|Examples of natural polymers:||
Stiffness, interatomic bonding
Synthetic mateirials for use in the body
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.
|Stiffness vs Strength||
Stiffness /= Strength
Smallest repeating unit in polymer chain
|Aquesous corrosion is an [blank] phenomenon||
|List the five types of stress:||
|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.
Suppress or kill T-cells- increased risk of infection & cancer
|Allografts - pros/cons||
PRO:- functioning heart, adaptableCON:- no innervated, surgical injury, infection/rejection
"Heart Transplant"- Brain dead source- Cold Static Storage transportation- Sternotomy - cut open sternum- Patient on immunosuppresents
- Unreacted Mer- Colorants- Manufacturing reminents
Material that exhibits both metallic and non-metallic behavior
Liquid capable of penetrating between the randomly oriented chains of a polymer
Point where plastic strain becomes very pronounced; rapid inc. in strain without accompanying stress
|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.
dry, crumbles. It has a low compressive strength, excessive expansion.
|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.
filler size: .5-5 microns, matrix has fumed resin, it controls resin- toughness and handling viscosity.
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.
"Atlas Knit"- intertwined fibers of multi-filament yarn in diamond patterns- Seams facing out- Low Profile
|Heart Failure Causes||
1) Work overload, mechanical abnormalities2) Myocardial abnormalities3) Abnormal cardiac rythym
A material won't break below this limit
|Three types of grain structure||
|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.
Constant load 360 kg/cm^2 for 24 hours
|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
|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.
|Ultimate Tensile Strength||
Resistance to necking (large localized strain in specific area)
- Critical determinant of any immune response are antigens- Major Histocompatibility Complex (MHC) is primary diff. between people
|Types of acrylic||
1- Acrylic fabric (not relevant to dental biomaterials)
2 - Acrylic resin (aka PMMA) used for dentures
3 - Acrylic acid - water soluble polymer for adhesive dental cements
|Modulus of resistance:||
Amount of energy a material can abosrob without permanently deforming; Area under the graph up to the proportional limit; has units of energy J/m3
|Effect of mecanical history on alloy:||
Deformation of structure
Hinders movement of dislocations
Material less easy to deform
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.
|Electrical insulation of cements||
under metallic restoraion to minimize galvanic effects.
|Advanatages of ZnPO4||
handles easily, has good record of clinical durability. High compressive strength, low film thickness values.
|Complex Syndrome of HF||
- Pathology at gene/tissue level- Hemodynamic alterations- Breathlessness, fatigue, chest pain
Branch off aorta to supply blood to heart
|Effect of cold working on metal||
Leads to a fibrous structure
|Because biomaterials are not as durable as sound tooth tissue it is important to recognize the importance of:||
1. Prevention of caries
2. Conservative treatments
3. Durability of treatments
|Effect of recrystallization on metal||
Further heating cuases reformation of equiaxed structure
|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%.
|Compressive strength and marginal breakdown||
the higher the slow compressive strength the less the observed rate of marginal breakdown.
|Increased powder/liq mixture for ZnPO4||
gives more viscous mix, shorter setting time, higher strength, lower solubility and less free acidity.
|Molecular Weight for Polymers||
- Number Average (Mn)- Weight Average (Mw)
|What happens in a viscoelastic material?||
There is breaking of intermolecular bonds (plastic behavior) and uncoiling of polymer molecules (elastic behavior)
|Effect of molecular weight on polymer||
Higher molecular weight = higher strength and rigidity
|Single Cu admixed alloy||
high Cu lathe cut and high Cu sperical.
|Effect of grain growth on metal||
Even more heating causes large grains to form
|The hardness of an alloy depends on:||
1 - chemical composition
2 - mechanical history
3 - thermal history
|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.
|List 4 steps in addition polymerization:||
1 - activator reacts with initiator to give free radicals
2 - Free radicals react with monomers to give larger free radical
3 - Propagation
|Biological effects of reinforced ZnO eug.||
bland and obtudent on the pulp, some inflammatory rxn in connective tissue,
|Effect of chemical composition on an alloy:||
An alloy is harder than any of the individual metals from which it has been prepared
Hardness depends on:
number of different compounds
relative amount of each component