NEET MDS Synopsis
CASTING
Dental Materials
CASTING: casting is the process by which the wax pattern of a restoration is converted to a replicate in a dental alloy. The casting process is used to make dental restorations such as inlays, onlays, crowns, bridges and removable partial dentures.
Objectives of casting
1) To heat the alloy as quickly as possible to a completely molten condition.
2) To prevent oxidation by heating the metal with awell adjusted torch .
3) To produce a casting with sharp details by having adequate pressure to the well melted metal to force into the mold.
STEPS IN MAKING A CAST RESTORATION
1. TOOTH PREPARATION
2. IMPRESSION
3. DIE PREPARATION
4. WAX PATTERN FABRICATION
5. SPRUING
BONE
Anatomy
BONE
A rigid form of CT, Consists of matrix and cells
Matrix contains:
organic component 35% collagen fibres
inorganic salts 65% calcium phosphate (58,5%), calcium carbonate (6,5%)
2 types of bone - spongy (concellous)
compact (dense)
Microscopic elements are the same
Spongy bone consists of bars (trabeculae) which branch and unite to form a meshwork
Spaces are filled with bone marrow
Compact bone appears solid but has microscopic spaces
In long bones the shaft is compact bone
And the ends (epiphysis) consists of spongy bone covered with compact bone
Flat bones consists of 2 plates of compact bone with spongy bone in-between
Periosteum covers the bone
Endosteum lines marrow cavity and spaces
These 2 layers play a role in the nutrition of bone tissue
They constantly supply the bone with new osteoblasts for the repair and growth of bone
Microscopically
The basic structural unit of bone is the Haversian system or osteon
An osteon consists of a central Haversian canal
- In which lies vessels nerves and loose CT
- Around the central canal lies rings of lacunae
- A lacuna is a space in the matrix in which lies the osteocyte
- The lacunae are connected through canaliculi which radiate from the lacunae
- In the canaliculi are the processes of the osteocytes
- The canaliculi link up with one another and also with the Haversian canal
- The processes communicate with one another in the canaliculi through gap junctions
- Between two adjacent rows of lacunae lie the lamellae, 5-7µm thick
- In three dimensions the Haversian systems are cylindrical
- The collagen fibres lie in a spiral in the lamellae
- Perpendicular to the Haversian canals are the Volkman's canals
- They link up with the marrow cavity and the Haversian canals
- Some lamellae do not form part of a Haversian system
- They are the:
- Inner circumferential lamellae - around the marrow cavity
- Outer circumferential lamellae - underneath the outer surface of the bone
- Interstitial lamellae - between the osteons
Endosteum
Lines all cavities like marrow spaces, Haversian- and Volkman's canals
Consists of a single layer of squamous osteoprogenitor cells with a thin reticular CT layer underneath it
Continuous with the inner layer of periosteum
Covers the trabeculae of spongy bone
Cells differentiate into osteoblasts (like the cells of the periosteum)
Periosteum
Formed by tough CT
2 layers
Outer fibrous layer: Thickest, Contains collagen fibres,
Some fibres enter the bone - called Sharpey's fibres
Contains blood vessels.
Also fibrocytes and the other cells found in common CT
Inner cellular layer
Flattened cells (continuous with the endosteum)
Can divide and differentiate into osteoprogenitor cells
spindle shaped
little amount of rough EPR
poorly developed Golgi complex
play a prominent role in bone growth and repair
Osteoblasts
Oval in shape, Have thin processes, Rough EPR in one part of the cell (basophilic)
On the other side is the nucleus, Golgi and the centrioles in the middle, Form matrix
Become trapped in the matrix
Osteocytes
Mature cells, Less basophilic than the osteoblasts, Lie trapped in the lacunae, Their processes lie in the canaliculi, Processes communicate with one another through gap junctions, Substances (nutrients, waste products) are passed on from cell to cell
Osteoclasts
Very large, Multinucleate (up to 50), On inner and outer surface of bone, Lie in depressions on the surface called Howships lacunae, The cell surface facing the bone has short irregular processes
Acidophylic
Has many lysosomes, polyribosomes and rough EPR
Lysosomal enzymes are secreted to digest the bone
Resorbs the organic part of bone
Histogenesis
Two types of bone development.
- intramembranous ossification
- endochondral ossification
In both these types of bone development temporary primary bone is deposited which is soon replaced by secondary bone. Primary bone has more osteocytes and the mineral content is lower.
Ampholytes, Polyampholytes, pI and Zwitterion
Biochemistry
Ampholytes, Polyampholytes, pI and Zwitterion
Many substances in nature contain both acidic and basic groups as well as many different types of these groups in the same molecule. (e.g. proteins). These are called ampholytes (one acidic and one basic group) or polyampholytes (many acidic and basic groups). Proteins contains many different amino acids some of which contain ionizable side groups, both acidic and basic. Therefore, a useful term for dealing with the titration of ampholytes and polyampholytes (e.g. proteins) is the isoelectric point, pI. This is described as the pH at which the effective net charge on a molecule is zero.
For the case of a simple ampholyte like the amino acid glycine the pI, when calculated from the Henderson-Hasselbalch equation, is shown to be the average of the pK for the a-COOH group and the pK for the a-NH2 group:
pI = [pKa-(COOH) + pKa-(NH3+)]/2
For more complex molecules such as polyampholytes the pI is the average of the pKa values that represent the boundaries of the zwitterionic form of the molecule. The pI value, like that of pK, is very informative as to the nature of different molecules. A molecule with a low pI would contain a predominance of acidic groups, whereas a high pI indicates predominance of basic groups.
Osteomyelitis
Oral Maxillofacial Surgery
Osteomyelitis
Staphylococcus aureus causes osteomyelitis.
TYPES OF OSTEOMYELITIS
1.Suppurative Osteomyelitis - onset 4 weeks - Deep bacterial invasion into medullary & cortical bone - polymicrobial infection anaerobes such as Bacteriods, Porphyromonas or Provetella.
Staphylococci may be a cause when an open fracture is involved. Mandible is more prone than maxilla as vascular supply is readily compromised.
2.Focal Sclerosing Osteomylitis(Condensing osteitis) - Localized areas of bone sclerosis. Bony reaction to low-grade peri-apical infection or unusually strong host defensive response. Association with an area of inflammation is critical.
3. Diffuse Sclerosing Osteomylitis - Chronic intraosseous bacterial infection creates a smoldering mass of chronically inflammed granulation tissue.
4. Proliferative Periostitis(Periostitis ossificans & Garee’s osteomyelitis) - periosteal reaction to the presence of inflammation. Affected periosteum forms several rows of reactive vital bone that parallel each other & expand surface of altered bone.
- Radiopaque laminations of bone roughly parallel each other & underlying cortical surface. Laminations may vary from 1-12 in number. Radiolucent separations often are present between new bone & original cortex.
Conditions that weaken the immune system increase a person's risk for osteomyelitis, including:
Diabetes (most cases of osteomyelitis stem from diabetes)
Sickle cell disease
HIV or AIDS
Rheumatoid arthritis
Intravenous drug use
Alcoholism
Long-term use of steroids
Hemodialysis
Poor blood supply
Recent injury
Bone surgery, including hip and knee replacements, also increase the chance of bone infection.
Osteomyelitis in Children and Adults
In children, osteomyelitis is usually acute. Acute osteomyelitis comes on quickly, is easier to treat, and overall turns out better than chronic osteomyelitis. In children, osteomyelitis usually shows up in arm or leg bones.
In adults, osteomyelitis can be either acute or chronic.
Acute osteomyelitis develops rapidly over a period of seven to 10 days. The symptoms for acute and chronic osteomyelitis are very similar
Clinical features of chronic osteomyelitis are usually limited to :
- Pain and tenderness: the pain is minimal,
- Non healing bony and overlying soft tissue wounds with induration of soft tissues,
- Intraoral or extraoral draining fistulae,
- Thickened or “wooden” character of bone,
- Enlargement of mandible, because of deposition of subperiosteal new bone.
- Pathological fractures may occur,
- Sterile abscess (Brodie’s abscess), common to long bones is rare in jaws.
- Teeth in the area tend to become loose and sensitive to palpation and percussion.
ADRENOCORTICAL TUMORS
General Pathology
ADRENOCORTICAL TUMORS
Functional adenomas are commonly associated with hyperaldosteronism and with Cushing syndrome, whereas a virilizing neoplasm is more likely to be a carcinoma. Determination of of the functional status of a tumor is based on clinical evaluation and measurement of the hormone or its metabolites. In other words, functional and nonfunctional adrenocortical neoplasms cannot be distinguished on the basis of morphologic features.
Patholgical features
Adrenocortical adenomas
- They are generally small, 1 to 2 cm in diameter.
- On cut surface, adenomas are usually yellow to yellow-brown due to presence of lipid within the neoplastic cells
- Microscopically, adenomas are composed of cells similar to those populating the normal adrenal cortex. The nuclei tend to be small, although some degree of pleomorphism may be encountered even in benign lesions ("endocrine atypia"). The cytoplasm ranges from eosinophilic to vacuolated, depending on their lipid content.
Adrenocortical carcinomas
These are rare and may occur at any age, including in childhood.
- Carcinomas are generally large, invasive lesions.
- The cut surface is typically variegated and poorly demarcated with areas of necrosis, hemorrhage, and cystic change.
- Microscopically, they are composed of well-differentiated cells resembling those of cortical adenomas or bizarre, pleomorphic cells, which may be difficult to distinguish from those of an undifferentiated carcinoma metastatic to the adrenal.
The Body Regulates pH in Several Ways
PhysiologyThe Body Regulates pH in Several Ways
Buffers are weak acid mixtures (such as bicarbonate/CO2) which minimize pH change
Buffer is always a mixture of 2 compounds
One compound takes up H ions if there are too many (H acceptor)
The second compound releases H ions if there are not enough (H donor)
The strength of a buffer is given by the buffer capacity
Buffer capacity is proportional to the buffer concentration and to a parameter known as the pK
Mouth bacteria produce acids which attack teeth, producing caries (cavities). People with low buffer capacities in their saliva have more caries than those with high buffer capacities.
CO2 gas (a potential acid) is eliminated by the lungs
Other acids and bases are eliminated by the kidneys
Angiotensin
Pharmacology
Angiotensin
It is generated in the plasma from a precursor plasma globulin. It is involved in the electrolyte balance, plasma
volume and B.P
Angiotensin I:
Renin is an enzyme produced by the kidney in response to a number of factors including adrenergic activity (β1-
receptor) and sodium depletion. Renin converts a circulating glycoprotein (angiotensinogen) into an inactive material angiotensin-I. It gets activation during passage through pulmonary circulation to angiotensin II by (ACE). ACE is located on the luminal surface of capillary endothelial cells, particularly in the lungs & also present in many organ (e.g brain).
Angiotensin II:
Is an active agent, has a vasoconstrictor action on blood vessels & sodium and water retention
Structure of Orbital Walls
Oral and Maxillofacial SurgeryStructure of Orbital Walls
The orbit is a complex bony structure that houses the eye and its associated
structures. It is composed of several walls, each with distinct anatomical
features and clinical significance. Here’s a detailed overview of the structure
of the orbital walls:
1. Lateral Wall
Composition: The lateral wall of the orbit is primarily
formed by two bones:
Zygomatic Bone: This bone contributes significantly
to the lateral aspect of the orbit.
Greater Wing of the Sphenoid: This bone provides
strength and stability to the lateral wall.
Orientation: The lateral wall is inclined at
approximately 45 degrees to the long axis of the skull,
which is important for the positioning of the eye and the alignment of the
visual axis.
2. Medial Wall
Composition: The medial wall is markedly different from
the lateral wall and is primarily formed by:
Orbital Plate of the Ethmoid Bone: This plate is
very thin and fragile, making the medial wall susceptible to injury.
Height and Orientation: The medial wall is about half
the height of the lateral wall. It is aligned parallel to the
antero-posterior axis (median plane) of the skull and meets the floor of the
orbit at an angle of about 45 degrees.
Fragility: The medial wall is extremely fragile due to
its proximity to:
Ethmoid Air Cells: These air-filled spaces can
compromise the integrity of the medial wall.
Nasal Cavity: The close relationship with the nasal
cavity further increases the risk of injury.
3. Roof of the Orbit
Composition: The roof is formed by the frontal bone and
is reinforced laterally by the greater wing of the sphenoid.
Thickness: While the roof is thin, it is structurally
reinforced, which helps protect the contents of the orbit.
Fracture Patterns: Fractures of the roof often involve
the frontal bone and tend to extend medially. Such fractures can lead to
complications, including orbital hemorrhage or involvement of the frontal
sinus.
4. Floor of the Orbit
Composition: The floor is primarily formed by the
maxilla, with contributions from the zygomatic and palatine bones.
Thickness: The floor is very thin, typically measuring about
0.5 mm in thickness, making it particularly vulnerable to
fractures.
Clinical Significance:
Blow-Out Fractures: The floor is commonly involved
in "blow-out" fractures, which occur when a blunt force impacts the eye,
causing the floor to fracture and displace. These fractures can be
classified as:
Pure Blow-Out Fractures: Isolated fractures of
the orbital floor.
Impure Blow-Out Fractures: Associated with
fractures in the zygomatic area.
Infraorbital Groove and Canal: The presence of the
infraorbital groove and canal further weakens the floor. The
infraorbital nerve and vessels run through this canal, making them
susceptible to injury during fractures. Compression, contusion, or
direct penetration from bone spicules can lead to sensory deficits in
the distribution of the infraorbital nerve.