Flashcards in Dental Materials Deck (293)
What are the 2 types of lab research?
1. In vitro
2. In vivo
What 5 basic factors are tested in in-vitro testing?
1. Physico-mechanical properties
2. Biological properties: cytotoxicity; organ, tissue, cell cultures
3. Genotoxicity: damage to genetic info causing mutations
4. Oestrogenic activity
5. Basic sciences: efficacy and safety of therapeutic, rehabilitative, preventative regimes
What kind of tests are done in-vivo?
Implants: material implanted into animal
Limited usage studies: animal/clinical testing; long, tedious but most clinically relevant
What types of animal tests are there?
Past: material ground and fed to animal; implanted into animal
Now: material used in required area
Why is clinical testing preferred?
Most accurate and efficacious depending on:
Number of patients
Group of patients
Length of trial
What is the downfall of clinical testing?
Clinical symptoms don't evaluate real world damage
Will have material in OC for years not weeks
What are some of the ways in which post-market surveillance is important?
Provide early warning signs of unsuspected adverse effects
Elicit predisposing factors to adverse reactions
Compare adverse reactions between similar products
Permit continued safety monitoring
Who are at risk of adverse reactions from DMs?
Who is most at risk of adverse reactions to DMs? Why?
Inc. risk as inc. exposure to material
How can risks be reduced?
Following manufactures instructions
Non-contact operative techniques
What are the 3 main types of force?
What are the 3 types of uniaxial force?
1. Tensile: away from each other
2. Compressive: towards each other
3. Shear: towards, one from top side other from bottom side
What are forces defined by?
Where they are applied, in what direction and how big they are
What is stress?
Force applied per unit area
Deformation of object due to stress
What is Hooke's law?
Stress is proportional to strain
What is Young's modulus?
Ratio of stress to strain i.e. stress/strain is a pressure (Pa)
What can be determined from a stress-strain curve?
Ductility, strength, elastic modulus, resilience, toughness, flexibility
What is a fracture?
Separation of a material into 2+ pieces under action of stress
What are the 2 types of fracture?
Brittle: little/no plastic deformation, low toughness
Ductile: significant plastic deformation, high toughness
What are the steps in a fractureb
1. Crack formation
2. Crack propagation
Describe the stress-strain plot for a brittle material
Almost linear due to low plastic deformation
Describe a direct tensile measurement
Dumbbell shaped test specimens, ensures central fracture
Used for metals, rigid polymers, rubbery polymers
What are compressive tests used for?
What is a diametral/indirect tensile test?
Compression across diameter
What are the 6 static strengths?
6. Diametral tensile
What is hardness?
Resistance to indentation/permanent deformation when compressive force applied
What is fracture toughness?
Resistance of a material to failure from fracture starting at pre-existing crack
Define tear strength and energy
Strength: force needed to initiate/continue tearing
Energy: measure of energy per unit area of newly torn surface