NEET MDS Synopsis
Dentinogenesis
Dental Anatomy
Dentinogenesis
Dentin formation, known as dentinogenesis, is the first identifiable feature in the crown stage of tooth development. The formation of dentin must always occur before the formation of enamel. The different stages of dentin formation result in different types of dentin: mantle dentin, primary dentin, secondary dentin, and tertiary dentin.
Odontoblasts, the dentin-forming cells, differentiate from cells of the dental papilla. They begin secreting an organic matrix around the area directly adjacent to the inner enamel epithelium, closest to the area of the future cusp of a tooth. The organic matrix contains collagen fibers with large diameters (0.1-0.2 μm in diameter). The odontoblasts begin to move toward the center of the tooth, forming an extension called the odontoblast process. Thus, dentin formation proceeds toward the inside of the tooth. The odontoblast process causes the secretion of hydroxyapatite crystals and mineralization of the matrix. This area of mineralization is known as mantle dentin and is a layer usually about 150 μm thick.
Whereas mantle dentin forms from the preexisting ground substance of the dental papilla, primary dentin forms through a different process. Odontoblasts increase in size, eliminating the availability of any extracellular resources to contribute to an organic matrix for mineralization. Additionally, the larger odontoblasts cause collagen to be secreted in smaller amounts, which results in more tightly arranged, heterogenous nucleation that is used for mineralization. Other materials (such as lipids, phosphoproteins, and phospholipids) are also secreted.
Secondary dentin is formed after root formation is finished and occurs at a much slower rate. It is not formed at a uniform rate along the tooth, but instead forms faster along sections closer to the crown of a tooth. This development continues throughout life and accounts for the smaller areas of pulp found in older individuals. Tertiary dentin, also known as reparative dentin, forms in reaction to stimuli, such as attrition or dental caries.
The dentin in the root of a tooth forms only after the presence of Hertwig's epithelial root sheath (HERS), near the cervical loop of the enamel organ. Root dentin is considered different than dentin found in the crown of the tooth (known as coronal dentin) because of the different orientation of collagen fibers, the decrease of phosphoryn levels, and the less amount of mineralization.
Lamotrigine
Pharmacology
Lamotrigine (Lamictal): newer; broad spectrum (for most seizure types)
Mechanism: ↓ reactivation of Na channels (↑ refractory period, blocks high frequency cell firing)
Side effects: dizziness, ataxia, fatigue, nausea, no significant drug interactions
Assessing New Attachment in Periodontal Therapy
PeriodontologyAssessing New Attachment in Periodontal Therapy
Assessing new attachment following periodontal therapy is crucial for
evaluating treatment outcomes and understanding the healing process. However,
various methods of assessment have limitations that must be considered. This
lecture will discuss the reliability of different assessment methods for new
attachment, including periodontal probing, radiographic analysis, and histologic
methods.
1. Periodontal Probing
Assessment Method: Periodontal probing is commonly used
to measure probing depth and attachment levels before and after therapy.
Limitations:
Coronal Positioning of Probe Tip: After therapy,
when the inflammatory lesion is resolved, the probe tip may stop coronal
to the apical termination of the epithelium. This can lead to misleading
interpretations of attachment gain.
Infrabony Defects: Following treatment of infrabony
defects, new bone may form so close to the tooth surface that the probe
cannot penetrate. This can result in a false impression of improved
attachment levels.
Interpretation of Results: A gain in probing
attachment level does not necessarily indicate a true gain of connective
tissue attachment. Instead, it may reflect improved health of the
surrounding tissues, which increases resistance to probe penetration.
2. Radiographic Analysis and Reentry Operations
Assessment Method: Radiographic analysis involves
comparing radiographs taken before and after therapy to evaluate changes in
bone levels. Reentry operations allow for direct inspection of the treated
area.
Limitations:
Bone Fill vs. New Attachment: While radiographs can
provide evidence of new bone formation (bone fill), they do not document
the formation of new root cementum or a new periodontal ligament.
Therefore, radiographic evidence alone cannot confirm the establishment
of new attachment.
3. Histologic Methods
Assessment Method: Histologic analysis involves
examining tissue samples under a microscope to assess the formation of new
attachment, including new cementum and periodontal ligament.
Advantages:
Validity: Histologic methods are considered the
only valid approach to assess the formation of new attachment
accurately.
Limitations:
Pre-Therapy Assessment: Accurate assessment of the
attachment level prior to therapy is essential for histologic analysis.
If the initial attachment level cannot be determined with certainty, it
may compromise the validity of the findings.
Nasal Complex Fractures
Oral and Maxillofacial SurgeryManagement of Nasal Complex Fractures
Nasal complex fractures involve injuries to the nasal bones
and surrounding structures, including the nasal septum, maxilla, and sometimes
the orbits. Proper management is crucial to restore function and aesthetics.
Anesthesia Considerations
Local Anesthesia:
Nasal complex fractures can be reduced under local anesthesia, which
may be sufficient for less complicated cases or when the patient is
cooperative.
General Anesthesia:
For more complex fractures or when significant manipulation of the
nasal structures is required, general anesthesia is preferred.
Per-oral Endotracheal Tube: This method allows for
better airway management and control during the procedure.
Throat Pack: A throat pack is often used to
minimize the risk of aspiration and to manage any potential hemorrhage,
which can be profuse in these cases.
Surgical Technique
Reduction of Fractures:
The primary goal is to realign the fractured nasal bones and restore
the normal anatomy of the nasal complex.
Manipulation of Fragments:
Walsham’s Forceps: These are specialized
instruments used to grasp and manipulate the nasal bone fragments
during reduction.
Asche’s Forceps: Another type of forceps that
can be used for similar purposes, allowing for precise control over
the fractured segments.
Post-Reduction Care:
After the reduction, the nasal structures may be stabilized using
splints or packing to maintain alignment during the healing process.
Monitoring for complications such as bleeding, infection, or airway
obstruction is essential.
Indication, Contraindication of SCC
PedodonticsIndications for Stainless Steel Crowns in Pediatric Dentistry
Extensive Tooth Decay:
Stainless steel crowns (SSCs) are primarily indicated for teeth with
significant decay that cannot be effectively treated with fillings. They
provide full coverage, preventing further decay and preserving the tooth's
structure.
Developmental Defects:
SSCs are beneficial for teeth affected by developmental conditions such as
enamel dysplasia or dentinogenesis imperfecta, which make them more
susceptible to decay.
Post-Pulp Therapy:
After procedures like pulpotomy or pulpectomy, SSCs are often used to
protect the treated tooth, ensuring its functionality and longevity.
High Caries Risk:
For patients who are highly susceptible to caries, SSCs serve as preventive
restorations, helping to protect at-risk tooth surfaces from future decay.
Uncooperative Patients:
In cases where children may be uncooperative during dental procedures, SSCs
offer a quicker and less invasive solution compared to more complex
treatments.
Fractured Teeth:
SSCs are also indicated for restoring fractured primary molars, which are
crucial for a child's chewing ability and overall nutrition.
Special Needs Patients:
Children with special needs who may struggle with maintaining oral hygiene
can benefit significantly from the durability and protection offered by
SSCs.
Contraindications for Stainless Steel Crowns
Allergy to Nickel:
Some patients may have an allergy or sensitivity to nickel, which is
a component of stainless steel. In such cases, alternative materials
should be considered.
Severe Tooth Mobility:
If the tooth is severely mobile due to periodontal disease or other
factors, placing a stainless steel crown may not be appropriate, as it
may not provide adequate retention.
Inadequate Tooth Structure:
If there is insufficient tooth structure remaining to support the
crown, it may not be feasible to place an SSC. This is particularly
relevant in cases of extensive decay or fracture.
Active Dental Infection:
If there is an active infection or abscess associated with the
tooth, it is generally advisable to treat the infection before placing a
crown.
Patient Non-Compliance:
In cases where the patient is unlikely to cooperate with the
treatment or follow-up care, the use of SSCs may not be ideal.
Aesthetic Concerns:
In anterior teeth, where aesthetics are a primary concern, parents
or patients may prefer more esthetic options (e.g., composite crowns or
porcelain crowns) over stainless steel crowns.
Severe Malocclusion:
In cases of significant malocclusion, the placement of SSCs may not
be appropriate if they could interfere with the occlusion or lead to
further dental issues.
Presence of Extensive Caries in Adjacent Teeth:
If adjacent teeth are also severely decayed, it may be more
beneficial to address those issues first rather than placing a crown on
a single tooth.
Nerves of the Palate
AnatomyNerves of the Palate
The sensory nerves of the palate, which are branches of the pterygopalatine ganglion, are the greater and lesser palatine nerves.
They accompany the arteries through the greater and lesser palatine foramina, respectively.
The greater palatine nerve supplies the gingivae, mucous membrane, and glands of the hard palate.
The lesser palatine nerve supplies the soft palate.
Another branch of the pterygopalatine ganglion, the nasopalatine nerve, emerges from the incisive foramen and supplies the mucous membrane of the anterior part of the hard palate.
Thickness of Dental Cements
Conservative DentistryFilm Thickness of Dental Cements
The film thickness of dental cements is an important property that can
influence the effectiveness of the material in various dental applications,
including luting agents, bases, and liners. .
1. Importance of Film Thickness
A. Clinical Implications
Sealing Ability: The film thickness of a cement can
affect its ability to create a proper seal between the restoration and the
tooth structure. Thicker films may lead to gaps and reduced retention.
Adaptation: A thinner film allows for better adaptation
to the irregularities of the tooth surface, which is crucial for minimizing
microleakage and ensuring the longevity of the restoration.
B. Material Selection
Choosing the Right Cement: Understanding the film
thickness of different cements helps clinicians select the appropriate
material for specific applications, such as luting crowns, bridges, or other
restorations.
2. Summary of Film Thickness
Zinc Phosphate: 20 mm – Known for its strength and
durability, often used for cementing crowns and bridges.
Zinc Oxide Eugenol (ZOE), Type I: 25 mm – Commonly used
for temporary restorations and as a base under other materials.
ZOE + Alumina + EBA (Type II): 25 mm – Offers improved
properties for specific applications.
ZOE + Polymer (Type II): 32 mm – Provides enhanced
strength and flexibility.
Silicophosphate: 25 mm – Used for its aesthetic
properties and good adhesion.
Resin Cement: < 25 mm – Offers excellent bonding and
low film thickness, making it ideal for aesthetic restorations.
Polycarboxylate: 21 mm – Known for its biocompatibility
and moderate strength.
** Glass Ionomer: 24 mm – Valued for its fluoride release and ability to
bond chemically to tooth structure, making it suitable for various
restorative applications.
Myocardial infarction (MI)—heart attack
General Pathology
Myocardial infarction (MI)—heart attack
A. Ischemia versus MI: Ischemia is a reversible mismatch between the supply and demand of oxygen. Infarction
is an irreversible mismatch that results in cell death caused by the lack of blood flow (oxygenation). For instance, chest pain caused by ischemia can be relieved by administering nitroglycerin (a vasodilator) to the patient. If the patient has an MI, the pain will not be relieved with nitroglycerin.
1. MIs most commonly occur when a coronary artery is occluded by a thrombus generated in an atherosclerotic artery.
2. Symptoms include:
a. Chest pain, shortness of breath.
b. Diaphoresis (sweating), clammy hands.
c. Nausea, vomiting.
3. Consequences:
a. Death (one third of patients).
b. Arrhythmias (most common immediate cause of death).
c. Congestive heart failure.
d. Myocardial rupture, which may result in death from cardiac tamponade.
e. Thrombus formation on infarcted tissue; may result in systemic embolism.