Materials Science 7 Flashcards
COMPOSITE RESINS
¢ Esthetic Direct Restorative
¢ Cured by Visible Light
¢ Primary Benefit is the Combination of Esthetics and
Ease of Placement
¢ Moderate Clinical Outcomes
Amalgams -Easy to Place
-Excellent Clinical Outcomes -Poor Esthetics
Ceramics -Good Esthetics
-Excellent Clinical Outcomes -More Difficult to Process
WHAT IS A COMPOSITE?
¢ Hybrid Material of an organic phase (resin) and an Inorganic (filler) phase
WHY DO WE USE COMPOSITES?
¢ Teeth are Composites
¢ Advantages of Both Organic and Inorganic
Components
¢ Easily Processed and Handled - Allows for Direct Restorations
ORGANIC-INORGANIC HYBRID
¢ Organic Polymers Tend to be Tougher but not as
Strong or Wear Resistant
¢ Inorganic Materials Tend to be Strong and Wear Resistant but Brittle
POLYMERIZATION OF RESIN
¢ Visible Light Curing is the Second Component of the ‘Ease of Use’
¢ Command Set – Allows for Long Working Time
¢ Curing Develops Mechanical Properties
¢ One of the Most Important Processes in Dental
Polymers
¢ Also Called Crosslinking
HOW TO CHANGE CROSSLINK DENSITY
¢ Number of Crosslinking Groups
¢ Degree of Crosslinking or Degree of Curing
TYPES OF CURING
¢ Mixing(Chemical)
Operator Dependent – Working Time No Special Tools
Chairside
¢ Heat
Consistent, High Degree of Cure Not good In Vivo
¢ Light
Command Cure
Good In Vivo
Lower Degree of Cure – Limited Thickness
COMPONENTS OF COMPOSITE RESIN
¢ Resin System
¢ Filler
¢ Bonding Agent
¢ Visible Light Initiator
CHARACTERISTIC POLYMER BONDS
¢ Covalent bonds
¢ High molecular weight
¢ Long molecules composed principally of nonmetallic
elements (organic chemistry C,O,N,H)
Polymers are Entangled Long Chains “Cooked Spaghetti”
Derive Strength and Properties From the Entanglement
RESIN SYSTEMS
¢ Resin System Allows for the Relative Ease of
Processing
¢ Unpolymerized Resin Like Honey – Flows
¢ BisGMA Provides the Physical Properties
¢ Viscosity Very High and Cannot be Used Alone
¢ Reactive Diluent Such as TEGDMA used in 30-50
wt%
Filler
¢ Silica or Zirconia Based Inorganics ¢ 50-80 wt% of the Composite
¢ Has Surface Hydroxyl Groups
TYPES OF FILLERS
¢ Micron (Fine)
¢ Nano (Microfine)
¢ Nano (Microfine) in Polymer Matrix
WHY SMALLER FILLER SIZE?
¢ Teeth are Nanocomposites
¢ Smaller Fillers Should have Better Wear
Properties
¢ Allows for betting Polishing and Finish
¢ Expectation of Better Mechanical Properties
MICRON (FINE) PARTICLES
¢ Early Composites Had 20-30 μm Filler Particles ¢ Fine Fillers 3-0.5 μm
¢ Can be loaded at 77-88 wt percent in a Composite
NANO (MICROFINE) FILLER
¢ Typically 0.2-0.04 μm in Size ¢ Very High Surface Area
¢ Tendency to Aggregate
¢ Maximum Loading 38 wt%
NANO (MICROFINE) IN POLYMER MATRIX
¢ Microfine Fillers Polymerized in Matrix and Ground to 20-30 μm Particles
¢ Allows for Inorganic Loading up to 50-60 wt %
¢ Reduces Aggregation
¢ Poorer Filler to Matrix Bonding - No Coupling Agent
HYBRID COMPOSITES
¢ Mixtures of Filler Sizes
¢ Can Take Advantage of Having Some Microfill ¢ Still have Loading of 70%
POLYMERIZATION SHRINKAGE
¢ Results from a Density Change of Monomer to Polymer ¢ Inherent Property of Double Bond Polymerization
Measured by Density Change (Dilatometer)
¢ Important for Direct Composite Restoratives
¢ Important for any Material that Required Dimensional
Stability
EFFECTS OF POLYMERIZATION SHRINKAGE
¢ Causes Stress on the Tooth Structure
¢ Can Cause Microleaks and Lead to Secondary Carries
WATER SORPTION
¢ In Filled Systems Water Sorption is 0.3 to 0.9 (mg/
cm2)
¢ In Unfilled Systems 2 (mg/cm2)
¢ Source: Craig, R.G. Restorative Dental Materials
8th ed. Pg 264
GLASS-IONOMER CEMENT
Two Component Cement Acidic Polymer in Aqueous Solution Basic Glass ¢ Cured by Acid-Base Reaction ¢ Releases Fluoride ¢ Good Adhesion to Tooth Structure
COMPONENTS OF A GLASS IONOMER
¢ Polyacid
¢ Basic Glass
¢ Water
¢ Modifiers (+) tartaric acid
BASIC GLASS
¢ Aluminafluorosilicate Glass ¢ Components Sintered at 1100-1500 oC ¢ Molten Glass Poured on Metal Surface and Cooled in Water ‘Shock Cooling’ ¢ Ground into 45 μm particles
SETTING REACTION
Poly Acid Will React with the Basic Glass
¢ Not all Glass Is Consumed in the reaction
¢ Salt Bridges will form from the Polyacid and
Glass
¢ Still Not a Well Characterized Process
FLUORIDE RELEASE
¢ Sodium and Fluoride ions will Be Released Upon Setting
¢ They will Continue to be released over Time
¢ Mechanism of Release not Clearly understood
¢ Erosive or Diffusive Mechanism or Both
RESIN MODIFIED GLASS IONOMERS
¢ Hybrid Between Glass Ionomer and Compostie Resin
¢ Has Both VLC and Acid-Base Curing Mechanisms
¢ Increases Physical Properties
¢ Decreases Initial Solubility of GI in Solution
