My thesis discusses the relation between periodontal diseases and psychological disorders, how many different psychological disorders such as stress for example has an effect on immune system, which in turn those people who experience stress are more likely to adopt negative behaviors which deleterious to their periodontal health. Or bad habit that those people adopt as reacting to stress such as smoking which also has a negative effect on periodontal health, due to the carbon monoxide content found in cigarettes decreases the oxygen saturation level of hemoglobin found in healthy gingiva and causes inflammation. On other hand a common disorder seen in dental clinics, is dental anxiety, patients who have dental anxiety may keep them away from visiting the dentist for a routine checkup, may do so due to past unpleasant dental clinic experiences, or they may be terrified of pain, needles, the numbness that follows an injection, or even other traumatic experiences like abuse, as a result scaling and other oral hygiene practices are therefore disregarded