NEET MDS Synopsis
Glomerular filtration
Physiology
Glomerular filtration
Kidneys receive about 20% of cardiac output , this is called Renal Blood Flow (RBF) which is approximatley 1.1 L of blood. Plasma in this flow is about 625 ml . It is called Renal Plasma Flow (RPF) .
About 20 % of Plasma entering the glomerular capillaries is filtered into the Bowman`s capsule .
Glomerular filtration rate is about 125 ml/min ( which means 7.5 L/hr and thus 180 L/day) This means that the kidney filters about 180 liters of plasma every day.
The urine flow is about 1ml/min ( about 1.5 liter /day) This means that kidney reabsorbs about 178.5 liters every day .
Filtration occurs through the filtration unit , which includes :
1- endothelial cells of glomerular capillaries , which are fenestrated . Fenestrae are quite small so they prevent filtration of blood cells and most of plasma proteins .
2- Glomerular basement membrane : contains proteoglycan that is negatively charged and repels the negatively charged plasma proteins that may pass the fenestrae due to their small molecular weight like albumin . so the membrane plays an important role in impairing filtration of albumin .
3- Epithelial cells of Bowman`s capsule that have podocytes , which interdigitate to form slits .
Many forces drive the glomerular filtration , which are :
1- Hydrostatic pressure of the capillary blood , which favours filtration . It is about 55 mmHg .
2- Oncotic pressure of the plasma proteins in the glomerular capillary ( opposes filtration ) . It is about 30 mm Hg .
3- Hydrostatic pressure of the Bowman`s capsule , which also opposes filtration. It is about 15 mmHg .
The net pressure is as follows :
Hydrostatic pressure of glomerular capillaries - ( Oncotic pressure of glomerular capillaries + Hydrostatic pressure of the Bowman capsule):
55-(35+10)
=55-45
=10 mmHg .
Te glomerular filtration rate does not depend only on the net pressure , but also on an other value , known as filtration coefficient ( Kf) . The later depends on the surface area of the glomerular capillaries and the hydraulic conductivity of the glomerular capillaries.
Radiation Physics
Radiology
DENTAL X-RAY TUBE
The dental X-ray tube is surrounded by a glass envelope that houses a vacuum.
The glass prevents low-grade radiation from escaping. The vacuum insures the protection of the equipment from catastrophic failure. Production of X-rays generates enormous amounts of heat; the vacuum prevents the risk of combustion and ensures the proper environment for conduction of electrons.
There are two separate energy sources, one that powers the energy potential between the cathode ?lament and the anode, and the other being
the controls for the cathode ?lament. The latter essentially is the on and off switch of the X-ray unit.
The cathode ?lament is heated which causes electrons to be emitted.
These electrons are then accelerated by the electrical potential of the circuit.
Between the two points is a tungsten target.
When electrons strike the target, X-rays are produced.
HALF-VALUE LAYER
- Property of a material whereas the thickness (mm) reduces 50% of a monochromatic X-ray beam.
- Half-value layer of a beam of radiation from an X-ray unit is about 2 mm of aluminum (Al).
PRIMARY RADIATION
- Is the main beam produced from the X-ray tube.
SECONDARY RADIATION
- Produced by the collision of the main beam with matter which causes scatter.
Amorphous Calcium Phosphate
Conservative DentistryAmorphous Calcium Phosphate (ACP)
Amorphous Calcium Phosphate (ACP) is a significant compound in dental
materials and oral health, known for its role in the biological formation of
hydroxyapatite, the primary mineral component of tooth enamel and bone. ACP has
both preventive and restorative applications in dentistry, making it a valuable
material for enhancing oral health.
1. Biological Role
A. Precursor to Hydroxyapatite
Formation: ACP serves as an antecedent in the
biological formation of hydroxyapatite (HAP), which is essential for the
mineralization of teeth and bones.
Conversion: At neutral to high pH levels, ACP remains
in its original amorphous form. However, when exposed to low pH conditions
(pH < 5-8), ACP converts into hydroxyapatite, helping to replace the HAP
lost due to acidic demineralization.
2. Properties of ACP
A. pH-Dependent Behavior
Neutral/High pH: At neutral or high pH levels, ACP
remains stable and does not dissolve.
Low pH: When the pH drops below 5-8, ACP begins to
dissolve, releasing calcium (Ca²⁺) and phosphate (PO₄³⁻) ions. This process
is crucial in areas where enamel demineralization has occurred due to acid
exposure.
B. Smart Material Characteristics
ACP is often referred to as a "smart material" due to its unique properties:
Targeted Release: ACP releases calcium and phosphate
ions specifically at low pH levels, which is when the tooth is at risk of
demineralization.
Acid Neutralization: The released calcium and phosphate
ions help neutralize acids in the oral environment, effectively buffering
the pH and reducing the risk of further enamel erosion.
Reinforcement of Natural Defense: ACP reinforces the
tooth’s natural defense system by providing essential minerals only when
they are needed, thus promoting remineralization.
Longevity: ACP has a long lifespan in the oral cavity
and does not wash out easily, making it effective for sustained protection.
3. Applications in Dentistry
A. Preventive Applications
Remineralization: ACP is used in various dental
products, such as toothpaste and mouth rinses, to promote the
remineralization of early carious lesions and enhance enamel strength.
Fluoride Combination: ACP can be combined with fluoride
to enhance its effectiveness in preventing caries and promoting
remineralization.
B. Restorative Applications
Dental Materials: ACP is incorporated into restorative
materials, such as composites and sealants, to improve their mechanical
properties and provide additional protection against caries.
Cavity Liners and Bases: ACP can be used in cavity
liners and bases to promote healing and remineralization of the underlying
dentin.
Gracey Curettes
PeriodontologyGracey Curettes
Gracey curettes are specialized instruments designed for periodontal therapy,
particularly for subgingival scaling and root planing. Their unique design
allows for optimal adaptation to the complex anatomy of the teeth and
surrounding tissues. This lecture will cover the characteristics, specific uses,
and advantages of Gracey curettes in periodontal practice.
Gracey curettes are area-specific curettes
that come in a set of instruments, each designed and angled to adapt to
specific anatomical areas of the dentition.
Purpose: They are considered some of the best
instruments for subgingival scaling and root planing due to their ability to
provide excellent adaptation to complex root anatomy.
Specific Gracey Curette Designs and Uses
Gracey 1/2 and 3/4:
Indication: Designed for use on anterior teeth.
Application: Effective for scaling and root planing
in the anterior region, allowing for precise access to the root
surfaces.
Gracey 5/6:
Indication: Suitable for anterior teeth and
premolars.
Application: Versatile for both anterior and
premolar areas, providing effective scaling in these regions.
Gracey 7/8 and 9/10:
Indication: Designed for posterior teeth,
specifically for facial and lingual surfaces.
Application: Ideal for accessing the buccal and
lingual surfaces of posterior teeth, ensuring thorough cleaning.
Gracey 11/12:
Indication: Specifically designed for the mesial
surfaces of posterior teeth.
Application: Allows for effective scaling of the
mesial aspects of molars and premolars.
Gracey 13/14:
Indication: Designed for the distal surfaces of
posterior teeth.
Application: Facilitates access to the distal
surfaces of molars and premolars, ensuring comprehensive treatment.
Key Features of Gracey Curettes
Area-Specific Design: Each Gracey curette is tailored
for specific areas of the dentition, allowing for better access and
adaptation to the unique contours of the teeth.
Offset Blade: Unlike universal curettes, the blade of a
Gracey curette is not positioned at a 90-degree angle to the lower shank.
Instead, the blade is angled approximately 60 to 70 degrees from
the lower shank, which is referred to as an "offset blade." This design
enhances the instrument's ability to adapt to the tooth surface and root
anatomy.
Advantages of Gracey Curettes
Optimal Adaptation: The area-specific design and offset
blade allow for better adaptation to the complex anatomy of the roots,
making them highly effective for subgingival scaling and root planing.
Improved Access: The angled blades enable clinicians to
access difficult-to-reach areas, such as furcations and concavities, which
are often challenging with standard instruments.
Enhanced Efficiency: The design of Gracey curettes
allows for more efficient removal of calculus and biofilm from root
surfaces, contributing to improved periodontal health.
Reduced Tissue Trauma: The precise design minimizes
trauma to the surrounding soft tissues, promoting better healing and patient
comfort.
Microbes in Periodontics
PeriodontologyMicrobes in Periodontics
Bacteria Associated with Periodontal Health
Primary Species:
Gram-Positive Facultative Bacteria:
Streptococcus:
S. sanguis
S. mitis
A. viscosus
A. naeslundii
Actinomyces:
Beneficial for maintaining periodontal health.
Protective or Beneficial Bacteria:
Key Species:
S. sanguis
Veillonella parvula
Corynebacterium ochracea
Characteristics:
Found in higher numbers at inactive periodontal sites (no
attachment loss).
Low numbers at sites with active periodontal destruction.
Prevent colonization of pathogenic microorganisms (e.g., S.
sanguis produces peroxide).
Clinical Relevance:
High levels of C. ochracea and S. sanguis are
associated with greater attachment gain post-therapy.
Microbiology of Chronic Plaque-Induced Gingivitis
Composition:
Roughly equal proportions of:
Gram-Positive: 56%
Gram-Negative: 44%
Facultative: 59%
Anaerobic: 41%
Predominant Gram-Positive Species:
S. sanguis
S. mitis
S. intermedius
S. oralis
A. viscosus
A. naeslundii
Peptostreptococcus micros
Predominant Gram-Negative Species:
Fusobacterium nucleatum
Porphyromonas intermedia
Veillonella parvula
Haemophilus spp.
Capnocytophaga spp.
Campylobacter spp.
Pregnancy-Associated Gingivitis:
Increased levels of steroid hormones and P. intermedia.
Chronic Periodontitis
Key Microbial Species:
High levels of:
Porphyromonas gingivalis
Bacteroides forsythus
Porphyromonas intermedia
Campylobacter rectus
Eikenella corrodens
Fusobacterium nucleatum
Actinobacillus actinomycetemcomitans
Peptostreptococcus micros
Treponema spp.
Eubacterium spp.
Pathogenic Mechanisms:
P. gingivalis and A. actinomycetemcomitans can
invade host tissue cells.
Viruses such as Epstein-Barr Virus-1 (EBV-1) and human
cytomegalovirus (HCMV) may contribute to bone loss.
Localized Aggressive Periodontitis
Microbiota Characteristics:
Predominantly gram-negative, capnophilic, and anaerobic rods.
Almost all localized juvenile periodontitis (LJP) sites harbor A.
actinomycetemcomitans, which can comprise up to 90% of the total
cultivable microbiota.
Nerve Supply of the Muscles of the Orbit
AnatomyNerve Supply of the Muscles of the Orbit (pp. 715-6)
Three cranial nerves supply the muscles of the eyeball; the oculomotor (CN III), trochlear (CN IV) and abducent (CN IV) nerves.
All three enter the orbit via the superior orbital fissure.
The trochlear nerve supplies the superior oblique muscle.
The abducent nerve supplies the lateral rectus muscle.
The oculomotor nerve supplies everything else.
A mnemonic that is used is this formula for this strange sulfate: SO4(LR6)3
Seddon’s Classification of Nerve Injuries
Oral and Maxillofacial SurgerySeddon’s Classification of Nerve Injuries
Neuropraxia:
Definition: This is the mildest form of nerve
injury, often caused by compression or mild trauma.
Sunderland Classification: Type I (10).
Nerve Sheath: Intact; the surrounding connective
tissue remains undamaged.
Axons: Intact; the nerve fibers are not severed.
Wallerian Degeneration: None; there is no
degeneration of the distal nerve segment.
Conduction Failure: Transitory; there may be
temporary loss of function, but it is reversible.
Spontaneous Recovery: Complete recovery is
expected.
Time of Recovery: Typically within 4 weeks.
Axonotmesis:
Definition: This injury involves damage to the
axons while the nerve sheath remains intact. It is often caused by more
severe trauma, such as crush injuries.
Sunderland Classification: Type II (20), Type III
(30), Type IV (40).
Nerve Sheath: Intact; the connective tissue
framework is preserved.
Axons: Interrupted; the nerve fibers are damaged
but the sheath allows for potential regeneration.
Wallerian Degeneration: Yes, partial; degeneration
occurs in the distal segment of the nerve.
Conduction Failure: Prolonged; there is a
longer-lasting loss of function.
Spontaneous Recovery: Partial recovery is possible,
depending on the extent of the injury.
Time of Recovery: Recovery may take months.
Neurotmesis:
Definition: This is the most severe type of nerve
injury, where both the axons and the nerve sheath are disrupted. It
often results from lacerations or severe trauma.
Sunderland Classification: Type V (50).
Nerve Sheath: Interrupted; the connective tissue is
damaged, complicating regeneration.
Axons: Interrupted; the nerve fibers are completely
severed.
Wallerian Degeneration: Yes, complete; degeneration
occurs in both the proximal and distal segments of the nerve.
Conduction Failure: Permanent; there is a lasting
loss of function.
Spontaneous Recovery: Poor to none; recovery is
unlikely without surgical intervention.
Time of Recovery: Recovery may begin by 3 months,
if at all.
Comparisons of primary and permanent teeth:
Pedodontics
1. Crown Dimensions
Primary Anterior Teeth: The crowns of primary anterior
teeth (incisors and canines) are characterized by a wider mesiodistal
dimension and a shorter incisocervical height compared to their permanent
counterparts. This means that primary incisors are broader from side to side
and shorter from the biting edge to the gum line, giving them a more squat
appearance.
Primary Molars: The crowns of primary molars are also
shorter and narrower in the mesiodistal direction at the cervical third
compared to permanent molars. This results in a more constricted appearance
at the base of the crown, which is important for accommodating the
developing permanent teeth.
2. Root Structure
Primary Anterior Teeth: The roots of primary anterior
teeth taper more rapidly than those of permanent anterior teeth. This rapid
tapering allows for a more pronounced root system that is essential for
anchoring the teeth in the softer bone of children’s jaws.
Primary Molars: In contrast, the roots of primary molars
are longer and more slender than those of permanent molars. This elongation
and slenderness provide stability while also allowing for the necessary
space for the developing permanent teeth beneath them.
3. Enamel Characteristics
Enamel Rod Orientation: In primary teeth, the enamel
rods in the gingival third slope occlusally (toward the biting surface)
rather than cervically (toward the root) as seen in permanent teeth. This
unique orientation can influence the way primary teeth respond to wear and
decay.
Thickness of Enamel: The enamel on the occlusal surfaces
of primary molars is of uniform thickness, measuring approximately 1 mm. In
contrast, the enamel on permanent molars is thicker, averaging around 2.5
mm. This difference in thickness can affect the durability and longevity of
the teeth.
4. Surface Contours
Buccal and Lingual Surfaces: The buccal and lingual
surfaces of primary molars are flatter above the crest of contour compared
to permanent molars. This flatter contour can influence the way food is
processed and how plaque accumulates on the teeth.
5. Root Divergence
Primary Molars: The roots of primary molars are more
divergent relative to their crown width compared to permanent molars. This
divergence is crucial as it allows adequate space for the developing
permanent dentition, which is essential for proper alignment and spacing in
the dental arch.
6. Occlusal Features
Occlusal Table: The occlusal table of primary molars is
narrower in the faciolingual dimension. This narrower occlusal surface,
combined with shallower anatomy, results in shorter cusps, less pronounced
ridges, and shallower fossae. These features can affect the functional
aspects of chewing and the overall occlusion.
Mesial Cervical Ridge: Primary molars exhibit a
prominent mesial cervical ridge, which serves as a distinguishing feature
that helps in identifying the right and left molars during dental
examinations.
7. Root Characteristics
Root Shape and Divergence: The roots of primary molars
are not only longer and more slender but also extremely narrow mesiodistally
and broad lingually. This unique shape contributes to their stability while
allowing for the necessary divergence and minimal curvature. Additionally,
primary molars typically have little or no root trunk, which is a stark
contrast to the more complex root structures of permanent molars.