NEET MDS Synopsis
Bases
Conservative DentistryBases in Restorative DentistryBases are an essential component in restorative dentistry, serving as a
thicker layer of material placed beneath restorations to provide additional
protection and support to the dental pulp and surrounding structures. Below is
an overview of the characteristics, objectives, and types of bases used in
dental practice.
1. Characteristics of BasesA. Thickness
Typical Thickness: Bases are generally thicker than
liners, typically ranging from 1 to 2 mm. Some bases may be
around 0.5 to 0.75 mm thick.
B. Functions
Thermal Protection: Bases provide thermal insulation to
protect the pulp from temperature changes that can occur during and after
the placement of restorations.
Mechanical Support: They offer supplemental mechanical
support for the restoration by distributing stress on the underlying dentin
surface. This is particularly important during procedures such as amalgam
condensation, where forces can be applied to the restoration.
2. Objectives of Using BasesThe choice of base material and its application depend on the Remaining
Dentin Thickness (RDT), which is a critical factor in determining the
need for a base:
RDT > 2 mm: No base is required, as there is sufficient
dentin to protect the pulp.
RDT 0.5 - 2 mm: A base is indicated, and the choice of
material depends on the restorative material being used.
RDT < 0.5 mm: Calcium hydroxide (Ca(OH)₂) or Mineral
Trioxide Aggregate (MTA) should be used to promote the formation of
reparative dentin, as the remaining dentin is insufficient to provide
adequate protection.
3. Types of BasesA. Common Base Materials
Zinc Phosphate (ZnPO₄): Known for its good mechanical
properties and thermal insulation.
Glass Ionomer Cement (GIC): Provides thermal protection
and releases fluoride, which can help in preventing caries.
Zinc Polycarboxylate: Offers good adhesion to tooth
structure and provides thermal insulation.
B. Properties
Mechanical Protection: Bases distribute stress
effectively, reducing the risk of fracture in the restoration and protecting
the underlying dentin.
Thermal Insulation: Bases are poor conductors of heat
and cold, helping to maintain a stable temperature at the pulp level.
Surgical Approaches in Oral and Maxillofacial Surgery
Oral and Maxillofacial SurgerySurgical Approaches in Oral and Maxillofacial Surgery
In the management of tumors and lesions in the oral and maxillofacial region,
various surgical approaches are employed based on the extent of the disease, the
involvement of surrounding structures, and the need for reconstruction. Below is
a detailed overview of the surgical techniques mentioned, along with their
indications and reconstruction options.
1. Marginal / Segmental / En Bloc Resection
Definition:
En Bloc Resection: This technique involves the complete
removal of a tumor along with a margin of healthy tissue, without disrupting
the continuity of the bone. It is often used for tumors that are
well-defined and localized.
Indications:
No Cortical Perforation: En bloc segmental resection is
indicated when there is no evidence of cortical bone perforation. This
allows for the removal of the tumor while preserving the structural
integrity of the surrounding bone.
Tumor Characteristics: This approach is suitable for
benign tumors or low-grade malignancies that have not invaded surrounding
tissues.
2. Partial Resection (Mandibulectomy)
Definition:
Mandibulectomy: This procedure involves the resection
of a portion of the mandible, typically performed when a tumor is present.
Indications:
Cortical Perforation: Mandibulectomy is indicated when
there is cortical perforation of the mandible. This means that the tumor has
invaded the cortical bone, necessitating a more extensive surgical approach.
Clearance Margin: A margin of at least 1 cm of
healthy bone is typically removed to ensure complete excision of the tumor
and reduce the risk of recurrence.
3. Total Resection (Hemimandibulectomy)
Definition:
Hemimandibulectomy: This procedure involves the
resection of one half of the mandible, including the associated soft
tissues.
Indications:
Perforation of Bone and Soft Tissue: Hemimandibulectomy
is indicated when there is both perforation of the bone and involvement of
the surrounding soft tissues. This is often seen in more aggressive tumors
or those that have metastasized.
Extensive Tumor Involvement: This approach is necessary
for tumors that cannot be adequately removed with less invasive techniques
due to their size or location.
4. Reconstruction
Following resection, reconstruction of the jaw is often necessary to restore
function and aesthetics. Several options are available for reconstruction:
a. Reconstruction Plate:
Description: A reconstruction plate is a rigid plate
made of titanium or other biocompatible materials that is used to stabilize
the bone after resection.
Indications: Used in cases where structural support is
needed to maintain the shape and function of the mandible.
b. K-wire:
Description: K-wires are thin, flexible wires used to
stabilize bone fragments during the healing process.
Indications: Often used in conjunction with other
reconstruction methods to provide additional support.
c. Titanium Mesh:
Description: Titanium mesh is a flexible mesh that can
be shaped to fit the contours of the jaw and provide support for soft tissue
and bone.
Indications: Used in cases where there is significant
bone loss and soft tissue coverage is required.
d. Rib Graft / Iliac Crest Graft:
Description: Autogenous bone grafts can be harvested
from the rib or iliac crest to reconstruct the mandible.
Indications: These grafts are used when significant
bone volume is needed for reconstruction, providing a biological scaffold
for new bone formation.
ATROPHY
General Pathology
ATROPHY
It is the acquired decrease in the size of an organ due to decrease in the size and/or number of its constituent cells.
Causes:
(1) Physiological
- Foetal involution.
o Branchial clefts.
o Ductus arterious.
- Involution of thymus and other lymphoid organs in childhood and adolescence.
- In adults:
o Post-partum uterus.
o Post-menopausal ovaries and uterus
o Post-lactational breast
o Thymus.
(2) Pathological:
- Generalised as in
o Ageing.
o Severe starvation and cachexia
- Localised :
o Disuse atropy of bone and muscle.
o Ischaemic atrophy as in arteriosclerotic kidney. .
o Pressure atrophy due to tumours and of kidney in hydronephrosis.
o Lack of trophic stimulus to endocrines and gonads.
Ketamine
Pharmacology
Ketamine
- Causes a dissociative anesthesia.
- Is similar to but less potent than phencyclidine.
- Induces amnesia, analgesia, catalepsy and anesthesia, but does not induce convulsions.
- The principal disadvantage of ketamine is its adverse psychic effects during emergence from anesthesia. These include: hallucinations, changes in mood and body image.
- During anesthesia, many of the protective reflexes are maintained, such as laryngeal, pharyngeal, eyelid and corneal reflexes.
- Muscle relaxation is poor.
- It is not indicated for intracranial operations because it increases cerebrospinal fluid pressure.
- Respiration is well maintained.
- Arterial blood pressure, cardiac output, and heart rate are all elevated.
COMPOSITE RESINS -Manipulation
Dental Materials
Manipulation
Selection
o Microfilled composites or hybrids for anterior class III, IV, V
o Hybrids or midifills for posterior class I, II, III, V
Conditioning of enamel and / or dentin
Do not apply fluorides before etching.-->Acid-etch --> Rinse for 20 seconds with water --> Air-dry etched area for 20 seconds but do not desiccate or dehydrate --> Apply bonding agent and polymerize
Mixing (if required)--> mix two pastes for 20 to 30 seconds
o Self-cured composite-working time is 60 to 120 seconds after mixing
o Light-cured composite-working time is unlimited (used for most anterior and some posterior composite restorations)
o Dual-cured composite-working time is > 10 minutes
o Two-stage cured composite-working time is >5 minutes
Placement
use plastic instrument or syringe --> Light curing --> Cure incrementally in <2 mm thick layers. Use matrix strip where possible to produce smooth surface and contour composite .Postcure to improve hardness
Helicobacter Pylori Agents
Pharmacology
Helicobacter Pylori Agents
Antimicrobial
• Amoxicillin,
• Clarithromycin,
• Metronidozole
• Tetracycline
Antisecreteory agents accelerates symptom relief and yield healing (omeprozole)
Bismuth subsalicylate
Therapy For H. Pylori
Original
• Tetracycline
• Metronidazole (Flagyl)
• Bismuth subsalicylate
• Given for 14 days
• >90% effective in eradicating microorganisms
New triple therapy
• Amoxicillin
• Clarithromycin
• Omeprazole (Prilosec)
• Given for 7 days
• >90% effective in eradicating microorganisms
Dual Therapy
Amoxicillin or clarithromycin
Omeprazole
Given for 14 days
60-80% effective in eradication of H. Pylori
Acrylic Appliances
Dental Materials
Acrylic Appliances
Use - space maintenance or tooth movement for orthodontics and pediatric dentistry
1. Components
a. Powder-PMMA powder. peroxide initiator, and pigments
b. Liquid-MMA monomer, hydroquinone inhibitor, cross-linking agents, and chemical accelerators (N, N-dimethyl-p-toluidine)
2. Reaction
PMMA powder makes mixture viscous for manipulation before curing . Chemical accelerators cause decomposition of benzoyl peroxide into free radicals that initiate polymerization of monomer . New PMMA is formed into a matrix that surrounds PMMA powder. Linear shrinkage of 5% to 7% during setting. but dimensions of appliances are not critical
Mouth Protectors
Dental Materials
Mouth Protectors
Use - to protect against effects of blows to chin, top of the head, the face, or grinding of the teeth
Types
o Stock protectors-least desirable because of poor fit
o Mouth-formed protectors-improved fit compared with stock type
o Custom-made protectors-preferred because of durability. low speech impairment, and comfort
I. Components
a. Stock protectors-thermoplastic copolymer of PYA-PE (polyvinyl acetate-polyethylene copolymer)
b. Mouth-formed protectors-thermoplastic copolymer
c. Custom-made protectors- thermoplastic copolymer, rubber. or polyurethane
2. Reaction-physical reaction of hardening during cooling
3. Fabrication
Alginate impression made of maxillary arch. High-strength stone cast poured immediately. Thermoplastic material is heated in hot water and vacuum-molded to cast .
Mouth protector trimmed to within ½ inch of labial fold, clearance provided at the buccal and labial frena, and edges smoothed by flaming. Gagging, taste, irritation. and impairment of speech are minimized with properly fabricated appliances
4. Instructions for use
a. Rinse before and after use with cold water
b. Clean protector occasionally with soap and cool water
c. Store the protector in a rigid container
d. Protect from heat and pressure during storage
e. Evaluate protector routinely for evidence of deterioration
Properties
1. Physical-thermal insulators
2. Chemical-absorbs after during use
3. Mechanical-tensile strength, modulus, and hardness decrease after water absorption, but elongation, tear strength, and resilience increase
4. Biologic-nontoxic as long as no bacterial, fungal, or viral growth occurs on surfaces between uses