• Caries is Latin for rot or rotten.• Dental caries means rotten teeth.• Caries is the noun which names the disease• Carious is the adjective, not a caries‘,• a carious area or an area of caries.
Dental caries can be defined as• Chronic progressive deconstructive disease of hard dental tissues• Bacterial infected diseases caused by specific bacteria• a reversible multifactorial process of tooth demineralization and remineralization.
Dental caries• Dental caries, a bacterial infection, may be define as a posteruptive pathological process of external origin, involving the softening of the hard dental tissue and proceeding to cavity formation. This is distinct from the dissolution of the hard dental tissues of an unerupted tooth which is not dental caries but tooth resorption.
The carious processa pathological process of localized destruction of calcifiedtooth tissues by acids produced by organisms. Etiologicallycaries is considered a multi-factorial disease, whichinvolves interplay between the host (saliva and teeth) microorganisms (streptococcus mutans), and the substrate(dietary carbohydrate sucrose), with the production ofLactic acid. Dental plaque (Bio-film) serves as the mediumfor caries development.
Basic pathological changes• demineralization of inorganic tissues of tooth• Disintegration of the organic tissues of tooth• involves enamel, dentin, cementum
Measuring caries activityPrevalence rate （患病率）： is the proportion of a population affected by a disease of a condition at one point time.Incidence （发病率）： is a mesurement of the rate at which a disease progresses the increase or decrease in the number of new cases occurring in a population within the same time period
DMF index• D the mean number of decayed teeth with untreated carious lesions• M the mean number of teeth which have been extracted and are therefore missing• F the mean number of filled teeth• DMF(T) to denote decayed,missing, and filled teeth• DMF(S) to denote decayed,missing, and filled surfaces in permanent teeth• dmf(t) dmf(s) similar indices for the primary dentition
Frequency distribution of dental caries according to various tooth location permanent dentition
distribution of dental caries according to tooth surface• Occlusal > interproximal >buccal
Caries is world wide in its distribution1. The prevalence of dental caries increases with the development of economy2. High DMF before 1970 in the industrialized country To decrease after 1970 in the industrialized country4. More prevalence in industrialized than in the third word country5. Caries experience tends to increase in the developing country and decline in many western countries.6. Caries experience is higher in urban than in rural communities in developing countries.
• Prevalence of dental caries (1995) ， special for 12-18Y age groupsis increased significantly （ 20-40% ）• In recent 10 years, prevalence of dental caries in primary dentition is increased significantly than the permanent
Why has caries prevalence decreased in modern population?The is possibly attributable to2. The fluoridation of drinking water, use of fluoride toothpastes and improved oral health3. A changing pattern of sugar consumption4. A decrease in virulence( 毒力 ) of the organsims
The organic deposits on the enamel surface 原发性釉护膜 (primary enamel cuticle) 残余釉上皮 （ reduced enamel epithelium) 获得性膜 （ acquired pellicle ） 食物碎片 （ food debris, material alba ） 牙菌斑（ dental plaque ） 牙结石（ calculus, tartar ）
four factors is essential for theinitiation of dental caries, namely: 1.Micro-organism b.mutans streptococci c.Lactobacilli d.Actinomyces
1. Substrate• Refined carbohydrates( 精制碳水化合物 ) such as sucrose 蔗糖 provide a suitable substrate on which the cariogenic micro-organisms act to produce the acids that lead to dissolution of the hard dental tissues• Caries experience is influenced by the quantity, quality and especially frequency of consumption of the refined carbohydrate
1. Susceptible teeth 易感牙• The ingestion of fluorides during tooth mineralization leads to the formation of fluor- apatite in enamel. Its presence in enamel makes the tooth less susceptible to dental caries because it is less soluble in acid than the hydroxyapatite( 羟磷灰石 ) which is normally present in the hard dental tissues
1. Time• All the factors should be present for sufficiently long time for the caries process to be initiated.
STRUCTURE OF DENTAL PLAQUEPlaque on smooth surface Plaque-dental surface Middle layer---- condensed microbial layer body of plaque The surface layer of plaquePlaque in pit and fissure
Composition of Dental plaque• bacteria which form 50-70% of dental plaque a small number of epithelial cells Leukocytes Macrophages• glycoproteins which, together with extracellular polysaccharides, form the plaque matrix• mucopolysaccharides ( 粘多糖 ) such as glucans and fructans( 右旋糖 )• Inorganic components calcium phosphorus fluorides.
MECHANISMS OF PLAQUE FORMATION The attachment, growth, removal andreattachment of bacteria to the tooth surfaceis a continuous and dynamic process.
Several distinct processes can be recognized Absorption of salivary proteins and glycoproteins, together with some bacterial molecules, to the tooth surface to form a conditioning film (the acquired pellicle).—— 获 得性膜的形成 non-specific interaction of microbial cell surfaces with the acquired pellicle via van der Walls attractive forces.
• Irreversible adhesion can occur if specific inter-molecular interactions take place between adhesions on the cell surface and receptors in the acquired pellicle.
• Secondary or late-colonizers attach to primary colonizers (coaggregation 共集 ), also by specific inter-molecular interactions.
FORMATION AND DEVELOPMENT OF DENTAL PLAQUE • Formation of acquired pellicle and primary aggregation • Bacteria growth and development • The mature of dental plaque
DevelopmentPellicle formation – Microorganisms do not attach thermselves directly to the mineralized tooth surface and the teeth are always covered by an a cellular proteinaceous film, the pellicle – Forms on the “naked” tooth surface within minutes to hours
Major constituents of Pellicle • Salivary glycoproterns • Carbohydrates • Lipid • a lesser extent components from the gingival crevicular fluid( 龈 沟液 )
Function of Pellicle• Because of its selective nature restrict transportation of irons in and out of the dental hard tissue. It may play an important modifying role in caries• Provide further protection against demineralization of the enamel• Modify the number of potential adsorption sites for different bacterial species• As the substrate for the microorganisms
microbial colonizationInitial microbial colonization• streptococcus mutans( 变形链球菌 ) accounting for 56% of the total initial microflora• Actinomyces spp( 放线菌 ) a minor proportion• gram-negative bacteria(G-)
Microbial succession• The initial establishment of a streptococcal flora appears to be a necessary antecedent for the subsequent proliferation of other organisms• The most striking changed is shift from streptococcus-dominated plaque to plaque dominated by Actinomyces.
MICROBIAL AETIOLOGY OF CARIES• animal studies micro-organisms are involved in the aetiology of dental caries
Cariogenic properties( 致龋菌的特性 ) • they are able to produce acid rapidly from fermentable carbohydrates (acidogenic). • They thrive under acid conditions (aciduric) • able to adhere to the tooth surface because of their ability to synthesize sticky extracelluar polysaccharides from dietary sugars
Micro-organism and caries• Advanced lesions often have a high proportion of lactobacilli• dentinal lesions have a diverse micro flora with many Gram positive Gram negative bacteria.• Root surface caries was originally associated with Actinomyces spp. but recent studies suggest a similar aetiology to enamel caries• Rampant caries can occur in xerostomic patients and in infants fed with high levels of sugar in pacifiers (nursing bottle caries). The plaque contains high levels of mutans streptococci and lactobacilli.
Hypotheses and theory relating to Aetiology of dental caries
1. Chemico-parasitic theory ( 化学细菌学说 )• This postulates that oral bacteria act on sugar to produce acid which demineralizes the inorganic component of enamel, resulting in the development of a carious lesion.
1. Proteolytic theory( 蛋白溶解学说 )• It is thought that the organic component of enamel is first broken down by proteolytic enzymes, opening up path-ways for bacteria to attack the enamel by other processes such as by acid or by chelation.
1. Chelation theory( 螯合学说 )• This postulates that enamel is demineralized by chelating agents at neutral pH.• Protein breakdown products as well as lactic acid are some chelating agents known to exist in nature.
1. Auto-immunity theory• In this theory, it is suggested that forbidden clones of lymphocytes attack target cells (odontoblasts) rendering the tooth vulnerable to caries attack.
• Four foctors theories microorganisms The four circle diagrammatically represent the parameters Host involved in the carious process. & caries substrate All four factors must be acting tooth concurrently (overlapping of the circles) for caries to occur. time
The role of dietary carbohydrate• Nutrition ------ systemic dietary effects• Diet ------ local dietary effects
epidemiological studies Caries prevalence is low in populations adhering to a primitive way of living and a diet of local products with little sugar A drastic increase in caries is invariably seen when these population “improve”their standard of living and adopt a modern “civilized”diet with high sugar content A strong correlation between caries development and sugar consumption
Sucrose( 蔗糖 )------called the arch-criminal in dental caries Monosaccharides ,disaccharides and of the polysaccharide starch can be fermented to acid by the plaque bacteria Sorbitol （山梨糖） xylitol ( 木糖醇 ) -----sugar substitutes used in sugar-free chewing-gums Dietary habits and caries prevalence
Host & tooth (susceptible teeth)• It was a clinical experience that not all individuals with poor oral hygiene and frequent sugar consumption develop caries• In the laboratory, extracted teeth exposed to the same acidic buffer challenge certainly do not develop artificatial caries- like lesions to the same degree within a short period of time
Host & tooth • Tooth morphology: susceptible sites • Environment of the tooth: » Saliva » fluoride
• Tooth morphology bacterial plaque is an essential precursor of caries , sites on the tooth surface which favour palque retention and stagnation are particularly prone to decay• Saliva under normal conditions, the tooth is continually bathed in saliva. It is capable of remineralizing the early carious lesion because it is supersaturated with Ca and P. when salivary buffering capacity has been lost, a low Ph environment is encouraged and persists longer• Fluoride particular interest was the discovery of the association between fluoride concentration in water supplies and prevalence of dental caries in children
Time1. It is evident that the mere existence of the three factors operating together does not result in instantaneous mineral loss2. therefore a fourth circle is often added to stress the time dimension taken for dental caries to develop
Other factors •Age •Sex •Geography •Race •Economics status •Nutrition •Health status