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Year 3 Prosthetics > Online stuff > Flashcards

Online stuff Flashcards

1
Q

What part of denture provides support

A

support: resistance of occlusally directed loads

- ->occlusal rests (stop mucosal damage)

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2
Q

what is bracing/ how is it provided

A

mechanical function, prevents lateral shifting of partial denture
supplied by bracing arm and rigid 2/3 of retentive clasp above survey line

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3
Q

what part of denture provides retention

A

clasp tips

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4
Q

what part of clasp enters undercut and why

A

terminal 1/3

stop damage to tooth/peri tissues

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5
Q

3 functions of surveying

A

poi
unwanted undercuts- block out
wanted undercuts- clasping teeth, mucosa for retention

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6
Q

when surveying, what to use as guide plane

a. mandibular with posterior saddles
b. maxillary with anterior saddles

A

a. mandibular: lingual surface (to accomodate lingual bar/plate) –> p
b. maxillary: labial contour –> posterior border lower

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7
Q

3 principles of clasping

A

-Active arm (retentive) will engage undercut for direct retention.
 Reciprocal arm (bracing/lateral resisiting) prevents active arm displacing/traumatising tooth.
 Occlusal rest distributes occlusal load through the teeth.

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8
Q

4 things clasp flexibility/effectiveness is dependent on

A
  • material
  • cross-sectional shape
  • clasp length
  • taper/angle of approaching arm
  • position of retainer in relation to displacing force
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9
Q

undercut depths for each clasp material

A

0.25mm cobalt chrome
0.5mm ss, cast gold
0.75 wrought gold
(alphabetical order nearly)

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10
Q

CENTRIC JAW RELATION

a. define
b. alternative names
c. when its important

A

a. The relation of the mandible to the maxilla with the mandible in its most retruded position.
b. Retruded Jaw Relation, (RJR) and Retruded Contact Position (RCP).
c. position needed for bite registration

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11
Q

CENTRIC OCCLUSION

a. define
b. alternative names

A

A. maximal contact between opposing teeth

b. intercuspal occlusion, maximum intercuspation

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12
Q

4 things to do at jaw registration stage

A
  • The centric jaw relation
  • Lip support and other muscular support
  • Mould and shade of teeth
  • The occlusal rim surfaces to conform to the patient’s existing occlusion and dentition
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13
Q

main purpose of jaw registration stage

A

relationship between arches –> can articulate master casts

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14
Q

define freeway space

A

The space between the maxillary and mandibular occlusal surfaces when then mandible is in the rest position

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15
Q

define embrasure

A

The space between two adjacent teeth which opens out from their contact point

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16
Q

2 things used to record bite registration

A
  • impression material paste

- modelling wax

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17
Q

what does fox’s occlusal plane do

A

aid in carving the maxillary rim until it is parallel to the line joining the inferior border of the ala of the nose to the midpoint of the tragus of the ear (alar tragal line)

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18
Q

when survery, function of tipping cast

a. laterally
b. antero-posteriorly

A

a. laterally: undercuts of a suitable depth may be generated on posterior teeth for clasping
b. antero-posteriorly: anterior (labial) undercut areas can be minimised or moved out of the denture bearing area (aesthetics)

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19
Q

what is path of displacement at 90 degrees to

A

horizontal occlusal plane

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20
Q

3 things that influence POI of a denture

A

-Retention
Guide surfaces
Aesthetics

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21
Q

minimum length of direct retainer and why

A

1cm (2/3 of this is retentive, 1/3 active in undercut)

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22
Q

what are face bows used to record

A

pt’s hinge axis of condyle

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23
Q

types of face bow

A

simple (Denatus/ denar)

Kinematic face-bow, also known as: adjustable, hinge axis locating and hinge-bow

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24
Q

function of

a. pantograph
b. face bow

A

a. pantograph: record protrusive and lateral border movements of the condyles
b. face bow: hinge axis of condyles

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25
Q

how to decide location of axis of rotiation of condyle

A

line canthus of eye –> tragus

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26
Q

what is the frankfort plane

A

line between inferior margin of orbit to superior margin of EAM

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27
Q

arcon/non-arcon articulators and which is better

A

arcon: condylar sphere in lower member (static difference between condyles and mandibular teeth in all directions –> more accurate
non-arcon: condylar sphere in upper member

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28
Q

Which articulator would you consider if there are sufficient teeth and the intercuspal position was stable for constructing dentures? why

A

average value

simple hinge not good enough, no need to overcomplicate with semi/fully adjustable

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29
Q

which articulator to use to create full path of border movements

A

fully adjustable

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30
Q

define balanced occlusion

A

Simultaneous contacts of the occluding surfaces of the teeth in various jaw positions.
Static

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31
Q

define balanced articulation

A

Simultaneous contacts of the occluding surfaces of the teeth during function.
Dynamic

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32
Q

4 advantages of balanced articulation

A

-Minimise trauma to supporting structures
 Preserve remaining structures and reduce lateral forces to residual ridges
 Enhance denture stability
 Restore masticatory efficiency to a reasonable level

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33
Q

how to achieve balanced articulation with partial dentures

A

creating balancing contacts and working contacts between the upper and lower posterior artificial teeth

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34
Q

types of balanced occlusion

A

Anatomic occlusion

 Lingualised occlusion

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35
Q

what governs articulation of artificial teeth and points 5

A 
Hanau’s Quint: 3 incl
 Condylar inclination
 Incisal guidance
 Occlusal plane inclination
 Compensating curve
 Cuspal inclination
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36
Q

which 3 of these can be adjusted by the dentist

A

Incisal Guidance – part of the articulator
 Cuspal Inclination – on the occlusal surfaces of the artificial teeth
 Compensating Curve – created during setting of the teeth

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37
Q

what is ideal incisal guidance

prob with partial dentures

A

minimal to stop tipping

partial dentures- minimal control due to natural overjet/overbite

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38
Q

what is the compensating curve

A

posterior teeth aligned with curve of spee

curve of mandibular incisal/occlusal surfaces

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39
Q

what is curve of wilson

A

curve between buccal and lingual cusps of mandibular posterior teeth

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40
Q

what is the BULL rule

A

if there are occlusal anomolies in finished dentures –> only the Buccal Upper and Lingual Lower cusps must be ground until balances is achieved

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41
Q

3 options of williams classification

A

tapering
square
ovoid

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42
Q

when is palatal vault used 2

A

They can act as a guide in determining arch form

They can act as an aid in determining tooth alignment

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43
Q

what does willis gauge measure 2

A

resting face height (when in rest position)

occluding face height (when in centric occlusion)

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44
Q

value of freeway space

A

2-3mm

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45
Q

how much incisor shows beneath resting lip line

A

2mm

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46
Q

ala tragal line

a. alternative name
b. what it is parallel to

A

a. camper’s line

b. occlusal plane

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47
Q

define curve of spee

A

An arc of a circle 65 mm to 70 mm radius that touches the tips of all the mandibular teeth when the skull is viewed laterally (ie on L or R side; when continued it touches the anterior surface of the condyles.

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48
Q

define curve of monson

A

lateral curve of the occlusion of natural teeth in which each cusp and incisal edge touches or conforms to a segment of the surface of a sphere 4 inches (102 mm) in radius with its centre in the region of the glabella

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49
Q

6 principles of every design

A
  • restoration of contact points completes arch (see next q)
  • denture base large as poss in mucosa-supported
  • gingivally free (wide embrasures) for OH, 3mm
  • flanges for antero-posterior stability
  • stops on distal molar to prevent drifting
  • free occlusion (minimise occlusal forces)
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50
Q

4 reasons to restore contact points

A
  • aids retention
  • protects gingiva
  • limits tooth movement
  • reduces stagnation areas
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51
Q

every principles: 3 ways to gain retention

A

friciton
adhesion
cohesion

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52
Q

how to note tooth for immediate replacement on denture design

A

mark with X on diagram

write ‘for immediate replacement’

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53
Q

define indirect retention

A

retention obtained by the extension of a
partial denture base to provide the fulcrum of
a class II lever
anterior and perpendicular to axis of rotation

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54
Q

define direct retention

A

component of denture that resists withdrawal along path of insertion

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55
Q

4 factors influencing POI

A
  • retention
  • guide surfaces
  • aesthetics
  • dead space interferences
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56
Q

3 types of rest and where they are

A

molar/premolar: occlusal rests
max canines: cingulum rests
mandibular canines: incisal rests

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57
Q

2 essential features of a rest

A
  • rigid

- does not interfere with occlusion

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58
Q

3 ways to gain retention

A
  • mechanical (clasps)
  • physical (saliva)
  • muscular
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59
Q

4 design criteria for effective clasp

A
  • flexible clasp arm
  • reciprocation
  • encirclement
  • passivity
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60
Q

when is indirect retention needed

A

free-ended saddles (class I or II)

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61
Q

define reciprocation

A

to balance horizontal forces from retention

when denture being taken in/out

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62
Q

define major connector and minor connector

A

major connector: links saddle areas

minor connector: links rests, clasps etc to major connector

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63
Q

5 major connectors of maxilla

A 
ring
horseshoe
palatal coverage
palatal strap
palatal bar
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64
Q

what max major connectors can be used with

a. anterior teeth need replacing
b. torus

A

a. ring, palatal coverage, horseshoe

b. horseshoe or ring

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65
Q

what type of denture is tooth and mucosa supported

A

free end dentures

other teeth provide tooth support, posterior saddles mucosa supported

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66
Q

3 outcomes of not surverying

A

loose/tight denture
loss of pt confidence
wasted surgery time

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67
Q

2 types of surveyor and which we use

A

Nesser: black bit at top
Krupp: all silver. we use this

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68
Q

3 rules of clasps(esp retentive arms)

A
  1. use with occlusal rests –> maintain the retaining arm in the desired vertical position
  2. use RECIPROCATION to stop tooth movement when active arm is working (ie resisting displacement away from tissues)
  3. does not compromise OH
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69
Q

what does indirect retention prevent

A

rotation

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70
Q

3 ways to prevent lateral denture displacement

A
  • bracing arms of clasps
  • flanges
  • connectors on inclined surfaces (eg lingual plate)
71
Q

what does the RPI system apply to

A

mandibular bi-lateral free end saddles dentures

72
Q

at what point do you design denture

A

after primary impression, using primary casts

73
Q

4 factors influencing dimensional stability of imp materials

A
  • continuation of reaction beyond setting time
  • internal stress mouth-room temp
  • possible shrinkage due to loss of volatile bi-products
  • slow elastic memory
74
Q

3 variables that affect how an impression material is manipulated

A
  • ideal characteristics of long work time and short set time
  • working time determined by room temp
  • setting time determined by mouth temp
75
Q

what does stability refer to

A

resistance to functional forces

76
Q

impression accuracy depends on 3

A
  • adequate adhesion/retention with tray
  • fluidity on insertion
  • sufficient elasticity and tear resistance
77
Q

which synthetic elastomer is used as monophase

A

medium-bodied

78
Q

which material can cause blistering/irritation if splashed on to skin

A

condensation cured silicone

79
Q

least hydrophobic elastomer

which can be made less hydrophobic, how

A

polyether

addition-cured silicone (ADDED surface active agen

80
Q

2 uses of zinc oxide-eugenol as impression material

A
  • close-fitting special trays for secondary impressions

- complete dentures

81
Q

describe alginate 3

A 
mucostatic
low viscosity
viscoelastic (use snap removal)
subject to dimensional change (esp if left to dry out)
susceptible to syneresis/ imbibition
82
Q

use of compound impression material

A

foundation for a wash impression

83
Q

types of compound impression material

A

high and low fusing

84
Q

a. what impression material must be cast immediately 4

b. what impression material must be left before casting and why

A

a.compound CAST COMPOUND
Condensation cured silicone
polyether
alginate (or kept in damp environment

b. addition-cured silicone. release of hydrogen during setting may cause surface pitting

85
Q

least viscoelastic elastomer

A

polyether

86
Q

type of acrylic used for

a. denture base
b. repairs and additions
c. special trays

A

a. denture base: class 1 type 1
b. repairs and additions: class 2 type 1
c. special trays: type 4

87
Q

what acrylic types have similar components

A 
type 1 class 1 (heat processed)
type 2 class 1 (auto polymerising)
88
Q

5 components of acrylic powder PPPIS

A 
polymer
pigments
plasticiser
initiator
synthetic fibres
89
Q

role of each of the following in acrylic powder:

a. dibutyl phthalate
b. salts of calcium/iron/organic dyes
c. peroxide
d. polymethylmethacrylate beads
e. nylon/acrylic

A

a. dibutyl phthalate: plasticiser
b. salts of calcium/iron/organic dyes: pigments
c. peroxide: initiator
d. polymethylmethacrylate beads: polymer
e. nylon/acrylic:synthetic fibres

90
Q

example and % of peroxide used

A

benzoyl peroxide 0.5%

91
Q

4 components of acrylic liquid

A

monomer
cross-linking agent
initiator
activator (only in auto-polymerising resins, type 2)

92
Q

role of each of the following in acrylic liquid:

a. N’N-dimethyl p toluidine
b. methylmethacrylate
c. ethyleneglycol dimethacrylate
d. hydroquinone

A

a. N’N-dimethyl p toluidine: activator (only in auto-polymerising resins, type 2)
b. methylmethacrylate: monomer
c. ethyleneglycol dimethacrylate : cross-linking agent
d. hydroquinone: initiator

93
Q

how much of these in acrylic liq

a. ethyleneglycol dimethacrylate
b. hydroquinone

A

a. ethyleneglycol dimethacrylate : 10%

b. hydroquinone: trace

94
Q

what is acrylic

a. monomer
b. polymer

A

a. monomer: methylmethacrylate

b. polymer: polymethylmethacrylate (beads)

95
Q

appearance of acrylic polymer before opacifiers/pigments/fibres

A

clear, glass like

96
Q

boiling point of monomer, why is this important

A

100.3 C

above this it will boil (turn to gas) in denture –> GASEOUS POROSITY

97
Q

vapour pressure of monomer at room temp

A

high

98
Q

what happens during polymerisation

A

monomer –> polymer

methylmethacrylate –> polymethylmethacrylate

99
Q

4 uses of type 1 class 1 acrylic

A
  • denture bases (full and partial)
  • splints
  • artificial teeth
  • relines
100
Q

ratio of powder: liq acrylic and why

A

2.5:1 powder:liquid

reduce volumetric shrinkage to 5-6%

101
Q

what happens to acrylic during polymerisation if there is

a. too much powder
b. too much liquid

A

a. too much powder: dry, unworkable, does not flow during bench pressing, plus GRANULAR POROSITY
b. too much liquid: 21% volumetric shrinkage

102
Q

stages of material consistency in acrylic setting 5

A

sandy

  • sticky
  • snap (dough)
  • rubber (leather)
  • hard
103
Q

what determines stages of material consistency in acrylic setting

A

condition of polymer beads as they dissolve in monomer –> inc viscosity

104
Q

ideal consistencies of acrylic material 2

A

long working time

short dough time

105
Q

what is used for trial closure of acrylic

A

thin polythene/acetate sheet

106
Q

2 functions of trial closure of acrylic

A
  • vertical dimension less likely to increase

- assess amount of resin needed to fill mould

107
Q

2 reasons flask is held in spring clamp during curing process

A

FLOW:

  • flow of dough in to mould
  • flow of excess out (reduce shrinkage, minimise inc in vertical dimension)
108
Q

describe injection moulding technique

A

resin in through sprue hole, excess out through vent hole

109
Q

why is injection moulding technique used

A

polymerisation starts far from sprue (entrance) hole –> more resin can flow in as polymerisation shrinkage occurs

110
Q

in acrylic polymerisation, what happens at 65 degrees

A

benzoyl peroxide (initiator) decomposes –> FREE RADICALS

111
Q

typical curing cylcle and what happens at each stage

A
  • several hours at 70 C: most polymerisation occurs (parts of denture reach 100C due to exotherm)
  • 3 hours at 100 C: complete polymerisation
  • allowed to cool
112
Q

alternative curing cycle

A
  • placed in cold water
  • heated to 100C over 1 hour
  • boiled for 1 hour
  • allowed to cool slowly to room temp
113
Q

do thin or thick parts of denture base polymerise first and why

A

thick- due to exothermic reaction occurring more in thicker parts

114
Q

2 causes of internal stresses during polymerisation of acrylic

A
  • high coefficient of thermal expansion

- volumetric shrinkage

115
Q

what causes warpage

A

internal stresses released by WARM WATER

116
Q

initial setting reaction of autopolymerising resins

A

activator (NN’-dimethyl-p-toluidine) + initiator (benzoyl peroxide) –> free radicals –> initiate polymerisation

117
Q

how polymerisation occurs for

a. large polymer beads
b. small polymer beads

A

a. large polymer beads: monomer absorbs in to surface

b. small polymer beads dissolve in to monomer liq

118
Q

2 disadvantages of type 2 class 1 compared to heat-processed acrylic

A
  • short working time –> no trial closure

- higher residual monomer content–> inferior chemical/mechanical properties eg 90C Tg temp

119
Q

how to use type 2 class 2 acrylic resin

A

pourable:
pour in to hydrocolloid mould
sets at room temp

120
Q

2 advantages of 2 class 2 acrylic resin

A
  • removed easily from hydrocolloid mould

- minimal trimming/finnishing

121
Q

2 disadvantages of 2 class 2 acrylic resin

A
  • distortion from mould flexing

- high residual monomer –> poor chemical/mechanical properties

122
Q

contents of type 4 LIGHT ACTIVATED acrylic

A
  • UDMA monomer
  • sub-micron particles of silica
  • polymethylmethacrylate beads (organic filler)
  • light-sensitive initiators: camphorquinone
  • light-sensitive activators: amines
  • non-reactive barrier compound: carboxymethyl/cellulose
123
Q

what provides free radicals in type 4 light-activated acrylic

A
  • light-sensitive initiators: camphorquinone

- light-sensitive activators: amines

124
Q

function of non-reactive barrier compound carboxymethyl/cellulose in type 4 light-activated acrylic

A

prevent inhibition of polymerisation by oxygen

125
Q

describe structure of set type 4 light-cured acrylic

effect of this on mechanical/ chemical prop

A

type of COMPOSITE material: polymethylmethacrylate beads bound in matrix
poor chemical/ mechanical properties compared to heat-processed type 1 acrylic

126
Q

term for surface cracks in acrylic and acrylic type theyre common in

A 
crazing
type 4 (light cured)
127
Q

3 reasons for crazing

A
  • porcelain teeth in acrylic resins (bc acrylic has 10xhigher thermal coefficient)
  • when monomer contacts existing denture during repair
  • repeated drying out (water absorption –> tensile stresses at surface
128
Q

function of cross-linking agent

A

bond polymer chains so monomer does not touch denture during repair –> minimise crazing

129
Q

should denture be kept dry or moist? why?

A

moist. stops water absorption, which would cause tensile stress (type 4 acrylic)

130
Q

type of denture subject to whitening/bleaching

causes 2 and how

A 
type 4 (light cured)
caused by too hot water/ exposure to solvents (eg acetone in saliva)
structural change in matrix phase --> mismatch in REFRACTIVE INDEX between matrix/bead polymers--> colour change
131
Q

what type of acrylic absorbs water
equilibrium % and when
2 effects

A

type 4
2% after several days
-crazing
-slight dimensional change

132
Q

what organisms freq colonise fit surface (hence cleaning and soaking of denture)

A

candida

133
Q

% residual monomer limits for acrylic types.

why is this limited

A

2.2% (type 1,3,4,5)
4.5% type 2 (autopolymerising)
(manufacturers limit to 1%)
excess monomer causes irritation

134
Q

function of these additions to modified acrylic materials:

a. elastomers/ acrylic-elastomer copolymer
b. carbon fibre inserts
c. atoms w higher atomic numbers than resin eg comonomers/ bromine

A

a. elastomers/ acrylic-elastomer copolymer: improve impact strength
b. carbon fibre inserts: improve fatigue strength (stiffen)
c. atoms w higher atomic numbers than resin eg comonomers/ bromine:radiopacity

135
Q

when are alternative polymers used and 2 examples

A

when pt allergic to polymethylmethacrylate

  • polycarbonates
  • vinyl polymers
136
Q

how to cure alternative polymers

a. vinyl polymers
b. polycarbonates

A

a. vinyl polymers: low softening temp –> careful handling

b. polycarbonates: high Tg 150C –> injection moulding

137
Q

ideal tear strength pf impression materials and why

A

moderate
too high –> problems with diastemas
too low –> tears when removed from undercut

138
Q

causes of internal stresses of impression compound 3

A
  • poor thermal conductivity
  • high coefficient of thermal expansion
  • large temp drop softening temp-room temp
139
Q

2 uses of gutta percha

A
  • record canal depth in endo

- lubricant in impression compound

140
Q

list mucostatic impression materials

A

alginate

141
Q

list mucodisplasive impression materials

A

impression compount

zinc oxide-eugenol

142
Q

alginate setting reaction

A

sodium alginate + calcium sulphate –> sodium sulphate + calcium alginate

143
Q

types of

a. impression compound
b. zinc oxide-eugenol
c. agar
d. synthetic elastomer

A

ALWAYS 1= MOST VISCOUS/HIGH FUSING

a. impression compound: 1 higher fusing, 2 lower fusing
b. zinc oxide-eugenol: 1 hard 2 soft
c. agar: 1 high viscosity, 2 med 3 low viscosity
d. synthetic elastomer: 0putty, 1 heavy body 2 medium body (monophase) 3 light body

144
Q

what impression materials are susceptible to imbibition/syneresis

A

both: alginate, agar

imbibition only: polyether,

145
Q

which impression material releases alcohol by-product

A

condensation-cured silicone

146
Q

what determines viscosity of condensation cured silicone

A

quantity of inert filler

147
Q

which material has sulphonic acid catalyst system that pts are often allergic to

A

polyethers

148
Q

use of polyether

A

monophase in stock of special tray

v rigid –> accurate orientation for dental implants, dummy attachments

149
Q

which impression material has highest tear strength

A

polysulphides

150
Q

bi-product of

a. addition cured silicone
b. condensation cured silicone
c. polyether
d. polysulphide

A

a. addition cured silicone: none (maybe hydrogen)
b. condensation cured silicone: alcohol
c. polyether: none
d. polysulphide: water

151
Q

2 impression materials that taste bad

A

zinc oxide eugenol

polysulphide

152
Q

with which impression material in impression wax often found

A

zinc oxide-eugenol paste

153
Q

which impression should not be handled with latex gloves and why

A

addition cured silicones

poisons catalyst

154
Q

angles of special tray handles

A

upper: 45 degrees, incisal edge/crest of ridge in midline
lower: 10 degrees, incisal edge/crest of ridge in midline

155
Q

when/ where finger rest is on special trays

A

lower close-fitting special trays

over premolar region

156
Q

function of butadiene styrene in acrylic

A

(rubber) reists crack/fracture

157
Q

when adding teeth to a denture, is denture base or tooth adapted first?

A

denture base

158
Q

2 causes of denture fracture

A

impact

fatigue

159
Q

4 factors of denture design that can cause fatigue fracture

A
  • non-flanged
  • large anterior diastema (stress between central incisors)
  • abnormally large frenae –> deep notches in flanges needed
  • posterior upper denture teeth too far buccally –> flexing of palate in midline when teeth occlude
160
Q

6 ways the oral anatomy of the pt can cause fatigure failure of dentures

A
  • high vaulted palate
  • tori
  • heavy bite
  • bruxists
  • opposed by natural teeth
  • v fibrous posterior tuberosities –> posterior teeth less supported over ridge –> flexing around midline
161
Q

6 ways the packing of acrylic in to processing flask can cause fatigue failure

A
  • voids by careless packing
  • contamination by dust/plaster
  • not shaking polymer –> fibres conc in one area
  • porosity
  • incomplete polymerisation
  • over polishing
162
Q

define
Syneresis:
imbibition:

A

Syneresis: expulsion of liquid from a gel
imbibition: displacement of one fluid by another

163
Q

what impression material has platinum catalyst

A

addition cured silicones

164
Q

direction of circumferential clasps

A

lower: inwards
upper: outwards

165
Q

denture base material for tooth borne designs and why

A

skeletal

using cobalt chrome anyway for clasps

166
Q

what is a cummer arm

A

vertical bar extended from baseplate to gain indirect retention

167
Q

difference between nesser and krupp surveyors

A

nesser tables can be removed

168
Q

stages of surveying

A

establishment of a path of insertion (POI) and provision of guide planes (using the analysing rod),
Marking the outline position and extent of undercut areas (using the carbon marker),
Utilisation of undercuts for retention (using the undercut gauges),
Elmination of unwanted undercuts (using the wax trimmer or chisel).

169
Q

gypsum setting time. What a) increases b) decreases

A

a) increases: Borax, Potassium Citrate, Sodium Chloride > 20%, water
b) decreases: Gypsum

170
Q

gypsum setting expansion. What a) increases b) decreases

A

a) increases: increased spatulation
b) decreases: Potassium Sulphate, Sodium Chloride, Borax
*NaCl in every category but >20% to INCREASE setting time
borax ↑ setting time, ↓ setting expansion
potassium sulphate DECREASES, potassium citrate INCREASES

171
Q

explain hygroscopic expansion and when its used

A

Setting expansion increases in water. Because crystals can grow freely, not limited by surface tension of water as they would be in air
gypsum-bonded investments, which are used specifically with full gold castings and bridgework

172
Q

most important influence on accuracy of wax

A

coefficient of thermal expansion

173
Q

types of modelling wax

A

Type 1 soft – hard at room temperature – used for veneers, etc.;
Type 2 hard – for wax patterns in moderate temperature climates;
Type 3 extra hard – used in warmer climates.
Types 2 and 3 can soften if left in the mouth for a prolonged period (a few minutes)

174
Q

when to use fox’s occlusal plane guide

2 measurements is includes

A

many posterior teeth missing on maxillary rim

interpupillary line, alar tragal line

Year 3 Prosthetics (8 decks)

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