Plaque index (PlI)    

    0 = No plaque in the gingival area.
    1 = A thin film of plaque adhering to the free gingival margin and adjacent to the area of the tooth. The plaque is not readily visible, but is recognized by running a periodontal probe across the tooth surface.
    2 = Moderate accumulation of plaque on the gingival margin, within the gingival pocket, and/or adjacent to the tooth surface, which can be observed visually.
    3 = Abundance of soft matter within the gingival pocket and/or adjacent to the tooth surface.

Gingival index (GI)    

    0 = Healthy gingiva.
    1= Mild inflammation: characterized by a slight change in color, edema. No bleeding observed on gentle probing.
    2 = Moderate inflammation: characterized by redness, edema, and glazing. Bleeding on probing observed.
    3 = Severe inflammation: characterized by marked redness and edema. Ulceration with a tendency toward spontaneous bleeding.

Modified gingival index (MGI)    

    0 = Absence of inflammation.
    1 = Mild inflammation: characterized by a slight change in texture of any portion of, but not the entire marginal or papillary gingival unit.
    2 = Mild inflammation: criteria as above, but involving the entire marginal or papillary gingival unit.
    3 = Moderate inflammation: characterized by glazing, redness, edema, and/or hypertrophy of the marginal or papillary gingival unit.
    4 = Severe inflammation: marked redness, edema, and/or hypertrophy of the marginal or papillary gingival unit, spontaneous bleeding, or ulceration.
    
Community periodontal index (CPI)    

    0 = Healthy gingiva.
    1 = Bleeding observed after gentle probing or by visualization.
    2 = Calculus felt during probing, but all of the black area of the probe remains visible (3.5-5.5 mm from ball tip).
    3 = Pocket 4 or 5 mm (gingival margin situated on black area of probe, approximately 3.5-5.5 mm from the probe tip).
    4 = Pocket > 6 mm (black area of probe is not visible).
    
Periodontal screening and recording (PSR)    

    0 = Healthy gingiva. Colored area of the probe remains visible, and no evidence of calculus or defective margins is detected.
    1 = Colored area of the probe remains visible and no evidence of calculus or defective margins is detected, but bleeding on probing is noted.
    2 = Colored area of the probe remains visible and calculus or defective margins is detected.
    3 = Colored area of the probe remains partly visible (probe depth between 3.5-5.5 mm).
    4 = Colored area of the probe completely disappears (probe depth > 5.5 mm).
 

Terms

Health—state of complete physical, mental, and social well-being where basic human needs are met. not merely the absence of disease or infirmity; free from disease or pain

Public health — science and art of preventing disease. prolonging life, and promoting physical and mental health and efficiency through organized community efforts

1. Public health is concerned with the aggregate health of a group, a community, a state, a nation. or a group of nations

2. Public health is people’s health

3. Concerned with four broad areas

a. Lifestyle and behavior

b. The environment

c. Human biology

d. The organization of health programs and systems

Dental public health—science and art of preventing and controlling dental diseases and promoting dental health through organized community efforts; that form of dental practice that serves the community as a patient rather than the individual; concerned with the dental education of the public, with applied dental research, and with the administration of group dental care programs. as well as the prevention and control of dental diseases on a community basis

Community health—same as public health full range of health services, environmental and personal, including major activities such as health education of the public and the social context of life as it affects the community; efforts that are organized to promote and restore the health and quality of life of the people

Community dental health services are directed to ward developing, reinforcing, and enhancing the oral health status of people either as individuals or collectively as groups and communities

Classifications of epidemiologic research

1. Descriptive research —involves description, documentation, analysis, and interpretation of data to evaluate a current event or situation

a. incidence—number of new cases of a specific disease within a defined population over a period of time

b. Prevalence—number of persons in a population affected by a condition at any one time

c. Count—simplest sum of disease: number of cases of disease occurrence

d. Proportion—use of a count with the addition of a denominator to determine prevalence:

does not include a time dimension: useful to evaluate prevalence of caries in schoolchildren or tooth loss in adult populations

e. Rate— uses a standardized denominator and includes a time dimension. for example. the number of deaths of newborn infants within first year of life per 1000 births

2. Analytical research—determines the cause of disease or if a causal relationship exists between a factor and a disease

a. Prospective study—planning of the entire study is completed before data are collected and analyzed; population is followed through time to determine which members develop the disease; several hypotheses may be tested at on time

b. Cohort study—individuals are classified into groups according to whether or not they pos- sess a particular characteristic thought to be related to the condition of interest; observations occur over time to see who develops dis ease or condition

c. Retrospective study— decision to carry out an investigation using observations or data that have been collected in the past; data may be incomplete or in a manner not appropriate for study

d. Cross-sectional study— study of subgroups of individuals in a specific and limited time frame to identify either initially to describe current status or developmental changes in the overall group from the perspective of what is typical in each subgroup

e. Longitudinal study—investigation of the same group of individuals over an extended period of time to identify a change or devel opment in that group

3. Experimental research—used when the etiology of the disease is established and the researcher wishes to determine the effectiveness of altering some factor or factors; deliberate applying or withholding of the supposed cause of a condition and observing the result

Berkson's Bias is a type of selection bias that occurs in case-control studies, particularly when the cases and controls are selected from a hospital or clinical setting. It arises when the selection of cases (individuals with the disease) and controls (individuals without the disease) is influenced by the presence of other conditions or factors, leading to a distortion in the association between exposure and outcome.

Key Features of Berkson's Bias

1. Hospital-Based Selection: Berkson's Bias typically occurs in studies where both cases and controls are drawn from the same hospital or clinical setting. This can lead to a situation where the controls are not representative of the general population.

2. Association with Other Conditions: Individuals who are hospitalized may have multiple health issues or risk factors that are not present in the general population. This can create a misleading association between the exposure being studied and the disease outcome.

3. Underestimation or Overestimation of Risk: Because the controls may have different health profiles compared to the general population, the odds ratio calculated in the study may be biased. This can lead to either an overestimation or underestimation of the true association between the exposure and the disease.

Example of Berkson's Bias

Consider a study investigating the relationship between smoking and lung cancer, where both cases (lung cancer patients) and controls (patients without lung cancer) are selected from a hospital. If the controls are patients with other diseases that are also related to smoking (e.g., chronic obstructive pulmonary disease), this could lead to Berkson's Bias. The controls may have a higher prevalence of smoking than the general population, which could distort the perceived association between smoking and lung cancer.

Implications of Berkson's Bias

• Misleading Conclusions: Berkson's Bias can lead researchers to draw incorrect conclusions about the relationship between exposures and outcomes, which can affect public health recommendations and clinical practices.
• Generalizability Issues: Findings from studies affected by Berkson's Bias may not be generalizable to the broader population, limiting the applicability of the results.

Mitigating Berkson's Bias

To reduce the risk of Berkson's Bias in research, researchers can:

1. Select Controls from the General Population: Instead of selecting controls from a hospital, researchers can use population-based controls to ensure a more representative sample.

2. Use Multiple Control Groups: Employing different control groups can help identify and account for potential biases.

3. Stratify Analyses: Stratifying analyses based on relevant characteristics (e.g., age, sex, comorbidities) can help to control for confounding factors.

4. Conduct Sensitivity Analyses: Performing sensitivity analyses can help assess how robust the findings are to different assumptions about the data.

Decayed-Missing-Filled Index ( DMF ) which was introduced by Klein, Palmer and Knutson in 1938 and modified by WHO:

1. DMF teeth index (DMFT) which measures the prevalence of dental caries/Teeth.
2. DMF surfaces index (DMFS) which measures the severity of dental caries.
The components are:

D component:
Used to describe (Decayed teeth) which include:
1. Carious tooth.
2. Filled tooth with recurrent decay.
3. Only the root are left.
4. Defect filling with caries.
5. Temporary filling.
6. Filled tooth surface with other surface decayed

M component:
Used to describe (Missing teeth due to caries) other cases should be excluded these are:
1. Tooth that extracted for reasons other than caries should be excluded, which include:
 a- Orthodontic treatment.
 b- Impaction.
 c- Periodontal disease.
2. Unerupted teeth.
3. Congenitally missing.
4. Avulsion teeth due to trauma or accident.

F component:
Used to describe (Filled teeth due to caries).

Teeth were considered filled without decay when one or more permanent restorations were present and there was no secondary (recurrent) caries or other area of the tooth with primary caries.
A tooth with a crown placed because of previous decay was recorded in this category.

Teeth restored for reason other than dental caries should be excluded, which include:
1. Trauma (fracture).
2. Hypoplasia (cosmatic purposes).
3. Bridge abutment (retention).
4. Seal a root canal due to trauma.
5. Fissure sealant.
6. Preventive filling.

1. A tooth is considered to be erupted when just the cusp tip of the occlusal surface or incisor edge is exposed.
The excluded teeth in the DMF index are:
a. Supernumerary teeth.
b. The third molar according to Klein, Palmer and Knutson only.

2. Limitations - DMF index can be invalid in older adults or in children because index can overestimate caries record by cases other than dental caries.

1. DMFT: a. A tooth may have several restorations but it counted as one tooth, F. b. A tooth may have restoration on one surface and caries on the other, it should be counted as D . c. No tooth must be counted more than once, D M F or sound.

2. DMFS: Each tooth was recorded scored as 4 surfaces for anterior teeth and 5 surfaces for posterior teeth. a. Retained root was recorded as 4 D for anterior teeth, 5 D for posterior teeth. b. Missing tooth was recorded as 4 M for anterior teeth, 5 M for posterior teeth. c. Tooth with crown was recorded as 4 F for anterior teeth, 5 F for posterior teeth.

Calculation of DMFT \ DMFS:

1. For individual

DMF = D + M + F

2. For population 

Minimum score = Zero

Primary teeth index:
1. dmft / dmfs Maximum scores: dmft = 20 , dmfs = 88
2. deft / defs, which was introduced by Gruebbel in 1944: d- decayed tooth. e- decayed tooth indicated for extraction . f- filled tooth.
3. dft / dfs: In which the missing teeth are ignored, because in children it is difficult to make sure whether the missing tooth was exfoliated or extracted due to caries or due to serial extraction.

Mixed dentition:

Each child is given a separate index, one for permanent teeth and another for primary teeth. Information from the dental caries indices can be derived to show the:

1. Number of persons affected by dental caries (%).

2. Number of surfaces and teeth with past and present dental caries (DMFT / dmft - DMFS / dmfs).

3. Number of teeth that need treatment, missing due to caries, and have been treated ( DT/dt, MT/mt, FT/f t).

When testing a null hypothesis, two types of errors can occur:

1. Type I Error (False Positive):

   • Definition: This error occurs when the null hypothesis is rejected when it is actually true. In other words, the researcher concludes that there is an effect or difference when none exists.
   • Consequences in Dentistry: For example, a study might conclude that a new dental treatment is effective when it is not, leading to the adoption of an ineffective treatment.

2. Type II Error (False Negative):

   • Definition: This error occurs when the null hypothesis is not rejected when it is actually false. In this case, the researcher fails to detect an effect or difference that is present.
   • Consequences in Dentistry: For instance, a study might conclude that a new dental material is not superior to an existing one when, in reality, it is more effective, potentially preventing the adoption of a beneficial treatment.