1. EPIDEMIOLOGY
- Study of the distribution of a disease or a physiologic condition in human populations
and of the factors that influence this distribution
- 3 components included:
1. population – groups of people defined either by geographic boundaries or
characteristics or attributes
2. Distribution – occurrence of a disease or condition in groups of people
3. Factors – causes responsible for the observed distribution
- Aims:
1. prevention of disease
2. maintenance of health
- Scope:
- studies of infectious diseases, chronic diseases, accidents, drug abuse,
suicide, injuries and health services research
- epidemic and inter-epidemic periods with sporadic and endemic occurrence of
diseases
- Uses:
1. can identify and measure the importance of health problems, describe the high
risk groups and elucidate the cause of these problems
2. for understanding the natural history of disease
3. is essential for disease surveillance and control
4. contributes to the planning, monitoring and evaluation of health services
5. serves as a key instrument in the formulation of health policies which may
incorporate social, behavioral and economic dimensions in addition to the
provision of health services
EPIDEMIOLOGIC REASONING
A. Descriptive studies
- begins with observations made in the course of clinical practice or examination
of disease patterns
- arouses suspicion concerning the possible effects of a particular factor on
diseases occurrence
- observations are utilized in descriptive studies that lead to formulation of
specific hypothesis
B. Model-building and formulation of hypothesis
- factor or factors being considered to be potentially playing significant role/s in
the observations are associated to the disease occurrence, patterns and distribution
C. Analytic Studies
- studies of individuals designed to include an appropriate control group and
whose aim is to determine if a statistical association exists between a given factor
and a particular outcome
D. Analysis of Results
- the observed statistical association can be considered to represent a causal
relationship between exposure (factor) and outcome on the basis of the following
criteria:

2. 1. strength of the association
2. consistency of findings from other studies
3. temporal sequence between exposure and outcome
4. biologic plausibility
EPIDEMIOLOGIC APPROACH
- Consist of procedures of scientific inquiry to describe the distribution and elucidate the
etiology of disease in a population
- Begins by reviewing the literature for available knowledge regarding the problem of
interest
- There’s discovery of what is already known about the problem and knowledge gaps are
identified
- Knowledge gaps are considered in the formulation of hypothesis
- Hypothesis is tested using epidemiologic study designs
- Conclusions are drawn based on the analysis of results
- Study Designs
1. Observational – examination of the natural course of events to simply document who
have/do not have the disease and who is exposed or unexposed to risk actors
a. Descriptive - characterize disease occurrence in a population; do not attempt to
analyze links between exposure (factor) and effects (disease)
a.1. Case study - medical occurrences in a single patient and can represent first
clues in the identification of new disease or adverse effects of exposures
a.2. Case Series - collection of individual case reports that may occur within short
period of time
a.3. Ecologic studies - considers patterns of disease among populations by
comparing disease rates in different geographic regions
- first step in investigating a possible exposure-disease relationship
- also called correlation study
EX. Cancer rates in communities with different patterns of MSG
consumption
a.4. Cross-sectional - measures exposure and disease status at the same time
among individuals in a well-defined population (“What is happening?”)
- can not determine whether exposure preceded or resulted from the disease
- also called prevalence study
EX. Occurrence of periodontitis among NIDDM (non-insulin dependent
diabetes mellitus) patients
b. Analytical – investigate and evaluate relationships between health status and
other variables
b.1. Cohort study - compares the occurrence of an exposure between cases (those
who have the disease) and controls (those who do not have the disease)
(“What will happen?”)
- a group of people (cohort) are classified according to exposure (w/ or
w/out) and subsequently followed up to compare the outcome between
the groups
- also called follow-up study or incidence study

3. EX. Relation between fluoride intake and fluorosis
b.2. Case-control - compares the occurrence of outcome between those exposed
and not exposed to specified risk factors (“What happened?”)
EX. Relation between thalidomide and unusual limb defects in babies
born in 1959 and 1960
b.3. Cross-sectional
2. Experimental – examination of outcomes in which there is control of the conditions
under which the study is conducted and of the assignment of subjects to either the
treatment or comparison group
a. Randomized controlled trials or Clinical trials - subjects with equivalent
characteristics are randomly allocated to treatment and control groups, and
the results are assessed by comparing the outcome
EX. The effect of sugar-free gum-chewing in reducing incremental dental
caries among 6 – 12 years old
b. Field trials - studies involving disease-free populations but presumed to be at
risk (ex. field trial of Salk vaccine to prevent polio among children)
- evaluate interventions aimed at reducing exposure like the elimination of
lead paints in home environment (ex. to prevent the risk of lead poisoning)
c. Community trials or community intervention studies - treatment groups are
communities rather than individuals; for diseases that have their origins in
social conditions which can be more effectively influenced by
interventions directed at group behavior
MEASURES OF ORAL DISEASE OCCURRENCE
A. Dental Caries
1. DMFT - describes the amount (prevalence) of dental caries in an individual
and is obtained by calculating the number of Decayed (D), Missing (M)
and Filled (F) teeth
- either calculated for 28 permanent teeth, excluding 3rd molars or for 32
teeth
- frequently employed in descriptive studies describing the prevalence of
dental disease
- sum of the three figures forms the DMFT-value (Ex: DMFT of 4-3-9=16
means that 4 teeth are decayed, 3 teeth are missing and 9 teeth have
fillings)
a. D/DMFT - measure of the lack of dental treatment for the individual or
community of individuals
b. M/DMFT - represents predominantly the end result of a caries in contrast to
another population group which does not have many missing teeth
c. F/DMFT - indicates the amount of dental treatment rendered to an individual or
to a population group
To present caries data for adults, the following designations are used:
a. DMFT Rate: Mean number of decayed, missing & filled teeth of population examined
b. %DMFT: Percentage of population affected with dental caries
c. MT: Mean number of missing teeth
d. %D: Percentage with untreated decayed teeth

4. e. MNT: Mean number of teeth
f. DT: Mean number of decayed teeth
g. %Ed: Percentage edentulous
2. DMFS – detailed index of DMF calculated per tooth surface
- Molars and premolars are considered having 5 surfaces, front teeth 4 surfaces
- Maximum value for DMFS comes to 128 for 28 teeth
- employed in therapeutic investigations or trials because it focuses upon the
incidence of disease (Ex. DMFS of 22-3-19=44 means that 22 surfaces are
decayed, 3 teeth are missing and 9 surfaces have fillings)
* For the primary dentition, consisting of maximum 20 teeth, the corresponding
designations are "deft" or "defs", where "e" indicates "extracted and not exfoliated tooth".
B. Periodontal Disease Indices
1. Community Periodontal Index
- formerly called Community Periodontal Index for Treatment Needs
- measure of the periodontal health
- uses 3 indicators of periodontal status:
a. presence or absence of gingival bleeding
b. supra- or subgingival calculus
c. periodontal pockets-subdivided into shallow (4-5mrn) and deep (6mm
or more
C. Oral Hygiene
1. OHI-S (Oral Hygiene Index-Simplified)
- has two components, the Debris Index and the Calculus Index
- based on numerical determinations representing the amount of debris or
calculus found on the pre-selected 6 tooth surfaces: four posterior (buccal &
lingual) and two anterior (labial) teeth
Debris Index = bu-scores + li-scores / Total number of examined surfaces
Calculus Index = bu-scores + li-scores / Total number of examined surfaces
OHI-S index = Debris Index + Calculus Index
Criteria for classifying debris
Scores Criteria
0 No debris or stain present
1 Soft debris covering not more than one third of the tooth surface, or
presence of extrinsic stains without other debris regardless of surface
area covered
2 Soft debris covering more than one third, but not more than two
thirds, of the exposed tooth surface.
3 Soft debris covering more than two thirds of the exposed tooth

5. surface.
Criteria for classifying calculus
Scores Criteria
0 No calculus present
1 Supragingival calculus covering not more than third of the exposed tooth
surface.
2 Supragingival calculus covering more than one third but not more than
two thirds of the exposed tooth surface or the presence of individual
flecks of subgingival calculus around the cervical portion of the tooth or
both.
3 Supragingival calculus covering more than two third of the exposed
tooth surface or a continuos heavy band of subgingival calculus around
the cervical portion of the tooth or both.
Right molar Anterior Left molar Total
Bu Li La Li Bu Li Bu Li
Max 3 - 2 - 3 - 8 -
Man - 2 - - 1 2 1 4
Debris Index = bu-scores + li-scores / Total number of examined surfaces
Debris Index = (9+4) / 6 = 2.2
Right molar Anterior Left molar Total
Bu Li La La Bu Lil Bu Li
Max 1 - 0 - 1 - 2 -
Man - 1 - 2 - 2 2 3
Calculus Index = bu-scores + li-scores / Total number of examined
surfaces)
Calculus Index = (4+3) / 6= 1.2
OHI-S index = 2.2 + 1.2 = 3.4
2. Silness-Löe plaque index - recording both soft debris and mineralized deposits
on 16, 12, 24, 36, 32, 44 (Missing teeth are not substituted)
- Each of the four surfaces of the teeth (bu, li, me & di) is given a score
from 0-3 & the scores are added and divided by four to give the plaque
index for the tooth

6. - The index for the patient is obtained by summing the indices for all six
teeth and dividing by six
Scores Criteria
0 No plaque
A film of plaque adhering to the free gingival margin and
adjacent area of the tooth. The plaque may be seen in situ only
1
after application of disclosing solution or by using the probe on
the tooth surface.
Moderate accumulation of soft deposits within the gingival
2 pocket, or the tooth and gingival margin which can be seen
with the naked eye.
Abundance of soft matter within the gingival pocket and/or on
3
the tooth and gingival margin.
Assuming a tooth (16) with the following scores on the four surfaces:
Surface Scores
Buccal 2 Plaque Index = (2+1+1+2) / 4 = 1.5,
Lingual 1 plaque index for the tooth is moderate
accumulation of soft deposit within the
Mesial 1 gingival pocket, or the tooth and gingival
Distal 2 margin which can be seen with the naked eye
Tooth Index The index for the patient is obtained by
summing the indices for all six teeth and
16 1.5
dividing by six
12 1.3
24 1.2
36 1.0
The index for patient is
32 1.6
44 1.3 = (1.5 + 1.3 +1.2 + 1 + 1.6 + 1.3) / 6
= 1.4
Fluorosis
- lesions are usually bilaterally symmetrical and tend to show a horizontal striated
pattern across the tooth
- premolars and second molars are most frequently affected, followed by the
upper incisors ; mandibular incisors are least affected
D. Fluorosis Index

7. - recording is made on the basis of the two teeth that are most affected
- if the two teeth are not equally affected, the score for the less affected of the two
should be recorded
- when teeth are scored, examiner should start at the higher end of the index, i.e.
"severe", and eliminate each score until he or she arrives at the condition present
- if there is any doubt, the lower score should be given
CODE and CRITERIA
The enamel surface is smooth, glossy and usually a pale
0 Normal
creamy-white colour.
The enamel shows slight aberrations from the translucency of
1 Questionable normal enamel, which may range from a few white flecks to
occasional spots.
Small, opaque, paper-white areas scattered irregularly over
2 Very mild the tooth but involving less than 25% of the labial tooth
surface.
The white opacity of the enamel of the teeth is more extensive
3 Mild
than for code 2, but covers less than 50% of the tooth surface.
The enamel surfaces of the teeth show marked wear and
4 Moderate
brown stain is frequently a disfiguring feature.
The enamel surfaces are badly affected and hypoplasia is so
marked that the general form of the tooth may be affected.
5 Severe
There are pitted or worn areas and brown stains are
widespread; the teeth often have a corroded appearance.
Excluded
8 (e.g. a crowned -
tooth)
9 Not recorded -
NATURAL HISTORY OF DISEASE
• Process by which disease occur and progress in the human host
• Involves 3 factors:
1.causative agent - Factor whose presence or absence causes a diseases
a. physical - mechanical forces or friction that may produce injury
- atmospheric conditions like extremes of temperature and
excessive radiation
b. chemical - those that affect human physiology through chemical actions
- include substances that may occur as dusts, gases, vapors, fumes
or liquids
c. nutrient - refer specifically to basic components of the diet
d. biological - all living organisms like insects, worms, protozoa, fungi
and bacteria; also viruses

8. e. genetic - those transmitted from parent to child through the genes
f. psychological agents - stressful social circumstances in the environment
that affect physiology by psychosomatic means
Characteristics of Agents
1. Infectious agents
a. infectivity – extent to which agent is able to cause infection
b. pathogenicity – ability of agent to cause a disease
c. virulence – power of agent to disable the host
2. Non-infectious agents
a. concentration and toxicity for chemical agents
b. size, shape and intensity for physical agents
c. chronicity or suddenness for psychological agents
d. homo- or heterozygocity of genetic material for genetic agents
2. susceptible host - Individual human in whom an agent produces disease when
susceptible due to lack of immunity or inherent resistance
3. environment
- All external conditions and influences affecting the life of living things
- Provide reservoirs where agents can reside &/or reproduce, and modes of
transmission for transporting agents from reservoir to a host
Categories:
1. Physical - geological structure of an area and the availability of resources
like water and flora, that influence the number and variety of animal
reservoirs and certain insects that function as vectors to carry an agent
from reservoir to host
- influenced by weather, climate and season
2. Socio-economic - relates to the social norms & economic status of an area
- influences infectious agents present as to extent of environmental
sanitation practices or the availability of medical facilities and services
- influences non-infectious agents as to extent of psychological stressors,
means of livelihood or place of residence
3. Biological - living plants and animal that may serve as either:
a. reservoir – environment in which infectious agents normally live and
multiply, are dependent for survival and reproduction
b. vector – living carrier that transports infectious agents from infected
individuals, or their wastes to susceptible individuals, their food or
immediate surroundings
• The Disease Process
1. Pre – pathogenesis
a. susceptibility - disease has not yet developed but the groundwork has
been laid through presence of risk factors that favor its occurrence
b. adaptation - disease may/not develop when exposed to agent at this time
depending on the ability of host cells or functional systems to
accommodate the agent
2. Pathogenesis

9. a. Early pathogenesis - no symptoms to indicate presence of disease but
pathogenic changes have begun
- changes may be detectable by sophisticated laboratory tests to
confirm disease
b. clinical disease - symptoms experienced by patient and signs apparent
to clinician on physical examination
b.1.early clinical stage – when clinical diagnosis can be made
b.2.. late clinical stage – when disease becomes severe
- patient may recover, suffer from residual defect or die
• Infectious
1. incubation period - relatively very short
2. short duration of illness
3. host generally recovers without any residual disability or need for long-term
therapy
• Non-infectious
1. latency period- relatively long
2. long duration of illness
3. host generally does not recover; with residual disability and requires long-
term therapy
Mode of Transmission
1. Direct contact such as sexual contact, animal bites, respiratory droplets
- air-borne, blood-borne
2. Indirect contact (via vehicles)
- fomites (mucus droplet, utensils)
- vector like arthropods
a. mechanical transmission
b. biological transmission
- food and water
Portal of entry and exit
a. respiratory tract
- air-borne
b. digestive tract
- food- and water-borne
c. genito-urinary tract
- fluid-borne via parenteral route
d. skin and mucous membranes
- blood-borne via parenteral route
- vector-borne
Prevention and Control of Disease
- Directed towards:
1. source or reservoir of infection or agent
a. Isolation – separation for the period of communicability of carriers from others
to prevent transmission of agents to susceptibles

10. b. Quarantine – limitation of freedom of movement of persons exposed to a
communicable disease (contacts) for a period of time not longer than the
longest usual incubation period of the disease
c. Cleaning – removal of infectious/non-infectious agents and organic matters by
washing or scrubbing surfaces or areas which favor survival and
replication of agents
d. Disinfection – killing of infectious agents on inanimate objects by
chemical or physical means
e. Treatment – use of antimicrobials to shorten the course of illness and period
of communicability
For non-infectious
a. Removal of actual agent from environment before contact with susceptible
b. Minimize amount of agent
2. agent or mode of transmission
a. Disinfestation – physical or chemical process that destroys or removes small
animal forms like arthropods on persons, clothing or environment
a. fumigation
b. insecticide
c. rodenticide
b. Provision of safe and adequate water
c. Proper sewage and waste disposal
d. Food sanitation and milk hygiene
e. Proper housing drainage
3. susceptible population
a. Health education – process by which individuals/groups of people learn to
promote, maintain or restore health
b. Personal hygiene – measures primarily within the individual’s responsibility
which promote health and limit the spread of diseases
c. Chemoprophylaxis – administration of chemicals like antibiotics to prevent
development of infection or its progression to actively manifest disease
d. Repellent – chemical applied to skin/clothing/areas to discourage arthropods
from alighting & attacking/penetrating persons
e. Immunization
* For non-infectious
a. Personal protective equipment
b. Biologic monitoring
c. Screening