DMS summary - restorative materials Flashcards
What is etchant also known as
dentine conditioner
What is in etchant
34% phosphoric acid
What are the functions of etchant
Removes smear layer
Opens dentine tubules
Decalcifies the uppermost layer of dentine
Exposes collagen network for penetration
What type of molecule does a primer contain
Bifunctional molecule that has a hydrophilic and hydrophobic end to connect the hydrophilic tooth to the hydrophobic resin.
What is an example of a bifunctional molecule used in primers
HEMA
What is adhesive made of
a mixture of resins
usually bis-GMA or HEMA
What is the function of adhesive
it is a resin which penetrates into the surface of dentine and will attach to the hydrophobic part of the primer. This then allows the composite to bond
What is the brand name for primer in GDH
Prime and Bond NT
What are the constituents of composite resin
resin glass filler particle camphorquinone silane coupling agent low weight methacrylate
What is the function of the resin in composite
Allow for composite to be moulded
Facilitates the cross linking
What is an example of a resin used in composite
bisGMA
What is the function of glass filler particle in the composite
Gives strength and hardness
More filler = stronger but also more viscous
What is an example of a glass filler particle
quartz
What is the function of camphorquinone in composite
Allows for light activation (blue light)
Initiates the free radical addition polymerisation reaction
What is the function of the silane coupling agent
Allows for good bond between filler particle and resin as water adheres to glass so stops the two from coming together nicely
What is the function of low weight methacrylates
Adjusts viscosity and reactivity
What are different types of composite
Glass filler types - fine, microfilled, hybrid (both)
Curing method
Area of use
Handling characteristics
What are good properties of composite
its generally strong (not as strong as amalgam though except for in tensile strength)
good aesthetics
low thermal conductivity (less than amalgam)
command set
bonds to tooth so allows for more conservative preparations
What are the not so good properties of composite
Shrinkage is an issue for composite (due to polymerisation)
High thermal coefficient - a gap forming between tooth and material is dependant on bond strength
Technique sensitive - requires good moisture control
When is composite useful
Restorations - especially when not large
Anterior restorations
Veneers
Temporary restorations (especially when wanting to preserve aesthetics)
What is composite not so useful for
You have restorations very near the gingival margin or subgingivally, will be difficult to get moisture control
Very large restorations will experience more polymerisation shrinkage - increments are important
Also not available on NHS for posterior restorations
What does amalgam consist of
powder & liquid
What is the constituents of amalgam powder
intermetallic compound (silver+tin)
copper
zinc
mercury
What is the formula for intermetallic compound
Ag3Sn
What is the function of the intermetallic compound in amalgam powder
it reacts with mercury
What is the function of copper in amalgam powder
increases strength and hardness
What is the function of zinc (if present in amalgam powder)
scavanger
What is the function of mercury in amalgam powder
Found in pre-amalgamated alloys to allow for a quicker reaction
What type of amalgams is mercury seen in the powder
pre-amalgamated
What is the function of mercury in the liquid
Triple distilled to ensure purity
What are different types of amalgam
lathe cut, spherical and admixed
copper enriched
What is the setting reaction for amalgam
Ag3Sn (γ) + Hg –> Ag3Sn (γ) + Ag2Hg3 (γ1) + Sn7Hg9 (γ2)
What does Ag3Sn provide amalgam with
strength + corrosion resistance
What does Ag2Hg3 provide amalgam with
corrosion resistance
What does Sn7Hg9 provide amalgam with
weak and poor corrosion resistance
What are good properties of amalgam
strong (poorer when initially setting)
high abrasion resistance (v hard)
lowest failure rate
What are not so good properties in amalgam
Prone to creep - makes it protrude at margins and prone to fracture
High thermal conductivity - requires a liner
Doesn’t bond to tooth - requires more tooth prep
Prone to corrosion - weakens tooth at margins (but is reduced by copper enriched alloys)
How may amalgams strength be reduced
Undermixed Too much mercury after condensation Too low condensation pressure Slow rate of packing so increments dont bond Corrosion
What is amalgam useful for
Useful for large cavities especially posteriorly were loads are high
What is amalgam not so useful for
small cavities (would need to extend prep) and for anterior restorations
Who is amalgam contraindicated in
Deciduous teeth
Under 15s
Pregnant women
Breastfeeding women
