Week 1 Dental Materials GIC+Alginate+Polyethers+Polysulphes Flashcards
Describe the properties, chemistry and clinical handling of Glass Ionomer Cements Describe the indications and contra-indications for use of Glass Ionomer Cements Describe the advantages and disadvantages of Glass Ionomer Cements Understand the chemical, physical and handling properties of differing impression materials Describe the indications of use for each of the impression materials Describe the setting reaction for each of the impression materials
What is impression material?
A negative or likeness copy in reverse of the subject of the object. An imprint of the teeth and adjacent structures for use in dentistry
How are Polyethers dispensed?
supplied as two pastes with a catalyst and base
What is the composition of the Polyethers?
Catalyst: containing reaction initiator
Base: forming oils and fillers in second syringe which is smaller than base
What is the chemical setting characteristics of Polyethers?
Base and catalyst upon mixing a cationic, ring opening addition to polymerisation
What are the properties of Polyethers?
Good tear resistance, elastic properties approaching those of silicon. They are rigid when they are set and force is required to to remove impression after setting.
What basically is alginate?
Irreversible hydrocholoids When powder is mixed with water to obtain a paste setting occurs
What are the two main setting reactions that occur in alginate?
- (tri)sodium phosphate + calcium sulphate
2. remaining calcium sulphate + sodium potasium alginate
Whats the mixing time on alginate?
1 minute
Whats the setting time of alginate?
1.5-3min
What basically are the physical properties of alginate?
Material that is flexible and elastic enough to be withdrawn past undercuts
Whats a disadvantage of alginate?
Care must be taken during withdrawal from mouth, to avoid tearing
How long should you wait before withdrawing an alginate impression from a patients mouth?
A further 2mins, as cross-linkage continues after material has set. This enhances the elastic nature of this material
What can influence the setting characteristics of alginate?
- Temperature of water
2. Power-Water Ratio
How does the temperature of water affect the setting properties?
Using warm water: reduces working time and setting time through accelerating rate by which sodium phosphate is consumed and increasing rate of cross linkage.
Using cold water: has the reverse effect
How does the Powder-water ratio affect the setting properties?
Too much powder: alginate too thick causes mixing to become difficult
Too much water: alginate mixture becomes runny, setting time increases, runs out of tray (higher risk of gag reflex)
When should alginate be cast?
As soon as possible to prevent inaccuracies due to dimensional changes, because alginate undergo synersis and imbibition
Describe the term synersis
Envisaged as squeezing out water between polysaccharide chains. Water lost by evaporation causing SHRINKAGE of impression and serious inaccuracies.
Describe the term Imbibition
presences of excess water causes seperation of aligned polysaccaride chains leading to SWELLING of the impression. Opposite to synersis
What is the chemistry (ingredients) of alginate?
Potassium titanium fluoride Potassium sodium alginate Tri-sodium phosphate Diatomaceous earth Calcium Sulphate Zinc oxide Colouring/flavouring
What does Potassium sodium alginate do? (Chemistry)
Thickening agent
How does diatomaceous earth react?
Adds bulk to material
How does Calcium Sulphate react?
Reacts with potassium alginate to form gel
How does Tirsodium phosphate react?
Slows down reaction time
How does Zinc Oxide react?
Adds to bulk of material
How does Potassium titanium fluroide react?
Added so it does not interfere with setting and surface strength
What are the physical phases of alginate?
- Solution (the material is a liquid or semiliquid form)
2. The material is semisolid similar to a gelatin dessert
How many physical phases are in alginate?
two
What is the chemical setting characteristics of alginate?
A chemical reaction occurs -
Soluable alginate reacts with calcium sulphate to produce a insoluble calcium alginate as a gel.
The production of calcium alginate is delayed by aading trisodium phosphate.
Describe in laymen terms the setting characteristics of alginate
First the soldium phosphate reacts with calcium sulphate to provide adequate working time.
Second after sodium phosphate has reacted, the remaining calcium sulphate reacts with sodium alginate to form an insoluable calcium alginate which forms a gel with water.
What do you use to decontaminate alginate impressions?
hypochlorite or foraldehyde
How do you store alginate impressions?
wrap in damp paper towel, placed in plastic bag, store only for short time frame.
What is a modified alginate?
Incorporation of silicon polymers, it’s a two paste system (mixed). Colour contrast between mixing allows thorough mixing.
Benefits of using a modified alginate
Shows a marginally better detail and tear resistance
Disadvantages of using a modified alginate
Mixing can be difficult as viscosity can vary. Has poor dimensional quality
Name another dental material
Reversible Hydrocolloids (agar)
How many impression dental materials are their?
5
What are the impression materials called?
Alginate, polyethers,modified alginate, reversible hydrocolloids (agar), polsulphides
What is the composition of Reversible hydrocolloids?
Supplied in gel, tooth-paste like syringe/tube. 15% colloidal suspension of agar in water. Agar is a complex polysaccharide extracted from seaweed
Disadvantages of using Reversible hydrocolloids?
Poor mechanical strength and tears at low levels of stress, has poor dimensional stability, subgingival and inter-proximal areas are difficult to record.
What is a poly sulphide?
It’s a two based system dispensed from tubes, a base (liquid polysulphide prepolymer) and catalyst (oxidising agent). It’s available in light, regular and heavy body.
What are the setting characteristics of polysulphides?
The terminal and pendant thiol groups of the prepolymer chains undergo a reaction with lead dioxide, result in chain cross-linkage.
What is the scientific term for polysulphides result in cross-linkage?
Known as condensation polmerization
What are the properties of Polysulphides?
Very good tear resistance. Heavy bodied are more accurate as they exhibit less setting and thermal contraction >better dimensional stability.
Why do we use impression materials?
To accurately record dimensions of oral tissues and their spatial relationships
What is alginate impression materials used for?
Bleeching trays, mouth guard, splint guards, orthodontic comparison, study models. opposing arch, duplicating models
What are the advantages of using Irreversible Hyrdocollids (alginate)
Ease of manipulate Reasonable cost Adequate flow and wetting properties Sufficient mechanical strength Appropriate setting time Safe nontoxic or irritating Good shelf life
How does alginate set?
◦ First the sodium phosphate reacts with calcium sulphate to provide
adequate working time.
◦ Second after sodium phosphate has reacted, the remaining calcium
sulphate reacts with sodium alginate to form an insoluble calcium
alginate which forms a gel with water
