"Dimensional Change" is expressed as a percentage of original length and volume. How do you calculate volumetric dimensional change from the given linear dimensional change?
Linear Dimensional Change x (3) = Volumetric Dimensional Change
Which material has the coefficient of thermal expansion (the linear thermal expansion when heated 1 degree higher) that compatible with human teeth? (2)
Ceramic (8-14) and gold alloy (12-15)
- Human teeth (8-15)
- Dental amalgam (22-28)
- Composites (25-68)
What is percolation phenomenon?
The movement of oral fluid in and out via a space between two material (filling/tooth)
- in: cold->restoration contracts
- out: temp returns to normal
Remember: percolation occurs in poorly bonded restoration. It can cause pulp irritation and recurrent decay!
When will galvanism occur? How will the patients experience?
- Galvanism results from the presence of dissimilar metals in the mouth. (gold-low electrode potential, aluminum-high electrode potential)
- Patient experiences pain and metallic taste
Remember: oral fluid acts as "electrolyte"
What is "absorption" and "adsorption"?
- absorption = the "uptake" of liquid by "the bulk solid"
- adsorption = the "concentration" of molecules at "the surface of solid or liquid"
How do we observe the wettability of a solid?
by the contact angle of a drop of liquid
- low contact angle: good wetting
- high contact angle: poor wetting
How are the surface energy of the solids and the liquids that encourage good wetting?
good wetting: high-energy solid, low energy liquid
Remember: low-energy solids such as wax and Teflon
Which tooth area has the highest maximum biting force?
- molar (580 Newtons)
- decrease to incisor region
Remember: bridges/ dentures will lower biting force.
What is "stress"?
Stress is the "force" per unit "area".
Remember: There are many types of force such as compressive, tensile, shear, twisting, bending
What is "Strain"?
Strain is the "change in length per unit length" of material produces by "stress".
The elastic modulus is equal to:
the ratio of the stress to the strain in the "linear or elastic portion" of the stress-strain curve.
Remember: elastic modulus is a measure of the stiffness (high EM = very stiff)
Which materials have similar elastic modulus to enamel (1) and dentine (2)?
- enamel: gold alloy
- dentine: composite, zinc phosphate cement
Proportional limit is:
- Proportional limit is "the stress" when:
- it ceases to be linear or
- the ration of stress to strain is no longer proportional
Yield strength is:
Yield strength is "the stress" at some selected value of permanent strain.
Remember: yield strength is always higher than the proportional limit.
Which stress will the materials function in elastic manner/ plastic manner?
- elastic manner: below proportional limit or yield strength
- plastic maner: above proportional limit or yield strength
Ultimate strength is:
the stress at which fracture occurs.
- If the fracture occurs from:
- tensile stress, it's tensile strengthshear, it's shear strength
What kind of ultimate strengths are used to describe bond strength? (2)
tensile and shear strength
"Resilience" indicates the energy absorbed up to:
Remember: resilience is area under graph within proportional limit
"Thoughness" indicates the energy absorbed up to:
Remember: toughness is total area under graph