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Principles of Tooth Preparations Flashcards

1
Q

What are the 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

A crown preparation is an __________ surgical procedure

A

irreversible

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3
Q

What are the biological factors to consider for a crown prep?

A

-Dental Pulp
-Gingival Tissues
-Adjacent teeth

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4
Q

What kind of injuries can occur from a crown prep?

A

-Mechanical damage
-Temperature damage
-Chemical damage
-Bacterial damage

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5
Q

What is important to know about the pulp during a crown prep?

A

-Any time a bur touches a tooth, the pulp is
stimulated to respond.
-A crown preparation “traumatizes” the pulp

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6
Q

What are the responses of the pulp to a crown prep?

A

-Most pulps respond with a healthy healing response
-Some pulps respond by dying (pulpal necrosis)
-Some remain hypersensitive with lingering pulpal inflammation

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7
Q

Why can the pulp be damaged during a crown prep?

A

-Decreased thickness of dentin remaining between prepared walls and pulp
-Heat transferred to tooth during preparation

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8
Q

Leave at minimum ____mm of dentin surrounding pulp/vital core

A

1mm

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9
Q

If there are risks like killing the pulp, why do we prepare teeth for crowns?

A

-Esthetics
-Prevention of catastrophic fracturing
-Protection of Root Canal Teeth
-Make tooth stronger

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10
Q

What must we balance for a crown prep?

A

-Unnecessary destruction of sound tooth structure
-Preservation of the structural integrity of the remaining tooth structure
VERSUS
-Mechanical requirements the patient needs
-Esthetic requirements the patient desires

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11
Q

When preparing a tooth for a crown in a conservative manner, the operator allows for a ___________ Reduction.

A

Morphological

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12
Q

What is morphological reduction?

A

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

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13
Q

What does morphological reduction of a crown prep allow for?

A

-Leaves the maximum thickness of residual tooth structure surrounding the pulp
-Also, leaves anti-rotational features, retentive and resistive features in the tooth preparations

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14
Q

As we create our crown preparation, we need to form the tooth utilizing geometric form criteria we call:

A

Retention
Resistance

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15
Q

What is retention?

A

Prevention of removal along the path of insertion

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16
Q

When does retention of a crown usually fail?

A

patient eating sticky foods

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17
Q

How is retention created?

A

-two opposing vertical surfaces with converging surfaces held to within certain parameters
- cements which offer frictional resistance to dislodgement (shear stress aiding in retention)
- mechanical factors such as Dental cements hold through mechanical interlocking of projections of cement into irregularities

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18
Q

What is resistance?

A

-Prevention of restoration being dislodged by apical or oblique forces

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19
Q

What is the reason for issues with resistance?

A

occlusal forces

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20
Q

_________ is the greatest determining factor in a crown’s dislodgment

A

Resistance

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21
Q

-Resistance is also aimed to oppose lateral forces which are not along the…

A

path of insertion

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22
Q

How is resistance build into a prep?

A

forming walls to block anticipated movement due to:
-Leverage
-Rotation (either vertically or horizontally)

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23
Q

What factors can affect the Resistance form of a tooth preparation?

A

-Total Occlusal Convergence (TOC)
-Preparation wall length
-Tooth Width after preparation
-Geometric forms (Grooves, Boxes, Vertical Planes, Pins, Morphological reduction)
-Surface area of the tooth preparation

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24
Q

What is total occlusal convergence?

A

the angle of convergence of taper between two opposing walls of a tooth preparation

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25
What is inclination?
the angle of convergence of taper of one wall of a preparation in relationship to the long axis of the preparation
26
What is the ideal total occlusal convergence (TOC)?
6 degrees
27
A tapered diamond bur will place a ______ degree converging angle to a tooth wall if the shank of the bur is held parallel to the intended path of insertion
2 or 3
28
Two opposing surfaces, each with 3 degree taper, addtogether for an overall TOC of ___ degrees
6
29
______ is the crown preparation feature most under operator control
TOC (total occlusal convergence)
30
Some _______ is required to seat crown
taper
31
Maximum crown retention is around ___ degrees of TOC
5
32
Approximately 1/5 the retention when TOC is ____ degrees
20
33
Convergence is inversely proportional to ________
retention
34
The average TOC of prepared teeth ends up in the range of _____ degrees
10-20
35
Molar tooth preps tend to have _________ TOC than premolars or anterior teeth
greater
36
Mandibular tooth preps tend to have _______ TOC than maxillary tooth preps
greater
37
Posterior preps are generally __________ (height) with _________ occlusal forces
shorter higher
38
Posterior preps require ______ angled TOC than anterior teeth to facilitate crown seating.
more
39
Acceptable TOC angle ______ degrees
10 – 20
40
The greater the height of the tooth preparation wall, the ________ the retention of the restoration
greater
41
Increased height = Increases the area of cementation = Increased __________
retention
42
For every 1mm increase in wall height, the retention and resistance form increases up to _____%
10%
43
The wall height should be greater than the...
tipping arc of displacement
44
The shorter the preparation, the _______ the taper MUST be
less
45
The taller the preparation, the ______ the taper MAY be
greater
46
What has greater resistance: - A narrow tooth with a smaller diameter preparation - A wider, larger diameter tooth
A narrow tooth with a smaller diameter preparation - This is because the small tooth has a shorter rotational radius for the Arc of Rotation (tipping arc)
47
Ideal and adequate Resistance and Retention, the height/width ratio should be greater than ____ for all teeth
0.4
48
If a molar is on average 10mm Facial-Lingually, and the minimal ratio is 0.4, then what should the wall height be?
10 X 0.4 = 4mm of wall height is ideal and adequate
49
What is the wall height ideals when preparation is within TOC 10-20 degrees for molars, incisors, and premolars?
-Molars 4mm -Incisors and premolars 3mm
50
If the tooth preparation does not have the resistance form you desire, what modifications can you make to the prep to increase the resistance?
-Decrease the TOC with axial re-shaping of prep walls -Addition of grooves / box forms (these must be parallel to path of insertion) -Increase wall height
51
What are ways to increase the crown prep wall height?
-lower margin -add wall height with core Build Up (possibly including pins) -Crown lengthening surgery -Orthodontic extrusion
52
T/F: There are times when leaving a crown preparation less than ideal will actually increase the resistance and retention form
True
53
What can you do if your TOC is not ideal (more than 20 degrees) or your wall height is less than ideal (molar 4mm, premolar and incisor 3mm)?
Geometric Forms can be added to your preparation - Box - Groove - Pin Hole
54
What are secondary retentive features for a crown prep?
-Most common to use Grooves for secondary retention. -Increases surface area -Established parallelism on opposing intra-coronal tooth surfaces -Limits the path of draw to one -Shorten the Arc of rotation, therefore, increasing resistance.
55
Retentive features should ideally be cut no deeper than ___mm axially and ___mm occlusally
1.5mm axially 2.0 mm occlusally
56
Grooves or Box forms must have a definite wall _________ to the direction of the displacing force
perpendicular
57
Retention is increased with increased _______
surface area
58
Increasing surface area helps with retention, but its not as vitally important as
TOC parameters and the Height/Width ratio
59
What is a good margin?
-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
60
What happens if margins are not closely adapted to the finish line of the preparation?
- Microleakage - Recurrent Caries - Possible de-cementation of restoration
61
The size of your finish line determines:
-The bulk of material at the margin -The fit of the restoration
62
Tooth Preparation Finish line should be...
-Needs to be conservative of tooth structure -Readily identifiable on tooth, impression and die -Provides sufficient bulk for restorative material
63
What are the types of finish lines (margins)?
64
What is important about morpholgical reduction?
-Adequate occlusal / incisal reduction and clearance without excessive removal -Uniform thickness of restoration material -Parallels the major planes of the tooth -No pulpal involvement
65
What are the preparation features that contribute to Structural Durability?
-Occlusal / Incisal Reduction -Functional Cusp Bevel -Axial Reduction
66
What is axial reduction?
-Creates space for an adequate bulk of material within normal contours of the tooth
67
What if you have not enough axial reduction?
– Thin restoration walls – difficult to finish and possible loss of strength
68
What if you have too much axial reduction?
Thick over contoured walls – plaque trap and periodontal inflammation
69
What happens if our preparation does not leave room for Structural Durability?
- Fracture of restoration - Grind through porcelain to adjust occlusion - Crown worn through due to thin material
70
Our crown preparation and final restorations should promote periodontal health by:
-Placement of margin for cleanse-ability -Marginal smoothness and crown adaptation -Axial contours and emergence profile
71
What are the main margin guidelines?
- Place margin where dentist can finish and evaluate - Place margin where patient can clean - Place margin where margin can be recorded during impression taking - Place margin on enamel when possible - Place margin supra-gingival when possible*** (depends) - Make margin as smooth as possible
72

Fixed (13 decks)

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