Demos = people
Ology = science
Epidemiology = the science which deals with
what falls upon people…..
The study of the
disease or a
& of the factor that
Number of new cases
Number of persons at risk
Number of persons with the disease
Number of persons in the population
describes how widespread the
disease is in subjects. (e.g., the %
of tooth sites with clinical
attachment loss > 2 mm)
e.g., mean CAL, mean bone loss
To study the rise and fall of disease in population
To diagnose community problem of health and
disease by study and analysis of
incidence,prevalence and morbidity.
To estimate the individual risk and chances of
To help in complete the clinical picture and natural
history of disease by group analysis
To identified clinical syndroms by observation of
To evaluate the need and effectiveness of health
services and need for man power
To search for cause of disease and health by
observation of group habits,customs and model of
presence or absence of disease and the
characteristics of the members of a
population are measured at a point in time.
studies are useful for providing
prevalence data on a disease, comparing the
characteristics of persons with and without
disease, and generating hypotheses regarding
the etiology of a disease.
It follows subjects over time. The purpose of a cohort
study is to determine whether an exposure or
characteristic is associated with the development of a
disease or condition.
At the beginning of the study, all subjects must be free of
the disease of interest.
Subjects are classified into exposed and unexposed
groups and then followed over time and monitored for the
development of the disease.
The disadvantage of cohort study is that they can require
long periods of follow-up and can be expensive to conduct.
It provide and efficient way to investigate the association
between an exposure and a disease, especially a rare
Because case-control studies do not follow subjects over
time, they require fewer resources and can be conducted
more quickly than cohort studies.
The prevalence or incidence of a disease cannot be
determined from a case-control study because the
subjects are recruited into study based on their disease
The major disadvantage is that the temporal relationship
between the exposure and the onset of disease cannot be
determined because the exposure is usually assessed when
the disease status is established.
is a numerical value describing the
relative status of population on graduated
scale with definite upper and lower limit
which is designed to permit and facilitate
comparison with other population classified
by the same criteria and method.
Absence of plaque deposits
Plaque disclosed after running the
periodontal probe along the gingival
Mild inflammation: slight change in
slight edema. No bleeding on probing.
Moderate inflammation: redness,
edema, and glazing. running along
soft tissue wall of gingival crevice.
Severe inflammation: marked
redness and edema. Ulceration,
Tendency toward spontaneous bleeding.
Bleeding on probing
I . Oral hygiene instruction
Supra andor Subgingival
calculus Iatrogenic marginal
II . I+ calculus removal
Shallow pockets up to
Deeper pockets from
III. I+II+ root planning
IV. I+II+ complex treatment