NEET MDS Synopsis
Sympatholytics - Antiadrenergic Agents
Pharmacology
Sympatholytics (Antiadrenergic Agents)
PHENOXYBENZAMINE
It is a potent alpha-adrenergic blocking agent
It effectively prevents the responses mediated by alpha receptors and diastolic blood pressure tends to decrease.
It interferes with the reflex adjustment of blood pressure and produces postural hypotension.
It increases the cardiac output and decreases the total peripheral resistance.
It is used in the management of pheochromocytoma and also to treat peripheral vasospastic conditions e.g. Raynaud’s disease and shock syndrome.
Phentolamine, another alpha blocker is exclusively used for the diagnosis of pheochromocytoma and for the prevention of abrupt rise in blood pressure during surgical removal of adrenal medulla tumors.
ERGOT ALKALOIDS
Ergotamine is an important alkaloid that possesses both vasoconstrictor and alpha-receptor blocking activity. Both ergotamine and dihydroergotamine are used in the treatment of migraine.
METHYSERGIDE
It is a 5-hydroxytryptamine antagonist ). It is effective in preventing an attack of migraine.
SUMATRIPTAN
It is a potent selective 5-HT 1D receptor agonist used in the treatment of migraine.
PRAZOSIN
It is an piperazinyl quinazoline effective in the management of hypertension. It is highly selective for α1 receptors. It also reduces the venous return and cardiac output. It is used in essential hypertension, benign prostatic hypertrophy and in Raynaud’s syndrome.
Prazosin lowers blood pressure in human beings by relaxing both veins and resistance vessels but it dilates arterioles more than veins.
TERAZOSIN
It is similar to prazosin but has higher bioavailability and longer plasma t½
DOXAZOSIN
It is another potent and selective α1 adrenoceptor antagonist and quinazoline derivative.
It’s antihypertensive effect is produced by a reduction in smooth muscle tone of peripheral vascular beds.
TAMSULOSIN
It is uroselective α1A blocker and has been found effective in improving BPH symptoms.
Other drugs used for erectile dysfunction
Sildenafil: It is orally active selective inhibitor of phosphodiesterase type 5 useful in treatment of erectile dysfunction.
COMPOSITE RESINS -Reaction
Dental Materials
COMPOSITE RESINS
Reaction
Free radical polymerization
Monomers + initiator. + accelerators-+ polymer molecules
Initiators-start polymerization by decomposing and reacting with monomer
Accelerators-speed up initiator decomposition
Amines used for accelerating self –curing systems
Light used for accelerating light-curing systems
Retarders or inhibitors-prevent premature polymerization
The Transition from the Deciduous to the Permanent Dentition.
Dental Anatomy
The Transition from the Deciduous to the Permanent Dentition.
1. The transition begins with the eruption of the four first permanent molars, and replacement of the lower deciduous central incisors by the permanent lower central incisors.
2. Complete resorption of the deciduous tooth roots permits exfoliation of that tooth and replacement by the permanent (successional) teeth
3. The mixed dentition exists from approximately age 6 years to approximately age 12 years. In contrast, the intact deciduous dentition is functional from age 2 - 2 /2 years of age to 6 years of age.
4. The enamel organ of each permanent anterior tooth is connected to the oral epithelium via a fibrous cord, the gubernaculum. The foramina through which it passes can be seen in youthful skulls
The deciduous second molars are particularly important. It is imperative that the deciduous second molars be preserved until their normal time of exfoliation. This prevent mesial migration of the first permanent molars.
Use a space maintainer in the event that a second deciduous molar is lost prematurely
OCCLUSION AND DENTAL DEVELOPMENT-Stages-Mixed Dentition Period
Dental Anatomy
Permanent dentition period
-Maxillary / mandibular occlusal relationships are established when the last of the deciduous teeth are lost. The adult relationship of the first permanent molars is established at this time.
-Occlusal and proximal wear reduces crown height to the permanent dentition and the mesiodistal dimensions of the teeth
occlusal and proximal wear also changes the anatomy of teeth. As cusps are worn off, the occlusion can become virtually flat plane. -In the absence of rapid wear, overbite and overjet tend to remain stable.
-Mesio-distal jaw relationships tend to be stable,
With aging, the teeth change in color from off white to yellow. smoking and diet can accelerate staining or darkening of the teeth.
Gingival recession results in the incidence of more root caries . With gingival recession, some patients have sensitivity due to exposed dentin at the cemento-enamel junction.
Curve of Spee.
-The cusp tips and incisal edges align so that there is a smooth, linear curve when viewed from the lateral aspect. The mandibular curve of Spee is concave whereas the maxillary curve is convex.
-It was described by Von Spee as a 4" cylinder that engages the occlusal surfaces.
-It is called a compensating curve of the dental arch.
There is another: the Curve of Wilson. Clinically, it relates to the anterior overbite: the deeper the curve, the deeper the overbite.
Osmotic diuretics
Pharmacology
Osmotic diuretics
An osmotic diuretic is a type of diuretic that inhibits reabsorption of water and sodium. They are pharmacologically inert substances that are given intravenously. They increase the osmolarity of blood and renal filtrate.
Mechanism(s) of Action
1. Reduce tissue fluid (edema)
2. Reflex cardiovascular effect by osmotic retention of fluid within vascular space which increases blood volume (contraindicated with Congestive heart failure)
3. Diuretic effect
o Makes H2O reabsorption far more difficult for tubular segments insufficient Na & H2O capacity in distal segments
o Increased intramedullary blood flow (washout)
o Incomplete sodium recapture (asc. loop). this is indirect inhibition of Na reabsorption (Na stays in tubule because water stays)
o Net diuretic effect:
Tubular concentration of sodium decreases
Total amount of sodium lost amount increases
GFR unchanged or slightly increased
Toxicity
Circulatory overload, dilutional hyponatremia, Hyperkalemia, edema, skin necrosis
Agents
Mannitol
Connective Tissue
Anatomy
Connective Tissue
Functions of Connective tissue:
→ joins together other tissues
→ supporting framework for the body (bone)
→ fat stores energy
→ blood transports substances
Connective tissue is usually characterized by large amounts of extracellular materials that separate cells from each other, whereas epithelial tissue is mostly cells with very little extracellular material. The extracellular substance of connective tissue consists of protein fibers which are embedded in ground substance containing tissue fluid.
Fibers in connective tissue can be divided into three types:
→ Collagen fibers are the most abundant protein fibers in the body.
→ Elastic fibers are made of elastin and have the ability to recoil to original shape.
→ Reticular fibers are very fine collagen fibers that join connective tissues to other tissues.
Connective tissue cells are named according to their functions:
→ Blast cells produce the matrix of connective tissues
→ Cyte cells maintains the matrix of connective tissues
→ Clast cells breaks down the matrix for remodeling (found in bone)
Casting Alloys
Dental Materials
Casting Alloys
Applications-inlay, onlay, crowns, and bridges
Terms
a. Precious-based on valuable elements
b. Noble or immune-corrosion-resistant element or alloy
c. Base or active-corrosion-prone alloy
d. Passive -corrosion resistant because of surface oxide film
e. Karat (24 karat is 100% gold; 18 karat is 75% gold)
f. Fineness (1000 fineness is I00% gold; 500 fineness is 50% gold)
Classification
High-gold alloys are > 75% gold or other noble metals
Type 1- 83% noble metals (e.g., in simple inlays)
Type II-≥78% noble metals (e.g.,in inlays and onlays)
Type IlI-≥75% noble metals (e.g., in crowns and bridges)
Type IV-≥75% noble metals (e.g., in partial dentures)
Medium-gold alloys are 25% to 75% gold or other noble metals
Low-gold alloys are <25% gold or other noble metals
Gold-substitute alloys arc alloys not containing gold
(1) Palladium-silver alloys-passive .because of mixed oxide film
(2) Cobalt-chromium alloys-passive because of Cr203 oxide film
(3) Iron-chromium alloys-passive because of Cr203 oxide film
Titanium alloys are based on 90% to 100% titanium ; passive because of TiO2 oxide film
Components of gold alloys
- Gold contributes to corrosion resistance
- Copper contributes to hardness and strength
- Silver counteracts orange color of copper
- Palladium increases melting point and hardness
- Platinum increases melting point
- Zinc acts as oxygen scavenger during casting
Manipulation
- Heated to just beyond melting temperature for casting
o Cooling shrinkage causes substantial contraction
Properties
Physical
- Electrical and thermal conductors
- Relatively low coefficient of thermal expansion
Chemical
- Silver content affects susceptibility to tarnish
- Corrosion resistance is attributable to nobility or passivation
Mechanical
- High tensile and compressive strengths but relatively weak in thin sections, such as margins, and can be deformed relatively easily
- Good wear resistance except in contact with Porcelain
Rigid Fixation
Oral and Maxillofacial SurgeryRigid Fixation
Rigid fixation is a surgical technique used to stabilize fractured bones.
Types of Rigid Fixation
Rigid fixation can be achieved using various types of plates and devices,
including:
Simple Non-Compression Bone Plates:
These plates provide stability without applying compressive forces
across the fracture site.
Mini Bone Plates:
Smaller plates designed for use in areas where space is limited,
providing adequate stabilization for smaller fractures.
Compression Plates:
These plates apply compressive forces across the fracture site,
promoting bone healing by encouraging contact between the fracture
fragments.
Reconstruction Plates:
Used for complex fractures or reconstructions, these plates can be
contoured to fit the specific anatomy of the fractured bone.
Transosseous Wiring (Intraosseous Wiring)
Transosseous wiring is a traditional and effective method for the fixation of
jaw bone fractures. It involves the following steps:
Technique:
Holes are drilled in the bony fragments on either side of the
fracture line.
A length of 26-gauge stainless steel wire is passed through the
holes and across the fracture.
Reduction:
The fracture must be reduced independently, ensuring that the teeth
are in occlusion before securing the wire.
Twisting the Wire:
After achieving proper alignment, the free ends of the wire are
twisted to secure the fracture.
The twisted ends are cut short and tucked into the nearest drill
hole to prevent irritation to surrounding tissues.
Variations:
The single strand wire fixation in a horizontal manner is the
simplest form of intraosseous wiring, but it can be modified in various
ways depending on the specific needs of the fracture and the patient.
Other fixation techniques
Open reduction and internal fixation (ORIF):
Surgical exposure of the fracture site, followed by reduction and fixation with
plates, screws, or nails
Closed reduction and immobilization (CRII):
Manipulation of the bone fragments into alignment without surgical exposure,
followed by cast or splint immobilization
Intramedullary nailing:
Insertion of a metal rod (nail) into the medullary canal of the bone to
stabilize long bone fractures
External fixation:
A device with pins inserted through the bone fragments and connected to an
external frame to provide stability
Tension band wiring:
A technique using wires to apply tension across a fracture site, particularly
useful for avulsion fractures
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