—Neglect: Result of the lack of proper oral hygiene. MICRO-ORGANISMS Salivary glands secrete about 1,500 ml of saliva on a  daily  basis.  Microscopic  counts  in  saliva  show  an average of 750 million micro-organisms per milliliter. Because the temperature in the oral cavity is around 98.6° Fahrenheit, the mouth is the perfect environment for micro-organisms to live. Micro-organisms have a dark, moist, warm area, and a good source of food supply to live. These micro-organisms can be divided into  four  major  classifications-bacteria,  protozoa, viruses, and fungi—which will be discussed in chapter 9,  "Infection  Control." ORAL LESIONS Oral lesions can be defined as any pathological or traumatic  disorder  of  tissue  that  creates  a  loss  of function  of  the  area  affected.  They  can  include wounds, sores, and any other tissue damage resulting from disease or injury. Many  types  of  lesions  can occur in the mouth. The location of the lesion can assist in determining the type. LESIONS BELOW THE SURFACE The types of lesions that extend below the surface of  the  mucosa  and  are  the  most  common  in  oral pathology are the following: Abscess—A localized collection of pus in a specific area of soft tissue or bone. Often it is confined in a particular space, and is commonly caused by a bacterial infection. Cyst—An enclosed pouch or sac that contains fluid or semisolid material. Ulcers—A    disruption    of    the    superficial covering of the mucosa or skin. May be caused by biting, denture irritation, toothbrush injury, viruses or other irritants. ELEVATED  LESIONS Numerous types of lesions are above the surface of the mucosa. Two of the most common are discussed below. Vesicles—A small elevation that contains fluid. Most of these lesions in the oral cavity rupture, leaving superficial ulcers. Hematoma —A localized collection of blood that escaped from blood vessels due to trauma. It is well-defined and with time, changes to a dark color. NONELEVATED LESIONS Two common lesions of the oral mucosa in this category are as follows: Petechiae—Round pinpoint, nonraised, purplish-red  spots,  caused  by  mucosal  or  dermal hemorrhage. Ecchymoses—Large, purplish-red areas caused by blood under the skin or mucosa; turns to a blue  or  yellow  color. DISEASES OF THE TEETH Teeth become diseased for many reasons. We will look at some of the more common diseases found in teeth  such  as  impaction,  attrition,  abrasion,  erosion, resorption, and dental caries. IMPACTION An impaction (fig. 5-2) is the condition in which a tooth is blocked by a physical barrier, usually teeth or bone. A tooth may not erupt in the normal time period if an impaction occurs.  Some of the causes of impacted teeth are: Movement  of  the  erupting  tooth  into  a horizontal, vertical, or other abnormal position. Early loss of deciduous teeth. Insufficient jaw space, abnormally large tooth crowns, supernumerary or other teeth in a dental arch. ABRASION AND ATTRITION Attrition (fig. 5-3) is the loss of substance of a tooth from a wearing away process caused by teeth against teeth. Whereas,  abrasion  results in the loss of tooth structure secondary to the action of external agents. In attrition, wear involves aspects on the incisal, occlusal, and interproximal surfaces of the teeth and is considered a normal or gradual loss of tooth substance because of the mastication of food.  Causes of occlusal attrition can result from bruxism (grinding of teeth), chewing of tobacco or gum, or other oral habits that involve mastication. In abrasion, one or more teeth may show wear, generally  brought  about  by  improper  toothbrushing, 5-2