NEET MDS Synopsis
Root canal Types
Endodontics
Common Canal Configurations:
There are many combinations of canals that are present in the roots of human permanent dentition, most of these root canal systems in any one root can be categorized in six different types. These six types are:
Type I : Single canal from pulp chamber to the apex.
Type II : Two separate canals leaving the chamber but merging short of the apex to form only one canal.
Type III : Two separate canals leaving the chamber and existing the root in separate apical foramina.
Type IV : One canal leaving the pulp chamber but dividing short of the apex into two separate canals with two separate apical foramina.
Type V : One canal that divides into two in the body of the root but returns to exist as one apical foramen.
Type VI : Two canals that merge in the body of the root but re-divide to exist into two apical foramina.
Root Canal Classes:
Another classification has been developed to describe the completion of root canal formation and curvature.
Class I : Mature straight root canal.
Class II : Mature but complicated root canal having-severe curvature, S-shaped course, dilacerations or bayonet curve.
Class III : Immature root canal either tubular or blunder bass.
Classification of Dental Fractures
Pedodontics
Weak Acids and pKa
Biochemistry
Weak Acids and pKa
• The strength of an acid can be determined by its dissociation constant, Ka.
• Acids that do not dissociate significantly in water are weak acids.
• The dissociation of an acid is expressed by the following reaction: HA = H+ + A- and the dissociation constant Ka = [H+ ][A- ] / [HA]
• When Ka < 1, [HA] > [H+ ][A- ] and HA is not significantly dissociated. Thus, HA is a weak acid when ka < 1.
• The lesser the value of Ka, the weaker the acid.
• Similar to pH, the value of Ka can also be represented as pKa.
• pKa = -log Ka.
• The larger the pKa, the weaker the acid.
• pKa is a constant for each conjugate acid and its conjugate base pair.
• Most biological compounds are weak acids or weak bases.
Nitrous Oxide
Anaesthesia
Pharmacodynamics of Nitrous Oxide
Overview
Nitrous oxide (N2O), commonly known as "laughing gas," is an inhalational
anesthetic used primarily for its analgesic and anxiolytic properties.
Understanding its pharmacodynamics is crucial for safe and effective use in
clinical settings.
Pharmacodynamics
CNS Depression:
Nitrous oxide produces nonspecific central nervous system (CNS)
depression.
While it is classified as an inhalational general anesthetic, it
provides limited analgesia, making surgical anesthesia unlikely unless
concentrations that produce anoxia are reached.
Potency:
Nitrous oxide is the weakest of all inhalation agents, with a minimum
alveolar concentration (MAC) of approximately 105%.
The MAC is a measure of the potency of an inhalation agent, defined as
the concentration required to produce immobility in 50% of patients in
response to a surgical stimulus.
Effects at Various Concentrations:
30% to 50% Concentration:
Produces a relaxed, somnolent patient who may appear dissociated and
is easily susceptible to suggestion.
Some patients may experience amnesia, but there is typically little
alteration in learning or memory.
Greater than 60% Concentration:
Patients may experience discoordination, ataxia, giddiness, and
increased sleepiness.
It is recommended that the concentration of nitrous oxide should not
routinely exceed 50% to avoid adverse effects.
Titration:
One of the advantages of nitrous oxide is its ability to be easily
titrated.
It can be increased for stimulating procedures (e.g., injections) and
decreased during less stimulating periods (e.g., restorations).
Physiological Considerations
Entrapment in Gas-Filled Spaces:
Nitrous oxide can become entrapped in gas-filled spaces such as the
middle ear, sinuses, and gastrointestinal tract.
This can lead to increased middle ear pressure, which is generally
insignificant in patients with normal Eustachian tube function but can
induce pain in patients with acute otitis media.
Contraindications:
Acute Otitis Media: Use should be avoided in patients with this
condition due to the risk of increased middle ear pressure and pain.
Severe Behavioral Problems and Emotional Illness: Patients who
are uncooperative or have a fear of "gas" may not tolerate nitrous oxide
well.
Claustrophobia: Patients with this condition may feel
uncomfortable with the nasal hood placement.
Maxillofacial Deformities: Conditions that prevent proper
placement of the nasal hood can contraindicate its use.
Nasal Obstruction: Conditions such as upper respiratory
infections, nasal polyps, or a deviated septum can hinder effective
administration.
Chronic Obstructive Pulmonary Disease (COPD): Patients with
COPD may have difficulty with nitrous oxide due to respiratory issues.
Pregnancy: Caution is advised when using nitrous oxide in
pregnant patients.
High Oxygenation Situations: Situations where high oxygenation
is inadvisable, such as during Bleomycin therapy, contraindicate the use
of nitrous oxide.
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.
POLYCARBOXYLATE CEMENT
Dental Materials
POLYCARBOXYLATE CEMENT
Use:. The primary use of polycarboxylate cement is as a cementing medium of cast alloy and porcelain restorations. In addition, it can be used as a cavity liner, as a base under metallic restorations, or as a temporary restorative material.
Clinical Uses
Polycarboxylate cement is used in the same way as zinc phosphate cement, both as an intermediate base and as a cementing medium.
c. Chemical Composition.
(1) Powder:. It generally contains zinc oxide, 1 to 5 percent magnesium oxide, and 10 to 40 percent aluminum oxide or other reinforcing fillers. A small percentage of fluoride may be included.
(2) Liquid. Polycarboxylate cement liquid is approximately a 40 percent aqueous solution of polyacrylic acid copolymer with other organic acids such as itaconic acid. Due to its high molecular weight, the solution is rather thick (viscous).
d. Properties.
The properties of polycarboxylate cement are identical to those of zinc phosphate cement with one exception. Polycarboxylate cement has lower compressive strength.
e. Setting Reactions:
The setting reaction of polycarboxylate cement produces little heat. This has made it a material of choice. Manipulation is simpler, and trauma due to thermal shock to the pulp is reduced. The rate of setting is affected by the powder-liquid ratio, the reactivity of the zinc oxide, the particle size, the presence of additives, and the molecular weight and concentration of the polyacrylic acid. The strength can be increased by additives such as alumina and fluoride. The zinc oxide reacts with the polyacrylic acid forming a cross-linked structure of zinc polyacrylate. The set cement consists of residual zinc oxide bonded together by a gel-like matrix.
Precautions.
The following precautions should be observed.
o The interior of restorations and tooth surfaces must be free of saliva.
o The mix should be used while it is still glossy, before the onset of cobwebbing.
o The powder and liquid should be stored in stoppered containers under cool conditions. Loss of moisture from the liquid will lead to thickening.
Factors Considered for Prescribing Fluoride Tablets
Public Health Dentistry
Factors Considered for Prescribing Fluoride Tablets
Child's Age:
Different age groups require different dosages.
Children older than 4 years may receive lozenges or chewable tablets,
while those younger than 4 are typically prescribed liquid fluoride drops.
Fluoride Concentration in Drinking Water:
The fluoride level in the child's drinking water is crucial.
If the fluoride concentration is less than 1 part per million (ppm),
systemic fluoride supplementation is recommended.
Risk of Dental Caries:
Children at higher risk for dental decay may need additional fluoride
supplementation.
Regular dental assessments help determine the need for fluoride.
Overall Health and Dietary Needs:
Consideration of the child's overall health and any dietary restrictions
that may affect fluoride intake.
Recommended Doses of Fluoride Tablets
For Children Aged 6 Months to 4 Years:
Liquid drops are typically prescribed in doses of 0.125, 0.25, and 0.5
mg of fluoride ion.
For Children Aged 4 Years and Older:
Chewable tablets or lozenges are recommended, usually at doses of 0.5 mg
to 1 mg of fluoride ion.
Adjustments Based on Water Fluoride Levels:
Doses may be adjusted based on the fluoride content in the child's
drinking water to ensure adequate protection against dental caries.
Duration of Supplementation:
Fluoride supplementation is generally continued until the child reaches
16 years of age, depending on their fluoride exposure and dental health
status.
Blood Disorder Drugs
Pharmacology
COAGULANTS
An agent that produces coagulation (Coagulation is a complex process by which blood forms clots).
ANTICOAGULANTS
An anticoagulant is a substance that prevents coagulation; that is, it stops blood from clotting.
Anticoagulants:
Calcium Chelators (sodium citrate, EDTA)
Heparin
Dalteparin Sodium (Fragmin) -Low molecular-weight heparin
Enoxaparin - Low molecular-weight heparin
Tinzaparin Sodium - Low molecular-weight heparin
Warfarin
Lepirudin - recombinant form of the natural anticoagulant hirudin: potent and specific Thrombin inhibitor
Bivalirudin - analog of hirudin: potent and specific Thrombin inhibitor
Procoagulants:
Desmopressin acetate
Antiplatelet Drugs:
Acetylsalicylic Acid, Ticlopidine, Sulfinpyrazone, Abciximab , Clopidogrel bisulfate
Fibrinolytic Drugs:
Tissue Plasminogen Activator (t-PA, Activase), Streptokinase (Streptase),
Anistreplase, Urokinase
Antagonists:
Protamine sulfate, Aminocaproic acid
Pharmacological agents used to treat blood coagulation disorders fall in to three major categories:
1. Anticoagulants: Substances that prevent the synthesis of a fibrin network which inhibits coagulation and the formation of arterial thrombi and thromboembolic clots.
2. Antiplatelet agents: Substances that reduce the adhesion and aggregation of platelets.
3. Fibrinolytic agents: Substances that promote the destruction of already formed blood clots or thrombi by disrupting the fibrin mesh.