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Dentistry > Pros single crowns > Flashcards

Pros single crowns Flashcards

1
Q

What factors do you assess first if a crown does not seat at try-in?

A
  1. contacts
  2. check for residual temp cement
  3. intaglio surface: verify internal interferences with fit checker, occlude, acufilm
  4. if all above fail- take new impression
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2
Q

what is the tickness of shim stock?

Accufilm?

A

shim stock: 8 ums

accufilm: 12 ums

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3
Q
  1. According to Goodacre- what are the clinical complications for all types single crowns and their prevalence?
  2. What are the complications and prevalence for all ceramic crowns?
  3. What is the biggest complication with all ceramic crowns?
A

1. Any type of Single Crown

• Need for endodontic treatment: 3%

• Porcelain fracture: 3%

  • Loss of retention: 2%
  • Periodontal disease: 0.6%
  • Caries: 0.4%

2. All ceramic crowns:

• Pulpal health: 1%

• Fracture: 7%

  • Loss of retention: 2%
  • Caries: 0.8%
  • Periodontal disease: No significant changes

3. • Fracture: 7%

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4
Q

When do you consider a prophylactic endo?

A

pulp exposure

hx of trauma

lack of supporting tooth structure that will require a post and core (ferrule)

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5
Q

What is the problem with an open margin?

A

biologic: bacteria (plaque) trap/inflammation/caries

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6
Q

What are the most common problems with base metals?

A

biocompatability: corrosion, allergy

physical properties: difficult to polish and finish

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7
Q

What are the risks of an overcontoured crown?

A

plaque retention and periodontal problems

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8
Q

All metals used in dentistry are formed by either which two processes?

gives examples of same

A

Casting alloys: A wax model of the restoration is made, and an alloy is melted and cast into the shape of the wax

-restorations made from these alloys are castings: gold crowns, RPD frameworks

Wrought alloys: are first cast but are then shaped by mechanical force (e.g.; machining) into their final forms.

-endo files, ortho wires, implants

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9
Q

Types of detal alloys

A

solder alloys: used to join alloys together; must be melted without distorting the alloys they join : Soldering is distinguished from welding by the use of a third body, the solder, between the two workpieces, but without melting either of them (ie- space maintaners- SS wire and bands soldered together)

alloy composites: formed by sintering and are used as metal substructures for ceramic–alloy restorations.

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10
Q

What distinguishes prosthodontics from operative dentistry?

A

Pros:

changes or loss of OVD/occlusion

multiple edentulous spaces

difficult esthetics

-the restoration to a state of health and harmonious occlusion through the replacment of missing teeth/tooth structure, restoration of function and esthetics

Operative:

disease management - perio and caries

single unit crowns, inlays, single implants

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11
Q

How do YOU define a successful crown?

A

Biocompatibility

Esthetics

Function

Comfort

Cleansable

Longevity

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12
Q

In order to acheive an optimal restoration, what three governing requirements must be satisfied?

A

biological requirements

mechanical requirements

esthetic requirements

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13
Q

What are the 5 biologic requirements for a single crown?

A
  1. Conservation of tooth structure
  2. Avoidance of over contouring
  3. Harmonious occlusion
  4. supraginigval margins
  5. protection against tooth fracture
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14
Q

What factors must you consider when preventing damage during tooth prepartion?

A

you must consider:

  • adjacent teeth (bur positioning, leave proximal enamel as buffer, matrix bands)
  • soft tissues (cheeks/tongues/ginival complex)
  • the pulp (conservation of tooth structure, heat/water, chemicals)
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15
Q

What are the 5 requirements to a successful crown?

A
  1. Preservation of tooth structure
  2. Retention and resistance form
  3. structural durability of the restoration (see crown materials lecture)
  4. Marginal integrity
  5. Preservation of the periodontium
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16
Q

What factors influence the amount of tooth material removed during a preparation?

A
  1. materials (AMCs requires less reduction than ACCs)
  2. Color/morpholgy/tooth angulations
  3. previous restoration margins/caries
  4. Occlusion: plane of occlusion/deep vertical- if you wish to change the plane of occlusion and correct a deep bite- effects the lingual reduction of the max incisors
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17
Q

1 a) what is the physiologic factor that effects thickness of enamel/dentin and why?

2) What treatment option needs to be modified because of same?

A

1 a) age- the younger the tooth the thinner the enamel/dentin due to the larger the pulp; as we age, we lay down secondary and tertiary dentin and pulp chamber recedes;

Age 10-19: central incisor 1.8mm

Age 40-60: central incisor 2.0-2.8 mm

  1. therefore we DO NOT CROWN teeth in teenagers.
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18
Q

How thick is the enamel/dentin layer?

A

central incisor: 1.7-3.1mm

cervical premolars: 2.2-2.5mm

mand central incisor: 2.08mm

mand molar: 2.97mm

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19
Q

Adult dentition are able to support what reductions, in mm, of the axial and incisal/occlusal surfaces?

  1. What is the caveat?
A
  1. Most adult teeth can support 1.0 to 1.5 mm axial reduction
  2. Most adult teeth can support 2.0 to 2.5 mm occlusal/incisal reduction
  3. caveat is varrying TOCs from 5-20 degrees: a 20 degree TOC with 1.2mm margin leaves ~0.3mm of dentin on certain surfaces… caution with large pulps (younger pts) and greater reduction/TOCs
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20
Q

What is the goal for a successful crown prep?

in our preps we want to avoid…?

A

goal: Optimal reduction to provide for adequate strength, optimal esthetics, and physiologic contours

avoid- over-reduction AND under-reuduction

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21
Q

What does under-reduction result in?

What does over-reduction result in?

A

under-reduction: esthetic and mechanical issues

-over contoured crowns: stick out esthetically/compromised morphology, plaque retentive areas, cheek/lip/tongue biting; risk of fx because material is thinner

over-reduction: results in biological issues- ie pulp stress

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22
Q

How do you verify sufficient reduction?

A
  • make a provisional crown!
  • Triad and calipers
  • Prep check/blue mousse
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23
Q

What are the reduction guidelines for All Metal Crowns (AMCs)?

Incisal/occlusal

facial/axial

lingual

finish line

finish line depth

A

AMCs

Incisal/occlusal: 1.0mm

facial/axial: 0.5 - 0.8mm

lingual: 0.5 - 0.8 mm

finish line: chamfer

finish line depth: 0.3mm

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24
Q

What are the reduction guidelines for PFMs?

Incisal/occlusal

facial/axial

lingual

finish line

finish line depth

A

PFMs

Incisal/occlusal: 2.0 mm - 2.5 mm for optimal form, color, and occusion;

1.5 mm minimal

facial/axial: 1.0 mm - 1.7 mm

lingual: 0.5 mm - 1.0 mm for metal
1. 0 mm - 1.2 mm for porcelain

finish line: shoulder

finish line depth: 1.0 mm

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25
Q

What are the reduction guidelines for Bonded All Ceramic Crowns (ACCs)?

Incisal/occlusal

facial/axial

lingual

finish line

finish line depth

A

Bonded ACCs

Incisal/occlusal: 2.0 mm

facial/axial: 1.0 mm if not discloured; 1.2 mm - 1.5 mm (if discoloured)

lingual: 1.0 mm - 1.5 mm

finish line: Shoulder

finish line depth: Bonded: 0.5 mm

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26
Q

What are the reduction guidelines for Luted All Ceramic Crowns (ACCs)?

Incisal/occlusal

facial/axial

lingual

finish line

finish line depth

A

Luted ACCs

Incisal/occlusal: 2.0 mm

facial/axial: 1.0 mm if not discloured; 1.2 mm - 1.5 mm (if discoloured)

lingual: 1.0 mm - 1.5 mm

finish line: Chamfer

finish line depth: 1.0 mm -1.5 mm

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27
Q

What are the reduction guidelines for Zirconia Crowns ?

Incisal/occlusal

facial/axial

lingual

finish line

finish line depth

A

Zirconia/polycrystalline Crowns

Incisal/occlusal: 1.25 mm

facial/axial: 0.8 mm (ADL recommends 1 mm)

lingual: 0.8 mm

finish line: Chamfer

finish line depth: 0.5 mm - 0.8 mm

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28
Q

What is retention?

A
  • The feature of a tooth preparation that resists dislodgement of a crown in a vertical direction or along the path of placement. (GPT)
  • is a quantitative measurement
  • Cement dependent- you cannot measure retention without cement.
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29
Q

What is resistance?

A

-the features of a tooth preparation that enhance the stability of a restoration and resist dislodgement along an axis other than the path of insertion. (GPT)

-resistance anwers YES or NO- you either have it or you do not

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30
Q

What are the factors that influence retention (in order of importance)?

A
  1. Taper (most important)
  2. Surface area- related to height of prep
  3. Type of preparation
  4. Surface texture
  5. Luting agent (cement) (least important)
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31
Q

What is the recommended TOC?

What is the problem with too parallel?

How do you achieve proper taper?

A

10 - 20 degrees

  • the more parallel- the more retentive, but too parallel leads to undercuts
  • keep your prep burs vertical- the taper is built into them- trust your burs
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32
Q

how does total occlusal convergence relate to taper? Equation?

A

TOC = 2 x taper

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33
Q

which teeth when prepared show greater degrees of TOC?

does experience seem to matter in improving TOC?

A
  • Posterior teeth prepared to greater TOC than anterior teeth
  • Mandibular teeth greater TOC than maxillary teeth
  • Mandibular molars have greatest TOC
  • FPD abutments prepared with greater TOC
  • Using monocular vision give greater TOC than binocular (use binocular vision)
  • no real correlation with improved TOC between education and experience
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34
Q

What is the recommended range of TOC?

A

Recommended range of 10-20°

  • TOC should be achievable pre-clinically and clinically
  • TOC should provide resistance/retention form
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35
Q

What margin-types are the following burs? and what is the degree of taper?

8856/018?

8847KR/018?

5845KR/025?

A

8856/018- tapered chamfer, 2 degrees

8847KR/018- modified shoulder, 2 degrees

5845KR/025- modified shoulder, 5 degrees

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36
Q

How does the height of a preparation (surface area) affect retention?

How does the addition of grooves affect retention?

A

the greater the heigth of the axial wall, the greater the retention

-unless the grooves restrict the path of insertion, there is no added retentive benifit to adding grooves

Rosentiel’s Contmeporary Fixed Pros: Adding grooves or boxes to a preparation with a limited path of placement does not markedly affect its retention, because the surface area is not increased significantly. However, where the addition of a groove limits the paths of placement, retention is increased.

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37
Q

What types of preparation (restoration) have greater/less retention?

A

order most to least retentive:

  • a complete crown
  • 3/4 crown
  • onlay/inlay
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38
Q

What is the conflicting evidence with surface roughness vs smooth surface?

what is a potenial problem with surface roughness?

what is a benifit with smooth surface?

What is the recommendation?

A
  • roughness was a requirement to improve retention when using ZnPO3 cement
  • With adhesive cements, the studies are inconclusive. Therefore, rough

surface does not improve retention with non-ZP cements.

  • Course/rough surface may distort final impressions.
  • Smooth tooth preparations appear to enhance the fit of the restorations.

• Overall recommendation: Smooth tooth surface

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39
Q
  1. According to Rosesteil Comptemporary Fixed Prosthodontics, what interface is likely to be involved in a lack of cement retention?
  2. What steps can be taken to prevent this?
  3. Why is roughening the tooth surface not advised?
A

1. Rosensteil: failure usually occurs at the restoration-cement interface

  1. retention is increased if the restoration is roughened or grooved- air abrasion/silane etch
  2. Failure rarely occurs at the cement-tooth interface. Therefore, deliberately roughening the tooth preparation hardly influences retention and is not recommended, because roughness adds to the difficulty of subsequent technical steps in crown fabrication such as impression making and waxing
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40
Q

List the cements in order form greatest to least retentive.

A
  • adhesive resin (greatest retention)
  • RMGIC
  • GIC
  • Polycarboxylate
  • ZnPO3
  • ZOE (least retentive)
41
Q

What are the 4 factors influencing resistance?

(grestest to least influence)

A
  • Taper (greatest)
  • diameter
  • type of prep
  • luting agent (least)
42
Q

Taper’s affect on resistance?

recommended TOC?

A

The less the degree of taper the higher the resistance

recommended TOC: 10-20 degrees

43
Q

Explain Dr Parker’s resistance form and the critical convergence angle.

What is the % of molars that lack resistance form?

A
  1. intersect a perpendicular line (90 degree) from the wall being assessed to the contalateral axis: the surface of the wall below the intersect is the non-retentive region; the surface above this line is the retentive region;
    * if the amount of taper exceeds the ability for the wall to intersect with the axis at 90 degrees, there will not be any resistance and the crown will dislodge
  2. the degree of taper that ensures a perpendicular intersect is the ‘limitting taper’ or ‘critcal convergence angle’ (there has to be axial wall length above the perpedicular line- this is the retentive region)

3. 46% of molars had resistance thus 54% lacked resistance form.

-from the slide: “resistance form is adequate if the preparation wall (height) interferes with a line perpendicular to the radius at the point for which resistance form is being evaluated”

Tooth preparations have a critical convergence angle or “limiting
taper”. If this is exceeded, crown will dislodge

44
Q

Explain Dr Parker’s resistance form and the minimum axial wall height.

What is the minimum axial wall height recommended by Parker?

A

• Dr Parker found resistance with

  • 10mm diameter tooth
  • at least 3 mm tall
  • with TOC of 17.4° or less (8.5 taper)
  • resistance with 1 mm and 2 mm height , TOC’S needed to be 5.8 and 11.6 ° respectively
  • clinician’s can’t actually achieve these TOCs

• thus minimum height should be 3mm

45
Q

What is the minimum axial wall heigth and occlusal reduction recommendation by Ivoclar with non-adhesive cements?

A

4 mm axial wall height

1.5 minimum occlusal reduction (room for cement)

46
Q
  1. What is the recommended axial wall height and TOC for anteriors and premolars?
  2. What is the recommended axial wall height for molars?
  3. Why?
A
  1. Occlusocervical/incisocervical (measured at proximal surface)
  • 3mm for premolars and anterior teeth if within 10-20 deg
  • 4 mm for molar teeth
  1. Why?
  • molar teeth are typically prepared to greater TOC values (esp lingual wall)
  • Present with greater diameters
  • Receive greater occlusal forces
47
Q
  1. What can be done to increase resistance if minimal height requirements cannot be met?
  2. What forces do proximal grooves provide resistance for?
  3. What is the caveat with resin cement?
A
  1. If requirements not met: need auxiliary features such as grooves, boxes, resin cement, etc.
  2. Proximal box grooves provide resistance against B/L forces
  3. caution with adhesive preps and resin cement-
  • relying soley on sdhesion for retention
  • need enamel for adhesion
  • if no enamel- you must use conventional resistance/retention form preps
48
Q

How does the diameter of the prep influence resistance?

What has more resistance, a premolar (small diameter) or a molar (large diameter)?

A

it involves the diameter/height ratio:

  • pemolar has higher resistance that a molar due to its lower diameter/height ratio
  • a shorter molar with wider diameter has lower resistance
    • tend to be over-tapered, and require a higher axial wall- this is often unacheivable
49
Q
  1. How does circumfrential morphology influence resistance?
  2. Which shapes have greater resistance?
  3. How can you compensate for shape in order to increase resistance?
  4. What is the problem with second premolars?
A
  1. Geometric shape of tooth contributes to resistance to rotation
  • Similar to placing an anti-rotational component to a post
  • Seating groove
  1. Rectangular and rhomboidal shapes have greater resistance form than oval/conical types
  2. -Preserve “corners” of preps
    - If oval preps: place interproximal groves or other auxiliary feature (anti-rotational)
  3. problem with second premolars- cylinder in shape- difficult to compensate for rotation
50
Q

List in order of greatest to least resistance: types of restorations

A

full crown (highest)

3/4 crown

inlay/onlay (lowest)

51
Q

list cements in order of higher to lowest resistance

A

adhesive resin (greatest retention)

RMGIC

GIC

Polycarboxylate

ZnPO3

ZOE (least retentive)

52
Q

Eqn for retention/resistance form

A
53
Q

What 5 requirements must a margin satisfy?

A
  • It should be easily identifiable on the preparation, working die and in the restoration.
  • It should provide adequate bulk to allow for finishing and polishing of the restoration (prevent chipping).
  • It should be placed to allow optimal evaluation of marginal integrity (supraginigval).
  • It should adapt to the finish line of preparation with minimal opening after the restoration has been luted to place.
  • It should have adequate strength to resist deformation during the fabrication process and when placed under occlusal loading.
54
Q

By what measurements is crown adaptation (fit) defined?

A

Defined by the measurements of the marginal and internal gaps of crown restorations

55
Q
  1. Define a marginal gap?
  2. Define an internal gap?
A
  1. The marginal gap is vertical discrepancy at the margin

•marginal opening measured vertically

  1. The internal gap is a horizontal discrepancy at the right angle to the two opposing surfaces
56
Q
  1. Where are you most likely to find a maginal deiscrepancy?
  2. Which margins are easier to evaluate for integrity?
A
  1. most of found interproximal (relying on radiograph and impression), then subgingival
  2. • there is a direct relationship between visually accessible margins and the ability to evaluate the marginal opening (gap)
  • Supragingival margins: 2-51 µm (39 µm)
  • Subgingival margins: 34-119 µm (74 µm)
57
Q
  1. How does cementation influence marginal integrity?
  2. What is the ADA spec no. 8 for cement film thickness?
  3. cement spacer thickness?
  4. Why is venting critical to cementation?
A
  1. Marginal discrepancies are commonly increased following cementation
  2. ADA specification no. 8 for:
  • cement film thickness: 25 µm range
  • cement spacer: 25 to 40µm
  1. cementation w/o venting can cause marginal discrepancies in excess of 100 µm
58
Q

What are the cement spacer options available for CADCAM system?

A

CADCAM options are 80um -100um

59
Q

What problems can defective margins contribute to?

A

Poor marginal fit will

  1. Increase plaque retention
  2. Predispose to caries due to cement dissolution
  3. Detrimental to periodontal health and increased
    gingival inflammation
60
Q

True or false:

Virtually margins are open.

A

True

61
Q

What is the average marginal opening? range?

What is the achievable marginal opening for a skilled lab technichian?

what is the size of a bacterial cell in ums?

What is the maximum tolerable margin opening?

A
  1. The average opening is about 100 µm (this is considered clinically achieveable)
    * a range from 25 to 500 µm.
  2. Lab: 20 µm opening is achievable if technician is skilled.
    (aka: your crowns are, at best, already 20ums open from the margin when you get them from the lab)
  3. Bacteria are 1 to 5 µm
  4. 120 µm is the maximum tolerable marginal opening
62
Q
  1. What is the average range for the internal gap of a conventional ceramic crown?
  2. What width of internal gap is thought to improve resin cement performance?
  3. Which type of restorations show the best marginal and internal gap adaptations?
A
  1. The internal gap of conventional ceramic crown: range of 123 to 154 µm
  2. internal gap of 50 to 100 µm could result in the most favorable resin
    cement performance.

*An internal gap value of 200 to 300 µm also may be clinically acceptable, this requires in vivo confirmation

  1. Heat press ceramic restorations showed the best marginal and internal crown adaptation results.
63
Q

What could potentially be a problem with a resin cement layer that is too thick and why is this important to glass based crowns?

A

Glass based crowns: their strength is dependant on the bonding of cement- increase in thickness of cement - decrease in strength;

if thick resin cement- polymerization and shrinkage- bond may not be reliable

64
Q

What are the four margin designs (finish line form)?

For which types of crowns can they be used?

A
  • Chamfer (metal or Zirconia; deep chamfer Glass ceramics)
  • Shoulder (PFM/ all ceramics/ Zirconia-though not required for strength, so unecessary removal of tooth structure)
  • Beveled chamfer or beveled shoulder (only for cast metal)
  • Feather edge, knife edge, or disappearing margin (only for cast metal)
65
Q

What are some advantages of the chamfer margin?

A
  • Easily made with chamfer bur & distinct on die
  • Provides adequate bulk for rigidity
  • adequate reduction for development of proper contours while conserving tooth structure
66
Q

What are the dimensions of a chamfer margin?

What is the typically used chamfer width?

A
  • 0.3 mm to 0.8 mm
  • 0.3 mm typically used – but no studies show this margin to be superior
67
Q

Why is a chamfer margin not recommended for a PFM?

A
  • marginal esthetics are more difficult- opaque porcelain shines through;
  • require adequate thickness for opaquing porcelain and dentin porcelain
  • porcelain distortion during firing (high shrinkage of surface porcelain)
68
Q
  1. What are the finish line dimensions of a shoulder margin?
    - Why?
  2. what are the dimensions of materials at the margin of a porcelain butt PFM?
A
  1. finish line dimensions: 1.0 mm to 1.5 mm
    - require a minimal material thickness for esthetics & to develop proper emergence profile.
  2. 0.3 mm for metal coping + opaque porcelain (0.2 mm) + translucent
    porcelain (1 mm)
69
Q

What are the advantages of a shoulder margin?

A

Advantages:

percise margins (shoulder porcelain does not shrink as much as surface porcelain)

maximum esthetics- allows for translucency of porcelain interproximally

improved seating

best choice for porcelain bearing areas due to providing the thickness for porcelain strength

70
Q

Why are shoulder margins not recommended for cast metal crowns?

A
  • not recommended for cast metal: shrinkage of metal would result in poor margin adaptation

*(we compensate for metal shrinkage with high expansion stone)

71
Q

What is opaque porcelain?

A

Opaque porcelain:

  • the first layer consisting of porcelain modified with opacifying oxides which is important for metal ceramic bonding
  • this layer also masks the color of the metal/underlying tooth structure
72
Q

What is a shoulder-bevel margin? ???

Which restorations?

Advantages?

A
  1. Polished metal surface at margin
  2. PFM (collar), FGC (AMC)
  3. the bevel buccal and lingual provides a ferrule effect Structurally compromised teeth:

Laboratory correction-burnish

73
Q

What restorations include a bevel in their prep?

A

cast metal margin restorations only

74
Q

Why bevel- 3 functions of a bevel?

A

a) to allow the cast metal margin to be bent or burnished against the prepared tooth structure
b) to minimize a margin discrepancy if the crown doesn’t seat fully
c) to protect unprepared tooth structure from chipping - the act of beveling removes unsupported enamel
d) a bevel reduces marginal defects- (Rosner’s study)

75
Q

What are the disadvantages of a bevel?

A
  1. sub-g margins- if you cannot access the bevel, there is little advatage of beveling (no reason for a bevel).
  2. beveling may lead to subgingival extensions of the preparation or placement of the margins on dentin or cementum (rather than enamel)
  3. beveling is only relevant to metal margins!
76
Q

Explain Rosner’s Bevel

A
  • Rosner’s study demonstrated that a bevel reduces marginal defects
  • as the bevel angle increases, the marginal discrepancy decreases
77
Q

Advantages and disavatages of a feather edge margin?

What are the recommendations for its use?

A
  1. Advantage:
    * Conserves tooth structure

Disadvantages:

  • creates over-contoured restorations
  • Poor esthetics with porcelain
  • Insufficient bulk with thin friable margin
  • Difficult to read margin on die
  1. Is not recommended-unacceptable
  • however it is still used for:
    • Furcation
    • Severely tilted mesial of molars
78
Q

What are the periodontium considerations with single crowns?

A
  1. osseous architecture
  2. dentogingival complex
  3. gingiva esthetics
79
Q
  1. What is the osseous architecture and how does it change from anterior to posterior?
  2. What determines the gingival levels?
A

the osseous architecture

  • follows contour of CEJ
  • is located 2 mm apical to CEJ (1-3 mm range)
  • scallops in the anterior: 3.5 mm interproximally
  • Flattens posteriorly
  1. Gingival levels are determined by the height of the bone (soft tissue follows the bone)
80
Q

What are the components of the dentogingival complex?

A

Dentogingival complex:

sulcus + epithelial attachment (JE) + connective tissue attachment

81
Q

What is the biological width? measurements?

In order to not violate the BW, what is the minimal distance required from the alveolar crest to the margin of the restoration?

A
  1. Biologic width (BW): approx 2mm
  • Junctional epithelium attachment ~ 1 mm
  • connective tissue attachment ~ 1 mm
  • remains constant but can have a range of less than 1mm to 4mm in the same individual
  1. minimal distance from heigth of alv bone to margin of restoration: 3mm
    * BW + 1mm minimal depth of sulcus- can usr the sulcus depth (if healthy) as guide for subgingival margin placement.
82
Q
  1. average width of sulcus?
  2. How is the depth of the sulcus determined? Can you determine it clinically?
A
  1. Arithmetic average : 0.69 mm
  2. -Determined histologically
    - Sulcus depth not equal to probing depth
    - Cannot determine base of sulcus clinically
83
Q

What is the average width of the JE?

How many cell layers thick?

What is the cell turnover rate?

How does it attach to the tooth? to an implant?

A
  1. Junctional epithelial attachment: arithmetic average 0.97 mm
  2. ~10 cell layers thick (can be up to 20 in later life)
    * junctional epithelium tapers from its coronal end, which may be 10 to 29 cells wide to one or two cells at its apical termination, located at the cementoenamel junction in healthy tissue
  3. Cell turnover 4-6 days

4, attachment to tooth by hemidesmosomes: tight approximation

  1. Attach to natural and artificial structures (JE will attach to implants)
84
Q
  1. What is the average width of the CT in the dentogingival complex?
  2. How does it attach to the tooth? implants?
  3. What does the connective tissue in the dentogingival complex consist of?
  4. Which fibers are involved with a BW invasion?
A
  1. CT attachment = 1.07 mm (average)
  2. connects directly to root surface: ends of collagen fibers: Sharpey fibers
    * it does not attach to implant or titanium abutment
  3. consists of:
  • multiple gingival fiber bundles
  • Nerve and blood supply: pain on probing
  1. Biologic width violation involves the circumferential fibers
85
Q

What happens when you violate the BW?

A

When you violate biologic width:

  • bone loss
  • apical migration of epithelial attachment
  • compromised periodontal health/gingival iflammation
86
Q

What is bone sounding?

Technique?

A
  1. Measure total dentogingival complex from FGM to osseous crest and biotype
  2. Technique:
  • local anaesthesia
  • probe sulcus (feel for resistance)
  • angle probe on root surface
  • force to occlusal crest
87
Q

What are the average distances in mm of the free gingival margin to the FACIAL crestal bone, and % of occurance?

A

• Osseous crest to free gingival margin distances

  • 85% Normal crest: 3 mm
  • 2% High crest: less than 3 mm
  • 13% Low crest: more than 3 mm (anterior teeth with bone dehiscience)
88
Q

What are considered normal, high and low distances (mm) from the free gingival margin to the INTERPROXIMAL crestal bone?

A

• Osseous crest to free gingival margin distance:

  • Normal crest 3-4.5 mm
  • High crest less than 3 mm
  • Low crest more than 5 mm

knowing the crestal heights helps determine supra vs subgingival margins

89
Q

What are the distances from FGM to facial and interproximal crestal bone for ‘normal crest’?

What are the considerations for a ‘normal crest’ crown preparation?

A

Normal crest:

  • 3 mm from free gingival margin (FGM) to crest of facial alveolar bone
  • 3-4.5 mm interproximal

Normal crest crown prep considerations

  • Tissue level stable
  • Margin location should be:
    • 0.5 mm to 1.0 mm apical to the FGM
    • 2.0-2.5 mm coronal to the bone
  • restoration margin should mimic the gingival scallop interproximal
  • Facial: the distance of the margin to the bone should be 2.0 mm to 2.5 mm and intracrevicular.
  • Distal: Less than 0.5 mm (high crest)
90
Q

What are the distances from FGM to facial and interproximal crestal bone for ‘low crest’?

What are the considerations for a ‘low crest’ crown preparation?

A
  1. distance from FGM to crestal bone in “low crest”:
  • facial: more than 3 mm (anterior teeth with bone dehiscience)
  • interproximal: more than 5 mm
  1. Crown prep considerations:
  • Tissue level unstable
  • High risk for facial recession or black triangle
  • Consult with periodontist
  • Retraction technique is critical
  • Finish line placement
  • Consider supragingival level or at FGM and at CEJ (do not place less than 2.0-2.5 mm coronal to bone
91
Q

What are the distances from FGM to facial and interproximal crestal bone for ‘high crest’?

What are the considerations for a ‘high crest’ crown preparation?

A
  1. distance from FGM to crestal bone in “high crest”
  • facial crest: less than 3 mm
  • interproximal: less than 3 mm

Considerations:

  • tissue level stable
  • Interproximal adjacent to edentulous space
  • Minimal room for retraction technique
  • Risk for biologic width violation: margin too close to the bone
  • Finish line placement: less than 0.5 mm apical to FGM

(recommend do not place margin sub-g in posterior teeth- place it equogingival)

92
Q
A
93
Q

When do you choose a supragingival margin?

A

Choose supragingival margins first:

  • When retention/resistance forms are adequate
  • Tooth condition permits (current restorations/fractures)
  • Esthetics permits
  • Check probing depth and biotype
94
Q

Why choose a subgingival margin?

A

Choose subgingival margins in order to:

  • in order to achieve adequate height for resistance and retention
  • for extension beyond caries, fractures, erosion/abrasion, or other defects
  • to obtain ferrule for endodontically treated teeth
  • to improve esthetics of discolored tooth
  • Sensitivity?
95
Q

What can you do to prevent underpreparation or over preparation?

A

use depth cuts and a system

96
Q

What are Dr. Kois’ 5 steps to crown preparation?

A
  1. Incisal reduction
  2. Facial reduction
  3. Determine cervical limitation (bone sounding and crest distances)
  4. Lingual reduction/blend
  5. Finish line/taper
97
Q

Which burs are easiest for interproximal reduction?

A

can start with 330

champfer bur is easiest- follow crestal scallop

98
Q

What are the consequecences of inadequate lingual reduction?

A

straight palatal surfaces of maxillary anterior teeth violate envelope of motion:

  • there will be:
    • Increased mobility of maxillary anterior teeth
    • worn out mandibular anterior teeth or
    • porcelain fx
99
Q

What are the 9 factors of tooth preparations for complete crowns according to Goodacre?

What are the recommendations for meeting the 9 requirements?

A
  1. Total Occlusal Convergence (TOC/Taper)
    * strive for 10-20 degrees
  2. Occlusocervical/Incisocervical dimension (height)
  • Incisors & premolars: 3 mm height with 10-20 deg TOC
  • Molars: 4 mm height with 10-20 deg TOC
  1. Ratio of OC.IC dimension to faciolingual dimension (height and diameter)
    * Ratio height/base should be 0.4 or higher for all teeth
  2. circumfrential morphology
  • Preserve line angles – enhances resistance form
  • Round teeth– place grooves or boxes
  • Most molars need grooves (3-D rotation)
  • Place proximal grooves or boxes routinely for molar FPD abutments
    5. axial and incisal/occlusal reduction depths
  • AMCs: 0.5-1 mm respectively
  • Greater than 1 mm reduction for metal ceramic can compromise pulp on young patients
  • 2 mm occlusal/incisal reduction is usually supported by adults.
  • ACCs- 2mm occlusal/incisal reduction
  • ACCs with semi-translucent porcelain: 1mm reduction is sufficient
    6. finish line location
  • Supragingival margins when conditions permit
  • If subgingival, avoid epithelial attachment
    7. finish line depth and form
  • Minimum 0.3 mm chamfer margin is adequate for all metal crowns
  • Metal ceramic margin choice based on personal preference.
  • Chamfer or shoulder for all ceramic bonded restoration. Depth greater than 1 mm not needed for Semi-translucent systems.
    8. line angle form
  • Round line angles on preparations
    9. surface texture
  • Smooth prep may enhance fit; roughness has not proven to benefit adhesive cements

Dentistry (16 decks)

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