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COPY BDS3 University of Adelaide Dentistry > Fixed Pros > Flashcards

Fixed Pros Flashcards

1
Q

What are examples of complex conservative dentistry in fixed prosthodontics?

A
  • Inlays
  • Onlays
  • Veneers
  • Posts
  • Cores
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2
Q

What are the main types of fixed pros

A
  • Complex Conservative Dentistry

- Crown and Bridge

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3
Q

What is meant by an indirect restoration?

A

A rigid restoration that is constructed outside the mouth and then fitted

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4
Q

What are materials used in indirect restorations?

A
  • Porcelain
  • Gold
  • Base Metals
  • Porcelain fused to gold
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5
Q

What is a fixed crown?

A

An artificial extra-coronal coverage replacement that restores missing tooth structure by surrounding part or all of the remaining structure with a material such as cast metal, porcelain or a combination of materials such as metal and porcelain

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6
Q

What are different types of crown?

A

Full Crown

Partial Crown: 3/4 Crowns, Onlays

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7
Q

What is a pontic?

A

An artificial tooth/teeth on a prosthesis that replaces a missing natural tooth

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8
Q

What is an abutment?

A

A tooth that serves to support or retain a bridge

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9
Q

What is a retainer?

A

Component of a restoration that is cemented to the abutment teeth to retain a bridge

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10
Q

What is an inlay?

A

A intra coronal restoration that is within the internal boundary of the tooth

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11
Q

What is an onlay?

A

An intracoronal restoration that covers a cusp or external boundary of the tooth

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12
Q

What are indications for crowns?

A
  1. Protection of weak tooth structure
  2. Re-establish occlusion
  3. Modification of tooth shape
  4. Replacement of missing tooth structure/tooth/teeth
  5. As retainers: e.g. to help retain a partial denture
  6. Aesthetics (minor reason)
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13
Q

What are contraindications for crowns?

A
  1. Poor Oral Hygiene / Active Dental Disease
  2. Cost
  3. Age / Ill Health
  4. Excessive Removal of Tooth Structure
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14
Q

What is the main reason for crown failure?

A

Recurrent Caries

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15
Q

What is the longevity for crowns at 10 years?

A

96%

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16
Q

What is the problem with placing crowns in younger patients?

A
  1. Inadequate secondary dentine increases the risk of pulp exposures
  2. Passive Eruption after 14 exposes crown margins if not subgingivally placed
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17
Q

What is the problem with placing crowns in old patients?

A

Mobility issues for complex work

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18
Q

What are indications for veneers?

A

Diastema Closure
Alter Shape, Contour, Position
Alter Tooth Colour
Mask Surface Anomalies (tetracycline staining, hypomin, hypoplasia))

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19
Q

What are advantages of veneers?

A
  • Excellent aesthetics
  • Alloy free (No Sensitivity issues)
  • Good clinical record
  • Conservative restoration
  • Very good colour stability
  • Good Biocompatibility
  • Cheaper than full crown
  • Very thin
  • Minimal/no prep on teeth, in enamel only (Good bond)
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20
Q

What are the 3 functions of a post?

A
  • Retain the core (foundation restoration)
  • Stabilise the core (primary function is supporting the core)
  • Obturation of the post canal
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21
Q

How can a post provide additional support to a tooth

A

1) Resistance of filling against fracture

2) Retention of filling against dislodgement

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22
Q

What are the functions of a core?

A
  • Foundation for coronal restoration
  • Retention and stabilisation of coronal restoration
  • To perform as an interim restoration
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23
Q

What are the 5 governing principles of a crown preparation?

A
  • Preservation of tooth structure
  • Retention and resistance form
  • Structural Durability
  • Marginal Integrity
  • Preservation of periodontium
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24
Q

What is retention form?

A

Prevents removal of the restoration along the path of insertion or long axis of the tooth preparation

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25
Q

What is resistance form?

A

Prevents dislodgement of the restoration by forces directed in an horizontal or oblique direction

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26
Q

What is the purpose of a taper?

A

Allows the restoration to be seated

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27
Q

What is the ideal taper angle?

A

The angle of the opposing walls meet at 6-10 degrees

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28
Q

What is the issue with having an idealised taper of 0 degrees? (Parallel)

A

Likely to get it wrong (angle is converged and an undercut created) and the restoration can’t be seated

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29
Q

What is the perfect taper angle?

A

0 degrees (Parallel)

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30
Q

Do taper angles apply for both intracoronal and extracoronal restorations?

A

Yes, but require tapering to seat and attach indirect restorations

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31
Q

What is the issue with short-walled preparation of a large tooth?

A

Prone to tipping displacement

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32
Q

How can you overcome displacement issues with a short walled preparation

A

Increase resistance by placing grooves (increased surface area)

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33
Q

What are issues that can occur with the path of insertion?

A

Crown seating can be locked out by interference from a neighbouring tooth

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34
Q

What are 5 rules to ensure structural durability for a crown?

A
  1. Restoration must contain adequate material to withstand occlusion
  2. Follow Anatomical Form during preps
  3. Ensure adequate height to length ratio
  4. Adequate Occlusal Thickness
  5. Small diameter of crow prep resists tipping
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35
Q

Why is a subgingival margin problematic?

A
  • Affects gingival health - biofilm accumulation + gingivitis
  • Harder for patients to clean
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36
Q

T/F: Dental Ceramics have good tensile strength

A

False, they have good compressive strength

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37
Q

What is the Teknik 847-012 bur used for?

A

Medium grit tapered diamond with a flat end for:

  • Cuts flat butt shoulder finish
  • PJC + PBM preparations
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38
Q

What is the Komet 8877-010 bur used for?

A

Torpedo shaped fine grit parallel diamond for:

  • Cutting fine chamfer margins
  • Axial reduction for crowns, gold, PBM
  • Finishing margins, proximal flares
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39
Q

What is the Teknik 856-014 bur used for?

A

Long 9mm medium grit tapered diamond with a round end for:

  1. Cuts flat shoulder with rounded internal line angle
  2. Axial reduction - FGC/PBM/Porcelain Veneer Preps
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40
Q

What is the Horico 239-018 bur used for?

A

Coarse grit pear shared for:

  • Concave reduction on palatal and occlusal
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41
Q

Why are non-vinyl gloves used for mixing PVS putty?

A

Sulphur content in some latex gloves inhibits the putty set

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42
Q

Which burs are suitable for clearing interproximal contacts?

A

L10 or TC 169L

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43
Q

Which bur would you use for a flat shoulder finish?

A

Teknik 847-012

L20

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44
Q

Which bur would you use for a chamfer finish?

A

Komet 8877-010

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45
Q

What are 6 main reasons for making a Temporary Crown from a Dentist’s perspective?

A
  1. Pulpal Protection (from dentinal sensitivity, decay and fracture)
  2. Positional Stability (horizontal drift or overerruption)
  3. Restoring Function
  4. Restoring Aesthetics
  5. Maintain Periodontium
  6. Protect Underlying Tooth Structure and Core Structure
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46
Q

What are 5 requirements that a patient might have for a temporary crown?

A
  1. Should look like natural tooth - matching shape and colour
  2. No pain or discomfort
  3. Comfortable when chewing and speaking
  4. No food impaction
  5. Doesn’t break or fall off
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47
Q

What are Anterior Prefabricated Crown Forms made of?

A

Polycarbonate - in order to be tooth coloured

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48
Q

What are Posterior Prefabricated Crown Forms made of?

A

Aluminium - in order to be functional on occlusal load areas

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49
Q

What are some composite materials that can be used for direct temporary crowns?

A

Bis-acryl (Bis-GMA) Composite Resins (Protemp 4)
Methyl Methacrylate (Duralay, Jet)
Vinyl Ethyl Methacrylate (Trim)

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50
Q

What were some issues with earlier generation temporary crown materials?

A

Very heavy resin smell - unpalatable to patients
Highly Exothermic
High Shrinkage

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51
Q

What are some properties of 4th generation Bis-acryl (Bis-GMA) Composite Resins (Protemp 4)?

A
  1. Low shrinkage
  2. High dimensional stability
  3. Low exothermic reaction
  4. Brittle in thin sections
  5. Irritative to Skin Contact
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52
Q

Where might Vinyl Ethyl Methacrylate (Trim) be more suitable than Bis-acryl (Bis-GMA) Composite Resins (Protemp 4) for temp crowns?

A

Higher strength and hardness - suitable for long span temp bridges

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53
Q

Why might Methyl Methacrylate (Duralay, Jet) be less suitable than Bis-acryl (Bis-GMA) Composite Resins (Protemp 4) for temp crowns?

A

Less suitable due to high shrinkage, high exothermic reaction and high pulp toxicity due to free monomer

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54
Q

What are the 10 steps for making a custom-made temporary crown?

A
  1. Make a pre-operative impression of the tooth
  2. Complete the crown preparation
  3. Make temporary crown - fill the pre-op impression with Protemp and place onto prepared tooth
  4. Remove temporary crown from tooth before resin has fully set
  5. Leave to harden outside mouth
  6. Take secondary impression of crown preparation
  7. Trim margins of temporary crown to the prepared finishing line
  8. Adjust occlusion
  9. Cement with suitable temporary cement
  10. Remove excess cement at margins and re-check occlusion before dismissing patient
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55
Q

What are the 5 defects that can occur with temp crowns?

A
  1. Open margins
  2. Bulky or overextended margins
  3. Open proximal contacts
  4. “High” or supra-occlusion
  5. Infra-occlusion
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56
Q

What are potential complications from a temporary crown with open margins?

A
  1. Microleakage
  2. Dentinal Hypersensitivity
  3. Pulpitis
  4. Caries (long term)
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57
Q

What are potential complications from a temporary crown with bulky/overextended margins?

A
  1. Plaque Retention
  2. Marginal Gingivitis
  3. Gingival Recession
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58
Q

What are potential complications from a temporary crown with open proximal contacts

A
  1. Gingivitis from Food Impaction
  2. Drift of adjacent teeth
  3. Contacts become too tight for permanent crown
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59
Q

What are potential complications from a temporary crown with high/supra-occlusion?

A
  1. Pain on biting

2. Fracture of Temp Crown

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60
Q

What are potential complications from a temporary crown with infra-occlusion?

A
  1. Over-eruption of opposing tooth

2. Final Crown will requires extensive occlusal adjustment

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61
Q

What are some desirable properties of temporary cements?

A
  1. Thin film thickness - 30-50 microns
  2. Non-irritating to soft tissue
  3. Fast setting with adequate strength
  4. Easy to remove set cement
  5. Compatible with composite resin luting cement
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62
Q

What are 3 different types of Temporary Cements

A
  1. Modified ZnO eugenol cement (Tempbond)
  2. Eugenol free temporary cements (Tempbond NE, RelyX TempNE)
  3. Polycarboxylate Cement (Poly-F cement)
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63
Q

What are the issues with the use of Modified ZnO eugenol cement (Tempbond)?

A
  1. Forms a poor bonding substrate against CR

2. Can cause hypersensitivity reaction / stomatitis on soft tissue

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64
Q

What are the benefits of a Eugenol free temporary cements such as Tempbond NE

A
  1. Better bonding to CR cores/restorations

2. Lower hypersensitivity to soft tissue around margins

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65
Q

When would a Polycarboxylate cement (Poly-F cement) be used?

A

When a stronger “temporary” cement needs to be in place - for example if the temp crown needs to be held for over 4 weeks because the patient is going away.

Polycarboxylate is actually an old permanent cement but has since been superceded so is ideal for this purpose

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66
Q

What are the steps for preparing a polycarbonate crown?

A
  1. Select the correct crown size: based on Mesio-distal width (Wide > Medium > Narrow)
  2. Shorten length to match adjacent teeth
  3. Leave tab for handle
  4. Roughen inside to improve bond
  5. Fill crown form with Protemp and seat on tooth
  6. Remove from tooth when “rubbery”
  7. Use soflex discs to trim until margin coincides with imprint of finish line on tooth
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67
Q

What are the steps for preparing an aluminium crown?

A
  1. Select crown size from mesio-distal width
  2. Shorten crown using crown and collar shears. occlusally level with adjacent teeth and margins just cover finish line on prepared tooth
  3. Ask the patient to bite down to contour occlusal surface of crown
  4. Make two holes using a Jet 330 but on buccal and lingual surfaces for resin retention
  5. Fill the crown with Protemp and seat on lubricated tooth
  6. Remove the crown before Protemp sets hard
  7. Trim margins to imprint of finishing line in Protemp using black coarse soflex disc
  8. Check and adjust occlusion
  9. Smooth with brown soflex discs
  10. Cement with temporary cement
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68
Q

What is a connector?

A

A Connector: The join between the Pontic and the retainer

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69
Q

How do direct and indirect restorations vary?

A

Material: Rigid (Indirect) vs Direct (Malleable)

Design: Must fit by insertion via long axis of tooth (Indirect) vs Retentive Design (Direct)

Clinical: Direct can be done in one appointment

Materials: Resins/Amalgam/GIC vs Ceramics/Metals

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70
Q

What are 6 considerations when planning to do an indirect restoration?

A
  1. Occlusion
  2. Endodontic Status/Vitality
  3. Other teeth requiring treatment (Strategic Value, Active Disease)
  4. Future Outlook for Tooth
  5. Future Outlook for Whole Dentition
  6. Restorability of the Tooth
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71
Q

If a patient has very darkly stained teeth and wants veneers, what aesthetic considerations would you have?

A

Veneers are semi-translucent, so teeth bleaching might be indicated if the patient is concerned about the current shade being too dark/stained

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72
Q

T/F: Veneers are the most conservative option for indirect restorations

A

Yes, as they require the least amount of prep removing healthy tooth structure

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73
Q

What materials are typically used for posts?

A

Titanium Posts

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74
Q

When would an elective post be considered?

A

If there was insufficient coronal tooth structure for a crown, an elective RCT could be performed to insert a titanium post, with a composite core created over it to support the crown

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75
Q

What are the risks of a core?

A

Vertical Root Fracture

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76
Q

T/F: Increasing crown height aids in increasing retention

A

True, because there is more surface area

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77
Q

Given a molar and pre-molar tooth of the same height, which has more retention and why?

A

Molar has more surface area = Greater retention

Pre-Molar has less width = less likely to for tipping displacement

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78
Q

Clinical, how would you ensure that a crown prep has an adequate path of insertion

A

By viewing the tooth directly at the long axis of the tooth, if all aspects of the crown prep can be seen, then the path of insertion will be successful.

If any aspect can not be seen, an undercut has been created and the crown will not seat adequately

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79
Q

What obstacles can occur when seating a crown, when consider the path of draw in the mesial/distal dimension

A

That an interproximal contact from adjacent teeth will “lock out” the crown and prevent adequate seating

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80
Q

What broader context consideration will a clinician need to consider with path of insertion

A

Whether the tooth is tilted or crowded, that the long axis of the tooth might need to be altered to allow for a path of draw that can fit despite interference from other teeth

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81
Q

What structural durability aspects does a clinician need to consider for a crown?

A
  1. Adequate thickness of material in all directions
  2. Following anatomical form
  3. Adequate height/length ratio
  4. Smaller diameter to resist tipping
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82
Q

What is the minimum occlusal reduction needed?

A

1.5-2mm

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83
Q

What is the minimum labial reduction needed at the gingival 1/3rd for an Mx anterior PFM?

A

1mm

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84
Q

What is the minimum labial reduction needed at the coronal 2/3rd for an Mx anterior PFM?

A

1.5mm

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85
Q

What is the minimum reduction needed at the lingual for an Mx anterior PFM?

A

0.5mm - as the lingual is metal only

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86
Q

What is the minimum reduction needed at the proximal for an Mx anterior PFM?

A

A transition between the 1mm on the labial, to the 0.5mm on the lingual

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87
Q

What is the Cavosurface finish line

A

The interface between the cavity prep and the finished restoration. The margin should transition seamlessly, without excess or deficiencies

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88
Q

On what material can a feather edge or chisel finish be considered?

A

Full/Partial Gold Crowns only

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89
Q

What is a chamfer?

A

A rounded crown prep margin created by a rounded bur tip

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90
Q

When can Chamfer margin be used?

A

Full Gold Crowns
Porcelain Crowns
Metal Crowns
PBM Crowns

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91
Q

When can a shoulder with bevel margin be used?

A
  • Proximal box of gold inlay/onlay

- PFM where aesthetics not important

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92
Q

What is biologic width?

A

Length between the base of the sulcus and the height of the alveolar crest. It covers the junctional epithelium and CT.

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93
Q

Why is having the crown margin above the biological width important

A

1) Aesthethics - the finishing line is not visible
2) Biocompatibility - if margin is into biological width (aka Junctional Epithelium), irritation and inflammation with bonding cements and plaque traps may occur

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94
Q

When would you consider subgingival margins for a crown prep?

A

When aesthetics is important - patient has a high smile line, tooth is in the aesthetic 5-5 zone

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95
Q

What are the steps involved with creating a crown for a patient over 2 appointments

A

Appointment 1

  • Consultation appointment
  • Impression to facilitate construction of temporary crown (e.g. pvs putty)
  • Tooth preparation
  • Soft tissue management
  • Impression of preparation + Bite registration/facebow => Send to Lab
  • Construct/fit temporary crown
  • Check occlusion

Appointment 2

  • Remove temporary crown
  • “Try-in” Casting: check for fit
  • Permanent cementation
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96
Q

What are 3 objectives for gingival retractions when doing a crown prep?

A
  1. Retract soft tissues to allow impression material to flow to the margins of the preparation
  2. Control Bleeding
  3. Moisture Control
97
Q

What 3 forms of gingival retraction are available?

A

Chemical (Astringents)
Mechanical (Retraction Cords)
Electrosurgery

98
Q

What is the technique for placing a retraction code prior to taking a crown prep impression?

A
  1. Place smaller retraction cord
  2. Place larger retraction cord, leave for 4 minutes
  3. Remove second cord prior to taking impression
99
Q

What should an operator do if the primary retraction cord comes off with the impression

A

Leave it. Let the dental lab technician remove it.

100
Q

What materials are possible to use for secondary impressions?

A
  1. Polysulphide
  2. Condensation reaction silicone
  3. Polyvinyl siloxane e.g. imprint III, honigum (used in ADH)
  4. Polyether e.g. Impregum (used in ADH)

Reversible hydrocolloids such as Alginates should not be used due to imbibition/syneresis

101
Q

What are the limitations of using a heavily hydrophobic impression material?

A

The mouth needs to be very dry before impression is taken

102
Q

What are the limitations of using a heavily hydrophilic impression material?

A

Excessive moisture leads to imbibition (swelling of the material from absorption of excess moisture)

103
Q

What are the steps for taking a secondary impression

A
  1. Place primary and secondary retraction cords
  2. Remove secondary retraction cord after 4 minutes
  3. Syringe Light Body Impression Material onto tooth preparation, ensuring flow into sulcus. Wait 4-5 minutes
  4. Place Heavy Body material into special impression tray. Allow to set. Remove from mouth
104
Q

What is the purpose of a temporary crown?

A
  1. Pulpal Protection: due to exposed dentine
  2. Prevent sensitivity : cover up exposed dentine
  3. Protect the preparation (e.g. margins)
  4. Stops teeth from drifting
  5. Stops opposing teeth from over-erupting
  6. Aesthetics
  7. Function
105
Q

What are 3 types of temporary crowns?

A
  1. Pre-formed
  2. Custom Direct (taken from alginate impressions)
  3. Custom Indirect (PVS Putty Keys)
106
Q

What are 3 different types of temp crown materials that can be used?

A
  1. Composite resin (biis-acrylic composite)
    e. g. Protemp 4 (used in ADH)
  2. Methyl methacrylate : e.g. Duralay, Jet
  3. Vinyl ethyl methacrylate: e.g. trim
107
Q

What are the stages for making a direct temporary crown?

A
  1. Mix
  2. Place in the impression (correct tooth)
  3. When rubbery (initial set) → remove temp crown
  4. Trim margins and excess → for easy seating
  5. Trim margins and excess (try-in) and check occlusion + polish the temp crown
  6. Cement
108
Q

What are the stages for making an indirect temporary crown?

A
  1. Alginate impression (full arch)
  2. Pour up model – Yellowstone
  3. Wax-up tooth (36) to ideal anatomy
  4. Construct “lab putty” key
  5. Fit Putty Key
  6. Adjust Temporary Crown
  7. Cement in Place
109
Q

What are the stages for fitting a preformed crown?

A
  1. Choose the correct width of crown (S/M/L, LHS vs RHS)
  2. Fill the anterior with temporary material and cement on
    May need to rough the inside if not already lined with protemp
  3. Remove and adjust margins
  4. Check occlusion
  5. Cement in place
110
Q

What are the stages for doing a permanent crown cementation?

A
  1. Remove temporary crown
  2. Remove remnants of temporary cement from preparation using pumice and brush
  3. “Try-in” permanent crown and check: Marginal fit, Occlusion, Proximal contacts
    Shade (aesthetics)
  4. Ensure to get 100% pt consent on fit and appearance
  5. Cement crown (Permanent cement)
111
Q

What are 9 desirable properties of a cement?

A
  1. Adhesion to enamel and dentine
  2. Adhesion to crown
  3. Biocompatibility (pulp/soft tissues)
  4. Adequate compressive strength (15,000 psi)
  5. Thin film thickness
  6. Rapid setting time
  7. Insoluble in oral fluids
  8. Colour (transparent)
  9. Anticariogenic
112
Q

What are the lab steps for a full gold crown?

A
  1. Master Cast Created from Impression
  2. Removable die of tooth cut out of master cast
  3. Wax Pattern of Crown designed on die
  4. Sprue added to die
  5. Negative of Wax Pattern created using investment material
  6. Hot water dissolves Wax Pattern
  7. Casting occurs with molten gold alloy poured through the sprue void
  8. Investment material broken after set
  9. Restoration checked for fit
  10. Sprue Removed
  11. Final Polishing
113
Q

What are the 6 evaluation criteria for a secondary impression?

A
  1. Clear recording of crown prep
  2. Absence of defects from contaminants
  3. Absence of air bubbles in critical areas
  4. Absence of voids
  5. Absence of drag lines
  6. No contact between teeth and tray except at occlusal stops
114
Q

What features should be evident on a satisfactory secondary impression?

A
  1. Vertical drop for core with no undercuts
  2. Circular band representing the finish line margin - appearing as a positive horizontal line
  3. Small circular fin - the interface between the gingival sulcus and the finishing line
  4. Any retentive features - post holes, grooves, pinholes
115
Q

What non crown prep features need to be taken in a secondary impression?

A
  1. Occlusal Stops - for articulation of upper and lower models
  2. Edentulous ridge for bridge work
116
Q

What are chemical contaminants for polyethers and how does this affect the secondary impression?

A

pH < 4 in hemostatics

Affects setting of polyether

117
Q

What are chemical contaminants for silicones and how does this affect the secondary impression?

A 
Sulphur Groups
Latex Gloves
Astringedent Haemostatic Agent
Freshly placed Composite Resin
Protemp
Eugenol

Contaminants “poison” chloroplatinic catalyst thus preventing full setting. Silicone becomes sticky and unset

118
Q

What are physical contaminants and how does this affect the secondary impression?

A

Contaminants like tooth debris, plaque, protemp cause distortion of the impression.

  • Surfaces should be smooth and cleaned with pumice prior to impression
  • CR should be wiped with alcohol
  • Dry working field and moisture control maintained
119
Q

What are drag lines in a secondary impression potentially a sign of?

A

Heavy and Light body failure to bond

120
Q

What are 2 indications for subgingival margins?

A
  1. Aesthetics - to hide visible faial crown margins in a high smile line
  2. Existing CR margins - removal of existing CR requires sub gingival prep to ensure bonding to sound tooth structure
121
Q

Which gingival retraction cord is impregnated with haemostatic aluminium potassium sulphate?

A

Gingibraid (not used in ADH)

Ultrapak is plain and requires dipping in a separate hemostatic agent

122
Q

Which is a knitted polycotton gingival retraction cord: Ultrapak or Gingibraid?

A

Ultrapak

123
Q

What are 3 haemostatic agents that can be used?

A
  1. Hemodent liquid (colourless aluminium chloride)
  2. Astringedent liquid (brown ferric sulphate)
  3. Atringedent liquid (colourless aluminium chloride)
124
Q

Which haemostatic agent can interfere with PVS setting with secondary impressions

A

Brown astringedent liquid due to it’s sulphate content

125
Q

What does the Primary Retraction Cord achieve?

A
  1. Vertical displacement of gingiva
  2. Improves vision and access to subgingival crown margins
  3. Protects epithelium and sulcus from burs
  4. Moisture Control
126
Q

What does the Secondary Retraction Cord achieve?

A
  1. Vertical and lateral displacement of gingiva away from crown margins
  2. Moisture control prior to secondary impression
  3. Sulcus widened sufficiently so secondary impression is thick enough to resist tear on removal
127
Q

If the sulcus is more than 2mm, what retraction cord should be used?

A

Primary: Size 1
Secondary: Same as primary or larger

128
Q

If the sulcus is less than 2mm, what retraction cord should be used?

A

Primary: Size 0 / 00
Secondary: Usually one size larger than primary

129
Q

What clinical materials are needed for gingival retraction cords?

A
  1. Cord lengths - order 3cm for anteriors, 4cm for posteriors
  2. Sharp scissors
  3. Large plastic (Size 6) or Cord Packer (like a flat plastic with serrated edge to push cord)
  4. Hemodent or astringent to dampen primary cord only
  5. Moisture control
    Cotton rolls, dry guard shields, gauze
130
Q

T/F: The primary retraction cord can still be seen in the sulcus

A

False

131
Q

Which aspect of the tooth should you start/end placement of a gingival retraction cord?

A

Mid Labially

132
Q

How long is a secondary retraction cord left and when is it removed

A

Left for 5 minutes whilst setting up for secondary impression

Remove once the DA starts dispensing heavy body material

133
Q

What materials can be used with custom trays?

A

PVS or Polyether

134
Q

What are benefits of custom trays for secondary impressions?

A

Already has occlusal stops

Can overcome issues with shape/size of dental arch

135
Q

What are disadvantages of custom trays for secondary impressions?

A

No mechanical retention around rim so adhesive is needed

Extra fabrication time/cost

136
Q

How long is the drying time for tray adhesives?

A

10 minutes

137
Q

What is the ideal clearance between teeth and tray when taking a secondary impression?

A

3-4mm

138
Q

What are the 10 steps for administering the dual viscosity technique for secondary impression

A
  1. Syringe light body around crown prep using tipe/syringe
  2. When tray half filled with heavy body, the Dental Assistant informs the operator
  3. Gently remove secondary cord with tweezers. Discard first 5mm of light body from mixing tip onto bracket tray and quickly syringe light body around the margins then over the tooth and adjacent teeth
  4. Keep tip below surface to avoid air bubble entrapment
  5. Seat the tray: avoid pressing down forcefully if using stock tray with no occlusal stops
  6. Allow to set in mouth for 5 minutes
  7. Remove tray – “snap removal” to minimise permanent distortion
  8. Immediately wash with water and detergent to remove blood and saliva
  9. Dry impression and check for defects
  10. If impression satisfactory, place in infection control bag
139
Q

What is a PBM crown indicated?

A
  1. When restoration of natural tooth appearance is required
  2. Maximum protection by full coverage for worn, broken down teeth
  3. When more conservative restorations are inappropriate and lack sufficient structural durability
140
Q

What are some clinical applications for PBM crowns?

A

Full coverage for fractures/cracked teeth
Protection for fractured/cracked teeth
Protection of posterior root filled teeth
High stress situations, deep overbite, bruxism
Anterior and posterior teeth as single crowns
Retainers and pontics for fixed bridgework
Splinting periodontally weakened teeth
Reshaping abutment teeth for removable partial denture

141
Q

What are the roles for both metal and ceramic in a PBM crown?

A

Metal: adequate thickness for strength
Ceramic: adequate thickness for aesthetics

142
Q

What is the minimum thickness of metal coping for noble alloys in a PBM crown?

A

0.3-0.5mm

143
Q

What is the minimum thickness of metal coping for base alloys in a PBM crown?

A

0.2mm

144
Q

T/F: High Noble Metal Allows have increased hardness (65% precious metal, gold, silver, platinum, palladium)

A

True - harder than semi-precious or base metal

145
Q

T/F: Enamel Porcelain provides translucence not main colour

A

True

Dentine Porcelain (body) provides main colour
Enamel Porcelain (incisal) provides translucence
146
Q

What is the minimum thickness for body porcelain?

A

Minimum 0.7mm

Optimum 1.0mm

147
Q

Why do palatal surfaces have unveneered metal?

A
  1. Aesthetics not important

2. Prep for just metal is more conservative

148
Q

When does Porcelain change to have compression forces that aid in Metal Ceramic Bonding Mechanisms

A

During furnacing, different thermal coefficients result in slight compression of ceramic to grasp the inner metal layer to increasing bonding strength

149
Q

What are the 4 bonding mechanisms for Metal Ceramic Bonding

A
  1. Micromechanical: air abrasion to roughen metal surface
  2. Compressive: ceramic shrinks into the metal during furnacing due to different thermal coefficients
  3. Molecular: attractional van der waal provide weak bonds
  4. Chemical: moderate metal oxides provide dissolve and bond to the glass phase of porcelain
150
Q

What is the risk of too much oxide formation in base metals?

A

Weak Bond due to thickness of oxide layer. This is a risk with base metals which are more unpredictable in metal oxide formation

151
Q

What is the risk of too little oxide formation in noble metals

A

Inadequate bonding between metal and ceramic

This is why noble metals must have a percentage of base metals to create an alloy that can result in oxide formation

152
Q

How do you create the metal oxide layer?

A

Metal coping is fired before adding ceramic layer

153
Q

What is the gold and palladium composition that is optimal for bonding to porcelain

A

Gold (44-55%) + Palladium (35-45%)

154
Q

What is cohesive failure in a metal / ceramic crown?

A

Fracture in the porcelain/oxide/metal layer itself

155
Q

What is adhesive failure in a metal / ceramic crown?

A

Fracture at the interface between layers

156
Q

What base metal must be there be consideration for hypersensitivity reactions?

A

Nickel

157
Q

What are the clinical and lab steps to construct a PBM crown?

A
  1. Prepare tooth, take impression and construct die
  2. Wax up and cast metal coping and oxidise surface at high temperature
  3. Apply opaque porcelain to hide grey metal colour : Powder + Water => Brush onto metal. Then Sintering in the furnace
  4. Sequentially build up dentine and enamel and porcelains and further sintering
158
Q

What occurs to porcelain when furnacing?

A
  1. Porcelain particles melt and coalesce fusing into a composite structure of crystals within a glass matrix
  2. Vacuum removes air bubbles that reduce translucence
  3. Material shrinks by 2%
159
Q

Why are PBM crowns aesthetically inferior to all-ceramic crowns?

A

Speculance: high light reflection due to white opaque layer

160
Q

What are disadvantages of PBM crowns?

A
  1. Non-Minimum Intervention
  2. Expensive
  3. Poorer aesthetics than all-ceramic crowns
  4. Requires thicker reduction in prep
  5. Brittle and can Fracture
  6. Increase wear of opposing teeth
  7. Inability to repair PBM
161
Q

What are alternatives to PBM crowns?

A
  1. Porcelain bonded to zirconium crowns (PBZ)
    (Digitally Designed, Excellent aesthetics, Less conservative
  2. Full contour zirconia crowns
  3. E. Max crowns (aluminium oxide infiltrated with ceramic, not as nice aesthetically)
  4. Full gold crowns (FGC’s)
162
Q

What are some conservative principles for Crown Prep designs?

A
  1. Minimum Reduction where aesthetics not required
  2. Supra-gingival / Equ-gingival margins
  3. Retention/Resistance Form
  4. Structural Durability through adequate thickness
  5. Marginal Integrity
163
Q

What are design considerations for Retention and Resistance form for Crown Prep

A
  1. Satisfactory Taper (6-10 degrees)
  2. Path of Insertion via Long Axis of tooth is unobstructed and without undercuts
  3. Use of Supplementary Retention
  4. Adequate height of prep
164
Q

What is the minimum tooth reduction needed for PBM crowns?

A
  1. Incisal: 2mm
  2. Labial
    Gingival 1/3 (1-1.3mm)
    Incisal 2/3 (1.5mm)
  3. Proximal
    Gingival 1/3 (0.5mm)
    Incisal Tip (1.5mm)
4. Lingual: 
Gingival cingulum wall = 0.5mm
Concave surface 
If metal + ceramic = 1.0mm
If metal only = 0.5-0.8mm
165
Q

What should be checked at the end of a crown prep?

A
  1. No undercuts on axial walls
  2. Check for continuous, flowing cavosurface margin
  3. Check for adequate occlusal clearance with opposing teeth
  4. Check labial margin hidden in gingival sulcus
166
Q

Which labial/buccal margin designs are best for aesthetics?

A

Ceramic radial shoulder

Ceramic heavy chamfer

167
Q

Which labial/buccal margin designs are best for conservative design?

A

Ceramic heavy chamfer

Heavy chamfer with gold collar (1.0mm)

168
Q

Which labial/buccal margin designs are best for structural durability?

A

Heavy chamfer with gold collar (1.0mm)

45 ° bevelled shoulder with gold collar (bevel = 0.5mm)

169
Q

Which labial/buccal margin designs are best for marginal adaptation?

A

Heavy chamfer with gold collar (1.0mm)

45 ° bevelled shoulder with gold collar (bevel = 0.5mm)

170
Q

What are 4 physical properties of ceramics?

A

Strong (Compression Strength)
Hard (Wear Resistance)
Brittle (Poor Tensile Strength)
Inert Thermal/Electrical non-conductors

171
Q

What are the basic components of dental porcelain?

A
  1. Feldspar: ceramic binder (75-85% weight)
  2. Silica Quartz: strength and optical qualities (15% weight)
  3. Kaolin: binder and opacity
  4. Metal Oxides: Colour Pigments
  5. Leucite: provides toughness (equalises thermal expansion coefficients)
  6. Spinel: limits crack propagation
172
Q

What are advantages of dental ceramics?

A 
Dimensional stability 
Aesthetics 
Good tissue tolerance
High wear resistance
High compressive strength
173
Q

What are disadvantages of dental ceramics?

A 
Abrasive when glaze lost 
Complex fabrication
Adjustment and polish chairside difficult 
Low fracture resistance 
Low tensile strength
If broken in mouth impossible to repair
174
Q

What are the 4 ways ceramics can be classified?

A
  1. Type (Composition)
  2. Processing Method
  3. Substructure/Foundation Metal
  4. Fusing Temperature
175
Q

What are the 2 types of fusing temperature for dental ceramics?

A 
High fusing (850-1100 ° C)
Low fusing (<850 ° C)
176
Q

What are the 5 types of Substructure/foundation materials for dental ceramics?

A 
Cast metal (high noble, noble, base metal)
Swaged metal (platinum foil)
Glass ceramic
CAD/CAM
Glass infused ceramic core
177
Q

What are the 3 types of Processing Methods for dental ceramics?

A

Sintering
Casting
Machining

178
Q

What are the 8 types of composition types for dental ceramics?

A 
Feldspathic (SiO2)
Leucite reinforced 
Lithium di-silicate 
Alumina-oxide based
Glass infiltrated alumina
Glass infiltrated spinel
Fluoro-apatite ceramic 
Zirconia ceramic
179
Q

What is sintering?

A

When ceramic particles fuse under intense furnace temperature (950-980 degrees)

180
Q

How can interfacial stress be minimised when selecting compatible metal and ceramicss?

A

The thermal expansion coefficients need to be broadly compatible

181
Q

What are some properties of High Gold Ceramo-Metal Alloys?

A 
Good biocompatibility 
Good adhesion between alloy and ceramic
Good casting accuracy for margins 
Less creep at high temperature 
Good physical properties 
Firing temperature close to ceramics 
More costly than less noble and base alloys
182
Q

What are some properties of Base-Metal Alloys?

A 
Cheaper than noble alloys
Better strength than noble alloys
More chemically reactive 
Hypersensitivity potential
Higher shrinkage on cooling 
Thicker oxide layer so adhesion of ceramic may be weaker if not processed correctly
183
Q

What is Hue?

A

Basic Colour Group

184
Q

What is Chroma?

A

The intensity of colour

185
Q

What is Colour Value?

A

Lightness vs Darkness

186
Q

What is Opalescence and why is this important?

A

Opalescence is the way light is reflected and refracted through the crystalline structures of the various tooth layers which have different moisture contents.

This determines the translucency/transparancy and aids in the “vital” appearance of natural / crowned teeth

187
Q

What is Metamerism?

A

Particular colour groups may appear different to the observer if viewed under altered lighting conditions

e.g. Natural sunlight, incandescent light, fluorescent light

188
Q

What is Fluorescence ?

A

The light emitted from a substance that has absorbed/reflected light

Natural teeth emit bluish-white light when exposed to UV illumination

Fluorescence gives tooth a “vital” appearance

189
Q

What is the halo effect (Rayleigh Scatter)?

A

The light scattered by passing through teeth/ceramics causing a different wavelength (colour) being transmitted to neighbouring teeth. This can affect how natural a restorative material can appear in context of natural dentition.

190
Q

What are methods to strengthen ceramics?

A 
Development of residual compressive stresses
Ion exchange
Thermal tempering 
Disruption to crack propagation
Dispersion of crystalline phase 
Transformation toughening 
Design of dental restoration
Minimising tensile stress
Reducing stress raisers
191
Q

What is the rationale behind posts?

A

Endodontically treated teeth that have insufficient sound coronal tooth structure remaining to retain the final restoration.

Post provide sufficient retention and stability for placement of a core

192
Q

When are direct posts contraindicated?

A
  1. Inadequate Tooth Structure
  2. Non-Restorable Tooth
  3. Short, Thin or Carious Roots
  4. Bends/Blockages in root canal
  5. Root Pathology
  6. Poor Periodontal Support
193
Q

When are direct posts indicated?

A
  1. Tooth is restorable
  2. Is remaining tooth structure sound
  3. Good periodontal support
  4. Good apical seal
  5. No apical/radicular pathology
  6. Sufficient root length
  7. No anatomical barriers/retained instruments in canal
  8. Good access + isolation possible
  9. Adequate preoperative radiographs
194
Q

What are the different post shapes?

A

Tapered
Parallel
Parallel > Tapered
Tiered

195
Q

What are the different post surfaces?

A

Smooth

Serrated

196
Q

What are the 2 types of posts?

A

Direct Posts: prefabricated and placed at one chair side visit
Indirect Posts: fabricated in the dental laboratory prior to placement

197
Q

What materials can be used for posts?

A 
Stainless Steel
Titanium Alloy
Gold Alloy
No-Ox (Noble Alloy)
Carbon, Quartz and Glass Fibre
Mineral-coated carbon fibre
Zirconium oxide 
Fibre-reinforced resin composite (non-impregnated)
Fibre-reinforced resin composite (impregnated)
198
Q

What are the 2 types of post placement techniques?

A

Passive: post placed without it actively cutting into dentine surface inside post canal

Active: placed and cemented with post actively engaging dentine

199
Q

What are complications that can occur from post placement?

A 
Aspiration-ingestion of drill
Eye injury/needlestick injury 
Spillage or leakage of irrigant
Drill breaking 
Over-preparation of length
Over-preparation canal width
Lateral or furcal perforation
Depth of cut not clear on radiograph
Drill not removing GP
200
Q

What drills are used to prepare a post hole?

A

Gates-glidden drills: cut sideways
Peeso drills: post preparation
Parapost drills: end cutting drill

201
Q

What are the steps for tooth preparation for a post?

A
  1. Preoperative radiograph
  2. Tooth isolation
  3. Access hole preparation
  4. Gates-Glidden Drills to access 4-5mm to apex
  5. Check radiograph
  6. Parapost Drill to cut and prepare end
  7. Cleaning of root canal/irrigation (Miltons + Paper Points)
  8. Post selection and Try-in
  9. Cementation with GIC/Resin Cement
202
Q

What are the functions of a core?

A

Foundations for coronal restoration
Retention and stabilisation of coronal restoration
To perform as in interim restoration

203
Q

What are the 2 types of cores?

A

Direct: placed with/out posts. Can be Amalgam, CR, GIC
Indirect: Fabricated in lab, usually Gold Alloys

204
Q

What are the 4 classes of dental impression materials?

A
  1. Non-Elastomeric materials
  2. Aqueous elastomers
  3. Non-Aqueous elastomers
  4. Optical Impressions + Virtual Models
205
Q

Why are non-elastomeric materials unsuitable for fixed pros impressions?

A

Material doesn’t have elastic qualities to get around undercuts

206
Q

Why are Aqueous elastomers not used for secondary impressions?

A

Dimensionally unstable due to imbibition (swelling), syneresis (liquid formation out of gel) and evaporation

207
Q

What is meant by wetting properties?

A

Contact angle when moisture is contact with the surface of a material.

A material with good wetting properties will allow moisture to spread and adapt to the surface, therefore reducing clumping and liquid bubble distortions in the impression.

208
Q

Why should an impression material have good wetting properties

A

The oral cavity is inherently moist and so the material needs to minimise distortion and defects in this environment

209
Q

How can wetting be improved?

A

By the introduction of a surfactant that reduces surface tension

Examples
Sorbitan mono/trilaureate
Polyoxyethylene sorbitan mono/trioleate

210
Q

What are desirable properties for a impression material?

A 
Easy to mix and dispense
Dimensionally stable 
Good wetting
Accuracy in detail
Accuracy after cold sterilisation
Good odour and taste neutral 
Good elastic recovery around undercuts
Good tear strength
Compatibility with die materials 
Long shelf life 
Reasonable Setting Time / Adequate working time
No irritation to tissues
Retention of Accuracy during transportation to lab
211
Q

Why are Polysulfides not generally used anymore?

A

Poor dimensional stability due to water loss in condensation reaction
Offensive odour and smell
Long setting time
Low elastic recovery compared to more modern materials
Irritation/Allergy Reaction

212
Q

What are examples of Polysulfides?

A

Permlastic (Kerr)

Omniflex (GC)

213
Q

What is the broad reaction for Polysulfides?

A

By mixing Base and Catalyst pastes

Base (Polysulfide Polymer reactant) + Catalyst (Lead Dioxide + Sulfur) => Condensation Reaction with lead dioxide and sulphur groups => di-sulphide links formed between groups + water released as bi-product

214
Q

How can Polysulfides setting times be accelerated

A

Adding more water

High room temperature

215
Q

What are the reasons for dimensional instability during polysulfide reaction?

A

Temperature transition upon removal from mouth
Water loss which is a setting reaction by-product
Shrinkage from continued polymerisation

216
Q

What are advantages of Condensation Silicones?

A

More stable than polysulfides
Good tear strength
Good working and setting time (approx. 9 minutes)

217
Q

What are disadvantages of Condensation Silicones?

A

Odour from alcohol byproduct
Dimensional stability: Poor once the impression is taken out
Bitter taste

218
Q

What is the broad reaction for Condensation Silicone?

A

Mixing Dimethyl Polysiloxane (Base) + Stannous Octoate (Catalyst) => Cross-linking of a hydroxyl terminated dimethyl polysiloxane by an alkyl silicate.

Alcohol is released as a by-product

219
Q

What issue does Polyvinyl SIloxanes (Addition-curing silicones) overcome as an impression material?

A

Different reaction to condensation reactions to overcome shrinkage issues from Polysulfides/Condensation Silicones

220
Q

What is the broad reaction for Polyvinyl SIloxanes?

A

Cross linking reaction of a vinyl terminated di-methyl polysiloxane

Base Paste (Dimethyl Sioxane)
Catalyst Paste (Chloroplatinic Acid)
Reactant (Siloxane prepolymer)

The reactive undergoes a cross linking reaction:

  1. Substitutes 2 separate hydrogen groups on the sioxane chain
  2. Producing 2x crossed linked polymers
  3. Catalysed by chloroplantinic acid
  4. Releasing Hydrogen gas as a by product
  5. Additives can scavenge Hydrogen gas
221
Q

What are examples of PVS impression material?

A 
Honigum: initially no change in viscosity, with pressure applied viscosity rapidly decreases
Imprint 3 (3M)
222
Q

What are advantages of PVS materials?

A 
Very stable dimensionally
Impression re-pours possible 
Odour and taste neutral
Good elastic recovery
Good tear strength
Good wetting of prep surface 
Good working and setting times 
Excellent delivery systems
223
Q

What are disadvantages of PVS materials?

A

Setting retardation via sulphur in latex gloves
Setting retardation from sulphur in Astringedent solution
Tearing of wash material away from tray material
Material is hydrophobic - so won’t deal well with moisture
Locking into undercuts and open embrasures
Porosities
May sometimes get an orange skin on the surface of the impression
Some dimensional change (H2 gas release)
Very expensive

224
Q

What materials can interfere with PVS setting reactions?

A
  1. Setting reaction can be inhibited via zinc diethyl dithiocarbonate, which interferes with the catalyst agent. This can be found in some latex gloves, haemostatic/coagulation agents
  2. Oxygen inhibition layer on resin composites
225
Q

What are delivery systems for PVS?

A

Automix Guns

Pentamix Machines

226
Q

How much stock trays be prepared before administering heavy body PVS?

A

Adhesive must be applied to the occlusal surface of the tray with a dispensing brush

227
Q

What sort of trays can be used to take secondary impressions?

A
  1. Stock Trays
  2. Position Trays (Adhesive Free)
  3. Custom Trays
  4. Triple Trays
228
Q

Why is polyether more dimensionally stable than alginates or PVS?

A

Because there are no by-products of the cross-linking reaction

229
Q

What is the composition of a polyether?

A
  1. Base
    Polyether polymer
    Colloidal silica filler
    Glycol ether or phthalate plasticizer
  2. Catalyst
    Alkyl aromatic sulfonate
    Plasticisers and fillers as above
230
Q

What are the broad steps of a polyether reaction

A

Base: Polyether polymer base

  • Main branch that consists of a copolymer of ethylene oxide + tetahydrofuran
  • Side branches: aziridine rings

Aromatic ester Catalyst (Alkyl aromatic sulfonate) initiates polymerisation cross linking of polymers of imine end groups located on the aziridine rings

No bi-products of reaction = therefore dimensionally stable

231
Q

How is polyether mixed?

A

Polyether is difficult to mix by hand (highly viscous), so is mixed either by applicator gun or pentamix

232
Q

What are advantages of Polyether?

A

Excellent accuracy and wetting
More hydrophilic than PVS: more moisture tolerant
Good dimensional stability
Good Elastic Properties
Very good shelf life (~5 years, less in warm conditions)

233
Q

What are disadvantages of Polyether?

A

Handling issues: very stiff when set/problem in undercuts, embrasures (contraindication)
Very sticky: very hard to get off soft tissue
Cold disinfection
Tear strength less than PVS
Odour unpleasant
Difficult to manually mix
Shorter working time than PVS silicones
Sensitivity to aromatic sulfonate (catalyst) may occur
Water condensation on chilled mixes
Poor Storage after mixed: Polyether degradation common
Type IV hypersensitivity reactions

234
Q

Rank elastomers by dimensional stability

A
  1. Addition Curing (PVS): 0.15% Shrinkage (Good)
  2. Polyethers: 0.2%
  3. Polysulphides: 0.4%
  4. Condensation Silicones: 0.6% (Poor)
235
Q

What are common reasons for failure of Nonaqueous Elastomeric Impression Materials?

A
  1. Rough/Uneven Surface on Impression
  2. Air Bubbles
  3. Irregularly Shaped Voids from debris/excess moisture
  4. Rough/Chalky Stone Cast
  5. Distortion
236
Q

What could be causes of distortions in Nonaqueous Elastomeric Impression Materials?

A

Continuing Polymerisation shrinkage of tray caused by inadequate aging
Lack of Rubber Adhesion to tray caused by too few coats of adhesive
Filling Tray with material too soon after applying adhesive
Using wrong adhesive
Lack of mechanical retention where adhesive in ineffective
Excessive Bulk Material
Insufficient Relief for reline material (if used)
Continued pressure against impression material that has elastic properties
Movement of tray during polymerisation
Premature removal from mouth
Improper Removal from mouth
Delayed pouring of polysulfide/condensation silicone impression

237
Q

What 6 things can you look out for when troubleshooting a PVS secondary impressions?

A

Delamination - light + heavy body don’t bond due to blood/saliva contamination
Irregularities - when placed in the mouth too quickly and can not flow
Repositioning - not correctly seated then moved
Poor Timing - higher room temperature means seating was too slow
Glove Contamination - use of latex gloves inhibits catalysts/accerlators
Pressure Release Channel Technique - light body not pressed thinly enough - abutments become too smore

238
Q

What does Vinyl Siloxanethers aim to overcome?

A

Clinical aims: combine excellent genuine hydrophilicity of polyethers with good mechanical and flow properties of poly vinyl siloxanes (PVS)

Example: Indentium (Kettenbach Gmbh)

239
Q

How are ROMP (Ring Opening Metathesis Polymer) reversible in nature?

A

Olefin Metathesis Reaction: the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon double bonds

COPY BDS3 University of Adelaide Dentistry (28 decks)

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