DMS Flashcards
What is the smear layer?
An adherent layer of organic and inorganic debris - remnant of the dentine surface after preparation of the dentine
Describe self etch
Incorporates the smear layer
1 stage
Uses Scotch bond I
Describe total etch
Removes the smear layer in 2 stages:
Etch
Prime and bond
How is the hybrid layer formed?
37% phosphoric acid etch removes the smear layer exposing the collagen network
Primer penetrates collagen network making the surface hydrophobic
Adhesive resin forms micro mechanical adhesion with tubules and exposed collagen network
What products are found in composites?
Resins Camphorquinone Low weight methacrylates Silane coupling agents Filler particles
What resin is commonly found in composite?
Bis-GMA
What is camphorquinone?
A blue light photoinitiator
What role do low weight methacrylates play in composite?
Improves viscosity and reactivity
What role do silane coupling agents play in composite?
Provides good bond between filler particles and resin
What filler particles are commonly used in composite?
Glass
What reaction takes place in the setting of composite?
Free radical addition polymerisation
What are the advantages of light cured composite?
Extended working time Less finishing Can be finished immediately Less waste Less porosity
What are the disadvantages of light cured composite?
Absorption/light spectrum mismatch Cure prematurely under dental light Depth of cure is optimistic Polymerisation shrinkage can occur Recommended setting times may be too short Ocular damage Soft tissue damage
What is the depth of cure of composite?
2mm
What is the bond strength of composite?
40MPa
Give some advantages of using composite
Strong - 350MPa Rigid - 15GPa Abrasion resistant Low thermal conductivity Can be light cured on demand
What liquid is used in amalgam?
Mercury
What are the powder constituents of amalgam and why is each element used?
Tin - intermetallic compound Silver - intermetallic compound Zinc - scavenger (removes impurities) Copper - increased strength and hardness Mercury - increases rate of reaction
What are the different types of amalgam particles?
Lathe-cut
Spherical
Describe the amalgam setting reaction
Powder and liquid react to form the amalgam matrix (Gamma-1 and Gamma-2) alongside unreacted particles (Gamma)
Describe Gamma, Gamma-1 and Gamma-2
Gamma - strong, corrosion resistant
Gamma-1 - not strong, corrosion resistant
Gamma-2 - not strong, not corrosion resistant
Describe copper enriched amalgam
Contains more than 6% copper
No Gamma-2 phase
What are the advantages of copper enriched amalgam?
Increased strength
Increased corrosion resistance
Higher marginal integrity
Less creep
What are the advantages of amalgam?
Strength - 500MPa Abrasion resistant Viscosity ideal for packing Radiopaque Okay working time
What are the disadvantages of amalgam?
Poor aesthetics Not anti cariogenic Experiences creep Corrosion Microleakage can occur
Describe creep
Repeatedly stressed for a long time
This results in flow and permanent deformation
Amalgam sits proud of the surface and vulnerable to fracture
Who should amalgam not be used on?
Children under 15
Pregnant women
Breastfeeding women
What do cavity lining materials allow protection from?
Unreacted chemicals
Thermal stimuli
Bacteria and endotoxins
What are the ideal properties of a cavity lining material
Low thermal conductivity Thermal expansion coefficient similar to dentine High compressive strength Radiopaque Low solubility Cariostatic Biocompatible
What are the most common lining materials?
Calcium hydroxide
GI and RMGIC
What is GI made up of?
Acid - polyacrylic acid and tartaric acid
Powder - Mainly silica
What are the setting phases of GI?
Dissolution
Gelation
Hardening
Describe Dissolution of GI
Acid is added to solution
H ions attack the glass surface
Ca, Al, Na and F ions are released
Left with silica gel around unreacted core particle
Describe Gelation of GI
Calcium ions released are bivalent so cross linking occurs
Polyacrylic acid reacts with carboxyl groups to form calcium polyacrylate
Describe Hardening of GI
Trivalent aluminium ions cross link to increase strength
This forms aluminium polyacrylate
Starts after 30 minutes and can last up to a week
What is RMGIC made up of?
Powder - Glass
Acid - Polyacrylic acid, tartaric acid, HEMA (monomer), water
Describe the setting reaction of RMGIC
Acid base reaction takes several days
Redox reaction takes 5 minutes
Free radical polymerisation reaction (light activated) takes 20 seconds
What are the advantages of GI?
Release flouride Forms chemical bond to enamel and dentine Little microleakage occurs Good thermal properties No contraction on setting
What are the disadvantages of GI?
Brittle Poor wear aesthetics Poor handling characteristics Poor aesthetics - opaque Moisture dependant
What are the advantages of RMGIC?
Releases flouride Forms a chemical bond to enamel and dentine Little microleakage occurs Better physical properties than GI Better handling properties than GI Lower solubility than GI Better translucency and aesthetics Stronger
What are the disadvantages of RMGIC?
Polymerisation contraction takes place
Monomer leaching - uncured HEMA can be toxic to the pulp
Reduced strength from uncured material
Exothermic acid base reaction
Swelling due to uptake of water due to HEMA
What is used clinically as a setting calcium hydroxide liner?
Two pastes - a base and a catalyst
eg - Life or Dycal
When is Zinc Oxide Eugenia Cement used?
Linings in deep cavities
Temporary restorations
Root canal sealer
Periodontal dressing
What are the properties of ZOE?
Adequate working time Relatively rapid setting time Low thermal conductivity Low strength Radiopaque High solubility
What are the properties of calcium hydroxide?
Quick setting time Radiopaque Easy to use Low compressive strength Unstable and soluble
What should be done after placing a calcium hydroxide lining?
Should be covered with RMGIC prior to a final restoration being placed to protect the calcium hydroxide and prevents its dissolution
What glass ionomer is used clinically?
Vitrebond
