B2 Flashcards
State the composition of impression compounds
1) Resin ( 30%) - for thermoplastic , flow and cohesion
2) Copal resin ( 30%) - same as above
3) Carnauba wax ( 10%) - provide smooth surface
4) Stearic acid ( 5%)- harden the compounds
5) Talc ( 25%) - improve str , reduce expansion
6) Colouring agents eg. Rouge ( trace amts)
State the fusion temperature of impression compound
43.5C
State some examples of die materials :
1) Gypsum product I) Type IV : high strength II) Type. : high str , high expansion - high expansion is to compasate for solidification shrinkage of base metal alloys 2) resins 3) polyester 4) Epoxy resins
State the uses of ZnOE
1) Secondary impression materials for edentulous patients
2) Bite registration paste
3) Periodontal surgical pack
4) Root canal filling
5) Temporary relining material
6) Luting cement
7) Temporary restoration materials
State the chemical reaction of zinc oxide eugenol
1) Hydrolysis - ZnO +H2O = Zn(OH)2
2) Acid -base reaction - Zn(OH2) + 2HE = ZnE2 +2H2O
State the advantages and disadvantages of ZnOE impression
Advantages
1) Accurate with good surface details
2) Dimensionally stable
3) Inexpensive
4) Does not require separating media
5) Adhere well to impression compound
Disadvantages
1) Messy
2) Eugenol can be irritating to tissue
3) Inelastic materials — cannot be used to record undercut otherwise it fractures
4) Can only be used for secondary impression in edentulous patients —hence it requires special tray
5) Sticky & adheres to tissue
Describe the 1 stage and 2 stage putty wash techniques with their difference
Similarities :
I)both are used for silicone impression materials
II) Both use perforated stock tray
III) both use putty & light body viscosities
Description for 1 stage putty wash techniques :
- tray is loaded with putty materials , then light body is placed into syringe . Syringe materials is ejected over the perpared tooth
-tray is seated in oral cavity
- both set simultaneously 2 stage putty wash techniques :
- tray is loaded with putty material with a thin layer of plastic sheet over it , then a preliminary impression is taken
- preliminary impression acts as a form custom tray
- syringe material ( light body ) is then ejected over the surface of preliminary impression and the prepared tooth surface
- tray seated back into oral cavity & allowed to set
Differences - 2 stage involves making preliminary impression
-2 stage involves using spacer
- in 2 stage syringe materials is ejected over the tooth & impression while in 1 stage it is only injected over the prepared tooth
Absolute strength refers to the amount of stress necessary to cause ( ……………… ) .Yield strength refers to the degrees of stress necessary to cause a ( ……………..)
Absolute strength refers to the amount of stress necessary to cause ( fracture ) .Yield strength refers to the degrees of stress necessary to cause a ( specific strength refers to the degree of stress necessary to cause a sepcified amt of plastic deformation , between (0.1-0.2%)
Proportional limits refers to the stress above which stress is no longer ( ………………… ) .Elastic limit refers to the ( …………….)
Proportional limits refers to the stress above which stress is no longer ( direct proportional to strain ) .Elastic limit refers to the ( to the maximum stress a material can withstand before it becomes plastically deformed
State the ideal properties of dental cements
1) Good physical properties
- low solubility
- extended working time & short setting time
- radioopaque
- low viscosity
- proper film thickness
- ensure optimum seating of the restoration
2) Good mechanical properties
- high shear , tensile , compressive strengths
- high bonding strength to tooth structure / restoration material
3) Biocompatible
4) Easy to manipulate & clean
State the classification of dental cements :
I) Based on usage (……………. )
2 Based on adhesive scheme (……………..)
3) Based on polymerization mechanism (…………….)
4) According to ADA (……….)
State the classification of dental cements :
I) Based on usage (I) Luting cements II) Pulp protection cements iii) restorative cements )
2 Based on adhesive scheme (I) etch and rinse resin cements )
3) Based on polymerization mechanism ( I) light cure resin cements II) Chemical cure resin cements iii) dual cure resin cements ( lights + chemical )
4) According to ADA (I) type 1 - fine grain for fermentation (luting )
II) Type 2 - medium grain for bases , orthodontic purpose )
The ideal thickness of a varnish /solution liner should be ( ……………….) . For suspension liner it should be ( …………………….. ) For cement liners , (………………………… ) .For bases , (…………………….) with minimum of (………………. )
The ideal thickness of a varnish /solution liner should be ( 2-5um thick ) . For suspension liner it should be ( 20-25 um thick ) For cement liners , (200-1000 um thick) .For bases , (1000-2000 um ) with minimum of ( 0.75mm )
Describe the varnishes or solution liner with an example ( description , uses , thickness )
- composed of natural gums ( copper , rosins ) or synthetic resin which are dissolved in an organic solvent like chloroform, ether or acetone
- the solution evaporates rapidly to form a thin film
- it should be applied in double layers
- thickness : 2-5 um )
- example : Copalite ( contains 10% copal resin dissolved in ether + alcohol + acetone )
- uses : prevent micro leakage of oral fluids through marginal crevices & reduce postoperative sensitivity
Varnishes are contraindicated in GIC & composite restoration. This is because the varnish will interfere with the ( ………………. ) of GIC while it will ( ………………. ) in the composite
Varnishes are contraindicated in GIC & composite restoration. This is because the varnish will interfere with the ( chemical bonding ) of GIC while it will ( soften the resin component ) in the composite
Describe suspension liner and cement liner with example
Suspension liner - thickness : 20-25 um
- water based which have dissolved components suspended in the solution
- example : CaOH - CaOH which is alkaline can neutralise acid and has antimicrobial properties , however it does not possess significant mechanical properties or thermal insulation capability.
- Cement liner : thickness: 200-1000 um ( 0.2-1mm )
Example 1) CaOH - stimulate formation of reparative dentin
Describe bases
- 1000 -2000 um ( 1-2 um) thick with minimum of 0.75 mm thickness
- provide thermal protection for pulp & supplement mechanical support for the restoration by distributing local stresses from the restoration across the underlying dentina, surface .
Example :
1) Zinc phosphate cement
2) resin reinforced ZOE cement
3) Zinc polycarboxylate cement
4) GIC
5) Resin-modified glass ionomer
Describe the composition of zinc phosphate cement
Powder - zinc oxide ( 75% ) , Magnesium oxide ( 13%) :aids in sintering , radioopaque powder
Liquid - phosphoric acid ( 38-59%) , water ( 30-55%) , aluminium phosphate (2-3%) , zinc phosphate (10%)
Describe the setting reaction of zinc phosphate cement
Zinc oxide + phosphoric acid -> zinc phosphate + H2O + unreacted ZnO
Zinc phosphate + aluminium phosphate -> zinc aluminophosphate gel
Zinc aluminophosphate gel is formed on the remaining unreacted ZnO particles
Set cement consists of ZnO particles encased in an amorphous matrix of zinc aluminophosphate
Why should a cavity liner ( Ca(OH)2) be placed when using zinc phosphate cement as a luting agent for prosthesis?
- due to phosphoric acid —> low pH -> cytotoxic -> can cause irritation of the pulp
- the pH increases from 3-6 as the reaction occur but remain acidic for 24h
- Ca(OH)2 -> alkali , can neutralise acidity
- especially in young patient ( patent tubules )
How is the working time of zinc phosphate cements controlled ?
1) Cool the mixing slab - temperature of the mixing slab should be above the dew point otherwise will condense & reduce the physical properties of the cement
- most viable method
2) Prolong the spatulation of the last increment of the powder
- destroys the cement matrix as it forms
- more time needs for cement matrix to rebuild
3) Mix smaller portions of the powder for the first few increment
- heat accelerate the reaction
- by mixing with smaller portions , heat is more efficiently dissipated hence the reaction is not accelerated
- addition in small increments also decrease the acidity of the liquid & retard the reaction rate
4) Lowering the P/L ratio
- using less powder willl produce a thinner mix
- however it will adversely the mechanical properties of the mix
Zinc phosphate does not ( ……………. ) bond to the prosthesis , instead it is ( ……………… ) bonded . Hence , the use of cavity liner will reduce ( …………… ) as it (………………)
Zinc phosphate does not ( chemically bond ) to the prosthesis , instead it is ( mechanically ) bonded . Hence , the use of cavity liner will reduce ( retention ) as it ( creates a smoother surface with less interlocking use of cavity is to protect pulp )
State the advantages & disadvantages of zinc phosphate cement
Advantages
1) Long working time
2) Short setting time
3) Good compressive strength
4) Good thermal insulation ability
5) Does not dissolve in oral fluids
6) Adequate film thickness
Disadvantages
1) Poor aesthetic
2) Can cause pulpal irritation
3) No chemical adhesion ( mechanical ) — prosthesis easier to get displaced
4) Low tensile strength
Describe the composition of zinc polycarboxylate
Powder
I) Zinc oxide (80%) - main reactive ingredient
II) Magnesium oxide (10%) - decrease sintering temperature
III) other oxides eg : aluminium oxide (2-8%) -improves strength
IV) Stannous fluoride (4-5%) - minimal anticariogenic effect , enhance str , mixing properties , modifies setting time
Liquid
I) aq. solution of polyacrylic acid OR aq.solution of copolymer of acrylic acid with other COOH like itaconic acid
Describe the setting reaction of zinc polycarboxylate
- acid base reaction , exothermic
Zinc oxide + polyacrylic acid -> zinc polycarboxylate +H2O
*** glossy cement mix indicates that the mix has not fully set —> can be used , if dull appearance -> all ZnO particles reacted , will not bond to the tooth
Describe how zinc polycarboxylate chemically binds to enamel and dentin
- unreacted -COO groups in the polyacrylic acid reacts with Ca2+ in enamel
- unreacted -COO- groups in the polyacrylic acid reacts with Ca2+ on the surface of the dentin
- unreacted -COO- groups in the polyacrylic acid also reacts with NH2 groups of collagen , forming hydrogen bonds and metal ions diffusing from the cement allow metallic ion bridges o be formed b/w the COO-group of polyacrylic acid and COO- group of collagen
- collagen contains NH3 group & COOH group
For good bonding of zinc polycarboxylate cement to the tooth structure , it should be used before it loses its (…………….) appearance.
A (……………… ) appearance indicates sufficient number of free -COO- groups which can binds to tooth structure
If mixing time is prolonged , the cement becomes ( …………….)
If (……………. ) is seen , the cement should be displaced
For good bonding of zinc polycarboxylate cement to the tooth structure , it should be used before it loses its (glossy ) appearance.
A (glossy) appearance indicates sufficient number of free -COO- groups which can binds to tooth structure
If mixing time is prolonged , the cement becomes ( dull & shows cobwebbing )
If (cobwebbing /dullness) is seen , the cement should be displaced
