complications based on the nature of the carious lesion. Starting from the small inactive white spot lesion, it may lead to osteomyelitis. Dental caries course through various stages, and its progression depends upon the host response and chronicity of the lesion. If the host immune response is weak, dental caries may result in inflammation of pulp leading to apical periodontitis, periapical abscess or periapical granuloma, periapical cyst, cellulitis, abscess, periostitis and may progress to osteomyelitis.
As prevention strategies of dental caries may have a relevant impact on avoiding further development of dental caries after restoration, several factors should be considered before implementation of preventive or restorative strategies like past caries experience, oral hygiene status, calculus deposits, and snacking level salivary flow.
Meticulous maintenance of oral hygiene: As dental caries cannot progress without the presence of microorganisms present in dental plaque, daily removal of dental plaque through tooth brushing and flossing is considered to be the best preventive method.
Topical fluoride application: Fluoride inhibits dental caries by inhibiting demineralization and enhancing remineralization of tooth structure by the formation of acid-resistant fluorapatite crystal. Various methods that incorporate fluoride in daily life include fluoridated water supply, use of fluoridated toothpaste, use fluoridated mouth rinse, and application of different professional fluoride gels and varnishes.
Application of pit and fissure sealants: Pits and fissures pose non-cleansable morphology and hence are the most susceptible site for the initial development of caries. Application of the pit and fissure sealants leads to the formation of a mechanical barrier that leads to deprivation of nutrition for underlying microbes and hence halts the progression of dental caries.
Xylitol: The main dietary culprit in the formation of dental caries is sucrose. Nowadays, sucrose is getting replaced by xylitol, an artificial sweetener that is not only non-cariogenic but also anti-cariogenic. The possible mechanism of anticariogenicity is the prevention of binding of sucrose to S. mutans and the prevention of adhesion of mutans to each other.
Vaccine: As dental caries is an infectious microbiologic disease, continuous attempts have been made to develop an anti-carious vaccine, but to date, none of the vaccines has appeared successful.
The decline of dental caries has been ascribed to several factors. Among all the factors, patient education plays a key role. The patient-related factors include oral hygiene maintenance, reduction in sugar consumption, effective use of fluorides, and routine oral checkup. Patients should be educated to perform regular tooth brushing with fluoridated toothpaste and dental flossing. As sugar consumption is one of the primary etiological factors for dental caries, it is necessary to evaluate the dietary habits of the patient. Patients should be advised to restrict the consumption of sugar-based snacks and drinks to re-establish the balance between demineralization and remineralization.
An excellent preventative regimen is one that optimizes protective factors and minimizes pathologic factors. It may be helpful to understand that the dental caries process is a continuum, from the first atomic-level of demineralization, through the initial enamel white spot, to eventual cavitation. The dynamic balance between demineralization and remineralization determines the result, whether it is oral health or dental disease. Pathologic factors include inadequate professional dental care, insufficient plaque control, prolonged and frequent carbohydrate intake, reduced salivary flow, and dental defects. The protective factors include dental home care, appropriate mechanical plaque removal, limitation of fermentable carbohydrate exposure, fluoride exposure, and a preventive plan based on caries risk.
Many patients, particularly geriatric patients, often suffer from systemic ailments such as diabetes mellitus, hypertension, osteoporosis, neurodegenerative disorders, respiratory diseases, and rheumatoid arthritis. These ailments compromise the physical and mental ability of the individual, necessitating supportive care from caregivers. Various studies have proven the existence of a strong correlation between general and oral health. These ailments or medications used for the treatment of these ailments may cause caries, and xerostomia (as a side effect of the drug). Thus, the health professionals providing treatment for the systemic conditions affecting the individual should be aware of the impact of these conditions and medications on oral health and should refer the patient to the dentist if required.
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