Fixed prosthodontics and Lost-wax casting process

Question 1

what is fixed prosthodontics?

Answer 1

branch of prosthodontics concerned with the replacement and/or restoration of teeth by artificial substitutes that aren’t removable from the mouth

Question 2

what is retention?

Answer 2

prevents removal of the restoration along the path of insertion/ long axis of tooth preparation

Question 3

what is resistance?

Answer 3

prevents dislodgement of the restoration by forces directed in an apical/oblique directions and prevents any movement of restoration under occlusal forces

Question 4

what surfaces do extracoronal restorations use for retention?

Answer 4

Use opposing external surfaces for retention

Question 5

what surfaces do intracoronal restorations use for retention?

Answer 5

use opposing internal surface for retention

Question 6

how does extracoronal restorations have retention?

Answer 6

provided by external surface (such as buccal and lingual walls) of the crown

Question 7

how does intracoronal restorations have retention?

Answer 7

provided by resisting displacement by wedge retention

Question 8

what 5 factors affect retention and resistance?

Answer 8

tapering, freedom of displacement, length, substitution of internal features and path of insertion

Question 9

what is tapering?

Answer 9

the more parallel the opposing walls of a preparation, the greater the retention

Question 10

what is the optimum angle of tapering?

Answer 10

16 degrees - 8 degree inclination on each side

Question 11

what are the 7 types of margins/finish lines?

Answer 11

feather edge, chisel, chamfer, bevel, shoulder, sloped shoulder and beveled shoulder

Question 12

what surface should the margin of the restoration be closely adapted to?

Answer 12

cavosurface finish line of the prepared tooth

Question 13

what is an impression?

Answer 13

a negative reproduction of anatomical parts including prepared teeth, ridge areas and other parts of the dental arch

Question 14

what is a die?

Answer 14

a positive reproduction of the prepared, it is sectioned, trimmed and ditched

Question 15

what are the 7 criteria’s for die materials?

Answer 15

should reproduce surface detail accurately

material should dimensionally accurate

strong and resistance to abrasion

easy to section and trim

compatible with separating agent

colour that contrasts with wax

easily wettable by wax

Question 16

what is the expansion of type IV die stone?

Answer 16

0.1% or less

Question 17

what is the expansion of type V die stone?

Answer 17

as much as 0.3%

Question 18

why does type V die stone expand more?

Answer 18

to compensate for relatively large solidification shrinkage of base metal alloys

Question 19

what are some advantages of gypsum?

Answer 19

inexpensive, easy to use, produces consistent results

Question 20

what is one disadvantage to gypsum?

Answer 20

it has poor abrasion resistance

Question 21

what is die hardener used for?

Answer 21

reduces the die’s susceptibility to abrasion during wax carving

Question 22

what is die spacers used for?

Answer 22

provides relief space for dental cement

Question 23

what are some advantages of polymeric die materials?

Answer 23

stronger than gypsum, abrasive resistance and provides good detail production with silicone and polyether

Question 24

what are some disadvantages of polymeric die materials?

Answer 24

expensive, epoxy die materials may shrink, not suitable for some impression materials

Question 25

what are electroplated dies?

Answer 25

formed by electroforming, when areas are electroplated with fine powder silver or graphite to make them conduct electricity, causing a layer of pure metal to be deposited on the impression

Question 26

what are some advantages of electroplated dies?

Answer 26

excellent abrasion resistance, moderately high strength, able to restore friction on worn telescopic crowns

Question 27

what are some disadvantages of electroplated dies?

Answer 27

labor intensive, time-consuming, can be toxic (use of cyanide in Ag plating), costly equipment, not suitable for all types of impression materials (only silicone and polyether)

Question 28

what are the 5 requirements for a working cast?

Answer 28

there should be an anatomical part and base base should be strong/rigid to provide stable platform anatomical part should be sectioned - 10-15mm thick exclusive of teeth anatomical parts should be able to be removed and replaced on base sectioned parts should retain dimensional relationship

Question 29

why is a solid "check" cast important?

Answer 29

dies and sections can become less accurate with repeated removal, use of solid check model ensures fit of restoration at final stage to verify accuracy of the restoration.

Question 30

what is dipping wax?

Answer 30

reinforces the wax copings in crown and bridge work by providing basis for precision

Question 31

what are the requirements of wax patterns?

Answer 31

accurately fit the die no thinner than 0.5mm occlusion must be correct wax coping should be allowed to cool before removal from die frequent removal will increase warpage/distortion marginal shape should be precise.

Question 32

why are proximal contacts important?

Answer 32

help stabilise the teeth within the arch

Question 33

what is the emergence profile?

Answer 33

part of the axial contour that extends from base of gingival sulcus past margin of gingiva and extends to height of contour

Question 34

what are embrasures?

Answer 34

the spillway spaces formed from curvatures adjacent to contact areas

Question 35

what are the functional cusps of maxillary teeth?

Answer 35

lingual (palatal) cusps

Question 36

what are the functional cusps of mandibular teeth?

Answer 36

buccal cusps

Question 37

what are the non-functional cusps of maxillary teeth?

Answer 37

buccal cusps

Question 38

what are the non-functional cusps of mandibular teeth?

Answer 38

lingual cusps

Question 39

why are provisional restorations used?

Answer 39

used to protect prepared tooth during time between preparation of tooth and placement of definitive restoration

Question 40

what should a provisional restoration have?

Answer 40

pulpal protection good marginal fit and seal stability function strength and retention good aesthetics

Question 41

what are the three components in structural durability?

Answer 41

occlusal reduction, functional cusp bevel and axial reduction

Question 42

what is occlusal reduction?

Answer 42

provides adequate bulk of metal and strength to the restoration

Question 43

what is a functional cusp bevel?

Answer 43

wide bevel on functional cusp provides space for adequate material in an area of heavy occlusal contact.

Question 44

what can happen if there is no functional cusp bevel?

Answer 44

thin area or perforations over contouring poor occlusion

Question 45

what is axial reduction?

Answer 45

provides adequate thickness of the restorative material

Question 46

what can occur if theres inadequate axial reduction?

Answer 46

the restoration will have thin walls subject to distortion

Question 47

what are some advantages of complete cast crowns?

Answer 47

high strength restoration high retentive qualities adequate resistance option to modify form to support RPD's

Question 48

what are some disadvantages of complete cast crowns?

Answer 48

aesthetics removal of large amount of tooth structure adverse effect on tissues

Question 49

what are the indications for a complete cast crown?

Answer 49

extensive destruction from caries or trauma endodontically treated teeth to compensate for loss of tooth structure need for maximum retention and strength provide contours to receive RPD correction of occlusal plane

Question 50

what is a sprue?

Answer 50

a channel in investment where molten alloy flows to reach hollow mould formed after burnout of wax patterns

Question 51

how can you minimize distortion during waxing up?

Answer 51

apply in small increments should not stand uninvested for more than 30 minutes store at room temp avoid unnecessary removal from die avoid inclusions in pattern avoid exposure to extreme temperatures

Question 52

what are the mechanisms of investment mould expansion?

Answer 52

setting expansion hygroscopic expansion wax pattern expansion thermal expansion

Question 53

what is setting expansion?

Answer 53

result of normal crystal growth

Question 54

what is hygroscopic expansion?

Answer 54

when investment is set in presence of water

Question 55

what is wax pattern expansion?

Answer 55

when investment is still fluid and wax is warmed above temperature that it was formed at

Question 56

What are high-noble alloys?

Answer 56

when at 40% weight is gold