Dental caries (also known as tooth decay) is a disease characterized by the chronic and progressive destruction of the hard tissues of the teeth, influenced by multiple factors with bacteria as the primary cause. Risk factors for dental caries refer to potential factors that may lead to the development of the disease, also called susceptibility factors or harmful factors. These factors are included in the bacterial, host, and dietary factors that contribute to the onset of dental caries. Since these factors are related to an individual's likelihood of developing dental caries, understanding them is a crucial part of caries prevention efforts.
The widely recognized cariogenic bacteria include: Streptococcus mutans, lactobacilli, and actinomycetes. These cariogenic bacteria exert their effects through cariogenic toxicities such as adhesion, acid production, and acid resistance, leading to the formation of caries.
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Streptococcus mutans group
There are four inherent groups of oral streptococci in the oral cavity, and the Streptococcus mutans group is one of the cariogenic bacterial groups, belonging to the normal oral flora. This bacterial group colonizes the oral cavity of infants between 19 and 31 months after birth (with an average of 26 months), which coincides with the period of primary tooth eruption and primary dentition formation. This period of Streptococcus mutans colonization is referred to as the "window of infectivity". The group produces various cariogenic toxic substances and can cause caries on all tooth surfaces.
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Lactobacillus
Lactobacilli are part of the normal human flora, present in the intestines, vagina, and oral cavity, and are gram-positive bacilli. Their cariogenic effects are manifested by rapid and large-scale acid production, and they can continue to grow and metabolize in an environment with a pH of 3.8. They have poor adhesion ability and often work synergistically with Streptococcus mutans to promote the progression of caries.
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Actinomyces
Actinomycetes are normal oral flora, gram-positive bacilli with polymorphic forms. They can decompose carbohydrates to produce acid, grow under acid conditions, and synthesize heteropolysaccharides. They can cause interproximal and root surface caries and often act in coordination with Streptococcus mutans and lactobacilli.
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Non-Streptococcus mutans
In recent years, attention has also been paid to the cariogenic effects of other acid-producing oral streptococcal species besides Streptococcus mutans.
Bacterial risk factors are characterized by an imbalance in the proportion of plaque flora in the oral cavity, where the number of cariogenic bacteria and their acidic products exceeds a certain critical threshold for caries risk.
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Increased proportion of Streptococcus mutans in saliva
In early caries, the number of Streptococcus mutans in local plaque is 10 times higher than that in healthy areas. A count of Streptococcus mutans exceeding 10^5 colony-forming units per milliliter (CFU/ml) in saliva is a potential risk factor for caries and is widely recognized as one of the indicator bacteria in caries activity tests.
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Increased proportion of lactobacilli in saliva
In the early caries plaque on tooth surfaces, the number of lactobacilli is 100 times higher than that in healthy areas. Lactobacilli are also indicator bacteria in caries activity tests. A count exceeding 10^4 CFU/ml in saliva indicates the possible occurrence of new caries.
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Acidic plaque on tooth surfaces
A plaque pH value below 5.5 on the tooth surface indicates a risk of enamel demineralization.
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Increased number of cariogenic and acid-producing bacteria in plaque
Compared with healthy areas, the number of cariogenic and acid-producing bacteria in plaque increases. Areas with a large amount of plaque that persists for a long time (such as the interproximal surfaces of teeth) are a warning sign for the development of caries.
Cariogenic foods mainly refer to carbohydrate-containing foods that remain in the oral cavity and are easily metabolized by pathogenic bacteria to produce acid and synthesize extracellular polysaccharides. The primary cariogenic carbohydrate is sucrose, followed by glucose, starch, and other sugars. Excessive and frequent intake of sugar, which remains in the oral cavity, promotes the proliferation of acid-producing bacteria, disrupts the balance of the oral microecological environment, and creates a cariogenic environment.
Cariogenic carbohydrate-containing foods include: sucrose and glucose in food flavorings, and staple foods rich in starch. These foods can be metabolized by cariogenic bacteria to produce acid, leading to a decrease in pH value. Sucrose, in particular, significantly increases the number of cariogenic bacteria and their toxic products.
Modern eating habits involve frequent snacks between main meals. Most of these snacks are sweet foods, such as cakes, biscuits, and sugary drinks. Additionally, many children and young people often replace water with sugary drinks in daily life. These phenomena have become risk factors for caries. The specific risk factors are elaborated as follows:
In daily life, a diet high in sweet foods or frequent sweet snacks leads to prolonged retention of sugar in the oral cavity. Cariogenic bacteria in plaque continuously metabolize sugar to produce acid, lowering the pH value. The prolonged retention of acidic products in plaque exceeds the buffering capacity of saliva, thereby increasing the favorable conditions for tooth surface demineralization.
Excessive consumption of acidic beverages exposes teeth to further acid erosion, which can easily accelerate the caries process on the tooth surface.
Infants often consume sugary milk or other nutritional supplements before bedtime. Due to work or lifestyle habits, adults also sometimes eat snacks (especially sweet ones) before bed. Neglecting oral hygiene after such late-night snacks creates a risk factor for caries. During sleep, chewing activity ceases, saliva secretion and the oral self-cleaning ability decrease, facilitating the massive proliferation of oral microorganisms. If the late-night food is high in sugar, it further promotes the proliferation of cariogenic bacteria and their cariogenic toxic effects.
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Conduct oral health education to popularize knowledge about oral health, enhance understanding of the causes of dental caries, foster self-care awareness, and develop good oral hygiene habits.
Emphasize early diagnosis and early intervention. Conduct regular clinical examinations and X-ray auxiliary examinations to detect early caries and perform timely restoration.
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Prevent complications of dental caries: Provide appropriate treatment for pulpitis and periapical periodontitis caused by caries to prevent the further progression of inflammation (such as alveolar abscess, osteomyelitis, and space infection). Promptly extract teeth that cannot be preserved.
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Restore function: Timely restore tooth defects, dentition defects, and tooth loss to restore normal oral function and maintain overall health.
Dental caries is a chronic, progressive destructive disease caused by multiple factors, so its prevention requires comprehensive preventive and control measures.
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Mechanical methods
Mechanical removal of plaque is a simple self-care method, involving tools such as toothbrushes, toothpaste, dental floss, toothpicks, interdental brushes, and interdental cleaners. Currently, there are various types of toothbrush heads available, but their basic functional principle is to maximize the removal of plaque from the tooth surface while minimizing wear on the tooth surface and damage to the gums.
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Chemical methods
(1) Disinfectants: Chlorhexidine (also known as hibitane) – see the relevant chapter for details.
(2) Triclosan: Also known as trichlorohydroxydiphenyl ether – see the relevant chapter for details.
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Other methods
(1) Plant extracts: These include extracts from Scutellaria baicalensis, Magnolia officinalis, Galla chinensis, Lonicera japonica, Berberis julianae, Zanthoxylum nitidum, Panax notoginseng, and tea leaves. Their main function is to inhibit cariogenic bacteria. These extracts are mostly used in mouthwashes and toothpaste; however, their active ingredients and mechanism of action require further investigation.
(2) Biological methods: These mainly refer to enzymes, including specific and non-specific enzymes. Non-specific enzymes are mostly proteases, which can destroy bacterial cell membranes. Specific enzymes include glucanases, which are used to dissolve glucans and reduce plaque accumulation on tooth surfaces, and can be added to toothpaste. Currently, most commercial products are toothpastes containing non-specific proteases.
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Control sugar intake
(1) Cariogenicity of sugar and sugar-containing foods: Sucrose is the most cariogenic sugar, but glucose, fructose, and maltose in the diet also have a certain degree of cariogenicity, while lactose has relatively weak cariogenicity. The sugar we obtain from the diet daily includes lactose in milk (milk sugar), sugars in fruits and vegetables (endogenous sugars), and exogenous sugars (free sugars). This distinction is crucial in dietary recommendations because lactose and endogenous sugars pose minimal harm to dental health, while free sugars are the main pathogenic factor for caries. Foods with starch as the main component (such as potatoes, bread, and rice) are less likely to cause caries; however, foods made from refined flour mixed with sugar after heat treatment (such as biscuits) are as cariogenic as sugar itself. In recent years, the consumption of beverages in China has been on the rise, and the cariogenicity of sugar in these beverages should not be ignored.
(2) Eating frequency: The frequency of sugar intake is very important for the development of caries, so it is necessary to reduce the frequency of sugar consumption. However, the amount of sugar intake should not be overlooked either. For developing children and adolescents, while ensuring sufficient sugar intake to meet growth needs, the frequency of sugar intake must be controlled. Many studies have shown a positive correlation between daily sugar intake and the incidence of caries. Especially in scattered populations, daily sugar intake and sugar intake frequency are closely related. Therefore, it is recommended that individuals susceptible to caries reduce both the amount and frequency of sugar intake. Additionally, attention should be paid to oral cleaning after each sugar intake.
(3) Sources of sugar in the diet: For school-age children, two-thirds of free sugars come from snacks, soft drinks, and table sugar. This situation may be more severe in some regions of China, which is a key focus of oral health education. Fruit-flavored sugary drinks are the greatest threat to dental health and are often the pathogenic factor for rampant caries. Snacks and beverages often cause significant damage to teeth in both children and adults. Furthermore, the addition of extra sugar to dairy products should not be ignored, as it is also a cause of caries susceptibility in children.
(4) Recommendations for caries prevention: The most important recommendation is to reduce the amount and frequency of free sugar intake. Currently, the intake of free sugars is high among children, adolescents, and even adults, which is the reason for the persistently high caries rate in primary teeth of children and the high incidence of caries in middle-aged and elderly people. With the significant increase in the variety of food available, the general principle for food selection is to consume more starchy foods, fresh fruits, and vegetables. In fact, changing dietary structure is quite difficult; however, a healthy dietary structure is very important not only for overall health but also for oral health.
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Use sugar substitutes
Carbohydrate-containing foods are one of the main nutrients for humans and are also additives in food and beverages. The sugars consumed in daily life include sucrose, starch, and lactose; among them, sucrose is widely recognized as a cariogenic food. Prolonged retention of sucrose in the oral cavity disrupts the balance of oral flora, stimulates the overgrowth of cariogenic Streptococcus mutans, and promotes the production of extracellular polysaccharides outside bacterial cells, which facilitates plaque formation. After sugar is absorbed, intracellular polysaccharides are produced and metabolized to generate acid, leading to demineralization of the tooth surface and the formation of caries lesions.
There are two types of sucrose substitutes:
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High-sweetness substitutes: Such as aspartame, saccharin, cyclamates, and stevioside. These are 20 to 400 times sweeter than sucrose and have bacteriostatic effects.
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Low-sweetness substitutes: Such as xylitol, sorbitol, mannitol, maltose, and isomalt. Currently, xylitol is the most commonly used in commercial products. In recent years, attention has been paid to the caries-preventive effects of new sugar substitutes such as isomalt, and related products have appeared on the market. Isomalt is a disaccharide alcohol, a mixture of α-D-glucopyranosyl-1,6-sorbitol and α-D-glucopyranosyl-1,1-mannitol. After hydrolysis, it produces glucose, sorbitol, and mannitol. It is fermented slowly by sugar-decomposing cariogenic bacteria, producing little acid and causing a minimal decrease in pH value. Animal experiments have confirmed its low cariogenicity.
Sugar substitutes such as xylitol cannot be used by cariogenic bacteria to produce acid or form polysaccharides and are usually used as sweeteners in chewing gum to avoid the adverse effects of sucrose. However, further in-depth research is needed to determine whether xylitol itself has anti-caries effects. Sugar-free chewing gum not only does not cause caries but also can exert anti-caries effects by stimulating saliva secretion.
Among sugar substitutes, intense sweeteners and xylitol are non-cariogenic. Other bulking sweeteners can be metabolized by bacteria in plaque, but the metabolic rate is very low, so they can be considered safe for teeth. The use of non-sugar sweeteners, especially in candies, soft drinks, and pastries, has played a positive role in caries prevention. In practical life, sugar substitutes cannot completely replace sucrose; therefore, it is particularly important to control the frequency of sugar consumption and clean the mouth promptly after eating sugar to reduce the retention time of sugar in the oral cavity.
The prenatal and infant periods are the developmental stages of primary teeth. Therefore, attention should be paid not only to the nutrition and health care of pregnant women during pregnancy but also to the nutrition and health care of infants during the infant period to prevent developmental defects in primary teeth. The 婴幼儿期 (infant and toddler period) and preschool period are the developmental stages of permanent teeth; thus, attention should be given to the nutrition and health care of children during these periods to prevent developmental defects in permanent teeth. At the same time, measures such as the use of fluoride (see the relevant chapter) and pit and fissure sealing (see the relevant chapter) should be implemented to enhance the caries resistance of both primary and permanent teeth.
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Strengthen health care during pregnancy and infancy
(1) Pregnancy:
① Pay attention to oral health care. Pregnant women with caries (especially active caries) should receive timely treatment; those with gingivitis or periodontitis should also receive timely treatment and strengthen oral hygiene to prevent preterm birth and low birth weight of the fetus. Preterm birth and low birth weight are prone to causing developmental defects in primary teeth, such as poor enamel mineralization and enamel hypoplasia, which increase the susceptibility of primary teeth to caries.
② Pay attention to the nutrition and overall health of pregnant women to ensure the normal growth and development of the fetus's body and oral cavity.
(2) Infancy: During the period from the eruption of primary teeth to the development of permanent tooth germs (within 3 years of age), attention should be paid to proper feeding and calcium supplementation, maintaining balanced nutrition and diet, promoting the normal development and eruption of primary teeth and the normal development of permanent teeth, and reducing the occurrence of incomplete crown calcification and enamel hypoplasia. Especially during infancy, attention should also be paid to the oral hygiene of mothers and caregivers, and active treatment of caries should be carried out to avoid the transmission of oral cariogenic bacteria to children during this period.
(3) Perform pit and fissure sealing on the buccal, lingual, and occlusal surfaces of primary molars and permanent molars to prevent plaque retention and reduce the incidence of caries.
(4) Establish a reasonable diet, enhance children's masticatory function, promote jaw development, ensure the normal replacement of teeth, and reduce dental crowding caused by abnormal tooth replacement. Strengthen health education for children and adolescents, establish good self-oral health care habits, and enhance awareness of oral health care.
It is recommended that preschool children undergo regular oral examinations every 3 to 6 months, school-age children every 6 months, and adults every 6 to 12 months. For individuals susceptible to caries, it is advisable to shorten the interval between regular re-examinations.
