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62 Cards in this Set

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Tensile strength(diametral tensile)
For amalgam it is one hour. It indicates rate of strength build up, important in class 2 preps, and also spherical faster than admixed.
Rate of strength development
90% within 8 hours. Maximun strength after 7 days or more.
Tensile stregth of amalgam and gamma phases
Amalgam tensile strength is 450-600. Gamma phase is 1750, gamma 1 is 1100, gamma 2 is 280.
Compressive strength and marginal breakdown
the higher the slow compressive strength the less the observed rate of marginal breakdown.
Amalgam cavosurface margin
as close to 90 deg as possible.
Creep
dimension change under load on a fully set specimen. The lower the creep value the lower the rate of marginal breakdown.
Static creep
Constant load 360 kg/cm^2 for 24 hours
Dynamic creep
alternating compressive and tensile loads over a given time period.
Undermix(trituration)
dry, crumbles. It has a low compressive strength, excessive expansion.
Overmix(trituration)
It is plastic ans clings to the capsule, it flows. It has high compressive strength, also may have reduced or negative expansion.
Dental amalgam vapor
is soluble in blood and is distributed to different systems. Most toxic form is methyl Hg which is readily absorbed thru gut and rapidly distributed.
conventional amalgam alloy composition: Ag
where Ag is 67-74%, has strenght and hardness but is difficult to handle and sets rapidly. High Ag content means a greater expansion during setting.
Increases expansion and compressive strength.
Conventional amagam: Tin composition
25-28% Sn, aids in amalgamation, reacts with Hg at room temperature. it reduces expantion when it is greater than 28%, it REDUCES corrosion resistance.
Decreases expansion and increases flow.
Conventional amalgam: Cu
0-10%, increases strength and hardness, setting time is more uniform.
Decreases flow.
Conventional amalgam: Zn content
aid in manufacture(its an oxide scavenger during casting). Greater than .01% causes excess expansion when it reats w/ H20 from any source.
Decreases expansiona nd compressive strenght.
Spherical amalg alloys
molted metal sprayed into inert gas. Advatage: space distribution of alloy less Hg to mix low Hg technique adaptation excellent, faster rise in strength.
Disadvantage of spherical alloys
maintaining adaptation during carving
High Cu admix alloy
blendin components: add alloy (30% by weight) spheres of silver copper eutectic( 72% Au 28% Cu). Get alloy fillings and AgCu spheres.
Amalgamated allay
intermetallic compound about the dispersant particle (AgCu) found to be Cu3Sn + Cu6Sn5(Asgar Mahler phase). There is gamma 1 but little gamma 2 present.
Results of high Cu admixed alloys
superior results:
low tarnish, maintains polish.
-low rate of mraginal breakdown- this is substantiated in several 3 - 4 yr clinical studies.
High Cu single composition alloys
major componeys prepared in single melt with the composition of Ag3Sn2. (Cu 9-29%).
High Cu single composition (ternary alloy)
major components prepared in single melt with composition of Ag3Sn2(Cu 9-295). Rapid cooling required for proper strcuture. Its amalgated alloy has no Sn present but u find Cu3Sn and Cu6Sn5.
Single Cu admixed alloy
high Cu lathe cut and high Cu sperical.
Cements requirements
nontoxic and nonirritant to pulp and tissue. Insolouble in saliva nd liquids taken in mouth. Should develop sufficient strength and protection of the pulp from effects of other restorative material. It should be bacteriostatic if inserted into a cavity with residual caries.
Electrical insulation of cements
under metallic restoraion to minimize galvanic effects.
Zinc Phosphate cement
used for cemntation(luting) of fixed cast alloy and percelain restorationd and orthodontic bands.
ZnPO4 composition
powder: mainly zinc oxide w/ up to 10% magnesium oxide and small amounts of pigments. Water content controls the ionization of the acid and thus the reaction rate w/ the powder. The set cement consists of a cores structure of residual ZnO particles in phosphate matrix.
ZnPO4 Properties
USES:Cementation of fixed cast alloy and porcelain rest, ortho bands; also used in past as cavitu lining or base.
compressive strength:12,00-16,000. Solubility-Dsiintegration: .3% by weight over first 3days. Film thickness- 40 to 25 microns. Setting time: 4-9 mins, working time is increased by using cold slab.
Increased powder/liq mixture for ZnPO4
gives more viscous mix, shorter setting time, higher strength, lower solubility and less free acidity.
Biological effects of ZnPO4
initial pulpal irritation due to its acidity and osmotic properties. It may permit marginal leakage which can result in pulpal pathology.
Advanatages of ZnPO4
handles easily, has good record of clinical durability. High compressive strength, low film thickness values.
Disadvantages of ZnPO4
Brittleness, solubility in organic acids and oral fluids, pulpal irritation(liner must be used in deep cavities), lack of adhesion to tooth structure which leads to leakage.
ZnO-Eugenol properties
USES: Temp cementation of rest, cavity lining , temp fillinfmat.
low compressive strength: 100 to 1000 psi. Tensile strenght is very low. High solubility, 1.5% by weight in distilled water in 24hours. Film thickness si about 40 micros.
Advantages/disadvantages of ZnO eugenol
Bland and obtudent effect on pulp, good sealing ability and resistance to marginal penetration.
Disadvantage:
Low strength and abrasion resistance, soluble and disintegrates in oral fluids. Also little anticariogenic action.
Reinforced ZnO eugenol cements properties
USES:cementing for restoration, cavity lining and base mat; also temp filling mat.
Strength:5000 to 8000 psi, tensile strength: 700 to 900 psi. Solubility seems to be lower than zno eugenol. Thickness is from 35 to 75 microns. Have long working time
Biological effects of reinforced ZnO eug.
bland and obtudent on the pulp, some inflammatory rxn in connective tissue,
Advantages/disadvantages of ZnO eug
advan: minimal biological effetcs, good initial sealing properties, adequate strength for final cemetaion of restos.
Disad: lower strength, higher solubility and disintegration than zinc phos cements, hydrolytic instability, softening and discoloration of some resin restorative materials.
EBA cements properties
(ethobenzoic acid- 50 to 66%, little ZnO)
USES:Cementing inlays,crwons,bridges; as a base or lining mat; temp filling. Strength: 8000 to 1000psi (similar to ZnPO4) by increasing powder/liq ratio; tensile strength: lower about 500 to 800psi. Solubility similar to ZOE. Thickness: 40 to 70microns. Setting time: 7 to 13mins.
Biological effects OF EBA
similar to ZOE materials- bladn obtudent on the pulp.
Advantages/disadvantages of EBA
Advantage: strength and flim thickness are comparable to those of ZnPO4 cements, little irritant effect on the pulp, long working time.Disad: high powder/liq ration for optimum properties, neccessitating long mixing time,, hydrolytic breakdown in oral fluids.
Polycarboxylate compounds
USES: cemeting cast alloy and porcelain resto and ortho bands; cavity liners;temp filling mat. Strength: 9000 to 12000 psi, tensile strength: 800 to 1000 psi. Strength increases with powder/liq ratio, also increased by additives such as alumina and stannous fluoride. Solubility:.05% after 7 days. Thickness: 25 microns. Setting time; 5 to 8mins, affected by powder/liq ratio, eactivity, part size, additives , mw and conc of polyacrylic acid. Adhesion to dentin may be limited but on clean surface can occur thru Ca complexation.
Biological effets of ploycarboxylate compounds
bland effetc on pulp similar to ZOE. Related to rapid rise of pH towards neutrality, min movement of fluid in dentin tubules in response to cement.
Advantages/disadvantages of Polycarboxylate
Advan: strength, solubilty, film thickness comprable to ZnPO4, easy mixing, little pulpal rxn. Dis: accurate proportioning req for optimum properties, moderate compressive strength, clean surfaces required for proper bonding and short working time.
Glass Ionomers cements properties
USES: luting cement, filling mat for erosion cavities, pit n fissure sealant, liner underneath other rest mat. Strength: 20,000psi, diametral strength is lower about 1600psi. Solubility: depending on powder/liq ration around .3 to 3%.
Biological effects
Pulpal rxn is similar to ZnO carboxylate cements, mild compared to silicate cements.
Resin modified GI: Self cured
modified polyacid w/ acrylate groups. cement has both acid-base rxn and polymerization by mircoencapsulation of catalyst in powder.
Light cured Resin modified GI
modified polyacid w/pendant acrylate groups for polymerization cross linking rxn. Cements has both acid-base rxn and polymerization by light curing. Increased physical properties, adhesion to enamel and dentin w/ reduced mircoleakage and very low solubility.
Resin cements(luting)
types: methylmethacrylate based, BISGMA based. Uses: limited due to pulpal response, film thickness a concern for early types. Advantage: very high strength, very low solubility.
GI trad composition
-polyacid
-liq thin: water with 4-5% tartaric acid, gives longer shelf life
-liq thick: constituted polyacid at 40% in water, limits shelf life to 1 year.
-powder- basic glass to react w/ midly acidic liq; 2 pahsed silica glass formed.
Bonding to enamel and dentin- of GI
enamel bonding by rxn of polyacid w/ Ca2+ on surface. bond strength limited by cohesive strength of the GI. dentin bonding improved by modification of the smear layer(mild acid for 10-20 sec).
metal modified GI
adding amalgam->set quickly but bonds less. silver particles has better physical properties. Bonds well to dentin but is too weak for core mat for crowns. Has increased wear resistance compared to normal GI.
Initial GI rxn
involves surface dissolution of glass powder releasing Al,Na, Ca ions- Na and Ca react to form ionomers. this step: sensitive to water.
Later rxn- sub Al for na,ca ionomers, new Al bonds for more xlinked structure. This step is sensitive to dessication. have to coat surface immediately after removal of matrix w/ varnish or resn bonding agent.
Composite resin
it is compromised of a continuous or matrix phase of resin in which there is discontinuous or dispersed phase of another material. eg fiberglass is a type of com resin , glass fib embedded in a matrix of fibers. The dispersed phase help reinforce the matrix phase.
Role of filler particle
strength, reduce shrinkage, increase wear strength, reduce coeeficient of thermal expansion.eg enamel 12,resin 70-100, composite 20-40ppm. interract w/ matrix resin, bonding the particle to the resin. Filler is 65-85% wt
Paste-paste system(self curing) - Universal paste
contains peroxide
Catalyst paste
contains tertiary amine in place of the peroxide. dark yello color.
One paste system
uses visible light to cause the breakdown of alight activated ring compound to form initiating free radicals.
coupling agent for paste compostion (resins)
silane which contains a vinyl or methacrylate group enter into the resin polymerization.
conventional
filler size: 5-50 microns, filler type: quartz, radio opaque glass.
Microfilled resin
filler: fumed silica(.02-.04 microns). paste has large particles due to method of fabrication. compared to conventional: brittle, low elastic moduus, high coeff of thermal expansion, H20 absroption ofset by shrinkage, high strength:compression, tension , transverse.
Hybrid/Blend
filler size: .5-5 microns, matrix has fumed resin, it controls resin- toughness and handling viscosity.
Composite wear
conventional: uniform loss, contact area wear.
MICROFILLED: margin ditching, localized wear in contact areas.
Hybrid; uniform wear at low rates