Lecture 4

Question 1

primary bonds

Answer 1

ionic
covalent - strongest
metallic

Question 2

secondary bonds

Answer 2

Hydrogen bonding
van der waals
(no electron sharing)

Question 3

example of ionic bond

Answer 3

CaSO4H2O - calcium sulfate dihydrate

ZO2MgO2 - zinc phosphate cement

Question 4

covalent bond

Answer 4

electron sharing by adjacent atoms

ex) H2, Dentin resin

Question 5

4 valence electrons

Answer 5

sp3

Question 6

metallic bond

Answer 6

electron sharing/formation of gas electrons

becomes + charged because of gas electrons

Question 7

hydrogen bonding

Answer 7

permanent dipole that represents an assymetric molecule

Question 8

van der waals forces

Answer 8

WEAK
electrons are equally distributed
fluctuating dipole will attract other similar dipoles

Question 9

space lattice

Answer 9

any arrangement of atoms in space in which every atom is situated similarly to every other atom.
(can be 1’ or 2’ bonds)

Question 10

Crystalline

Answer 10

amalgam, cast alloy, wrought metal, gold foil, dental amalgam, pure ceramics - alumina, zirconia.
Other ceramics like dental porcelains consists of noncrystalline glass matrix and crystalline inclusions that provide desired properties including color, opacity, and increase in thermal expansion coefficients, radiocapacity, strength, fracture toughness.

Question 11

supercooled liquids

Answer 11

glass is non-crystalline, short-ranged order

crystalline is long ranged order

Question 12

non-crystalline vacant position

Answer 12

in non-crystalline, High energy atom will be next to vacant position

Question 13

self-diffusion

Answer 13

atoms change position in pure, single-element solids even under equlibrium condition

Question 14

adhesion

Answer 14

unlike molecules are attrached to each other
soft tissue to saliva
saliva to dentuse
plaque/calculus to tooth

Question 15

cohesion

Answer 15

molecules of same kind are attracted

Question 16

material to which adhesive is applied

Answer 16

adherend

Question 17

micromechanical bonding

Answer 17

because of no truly adhesive material,
By retention rather than molecular attraction
velcro effect
Friction

Question 18

surface of solid has greater energy

Answer 18

True

because not uniform attraciton

Question 19

acid-etching technique

Answer 19

expose to phosphoric acid for short time before inserting resin to improve mechanical retention.

Question 20

greater surface energy greater

Answer 20

the capacity for adhesion

Question 21

surface tension

Answer 21

the increase in energy per unit area of surface

Question 22

chemisorption

Answer 22

when chemical bond is formed between adhesive and adherened.
ex) oxide film formed on the surface of metal or a layer of solder bounded to a metallic substrate.
(van der waals is weaker than primary bonding b/c they are intermolecular rather than intra)

Question 23

wetting

Answer 23

ability for material to spread on another

Question 24

attraction is negligible when the surface molecules are separated by distances greater than 0.7nm

Answer 24

True

Question 25

failure when wetting is perfect?

Answer 25

failure in such instances occur cohesively in the solid or in the adhesive itself.

Question 26

Low SE liquid okay with High SE solids

Answer 26

true

Question 27

contact angle

Answer 27

the angle formed at the interface of the adhesive and the adherend ex) no contact angle formed if adhesive and adherend are attracted perfectly

Question 28

adhesion is stronger than cohesive forces.

Answer 28

true

Question 29

contact angle

Answer 29

``` 0 = water on glass high = water on teflon ```

Question 30

contact angle >90degree

Answer 30

hydrophobic | Add hydrophilic or wetting agent to improve

Question 31

no wetting occurs at 180'

Answer 31

true

Question 32

smear layer

Answer 32

surface contamination

Question 33

greatest problem with bonding to tooth

Answer 33

inadequate removal of etching debris and contamination by water,saliva