NEET MDS Synopsis
Thiamin: Vitamin B1
Biochemistry
Thiamin: Vitamin B1
Thiamin, or vitamin B1, helps to release energy from foods, promotes normal appetite, and is important in maintaining proper nervous system function.
RDA (Required Daily allowance) Males: 1.2 mg/day; Females: 1.1 mg/day
Thiamin Deficiency
Symptoms of thiamin deficiency include: mental confusion, muscle weakness, wasting, water retention (edema), impaired growth, and the disease known as beriberi.
Periodontium
Dental Anatomy
The periodontium consists of tissues supporting and investing the tooth and includes cementum, the periodontal ligament (PDL), and alveolar bone.
Parts of the gingiva adjacent to the tooth also give minor support, although the gingiva is Not considered to be part of the periodontium in many texts. For our purposes here, the groups Of gingival fibers related to tooth investment are discussed in this section.
CASTING
Dental Materials
CASTING
Melting & Casting Technique Melting & Casting requires Heat source to melt the alloy Casting force, to drive the alloy into the mould
Casting Torch Selection Two type of torch tips: Multi-orifice Single-orifice Multi-orifice tip is widely used for metal ceramic alloys. Main advantage is distribution of heat over wide area for uniform heating of the alloy. Single-orifice tip concentrate more heat in one area.Three fuel sources are used for Casting Torch; Acetylene ,Natural Gas ,Propane
CASTING CRUCIBLES
Four types are available ;
1) Clay .
2) Carbon .
3) Quartz .
4) Zirconia –Alumina .
Casting Machines
It is a device which uses heat source to melt the alloy casting force .
Heat sources can be :
1) Reducing flame of a torch .( conventional alloys & metal ceramic alloys )
2) Electricity .(Base metal alloys )
Advantages of electric heating :
-heating is evenly controlled .
-minimal undesirable changes in the alloy composition .
- Appropriate for large labs .
Disadvantage :
Expensive .
Casting machines use :
1) Air pressure .
2) Centrifugal force .
3) Evacuation technique .
Alloys can be melted by :
1) Alloy is melted in a separate crucible by a torch flame & is cast into the mold by centrifugal force .(centrifugal C M )
2) Alloy is melted by resistance heating or by induction furnace & then cast centrifugally by motor or spring action (springwound CM electrical resistance )
3) Alloy is melted by induction heating cast into mold centrifugally by motor or spring action .(Induction CM )
4) Alloy is vacum melted by an argon atmosphere
Torch melting / Centrifugal casting machine
Electrical resistance /Heated casting machine
Melting of the alloy should be done in a graphite or ceramic crucible .
Advantage :
-Oxidation of metal ceramic restorations on
overheating is prevented .
-Help in solidification from tip of the casting to the button surface .
Induction casting machine
Commonly used for melting base metal alloys.
Advantage :
- Highly efficient .
- Compact machine withlow power consumption
-No pre heating needed ,
- safe & reliable.
Direct current arc melting machine
A direct current arc is produced between two electrodes :
The alloy & the water cooled tungsten electrode .Temp used is 4000 degrees .
Disadvanage :
High risk of overheating the alloy .
Vacuum or pressure assisted casting machine
Molten alloy is drawn into the evacuated mold by gravity or vacuum & subjected to aditional pressure
For Titanium & its alloys vacuum heated argon pressure casting machines are used .
Accelerated casting method
This method reduces the time of both bench set of the investment & burnout .
Uses phosphate bonded investments which uses 15 mnts for bench set & 15mnts for burnout by placing in a pre – heated furnace to 815 degrees .
Effect of burnout on gypsum bonded investments
Rate of heating has influence on smoothness & on overall dimensions of the investment
Rapid heating causes cracking & flaking which can cause fins or spines .
Avoid heating gypsum bonded investment above 700 degrees .Complete the wax elimination below that temp .
Effect of burnout on phosphate bonded investments
Usual burnout temp is 750 -1030 degrees.
Although they are strong they are brittle too .
Since the entire process takes a long time two stage burnout & plastic ring can be used .
Drugs Used in Diabetes -GLP-1 analogs
Pharmacology
GLP-1 analogs
Exenatide
Mechanism
GLP-1 is an incretin released from the small intestine that aids glucose-dependent insulin secretion
basis for drug mechanism is the observation that more insulin secreted with oral glucose load compared to IV
Exenatide is a GLP-1 agonist
↑ insulin
↓ glucagon release
the class of dipeptidyl peptidase inhibitors ↓ degradation of endogenous GLP-1
e.g.) sitagliptin, -gliptins
Clinical use
type II DM
Toxicity
nausea, vomiting
pancreatitis
hypoglycemia
if given with sulfonylureas
PFM Alloys
Dental Materials
PFM Alloys
Applications-substructures for porcelain-fused-to-metal crowns and bridges
Classification
o High-gold alloys
o Palladium-silver alloys
o Nickel-chromium alloys
Structure
Composition
o High-gold alloys are 98% gold. platinum. And palladium
o Palladium-silver alloys are 50% to 60% palladium and 30 to 40% silver
o Nickel-chromium alloys are 70% to 80% nickel and 15% chromium with other metals
Manipulation
o Must have melting temperatures above that of porcelains to be bonded to their surface
o More difficult to cast (see section on chromium alloys)
Properties - Physical
Except for high-gold alloys, others are less dense alloys
Alloys are designed to have low thermal expansion coefficients that must be matched to the overlying porcelain
Chemical-high-gold alloys are immune, but others passivate
Mechanical-high modulus and hardness
Beta - Adrenergic Blocking Agents
Pharmacology
Beta - Adrenergic Blocking Agents
Mechanisms of Action
- Initial decrease in cardiac output, followed by reduction in peripheral vascular resistance.
- Other actions include decrease plasma renin activity, resetting of baroreceptors, release of vasodilator prostaglandins, and blockade of prejunctional beta-receptors.
Advantages
- Documented reduction in cardiovascular morbidity and mortality.
- Cardioprotection: primary and secondary prevention against coronary artery events (i.e. ischemia, infarction, arrhythmias, death).
- Relatively not expensive.
Considerations
- Beta blockers are used with caution in patients with bronchospasm.
- Contraindicated in more than grade I AV, heart block.
- Do not discontinue abruptly.
Side Effects
- Bronchospasm and obstructive airway disease.
- Bradycardia
- Metabolic effects (raise triglyerides levels and decrease HDL cholesterol; may worsen insulin sensitivity and cause glucose intolerance). Increased incidence of diabetes mellitus.
- Coldness of extremities.
- Fatigue.
- Mask symptoms of hypoglycemia.
- Impotence.
Indications
- First line treatment for hypertension as an alternative to diuretics.
- Hypertension associated with coronary artery disease.
- Hyperkinetic circulation and high cardiac output hypertension (e.g., young hypertensives).
- Hypertension associated with supraventricular tachycardia, migraine, essential tremors, or hypertrophic cardiomyopathy.
Beta adrenergic blocker Drugs
Atenolol 25-100
Metoprolol 50-200
Bisoprolol 2.5-10
Endochondral ossification
Anatomy
Endochondral ossification
A cartilage model exists
Through intramembraneous ossification in the perichondrium a collar of bone forms around the middle part of the cartilage model
The perichondrium change to a periostium
The bone collar cuts off the nutrient and oxygen supply to the chondrocytes in the cartilage model
The chondrocytes then increase in size and resorb the surrounding cartilage matrix until only thin vertical septae of matrix are left over
These thin plates then calcify after which the chondrocytes die
The osteoclasts make holes in the bone collar through which blood vessels can now enter the cavities left behind by the chondrocytes
With the blood vessels osteoprogenitor cells enter the tissue
They position themselves on the calcified cartilage septae, change into osteoblasts and start to deposit bone to form trabeculae
In the mean time the periosteum is depositing bone on the outside of the bone collar making it thicker and thicker
The trabeculae,consisting of a core of calcified cartilage with bone deposited on top of it, are eventually resorbed by osteoclasts to form the marrow cavity
The area where this happens is the primary ossification centre and lies in what is called the diaphysis (shaft)
This process spreads in two directions towards the two ends of the bone the epiphysis
In the two ends (heads) of the bone a similar process takes place
A secondary ossification centre develops from where ossification spreads radially
Here no bone collar forms
The outer layer of the original cartilage remains behind to form the articulating cartilage
Between the primary and the secondary ossification centers two epiphyseal cartilage plates remain
This is where the bone grows in length
From the epiphyseal cartilage plate towards the diaphysis a number of zones can be identified:
Resting zone of cartilage
Hyaline cartilage
Proliferation zone
Chondrocytes divide to form columns of cells that mature.
Hypertrophic cartilage zone
Chondrocytes become larger, accumulate glycogen, resorb the surrounding matrix so that only thin septae of cartilage remain
Calcification and degeneration zone
The thin septae of cartilage become calcified.
The calsified septae cut off the nutrient supply to the chondrocytes so subsequently they die.
Ossification zone.
Osteoclasts make openings in the bone collar through which blood vessels then invade the spaces left vacant by the chondrocytes that died.
Osteoprogenitor cells come in with the blood and position themselves on the calcified cartilage
septae, change into osteoblasts and start to deposit bone.
When osteoblasts become trapped in bone they change to osteocytes.
Growth and remodeling of bone
Long bones become longer because of growth at the epiphyseal plates
They become wider because of bone formed by the periosteum
The marrow cavity becomes bigger because of resorbtion by the osteoclasts
Fracture repair
When bone is fractured a blood clot forms
Macrophages then remove the clot, remaining osteocytes and damaged bone matrix
The periosteum and endosteum produce osteoprogenitor cells that form a cellular tissue in the fracture area
Intramembranous and endochondral ossification then take place in this area forming trabeculae.
Trabeculae connect the two ends of the broken bone to form a callus
Remodelling then takes place to restore the bone as it was
Joints
The capsule of a joint seals off the articular cavity,
The capsule has two layers
fibrous (outer)
synovial (inner)
The synovial layer is lined by squamous or cuboidal epithelial cells, Under this layer is a layer of loose or dense CT, The lining cells consists of two types:
- A cells
- B cells
They secrete the synovial fluid
They are different stages of the same cell, They are also phagocytic., The articular cartilage has fibres that run perpendicular to the bone and then turn to run parallel to the surface
Str. Pneumoniae
General Pathology
Str. Pneumoniae
Probably the most important streptococci. Primary cause of pneumonia. Usually are diplococci. Ste. pneumoniae are α-hemolytic and nutritionally fastidious. Often are normal flora.
Key virulence factor is the capsule polysaccharide which prevents phagocytosis. Other virulence factors include pneumococcal surface protein and α-hemolysin.
Major disease is pneumonia, usually following a viral respiratory infection. Characterized by fever, cough, purulent sputum. Bacteria infiltrates alveoli. PMN’s fill alveoli, but don’t cause necrosis. Also can cause meningitis, otitis, sinusitis.
There are vaccines against the capsule polysaccharide. Resistance to penicillin, cephalosporins, erythromycins, and fluoroquinalones is increasing.