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
Pulp capping
¢ Near exposure RDT <0.5 mm Indirect pulp cap ¢ Pulp exposure Direct pulp cap Apply Calcium Hydroxide (CaOH2) liner
Defensive reparative dentin
15 days -cells differentiate
30 days-microscopic reparative dentin 100 days -radiographic reparative dentin
CAOH2 LINERS
¢ Paste(CaOH2)/Paste (polyphenolics)
¢ Acid - base reaction
¢ Ca+ ions act to crosslink polyphenol groups ¢ Insulator
¢ High solubility (10-30% vol loss in 10yrs) ¢ Stimulates reparative dentin
Works by: ¢ Release hydroxide ions (pH>11)
¢ When ionized in low concentration Stimulateodontoblastformation
¢ Dycal-brand name
REINFORCED ZOE
¢ IRM (intermediate Restorative Material)
¢ B&T (base and temporary)
Reinforced fillers (PMMA beads-powder)
ZnO (powder)
Eugenol (liquid) oil of clove
¢ Oil of clove acts as obtundent (dulls pain) ¢ Expands when set –seals
¢ *cannot use under composite ¢ *Inhibits polymerization
BASES
¢ Are used to provide thermal protection for the pulp and to supplement mechanical support for the restoration by distributing local stresses from the restoration across the underlying dentin surface during amalgam condensation (or cementation of indirect restorations)
¢ Require Greater Mechanical Properties
All water based and acid-base reactions
ADVANTAGES OF GLASS IONOMER
¢ Adheres to tooth structure Mineralportion Dynamicionicprocess ¢ Fluoriderelease ¢ Proven clinical record of retention Better than composite ¢ Dimensionally stable ¢ Biocompatible
DISADVANTAGES OF GLASS IONOMER
¢ slow setting ¢ early dissolution ¢ optical properties ¢ stain resistance ¢ poor physical properties
WAXES
¢ Temporary Materials
¢ Should Melt at Lower Temperatures ¢ Be Carveable
¢ Burn off
¢ Dimensionally stable
DIMENSIONAL STABILITY
¢ Desirable So That Restoration is Accurate
¢ Wax is Normally Used Above Tm Then Cooled
¢ Above Tm Thermal Expansion Coefficient is Large
