NEET MDS Synopsis
Headgear
OrthodonticsHeadgear is an extraoral orthodontic appliance used to
correct dental and skeletal discrepancies, particularly in growing patients. It
is designed to apply forces to the teeth and jaws to achieve specific
orthodontic goals, such as correcting overbites, underbites, and crossbites, as
well as guiding the growth of the maxilla (upper jaw) and mandible (lower jaw).
Below is an overview of headgear, its types, mechanisms of action, indications,
advantages, and limitations.
Types of Headgear
Class II Headgear:
Description: This type is used primarily to correct
Class II malocclusions, where the upper teeth are positioned too far
forward relative to the lower teeth.
Mechanism: It typically consists of a facebow that
attaches to the maxillary molars and is anchored to a neck strap or a
forehead strap. The appliance applies a backward force to the maxilla,
helping to reposition it and/or retract the upper incisors.
Class III Headgear:
Description: Used to correct Class III
malocclusions, where the lower teeth are positioned too far forward
relative to the upper teeth.
Mechanism: This type of headgear may use a
reverse-pull face mask that applies forward and upward forces to the
maxilla, encouraging its growth and improving the relationship between
the upper and lower jaws.
Cervical Headgear:
Description: This type is used to control the
growth of the maxilla and is often used in conjunction with other
orthodontic appliances.
Mechanism: It consists of a neck strap that
connects to a facebow, applying forces to the maxilla to restrict its
forward growth while allowing the mandible to grow.
High-Pull Headgear:
Description: This type is used to control the
vertical growth of the maxilla and is often used in cases with deep
overbites.
Mechanism: It features a head strap that connects
to the facebow and applies upward and backward forces to the maxilla.
Mechanism of Action
Force Application: Headgear applies extraoral forces to
the teeth and jaws, influencing their position and growth. The forces can be
directed to:
Restrict maxillary growth: In Class II cases,
headgear can help prevent the maxilla from growing too far forward.
Promote maxillary growth: In Class III cases,
headgear can encourage forward growth of the maxilla.
Reposition teeth: By applying forces to the molars,
headgear can help align the dental arches and improve occlusion.
Indications for Use
Class II Malocclusion: To correct overbites and improve
the relationship between the upper and lower teeth.
Class III Malocclusion: To promote the growth of the
maxilla and improve the occlusal relationship.
Crowding: To create space for teeth by retracting the
upper incisors.
Facial Aesthetics: To improve the overall facial
profile and aesthetics by modifying jaw relationships.
Advantages of Headgear
Non-Surgical Option: Provides a way to correct skeletal
discrepancies without the need for surgical intervention.
Effective for Growth Modification: Particularly useful
in growing patients, as it can influence the growth of the jaws.
Improves Aesthetics: Can enhance facial aesthetics by
correcting jaw relationships and improving the smile.
Limitations of Headgear
Patient Compliance: The effectiveness of headgear
relies heavily on patient compliance. Patients must wear the appliance as
prescribed (often 12-14 hours a day) for optimal results.
Discomfort: Patients may experience discomfort or
soreness when first using headgear, which can affect compliance.
Adjustment Period: It may take time for patients to
adjust to wearing headgear, and they may need guidance on how to use it
properly.
Limited Effectiveness in Adults: While headgear is
effective in growing patients, its effectiveness may be limited in adults
due to the maturity of the skeletal structures.
Ketone Body
Biochemistry
During fasting or carbohydrate starvation, oxaloacetate is depleted in liver because it is used for gluconeogenesis. This impedes entry of acetyl-CoA into Krebs cycle. Acetyl-CoA then is converted in liver mitochondria to ketone bodies, acetoacetate and b-hydroxybutyrate.
Three enzymes are involved in synthesis of ketone bodies:
b-Ketothiolase. The final step of the b-oxidation pathway runs backwards, condensing 2 acetyl-CoA to produce acetoacetyl-CoA, with release of one CoA.
HMG-CoA Synthase catalyzes condensation of a third acetate moiety (from acetyl-CoA) with acetoacetyl-CoA to form hydroxymethylglutaryl-CoA (HMG-CoA).
HMG-CoA Lyase cleaves HMG-CoA to yield acetoacetate plus acetyl-CoA.
b-Hydroxybutyrate Dehydrogenase catalyzes inter-conversion of the ketone bodies acetoacetate and b-hydroxybutyrate.
Ketone bodies are transported in the blood to other tissue cells, where they are converted back to acetyl-CoA for catabolism in Krebs cycle
Keloids
General Pathology
Keloids
1. Characterized by a progressively enlarging scar.
2. Caused by an abnormal accumulation of collagen at the site of injury.
3. More common in African-Americans.
Neck Dissection
Oral and Maxillofacial Surgery1. Radical Neck Dissection
Complete removal of all ipsilateral
cervical lymph node groups (levels I-V) and three key non-lymphatic
structures:
Internal jugular vein
Sternocleidomastoid muscle
Spinal accessory nerve
Indication: Typically performed for extensive lymphatic
involvement.
2. Modified Radical Neck Dissection
Similar to radical neck dissection in terms
of lymph node removal (levels I-V) but with preservation of one or more of
the following structures:
Type I: Preserves the spinal accessory nerve.
Type II: Preserves the spinal accessory nerve and
the sternocleidomastoid muscle.
Type III: Preserves the spinal accessory nerve,
sternocleidomastoid muscle, and internal jugular vein.
Indication: Used when there is a need to reduce
morbidity while still addressing lymphatic involvement.
3. Selective Neck Dissection
Preservation of one or more lymph node
groups that are typically removed in a radical neck dissection.
Classification:
Originally had named dissections (e.g., supraomohyoid neck
dissection for levels I-III).
The 2001 modification proposed naming dissections based on the
cancer type and the specific node groups removed. For example, a
selective neck dissection for oral cavity cancer might be referred to as
a selective neck dissection (levels I-III).
Indication: Used when there is a lower risk of
lymphatic spread or when targeting specific areas.
4. Extended Neck Dissection
Involves the removal of additional lymph
node groups or non-lymphatic structures beyond those included in a radical
neck dissection. This may include:
Mediastinal nodes
Non-lymphatic structures such as the carotid artery or hypoglossal
nerve.
Indication: Typically performed in cases of extensive
disease or when there is a need to address additional areas of concern.
Epoxy Resin Sealers Composition in Endodontics
EndodonticsEpoxy resin sealers are widely used in endodontics due to their favorable
properties, including excellent sealing ability, biocompatibility, and
resistance to washout. Understanding their composition is crucial for dental
professionals to select the appropriate materials for root canal treatments.
Here’s a detailed overview of the composition of epoxy resin sealers used in
endodontics.
Key Components of Epoxy Resin Sealers
Base Component
Polyepoxy Resins:
The primary component that provides the sealing properties. These
resins are known for their strong adhesive qualities and dimensional
stability.
Commonly used polyepoxy resins include diglycidyl ether of bisphenol
A (DGEBA).
Curing Agent
Amine-Based Curing Agents:
These agents initiate the curing process of the epoxy resin, leading
to the hardening of the material.
Examples include triethanolamine (TEA) and other amine compounds
that facilitate cross-linking of the resin.
Fillers
Inorganic Fillers:
Materials such as zirconium oxide and calcium oxide are often added
to enhance the physical properties of the sealer, including
radiopacity and strength.
Fillers can also improve the flowability of the sealer, allowing it
to fill irregularities in the canal system effectively.
Plasticizers
Additives:
Plasticizers may be included to improve the flexibility and
workability of the sealer, making it easier to manipulate during
application.
Antimicrobial Agents
Incorporated Compounds:
Some epoxy resin sealers may contain antimicrobial agents to help
reduce bacterial load within the root canal system, promoting
healing and preventing reinfection.
Examples of Epoxy Resin Sealers
AH-Plus
Composition:
Contains a polyepoxy resin base, amine curing agents, and inorganic
fillers.
Properties:
Known for its excellent sealing ability, low solubility, and good
adhesion to dentin.
AD Seal
Composition:
Similar to AH-Plus, with a focus on enhancing flowability and
reducing cytotoxicity.
Properties:
Offers good sealing properties and is used in various clinical
situations.
EndoSeal MTA
Composition:
Combines epoxy resin with bioceramic materials, providing additional
benefits such as bioactivity and improved sealing.
Properties:
Known for its favorable physicochemical properties and
biocompatibility.
Clinical Implications
Selection of Sealers: The choice of epoxy resin sealer should be
based on the specific clinical situation, considering factors such as the
complexity of the canal system, the need for antimicrobial properties, and
the desired setting time.
Application Techniques: Proper mixing and application techniques
are essential to ensure optimal performance of the sealer, including
achieving a fluid-tight seal and preventing voids.
Conclusion
Epoxy resin sealers are composed of a combination of polyepoxy resins, curing
agents, fillers, and additives that contribute to their effectiveness in
endodontic treatments. Understanding the composition and properties of these
sealers allows dental professionals to make informed decisions, ultimately
enhancing the success of root canal therapy.
Here are some notable epoxy resin sealers used in endodontics, along with their
key features:
1. AH
Plus
Description: A widely used epoxy resin-based root canal sealer.
Properties:
Excellent sealing ability.
High biocompatibility.
Good adhesion to gutta-percha and dentin.
Uses: Suitable for permanent root canal fillings.
2. Dia-ProSeal
Description: A two-component epoxy resin-based system.
Properties:
Low shrinkage and high adhesion.
Outstanding flow characteristics.
Antimicrobial activity due to the addition of calcium hydroxide.
Uses: Effective for sealing lateral canals and suitable for warm
gutta-percha techniques.
3. Vioseal
Description: An epoxy resin-based root canal sealer available in a
dual syringe format.
Properties:
Good flowability and sealing properties.
Radiopaque for easy identification on radiographs.
Uses: Used for permanent root canal fillings.
4. AH
Plus Jet
Description: A variant of AH Plus that features an auto-mixing
system.
Properties:
Consistent mixing and application.
Excellent sealing and adhesion properties.
Uses: Ideal for various endodontic applications.
5. EndoREZ
Description: A resin-based sealer that combines epoxy and
methacrylate components.
Properties:
High bond strength and low solubility.
Good flow and adaptability to canal irregularities.
Uses: Suitable for permanent root canal fillings, especially in
complex canal systems.
6. Resilon
Description: A thermoplastic synthetic polymer-based root canal
filling material that can be used with epoxy resin sealers.
Properties:
Provides a monoblock effect with the sealer.
Excellent sealing ability and biocompatibility.
Uses: Used in conjunction with epoxy resin sealers for enhanced
sealing.
Conclusion
Epoxy resin sealers are essential in endodontics for achieving effective and
durable root canal fillings. The choice of sealer may depend on the specific
clinical situation, the complexity of the canal system, and the desired
properties for optimal sealing and biocompatibility.
Connective Tissue of the Gingiva
PeriodontologyConnective Tissue of the Gingiva and Related Cellular Components
The connective tissue of the gingiva, known as the lamina propria,
plays a crucial role in supporting the gingival epithelium and maintaining
periodontal health. This lecture will cover the structure of the lamina propria,
the types of connective tissue fibers present, the role of Langerhans cells, and
the changes observed in the periodontal ligament (PDL) with aging.
Structure of the Lamina Propria
Layers of the Lamina Propria:
The lamina propria consists of two distinct layers:
Papillary Layer:
The upper layer that interdigitates with the epithelium,
containing finger-like projections that increase the surface
area for exchange of nutrients and waste.
Reticular Layer:
The deeper layer that provides structural support and
contains larger blood vessels and nerves.
Types of Connective Tissue Fibers:
The lamina propria contains three main types of connective tissue
fibers:
Collagen Fibers:
Type I Collagen: Forms the bulk of the
lamina propria and provides tensile strength to the gingival
fibers, essential for maintaining the integrity of the gingiva.
Reticular Fibers:
These fibers provide a supportive network within the
connective tissue.
Elastic Fibers:
Contribute to the elasticity and flexibility of the gingival
tissue.
Type IV Collagen:
Found branching between the Type I collagen bundles, it is
continuous with the fibers of the basement membrane and the walls of
blood vessels.
Langerhans Cells
Description:
Langerhans cells are dendritic cells located among keratinocytes at
all suprabasal levels of the gingival epithelium.
They belong to the mononuclear phagocyte system and play a critical
role in immune responses.
Function:
Act as antigen-presenting cells for lymphocytes, facilitating the
immune reaction.
Contain specific granules known as Birbeck’s granules and
exhibit marked ATP activity.
Location:
Found in the oral epithelium of normal gingiva and in small amounts
in the sulcular epithelium.
Absent from the junctional epithelium of normal gingiva.
Changes in the Periodontal Ligament (PDL) with Aging
Aging Effects:
With aging, several changes have been reported in the periodontal
ligament:
Decreased Numbers of Fibroblasts: This
reduction can lead to impaired healing and regeneration of the PDL.
Irregular Structure: The PDL may exhibit a more
irregular structure, paralleling changes in the gingival connective
tissues.
Decreased Organic Matrix Production: This can
affect the overall health and function of the PDL.
Epithelial Cell Rests: There may be a decrease
in the number of epithelial cell rests, which are remnants of the
Hertwig's epithelial root sheath.
Increased Amounts of Elastic Fibers: This
change may contribute to the altered mechanical properties of the
PDL.
The Bicarbonate Buffer System
Biochemistry
The Bicarbonate Buffer System
This is the main extracellular buffer system which (also) provides a means for the necessary removal of the CO2 produced by tissue metabolism. The bicarbonate buffer system is the main buffer in blood plasma and consists of carbonic acid as proton donor and bicarbonate as proton acceptor :
H2CO3 = H+ + HCO3–
If there is a change in the ratio in favour of H2CO3, acidosis results.
This change can result from a decrease in [HCO3 − ] or from an increase in [H2CO3 ]
Most common forms of acidosis are metabolic or respiratory
Metabolic acidosis is caused by a decrease in [HCO3 − ] and occurs, for example, in uncontrolled diabetes with ketosis or as a result of starvation.
Respiratory acidosis is brought about when there is an obstruction to respiration (emphysema, asthma or pneumonia) or depression of respiration (toxic doses of morphine or other respiratory depressants)
Alkalosis results when [HCO3 − ] becomes favoured in the bicarbonate/carbonic acid ratio
Metabolic alkalosis occurs when the HCO3 − fraction increases with little or no concomitant change in H2CO3
Severe vomiting (loss of H+ as HCl) or ingestion of excessive amounts of sodium bicarbonate (bicarbonate of soda) can produce this condition
Respiratory alkalosis is induced by hyperventilation because an excessive removal of CO2 from the blood results in a decrease in [H2CO3 ]
Alkalosis can produce convulsive seizures in children and tetany, hysteria, prolonged hot baths or lack of O2 as high altitudes.
The pH of blood is maintained at 7.4 when the buffer ratio [HCO3 − ] / [ H2CO3] becomes 20
Plaque Formation
PeriodontologyPlaque Formation
Dental plaque is a biofilm that forms on the surfaces of teeth and is a key
factor in the development of dental caries and periodontal disease. The process
of plaque formation can be divided into three major phases:
1. Formation of Pellicle on the Tooth Surface
Definition: The pellicle is a thin, acellular film that
forms on the tooth surface shortly after cleaning.
Composition: It is primarily composed of salivary
glycoproteins and other proteins that are adsorbed onto the enamel surface.
Function:
The pellicle serves as a protective barrier for the tooth surface.
It provides a substrate for bacterial adhesion, facilitating the
subsequent stages of plaque formation.
2. Initial Adhesion & Attachment of Bacteria
Mechanism:
Bacteria in the oral cavity begin to adhere to the pellicle-coated
tooth surface.
This initial adhesion is mediated by specific interactions between
bacterial adhesins (surface proteins) and the components of the
pellicle.
Key Bacterial Species:
Primary colonizers, such as Streptococcus sanguis and Actinomyces
viscosus, are among the first to attach.
Importance:
Successful adhesion is crucial for the establishment of plaque, as
it allows for the accumulation of additional bacteria.
3. Colonization & Plaque Maturation
Colonization:
Once initial bacteria have adhered, they proliferate and create a
more complex community.
Secondary colonizers, including gram-negative anaerobic bacteria,
begin to join the biofilm.
Plaque Maturation:
As the plaque matures, it develops a three-dimensional structure,
with different bacterial species occupying specific niches within the
biofilm.
The matrix of extracellular polysaccharides and salivary
glycoproteins becomes more pronounced, providing structural integrity to
the plaque.
Coaggregation:
Different bacterial species can adhere to one another through
coaggregation, enhancing the complexity of the plaque community.
Composition of Plaque
Matrix Composition:
Plaque is primarily composed of bacteria embedded in a matrix of
salivary glycoproteins and extracellular polysaccharides.
Implications for Removal:
The dense and cohesive nature of this matrix makes it difficult to
remove plaque through simple rinsing or the use of sprays.
Effective plaque removal typically requires mechanical means, such
as brushing and flossing, to disrupt the biofilm structure.