NEET MDS Synopsis
Primary Retention Form
Conservative DentistryPrimary Retention Form in Dental Restorations
Primary retention form refers to the geometric shape or design of a prepared
cavity that helps resist the displacement or removal of a restoration due to
tipping or lifting forces. Understanding the primary retention form is crucial
for ensuring the longevity and stability of various types of dental
restorations. Below is an overview of primary retention forms for different
types of restorations.
1. Amalgam Restorations
A. Class I & II Restorations
Primary Retention Form:
Occlusally Converging External Walls: The walls of
the cavity preparation converge towards the occlusal surface, which
helps resist displacement.
Occlusal Dovetail: In Class II restorations, an
occlusal dovetail is often included to enhance retention by providing
additional resistance to displacement.
B. Class III & V Restorations
Primary Retention Form:
Diverging External Walls: The external walls
diverge outward, which can reduce retention.
Retention Grooves or Coves: These features are
added to enhance retention by providing mechanical interlocking and
resistance to displacement.
2. Composite Restorations
A. Primary Retention Form
Mechanical Bond:
Acid Etching: The enamel and dentin surfaces are
etched to create a roughened surface that enhances mechanical retention.
Dentin Bonding Agents: These agents infiltrate the
demineralized dentin and create a hybrid layer, providing a strong bond
between the composite material and the tooth structure.
3. Cast Metal Inlays
A. Primary Retention Form
Parallel Longitudinal Walls: The cavity preparation
features parallel walls that help resist displacement.
Small Angle of Divergence: A divergence of 2-5 degrees
may be used to facilitate the seating of the inlay while still providing
adequate retention.
4. Additional Considerations
A. Occlusal Dovetail and Secondary Retention Grooves
Function: These features aid in preventing the proximal
displacement of restorations by occlusal forces, enhancing the overall
retention of the restoration.
B. Converging Axial Walls
Function: Converging axial walls help prevent occlusal
displacement of the restoration, ensuring that the restoration remains
securely in place during function.
Antiarrhythmic Drugs - Class III Potassium Channel Blockers
Pharmacology
Class III Potassium Channel Blockers
Prolong effective refractory period by prolonging Action Potential
Treatment: ventricular tachycardia and fibrillation, conversion of atrial fibrillation or flutter to sinus rhythm, maintenance of sinus rhythm
– Amiodarone (Cordarone) – maintenance of sinus rhythm
– Bretylium (Bretylol)
– Ibutilide (Corvert)
– Dofetilide (Tykosyn)
– Sotalol (Betapace)
Amiodarone
- Has characteristics of sodium channel blockers, beta blockers, and calcium channel blockers
- Has vasodilating effects and decreases systemic vascular resistance
- Prolongs conduction in all cardiac tissue
- Decreases heart rate
- Decreases contractility of the left ventricles
Class III - Adverse Effects
- GI- Nausea vomiting and GI distress
- CNS- Weakness and dizziness
- CV-Hypotension, CHF, and arrhythmias are common.
- Amiodarone associated with potentially fatal Hepatic toxicity, ocular abnormalities and serious cardiac arrhythmias.
Drug – Drug Interactions
These drugs can cause serious toxic effects if combined with digoxin or quinidine.
Muscles Around the Nose
AnatomyMuscles Around the Nose
The Nasalis Muscle
This muscle consists of a transverse (compressor naris) and alar (dilator naris) parts.
It is supplied by the buccal branch of the facial nerve.
NITRIC OXIDE-DEPENDENT KILLING
General Microbiology
NITRIC OXIDE-DEPENDENT KILLING
Binding of bacteria to macrophages, particularly binding via Toll-like
receptors, results in the production of TNF-alpha, which acts in an autocrine
manner to induce the expression of the inducible nitric oxide synthetase gene (i-nos
) resulting in the production of nitric oxide (NO) . If the cell is also exposed
to interferon gamma (IFN-gamma) additional nitric oxide will be produced (figure
12). Nitric oxide released by the cell is toxic and can kill microorganism in
the vicinity of the macrophage.
Skeletal Muscle:
Anatomy
Skeletal Muscle: 1-40 cm long fibres, 10- 60 µm thick, according to myoglobin content there are:
Red fibres: lots of myoglobin, many mitochondriam slow twitching - tire slowly
White fibres: less myoglobin, less mitochondria, fast twitching - tire quickly
Intermediate fibres:
mixture of 2 above
Most muscles have all three - in varying ratios
Structure of skeletal muscle:
Light Microscopy: Many nuclei - 35/mm, Nuclei are oval - situated peripheral, Dark and light bands
Electron Microscopy: Two types of myofilaments
Actin
- 5,6 nm
3 components:
-actin monomers,
-tropomyosin - 7 actin molecules long
- troponin
actin monomers form 2 threats that spiral
- tropomyosin - lie in the groove of the spiral
- troponin - attach every 40 nm
- one end attach to the Z line
- other end goes to the middle of the sarcomere
- Z line consists of á actinin
Myosin:
- 15 nm
- 1,6 µm long
- The molecule has a head and a tail
- tails are parallel
- heads project in a spiral
- in the middle is a thickening
- thin threats bind the myosin at thickening (M line)
Contraction:
A - band stays the same, I - band, H - bands become narrower
Myosin heads ratchet on the actin molecule
Sarcolemma: 9 nm thick, invaginate to form T-tubule,
myofibrils - attach to the sarcolemma
Sarcoplasmic Reticulum:
specialized smooth EPR, Consists of T-tubules, terminal sisternae and sarcotubules
It is speculated that there are gap junctions between the T-tubule and terminal sisterna
An impulse is carried into the fiber by the T-tubule from where it goes to the rest of the sarcoplasmic reticulum
Connective tissue coverings of the muscle
Endomycium around fibres, perimycium around bundles and epimycium around the whole muscle
Blood vessels and nerves in CT
CT goes over into tendon or aponeurosis which attaches to the periosteum
Nerves:
The axon of a motor neuron branches and ends in motor end plates on the fiber
Specialized striated fibres called spindles (stretch receptors) form sensory receptors in muscles telling the brain how far the muscle has stretched
Model. Cast. and Die Materials
Dental Materials
Model. Cast. and Die Materials
Applications
- Gold casting, porcelain and porcelain-fused–to metal fabrication procedures
- Orthodontic and pedodontic appliance construction
- Study models for occlusal records
Terms
a. Models-replicas of hard and soft tissues for study of dental symmetry
b. Casts-working replicas of hard and soft tissues for use in the fabrication of appliances or restorations
c. Dies :- working replicas of one tooth (or a few teeth) used for the fabrication of a restoration
d. Duplicates-second casts prepared from original casts
Classification by materials
a Models :- (model plaster or orthodontic stone; gypsum product)
b. Stone casts (regular stone; gypsum product)
c. Stone dies (diestone; gypsum product)-may electroplated
d. Epoxy dies (epoxy polymer)-abrasion-resistant dies
NEUROHISTOLOGY
Anatomy
NEUROHISTOLOGY
The nervous system develops embryologically from ectoderm, which forms the neural plate
Successive growth and folding of the plate results in the formation of the primitive neural tube.
The neuroblasts in the wall of the tube differentiates into 3 cell types:
Neurons: conduction of impulses
Neuroglial cells: connective tissue and support of CNS
Ependymal cells: Lines the lumen of the tube.
- Specialized neuro-ectodermal cells which lines the ventricles of the adult brain
- Essentially also a neuroglial cell
Basic Unit = neuron
Exhibits irritability (excitability) and conductivity
A typical neurons consists of:
Cell body : Has nucleus (karyon) and surrounding cytoplasm (perikaryon) which contains organelles cell's vitality
Dendrites: Several short processes
Axon:One large process
Terminates in twig like branches (telodendrons)
May also have collateral branches projecting along its course. These exit at nodes of Ranvier
Axon enveloped in a sheath, and together forms the nerve fiber
Classification:
May be done in different ways, i.e.
Functional = afferent, efferent, preganglionic, postganglionic, etc.
Morphological = shape, processes, etc
A typical morphological classification is as follows
a. Unipolar: Has one process only Not found in man
b. Bipolar (so-called ganglion cell):Has two processes Found in sensory systems, e.g. retina olfactory system
c. Multipolar: Has several process Most common in CNS
Cell bodies vary in shape, e.g. stellate (star) , pyramidal
d. Pseudo-unipolar: Essentially bipolar neurons, but processes have swung around cb and fused with each other. They therefore enter and leave at one pole of the cell.
Typical neuron:
- Has 2 or more dendrites
Close to the cb the cytoplasm of dendrites has Nissl granules as well as mitochondria
Only one axon Arises from axon hillock, Devoid of Nissl granules, Encased in myelin sheath
No additional covering except for occasional foot processes of neuroglial cells
May branch at right angles
Branches at a node of Ranvier is known as a collateral
Ends of axons break up into tree-like branches, known as telodendria
Axons may be short (Golgi Type II) e.g. internuncial long (Golgi Type I) e.g. pyramidal neuron
Nucleus Central position Large and spherical
Chromatin is extended and thus not seen in LM. This allows the nucleolus to be prominent
Cytoplasm (perikaryon)
Surrounds nucleus May be large or small, shape may be round, oval, flattened, pyramidal, etc
Contains aggregates Nissl granules(Bodies) which is also sometimes referred to as rhomboid flakes
aggregation of membranes and cisternae of rough endoplasmic reticulum (RER)
numerous ribosomes and polyribosomes scattered between cisternae
(Polyribosome = aggregate of free ribosomes clumped together)
responsible for ongoing synthesis of new cytoplasm and cytoplasmic substances
needed for conduction of impulses
highly active in cell protein synthesis
resultant loss of power to divide which is characteristic of neurons
- Golgi network surrounding nucleus (seen in EM only)
- Fibrils made up of:
- neurofilaments
- microtubules
Tubules involved in:
1. plasmic transport
2. maintenance of cell shape
3. essential for growth and elongation of axons and dendrites
Neurofilament:
1. provide skeletal framework
2. maintenance of cell shape
3. possible role in axonal transport
(Axonal [axoplasmic; plasmic] transport may be antero- or retrograde. Anterograde transport via neurotubules is fast and moves neurotransmitters. Retrograde transport is slow and is the reason why viruses and bacteria can attack and destroy cell bodies. E.g. polio in the ventral columns and syphilis in the dorsal columns).
- Numerous mitochondria
- Neurons lack ability to store glycogen and are dependent for energy on circulating glucose
Impulses are conducted in one direction only
Dendrites conduct towards the cb
Axons conduct away from cb
Synapses:
- Neurons interconnect by way of synapses
- Normally the telodendria of an axon synapse with the dendrites of a succeeding axon
axo-dendritic synapse
This is usually excitatory
- Other types of synapses are:
axo-axonic
May be excitatory and/or inhibitory
axo-somatic
May be excitatory and/or inhibitory
dendrodendritic
Usually inhibitory
- Synapses are not tight junctions but maintain a narrow space the so-called synaptic cleft
- The end of an telodendron is usually enlarged (bouton) and contains many synaptic vesicles,
mitochondrion, etc. Its edge that takes part in the synapse is known as the postsynaptic membrane and no
vesicles are seen in this area
- Synapses may be chemical (as above) or electrical as in the ANS supplying smooth muscle cells subjacent to adjacent fibres
Gray and White Matter of Spinal Cord:
- Gray matter contains:
- cb's (somas) of neurons
- neuroglial cells
- White matter contains:
- vast number of axons
- no cb's
- colour of white matter due to myelin that ensheathes axons
Myelin:
- Non-viable fatty material contains phospholipids, cholesterol and some proteins
- Soluble and not seen in H&E-sections because it has become dissolved in the process, thus leaving empty spaces around the axons
- Osmium tetroxide (OsO4) fixes myelin and makes it visible by staining it black. Seen as concentric rings in cross section
- Myelin sheath (neurolemma) is formed by two types of cells
- Within the CNS by Oligodendrocytes
- On the peripheral neurons system by Schwann cells
- Sheath is formed by being wrapped around the axon in a circular fashion by both types of cells
Neuroglial Cells:
- Forms roughly 40% of CNS volume
- May function as: 1. support
2. nurture ("feeding")
3. maintain
Types of glial cells:
Oligodendrocytes:
- Small dark stained dense nucleus
- Analogue of Schwann cell in peripheral nervous system
- Has several processes which forms internodal segments of several fibres (one cell ensheathes more than one axon)
- Provides myelin sheaths in CNS
- Role in nurturing (feeding) of cells
Astrocytes:
Protoplasmic astrocytes:
- found in gray matter
- round cell body
- large oval nucleus with prominent nucleolus
- large thick processes
- processes are short but profusely branched
- perivascular and perineurial foot processes
- sometimes referred to as mossy fibres
Fibrous Astrocytes:
- found in white matter
- polymorphic cells body
- large oval nucleus
- long thin processes
Microglia:
- Neural macrophages
- smallest of the glial cells
- intense dark stained nucleus
- conspicuously fine processes which has numerous short branches
Cerebral Cortex:
Consists of six layers which are best observed in the cortex of the hippocampus
From superficial to deep:
- Molecular layer:
- Has few cells and many fibres of underlying cells
- Outer granular layer:
- Many small nerve cells
- Pyramidal layer:
- Pyramidally-shaped cells bodies
- Inner granular layer:
- Smaller cells and nerve fibres
- Internal (inner) pyramidal layer:
- Pyramidal cells bodies
- Very large in the motor cortex and known as Betz-cells
- Polymorphic layer:
- Cells with many shapes
Cerebellar Cortex:
Consists of three layers
Connections are mainly inhibitory
From superficial to deep
- Outer molecular layer:
- Few cells and many fibres
- Purkinje layer:
- Huge flask-shaped cells that are arranged next to one another
- Inner granular layer:
- Many small nerve cells
Motor endplate:
Seen in periphery on striated muscle fibres
- known as boutons
- has no continuous myelin covering from the Schwann cells
- passes through perimysium of muscle fiber to "synapse"
- multiple synaptic gutter (fold) in sarcoplasma of muscle fiber beneath bouton
- contains numerous synaptic vesicles and mitochondria
Ganglia:
- Sensory Ganglia:
(e.g. trigeminal nerve, ganglia and dorsal root ganglia)
- No synapse (trophic unit)
- pseudo-unipolar neurons
- centrally located nucleus
- spherical smooth border
- conspicuous axon hillock
- Surrounded by cuboidal satellite cells (Schwann cells)
- Covered by spindle shaped capsular cells of delicate collagen which forms the endoneurium
- Visceral and Motor Ganglia (Sympathetic and Parasympathetic):
- Synapse present
- Ratio of preganglionic: postganglionic fibres
1. Sympathetic 1:30
Therefore excitatory and catabolic
2. Parasympathetic 1:2
Therefore anabolic
Except in Meissner and Auerbach's plexuses where ratio is 1:1000 '2 because of parasympathetic component's involvement in digestion
- Preganglionic axons are myelinated (e.g. white communicating rami)
- Postganglionic axon are non-myelinated (e.g. gray communicating rami)
- small multipolar cell body
- excentrally located nucleus
- Inconspicuous axon hillock
- satellite cells few or absent
- few capsular cells
Histopathological techniques
General Pathology
Histopathological techniques
Histopathological examination studies tissues under the microscope. During this study, the pathologist looks for abnormal structures in the tissue. Tissues for histopathological examination are obtained by biopsy. Biopsy is a tissue sample from a living person to identify the disease. Biopsy can be either incisional or excisional.
Once the tissue is removed from the patient, it has to be immediately fixed by putting it into adequate amount of 10% Formaldehyde (10% formalin) before sending it to the pathologist.
The purpose of fixation is:
1. to prevent autolysis and bacterial decomposition and putrefaction
2. to coagulate the tissue to prevent loss of easily diffusible substances
3. to fortify the tissue against the deleterious effects of the various stages in the preparation of sections and tissue processing.
4. to leave the tissues in a condition which facilitates differential staining with dyes and other reagents.