dental2.3

Question 1

what are colloids

Answer 1

substances with 2 or more phases with at least of of the phases having a dimension greater than simple molecular size

Question 2

e.g of colloids systems

Answer 2

gels
films
emulsions
foams

Question 3

typical colloidal system

Answer 3

sol- colloidal particles dispersed in a L), when chilled or reacts it can be transformed into gel
gel- hydrophilic

Question 4

what are alginate gels in colloids system

Answer 4

are used as flexible impression metals

are hydrocolloids - particle in h20 that bind with h20 and 1 other substance

Question 5

what is thermal conductivity

Answer 5

quantity of heat passing through a material 1cm thick with a cross section of 1 cm2, having a temp difference of 1’c

Question 6

what is thermal diffusivity

Answer 6

measure of heat transfer of a material in the time dependent state

Question 7

what is linear coefficient of-thermal expansion

Answer 7

change in length per unit compared to original length for a 1’c temp change
dentine- 8,3 х 10-6/оС
enamel enamel is 11,4 х 10-6/оС

Question 8

what is percolation

Answer 8

pumping of oral fluid in and out of tooth restoration interface because the restoration expands as the temp changes.
percolation occurs when the thermal expansion coeff is markedly diff from the tooth structure

Question 9

what is electrochemical series

Answer 9

listing of elements that have the tendency to lose or gain electrons in a solution

Question 10

what is a noble metal

Answer 10

has a large positive electrode potential
are resistant to oxidation and corrosion in the oral cavity
e.g platinum and gold

Question 11

electrolytic metals (reaction)

Answer 11

occur when 2 metals with large electrode potential diff are put in the same solution

causes great discomfart

Question 12

what is the electromotive series

Answer 12

listing of electrode potentials of metals according to the order of their decreasing tendency to be oxidises in a asolution

Question 13

what is a short circuit

Answer 13

when 2 opposite filings contact each other

Question 14

what is galvanism

Answer 14

is. due to diff in potential between dissimilar fillings is opposing or adjacent teeth
sensitivity of patient also contributes to how much pain is felt

Question 15

what is a dielectric

Answer 15

material that provide electrical insulation

dentine- 8.6 constant

Question 16

tarnish and discolarisation

Answer 16

process of steam sterilization of surgical equipment can cause corrosion. and many nonmetal material e.g cement display discolor in service because coloured substances penetrate the material

Question 17

setting time

Answer 17

varies depending on the application

does not indicate the completion of the reaction

Question 18

shelf life

Answer 18

general deterioration in quality of materials during shipment and storage

Question 19

what is a metal

Answer 19

cfrystalline matreialconsists of positively charged ions in a closely packed arrangement and bonded with a cloud of free electrons. the metalic bond is responsible for many of the properties of metals: electrical and thermal conductivity, high strength.​