Clinical Composite Flashcards
What material is most likely to fail in a restoration?
amalgam
What happens to composite materials when they turn from plastic to solid state?
change in volume
Where must caries never be left?
at the margins of cavities
caries left at the dentine-enamel junction will result in unsupported enamel and early breakdown of the restoration margin if microleakage occurs (bacteria can also colonise)
What does poor enamel preparation margin cause?
Composite dimensional change
Etch/bond is stronger than interstitial enamel strength
Interstitial enamel failure - Microleakage
Unsupported enamel
Dentine fracture
Why does enamel fracture occur?
due to placement of restoration in a large sum
causes high stress as the large increment changes dimension
What layer is favorable in restorations?
hybrid layer - resin interacts with the demineralised structure of dentine
Where is the hybird layer favorable and unfavourable?
favourable in primary dentine - open tubules
unfavourable in tertiary dentine - irregular structure
What must be considered with applying the restoration to dentine?
Removal of smear layer
Creation of Hybrid layer
Dentine physiology
Peri/inter tubular
Tubule size
Tubule density
Water content
Water transport
What is the smear layer?
What removes it?
a layer of material composed of dentine, remnants of pulp tissue and odontoblastic processes, and sometimes bacteria creating during drilling.
it is removed by etching
What is the characteristics of deeper dentine? (secondary)
Wetter
More mineralised
More tubules
(closer to pulp)
What is the characteristics of older dentine? (primary)
Fewer tubules
More Mineralised
Occluded tubules
What are the characteristics of reactive dentine?
Occluded tubules
More mineralised / contaminated
Irregular tubules
What type of mineralisd is best for bonding?
bonding happens best when dentine is demineralised and the collagen fibres are exposed for resin to infiltrate into
Is there water in the hybrid layer?
no
What adhesion does poor quality dentine allow?
adhesion through ion exchange
What are the most important things to think about in a restoration?
Cavity preparation
Bonding
Contacts (opposing/adjacent teeth)
Placement
Countering contraction stresses (material changes from plastic>solid)
What is the configuation factor?
ratio of bonded surfaces to unbonded surfaces
What does a high CF factor cause?
high polymerisation contraction stress
What does polymerisation contraction shrinkage cause?
plastic deformation
in turn increasing the stress
marginal and internal gaps, and decreased bond strength.
What can polymerisation contraction shrinkage be caused be?
Materials
Polymers
Δ Volume
Conversion
Air inhibition
What is plasticity?
a property of a material to undergo a non-reversible change of shape in response to an applied force (polymerisation)
What is deformation?
change in shape due to an applied force (contraction)
What is plastic deformation also known as?
polymerisation contraction
What happens if the cavity is perfect, the enamel bond is ideal, however the dentine bond is imperfect and it has been restored in a single increment?
interior of restoration peels away from the cavity, material fills with dentinal fluid
when patient chews on tooth, stresses will be transmitted into fluid, causing pain
What is the nature of dentine?
Type
1°/2°/3°
Intra/Inter/Peri tubular
Diameter
Density
Contents/Mineralization
What type of material is useful for contact point prevention?
contoured bands allow positioning better than flat bands
In what stage of the clinical procedure do issues with CF occur?
placement
What acid is used for etching?
30% phosphoric acid
If the dentine is poor quality/tertiary, what should be created to ensure well bonding?
a lining usually resin modified glass (RMG)
How long does an enamel etch take and how much does a dentine etch take?
10 seconds
How is the smear layer produced?
whenever a handpice is used on dentine, it creates an orangic material that occludes the tubules
How should the etch be applied to dentine?
after etching enamel, move etchant to surface of dentine to remove smear layer
Why should dentine be moist?
overdry dentine causes post-operative sensitivity and tubules can collapse inward
most bonding agents contain a solvent which drives off moisture so no need to worry about wet surfaces
Why would a lesser filled composite/ more flowable composite be used as a liner?
a lesser filled composite will reduce contracion stresses
How is the composite placed?
in increments touching as few surfaces as possible (low CF)
What should the final increments not join?
enamel margins
What techniques of curing should be used for different goals?
- High Power for fast,
- Low Power for close-to-pulp
- Soft Start for polymerisation with reduced contraction stress
What are the methods of countering contraction stresses?
Strategic Incremental (Cuspal Build-up, C-Factor considerations)
Flowable composite
Warm composite
Curing regime (Intensity, timing and vector)
What is the shrinkage direction determidned by?
bonded surfaces and free surfaces
When do composities shrink towards the light?
when bonding fails
What tool can help with placing composite shell?
silicone matrix
What is placed between inscial teeth to avoid contact?
proximal strip
What is placed between occlusal teeth to avoid contact?
sectional matrix and wedge in place
What should be done after each increment is placed?
curing
What should be removed after the mesio-distal side of the tooth has been restored?
matrix removed
