Bacterial Flora in Human Oral Cavity Made by Luan Yijun, Zhang Yanhui, Liu Junying, Li Na, Xuxia, Liu Song, Wang Ge, Zhang Tianqi, Ying Wanggui, Li Shengfeng.

Bacterial Flora in Human Oral Cavity

•Made by•Luan Yijun, Zhang Yanhui, Liu Junying, Li Na, Xuxia, Liu Song, Wang Ge, Zhang Tianqi, Ying Wanggui,•Li Shengfeng

1.Normal flora in human oral cavity

2.Several dental diseases caused by bacteria

3.What can we do to prevent dental disease

The human mouth is home to more than 500 species of bacteria.

Oral bacteria include streptococci, lactobacilli, staphylococci and corynebacteria( 棒状杆菌 ), with a great number of anaerobes, especially bacteroides( 类杆菌 ).

Normal flora changes with age

At birth the oral cavity is sterile

It rapidly becomes colonized from the environment

Streptococcus salivarius is dominant and may make up 98% of the total oral flora until the appearance of the teeth (6 - 9 months in humans)

The eruption of the teeth during the first year leads to colonization by S. mutans （变形链球菌） and S. sanguis ,they will persist as long as teeth remain

Other strains of streptococci adhere strongly to the gums （牙龈） and cheeks but not to the teeth

The creation of the gingival crevice （齿龈裂 缝） area increases the habitat for the

variety of anaerobic species found

Bacteroides and spirochetes colonize around puberty

Functions of normal flora

occupy available colonization sites contribute to host nutrition contribute to immunity exert microbial antagonism against

heterogenous species

Since some of these bacteria are parasites or opportunistic pathogens, if they invade tissues not normally accessible to them, characteristic diseases result

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Dental Plaque （牙菌斑）

Dental Caries （龋齿）

Periodontal Disease （牙周病）

Dental Plaque

material adhering to the teeth, consists of bacterial cells (60-70% the volume of the plaque), salivary polymers, and bacterial extracellular products

Streptococcus sanguis and Streptococcus mutans

a weak attachment of the streptococcal cells to salivary glycoproteins →a pellicle on the surface of the teeth → a stronger attachment →( glycosyl transferase, an enzyme on the cell surface of Streptococcus mutans, is apparently involved in initial attachment of the bacterial cells to the tooth surface and ) → conversion of Sucrose ( 蔗糖） to dextran （右旋糖酐） and levan （左旋糖酐） polymers → form the extracellular matrix of plaque

Mechanism

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Dental Caries

the destruction of the enamel （釉质） , dentin （牙质） or cementum （牙骨质）

of teeth due to bacterial activities

Streptococcus mutans, Lactobacilli ，

Actinomyces （放线菌） , and various proteolytic bacteria

Physiological and Biochemical Properties of Streptococcus mutans

a regular component of the normal oral flora of humans

contains the enzyme glycosyl transferase produces lactic acid, produces more lactic acid

and is more acid-tolerant than most other streptococci

stores polysaccharides made from dietary sugars, can be utilized as reserve carbon and energy sources for production of lactic acid

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Periodontal Disease

bacterial infections that affect the supporting structures of the teeth (gingiva, cementum （牙骨质） , periodontal membrane and alveolar bone)

Actinomyces, streptococci, spirochetes and Bacteroides

The mechanisms of tissue destruction in periodontal disease are not clearly defined but hydrolytic enzymes, endotoxins, and other toxic bacterial metabolites seem to be involved

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How to prevent dental diseases

Brush your teeth two times everyday, after arousing and before sleeping

Use toothpastes which contains fluoride

Use dental floss to clean your teeth-gaps everyday