compound structures Flashcards
What are properties of enamel and dentine?
Elastic modus- E=85GPa, D=15GPa
Fracture strength- E=10MPa, D=50MPa
Compressive strength- E=400MPa, D=300MPa
What needs to be considered in compound structures?
Structure
Form
Colour/shade
Resist para/functional forces
Resist wear and degradation
Resist static and dynamic fatigue
NEED TO RESTORE COMPOUND STRUCTURES W COMPOUND SYSTEMS
How do we aim to restore the compound structure of teeth?
Use compound systems w desirable properties
Careful biomechanic design considerations
Effective and reliable adhesive interface assembly
What are relevant properties of restorative materials?
Elastic modulus
Compressive strength
Flexural strength
Fracture toughness
Coefficient of thermal expansion
Hygroscopic expansion
Wear and fatigue
What is the coefficient of thermal expansion?
The size of an object changes with a change in temp
Tooth= 10ppm/C
Composite= 500ppm/C
What is a composite material?
A single entity containing 2+ constituent phases
What do composite fillers do?
Reduces polymerisation shrinkage
Limits fracture propagation
Increases wear resistance
Improves optical properties
What is a compound system?
A function unit comprising 2+ constituent materials
Eg. Porcelain bonded to metal crown
How are materials joined in a compound system?
Specific adhesion
Micromechanical adhesion
Mechanical interlocking
Moulding base material
Casting second material
Welding
Soldering
Adhesives
What are useful interactions between materials?
Complementary properties
Mechanical protection
Adhesion
What are unwanted interactions between materials?
Electromechanical corrosion
Mismatched thermal expansion interface damage
Unstable dimensional form
What are the ideal properties of enamel replacement?
High elastic modulus
Tooth coloured
Reliable bonding mechanism
High strength
Abrasion matched to enamel
Restart to mechanical and static fatigue
What are the ideal properties of dentine replacement?
Low elastic modulus
Adhesive
Resilient to absorb shocks
Fluoride releasing
Resistant to degradation
What are the constructional forms?
Block form eg. Intra coronal restoration (absorbs load into mass avoiding crack propagation)
Shell form eg. Crown (deforms slightly and supported by core)
Laminate form eg. Veneer (supported by underlying dentine)
What is the key to success?
Match system to substrate-
Correct compound system and design construct choice
Compensate for property inadequacies w design construct vice versa
Effective and reliable adhesive assembly
