Dental Plaque and Caries

Dental Plaque and Caries

• Dental plaque is a complex biofilm that forms on teeth
• Initial colonizing organisms in dental plaque are mainly gram-positive bacteria, such as Streptococcus sanguis, S. mutans, S. mitis, S. salivarius, S. oralis, and S. gordonii
• Late colonizers in dental plaque include gram-negative anaerobes, such as Porphyromonas, Prevotella, Fusobacterium, and Veillonella species, as well as anaerobic spirochetes like Treponema denticola
• High-molecular-weight extracellular glucan polymers are synthesized in dental plaque, acting as a cement to bind the biofilm together
• There are approximately 300-400 bacterial species present in mature dental plaque
• S. mutans is considered the dominant organism in the initiation of caries

Control of Caries

• Physical removal of plaque is an effective method of controlling caries
• Limiting sucrose intake and maintaining good nutrition with adequate protein intake can help prevent caries
• Frequent cleansing of the teeth and mouth is also important for preventing caries

Gastrointestinal Tract

• The stomach has few bacteria due to gastric enzymes and acidic pH
• The small intestine has few normal flora in its upper part, but more in its lower parts
• The large intestine has the most bacteria of any part of the body, with 99% being anaerobic Bacteroides species
• Many fungi, protozoa, and viruses can live in the large intestine
• Some normal flora in the large intestine are opportunistic, meaning they can cause infection if they move to other areas of the body

Human Normal Microbiota

• The human normal microbiota is the mixture of microorganisms that regularly inhabit the human body
• The normal microbiota consists of a few eukaryotic fungi, many bacteria, and some viruses and parasites
• The normal microbiota varies in number and kind from one site to another
• Internal organs are usually sterile, but the normal microbiota can be present in asymptomatic individuals

Normal Flora

• A fetus is sterile when born, but starts acquiring normal flora from its mother, air, food, and environment
• Normal flora differs from one human to another depending on age, diet, and geographic habitat
• The skin and mucous membranes always harbor a variety of microorganisms, which can be classified into two groups: resident flora and transient flora
• Resident flora is the microorganisms regularly found in a given area at a given age, and can reestablish itself if disturbed

Urogenital Tract

• The urinary tract is usually sterile, except for the lower urethra and external opening, which has bacteria similar to those found on the skin
• The female urethra can become colonized with fecal flora, which can predispose to urinary tract infections
• The genital organs are usually sterile, except for the vagina, which has a normal flora of Lactobacillus spp. that keeps the pH acidic to protect against opportunistic infections

Colonization vs Infection

• Colonization is the presence of microorganisms on skin or mucosa, without penetration into tissues
• Infection is the invasion of a host organism by microorganisms, followed by proliferation and host reaction

Relationship Between Individuals

• Symbiosis is the permanent association between two different organisms
• Types of symbiosis include mutualism, commensalism, and parasitism

Microecosystem and Microecology

• The human body has various microecosystems, such as the skin, mouth, nasopharynx, ear, eye, and gastrointestinal tract, each with its own unique microecology
• Each microecosystem has its own specific microorganisms that inhabit it

Medically Important Members of Normal Flora

• Skin: Staphylococcus epidermidis, Staphylococcus aureus, Propionibacterium acnes
• Mouth: E. coli
• Nasopharynx: Pseudomonas
• Ear: Streptococcus
• Eye: Neisseria
• Gastrointestinal tract: Corynebacteria
• Urinary tract: various bacteria
• Reproductive tract: various bacteria