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FIXED > lecture 3- principles of tooth preparations > Flashcards

lecture 3- principles of tooth preparations Flashcards

1
Q

7 principles of tooth design and restoration design

A
  1. preservation of tooth structure
  2. retention form
  3. resistance form
  4. added preparation features
  5. marginal integrity
  6. structural durability of the restoration
  7. preservation of the periodontium
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2
Q

crown preparation is an _____surgical procedure

A

irreversible

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3
Q

in consideration of preservation of tooth structure for crowns are biologic factors such as:

A

dental pulp
gingival tissues
adjacent teeth

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4
Q

in not careful in preservation of tooth structure when prepping crown, injury can occur such as

A

-mechanical damage
-temperature damage
-chemical damage
-bacterial damage

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5
Q

any time a bur touches a tooth, the pulp is:
crown prep traumatizes the:

A

stimulated to respond
(pulpal integrity)

pulp

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6
Q

some pulps respond with healthy healing, some by dying (pulpal necrosis), some hypersensitive with lingering pulpal inflammation.

why?

A

decreased thickness of dentin remaining between prepared walls and pulp
-heat transferred to tooth during prep

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7
Q

level at minimum 1mm of dentin surrounding pulp

A

vital core

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8
Q

why prepare teeth for crowns if risks?

A

esthetics, prevention of catastrophic fracturing, protection of root canal teeth, make tooth stronger

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9
Q

when preparing a tooth for a crown in a conservative manner, the operator allows for a

A

morphological reduction

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10
Q

preservation of the basic primary tooth anatomy within the preparation (axial wall and occlusal anatomy)

A

morphological reduction

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11
Q

morphological reduction leaves:

A

max thickness of residucal tooth structure surrounding the pulp
and
anti-rotational features, retentive and resistive features in the tooth preparation

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12
Q

as we create our crown prep, we need to form the tooth utilizing geometric form criteria we call

A

retention and resistance

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13
Q

prevention of removal along the path of insertion
(usually fails in patients chewing sticky foods)

A

retention

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14
Q

retention is created by:

A

-two opposing vertical surfaces with converging surfaces held to within certain parameters

-also with using cements which offer frictional resistance to dislodgement. this is a shear stress aiding in retention

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15
Q

prevention of restoration being dislodged by apical or oblique forces
-typically through occlusal forces

A

resistance

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16
Q

aimed to oppose lateral forces which are not along path of insertion

A

resistance

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17
Q

greatest determining factor in a crown’s dislodgement

A

resistance

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18
Q

how is resistance built into prep

A

by forming walls to block anticipated movement due to :
1. leverage
2. rotation (either vertically or horizontally)

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19
Q

what factors can affect the resistance from of a tooth preparation?

A
  1. TOC- total occlusal convergence
  2. prep wall length
  3. tooth width after preparation
  4. geometric forms [these limit the paths of insertion-grooves, boxes, vertical planes, pins; morphological reduction]
  5. surface area of the tooth prep
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20
Q

defined as the angle of convergence of taper between two opposing walls of a tooth prep

[resistance form]

A

Total Occlusal Convergence

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21
Q

the angle of convergence of taper of one wall of a prep in relationship to the long axis of the preparation

A

inclination of TOC

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22
Q

ideal TOC

A

6 degrees

-two opposing surfaces, each with 3 degrees taper, add together for an overall toc of 6 degrees

average toc ends up 10-20 degrees

23
Q

what is the crown preparation feature most under operator control

A

TOC- total occlusal convergence

24
Q

as occlusal convergence increases, retention:

A

decreases

25
Q

max crown retention is around ____degrees of TOC

about 1/5 the retention when toc is ____ degrees

A

5 degrees

20 degrees

26
Q

which teeth have greater TOC

A

molar preps have greater TOC than anterior and premolars

mandibular preps have greater TOC than maxillary

(due to visibility)

27
Q

what teeth require more angulation and what are generally shorter?

A

posterior preps require more angled TOC to facilitate crown seating

posterior preps generally shorter with higher occlusal forces

28
Q

the greater the height of the tooth prep wall, the ____the retention of the restoration

A

greater

29
Q

increased wall height=

A

increased area of cementation =
increased retention

30
Q

decreased wall length (height) creates a _______in resistance

A

disproportionate decrease

31
Q

the wall height should be greater than the

A

tipping arc of displacement

32
Q

shorter the prep, the (more/less) the taper MUST be

taller the prep, the (more/less) taper MAY be

A

shorter= less
taller= more

33
Q

why would a narrow tooth with smaller diameter prep have greater resistance than wider, larger diameter tooth when both have same wall height

A

because small tooth has shorter rotiational radius for the Arc of Rotation (tipping arc)

34
Q

for ideal and adequate resistance and retention, the height/width ratio should be greater than ___ for all teeth

A

0.4
(implies TOC is less than 20 degrees)

35
Q

wall height ideals when prep is within 10-20 degrees

A

molars 4mm
incisors and premolars 3mm

36
Q

if the tooth prep does not have the resistance form you desire, what modifications can you make to the prep to increase the resistance?

A
  1. decrease the TOC with axial re-shaping of prep walls
  2. addition of grooves / box forms (these must be parallel to path of insertion)
  3. increase wall height:
    -lower margin
    -add wall heigh with core build up (possibly pins)
    -crown lengthening surgery
    -orthodontic extrusion
37
Q

secondary retentive features:

A

-most common to use grooves for secondary retention
-increase surface area
-establish parallelism on opposing intra-coronal tooth surfaces
-limits the path of draw to one
-shorten the Arc of rotation, therefore, increasing resistance

38
Q

retentive features should ideally be cut no deeper than _____mm axially and ___mm occlusally

A

1.5mm axially
2mm occlusally

39
Q

grooves or box forms must have a definite wall _____ to direction of displacing force

A

perpendicular

40
Q

retention is (increased/decreased) with surface area

A

increased

41
Q

increasing surface area helps with retention, but its not as vitally important as

A

TOC parameters and height/width ratio

42
Q

what makes good margin?

A

-fits as closely as possible to minimize cement film width (25 microns)
-sufficient strength to withstand forces of mastication
-located where dentist can finish and inspect and patient can clean

43
Q

if margins are not closely adapted to finish line of prep:

A

-microleakage
-recurrent caries
-possible de-cementation of restoration

44
Q

tooth prep finish line:

A

-needs to be conservative of tooth structure
-readily identifiable on tooth, impression and die
-provides sufficient bulk to restorative material

45
Q

size of your finish line determines:

A

bulk of material at margin
and
fit of the restoration

46
Q

what kind of finish lines (margins) do you want for crown

A

chamfer or shoudler

(bevel for metal)
(feather-edge or knife-edge for gold)

47
Q

what morphological reduction will create structural durability

A

-adequate occlusal / incisal reduction and clearance without excessive removal (do not want flat)

-uniform thickness of restoration material

-parallels the major planes of the tooth

-no pulpal involvement

48
Q

preparation features that contribute to structural durability

A

-occlusal / incisal reduction
-functional cusp bevel
-axial reduction

49
Q

creates space for an adequate bulk of material within normal contours of the tooth

A

axial reduction

50
Q

if not enough reduction is done axially, then will have what type of walls? which would be a problem, why?

A

thin walls which are difficult to finish and possible loss of strength

51
Q

if too much reduction done axially, then will have what type of walls? and this is a problem, why?

A

thick over contoured walls

-plaque traps and periodontal inflammation

52
Q

what happens if our preparation does not leave room for structural durability?

A

-fracture of restoration
-grind through porcelain to adjust occlusion
-crown worn through due to thin material

53
Q

our crown prep and final restorations should promote periodontal health by:

A

-placement of margin for cleanse-ability
-marginal smoothness and crown adaptation
-axial contours and emergence profile

54
Q

margin guidlines:

A
  1. place where dentist can finish and evaluate
  2. place where pts can clean
  3. place on enamel when possible
  4. place supra-gingival when possible (0.5mm supragingival ideally)
  5. make margins as smooth as possible

FIXED (8 decks)

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