Principles of cavity preparation (amalgam 2)

Question 1

what components of cavity preparation fall under stage 1 initial preparation steps :

Answer 1

=outline form
=primary resistance form
=primary retention form
=convenience form

Question 2

what is the function of good resistance form ?

Answer 2

it enables booth the tooth structure and the restoration to withstand stresses without fracture

Question 3

which type of force on restored tooth causes more destruction ?

Answer 3

lateral force

Question 4

brittle materials (bulk for strength)

Answer 4

-amalgam
-composite
-ceramic\
weak against tensile forces

Question 5

as opposed to brittle materials , ductile materials such as gold have some advantages such as:

Answer 5

• can be finished into thin margins as there is no need for bulk

-used to protect and support weak tooth structure

Question 6

what is the correct width of a cavity prepared for amalgam?

Answer 6

1/4 intercuspal distance

-not more in order to preserve as much of the cusp as possible –>stronger tooth

-also to decrease surface area of restoration , making it less likely to fracture

Question 7

shape of amalgam cavity should be ____ in order to optimize resistance form

Answer 7

box shaped with flat pulpal and gingival floor(also helps in retention form )–helps neutralize stresses at the cavity seat

Question 8

uneven surface in a prepared cavity will result in:

Answer 8

stress concentration in the deepest areas in the cavity , resulting in fracture of tooth structure .

forces concentrated on elevated areas will cause fracture of the restoration itself

Question 9

minimum occlusal thickness of amalgam :
-ceramic:
-cast metal:
-composite:

Answer 9

-amalgam:1.5mm
-cermaic: 2mm
cast metal : 1-2mm
composite : variable

Question 10

what is undermined enamel and what should be done with it ?

Answer 10

undermined enamel is enamel with no dentine support ( carious dentine ) and it is to be removed

Question 11

other than having smooth surfaces , how else may a dentist limit stress concentration when restoring a tooth ?

Answer 11

by roundening the sharp line angles

Question 12

what is the only line angle , that if left sharp , has the capability to break the amalgam restoration itself and not the tooth structure.

Answer 12

the axio-pulpal line angle

(should be beveled or rounded)

Question 13

what is the function of cusp capping ?

Answer 13

decreasing the height of the cusp in relation to its width in order to have better resistance form

Question 14

when using amalgam , cusp capping is called___

Answer 14

cusp tipping (make sure not to have any thin surfaces and to do it uniformly)

Question 15

the cavo-surface angle for the following restorations

-amalgam :
-gold inlays :

Answer 15

amalgam : 90 degrees
gold inlay: 135

Question 16

gingival cavosurface line angle should be :

Answer 16

slightly beveled , to removed any undermined enamel that is destined to crack

Question 17

primary retention form is resistance against tipping or lifting

Question 18

factors affecting retention form :(not obvious ones)

Answer 18

-thickness of restoration
-amount of remaining tooth structure
-total surface of restoration exposed to masticatory forces

Question 19

main retention mechanism of amalgam restorations ?

Answer 19

converging cavity walls , mechanical undercut retention

Question 20

frictional wall retention (parallel walls having friction with the restoration and hence holding it in place) is most utilized by which type of restoration?

Answer 20

cast gold restoration

Question 21

gripping action of dentin is heavily relied on when using which type of restoration ?

Answer 21

gold foil

Question 22

which tooth is the occlusal dovetail most useful in ?

Answer 22

maxillary premolar

Question 23

how does the box form of a cavity affect resistance and retention ?

Answer 23

resistance:
neutralizes stresses at the cavity seat

retention :
-frictional retention due to parallel walls

Question 24

how does adding bulk to the restoration affect retention and resistance ?

Answer 24

retention:augments retention by more friction

resistance: prevent fracture of brittle restoration

Question 25

cast gold metal restoration CSA:

Answer 25

diverging (feature of convenience form)

Question 26

stage II of cavity preparation includes:

Answer 26

-removal of any remaining infected dentin or old restoration ( so prepare the normal form of the cavity first and THEN proceed ) - this is done because it allows for optimal visibilitywhen removing caries and permits immediate placement of a base and the restoration

Question 27

why must an amalgam cavity extend deeper to DEJ ?

Answer 27

-to avoid cutting exactly at the DEJ which is a very sensitive area -to be able to detect the spread of caries in dentine laterally -to make sure that all remaining enamel is supported by sound dentine and there is no undermined enamel \ -provides bulk for restoration -retention

Question 28

round bur is used on lowspeed hand piece for caries removal (or excavator )

Question 29

motion of excavator when removing caries:

Answer 29

directed laterally parallel to pulp horns from periphery to center with scooping motion

Question 30

what is the minimum ammount of remaining dentin thickness that makes it not necessary to do pulp capping ?

Answer 30

2mm

Question 31

what is the difference between varnishes , liners , and bases ?

Answer 31

both varnishes and liners provide a barrier to protect remaining dentin and pulp and provide galvanic insulation the difference is varnish can be applies on all of the cavity walls while liners (is used in shallow cavities with dentin thickness being more than 2mm) are placed on the deepest portion of the ccavity bases are used in cavities with little remaining dentin (0.5-2 mm). they provide thermal , galvanic , chemical , and mechanical protection to the pulp

Question 32

which pulp protecting material provides thermal insulation?

Answer 32

bases

Question 33

secondary retention and resistance forms :

Answer 33

mechanical features: retention lock , grooves , coves , skirts , pins , slots , bevelled enamel margins treatment of prepared walls: etching priming m bonding

Question 34

what is the difference between proximal axial grooves and proximal retention locks ?

Answer 34

both are modifications done to increase retention but proximal axial grooves enters enamel (extends up to CSA) and has no undercut while proximal retention locks are only in dentine and have an undercut

Question 35

skirts improve both resistance and retention -they are done mostly in enamel -non vital pulp will not provide gripping action of dentin due to dehydration -enamel must be bevelled in case of using high strength restorative material

Question 36

NOYs rule for keeping strong enamel wall at margins :

Answer 36

-enamel must rest on sound dentine -enamel rods which formes CSA must have their inner ends resting on sound enamel -outer ends of enamel rods must be covered by restorative material

Question 37

best fluid for cavity toileting ?

Answer 37

water spray

Question 38

Correct anatomic form renders teeth more___

Answer 38

self cleansing

Question 39

what is meant by static forces , dynamic forces and cyclic forces

Answer 39

static:centric dynamic:eccentric cyclic:functional

Question 40

The routine cavity depth ●1. Pulpal depth: ☞ 0.2 – 0.5 mm beyond the DEJ. ●2. Axial depth: ☞ 0.5 – 0.8 mm beyond DEJ

Question 41

how do you differentiate between affected and infected dentin?

Answer 41

affected dentine is affected by acute caries , has a yellow color and is soft and is removed in flakes. infected dentin is infected by chronic caries , has a dark brown color and is harder(removed in debris)

Question 42

secondary resistance and retention forms are required in ______

Answer 42

complex and compound tooth preparations

Question 43

requirements of enamel wall:

Answer 43

●The enamel walls and margins should be finished → smooth, free from short, loose, friable or undermined enamel rods. ●The enamel wall must take the same inclination of enamel rods. ●The enamel wall must have an inclination suitable with the physical properties of the restorative material. ●The enamel wall must be beveled in case of using high strength restorative material.

Question 44

short bevel: long bevel: full bevel: counter bevel:

Answer 44

short bevel: part of enamel long bevel: all of enamel , up to DEJ full bevel: enamel and dentin counter : against enamel rods of cusp

Question 45

what are coves and what are slots ?

Answer 45

coves: small conical depressions prepared unhealthy dentin to provide additional retention slots : retention grooves whose length is in a horizontal plane . prepared in gingival floor axial to DEJ

Question 46

WHAT ARE skirts ?

Answer 46

thin extensions of facial and lingual proximal margins of cast metal only . they increase the total surface are of the preparation. they are usually prepared entirely in enamel. they increase both resistance and retention forms

Question 47

pin dimensions

Answer 47

0.5mm in dentin with 1-2mm depth and 0.5-1 mm width