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Biomaterials 2 (Successful Rem Pros Impressions (Definitions (Primary…

- - - - White-wax
        
        can be shaped w/o applying heat
      - Green Compound Wax
        
        plastic when heated, rigid when cooled
      - Exahiflix - Tray Type Addition Silicone
- - - - Biological: non-toxic and non-irritant, chemically inert
        
        Chemical: it should be unaffected by oral fluids
        
        Mechanical: adequate mechanical properties (i.e. high elastic modulus)
        
        Physical: High value of thermal conductivity, radioopaque
        
        Aesthetic: aesthetically satisfactory.
    - - Polymerization: activation, initiation, propagation, termination
    - - Ex. heat-cure,
        Ex. auto-cure
        Ex. light cure
        nb: similar compositions, but differ in their initiation/activation mechanisms
  - - - Types:
        
        Type 1
        
        Type 2
        
        is less irritation to the oral cavity
      - Definition: Temporary/semi-permanent solution to ridge resorption, where materials are placed in the mouth and changes fabricated in the lab
    - - Definition: help to relieve pain and increase patient adaptation which is done over a longer period of time
      - Types:
        
        Temporary soft liner
        
        When frequent replacement is difficult, to assess patient’s response to soft liners and to improve fitness before definite denture constructed
        
        Permanent soft liner
        
        permanent soft cushion for patients who cannot tolerate a hard denture
- - - - Elastomers
        
        Polysulphides
        
        Adv.
        
        good detail reproduction (Hydrophilic)
        
        flexible
        
        Disadv.
        
        Long setting time (indicated in Maxfac face impressions)
        
        hydrophobic
        
        smell
        
        Properties
        
        The impression must be poured within one hour to prevent distortion as a result of the evaporation of the by-product (water)
        
        long working and setting time of 10 to 20 minutes
        
        Highly flexible hence favoured for use in patients with periodontally compromised teeth or facial malformations
        
        bad odour and hence not preferred by patients
        
        Addition Silicone (PVS)
        
        Viscosities
        Change w/ filler content
        
        available as heavy, medium, light
        
        Affected by the shear force(working) placed on the material, such as when they are extruded from a syringe, they will exhibit low viscosity. When placed in the impression tray with a spatula, they have a high viscosity (shear thinning)
        
        Setting Reaction
        
        Hydrogen can also be released in a secondary reaction. commonly due to impurities from the reaction, palladium is added to absorb the hydrogen (NOT A BYPRODUCT)
        = recommended to wait at least 60 minutes before pouring
        
        In the polymerization of addition silicone, hydrogen atoms from the siliane group move along the backbone structure onto the vinyl silicone. Following the platinum salt initiator, the units join as repeating units of dimethylsiloxane and terminate w/ vinyl group
        
        Advantages/Disadvantages:
        
        Advantages:
        High accuracy
        Good dimensional stability (up to 3-7 days)
        Low setting shrinkage
        Short setting time
        Auto mixed & Dual-phase system
        No hypersensitivity reactions
        
        Disadvantages:
        Inhibition by sulfur-containing materials
        ie latex gloves
        Relatively expensive
        Actually hydrophobic, despite manufacturer claims
        
        Non-ionic surfactant added to the paste to render the surface of the impression hydrophilic (uses include RPD, FPD, F/F, Fi/Fi) ex. Exaflex
        
        Polyethers
        
        Adv.
        
        Good surface detail/most accurate
        
        Dimensional stable
        
        Disadv.
        
        Long setting time
        
        Rigid set
        
        properties
        
        hydrophilic of the elastomers and exhibits excellent dimensional stability when stored in a dry environment
        
        most rigid of the elastomers which may contraindicate in uses where presence of deep undercuts or periodontally-involved teeth
        
        appreciable elastic recovery, high tear strengths and are extremely accurate (indicated for FPDs) ex. 3M Impregum
        
        Condensation Silicone
        
        produces ethanol as a reactionary by-product
        
        reasonable setting time, high accuracy and elastic recovery, however their hydrophobicity and dimensional instability has made their use in dentistry relatively limited
        
        with high filler content (putty) are rigid and may be used to make stents or customise a stock tray with the putty-wash technique
      - Hydrocolloids
        
        Alginate (irreversible)
        
        Setting Reaction
        Alginate & water (4:1) ---> sol ---> gel
        Sodium alginate reacts with calcium sulfate to form calcium alginate forming crosslinks in solute. It then sets to form a gel.
        
        Properties
        
        syneresis
        = cross-linking reaction continues and water is extruded from the surface, resulting in a dimensional change
        
        Imbibition
        = is the absorption of water by the material from the environemnt
        
        Indications
        = primary impression material but also has uses as secondary and impressions and duplicating models
        
        Advantages of alginate:
        
        Easy to use
        
        Flexible
        
        Smells nice
        
        Cheap
        
        Mainly its hydrophilic → therefore good surface detail in presence of saliva
        
        Disadvantages:
        
        Low tear strength
        
        Dimensionally unstable
        
        Low detail production
        
        Trouble Shooting:
        Early removal
        Sticking to teeth
        Improper tray placement/seating
        
        Disinfect/Pouring
        Placed in disinfection for 5 mins
        It should be poured within 60 minutes of
        taking the impression
        
        Agar (reversible)
        
        Used for duplication of impressions
        
        Not really used in primary impression
        
        long setting time
        
        unstable out of the mouth
        
        less permanent deformation than alginate
        
        more hydrophilic than alginate
        
        Agar is an excellent impression material and yields accurate impressions, it has been replaced by other impression materials due to its complexity and needing special equipment
    - - Impression Compound
        
        thermoplastic materials that can be softened to their working consistency by working over a flame or in a hot bath
        
        Types:
        
        Type 1 - Impression compound(Lower fusing)
        = sticks, are used for border moulding or impressions
        
        Type 2 -Tray compound(Higher fusing)
        = sheets, are used for secondary impression trays
        (now been replaced by acrylics due instability)
        
        Ideal characteristics
        
        soft at a point above oral temperature (flow over tissues)
        
        harden at mouth temperature (minimum flow to reduce distortion)
        
        Adv.
        
        Sufficient displacement of the lingual and soft tissues
        
        good peripheral seal
        Disadv.
        
        poor stability
        
        low detail reproduction
        
        mucocompressive
        
        stiff
      - ZnOE
        
        A metallic oxide paste
        Uses:
        
        secondary impression materials for complete full dentures
        
        relining distal extension denture bases
        
        non-undercut edentulous ridges
        
        acid base/chelation reaction that forms a chelate, that is zinc eugenolate.
        nb: Eugenol can be substituted for patients with allergie w/ lauric acid.
        
        Setting
        
        Delayed by
        
        Cooling mixing slab or spatula
        
        Adding small amount of retarder/old waxes
        
        Increased by
        
        Zinc acetate/additional accelerator
        
        Drop of water in the paste before mixing
        
        properties
        inelastic, low shrinkage , stable, difficult to handle