Figure 1-4. Shapes of viruses.
MICROBES IN THE MOUTH
Microbes normally inhabit certain parts of the body, such as the normal, healthy
adult mouth that has a highly varied and concentrated population. The saliva from the
dorsal surface of the tongue contains about 750 million bacteria per milliliter (about 20
drops of saliva). Although the types of bacteria are different, plaque and the gingival
sulcus contain one hundred times this number. Facultative streptococci (bacteria that
thrive either in the presence or the absence of oxygen) are the most numerous. They
account for perhaps 50 percent of the total count. Lactobacilli, although often implicated
in dental caries activity, account for only a small fraction of the total count. Oral
spirochetes are anaerobic (require the absence of oxygen) and inhabit the gingival
sulcus. Certain fungi, such as Candida albicans, may also be present. Various normal
microbe populations safely exist in an oral environment until something such as
antimicrobial therapy, poor oral hygiene, improper diet, or periodontal or other disease
upsets this environment.
TRANSMISSION ROUTES FOR INFECTIONS
a. Through the Respiratory Tract. Infections may be transmitted via airborne
droplet into the respiratory tract. Examples include the common cold viruses, influenza
viruses, and tuberculosis bacteria.
b. Through the Gastrointestinal Tract. Infections may be transmitted via
contaminated food or other entry into the gastrointestinal tract. Examples include
dysentery and diarrhea.