NEET MDS Synopsis
OCCLUSION AND DENTAL DEVELOPMENT-Stages-Mixed Dentition Period
Dental Anatomy
Mixed Dentition Period.
-Begins with the eruption of the first permanent molars distal to the second deciduous molars. These are the first teeth to emerge and they initially articulate in an 'end-on' (one on top of the other) relationship.
-On occasion, the permanent incisors spread out due to spacing. In the older literature, is called by the 'ugly duckling stage.' With the eruption of the permanent canines, the spaces often will close.
-Between ages 6 and 7 years of age there are:
20 deciduous teeth
4 first permanent molars
28 permanent tooth buds in various states of development
Periodontal Fibers
PeriodontologyPeriodontal Fibers
Periodontal fibers play a crucial role in maintaining the integrity of the
periodontal ligament and supporting the teeth within the alveolar bone.
Understanding the different groups of periodontal fibers is essential for
comprehending their functions in periodontal health and disease.
1. Gingivodental Group
Location:
Present on the facial, lingual, and interproximal surfaces of the
teeth.
Attachment:
These fibers are embedded in the cementum just beneath the
epithelium at the base of the gingival sulcus.
Function:
They help support the gingiva and maintain the position of the
gingival margin.
2. Circular Group
Location:
These fibers course through the connective tissue of the marginal
and interdental gingiva.
Attachment:
They encircle the tooth in a ring-like fashion.
Function:
The circular fibers help maintain the contour of the gingiva and
provide support to the marginal gingiva.
3. Transseptal Group
Location:
Located interproximally, these fibers extend between the cementum of
adjacent teeth.
Attachment:
They lie in the area between the epithelium at the base of the
gingival sulcus and the crest of the interdental bone.
Function:
The transseptal fibers are primarily responsible for the
post-retention relapse of orthodontically positioned teeth.
They are sometimes classified as principal fibers of the periodontal
ligament.
Collectively, they form the interdental ligament of the arch,
providing stability to the interproximal areas.
4. Semicircular Fibers
Location:
These fibers attach to the proximal surface of a tooth immediately
below the cementoenamel junction (CEJ).
Attachment:
They go around the facial or lingual marginal gingiva of the tooth
and attach to the other proximal surface of the same tooth.
Function:
Semicircular fibers help maintain the position of the tooth and
support the gingival tissue around it.
5. Transgingival Fibers
Location:
These fibers attach to the proximal surface of one tooth and
traverse the interdental space diagonally to attach to the proximal
surface of the adjacent tooth.
Function:
Transgingival fibers provide support across the interdental space,
helping to maintain the position of adjacent teeth and the integrity of
the gingival tissue.
Hybridization
Conservative DentistryHybridization in Dental Bonding
Hybridization, as described by Nakabayashi in 1982, is a critical process in
dental bonding that involves the formation of a hybrid layer. This hybrid layer
plays a vital role in achieving micromechanical bonding between the tooth
structure (dentin) and resin materials used in restorative dentistry.
1. Definition of Hybridization
Hybridization refers to the process of forming a hybrid
layer at the interface between demineralized dentin and resin materials. This
phenomenon is characterized by the interlocking of resin within the
demineralized dentin surface, which enhances the bond strength between the tooth
and the resin.
A. Formation of the Hybrid Layer
Conditioning Dentin: When dentin is treated with a
conditioner (usually an acid), it removes minerals from the dentin, exposing
the collagen fibril network and creating inter-fibrillar microporosities.
Application of Primer: A low-viscosity primer is then
applied, which infiltrates these microporosities.
Polymerization: After the primer is applied, the resin
monomers polymerize, forming the hybrid layer.
2. Zones of the Hybrid Layer
The hybrid layer is composed of three distinct zones, each with unique
characteristics:
A. Top Layer
Composition: This layer consists of loosely arranged
collagen fibrils and inter-fibrillar spaces that are filled with resin.
Function: The presence of resin in this layer enhances
the bonding strength and provides a flexible interface that can accommodate
stress during functional loading.
B. Middle Layer
Composition: In this zone, the hydroxyapatite crystals
that were originally present in the dentin have been replaced by resin
monomers due to the hybridization process.
Function: This replacement contributes to the
mechanical properties of the hybrid layer, providing a strong bond between
the dentin and the resin.
C. Bottom Layer
Composition: This layer consists of dentin that is
almost unaffected, with a partly demineralized zone.
Function: The presence of this layer helps maintain the
integrity of the underlying dentin structure while still allowing for
effective bonding.
3. Importance of the Hybrid Layer
The hybrid layer is crucial for the success of adhesive dentistry for several
reasons:
Micromechanical Bonding: The hybrid layer facilitates
micromechanical bonding, which is essential for the retention of composite
resins and other restorative materials.
Stress Distribution: The hybrid layer helps distribute
stress during functional loading, reducing the risk of debonding or failure
of the restoration.
Sealing Ability: A well-formed hybrid layer can help
seal the dentin tubules, reducing sensitivity and protecting the pulp from
potential irritants.
Cells of the Nervous System
Pharmacology
Cells of the Nervous System
1-Neurons (Nerve Cells):function units of the nervous system by conducting nerve impulses, highly specialized and amitotic. Each has a cell body (soma), one or more dendrites, and a single axon.
• Cell Body: it has a nucleus with at least one nucleolus and many of the typical cytoplasmic organelles, but lacks centriolesfor cell division.
• Dendrites:Dendrites and axons are cytoplasmic extensions (or processes), that project from the cell body. They are sometimes referred to as fibers. Dendrites (afferent processes) increase their surface area to receive signals from other neurons, and transmit impulses to the neuron cell body.
• Axon: There is only one axon (efferent process) that projects from each cell body.
It carries impulses away from the cell body.
2-Glial cells: do not conduct nerve impulses, but support, nourish, and protect the neurons. They are mitotic, and far more numerous than neurons.
Astrocyte: A glialcell that provides support for neurons of the CNS, provides nutrients regulates the chemical composition of the extracellularfluid.
• Oligodendrocyte: A type of glialcell in the CNS that forms myelin sheaths.
• Microglia:The smallest glialcells; act as phagocytes (cleaning up debris) and protect the brain from invading microorganisms.
• Schwann cell:A cell in the PNS that is wrapped around a myelinatedaxon, providing one segment of its myelin sheath.
Langerhans cell granulomatosis
General Pathology
Langerhans cell granulomatosis (histocytosis X)
a. A group of diseases that are caused by the proliferation of Langerhans’ cells (previously known as histocytes).
b. Most commonly causes bone lesions; however, other tissues can be affected.
c. Histologic findings include Langerhans’ cells containing Birbeck granules and eosinophils.
d. Three types:
(1) Letterer-Siwe disease—an acute, disseminated form that is fatal in infants.
(2) Hand-Schüller-Christian disease—a chronic, disseminated form that has a better prognosis than LettererSiwe disease. It usually presents
before the age of 5 and is characterized by a triad of symptoms:
(a) Bone lesions—found in skull, mandible (loose teeth).
(b) Exophthalmos.
(c) Diabetes insipidus.
(3) Eosinophilic granuloma of bone—a localized, least severe form of the three. Lesions may heal without treatment.
(a) Most commonly occurs in young adults.
(b) Lesions in the mandible may cause loose teeth.
Stylohyoid Muscle
AnatomyStylohyoid Muscle
Origin: Posterior border of the styloid process of the
temporal bone.
Insertion: Body of the hyoid bone at the junction with
the greater horn.
Nerve Supply: Facial nerve (CN VII).
Arterial Supply: Muscular branches of the facial artery
and muscular branches of the occipital artery.
Action: Elevates the hyoid bone and base of the tongue.
COMPOSITE RESINS -ACID ETCH TECHNIQUE
Dental Materials
ACID ETCH TECHNIQUE
Cavities requiring added retention (to hold firmly) are treated with an acid etching technique. This technique improves the seal of the composite resin to the cavity wall. The enamel adjacent to the margins of the preparation is slightly decalcified with a 40 to 50 percent phosphoric acid solution. This etched enamel enhances the mechanical retention of the composite resin. In addition, the acid etch technique is used to splint unstable teeth to adjacent teeth. The acid is left on the cut tooth structure only 15 seconds, in accordance with the directions for one common commercial brand. The area is then flushed with water for a minimum of 30 seconds to remove the decalcified material. Etched tooth structure will have a chalky appearance.
ANAEMIA
General Pathology
ANAEMIA
Definition. Reduction of the hemoglobin level below the normal for the age and sex of the patient
Classification
1. Blood loss anaemia:
- Acute.
- Chronic (results in iron deficiency).
2. Deficiency anaemia:
- Iron deficiency.
- Megaloblastic anaemia-BI2 and Folic acid deficiency.
- Protein deficiency.
- Scurvy-Vitamin C deficiency.
3. Marrow dysfunction:
- Aplastic anaemia.
- Marrow infiltration.
- Liver failure.
- Renal failure.
- Collagen diseases.
4 Increased destruction (Heamolysis)
- Due to corpuscular defects.
- Due to extra corpuscular defects