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fixed pros. > principles of tooth prep > Flashcards

principles of tooth prep Flashcards

1
Q

5 Principles of Tooth Preparation and
Restoration Design

A

1) Preservation of tooth structure
2) Retention and resistance form
3) Structural durability of the restoration
4) Marginal integrity
5) Preservation of the periodontium

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2
Q

biologic factors of tooth prep

A

Biologic
•Adjacent teeth
•Gingival Tissues
•Dental Pulp

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3
Q

•Causes of Injury

A

•Mechanical
•Temperature
•Chemical
•Bacterial

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4
Q

•Pulpal Insult due to?
will cause what?

A

•Trauma from tooth preparation
•Decreased thickness of dentin protection
•Remaining dentin thickness (between prepared walls and pulp) key to its protective nature
without enough dentin→Hypersensitivity and Pulpal inflammation and necrosis

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5
Q

Vital core:
guide to?
minimum dentin?
max reduction at axial/central fossa?

A

• A guide as to how much tooth structure can be removed w/o harming the pulp
• Pulp + 1mm minimum surrounding dentin
• Retentive features cut no deeper than 1.5mm (axial) - 2mm (central fossa)

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6
Q

•Tooth flexure / fracture – undermining cusps, how to counter this?

A

•Cuspal Coverage: reinforcement and protection of remaining tooth structure

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7
Q

•Must balance when prepping tooth

A

ØUnnecessary destruction of sound tooth structure
ØPreservation of the structural integrity of the remaining tooth
Vs.
ØMechanical requirements
ØEsthetic requirements

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8
Q

Morphologic reduction: benefits?

A

•Preserves the basic primary axial and occlusal tooth anatomy within the preparation.
•Maximal thickness of residual tooth structure surrounding the pulp is retained.
•Anti-rotational effects for increased

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9
Q

Preparations must be designed to resist _______ forces.

A

dislodging

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10
Q

most important factor under operator control which will determine if a restoration will remain cemented in place?

A

•The geometric form of the preparation is the most important of the factors under operator
control which will determine if a restoration will remain cemented in place.

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11
Q

Retention Form Prevents

A

•Prevents removal along path of insertion
• Occurs with sticky foods
• (least common problem)

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12
Q

rentention form Provided for by:

A

• Two opposing vertical surfaces with minimal convergence 6-10 degrees

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13
Q

cement offers what for retention, mechanical factor of this? weakest and strongest force?

A

Cement offers frictional resistance – shear stress.
Mechanical Factors: Dental Cements hold through the mechanical interlocking of projections of cement into irregularities of the surfaces being joined.
Weakest -tension
Strongest –compression

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14
Q

resistance form resist what forces? greatest determining factor to dislodgement resistance?

A

•Prevents restoration dislodgement by apical or oblique forces= Occlusal forces
•Resistance to lateral forces is the greatest determining factor in a crown’s resistance to dislodgement.

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15
Q

Resistance form is built into a preparation by ?

A

Resistance form is built into a preparation by forming walls to block anticipated movement due to:
•Leverage
•Rotation around a vertical or horizontal axis

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16
Q

Factors Affecting Resistance Form
(“Freedom from Displacement”)

A
  1. TOC
  2. OC
  3. Tooth Width (FL Dimension) - (Ratio of wall length : tooth width)
  4. Geometric Form
  5. Surface Area
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17
Q

Total Occlusal Convergence

A

•Inclination: relationship of one wall of a preparation to the long axis of the preparation
(“Taper”)
•Angle of convergence or total occlusal convergence: the relationship of taper between two opposing walls of a preparation.
• ideal TOC is 6o
•A tapered diamond or bur will impart an inclination of 2 to 3 degrees to any surface it cuts if the shank of the instrument is held parallel to the intended path of insertion of the preparation. Two opposing surfaces, each with a 3-degree inclination, would give the preparation a 6-degree taper.

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18
Q

Retention & Resistance Form: TOC
when is maximum R/R form obtained?
what is required?
under our control?

A

•Maximum R&R form obtained as opposing axial walls approach parallelism.
•Some taper (total occlusal convergence) is required.
•Feature most under operator control.

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19
Q

excessive convergence?

A

causes loss of retention.

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20
Q

•As occlusal convergence increases, retention?
max retentions at what angle?
what angle is there a significant decrease?
for every 5-degree increase?
Is taper proportional to retention?

A

•As occlusal convergence increases, retention decreases.
•Maximum retention @ 5o;
significant decrease > 20o TOC
•For every 5 degree increase in the total convergence angle, the retention and resistance
form may decrease up to 50%.
•Taper is inversely proportional to retention

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21
Q

acceptable TOC
molars vs. PM and antieror
man vs. Max
why?

A

• Average TOC of prepared teeth is in the range of 10-20 degrees.
• Molar tooth preps have > TOC than premolars and anterior preps.
• Mandibular tooth preps have > TOC than maxillary tooth preps.
• Due to access and visibility.

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22
Q

posterior preparations generally require more or less TOC
why?

A

However, posterior preparations generally require more TOC than anterior preparations.
•Posterior preparations are generally shorter.
•Posterior occlusal forces are generally higher.

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23
Q

TOC angle ranges: good, acceptable and mod required?

A

•Ideal TOC angle is: 6 to 10 degrees.
•Clinically acceptable TOC angle: 10 to 20 degrees.
•If the TOC angle is > 20 degrees, the preparation requires modification.

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24
Q

occlusocervical deminsion

A

Preparation Wall Length (Height) (Occlusocervical Dimension)
•Tooth preparation height measured from the incisal/occlusal surface to the margin.

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25
Q

increased OC and retention, why?

A

•Greater height of the crown better the retention of the restoration.
•Increase height = increases the area of cementation = Good retention

26
Q

•Wall length (height of the preparation) should be greater than_____

A

should be greater than the tipping arc of displacement, to prevent displacement of the restoration.
•“The preparation with longer walls (a) interferes with the tipping displacement of the restoration better than the short preparation (b).”

27
Q

Decreased wall length causes disproportionate decrease in: (choose 1)

A

disproportionate decrease in the resistance.

28
Q

increased length of prep increases______

A

resistance and retention

29
Q

For every 1 mm increase in preparation length, the retention and resistance form increases____%

A

up to 10%

30
Q

Retention / Resistance: Length vs Taper
•Wall length must interfere with?
•The shorter the preparation?
•The longer the preparation?

A

•Wall length must interfere with arc of rotation.
•The shorter the preparation the less the taper must be.
•The longer the preparation, the greater the taper may be.

31
Q

(OC / FL Ratio)
Height-Base Ratio – Arc of Rotation

A

•A narrow (smaller diameter) tooth can have greater resistance than a wider (larger diameter) tooth with same wall length
• Shorter rotational radius for the arc of rotation resists displacement

32
Q

OC/FL ratio should be?

A

ideally more than .4

33
Q

incisors/PM and molar prep minimal heights

A

•Incisors and Premolars: 3 mm minimum height.
•Molars: 4 mm minimum height
•(TOC = 10-20 degrees!)

34
Q

Retention and Resistance: Geometric Forms secondary Features:

A

Boxes – Grooves – Pin holes

35
Q

when to use geometric forms?
what do these establish?
effect on path of withdrawal?

A

•Used when R&R form of primary features is inadequate.
•Establishes parallelism on opposing Intracoronal tooth surfaces.
•2o Auxiliary Retentive Features limits the paths of withdrawal to ONE

36
Q

2oAuxiliary Retentive Features _______ the rotational radius
_______resistance to dislodgement

A

2oAuxiliary Retentive Features shorten the rotational radius
improving resistance to dislodgement

37
Q

•Grooves and box forms must have a wall doing what?

A

•Grooves and box forms must have a definite wall perpendicular to the direction of the displacing force.

38
Q

Resistance: Geometric Forms Rotation around a horizontal axis

A

Horizontal component of occlusal force has a rotating effect on a crown in a horizontal plane.
•Walls must be created to block the movement
•Preservation of axial line angles in preparation
•Vertical planes (perpendicular to arc of rotation)

39
Q

Resistance: Geometric Form
Pyramidal vs. Conical Form

A

•Pyramidal preparations have increased resistance form (morphologic reduction).
•Preserve facioproximal and linguoproximal corners (line angles)

40
Q

Retention and Resistance Form: Surface Area
effects of increased SA?
importance relative to TOC and OC/FL

A

•Retention is increased with increased surface area in sliding contact.
•The greater the surface area, the greater the retention (especially if consider longer walls).
•Not as important as TOC, and Height/Base ratio.

41
Q

How is resistance form assessed?

A

•Measure TOC between 2 opposing walls (convergence guide)
—(6o)10o– 20o(maximum)
•Measure wall length parallel with long axis
—3mm minimum OC dimension (4mm – molars)
•Measure tooth width (FL dimension) and wall height
—OC:FL ratio should be at least 0.4

42
Q

What modifications can be made to increase
resistance form?
axial walls?
addition of what?
wall length? how can this be done?

A

•Decrease TOC with axial wall re-shaping.
•Addition of grooves / small boxes (parallel to path of insertion).
•Increase wall length- Place margin at a more apical position, Possibly subgingival
—Pin-retained core
—(Crown lengthening surgery)
—(Orthodontic extrusion)

43
Q

How can inadequate Retention / Resistance
Form be improved?

A

•Reducing the TOC from 20°to 8°in the cervical 2 mm of the axial walls significantly increased the resistance form.
•Limiting the paths of withdrawal to ONE path with the use of grooves parallel to the intended path of withdrawal- Grooves must not be over-tapered in relation to the path of withdrawal.

44
Q

Preparation modifications for over-converged tooth with amalgam

A

•Amalgam restorations removed; intracoronal walls prepared for minimally convergent isthmus, boxes and grooves= preserves tooth structure
•Axial walls prepared for minimal convergence in cervical 1/3; forming a shoulder with bevel.

45
Q

STRUCTURAL DURABILITY OF THE RESTORATION
the rigidity of restoration?
how much tooth structure should be removed? why?

A

•Casting must be rigid enough not to flex.
•Sufficient tooth structure must be removed to create space for an adequate bulk of restorative material without over-contouring the restoration.

46
Q

Preparation Features that contribute to Structural Durability:

A
  1. Occlusal / Incisal Reduction
  2. Functional Cusp Bevel
  3. Axial Reduction
47
Q

inadequate Occlusal Reduction / Clearance presentation

A

•Thin area → hole in casting with wear
•Fractured ceramic
•Occlusal “adjustment” to opaque porcelain or metal on metal-ceramic crown

48
Q

•Morphologic Occlusal Reduction provides:

A

•Adequate occlusal/incisal clearance without excessive removal of tooth structure.
•Uniform restoration thickness
•Parallels the major planes of the tooth (not flat)

49
Q

•Morphologic Functional Cusp Bevel Reduction allow for?

A

•Allows for adequate thickness of restorative material
•without undue sacrifice of tooth structure
•without over-convergence

50
Q

Axial Reduction creates

A

Axial Reduction: creates space for an adequate bulk of metal within the normal axial contours of the tooth.

51
Q

Inadequate axial reduction leads to?
two possibilities?

A

Inadequate axial reduction →
B) thin walls → weak or difficult to cast and finish
C) bulky contours → plaque retention and periodontal inflammation (poor emergence profile)

52
Q

Requirements for successful restoration margins:
fit?
strength?
location?

A
  1. Fit as closely as possible to minimize cement film width (25μ)
  2. Sufficient strength to withstand forces of mastication (geometry of prep)
  3. Located where dentist can finish and inspect, and patient can clean
53
Q

Considerations of marginal integrity

A

•Marginal Geometry
•Margin Location

54
Q

margin should fit how?

A

•The margin should fit as closely
as possible to minimize cement
film width (25 μ).

55
Q

margins adaptio in relation to the cavosurface, why?

A

Margins must be closely adapted to the cavosurface finish line of the preparation to prevent:
•Microleakage and recurrent caries
•De-cementation of restoration

56
Q

Marginal Geometry – Cervical Finish Line requirements
tooth structure?
able to ID? on what?
provide?
allow ease of?

A

•Conservation of tooth structure
•Readily identifiable on tooth, impression and die
•Provide sufficient bulk of restorative material
•Relative ease of tooth preparation

57
Q

The design of the preparation finish line will dictate:

A

•The bulk of restorative material at the margin.
•The restoration fit.

58
Q

Marginal Geometry – Margin Types

A

•Knife Edge
•Chamfer
•Shoulder/ Radial (Modified) Shoulder
•Bevel (Beveled Shoulder)

59
Q

Preservation of the Periodontium

A

•Maintain periodontal health with
•Proper Margin location
•Marginal adaptation and smoothness
•Axial contours, emergence profiles

60
Q

Margin Location factors:
•Location must preserve?
•Placed where the dentist can?
•Placed where the patient can?
•Placed where they can be recorded?
•Placed on what tooth tissue ideally?
•Supragingival vs subg placement?
•ideal texture?

A

•Location must preserve the optimal health and prognosis of the periodontium.
•Placed where the dentist can finish/evaluate.
•Placed where the patient can clean.
•Placed where they can be recorded during impression making.
•Placed on enamel whenever possible.
•Supragingival placement is optimal when possible.
•Smooth as possible

fixed pros. (11 decks)

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