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composites, ceramics, adhesions and implants in dentistry applications -…

- - - - fissure sealants
      - endodontic post and cores
      - adhesive/bonding agents and cements
      - dentures
        
        bases
        
        soft linings
        
        fake teeth
      - composite fillings
  - - - spherical, round & equiaxed from spray dicing. give low stress concentrations and medium packing density
      - rectangular, sharp corners & relatively equiaxed. stress concentrations at corners, isotropic properties and medium packing density.
      - flakes, 2 long one short dimension, common form. some anisotropy with good packing density
      - needles, one long and 2 short dimensions. aligned for good packing which gives anisotropy, non-aligned can give interlocking
    - - small particles packed between larger ones gives higher packing density allowing more filler without particle particle contact=greater reinforcement
      - multimodal- 2 or more particle size ranges
      - monomodal- all particles same size range
  - - - only when excess or non-optimised filler
    - - rare in polymers
    - - most common source of failure
      - can be reduced by using coupling agent
  - - - UV/blue weight (470nm=λ) acts on photoinhibitor
      - reaction accelerated by organic amines with C double bond
      - UV more reactive but not seen by dentist
      - blue light less effective but visible (easier for dentists to use)
      - light cannot get fully through the material so have to pack a bit them cure and repeat building up the material incrementally
      - darker colored composites have reduced cure depth because the particles scatter light more
      - amalgam allows whole structure to be cured in 1 go so more efficient
    - - organic amine & organic peroxide produce free radicals which breaks carbon double bond allowing polymerisation
  - - - act as adhesive
      - self curing
    - - take mould of built up tooth after build up
      - use light curing cements
    - - protect tooth
      - use dental cements
    - - only small amounts
      - cant have multiple cracks
- - - - zinc phosphate
        
        chemically bonds to enamel and dentine
      - zinc polyacrylate
        
        alkaline and therapeutic
      - calcium hydroxide
      - glass ionomer
        
        bond directly to enamel and dentine
  - - - Fluoride release forming fluoroapatite making the surface more resistant to acid dissolution and caries
      - chemically adhesive to apatite phase of enamel and dentine
    - - chemical bond between carboxyl groups, calcium ions and phosphate groups on mineral surface
      - ionic bonding between carboxyl groups and calcium ions on mineral surface
      - displacemet of calcium and phosphate ions on reaction with polyacids creating an intermediate calcium & phosphate ion enriched polyacrylate interlayer binding to the mineral phase
      - both hydrogen bonding between collagen and ionic bonding with mineral believed to be involved
      - bond strength to enamal higher than dentine as mineral content higher
      - interface rarely fails as failure occurs through body of GIC restoration (low tensile strength)
      - polyacrylic acid primer improves bond strength
    - - sensitivity in some patients due to pH
      - acid dissolution in mouth (coke, juice, ect)
      - low fracture toughness, tensile and flexural strength
  - - - increased strength vs conventional
      - increased bond strength with tooth
      - less translucent than conventional
      - greater shrinkage than conventional
    - - addition of silver particles increases strength, fracture toughness and wear resistance
      - known as CERMET
      - store and release less Fl than conventional (bad)
- - - - long setting time (>10min)
      - messy and can stain clothing
      - poor smell
      - susceptible to distortion (shrinkage and anisotropic shape)
      - compromised dimensional stability by water evaporation
      - requires custom tray
      - impression must be made immediatly
      - second pour gives lower accuracy
    - - long working time
      - proven accuracy
      - less hydrophobic
      - inexpensive
      - long shelf life
  - - - fast setting time (<5min)
      - adequate tear resistance
      - good elastic properties
      - relatively hydrophillic (forgiving of low moisture)
      - good dimensional stability if stored dry
      - high accuracy once set
      - multiple casts can be poured, but should delay pour
      - less distortion on removal
      - 2 year shelf life
    - - base paste= 50-60% polyether polymer, 5-10% filler (colloidal silica), 10% plasticiser (glycoether or phthalate) and colouring agents
      - accelerator/catalyst paste= initiator (alkyl aromatic sulphonate), filler (colloidal silica) and plasticiser (glycoether or phthalate)
    - - only adequate accuracy if poured immediatly
      - poor dimensional stability if incorrectly stored
      - clean but bitter taste
      - relatively stiff
      - expensive
      - sensitivity to moisture complicates disinfection
  - - - good tear resistance
      - reduced stiffness
      - good biocompatibility
      - adequate working and setting time
      - pleasant odor
      - less hydrophobic than alternatives
      - better elastic properties on removal
      - less distortion on removal
    - - highly hydrophobic
      - poor dimensional stability
      - limited shelf life
      - adequate accuracy if poured immediately
      - potential for distortion
      - putty wash method is technique sensitive
      - more expensive
      - limited shelf life
  - - - salts dissolved in solvent, a solution is formed
      - solution chains are crosslinked (irreversible) through chemical reaction to become a gel
      - secondary bonds are formed at elevated temperatures to form a gel (may reform on cooling, reversible)
    - - first elastomeric impression material (1937)
      - extracted from certain types of seaweed
      - very large monomer so created a very large polymer chain
      - gelation occurs as a result of spontaneous formation of secondary bonds between agar chais or fibrils, which break at elevated temperatures and are reformed upon cooling
      - principle ingrediant is water(>79%), agar only (13-17%)
      - borax added to produce intermolecular attraction for strength
      - accelerators added to counteract the retardant effect borate has on setting gypsum based model plaster
      - fillers added to control strength, viscosity and rigidity
      - advantages
        
        reasonable elastic properties once set
        
        reasonable surface detail when used correctly
        
        good elastic recovery
      - disadvantages
        
        low dimensional stability due to loss/absorption of water when in dry or wet environments
        
        uncomfortable for some patients (thermal shock)
        
        skill required to use
        
        expensive apparatus required
    - - originally made form specific seaweed to give alginic acid
      - linear polymer with carboxyl acid groups
      - sodium, potassium and ammonium some of the few soluble salts
      - produces alginate plus reactor, accelerator and fillers
      - cross linked polymer network formd on gelation
      - very rapid reaction so retarders (trisodium-phosphate or sodium oyrophosphate) used to extend working time
      - gelation process
        
        mixed with water to produce colloid
        
        alginate reacts with calcium sulphate to produce calcium alginate gel
        
        once all retarders used up reaction with aliginate starts
        
        shelf life limited by depolymerisation of alginate
        
        irreversible process
      - advantages
        
        fast setting (1-2min)
        
        easy to use
        
        easy to manipulate
        
        clean and comfortable for patients
        
        relatively inexpensive
        
        long shelf life
        
        hydrophillic, moist surfaces not an issue
      - pH changes during setting are critical, more alkaline=poor plaster surface
      - disadvantages
        
        tendancy for settling out in storage
        
        tears easily
        
        poor dimensional stability
        
        typically must pour within 30-120min of taking impression
        
        not record fine detail required
        
        can retard setting of gypsum
      - tin should be shaken before use, then left 2 min for dust to settle (currently most are dust free)
- - - - requires less water on mixing
      - cubic crystallites
      - lower surface area
      - less exothermic reaction
    - - stronger material
      - acicular crystallites
      - higher surface area
      - more exothermic
    - - when water added hemihydrate powder forms a slurry or as as some dissolves
      - once dissolved becomes a dihydrates and an exothermic reaction occurs
      - dihydrate has lower solubility so a supersaturated solution develops and nuclei form and precipitate
    - - Impression plaster
        
        low strength
        
        quick setting
        
        fluffy and porous
        
        now replaced by hydrocolloids
      - model plaster
        
        some setting contraction
        
        medium strength
        
        made from hydrocal
      - dental stone
        
        high strength
        
        low setting contraction
        
        made from densite
  - - - dehydrated under pressure (125degrees C) in presence of water vapour
      - powder crystals have higher density and more uniform in shape, relatively needle like
    - - gypsum rock boiled in 30% CaCl sol which is washed away with water (100degree C)
      - dried and ground into powder
      - forms dense cubic crystals
  - - - max effect at c.0.9%
      - develops insoluble layer (coats crystals) preventing hemihydrate dissolving and being able to reprecipitate
  - - - flat ended needles with static load
      - initial needle: 2.12+/-0.05mm=diameter, and end load=113+/-0.5g giving 0.3MPa pressure
      - final needle: diameter=1.06+/-0.05mm, and end load=453.6+/-0.5g giving pressure=5MPa
      - this should leave no mark if done correctly
    - - 1mm diameter and end load 300g, giving 3.7MPa prssure
      - only 1 needle
      - setting time that when needle doesn't penetrate bottom of container
    - - final gilmore measurement gives sufficient mechanical properties such that plaster can be moved
      - initial gilmore gives start to stiffeening
      - vicat gives intermediate set
      - both very easy to use
  - - - typically cylindrical specimens used, with height twice the diameter
      - failure typically observed in the longitudinal direction due to transverse tension
    - - measure indentation
      - drive a diamond or steel ball of appropriate shape into surface with known load and measure indent
      - Knoop or Vickers method possible
        
        vickers diamond angle is 136 degrees
        
        Knoop diamond angle has length to width ration 7:1 and angles of 172 & 130 degrees
    - - measure by scratch resitance
    - - measure by brazilian disk (or diametrical compression)
      - disk generates tensile load perpendicular to direction of load
  - - - no air bubbles
      - good surface finish
    - - air bubble produced by incorrect mixing
      - poor surface finish
- - - - adhesives harden to form a joint purely by physical means via forces (VDW)
      - often vaporization or evaporation of solvent or cooling of liquid to harden
      - can also occur when hardened via reaction between 2 components in the adhesive system
    - - much stronger covalent bonds can be achieved
      - chemical reaction occurs between adhesive and adherend
    - - friction/mechanical interlock opposes movement between surfaces
      - can be hardened by evaporation or chemical reaction between components
  - - - etchant
      - coupling agent
      - primer
      - adhesive
    - - removes smear layer
      - etch/chemically roughen surface
      - produce microinterlock with tooth
      - 37% phosphoric acid typically used
      - gels contain cellulose thickening agents/microfillers (so doesn't flow all over mouth)
    - - enable bonding between hydrophillic surfaces and resin based adhesives
      - silane coupling agents are hydrolysed forming tri-hydroxyl silanol groups
      - surfaces can be coated with hydrolysed silance which covalently bond to surface with the elimination of water
    - - to encourage wetting and penetration of adhesives
      - hydrophilic monomers in solvent
        
        used for good wetting
        
        self etching
      - solvents include acetone, ethanol-water and water up to 70%
    - - micro-mechanical interlock requires atching to dissolve HA and remove smear layer
      - can pre-treat with coupling agent to facilitate chemical bonding, then apply adhesive
      - forms macro/micro tags through penetration of bonding agent into enamel rods giving tension and shear resistance
      - much more forgiving than dentine
    - - high water content so require 3 steps
      - 1) etch to remove smear layer and open tubeules
      - 2)prime surface to encourage wetting and promote resin penetration
      - 3) apply adhesive to form mechanical bonds
      - drying is critical but overdrying can collapse structure, due to significant initial water content (due to collagen)
      - in final week whole slide on problems and solutions look there if asked cba to copy
- - - - very rarely used modernly
      - non-osseointergrative
      - rests directly onbone
    - - penetrates through bone
      - relatively invasive
    - - 3 main components
      - most common type
      - less invasive
      - various types of
      - Bone implant interface
        
        need a material where bone can develop a strong interface both initially and for a long time
        
        fatigue resistance is needed (chewing)
        
        key for good implant
      - Branemark Implants
        
        made of titanium which forms oxide layer on surface within ms of air exposure
        
        range of oxides including TiO2 support osteoblast adhesion and growth
        
        at room temp compercially pure (cp) Ti is HCP alpha phase, above 883 degrees BCC beta phase (stronger but more brittle)
        
        Vernadium beta phase stabilizer, aluminium alpha phase stabilizer, alpha and beta phase materials are strong, formable but no easily weldable
        
        cpTi expensive but has better bioactivity than Ti alloys which can be used aswell as 316 stainless steel but possibility of more issues with steal modulus (higher than bone)
        
        bioactive coatings applied to aid and speed up healing process
        
        interest in use of PEEK for improved modulus but bioactivity still and issue
        
        Ha-PEEK composites in development (plain polymer, not bioactive)
        
        implant inserted into jaw and sewed over, after 3 to 6 months (allow bonding to bone) opened up and root stem screwed in
        
        bone needs time to repair and bond otherwise movement may cause gaps between implant and bone significantly reducing strength
        
        permenant
        
        advantages
        
        very stable implant system
        
        good patient feel
        
        disadvantages
        
        expensive
        
        time delay between implantation and use
        
        if infection occurs leads to major problems
      - 15 year survival rates of 91-96%, most failure occur within 1st year
      - implant should osseointegrate (form direct contact with bone)
      - materials should be osteoconductive and encourage osteoblast progress along material surface
  - - - can be done with/without simulated body fluid aging treatments
      - interest in increasing application to Ti and PEEK to increase bioactivity
      - use electrolytes to stimulate cation and anion production which deposit on cathode and anode before undergoing treatment
    - - may need acid or alkaline covering to deposit
      - developed to be the non-biological and non-organic parts of blood plasma
      - at single strength indicates likely bioactivity of a material
      - at super strength (x2 to x5) will deposit a mineral layer on most materials
      - very extensive process but simple concept
    - - powder fired through high temp plasma (thousands of degrees C)
      - powder heated (not to plasma temp) and accelerated to allow easier bonding to surface
      - powder particles splatted on coating surface
      - done one base metals and Ti alloys
      - if not properly cleaned strength is lost at coating surface interface
  - - - high strength
      - versatile
      - low aesthetic, so normally only posterior teeth
      - expensive
    - - ceramic particles in a glass matrix can be tougher than pure ceramic
      - dicor used in glass phase the heat treatment leads to deposition of ceramic phase
      - gives good aesthetics
      - Pressing
        
        placed in mould under load and temperature
        
        material flows into mould
        
        temp needs to be such that glass phase flows and ceramic particle production is low
        
        more ceramic particles leads to more interaction between flowing particles so less flow
        
        more particles also provides stiffness and cracking stopping mechanism so needs to be balances
      - leucite reinforces crowns
        
        pressed into a mould
        
        crystals in glassy matrix
        
        more translucent than other materials, so makes a good tipping material
      - Feldspar machinable ceramic
        
        very fine structure so can be easily machined
        
        good chipping resistance
        
        good wear resistance
      - Mica machinable glass ceramic
        
        crack stopping
        
        crack propagation more difficult as has to move around particles
        
        cracks cover more surface area so needs more energy
    - - base metal used for core include nickel chromium, cobalt chromium and titanium (cp and alloys)
      - gives same visual impression as natural tooth with ceramic layers
      - metal core for strength and loading
      - at least 2 layers of ceramic covering metal base
        
        first layer opaque to hide metal and is bound to the metal
        
        second layer are dentin and enamel appearing layers for aesthetics
      - must be high temperature fusing alloy (>100degrees C), must be above ceramic firing temp
      - ceramics need low fusing temp to prevent distortion
      - sandblast prior to application of ceramic to improve bonding, ceramic flurry must wet alloy surface (>60degrees), if appropriate metal oxides formed on surface it will bond with ceramic
      - bonding between metal and ceramic relies on combination of mechanical interlock and chemical bonding
      - coefficient of expansion of ceramic should be less than that of metal
      - on cooling metal will contract more than ceramic inducing compression on the ceramic increasing the resistance to fracture
      - failure modes
        
        metal-metal oxide interface due to poor bonding
        
        metal oxide-metal oxide interface due to poor bonding (common in base metal devices)
        
        metal oxide-ceramic interface