Materials Science 3 Flashcards
SEALANTS
¢ Polymeric Coating to Protect Teeth
¢ Flowable Resin That is Light Cured
¢ Designed to Flow into Pits
¢ Seal Tooth Surface to Prevent Further Decay ¢ Etching is Recommended to Prepare Enamel ¢ Balance between Flow and Sealing Capability
SEALANT CHEMISTRY
Considered a Preventive Material
¢ Usually a BisGMA-TEGDMA system but no Filler
¢ Low Viscosity – Easy to Flow and Coat a Surface
BONDING
¢ Bonding is Mostly Mechanical
¢ Not Designed for Longevity
¢ Etching Creates a Clean, Rough Surface
BOND TO ENAMEL
Macrotags Interprism resin penetration ¢ Microtags Intraprism resin penetration ¢ Microtags provide the major retention
OXYGEN INHIBITION LAYER
¢ Oxygen Interferes with Radical Polymerizations
¢ Surface of VLC Materials are often Uncured
¢ For thin Layers such a Sealants more of a Problem
ADHESIVES
¢ Based on Composite Resin Chemistry
¢ Contains Acidic Groups to Promote Bonding ¢ Dimethacrylates that Are Visibly Light Cured ¢ Unfilled or Lightly Filled
REQUIREMENTS FOR GOOD BONDING
¢ Flowable
¢ Compatible With Both Surfaces Surface Energy
Forming Bonds or Interactions
¢ Mechanical Properties ¢ Long-Term Stability
Resin
Increase in Mechanical Properties = Increase in
Viscosity
Increased Filler Loading
Decreases Flowability (Increases Viscosity) Improves Mechanical Properties
BONDING TO TUBULAR DENTIN
Smear layer created from preparation Ground collagen and HA Adhered to surface ¢ Interferes with bonding
TRADITIONAL STEPS FOR DENTIN BONDING
¢ Etch
¢ Prime
¢ Adhesive
¢ Restoration
¢ 30 sec etch with 37% H3PO4
¢ Rinse
PRIMER
Hydrophilic Monomer
To Stabilize Dentin
Followed by Adhesive and Composite
TWO OR ONE STEPS
Most Current Adhesive Systems Require Only
One or Two Steps
¢ Combine Etchant and Primer
¢ Combine Etchant, Primer and Adhesive
¢ All These Components are Based on Methacrylate Monomers
CEMENTS, LINERS AND BASES
¢ In Dentistry Cements, Liners and Bases describe more of a Function than a Specific Class of Materials.
¢ Often There is Overlap Between the Function and Chemical Classification
¢ Cements also refer to a Type of Materials such as a Glass-Ionomer Cement
¢ Confusing because a Glass-Ionomer Cement can be used as a Base.
¢ Glass-Ionomers can be Cements and a Base
¢ Zinc Oxide Eugenol (ZOE) can be a cement, liner
and a Base
¢ Calcium Hydroxide can be a liner and a Base
Water-Based Cements
Glass-Ionomers
Resin Modified Glass-Ionomers Zinc Phosphate
Zinc Polyacrylate
Resin Based Cements
Composites
Compomers
Oil Based Cements
Zinc Oxide Eugenol
Curing mechs.
CURING MECHANISMS
¢ Sometimes Light Cure Not Possible ¢ Cold-Cure for Methacrylate
¢ Water Cure for Cements
REQUIREMENT FOR CEMENTS
¢ Low Viscosity but Good Mechanical Properties
¢ 25 μm Thickness
HOW TO BALANCE MECHANICAL PROPERTIES AND VISCOSITY?
¢ For Glass-Ionomers it is the Powder to Liquid Ratio
¢ Powder = Filler
¢ More Filler = More Viscosity More Filler = More Modulus
¢ This concept is true for most Materials that Are
Set by Mixing a Powder and Liquid
¢ ZOE, Calcium Hydroxide
¢ Low Powder to Liquid also Increasing Working and Setting Time
4-META MODIFIER
¢ Additive to Promote Bonding
¢ Very Common in Resin Adhesives
¢ Manufactures will Tailor Cements to Products
ZINC PHOSPHATE
¢ ZnO + H3PO4 = Zn3(PO4)2
¢ Used for Crowns
¢ More of Legacy Material?
¢ Handling Can be Controlled by Powder to Liquid Ratio
ZINC POLYACRYLATE (POLYCARBOXYLATE)
¢ Polyacid + ZnO = Cement
¢ Zn is only Divalent
¢ More of a Legacy Material
¢ Controlled by Powder to Liquid Ratio
LINER
¢ A relatively thin layer of material used to protect the dentin from residual reactants that diffuse out of the restoration or oral fluids that may penetrate leaky restoration interface
¢ Thin Layer so Materials are Lower Viscosity
¢ Solution liners (2-5μm)
Copal varnish-under Amalgam Adhesives- under composites
¢ Suspension Liners (20-25μm)
CaOH2 (Dycal)-under Ag or Comp
¢ Cement Liners (200-1000μm)
GI (KetacCem), RMGI (vitrebond) Under amalgam (Ag) or Composite
