📚 NEET MDS Lecture Notes
Neurophysiology - Local Anesthetics
Anaesthesia1. Refractory periods: absolute (neuron cannot fire) and relative (can fire with greater than normal depolarization)
2. Specific receptor theory: local anesthetics bind inside Na channel, block entry of Na
3. Membrane expansion theory: anesthetics work by disrupting lipid bilayer around ion channel
4. Mechanism of action for local anesthetics: local must be in uncharged form to cross lipid bilayer of axon
a. Locals made as salts (usually mixed with HCl). [Uncharged form] depends on pH of tissue, pKa of local-found by Henderson-Hasselbach equation- pH = pKa + log ( [RN] / [RNH+] )
b. Once inside axon, only charged form will bind to Na channel.
c. At physiologic pH, enough base exists outside nerve so anesthetic rapidly diffuses into axon. Rate-limiting step is how much uncharged local is present outside neuron.
d. So, starts with 100 molecules of local, 25 of which are uncharged and 75 charged. The 25 uncharged enter the neuron, leaving 0 on outside so the remaining 75 re-equilibrate to produce more uncharged which enters neuron . Inside neuron the reverse happens as converted to ionic form then rapidly binds channel.
5. Inflammatory effects: ® an acidic environment, less of local can be converted to uncharged form (less enters).
6. Pharmakokinetics: pool of local outside neuron depleted as local diffuses into adjacent muscles, tissues, enters blood vessels. Since locals are water soluble, they go throughout body (even cross BBB and placenta)
7. Autonomic nervous system: sympathetic and parasympathetic divisions. Both secrete pre-ganglionic acetylcholine. Postganglionic NT is acetylcholine for parasympathetic, norepinephrine for sympathetic (also secrete E, dopamine, and seratonin, all are catecholamines).
a. Sympathetic catecholamines affect receptors (local anesthetics affect a1-mediated actions which cause vasoconstriction) ® fight or flight responses (pupil & bronchiole dilation, HR, BP, blood glucose; ¯ GI)
b. Catecholamines inactivated by reuptake, diffusion, or metabolized by monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT) then metabolites excreted in urine.
c. When choosing sympathomimetic drug, consider receptor subtype in tissue and choose drug that affects it.
Gypsum Products
Dental MaterialsGypsum Products
|
Characteristics |
Plaster |
Stone |
Diestone |
|
Chemical Name |
Beta-Calcium Sulfate hemihydrate |
Alpha-Calcium sulfate hemihydrate |
Alpha-Calcium sulfate hemihydrate |
|
Formula |
CaSO4 – ½ H2O |
CaSO4 – ½ H2O |
CaSO4 – ½ H2O |
|
Uses |
Plaster Models ,Impression Plasters |
Cast Stone, Investment |
Improved Stone, diestone |
|
Water(W) Reaction Water Extra Water Total water Powder (P) W/P Ratio |
18ml 32ml 50ml 100g 0.50 |
18ml 12ml 30ml 100g 0.30 |
18ml 6ml 24ml 100g 0.24 |
Control of processes in the stomach
PhysiologyControl of processes in the stomach:
The stomach, like the rest of the GI tract, receives input from the autonomic nervous system. Positive stimuli come from the parasympathetic division through the vagus nerve. This stimulates normal secretion and motility of the stomach. Control occurs in several phases:
Cephalic phase stimulates secretion in anticipation of eating to prepare the stomach for reception of food. The secretions from cephalic stimulation are watery and contain little enzyme or acid.
Gastric phase of control begins with a direct response to the contact of food in the stomach and is due to stimulation of pressoreceptors in the stomach lining which result in ACh and histamine release triggered by the vagus nerve. The secretion and motility which result begin to churn and liquefy the chyme and build up pressure in the stomach. Chyme surges forward as a result of muscle contraction but is blocked from entering the duodenum by the pyloric sphincter. A phenomenon call retropulsion occurs in which the chyme surges backward only to be pushed forward once again into the pylorus. The presence of this acid chyme in the pylorus causes the release of a hormone called gastrin into the bloodstream. Gastrin has a positive feedback effect on the motility and acid secretion of the stomach. This causes more churning, more pressure, and eventually some chyme enters the duodenum.
Intestinal phase of stomach control occurs. At first this involves more gastrin secretion from duodenal cells which acts as a "go" signal to enhance the stomach action already occurring. But as more acid chyme enters the duodenum the decreasing pH inhibits gastrin secretion and causes the release of negative or "stop" signals from the duodenum.
These take the form of chemicals called enterogastrones which include GIP (gastric inhibitory peptide). GIP inhibits stomach secretion and motility and allows time for the digestive process to proceed in the duodenum before it receives more chyme. The enterogastric reflex also reduces motility and forcefully closes the pyloric sphincter. Eventually as the chyme is removed, the pH increases and gastrin and the "go" signal resumes and the process occurs all over again. This series of "go" and "stop" signals continues until stomach emptying is complete.
Recent Advances
Conservative DentistryRecent Advances in Restorative Dentistry
Restorative dentistry has seen significant advancements in materials and techniques that enhance the effectiveness, efficiency, and aesthetic outcomes of dental treatments. Below are some of the notable recent innovations in restorative dentistry:
1. Teric Evoflow
A. Description
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B. Applications
- Class V Restorations: Particularly suitable for Class V cavities, which are often challenging due to their location and shape.
- Extended Fissure Sealing: Effective for sealing deep fissures in teeth to prevent caries.
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2. GO
A. Description
- Type: Super quick adhesive.
- Characteristics:
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B. Applications
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3. New Optidisc
A. Description
- Type: Finishing and polishing discs.
- Characteristics:
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- Extra Coarse Disc: An additional extra coarse disc is available for gross removal of material before the finishing and polishing stages.
B. Applications
- Final Polish: Allows restorations to achieve a final polish that closely resembles the natural dentition, improving aesthetic outcomes and patient satisfaction.
4. Interval II Plus
A. Description
- Type: Temporary filling material.
- Composition: Made with glass ionomer and leachable fluoride.
- Packaging: Available in a convenient 5 gm syringe.
B. Characteristics
- Dependable: A one-component, ready-mixed material that simplifies the application process.
- Safety: Safe to use on resin-based materials, as it does not contain zinc oxide eugenol (ZOE), which can interfere with bonding.
C. Applications
- Temporary Restorations: Ideal for use in temporary fillings, providing a reliable and effective solution for managing carious lesions until permanent restorations can be placed.