Materials Science 7

Question 1

COMPOSITE RESINS

Answer 1

¢ 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

Question 2

WHAT IS A COMPOSITE?

Answer 2

¢  Hybrid Material of an organic phase (resin) and
an Inorganic (filler) phase

Question 3

WHY DO WE USE COMPOSITES?

Answer 3

¢ Teeth are Composites
¢ Advantages of Both Organic and Inorganic
Components
¢ Easily Processed and Handled - Allows for Direct Restorations

Question 4

ORGANIC-INORGANIC HYBRID

Answer 4

¢ Organic Polymers Tend to be Tougher but not as
Strong or Wear Resistant
¢ Inorganic Materials Tend to be Strong and Wear Resistant but Brittle

Question 5

POLYMERIZATION OF RESIN

Answer 5

¢ 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

Question 6

HOW TO CHANGE CROSSLINK DENSITY

Answer 6

¢ Number of Crosslinking Groups

¢ Degree of Crosslinking or Degree of Curing

Question 7

TYPES OF CURING

Answer 7

¢ 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

Question 8

COMPONENTS OF COMPOSITE RESIN

Answer 8

¢ Resin System
¢ Filler
¢ Bonding Agent
¢ Visible Light Initiator

Question 9

CHARACTERISTIC POLYMER BONDS

Answer 9

¢ 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

Question 10

RESIN SYSTEMS

Answer 10

¢ 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%

Question 11

Filler

Answer 11

¢ Silica or Zirconia Based Inorganics ¢ 50-80 wt% of the Composite
¢ Has Surface Hydroxyl Groups

Question 12

TYPES OF FILLERS

Answer 12

¢ Micron (Fine)
¢ Nano (Microfine)
¢ Nano (Microfine) in Polymer Matrix

Question 13

WHY SMALLER FILLER SIZE?

Answer 13

¢ Teeth are Nanocomposites
¢ Smaller Fillers Should have Better Wear
Properties
¢ Allows for betting Polishing and Finish
¢ Expectation of Better Mechanical Properties

Question 14

MICRON (FINE) PARTICLES

Answer 14

¢ 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

Question 15

NANO (MICROFINE) FILLER

Answer 15

¢ Typically 0.2-0.04 μm in Size ¢ Very High Surface Area
¢ Tendency to Aggregate
¢ Maximum Loading 38 wt%

Question 16

NANO (MICROFINE) IN POLYMER MATRIX

Answer 16

¢ 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

Question 17

HYBRID COMPOSITES

Answer 17

¢ Mixtures of Filler Sizes

¢ Can Take Advantage of Having Some Microfill ¢ Still have Loading of 70%

Question 18

POLYMERIZATION SHRINKAGE

Answer 18

¢ 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

Question 19

EFFECTS OF POLYMERIZATION SHRINKAGE

Answer 19

¢ Causes Stress on the Tooth Structure

¢ Can Cause Microleaks and Lead to Secondary Carries

Question 20

WATER SORPTION

Answer 20

¢ 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

Question 21

GLASS-IONOMER CEMENT

Answer 21

Two Component Cement
—  Acidic Polymer in Aqueous Solution
—  Basic Glass
¢  Cured by Acid-Base Reaction
¢  Releases Fluoride
¢  Good Adhesion to Tooth Structure

Question 22

COMPONENTS OF A GLASS IONOMER

Answer 22

¢ Polyacid
¢ Basic Glass
¢ Water
¢ Modifiers (+) tartaric acid

Question 23

BASIC GLASS

Answer 23

¢  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

Question 24

SETTING REACTION

Answer 24

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

Question 25

FLUORIDE RELEASE

Answer 25

¢ 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

Question 26

RESIN MODIFIED GLASS IONOMERS

Answer 26

¢ 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