Biomaterials Exam - Introduction to Biomaterials Flashcards
questions taken from lecture slides with guidance from Schricker's study guide
What are the three main classes of materials?
metals, ceramics, and polymers
Give the characteristics of metals (hard/soft, ductile/brittle, strong/weak).
hard, ductile (tough), strong
Give the characteristics of ceramics (hard/soft, ductile/brittle, strong/weak).
hard, brittle, strong
Give the characteristics of polymers (hard/soft, ductile/brittle, strong/weak).
soft, ductile (tough), weak
Do metals have high or low processing temperatures?
high
Do ceramics have high or low processing temperatures?
high
Do polymers have high or low processing temperatures?
low
True or false: Polymers tend to be used as direct processing materials.
true
What factors contribute to each materials mechanical properties?
- Atomic arrangement (crystalline vs. non-crystalline)
- Bonding
- primary (metallic, ionic, covalent)
- secondary (hydrogen, van der Waals)
- Composition (elements and phases)
- Defects
- macroscopic (pores)
- atomic scale (microflaws)
- Remember: ABCD!
What is key to metallic bonds?
Electrons!
-metallic elements have 1, 2, or 3 electrons in their outer shell and electrons are loosely bound to nucleus
What two characteristics do metallic bonds possess due to the mobility of electrons?
- thermal and electrical conductivity
- ductility (can bend without breaking)
When a metal alloy is created (mixture of 2 or more metals), how does the characteristics of the material change?
A pure metal is ductile since the atoms are all the same size and are able to slide.
An alloy is stronger, but less ductile since there are different sized atoms.
What types of bonds are associated with ceramic bonds? Are they stronger or weaker than metallic bonds?
- ionic and covalent bonds (covalent > ionic)
- both are stronger than metallic bonds
What makes up the microstructure of ceramics?
mixture of metallic and non-metallic elements
What are the most common compounds in ceramics for dentistry? What is the building block of ceramics?
- 3 metallic oxides: SiO2, Al2O3, and K2O are most common
- SiO4 tetrahedron is the building block
What makes up the microstructure of dental porcelain?
- SiO4 is the building block
- primarily a glass with some crystalline residuals (quartz and leucite)
What type of bond is found in polymer bonds?
covalent bonds
What elements primarily make-up polymers?
nonmetallic elements (C, O, N, and H)
How may polymerization be initiated?
by light, heat, and chemical mixing
Name and describe the 4 stages of chain reaction polymerization.
- Activation - free radical initiation (with light, heat, or chemical mixing)
- Initiation - free radical combination with monomer unit; double-bond opening
- Propagation - chain growth, volume decrease, shrinkage
- Termination
Name the monomer functional group needed to make a linear polymer.
monomethacrylates - each only has one polymerizable unit so it makes linear chains
Name the monomer functional group needed to make a branched and cross-linked polymer.
dimethacrylates - has two polymerizable units so it may make branched and cross-linked polymers
What is needed in a direct placement material?
- flowable material
- stable material
- trigger for setting
- rapid setting
- room temperature setting reaction
What are the pros and cons of a direct placement material?
Pros: less preparation needed, one visit
Cons: material often does not last as long
What are the pros and cons of an indirect placement material?
Pros: longevity of restoration
Cons: multiple visits needed, expensive
Metals are typically used for indirect placement with one exception. What is that exception?
amalgam
Ceramics are typically used for indirect placement with one exception. What is that exception?
cements
Are polymers generally used for direct or indirect placement?
direct placement
What is a composite?
a physical mixture of metals, ceramics, and/or polymers in order to achieve some intermediate properties between the two material types
What is the rule of mixtures?
by knowing the phases present in the structure of any material and the interfacial interactions, it is possible to predict the overall properties fairly well
When the volume of filler increases, does the strength of the material increase or decrease?
increase
When the volume of filler increases, does the modulus (stiffness) increase or decrease?
increase
When the volume of filler increases, does the viscosity increase or decrease?
increase
When the volume of filler increases, does the shrinkage increase or decrease?
decreases
When the filler size increases, does the surface roughness increase or decrease?
increase
Rank the thermal expansion coefficient from smallest to largest for polymers, ceramics, and metals.
smallest: ceramics (1-15 ppm/*C)
metals (10-30)
largest: polymers (30-600)
Rank the thermal expansion coefficient from smallest to largest for amalgam, tooth, and composite.
smallest: tooth (9-11)
amalgam (25)
largest: composite (28-35)
When a material is heated, does it expand or contract?
expand
Explain heat flow in a tooth. What are the clinical consequences of heat flow in dentistry?
- teeth are insulators due to high mineral content
- pulp can only withstand small temperature changes for a short time due to the restricted circulation of pulp which cannot dissipate heat and carry it away
Do metals have a high or low thermal conductivity?
high thermal conductivity so they need a thermal insulator-like base
Do composites have a high or low thermal conductivity?
low thermal conductivity so they do not need a thermal insulator-like base
How many dimensions define color? What are those dimensions?
3 dimensions (3D); hue, value, and chroma
What is hue?
wavelength and color (ROYGBIV)
What is value?
intensity and brightness
What is chroma?
purity and density/concentration
What is metamerism?
two objects that appear the same color under one light source and different under another light source; they have different spectral characteristics
