Cons Flashcards
Cavity Classification I-V
Blacks classification of caries lesions
I - Posterior Occlusal II - Posterior including Approximal surface III - Anterior Approximal only IV - Anterior Incisal Edge V - Buccal cervical
Setting mechanism of resin composite
Free Radical Addition Polymerisation
Outline setting Reaction of Resin Composite
ACTIVATION
450 nm blue light causes photo-initiator camphorquinone to release free radicals
INITIATION
Free radical reaction with resin matrix monomers
PROPAGATION
Monomers -> cross-linked polymers in an ‘addition polymerisation’ reaction
TERMINATION
Reaction runs out of monomers
Composition of Resin Composite
** Resin Matrix -
Bis-GMA, UDMA (both viscous) and TEGDMA (added to improve flow)
NB: Bis-GMA -> environmental concern (oestrogen like activity) however materials safe once cured.
** Filler Particles -
Inert glass e.g. barium/strontium glass, quartz…
- Reduce polymerisation shrinkage upon curing .’. better seal
- Reduces water sorption
- Reduces thermal expansion
- Increases compressive/tensile strength
- Increases modulus of elasticity
- Increases abrasion resistance
⇒ Radiopacity so visible on radiographs
Shape: Spherical/Irregular
Size: Mixture of small & large particles to occupy more space .’. less resin remaining .’. less shrinkage in curing e.g. Nanohybrid/Nanofilled
** Silane Coupling agent -
(coats filler, allows resin matrix and filler to mix)
Organosilane ( = bifunctional molecule)
- Siloxane end bonds to hydroxyl groups on filler
- Methacrylate end polymerises with resin
** Coupling agent = Sensitive to water - silane filler bond breaks down with moisture!! .’. water absorbed into composites results in hydrolysis of the silane bond and eventual filler loss.
Types of Composite:
Types of Composite:
FLOWABLE Composites
- 50-70% filler content by weight (less than traditional hybrid composite resins → lower viscosity)
- Indications:
o Class V restorations (buccal cervical surface)
o Micro-preparations
o Extended fissure sealing
o Adhesive cementation of ceramic restorations
o Blocking out cavity undercuts
o Initial base layer in any classification - Disadvantages
o Lower filler volumes -> increased shrinkage and wear, decreased strength
PACKABLE Composites (Macrofilled Hybrids)
- E.g.: SDR, BULKFILL
- Firm, can be packed into a preparation
- Contain larger filler particles, or even fibres to improve packing qualities
- High viscosity -> more difficult to sculpt, voids more common
Advantages of Composite
• Appearance - Tooth coloured - Mimics translucency of enamel • Conservation of tooth structure • Adhesion to t.structure via a bonding system • Low thermal conductivity • Command set (LC) • Wear resistant • Withstands occlusal load
Disadvantages of Composite
• Technique sensitive
- Moisture control .’. need rubber dam
- Cannot be placed in wet environments, (subgingival/patients that do not tolerate moisture control)
- Many steps
- Has to be placed in 2mm increments for light penetration
• Polymerisation shrinkage
- Marginal leakage
- Generates lots of stress -> cusp movement
- 2° caries
- Post-operative sensitivity
- Staining
• Lower wear resistance than amalgam
- Not suitable for pts with heavy bruxism
Indications for composite
CLINICAL INDICATIONS • Class III (anterior interproximal), IV (anterior and incisal edge) and V (cervical) • Where aesthetics is important • Rebuilding fractured teeth • Where moisture control can be achieved • Patients with good oral hygiene • Low occlusal load
TYPICAL CLINICAL PROCEDURE OUTLINE FOR COMPOSITE
- Give LA
- Place moisture control
- Gain enamel access and clear ADJ
- Remove infected dentine
- Remove unsupported enamel and bevel margins (if an anterior tooth)
- Etch with 37% phosphoric acid for 15 seconds
- Rinse for 15 seconds
- Dry for 15 seconds (less if dentine to prevent collapse of collagen)
- Apply primer and bond
- Dry lightly with 3in1 to evaporate solvent
- Light cure for 20 seconds
- Place composite in 2mm increments
- Pack and shape
- Light cure for 20 seconds
- Finish
• No flash
• Correct tooth morphology
• Correct occlusion - Polish
• Smooth surface
COMPOSITE IDEAL CAVITY PREPARATION CRITERIA
- No wider than necessary to access caries
- Infected dentine removed
- Affected dentine left
- No unsupported enamel
- Smear layer removed with etch ( bond strength to dentine)
- Bevelled margins if anterior tooth ( surface area for retention and improves transition from tooth to composite for aesthetics)
- Etched enamel and dentine
Bonding system for resin composite
ETCH
37% Phosphoric Acid
Increases SA for bonding -> space/pores for bonding agent to flow into
Enamel -> Calcium salts dissolve, exposes interprismatic and prism areas for interlocking tag formation with the bonding resin = Purely Mechanical Bonding (not true adhesion); bond strength ~20 MPa
Dentine
- > Removes smear layer (Created by any mechanical cutting of dentine, Impairs bond of composite to dentine, Only relatively loosely bound to dentine itself, Can harbour bacteria)
- > Exposing collagen fibres, dentinal tubules & decalcifies intertubular dentine
- >
- Allows penetration of bonding agent into dentine -> Hybrid Layer = infiltration of resin monomers into the collagen fibrillar matrix of demineralised dentine, followed by polymerisation
PRIMER
= solvent + HEMA (resin monomer), an amphiphilic molecule. Hydrophilic end binds to collagen, hydrophobic end binds to bond.
• Penetrates etched dentine tubules
• Applied in a thin layer, thinned with air
• May require light-curing
BOND
= solvent + unfilled resin (hydrophobic).
Binds to HEMA to form resin tags between hydroxyapatite crystals and a hybrid layer where both collagen and resin are found.
- Ultimate goal is achieving marginal integrity and sealing tubules to prevent ingress of bacteria
Why is it possible to use an incremental technique with composite?
OXYGEN INHIBITION LAYER
inhibits polymerisation of monomers .’. top layer sticky to touch - un-polymerised monomer
-> allows next layer of composite to adhere
removed by polishing
Factors in Caries Prevention
Diet control
Toothbrushing
Fluoride
Fissure Sealants
Mechanisms of Fluoride Action
- During tooth formation -> increased stability, increased prism size
- Inhibition of plaque bacteria - interferes with bacterial acid production by inhibition of enolase
- Inhibits demineralisation when in solution
- Enhances remineralisation by forming fluorapatite -> more resistant to subsequent demineralisation (critical pH 3.5 compared to 5.5 for apatite)
- Affects crown morphology making pits & fissures shallower
- Recommend 5:2 (Sugar exposure: F exposure)
Fluoride methods of delivery
Toothpaste- daily
Rinses - daily/weekly
Supplements
Varnishes e.g Duraphat - 2/4 x per year; professional application
Gels - 2/4 x per year; professional application
Water Fluoridation
Devices - slow release F devices
Methods of caries detection
- Visual Inspection - clean, dry tooth, good lighting
- Temporary elective tooth separation
- FOTI - Fibre Optic Transillumination
Used for detection of approximate caries
White light, 0.5mm diameter probe - Bitewing Radiograph
-> minimum radiation dose for maximum caries diagnosis
Caries detectable as radiolucency (darker) on image
Problems of caries diagnosis via radiography
- Overlapping contact points (1/2 enamel thickness = permissible)
- > under diagnosis of early enamel smooth surface caries
- Subjective - inter&intra-observer variability
- Cervical burn out can be mistaken for caries
= relative radiolucency around necks of teeth
Due to X-rays over-penetrating (or burning out) the thinner tooth edge - if CAN see edge of root -> cervical burnout
if Can’t -> possible caries - inner edge more diffuse and rounded in cervical burnout than caries
- Heavily restored dentition
- can’t see what’s happening under restoration
*Angulation of x-ray beam can project enamel lesion so appears to go into dentine
- Mach band effect
= visual illusion
mach band = perceived shadow between enamel and dentine due to different densities
Mask enamel and mach band will disappear - Corrosion products
deposits of heavy metal ions e.g. tin, zinc leached in softened dentine-> radiopaque line under restoration with radiolucency immediately underneath
Reason for restoration failure
- Discolouration
- underlying from stained dentine
- superficial surface staining
- underlying from amalgam corrosion products
*Loss of marginal integrity –> plaque retention
Causes:
-long term creep/corrosion/ditching of amalgams
-marginal shrinkage of resin comp/bonding agent
-marginal dissolution of GICs
-marginal ledges/poor contour/overhangs/marginal chipping under occlusal loading
- Marginal discolouration
= indication of marginal integrity failure; not necessarily recurrent caries - Loss of bulk integrity
- restoration may be bulk fractures /partially/completely lost
- heavy occlusal loading: lack of occlusal analysis before restoring
- poor cavity design: weakened, thin section restorations esp. amalgams
- Poor bonding technique/contamination –> adhesive bond failure/lack of retention
- inadequate condensation technique –> intrinsic structural weakness e.g. voids, soggy bottoms
Factors contributing to appearance of teeth
Outline form Contour Symmetry Proportion Colour - translucency
Facial Symmetry
0.6:1 - relationship between proportions between central & lateral, lateral & canine
Amalgam Advantages
Cheap Longevity; average lifespan 12 years (2001 study) Less technique sensitive than composite Strong Hard wearing Kind to opposing teeth Ag -> antibacterial properties Corrosion products form an effective marginal seal against secondary caries Radiopaque
Amalgam Disadvantages
Non-adhesive
- Requires undercut, retention grooves
- No seal against marginal leakage until corrosion products form
Chemically cured
- No control over setting time; often sets too quickly to carve effectively
Weak in thin section
- Cavity must be made deep enough (>2mm)
Weak if unsupported from underneath
Thermal conductor (however dentine sufficient insulator to prevent being a problem)
Coefficient of thermal expansion
- Expands/contracts depending on temp
Corrosion and creep
Un-aesthetic
Environmental risks of Hg
Can cause lichenoid-type reaction to nearby mucosa
Amalgam Composition
Solid phase=
*Silver (65-70%)
*Tin (26-29%)
*Copper (Low 12%) – reacts with γ2 on setting converting it to γ1
*Zinc (2% max)
– Scavenger; more reactive so prevents oxidation of silver and tin during manufacture by any impurities e.g. oxygen (weakens material). Low % as in presence of moisture can lead to uncontrolled expansion of amalgam filling as it sets.
Liquid phase = Mercury
Amalgam Alloy particles
SPHERICAL (more workable, flows more easily)
or
LATHE CUT (move less freely, helpful when trying to build up teeth). - Modern amalgams contain some of both types – admixed.
AMALGAM SOLID PHASE PARTICLES
**Lathe-Cut Particles – ground up metal, irregular in shape
Does not flow readily
Good for build-up of large cavities
**Spherical Particles – forms by spraying molten metal into water, produces particles of variable sizes
Easily manipulated
Less mercury needed
Less γ_2 produced
**Admixed Particles – mixture of the two (most common)
Best of both
Amalgam Setting Reaction
Once mixed the mercury (Hg) dissolves the alloy powder -> silver (Ag) and tin (Sn) molecules are freed, able to react together or with the Hg forming grains as the material sets.
Ag + Sn -> Ag3Sn (γ)
Ag + Hg -> Ag2Hg3 (γ1)
Sn + Hg -> Sn7Hg (γ2) - undesirable phase; causes amalgam to be weaker and more prone to corrosion and creep
To avoid too much γ2 forming copper is included. Cu undergoes a reaction with any γ2 as follows:
Sn7Hg (γ2) + Ag-Cu -> Cu6Sn5 + Ag2Hg3 (γ1)
γ_2 = undesirable, causes strength, corrosion (results in a dull appearance) and creep (results in marginal failure and secondary caries)
Amalgam corrosion products
Although amalgam does not bond to dentine, the corrosion products formed around the edges of the restoration form an extremely effective seal. This combined with the inherent antibacterial properties of silver form a good barrier to microleakage and secondary caries.
