NEET MDS Synopsis
Immunohistochemistry
General Pathology
Immunohistochemistry
This is a method is used to detect a specific antigen in the tissue in order to identify the type of disease.
BONE
Anatomy
BONE
A rigid form of CT, Consists of matrix and cells
Matrix contains:
organic component 35% collagen fibres
inorganic salts 65% calcium phosphate (58,5%), calcium carbonate (6,5%)
2 types of bone - spongy (concellous)
compact (dense)
Microscopic elements are the same
Spongy bone consists of bars (trabeculae) which branch and unite to form a meshwork
Spaces are filled with bone marrow
Compact bone appears solid but has microscopic spaces
In long bones the shaft is compact bone
And the ends (epiphysis) consists of spongy bone covered with compact bone
Flat bones consists of 2 plates of compact bone with spongy bone in-between
Periosteum covers the bone
Endosteum lines marrow cavity and spaces
These 2 layers play a role in the nutrition of bone tissue
They constantly supply the bone with new osteoblasts for the repair and growth of bone
Microscopically
The basic structural unit of bone is the Haversian system or osteon
An osteon consists of a central Haversian canal
- In which lies vessels nerves and loose CT
- Around the central canal lies rings of lacunae
- A lacuna is a space in the matrix in which lies the osteocyte
- The lacunae are connected through canaliculi which radiate from the lacunae
- In the canaliculi are the processes of the osteocytes
- The canaliculi link up with one another and also with the Haversian canal
- The processes communicate with one another in the canaliculi through gap junctions
- Between two adjacent rows of lacunae lie the lamellae, 5-7µm thick
- In three dimensions the Haversian systems are cylindrical
- The collagen fibres lie in a spiral in the lamellae
- Perpendicular to the Haversian canals are the Volkman's canals
- They link up with the marrow cavity and the Haversian canals
- Some lamellae do not form part of a Haversian system
- They are the:
- Inner circumferential lamellae - around the marrow cavity
- Outer circumferential lamellae - underneath the outer surface of the bone
- Interstitial lamellae - between the osteons
Endosteum
Lines all cavities like marrow spaces, Haversian- and Volkman's canals
Consists of a single layer of squamous osteoprogenitor cells with a thin reticular CT layer underneath it
Continuous with the inner layer of periosteum
Covers the trabeculae of spongy bone
Cells differentiate into osteoblasts (like the cells of the periosteum)
Periosteum
Formed by tough CT
2 layers
Outer fibrous layer: Thickest, Contains collagen fibres,
Some fibres enter the bone - called Sharpey's fibres
Contains blood vessels.
Also fibrocytes and the other cells found in common CT
Inner cellular layer
Flattened cells (continuous with the endosteum)
Can divide and differentiate into osteoprogenitor cells
spindle shaped
little amount of rough EPR
poorly developed Golgi complex
play a prominent role in bone growth and repair
Osteoblasts
Oval in shape, Have thin processes, Rough EPR in one part of the cell (basophilic)
On the other side is the nucleus, Golgi and the centrioles in the middle, Form matrix
Become trapped in the matrix
Osteocytes
Mature cells, Less basophilic than the osteoblasts, Lie trapped in the lacunae, Their processes lie in the canaliculi, Processes communicate with one another through gap junctions, Substances (nutrients, waste products) are passed on from cell to cell
Osteoclasts
Very large, Multinucleate (up to 50), On inner and outer surface of bone, Lie in depressions on the surface called Howships lacunae, The cell surface facing the bone has short irregular processes
Acidophylic
Has many lysosomes, polyribosomes and rough EPR
Lysosomal enzymes are secreted to digest the bone
Resorbs the organic part of bone
Histogenesis
Two types of bone development.
- intramembranous ossification
- endochondral ossification
In both these types of bone development temporary primary bone is deposited which is soon replaced by secondary bone. Primary bone has more osteocytes and the mineral content is lower.
Hormones of the Hypothalamus
Physiology
The hypothalamus is a region of the brain. It secretes a number of hormones.
Thyrotropin-releasing hormone (TRH)
Gonadotropin-releasing hormone (GnRH)
Growth hormone-releasing hormone (GHRH)
Corticotropin-releasing hormone (CRH)
Somatostatin
Dopamine
All of these are released into the blood, travel immediately to the anterior lobe of the pituitary, where they exert their effects.
Two other hypothalamic hormones:
Antidiuretic hormone (ADH) and
Oxytocin
travel in neurons to the posterior lobe of the pituitary where they are released into the circulation.
Procedure for Test of Significance
Public Health DentistryA test of significance in dentistry, as in other fields of research, is a
statistical method used to determine whether observed results are likely due to
chance or if they are statistically significant, meaning that they are reliable
and not random. It helps dentists and researchers make inferences about the
validity of their hypotheses.
The procedure for conducting a test of significance typically involves the
following steps:
1. Formulate a Null Hypothesis (H0) and an Alternative Hypothesis (H1):
The null hypothesis is a statement that assumes there is no significant
difference between groups or variables being studied, while the alternative
hypothesis suggests that there is a significant difference. For example, in a
dental study comparing two different toothpaste brands for their effectiveness
in reducing plaque, the null hypothesis might be that there is no difference in
plaque reduction between the two brands, while the alternative hypothesis would
be that one brand is more effective than the other.
2. Choose a significance level (α): This is the probability of
incorrectly rejecting the null hypothesis when it is true. Common significance
levels are 0.05 (5%) or 0.01 (1%).
3. Determine the sample size: Depending on the research
question, power analysis or literature review may help determine the appropriate
sample size needed to detect a clinically significant difference.
4. Collect data: Gather data from a sample of patients or
subjects under controlled conditions or from existing databases.
5. Calculate test statistics: This involves calculating a value
that represents the magnitude of the difference between the observed data and
what would be expected if the null hypothesis were true. Common test statistics
include the t-test, chi-square test, and ANOVA (Analysis of Variance).
6. Determine the p-value: The p-value is the probability of
obtaining the observed results or results more extreme than those observed if
the null hypothesis were true. It is calculated based on the test statistic and
the chosen significance level.
7. Compare the p-value to the significance level (α): If the
p-value is less than the significance level, the result is considered
statistically significant. If the p-value is greater than the significance
level, the result is not statistically significant, and the null hypothesis is
not rejected.
8. Interpret the results: Based on the p-value, make a decision
about the null hypothesis. If the p-value is less than the significance level,
reject the null hypothesis and accept the alternative hypothesis. If the p-value
is greater than the significance level, fail to reject the null hypothesis.
Here is a simplified example of a test of significance applied to dentistry:
Suppose you are comparing two different toothpaste brands to determine if there
is a significant difference in their effectiveness in reducing dental plaque.
You conduct a study with 50 participants who are randomly assigned to use either
brand A or brand B for a month. After a month, you measure the plaque levels of
all participants.
1. Null Hypothesis (H0): There is no significant difference in plaque reduction
between the two toothpaste brands.
2. Alternative Hypothesis (H1): There is a significant difference in plaque
reduction between the two toothpaste brands.
3. Significance Level (α): 0.05
Now, let's say you collected the data and found that the mean plaque reduction
for brand A was 25%, with a standard deviation of 5%, and for brand B, the mean
was 30%, with a standard deviation of 4%. You could use an independent samples
t-test to compare the two groups' means.
4. Calculate the t-statistic: t = (Mean of Brand B - Mean of Brand A) /
(Standard Error of the Difference)
5. Find the p-value associated with the calculated t-statistic. If the p-value
is less than 0.05, you reject the null hypothesis.
If the p-value is less than 0.05, you can conclude that there is a statistically
significant difference in plaque reduction between the two toothpaste brands,
supporting the alternative hypothesis that one brand is more effective than the
other. This could lead to further research or a change in dental hygiene
recommendations.
In dental applications, tests of significance are commonly used in studies
examining the effectiveness of different treatments, materials, and procedures.
For instance, they can be applied to compare the success rates of different
types of dental implants, the efficacy of various tooth whitening methods, or
the impact of oral hygiene interventions on periodontal health. Understanding
the statistical significance of these findings allows dentists to make
evidence-based decisions and recommendations for patient care.
PHOSPHOLIPIDS
Biochemistry
PHOSPHOLIPIDS
These are complex or compound lipids containing phosphoric acid, in addition to fatty acids, nitrogenous base and alcohol
There are two classes of phospholipids
1. Glycerophospholipids (or phosphoglycerides) that contain glycerol as the alcohol.
2. Sphingophospholipids (or sphingomyelins) that contain sphingosine as the alcohol
Glycerophospholipids
Glycerophospholipids are the major lipids that occur in biological membranes. They consist of glycerol 3-phosphate esterified at its C1 and C2 with fatty acids. Usually, C1 contains a saturated fatty acid while C2 contains an unsaturated fatty acid.
In glycerophospholipids, we refer to the glycerol residue (highlighted red above) as the "glycerol backbone."
Glycerophospholipids are Amphipathic
Glycerophospholipids are sub classified as
1. Phosphatidylethanolamine or cephalin also abbreviated as PE is found in biological membranes and composed of ethanolamine bonded to phosphate group on diglyceride.
2. Phosphatidylcholine or lecithin or PC which has chloline bonded with phosphate group and glycerophosphoric acid with different fatty acids like palmitic or hexadecanoic acid, margaric acid, oleic acid. It is a major component of cell membrane and mainly present in egg yolk and soy beans.
3. Phosphatidic acid (phosphatidate) (PA)
It consists of a glycerol with one saturated fatty acid bonded to carbon-1 of glycerol and an unsaturated fatty acid bonded to carbon-2 with a phosphate group bonded to carbon-3.
4.Phosphatidylserine (PS)
This phospholipid contains serine as an organic compound with other main components of phospholipids. Generally it found on the cytosolic side of cell membranes.
5. Phosphoinositides
It is a group of phospholipids which are negatively charged and act as a a minor component in the cytosolic side of eukaryotic cell membranes. On the basis of different number of phosphate groups they can be different types like phosphatidylinositol phosphate (PIP), phosphatidylinositol bisphosphate(PIP2) and phosphatidylinositol trisphosphate (PIP3). PIP, PIP2 and PIP3 and collectively termed as phosphoinositide.
6. Cardiolipin :
lt is so named as it was first isolated from heart muscle. Structurally, a cardiolipin consists of two molecules of phosphatidic acid held by an additional glycerol through phosphate groups. lt is an important component of inner mitochondrial membrane. Cardiolipin is the only phosphoglyceride that possesses antigenic properties.
Water Acid Bases & Buffers -pKa
Biochemistry
Acids and bases can be classified as proton donors and proton acceptors, respectively. This means that the conjugate base of a given acid will carry a net charge that is more negative than the corresponding acid. In biologically relavent compounds various weak acids and bases are encountered, e.g. the acidic and basic amino acids, nucleotides, phospholipids etc.
Weak acids and bases in solution do not fully dissociate and, therefore, there is an equilibrium between the acid and its conjugate base. This equilibrium can be calculated and is termed the equilibrium constant = Ka. This is also referred to as the dissociation constant as it pertains to the dissociation of protons from acids and bases.
In the reaction of a weak acid:
HA <-----> A- + H+
the equlibrium constant can be calculated from the following equation:
Ka = [H+][A-]/[HA]
As in the case of the ion product:
pKa = -logKa
Therefore, in obtaining the -log of both sides of the equation describing the dissociation of a weak acid we arrive at the following equation:
-logKa = -log[H+][A-]/[HA]
Since as indicated above -logKa = pKa and taking into account the laws of logrithms:
pKa = -log[H+] -log[A-]/[HA]
pKa = pH -log[A-]/[HA]
From this equation it can be seen that the smaller the pKa value the stronger is the acid. This is due to the fact that the stronger an acid the more readily it will give up H+ and, therefore, the value of [HA] in the above equation will be relatively small.
Test for Antigen - Antibody Reactions
General MicrobiologyTest for Antigen - Antibody Reactions
Antigens are those substance that stimulates the production of antibodies which, when enter into the body it reacts specifically in a manner that are clearly visible.
Some antigens may not induce antibody production, but instead creates immunological tolerance.
An antigen introduced into the body produces only specific antibodies and will react with only those specific antigens.
These antibodies appear in the serum and tissue fluids. All antibodies are considered as immunoglobulin. They are mainly of five classes; IgG, IgA, IgM, IgD and IgE.
Antigen- antibody reactions are known as serological reactions and are used as serological diagnostic tests for the identification of infectious diseases.
The reaction occurs mainly in three stages;
1. The initial interaction between the antigen and antibody, which produces no visible effects. It is a reversible and rapid reaction.
2. The secondary stage leads to the demonstration proceedings, such as precipitation, agglutination, etc.
3. The tertiary reaction follows the neutralization or destruction of injurious antigens. These results in clinical allergy and other immunological diseases.
There are certain characteristics for antigen-antibody reactions;
1. Reaction is specific.
2. The whole molecules participate in the reaction, and not just a part of it.
3. No denaturation of antigen or antibody occurs during the reaction.
4. The combination usually occurs at the surface.
5. The combination is firm, but reversible
6. Agglutinins formed after agglutination usually are formed by both antigen and antibody together.
7. They can combine in varying proportions.
Measurement of antigen and antibody are made in terms of mass or as units or titre.
Serological reactions include;
1. Precipitation reaction
a soluble antigen combining with the specific antibody in the presence of electrolytes at a suitable temperature and pH forming insoluble precipitins. Commonly used tests are ring test, slide test, tube test, immunodiffusion, etc.
Radial Immunodiffusion
In radial immunodiffusion antibody is incorporated into the agar gel as it is poured and different dilutions of the antigen are placed in holes punched into the agar. As the antigen diffuses into the gel, it reacts with the antibody and when the equivalence point is reached a ring of precipitation is formed .
This test is commonly used in the clinical laboratory for the determination of immunoglobulin levels in patient samples.
Immunoelectrophoresis
In immunoelectrophoresis, a complex mixture of antigens is placed in a well punched out of an agar gel and the antigens are electrophoresed so that the antigen are separated according to their charge. After electrophoresis, a trough is cut in the gel and antibodies are added. As the antibodies diffuse into the agar, precipitin lines are produced in the equivalence zone when an antigen/antibody reaction occurs .
This tests is used for the qualitative analysis of complex mixtures of antigens
This test can also be used to evaluate purity of isolated serum proteins.
Countercurrent electrophoresis
In this test the antigen and antibody are placed in wells punched out of an agar gel and the antigen and antibody are electrophoresed into each other where they form a precipitation line.
2. Agglutination reaction
when a particulate antigen is mixed with its antibody in the presence of electrolytes at a suitable temperature and pH, the particles are clumped or agglutinated. When the antigen is an erythrocyte the term hemagglutination is used.
Applications of agglutination tests
i. Determination of blood types or antibodies to blood group antigens.
ii. To assess bacterial infections
e.g. A rise in titer of an antibody to a particular bacterium indicates an infection with that bacterial type. N.B. a fourfold rise in titer is generally taken as a significant rise in antibody titer.
Passive hemagglutination
The agglutination test only works with particulate antigens. However, it is possible to coat erythrocytes with a soluble antigen (e.g. viral antigen, a polysaccharide or a hapten) and use the coated red blood cells in an agglutination test for antibody to the soluble antigen . This is called passive hemagglutination.
The test is performed just like the agglutination test.
Applications include detection of antibodies to soluble antigens and detection of antibodies to viral antigens.
Coomb's Test (Antiglobulin Test)
DIRECT ANTIGLOBULIN TEST (DAT)
The DAT is used to detect IgG or C3 bound to the surface of the red cell. In patients with hemolysis, the DAT is useful in determining whether there is an immune etiology.
A positive DAT can occur without hemolysis
Immune causes of hemolysis including autoimmune hemolytic anemias, drug induced hemolysis, and delayed or acute hemolytic transfusion reactions are characterized by a positive DAT.
INDIRECT ANTIGLOBULIN TEST (IAT)
The IAT (antibody screen) is performed by incubating patient serum with reagent screening red cells for approximately 20 minutes and then observing for agglutination. If the antibody screen is positive, additional testing is required to determine the specificity of the antibody.
The IAT is used to detect red cell antibodies in patient serum. Approximately 5% of patients have a positive IAT due to IgG antibodies, IgM antibodies, or both.
3. Complement fixation test (CFT)
the ability of antigen antibody complexes to fix complement is made use in this test. Complement is something which takes part in any immunological reaction and absorbed during the combining of antigen with its specific antibody.
The best example of CFT is the Wassermann reaction done for the detection of Syphilis.
4. Neutralization test
different types of these are available. Virus neutralization, toxin neutralization, etc. are some of its kind.
5. Opsonization
this makes use of the determination of opsonic index, which is the ratio of the phagocytic activity of patient’s blood to the phagocytic activity of the normal patient’s for a given bacterium.
6. Immunfluorescence
the method of labeling the antibodies with fluorescent dyes and using them for the detection of antigens in tissues.
7. Radioimmunoassay (RIA)
is a competitive binding radioisotopes and enzymes are used as labels to conjugate with antigens or antibodies.
8. Enzyme Immuno Assay (EIA)
the assays based on the measurement of enzyme labeled antigen or antibody. The most common example is ELISA used to detect HIV.
9. Immunoelectroblot
it uses the sensitivity of Enzyme immunoassay with a greater specificity. Example is Western blot done for the serodiagnosis of HIV infection.
CASTING DEFECTS
Dental Materials
CASTING DEFECTS
Classification :
1) Distortion.
2) Surface roughness .
3) Porosity .
4)Incomplete casting .
5) Oxidation .
6) Sulfur contamination .
Distortion
It is usually due to the distortion of wax pattern.
To avoid this :
Manipulation of the wax at its softening temp
Invest the pattern at the earliest .
If storage is necessary store it in a refrigerator .
Surface roughness
May be due to :
Air bubbles on the wax pattern .
Cracks due to rapid heating of the investment .
High W/P ratio .
Prolonged heating of the mold cavity .
Overheating of the gold alloy .
Too high or too low casting pressure .
Composition of the investment .
Foreign body inclusion.
POROSITY
May be internal or external .
External porosity causes discolouration .
Internal porosity weakens the restoration .
Classification of porosity .
I .Those caused by solidification shrinkage :
a) Localised shrinkage porosity .
b) Suck back porosity .
c) Microporosity .
They are usually irregular in shape .
II ) Those caused by gas :
a) Pin hole porosity .
b) Gas inclusions .
c) Subsurface porosity .
Usually they are spherical in shape .
III ) Those caused by air trapped in the mold :
Back pressure porosity .
Localised shrinkage porosity
Large irregular voids found near sprue casting junction.
Occurs when cooling sequence is incorrect .
If the sprue solidifies before the rest of the casting , no more molten metal is supplied from the sprue which can cause voids or pits (shrink pot porosity )
This can be avoided by -
- using asprue of correct thickness .
- Attach the sprue to the thickest portion of the pattern .
-Flaring of the sprue at the point of atttachment .
-Placing a reservoir close to the pattern .
Suck back porosity
It is an external void seen in the inside of a crown opposite the sprue .
Hot spot is created which freezes last .
It is avoided by :
Reducing the temp difference between the mold & molten alloy .
Microporosity :
Fine irregular voids within the casting .
Occurs when casting freezes rapidly .
Also when mold or casting temp is too low .
Pin hole porosity :
Upon solidification the dissolved gases are expelled from the metal causing tiny voids .
Pt & Pd absorb Hydrogen .
Cu & Ag absorb oxygen .
Gas inclusion porosities
Larger than pin hole porosities .
May be due to dissolved gases or due to gases Carried in or trapped by molten metal .
Apoorly adjusted blow torech can also occlude gases .
Back pressure porosity
This is caused by inadequate venting of the mold .The sprue pattern length should be adjusted so that there is not more than ¼” thickness of the investmentbetween the bottom of the casting .
This can be prevented by :
- using adequate casting force .
-use investment of adequate porosity .
-place the pattern not more than 6-8 mm away from tne end of the casting .
Casting with gas blow holes
This is due to any wax residue in the mold .
To eliminate this the burnout should be done with the sprue hol facing downwards for the wax pattern to run down.
Incomplete casting
This is due to :
- insufficient alloy .
-Alloy not able to enter thin parts of the mold .
-When the mold is not heated to the casting temp .
-Premature solidification of the alloy .
-sprues blocked with foreign bodies .
-Back pressure of gases .
-low casting pressure .
-Alloy not sufficiently molten .
Too bright & shiny casting with short & rounded margins :
occurs when wax is eliminated completely ,it combines with oxygen or air to form carbon monoxide .
Small casting :
occurs when proper expansion is not obtained & due to the shrinkage of the impression .
Contamination of the casting
1) Due to overheating there is oxidation of metal .
2) Use of oxidising zone of the flame .
3) Failure to use a flux .
4) Due to formation sulfur compounds .
Black casting
It is due to :
1) Overheating of the investment .
2) Incomplete elimination of the wax .