EPIDEMIOLOGY
Is defined as the study of health and
disease in populations and of how
these states are influenced by
hereditary, biology, physical
environment, social environment and
ways of living.
TYPES OF
EPIDEMIOLOGICAL STUDIES

DESCRIPTIVE STUDIES (observational
epi). Surveys records the prevalence of
various conditions “meaning” The word
prevalence serve to indicate per age group,
the proportion of the population affected,
with a given degree of severity of
periodontal disease, as their highest score,
and is given in percent of the population
examined. (Age, sex, and geographic
location).

ANALYTICAL STUDIES: Attempts to
determine associations between disease and
possible risk factors determinants, and
quantify the degree of risk.
RISK: Is the probability that a specified event
will occur e.g. that an individual will become
ill or die within a stated period of time or
particular age. Then trying to remove or
modify the risk factor e.g. smoking, sugar,
etc…
Analytical studies, frequently require at least
TWO sets of measurements among the
same people at different times to determine
the progress of the condition.

INCIDENCE STUDIES: It is defined as the
change in prevalence of a condition over a
given period of time. In another word, it is
the rate at which new cases of the disease
appear in a population.

CROSS-SECTIONAL STUDIES: A comparison of

LONGITUDINAL STUDIES: If all the children
the prevalence of dental caries in TODAYS sixthgrades with that of ten years ago, must be crosssectional study, though it is obvious that different
persons are studied each time.
originally in first grade in a school system are
studied periodically until they finish sixth grade, the
study would be longitudinal because same children
would be seen on several occasions.

EXPERIMENTAL STUDIES: “Clinical
trials”. Is a controlled study of group
comparison based on epidemiological
principles and designs to test the hypothesis
that a particular agent or procedure
favorably alters the natural history of a
disease. The group receiving the agent is
the test group, and the comparable group
not subjected to the agent is the control
group. (Age, sex, race and socioeconomic
status are similar, and most importantly
Disease Experience).
INDICES USED TO EVALUATE
SIGNS, SYPTOMS AND
ETIOLOGICAL FACTORS
ASSOCIATED WITH THE DISEASE
OF THE PERIODONTIUM.

Definition of an Index: As defined
by Russell 1966. Is a numerical value
describing the relative status of a
population on a graduated scale with
definite upper and lower limits, which
is designed to permit and facilitate
comparisons with other populations
classified by the same criteria and
methods.
Ideally an Index, including its scoring criteria
should posses the following properties:


Clarity, Simplicity and Objectivity.
The examiner should be able to
memorize the criteria, and the Index
should be reasonably easy to apply so
as not to lose time in field
examination.
Acceptability.
The use of an Index should not be
painful or demeaning to the subject.


Validity.
The Index must measure what it is intended
to measure, it should correspond with
clinical stages of the disease under study at
each point (reflects the true disease
situation).
Quantifiability.
Should be amenable to statistical analysis.
So as the status of a group can be
expressed by a distribution, MEAN and
MEDIAN, or other statistical measures.

Reliability.
The Index should be able to measure
consistently at different times and under
variety of conditions (Reproducibility).
– Inter-examiner-variability.
– Intra-examiner-variability.

Sensitivity.
The Index should be able to detect
reasonably small shifts in either direction.
Classification and Characteristics:
INDICES TO MEASURE
GINGIVITIS
Gingival Index: “Loe and Silness 1963”



The first index to evaluate every single
tooth surface.
A blunt probe “Instrument is usually
used”.
Gingival tissue is divided into four
scoring units.
Buccal – Mesial – Lingual and Distal.
 Scores from 0 – 3.
 GI for single surface.
 GI for a tooth “4 surface” Total = GI tooth.
4
 GI for individuals = Total GI/per tooth
Number of teeth
 Can be used for a group of teeth GI for e.g.
6 teeth.
Converting numerical scores into subjective or
varying degrees of clinical gingivitis as
follows:
Gingival Scores
0.1 – 1.0
1.1 – 2.0
2.1 – 3.0
Condition
Mild Gingivitis
Moderate Gingivitis
Severe Gingivitis
Criteria for Gingival Index





0 = Normal gingiva.
1 = Mild inflammation, slight change in
color, slight edema. No bleeding on
probing.
2 = Moderate inflammation, redness,
edema and glazing. Bleeding on probing.
3 = Severe inflammation, marked redness
and edema, ulceration and tendency to
spontaneous bleeding.
This Index can be used also as simplified
form.
6
2 4
4 2
6
INDICES TO MEASURE
PLAQUE
Plaque Indices: “Silness and Loe 1964”
 Epidemiological studies: It provides a
quick and representative picture of the
level of oral hygiene in a population.
 In private practice: Is not intended to
determine the average plaque
accumulation but to record the
distribution of plaque in the oral cavity
i.e. to determine the “Plaque
Picture” of an individual patient.

1.
2.
Some areas of the patient’s dentition may
be cleaned quite effectively, while others
e.g. the lingual surfaces of mandibular
molars remain routinely uncleaned.
The most important consideration in the
plaque index is the thickness of plaque
along the gingival margin.
It involves the same scoring units of the
tooth of the Gingival Index. “Loe and
Silness 1963”.
3.
4.
5.
A mouth mirror and dental explorer are
used.
To visualize plaque, it is important that
compressed air be used to dry the tooth
surfaces prior to the evaluation of the
unstained plaque deposits.
PLAQUE IS NOT STAINED.
It does not exclude or substitute for teeth
with gingival restorations, or crowns, or
“missing teeth” if partial scoring is used.
PERIODONTAL SCREENING
AND RECORDING Index
Principles of the P.S.R.
In this system, the dentition is divided
into six sextants:
Premolars & Molars
R.
Premolars & Molars
Canines & Incisors
Ant.
Canines & Incisors
Premolars & Molars
L.
Premolars & Molars
THE PROBE

The tip is 0.5 mm spherical ball.

Calibration of its use.

Force 20-25 grams.

Path of insertion.
Prepared by: Dr. Nicola Barghout
P.S.R. CODING
0 – The black band remains fully visible.
1 – As code 0 – except bleeding on probing.
2 – As code 1 – except the probe detects
supra and subgingival calculus, overhangs.
3 – The black band disappears partly into
the gingival crevice.
4 – The black band disappears into the
gingival crevice.
P.S.R. SCORING EXAMPLE
*
4
2
1
0
3
X