Properties of Amalgam.
The most important physical properties of amalgam are
Dimensional change. An amalgam can expand or contract depending upon its usage. Dimensional change can be minimized by proper usage of alloy and mercury. Dimensional change on setting, less than ± 20 (excessive expansion can produce post operative pain)
Fatty acids consist of a hydrocarbon chain with a carboxylic acid at one end.
• are usually in esterified form as major components of other lipids
• are often complexed in triacylglycerols (TAGs)
• most have an even number of carbon atoms (usually 14 to 24)
• are synthesized by concatenation of C2 units.
• C16 & C18 FAs are the most common FAs in higher plants and animals
• Are either:
—saturated (all C-C bonds are single bonds) or
—unsaturated (with one or more double bonds in the chain)
—monounsaturated (a single double bond)
1.Example of monounsaturated FA: Oleic acid 18:1(9) (the number in unsaturated FA parentheses indicates that the double bond is between carbons 9 & 10)
2. Double bonds are almost all in the cis conformation
—polyunsaturated (more then one double bond)
Polyunsaturated fatty acids contain 2 or more double bonds. They usually occur at every third carbon atom towards the methyl terminus (-CH3 ) of the molecule. Example of polyunsaturated FA: Linoleic acid 18:2(9,12)
• the number of double bonds in FAs varies from 1 to 4 (usually), but in most bacteria it is rarely more than 1
Saturated FAs are highly flexible molecules that can assume a wide range of conformations because there is relatively free rotation about their C-C bonds.
The formation of glycogen from glucose is called Glycogenesis
Glycogen is a polymer of glucose residues linked mainly by a(1→ 4) glycosidic linkages. There are a(1→6) linkages at branch points. The chains and branches are longer than shown. Glucose is stored as glycogen predominantly in liver and muscle cells
Uridine diphosphate glucose (UDP-glucose) is the immediate precursor for glycogen synthesis. As glucose residues are added to glycogen, UDP-glucose is the substrate and UDP is released as a reaction product. Nucleotide diphosphate sugars are precursors also for synthesis of other complex carbohydrates, including oligosaccharide chains of glycoproteins, etc.
UDP-glucose is formed from glucose-1-phosphate and uridine triphosphate (UTP)
glucose-1-phosphate + UTP → UDP-glucose + 2 Pi
Cleavage of PPi is the only energy cost for glycogen synthesis (1P bond per glucose residue)
Glycogenin initiates glycogen synthesis. Glycogenin is an enzyme that catalyzes glycosylation of one of its own tyrosine residues.
Physiological regulation of glycogen metabolism
Both synthesis and breakdown of glycogen are spontaneous. If glycogen synthesis and phosphorolysis were active simultaneously in a cell, there would be a futile cycle with cleavage of 1 P bond per cycle
To prevent such a futile cycle, Glycogen Synthase and Glycogen Phosphorylase are reciprocally regulated, both by allosteric effectors and by covalent modification (phosphorylation)
Glycogen catabolism (breakdown)
Glycogen Phosphorylase catalyzes phosphorolytic cleavage of the →(1→4) glycosidic linkages of glycogen, releasing glucose-1-phosphate as the reaction product.
Glycogen (n residues) + Pi → glycogen (n-1 residues) + glucose-1-phosphate
The Major product of glycogen breakdown is glucose -1-phosphate
Fate of glucose-1-phosphate in relation to other pathways:
Phosphoglucomutase catalyzes the reversible reaction:
Glucose-1-phosphate → Glucose-6-phosphate
• Thermal insulation below a restoration
• Mechanical protection where there is inadequate dentin to support amalgam condensation pressures
• Zinc phosphate cement bases
• Polycarboxylate cement bases
• Glass ionomer cement bases (self-curing and light-curing)
o Reactive powder (chemically basic)
o Reactive liquid (chemically acidic)
o Acid-base reaction that forms salts or cross linked matrix
o Reaction may be exothermic
Manipulation-consistency for basing includes more powders, which improves all of the cement properties
Physical-excellent thermal and electrical insulation
Chemical-much more resistant to dissolution than cement liners
Polycarboxylate and glass ionomer cements are mechanically and chemically adhesive to tooth structure
Solubility of all cement bases is lower than cement liners if they are mixed at higher powder- to-liquid ratios
Mechanical- much higher compressive strengths (12,000 to 30,000 psi)
Light-cured hybrid glass ionomer cements are the strongest
Zinc oxide-eugenol cements are the weakest
Biologic (see section on luting cements for details)
Zinc oxide-eugenol cements are obtundent to the pulp
Polycarboxylate and glass ionomer cements are kind to the pulp
LOCATION OF THE TEETH
Normally, a human receives two sets of teeth during a lifetime.
The first (deciduous or primary) set consists of 20 teeth ("baby" teeth).
The second (permanent) set usually consists of 32 teeth. In each quadrant, there are eight permanent teeth: two incisors, one cuspid, two bicuspids, and three molars
The tooth positioned immediately to the side of the midline is the central incisor, so called because it occupies a central location in the arch.
To the side of the central incisor is the lateral incisor. Next is the cuspid, then the two bicuspids (the first bicuspid, followed by the second bicuspid). The last teeth are three molars. After the second bicuspid comes the first molar, followed by the second molar, followed by the third molar or more commonly called the "wisdom tooth."
Another method of describing the location of teeth is to refer to them as anterior or posterior teeth .
Anterior teeth are those located in the front of the mouth, the incisors, and the cuspids. Normally, these are the teeth that are visible when a person smiles.
The posterior teeth are those located in the back of the mouth-the bicuspids and molars.
2) Surface roughness .
3) Porosity .
4)Incomplete casting .
5) Oxidation .
6) Sulfur contamination .
It is usually due to the distortion of wax pattern.
To avoid this :
Manipulation of the wax at its softening temp
Invest the pattern at the earliest .
If storage is necessary store it in a refrigerator .
May be due to :
Air bubbles on the wax pattern .
Cracks due to rapid heating of the investment .
High W/P ratio .
Prolonged heating of the mold cavity .
Overheating of the gold alloy .
Too high or too low casting pressure .
Composition of the investment .
Foreign body inclusion.
May be internal or external .
External porosity causes discolouration .
Internal porosity weakens the restoration .
Classification of porosity .
I .Those caused by solidification shrinkage :
a) Localised shrinkage porosity .
b) Suck back porosity .
c) Microporosity .
They are usually irregular in shape .
II ) Those caused by gas :
a) Pin hole porosity .
b) Gas inclusions .
c) Subsurface porosity .
Usually they are spherical in shape .
III ) Those caused by air trapped in the mold :
Back pressure porosity .
Localised shrinkage porosity
Large irregular voids found near sprue casting junction.
Occurs when cooling sequence is incorrect .
If the sprue solidifies before the rest of the casting , no more molten metal is supplied from the sprue which can cause voids or pits (shrink pot porosity )
This can be avoided by -
- using asprue of correct thickness .
- Attach the sprue to the thickest portion of the pattern .
-Flaring of the sprue at the point of atttachment .
-Placing a reservoir close to the pattern .
Suck back porosity
It is an external void seen in the inside of a crown opposite the sprue .
Hot spot is created which freezes last .
It is avoided by :
Reducing the temp difference between the mold & molten alloy .
Fine irregular voids within the casting .
Occurs when casting freezes rapidly .
Also when mold or casting temp is too low .
Pin hole porosity :
Upon solidification the dissolved gases are expelled from the metal causing tiny voids .
Pt & Pd absorb Hydrogen .
Cu & Ag absorb oxygen .
Gas inclusion porosities
Larger than pin hole porosities .
May be due to dissolved gases or due to gases Carried in or trapped by molten metal .
Apoorly adjusted blow torech can also occlude gases .
Back pressure porosity
This is caused by inadequate venting of the mold .The sprue pattern length should be adjusted so that there is not more than ¼” thickness of the investmentbetween the bottom of the casting .
This can be prevented by :
- using adequate casting force .
-use investment of adequate porosity .
-place the pattern not more than 6-8 mm away from tne end of the casting .
Casting with gas blow holes
This is due to any wax residue in the mold .
To eliminate this the burnout should be done with the sprue hol facing downwards for the wax pattern to run down.
This is due to :
- insufficient alloy .
-Alloy not able to enter thin parts of the mold .
-When the mold is not heated to the casting temp .
-Premature solidification of the alloy .
-sprues blocked with foreign bodies .
-Back pressure of gases .
-low casting pressure .
-Alloy not sufficiently molten .
Too bright & shiny casting with short & rounded margins :
occurs when wax is eliminated completely ,it combines with oxygen or air to form carbon monoxide .
Small casting :
occurs when proper expansion is not obtained & due to the shrinkage of the impression .
Contamination of the casting
1) Due to overheating there is oxidation of metal .
2) Use of oxidising zone of the flame .
3) Failure to use a flux .
4) Due to formation sulfur compounds .
It is due to :
1) Overheating of the investment .
2) Incomplete elimination of the wax .
Candida spp. are sensitive to nystatin.
Uses: Cutaneous, vaginal, mucosal and esophageal infections.
Candida infections can be treated with nystatin.
Cryptococcus is also sensitive to nystatin.
Nystatin is often used as prophylaxis in patients who are at risk for fungal infections, such as AIDS patients with a low CD4+ count and patients receiving chemotherapy.
nystatin binds to ergosterol, the main component of the fungal cell membrane. When present in sufficient concentrations, it forms a pore in the membrane that leads to K+ leakage and death of the fungus.
Maxillary First Deciduous Molar.
-The notation is B or I.
-It looks a bit like an upper 1st premolar.
-There are three roots.
-It has a strong bulbous enamel bulge that protrudes buccally at the mesial.
-It is the smallest of the deciduous molars in crown height and in the mesiodistal dimension.
Internal Muscles of the Pharynx
The Stylopharyngeus Muscle
The Palatopharyngeus Muscle
The Salpingopharyngeus Muscle
Water: comprises 60 - 90% of most living organisms (and cells) important because it serves as an excellent solvent & enters into many metabolic reactions
40% of blood is red blood cells (RBCs)
plasma is similar to interstitial fluid, but contains plasma proteins
serum = plasma with clotting proteins removed
intracellular fluid is very different from interstitial fluid (high K concentration instead of high Na concentration, for example)
Ions = atoms or molecules with unequal numbers of electrons and protons:
Ions (Charged Atoms or Molecules) Can Conduct Electricity
Na+ & K+ are the Major Cations in Biological Fluids