The Caries Process
Karen Nelson
Saint Petersburg College
June 24, 2012

The Caries Process
The caries process or how a cavity develops in the oral cavity is a complex process and requires several contributing factors to occur. In order to understand the caries process fully we will discuss all of the factors involved. Such factors include: the agent (acidogenic bacteria), the host (the tooth, quality and quantity of saliva, and immune responses) and the environment (the patient’s diet, amount/frequency and kind of food or drink consumed and the intake of fermentable carbohydrates). We will then discuss demineralization and remineralization (the body’s natural repairing of the tooth) and their roles in the caries process. We will also take a look at how caries are diagnosed and detected, what a caries risk assessment is, its factors and how it can be utilized on individual patients for caries prevention. Finally, we will discuss how dental caries is treated at all levels of the caries process.
Caries, also known as tooth decay or cavities, is a bacterial infection transmitted primarily through saliva, leading to the destruction of enamel, cementum and dentin. Although caries is an infectious disease of the teeth, it is more accurate to say caries is caused by a shift in oral micro-flora to caries-causing types in response to acidity resulting from metabolism of sugars. (Higham, 2010) Three major factors contribute to the caries process: food or beverages that are consumed (sugary in content), the bacteria in plaque, and your teeth. The simplest way to think of it is that each time you eat there is an acid attack on your teeth. That’s because plaque, a sticky film of bacteria, constantly forms on your teeth. When you eat or drink foods containing sugars or starches, the bacteria in plaque uses the sugar & starches as fuel to produce acids that attack your tooth enamel. The stickiness of the plaque keeps these acids on your teeth and after many such attacks, the enamel break down and a cavity forms.
Historically, research on caries dates back to 2500 BC where “toothworms” were thought to cause cavities. In 1819, Levei Parmly was the first person to hint at the real cause of the caries process. He proposed, “Decay begins on the surface of the teeth by bacteria growing on food particles which lodge around and between teeth, causing destruction of tooth structure.” (Higham, 2010) With today’s science we have come to learn the complexity of dental caries and the relationship sugar has in the decaying process. Even with today’s science, people still have little education on the true health risks that can result from poor oral hygiene. Caries can affect anyone at any age and knowledge of the caries process enables the hygienist to educate the patient on caries prevention and oral hygiene. It is very important for the dental hygienist to stay current in the research of caries and educate their patients in order to help prevent the process from occurring and/or progressing. The caries process includes four primary contributing factors, the agent, the host, the oral environment and of course time. If all of these factors are off balance the caries process will occur and continue to progress until it is interrupted. The first factor to consider in the caries process is the agent. The agent is composed of bacteria that form a plaque called biofilm. There are many acid-forming bacteria present in the mouth but the primary bacteria that make up the biofilm are Streptococcus mutans, Strepoccus sobrinus and Lactobaccilli. The bacteria begin to form a plaque biofilm in our mouth within hours after birth and transfection continues through life. This layer of biofilm acts as a favorable environment and an anchor for bacterial reproduction due to its ability to create a sticky environment. Bacteria is transferred through our own saliva as well as acquired from others, usually from a mother to her child. Permanent colonization of a child’s teeth with Mutans streptocci can take place soon after tooth eruption. (Wilkins, 2013) The bacteria begin the caries process by adhering to the acquired pellicle almost immediately on a clean enamel surface. The acquired pellicle is an acellular glycoprotein-rich layer that serves as a nutrient source for bacterial growth. As layers form due to uninterrupted plaque formation, the bacteria replicate and form microcolonies. Cell division and recruitment of new bacteria also allows the bacterial population to increase. (Higham, 2010) Microbes in plaque produce acids which lower the pH level in the oral cavity from a neutral 7 to 5.5 or lower. The more acidic the environment is, the less “good bacteria” such as S sanguinis will survive and the more “bad bacteria”, S. Mutans and Lactobaccilli, thrive because they are able to tolerate acid. This causes an imbalance in the relationship of plaque and the tooth, thus producing more acid and favoring demineralization. Demineralization will be discussed further in paragraph seven.
The second factor to consider in the caries process is the host. The host includes the tooth, quantity and quality of saliva, and immune responses. The tissues of the tooth affected by the agent are enamel, dentin, cementum, and the pulp if the caries process is successful. The host usually acts to protect against caries attacks but can also contribute to the progression of decay under unfavorable conditions. When these elements are exposed to acids, demineralization or the reduction of mineral content occurs. This is when the carbohydrate hydroxyapation crystals lose calcium and phosphate ions causing the crystalline structure to shrink in size allowing crystalline spaces or pores to enlarge. Post eruptive teeth are found to have reduced mineral content and over time will complete post-eruptive maturation. Enamel is the first surface affected. Due to the breakdown of ameloblasts in enamel, it is unable to repair itself; therefore once the enamel is destroyed it cannot be restored. The host also includes saliva.
Saliva plays a major role in the reducing caries risk. The properties of saliva maintain balance in the oral cavity by cleansing the mouth of food and debris as well as removing organic acids from plaque. Saliva contains electrolytes and organic molecules that help minimize the dropping of pH levels. Saliva acts to buffer acids produced in the mouth and supplies minerals to the tooth replacing calcium and phosphate lost during demineralization and ultimately creating an environment that favors remineralization. A protein found in saliva called sialin acts to increase the pH to neutral levels. Other protecting elements found in saliva are mucins, proteins that trap and clear bacteria from the mouth and amylases, enzymes that break down food particles that stick to the teeth. If very little saliva is produced, the host is more susceptible to decay. The primary immunoglobulin found in saliva is Secretory IgA. A dimeric molecule, IgA, is secreted from the minor salivary glands adjacent to the teeth. A major immunoglobulin, IgG, is predominately in human serum, or blood and is strong in complement-activating and opsonizing that can lead to antibody-mediated phagocytosis. (Higham, 2011)
The oral environment also plays a major role in the caries process. The factors that influence the oral environment are the patient’s diet, amount, frequency and kind of food or drink consumed and the intake of fermentable carbohydrates. Fermentable carbohydrates are disaccharides or sugars such as glucose and sucrose that are metabolized by microorganisms to produce lactic acid, causing them to be the most cariogenic. (Higham, 2011) The type of oral environment that contributes to the caries process is an acidic one. It is very important to keep the pH in the oral cavity at a level around 6 or 7 (neutral). Cariogenic foods such as caramels and crackers tend to get stuck in the pits and grooves of the teeth increasing the potential for caries. They create an environment with a consistently low pH due to the length of time the food in retained in the mouth. The food then produces lactic acid, allowing the bacteria to flourish and eat away at the teeth. When the mouths pH falls below a level of 5.5, saliva and dental plaque becomes saturated with acid and demineralization begins.
“Demineralization is the process by which the minerals of the tooth structure are dissolved out by the organic acids produced from the fermentable carbohydrates by the acidogenic bacteria.” (Wilkins, 2013, p. 378) Demineralization is basically the breakdown of the tooth’s enamel. Enamel is the most mineralized structure in the body. The composition of enamel is approximately 95% calcium and phosphate ions. It has a surface that is composed of tiny rod shaped crystals called hydroxyapatites. When the oral cavity is under an acid attack, calcium, phosphate and hydroxyl ions are depleted from saliva and plaque fluids causing the tooth’s hard structures to dissolve. The more frequent the acid attacks the less chance the pH will maintains its neutral level essentially allowing the bacteria to invade the enamel. This eventually creates a chalky white carious subsurface lesion. If the process of demineralization is interrupted by fluoride supplements or a decrease in sucrose intake at this point the process can be reversed. The reversal of demineralization is known as remineralization.
“Remineralization is the body’s natural healing process in which minerals are redeposited in the demineralized tooth structure.” (Wilkins, 2013, p. 378) When the pH is restored to a level above 5.5 the remineralization process can start to occur. The protective factors in saliva, discussed earlier, take over and interfere with the enzymatic requirements of bacteria and essentially repair the tooth surface. If the tooth structure has dissolved beyond the white carious lesion, forming a cavity, the natural process of remineralization cannot restore the tooth to its functional form. In the case where the tooth cannot be restored or repaired naturally, the tooth must be repaired by a dentist. A carious lesion needing repair can be detected during a dental examination by a dentist and/or a hygienist.
Detecting caries used to be when a dental provider discovered a break in the tooth structure creating a hole or cavity in the tooth. The focus was on restoring the holes that were found. Now that we focus on diagnosing dental caries as an infection, a cavity is the end-stage of the infection. (Wilkins, 2013, p. 379) Dental caries are detected much earlier, and can first appear as a white area lesion of subsurface demineralization. At this stage, the tooth can be restored by remineralization as long as the environment is conducive and in favor of remineralization. An increase in fluoride and the actions of ones saliva as well as good oral hygiene practices are all that may be needed to treat the tooth at this stage. The later stage of caries, in which can be detected by running a blunt probe gently over the surface of the tooth can be detected by its slight roughness and beginning breakage. This stage of caries is classified as a non-cavitated lesion. At this point, there is still a chance that remineralization may be effective. Once the carious lesion has become an open cavity it may be visible without exploration or use of instrumentation and may only need gentle blasts of air to be seen. Thhis type of caries is classified as a cavitated lesion defined as a hole that has developed in the tooth that needs to be restored by operative intervention such as a filing. (Higham, 2011)
Another way caries can be detected is by use of radiographs or more commonly known as x-rays. Radiographs can help to determine the extent of the caries into the dentin and/or into the pulp of the tooth. Horizontal bitewing radiographs are most commonly used in detecting proximal caries, caries in between the teeth, while vertical bitewings are primarily used to detect root caries. While it is important to detect caries at the earliest stage possible it is even more important to prevent caries all together. By accomplishing a patient’s caries risk assessment the provider can essentially help the patient reverse and prevent the caries process for occurring now and in the future.
A risk assessment is defined as: “The qualitative or quantitative estimation of adverse effects that may result from exposure to specific hazards or absence of biological influences.” (Hovius, 2011) Risk factors that contribute to a patient’s risk in developing caries are biological, environmental, behavioral and social factors. To determine a patient’s biological risk factors a medical history must be evaluated, identifying past and current diseases, medications and treatments. Certain medications, diseases and treatments can be linked to an increase in caries risk. Some medications can cause the mouth to become dry and many diseases suppress the immune system creating an oral environment in favor of bacteria reproduction. It is also important to identify a patient’s dental health history, such as previous caries, frequency of or sudden onset of dental caries. It is important to ask the patient about their current diet, such has intake and frequency of soda and sugary foods. If the patient frequently sips on soda and eats foods high in sugar their caries risk will be high.
The patient’s current oral health as well as current oral hygiene practices can also help to identify if the patient is at a high risk for dental caries development. Another factor to consider in risk assessment is a person’s social or economic influences or risks. Some people think it is acceptable to but their children to sleep with a bottle because that is how they were taught by their parents, when in fact sleeping with a bottle filled with milk or other sugary substances can be detrimental to a child’s oral health. Some patients come from poverty or a family with poor oral health and do not have access to oral hygiene essentials such as toothbrushes, floss and fluoride. The patient may not understand the importance of good oral hygiene such as brushing and flossing in preventing diseases. The purpose of a caries risk assessment is to help manage caries and prevent future caries, but can also be used to motivate patients to take better care of their oral health. Assessments are also used to help educate patients of the effects of their behaviors on their oral health. Once the provider has established the caries risk assessment they must select a treatment plan.
The most important step in treatment of dental caries is prevention. In most cases, education on proper oral hygiene techniques, nutritional counseling and the use of fluoride can be enough to prevent caries. Drinking water or rinsing after meals can prevent cavities by acting as a buffer to neutralize the harmful acids produced by bacteria. Sealants, a material containing fluoride placed primarily in molars can also be effective. “Based on information obtained from 3 meta-analyses (derived from 27 studies), sealants are effective in preventing the development of caries on sound pit-and-fissure surfaces in children and adolescents.” (Chalmers, 2011) In other cases, restorative treatment may be needed. A dental cleaning can be helpful in reducing the bacterial count in the mouth prior to the placement of a restoration. The first step is to treat the caries as an infectious disease and eliminate as many causative factors as possible. (Wilkins, 2013, p. 383) Restorative treatment includes, removing decay and placing a filling material, such as resin or amalgam into the tooth with marginal seals to lower the bacterial counts in the oral cavity.
The caries process is a complex process that requires several contributing factors to occur such as the agent, the host, and the environment. The oral cavity is in a constant battle of demineralization and remineralization. Educating our patients on proper oral hygiene methods and dietary habits can stop or slow the progression of caries. By assessing the patient’s caries risk and detecting a carious lesion in its early stages we can prevent caries long before they ever need to be treated.

References
Chalmers, N. I. (2011). Application of Sealants Through School-Based Sealant Programs Decreases Dental Caries Prevalence. Journal of Evidence-Based Dental Practice, Volume 11, Issue 1, pages 14-17.
Higham, S. (2010, December 9). Caries Process and Prevention Strategies: The Agent. Retrieved from DentalCare.com.
Higham, S. (2011, January 13). Caries Process and Prevention Strategies: Demineralization/Remineralization. Retrieved from DentalCare.com.
Higham, S. (2011, January 13). Caries Process and Prevention Strategies: The Environment. Retrieved from DentalCare.com.
Higham, S. (2011, January 13). Caries Process and Prevention Strategies: The Host. Retrieved from DentalCare.com.
Hovius, M. (2011, August 19). Procter & Gamble Caries Process and Prevention Strategies: Risk Assessment. Retrieved from DentalCare.com.
Ismail, A. I. (2011, August 19). Caries Process and Prevention Strategies: Diagnosis. Retrieved from DentalCare.com.
Wilkins, E. M. (2013). Clinical Practice of the Dental Hygienist 11th Edition. Philadelphia: Lippincott Williams & Wilkins.