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Dentistry Module 6 > Fixed Prosthodontics > Flashcards

Fixed Prosthodontics Flashcards

1
Q

Define, a full coverage extra-coronal indirect restoration which is cemented/luted to a prepared tooth.

A

A crown

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2
Q

How can a crown be used in conjunction with a partial denture?

A

Can be used as an abutment to help retain a prosthesis

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3
Q

What is the indication for use of an inlay or onlay over a direct restoration?

A

Where the tooth structure is insufficient to place a direct restoration.

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4
Q

What is the difference between an inlay and onlay?

A
  1. An inlay is placed inside a cavity (bonded within centre of tooth)
  2. An onlay replaces one or more cusp tips and covers entire occlusal surface
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5
Q

Which indirect restoration is full coverage?

  1. Inlay
  2. Onlay
  3. Crown
  4. Veneer
A
  1. Crown
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6
Q

What are the consequences of inadequate occlusal contacts due to a large direct restoration?

A

There is an increased risk of restoration fracture and subsequent micro leakage leading to secondary caries

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7
Q

What are the consequences of an inadequate contact point between teeth due to a large direct restoration?

A
  • increased food packing
  • difficulty cleaning and maintaining restoration
  • risk of secondary caries and periodontal disease
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8
Q

What is the main advantage of being able to articulate a crown prior to placement?

A

Able to check excursive movements (guidance) are correct

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9
Q

How does placement of a crown help to prevent tooth fracture?

A

It will direct occlusal forces straight down the long axis of the tooth

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10
Q

What is the first-line treatment for a crack that extends into the pulp of a tooth?

A

RCT

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11
Q

Why are root treated molar teeth more likely to crack/fracture compared to molar teeth that are not root treated?

A

The amount of tooth lost due to caries removal and removal of tooth structure due to creation of endo access cavity.

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12
Q

What advantages do crowns as denture abutment teeth have in regards to fit of a removable denture?

A

Help with:
1. retention
2. resistance
3. support

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13
Q

What type of guide plane should be prescribed for in order to increase retentive factor of crown abutment teeth?

A

Long guide plane

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14
Q

What are guide planes?

A

Vertical parallel surfaces of retention teeth and abutments, so oriented that they contribute to the determination of path of insertion and displacement

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15
Q

What is the indication for a conventional bridge to be used?

A

Where the abutment tooth is heavily restored and you can justify preparing the abutment for a full coverage restoration

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16
Q

What 3 ways can crowns fail? Give an example for each.

A
  1. Biological failure (e.g. secondary caries, encroachment of biologic width)
  2. Mechanical failure (e.g. fracture)
  3. Aesthetic failure (e.g. visible margin)
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17
Q

What is a classic sign that crowns have invaded biologic width?

A

Inflammation around gingival margins

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18
Q

What is the “biologic width”?

A

Width comprised of the junctional epithelium and connective tissue

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19
Q

On average, where does the biological width sit in regards to the crest of the underlying bone?

A

Sits 3-4mm above the crest of the bone

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20
Q

What is the consequence of encroaching biologic width?

A

Essentially, crown will fail as the distance between the crown margin and crest of the bone is too short, so the gingiva will reject the restoration - this is shown as inflammation around gingival margins- and the result can be loss of bone around the tooth.

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21
Q

What two ways can crown prep lead to pulp necrosis?

A
  1. Exposure of dentinal tubules or pulp can lead to potential ingress of bacteria leading to necrosis
  2. Heat generation causes trauma leading to necrosis
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22
Q

What are the 5 contraindications of placing a crown?

A
  1. Lifestyle factors (e.g. poor OH)
  2. Active caries/periodontal disease
  3. Inadequate crown height
  4. Inadequate access to oral cavity
  5. When more minimally invasive option is suitable
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23
Q

What are parafunctional habits?

A

Repetitive behaviour that targets the oral structure (e.g. bruxism)

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24
Q

What are the 4 lifestyle factors that contraindicate crown placement as they are risk factors for active disease?

A
  1. High sugar intake
  2. Poor OH
  3. Smoking
  4. Parafunction
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25
Q

What medical conditions might cause inadequate access to the oral cavity for tooth prep or impression taking?

A
  • Systemic sclerosis
  • Post-radiation sclerosis
  • Post-surgical changes
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26
Q

Why is canine guidance ideal for placement of a crown?

A

Because you only need to ensure that crown is fitting in ICP.

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27
Q

Why is group function less favourable in regards to placement of a crown?

A

The crown has to fit in ICP and excursive movements, without causing interference with the guidance pattern. This can be more difficult to achieve compared to canine guidance.

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28
Q

Define, a restoration placed in teeth prior to preparation for an indirect restoration.

A

A core

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29
Q

In what situation would a core be required prior to placement of an indirect restoration?

A

If the tooth is heavily restored/broken down

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30
Q

Name 6 materials that can be utilised for direct cores.

A
  1. Amalgam
  2. Composite
  3. GI
  4. RMGI
  5. Compomer
  6. Metal alloy
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31
Q

True or false?

Amalgam has high initial tensile/compressive strength and is therefore strong in thin section.

A

False. Amalgam has low initial tensile/compressive strength and is weak in thin section. It is only strong if placed in sufficient bulk.

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32
Q

What are the two main disadvantages of composite resin as a core material?

A
  1. Very technique sensitive
  2. Can be difficult to distinguish between composite and tooth structure when preparing crown margins
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33
Q

If a core material was to be placed in thin section, which material is better to use? Amalgam or composite resin.

A

Composite resin

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34
Q

What are the 5 disadvantages of using GIC and RMGIs as core materials?

A
  1. Low compressive and tensile strength
  2. Deterioration at low pH
  3. Sensitivity to moisture
  4. Can be difficult to distinguish between GIC and tooth structure when preparing crown margins (unless using Fuji pink)
  5. Not packable which may lead to voids
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35
Q

What are the 4 ways that core retention can be improved?

A
  1. Undercut preparation
  2. Dentine pins
  3. Adhesive materials (e.g. composite)
  4. Elective endodontics (pulp chamber and post utilised)
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36
Q

What are the main disadvantages of self-threading pins for retention of a core?

A
  • induce stress
  • dentinal crazing
  • perforation into Periodontium
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37
Q

Describe the amalgam bonding technique in 7 steps, from cavity prep to placing amalgam.

A
  1. Complete cavity preparation
  2. Place lining if necessary in deep aspects of cavity
  3. Etch enamel 20 secs, dentine 10 secs
  4. Rinse and dry - good isolation
  5. Dentine bonding agent & light cure
  6. Adhesive resin cement placement on base and walls of cavity
  7. Pack amalgam onto unset cement
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38
Q

What is a nayyar core?

A

“A retentive core produced by preparing the coronal 2 to 4 mm of the root canals and slightly undercutting the pulp chamber”

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39
Q

What material is a nayyar core best made from?

A

Amalgam

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40
Q

What is the benefit of a nayyar core?

A

Avoids the use of posts

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41
Q

True or false?

It is sensible to place posts in posterior teeth to retain a core.

A

False, the roots are often narrow and curved in molar teeth, post placement could lead to perforation or root fracture.

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42
Q

What bur should be used for mechanical removal as part of post preparation?

A

Gates-glidden bur

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43
Q

When preparing space for a post, why should you initially start with the smaller size gates-glidden?

A

To reduce heat generated and preferential cutting to one side of the post space

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44
Q

Describe the cutting action of a gates-glidden bur?

A

A blunt, non-cutting tip, used in an up and down motion.

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45
Q

What is the advantage of a ferrule?

A

Minimises chances of root fracture upon core/crown placement

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46
Q

Give 4 requirements for success of posts.

A
  1. Leave 4mm GP apically
  2. Post must be longer than crown being placed (longer the better)
  3. Diameter of post apically must be no greater than 1/3rd of root
  4. Ferrule to crown or core
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47
Q

What is the difference between active and passive posts?

A
  1. Active posts have retentive features that engage the root , there is risk with fracture.
  2. Passive posts passively seat in the canal space and are retained by a luting cement.
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48
Q

Is a threaded post active or passive?

A

Active

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49
Q

Are serrated and smooth posts passive or active?

A

Passive

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50
Q

What is the main advantage and disadvantage of threaded posts?

A

Advantage: very retentive
Disadvantage: higher risk of vertical root fracture

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51
Q

What aspect of a post has the most significant effect on its retention?

A

Length (longer the more retentive)

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52
Q

What type of post design is more retentive? Parallel-sided posts or tapered posts?

A

Parallel-sided post

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53
Q

What is the main disadvantage of a parallel-sided post?

A

More tooth structure must be removed to facilitate its placement compared to a tapered post.

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54
Q

What is the main advantage of a custom made post?

A
  1. Good adaptation to the morphology of the prepared canal
  2. Indicated for use where there is a change in angulation of the core
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55
Q

What are the 2 main advantages of pre-formed serrated posts?

A
  1. Parallel sided so better retention
  2. Less stress in root
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56
Q

Name a self-etching resin luting cement used for post placement.

A

Rely X Unicem

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57
Q

How would an immature apex be prepared prior to post placement? (4 steps)

A
  1. Open and clean canal, dress with CaOH for 2 weeks
  2. Place MTA as apical plug
  3. Next visit, etch post space, rinse and dry
  4. Use bond and composite- insert luminex smooth sided post with Vaseline
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58
Q

What type of post should replace the luminex smooth post in immature root preparation, before a composite core is built up?

A

quartz fibre post (cemented with adhesive resin)

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59
Q

Why should use of RMGI cores be avoided for use under all ceramic restorations?

A

The material undergoes hygroscopic expansion which could lead to ceramic fracture

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60
Q

What type of core utilises the shape of an access cavity/pulp to retain a restoration, meaning that a post is not required?

A

Nayyar core

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61
Q

What is the main disadvantage of stainless steel and brass posts?

A

They can form corrosion products within the post space that can lead to discolouration of the root, compromising aesthetics.

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62
Q

What is the disadvantages of a titanium post?

A

Fracture easily and have same radiopacity as gutta percha so are difficult to see on a radiograph and can make re-treatment RCT cases more difficult.

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63
Q

What is the minimum required height of a ferrule?

A

2mm

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64
Q

Name 3 indirect, extra-coronal fixed prostheses.

A
  1. Crowns (full/partial coverage)
  2. Veneers
  3. Onlays
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65
Q

Name 2 indirect, intra-coronal fixed prostheses.

A
  1. Inlays
  2. Onlays
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66
Q

Name the boundaries of the three dimensional space that an extra-coronal restoration has to occupy.

A
  • the proximal surfaces of adjacent teeth
  • the occlusal surfaces of the opposing tooth/teeth
  • the soft tissues buccally and lingually/palatally
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67
Q

What are the consequences of an over-contoured crown?

A

Risk of being difficult to clean so at higher risk of secondary caries and periodontal disease

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68
Q

What are the boundaries of the three-dimensional space that an intra-coronal restoration (inlay) must occupy?

A
  • the proximal surfaces of adjacent teeth
  • the occlusal surface of the opposing tooth/teeth
  • the tooth preparation buccally and lingually/palatally
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69
Q

What are the 6 principles of tooth preparation?

A
  1. Conservation of tooth tissue
  2. Resistance form
  3. Retention form
  4. Structural durability
  5. Marginal integrity
  6. Preservation of Periodontium
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70
Q

What is the statistic for the number of vital teeth prepared for crowns that subsequently need root canal therapy due to pulpal damage?

A

Up to 20%

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71
Q

When preparing tooth tissue for a crown, what two things should be avoided during your preparation so that retention isn’t compromised?

A
  1. Avoid over-tapering prep
  2. Avoid cutting too much occlusally as prep will be short
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72
Q

What are the issues that can arise during tooth prep if you under-prepare tooth structure?

A
  1. Inadequate thickness of material from crown Which can impair aesthetics
  2. Inadeqaute strength of restoration when placed
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73
Q

What are the issues that can arise during tooth prep if you don’t prepare enough and overbuild the crown?

A
  1. Crown will be large and bulbous, aesthetically displeasing
  2. Over-contoured gingival margins create plaque traps
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74
Q

Define, the ability of the preparation to retain a restoration in an occlusal direction.

A

Retention form

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75
Q

Define, the ability of the preparation to prevent dislodgement of a restoration to lateral and oblique forces.

A

Resistance form

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76
Q

When is chemical retention of a crown with luting cement best achieved?

A

When crown has tall preparation and is loaded in compression (two surfaces pushing against each other in equal force)

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77
Q

In what scenario is chemical retention of a crown with luting cement inadequately achieved?

A

When tooth preparation is short/tapered so there are less compressive forces and more shearing forces (tooth surfaces slide against each other)

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78
Q

What are the two terms used to describe how tapered a tooth is?

A
  1. Taper
  2. Total occlusal convergence angle
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79
Q

For maximum retention and resistance, in what position should the ideal preparation taper be?

A

NEAR Parallel to the long axis of the tooth

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80
Q

What is meant by taper?

A

Refers to the angle of one axial wall in relation to the long axis of the tooth

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81
Q

What is meant by total occlusal convergence angle?

A

The taper of one axial wall in relation to the taper of the opposing axial wall, with the reference line being the long axis of the tooth.

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82
Q

If the taper is too parallel, what are the consequences?

A
  1. Risk of undercuts
  2. More difficult to place and remove crown on/off tooth
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83
Q

What is the ideal taper to be aimed for in degrees when preparing tooth?

A

6 degrees

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84
Q

In round preparations and non full coverage preparations, what additional feature may they require to help with retention and why?

A

Grooves, to help stop the crown from rotating around the tooth.

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85
Q

Why do you always need more tooth reduction occlusally in your preparation?

A

To help resist the occlusal forces in function of the restoration

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86
Q

What is the tooth reduction required for a metal crown, axial and occlusal?

A

Axial = 0.5mm
Occlusal = 1mm

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87
Q

What type of margin should be used for reduction when intending to place a metal crown?

A

Chamfer margin

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88
Q

What is the tooth reduction required for a metal-ceramic crown, axial and occlusal?

A

Axial:
Metal: 0.5mm
Ceramic: 1mm

Occlusal:
Metal: 0.5mm
Ceramic: 1-2mm

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89
Q

What type of margin should be used for reduction when intending to place a metal ceramic crown?

A

Use chamfer margin for metal component and shoulder margin for ceramic component

90
Q

What is a metal-ceramic crown?

A

A crown that has a metal substructure with ceramic bonded over the top of it

91
Q

What is the tooth reduction required for an all-ceramic crown, axial and occlusal?

A

Axial = 0.6-1.0mm
Occlusal = 1.0-1.5mm

92
Q

What type of margin should be used for reduction when intending to place an all-ceramic crown?

A

Rounded Shoulder or chamfer margin

93
Q

Why is it imperative that all line angles inside an all-ceramic crown are smooth/rounded with no sharp angles?

A

Because any sharp angles within the preparation can lead to propagation of cracks/fracture in ceramic.

94
Q

What bur in the high speed hand piece is used to gut depth grooves and shoulder preparations?

A

Parallel sided, flat ended diamond bur

95
Q

What bur in the high speed hand piece is used for occlusal reduction, axial reduction, proximal reduction and chamfer preparation?

A

Round (chamfer) ended, tapered diamond bur

96
Q

What bur in the high speed hand piece is used for initial proximal reduction?

A

Long needle diamond bur

97
Q

What bur in the high speed hand piece is used for lingual/palatal reduction of canines?

A

Rugby ball diamond bur

98
Q

What bur in the high speed hand piece is used for refinement of preparation?

A

Smooth (red band) round ended, tapered diamond bur (has a goldish colour in appearance)

99
Q

Explain the technique to cutting a chamfer margin?

A

Only put 0.5mm (half the 1mm bur) onto the tooth tissue to cut the margin

100
Q

What is the consequence of placing the whole chamfer bur onto the tooth to cut the margin?

A

You will end up with J-shaped margin with a sharp edge

101
Q

Name the four factors that identify where a finishing margin should be placed on a tooth.

A
  1. On sound tooth structure
  2. Below the contact point
  3. Not subgingival
  4. Allow adequate preparation height
102
Q

When cutting margins on a tooth inter-proximally, what contour should be followed to ensure that you do not cut subgingivally?

A

Follow the contour of the gingiva, ensure to move the bur up slightly as you reach the centre of the tooth and then down again.

103
Q

Name the 4 stages of crown preparation sequence.

A
  1. Occlusal reduction
  2. Axial reductions (interproximal, lingual/palatal, buccal)
  3. Finish line
  4. Smoothing
104
Q

What is the advantage of starting crown prep with occlusal reduction?

A

The whole of the preparation is shorter after this point. The amount of cutting from here onwards will Therfore be less because you are cutting a shorter height of tooth.

105
Q

As part of occlusal reduction in posterior tooth preparations, what is a functional cusp bevel?

A

Increased reduction on the functioning cusp made to remove slightly more tissue so you can accommodate for a thicker amount of overlying material on the functional cusp.

106
Q

What is the advantage of a functional cusp bevel?

A

Reduces chance of crown being damaged when tooth is in function

107
Q

What is the most common functional cusp in molars?

A

Generally,

Maxillary: palatal cusp
Mandibular: buccal cusp

108
Q

Explain the two planes of buccal reduction required for crown prep?

A

Plane 1: Hold bur parallel to long axis of tooth
Plane 2: Hold bur to be angled on incisal third of tooth

109
Q

For palatal/lingual reduction, how many planes of reduction are normally required?

A

One, the long axis of tooth.

110
Q

What is meant by interproximal slice?

A

Reduction of margin below the contact point (use long needle bur)

111
Q

Why is the long needle bur used for interproximal slicing?

A

Creates space for chamfer bur to fit interproximally

112
Q

On a crown prep of a canine (or any other anterior tooth), how many reduction planes are required buccaly?

A

2 planes of reduction ( long axis + incisally angled)

113
Q

Explain lingual/palatal reduction on anterior maxillary teeth.

A

As a cingulum is normally present, initial part of reduction is just on gingival 3rd of tooth with chamfer bur (parallel to long axis of tooth). Second part of reduction is to the cingulum which is created with a rugby ball bur.

114
Q

What type of crown requires a “buccal shoulder” to be prepared?

A

Metal-ceramic crown

115
Q

What is a silicone index?

A

Where Pre-operative silicone putty impression recorded and then after prep you can fit this back onto preparation and compare to original tooth structure.

116
Q

How do you check for sufficient occlusal reduction?

A

Use wax.

Get patient to occlude onto wax, you will be able to see areas that are too thin and this suggests the tooth is under-prepared.

117
Q

What are the two main advantages of all-ceramic restorations?

A
  1. High aesthetics
  2. Highly biocompatible
118
Q

What are the 4 main disadvantages of all-ceramic restorations?

A
  1. Prone to fracture under oral function (poor mechanical properties)
  2. Require large reductions in tooth tissue
  3. Expensive
  4. Reduced scope for adjustment or repair
119
Q

How many classifications of dental ceramic by composition are there?

120
Q

Name the 4 dental ceramic classifications by composition.

A
  1. Glass-based ceramics
  2. Glass infiltrated ceramics
  3. Polycrystalline (non-glass) ceramics
  4. Resin-matrix ceramics
121
Q

What class of dental ceramic highly aesthetic and most prone to fracture?

A

Glass-based ceramics (in particular, feldspathic glass)

122
Q

What class of dental ceramic is characterised by alumina, magnesium or zirconia infiltrated with low viscosity glass, exhibiting improved mechanical properties, however poorer aesthetic properties?

A

Glass infiltrated ceramics

123
Q

What class of dental ceramic is alumina or zirconia based with good mechanical properties?

A

Polycrystalline (non-glass) ceramics

124
Q

What class of dental ceramics are analogues to composites?

A

Resin-matrix ceramics

125
Q

What are the three different methods of manufacture of ceramics?

A
  1. Sintering
  2. Hot pressing/injection moulding
  3. Machining
126
Q

What manufacture method of ceramics is described:

Ceramic powder mixed with water is built to the required shape and exposed to high temperature causing partial melting and fusing of particles.

127
Q

What manufacture method of ceramics is described:

CAD/CAM represents a significant technological advancement with regards to all-ceramic restoration manufacture. Following a digital impression and design process, the restoration is milled from a block of ceramic. Blocks may be mono- or multi- chromatic. Milling may be done in a soft or hard state.

128
Q

What manufacture method of ceramics is described:

Similar to the lost wax technique, a wax up of the restoration is invested in refractory die and a heated block of ceramic is injected under pressure.

A

Hot pressing/injection moulding

129
Q

What are monolithic crowns?

A

Crowns that are machined from a single block of ceramic.

130
Q

What are the three factors that choice of luting cement for fitting and cementing all-ceramic restorations depends upon?

A
  1. Preparation characteristics (height, taper)
  2. Types of ceramic (glass vs glass infiltrated vs polycrystalline)
  3. Aesthetic demands (anterior vs posterior)
131
Q

What materials are usually ideal for fitting and cementing an all ceramic restoration?

A
  1. RMGI
  2. Resin luting cement
132
Q

What is a dual cured system?

A

Involves mixing two components to chemically activate a self-cure reaction, while the photoinitiators are independently activated by light curing.

133
Q

What type of acids are ceramics etched with?

A

Hydrofluoric acid

134
Q

What is the 5 year survival rate of most types of all-ceramic restorations?

135
Q

What is a cuspal coverage restoration?

A

A restoration that covers all of the posterior tooth cusps (can be direct or indirect)

136
Q

When are cuspal coverage restorations indicated for use?

A

To preserve the integrity of a weakened tooth against the forces of occlusion.

137
Q

What are the 4 designs of cuspal coverage restorations most commonly considered?

A
  1. Onlays
  2. Inlays with cuspal coverage
  3. 3/4 crowns
  4. 7/8 crowns
138
Q

What is the main advantage of using gold as the material for a cuspal coverage restoration?

A

Gold is strong in thin section and Therfore requires minimal preperation of tooth structure.

139
Q

What is the main disadvantage of using gold as the material for a cuspal coverage restoration?

A

Very expensive material

140
Q

What is a 3/4 crown?

A

Crown that cover all surfaces except buccal surface

141
Q

Name the advantage of a full coverage indirect restoration that an intracoronal restoration cannot provide.

A

Protects cusps

142
Q

Name the advantages of an intracoronal restoration which a full coverage indirect restoration cannot provide.

A
  1. Reduces sound tooth removal
  2. Reduces amount of restorative material required
  3. Easier to inspect margins
  4. Potentially better aesthetics buccaly
143
Q

What material/s can be used for construction of an indirect cuspal coverage restoration?

A
  1. Gold
  2. All ceramic
  3. Composite
144
Q

What material/s can be used for construction of a direct cuspal coverage restoration?

145
Q

Name the two types of materials for cementation of an indirect restoration and give an example for each.

A
  1. Luting cement(e.g. Rely X luting cement)
  2. Bonding cement (e.g. panavia)
146
Q

Which type of cement is better for use when metal (e.g. gold) is utilised for indirect restoration?

A

Bonding cement (e.g. panavia) as the cement will bond onto metal as well as tooth structure.

147
Q

Give an example of a hydrophilic irreversible hydrocolloid impression material?

148
Q

Give an example of a hydrophilic reversible impression material?

149
Q

Name three types of hydrophobic elastomeric impression materials?

A
  1. Silicones (addition or condensation cured)
  2. Polysulphides (Permlastic)
  3. Polyethers (Impregum)
150
Q

What type of silicone impression material is more accurate, Addition or condensation silicone?

A

Additional silicone (e.g. aquasil)

151
Q

What type of impression tray is required for fixed pros?

A

Rigid polycarbonate trays

152
Q

What are the 5 main consequneces of invading biological width when preparing a crown?

A
  1. Inflammation of the gingival tissues
  2. Inflammation of periodontal tissues
  3. Bone loss
  4. Re-established biologic width which is apical to original position
  5. Recession
153
Q

Before impression taking, how would you temporarily displace the gingival margin?

A

Retraction, either by:
1. Braided cord
2. Injectable material

154
Q

What patients cannot undergo electrosurgery?

A

Those with pacemakers

155
Q

What is electrocautery? And its use in dentistry?

A

A crown lengthening procedure using heat from electric current to destroy tissue and control bleeding. Can be used in dentistry where a tooth has inadequate occluso-gingival height for crown prep.

156
Q

What is the regime for disinfection of impressions?

A

10 x1.7g actichlor tablets per 1 litre of water. Soak impressions for 3 minutes.

157
Q

What is a pick up impression?

A

Technique where the impression copings are maintained within the impression upon removal from the mouth. It gives an exact reproduction of how the appliance will fit in the oral cavity.

158
Q

When are provisional restorations required for fixed prosthodontics?

A

For:
1. Provisional crowns
2. Provisional bridges
3. Provisional dentures/overdentures

159
Q

What are the 5 different methods to create a provisional restoration?

A
  1. Pre-operative putty impression
  2. Pre-formed crown
  3. Pre-operative wax-up followed by duplication and vacuum formed stent
  4. Free-hand bis-acrylic resin
  5. Use of old crown if possible
160
Q

What material is placed into the pre-operative putty impression to make a provisional crown?

A

Chemically-cured bis-acrylic composite resin

161
Q

What are the 4 materials used for pre-operative crowns?

A
  1. Polycarbonate
  2. Cellulose-acetate
  3. Composite
  4. Metal
162
Q

What type of acrylic resin must be used with preformed polycarbonate crowns?

A

Cold-cured acrylic resin

163
Q

What type of composite can be used to make a preformed crown? and why?

A

Semi-cured composite as it is malleable and mouldable

164
Q

When is a free-hand bis-acrylic resin technique indicated to make a provisional crown?

A

When a matrix can not be put in place.

165
Q

When are provisional post crowns not suitable? And why?

A

When undertaking root canal therapy or replacing a root canal filling, this is not a suitable provisional restoration for between appointments as these post-crowns leak a lot and will allow bacterial ingress.

166
Q

Why is a provisional overdenture a suitable choice as a temporary restoration for a tooth undergoing RCT?

A
  1. It is easy to access the root surface
  2. Less coronal leakage during tx
  3. Likely better long term result
167
Q

What has happened if a provisional restoration will not withdraw from a tooth preparation or tears when withdrawn?

A

There are undercuts present in crown preparation

168
Q

At what stage should a a provisional restoration be made during crown preparation?

A

AFTER tooth prep
BEFORE the impression stage

169
Q

Why should the provisional restoration be made before impression are taken?

A

So you can modify the tooth prep before the impression is taken

170
Q

What are the advantages of a fixed bridge?

A
  1. Small prosthesis
  2. No/minimal mucosal coverage
  3. Good patient tolerance
  4. Not removable
171
Q

What are the disadvantages of a fixed bridge?

A
  1. Destructive on abutment teeth
  2. Does not replace alveolar bone
  3. Difficult to maintain heathy tissues
  4. Difficult to access root canals of abutment teeth
  5. May fracture
  6. Difficult to remove
  7. Long appointments
172
Q

What are the 6 fixed bridge options?

A
  1. Resin retained cantilever bridge
  2. Conventional fixed cantilever bridge
  3. Conventional fixed-fixed bridge
  4. Conventional fixed-moveable bridge
  5. Hybrid bridge
  6. Implant retained prosthesis
173
Q

What luting cement is used to bond resin retained cantilever bridges?

174
Q

What type of resin-retained bridges can you get?

A
  1. Cantilever
  2. Fixed-fixed
  3. Hybrid
175
Q

If extraction of a tooth that is part of a fixed-fixed bridge is required, how would you manage this?

A

Cut fixed-fixed bridge to extract tooth and this becomes a cantilever bridge

176
Q

What are the 4 advantages of a conventional fixed-moveable bridge?

A
  1. Allows two paths of insertion
  2. Avoids destructive preparation in some cases
  3. Allows independent tooth movement of abutments in a vertical direction
  4. Allows components to be replaced individually
177
Q

Why do occlusal loads need to be considered before placing an implant retained prosthesis? What type of patient should avoid this prosthesis?

A

There is no movement with implants like in a natural tooth, so careful distribution of load is required to reduce stress.

Patients with parafunctional habits such as British or clenching should avoid this prosthesis.

178
Q

What is “conventional bridgework”?

A

A fixed prosthesis where the abutments are natural teeth and the retainers are indirect restorations where adhesive is not generally recognised as the primary method of retainer retention

179
Q

What is the anatomy of a conventional bridgework?

A
  1. Abutment
  2. Retainer
  3. Connector (connects retainer to Pontic)
  4. Pontic
  5. Saddle (alveolar ridge after tooth loss)
180
Q

Name 4 design types of conventional bridgework.

A
  1. Fixed-fixed
  2. Cantilever
  3. Fixed-moveable
  4. Complex
181
Q

What type of conventional bridgework is most suitable for longer span bridges?

A

Fixed-fixed

182
Q

What type of conventional bridgework requires teeth involved to be within the same long axis?

A

Fixed-fixed bridge

183
Q

What type of conventional bridgework is described?

  • generally a mesial pontic
  • no excursive loading on Pontic
  • simple design (max 2 units)
  • very successful
A

Cantilever bridge

184
Q

What type of conventional bridgework is described:

  • old-fashioned
  • includes a bar that sits on hard palate attaching to Pontic anteriorly
  • originally for spaced anterior dentition
  • expensive
  • last a long time
A

Spring cantilever bridge

185
Q

What type of conventional bridgework is used for mal-aligned teeth, where the long axis of prepared teeth may vary?

A

Fixed-moveable bridge

186
Q

What is the main advantage of fixed-moveable prosthesis?

A

Breaking of stress, which prevents unfavourable torquing on retainers.

187
Q

What are the 4 main disadvantages of fixed-moveable bridgework?

A
  1. Limited areas of use
  2. Complicated
  3. Expensive
  4. Increased stress on major abutment
188
Q

What is meant by “physiological mesial drift”?

A

Tendency of teeth to move forwards in an arch

189
Q

Where should the female component of a fixed-moveable bridge ideally be sited in comparison with the male component?

A

Ideally female component sited mesial to male component

190
Q

What is a pier abutment?

A

A freestanding abutment with edentulous space on both sides

191
Q

Why are pier abutments generally avoided?

A
  • middle abutment acts as a pivot
  • minor retainer likely to spring becoming a plaque trap
192
Q

What are the 5 main roles that Pontic’s should fulfill?

A
  1. Replacing the function of a lost tooth
  2. Achieve an aesthetic appearance
  3. Enable adequate oral hygiene
  4. Prevent tissue irritation
  5. Meet certain structural requirements
193
Q

What is a ridge lap?

A

The amount of contact between a restoration and the alveolar ridge

194
Q

If a Pontic is described as having a ridge lap design, what does this mean? what are the advantages and disadvantages?

A

The Pontic overlaps the alveolar ridge. Advantage is that the aesthetics is good, however this is impossible to clean under so becomes a plaque trap.

195
Q

What is a modified ridge lap Pontic?

A

Where the palatal or lingual aspect of the Pontic is removed to prevent plaque trap and allow for better hygiene to be maintained

196
Q

What is a hygienic Pontic? What is the advantage?

A

A Pontic that doesn’t touch the ridge at all (almost floating) connected to abutments. Very easy to clean.

197
Q

What design of Pontic is most appropriate for anterior bridge?

A

Modified ridge lap Pontic

198
Q

What is the disadvantage of a dome Pontic design?

A

Food packing

199
Q

What two Pontic designs are most commonly used in posterior bridges?

A

Modified ridge lap and hygienic

200
Q

What is the Pontic design of choice?

A

Modified ridge lap

201
Q

What are 4 methods to assess undercuts in conventional fixed-fixed bridge preps?

A
  1. Direct monocular vision
  2. Indirect monocular vision
  3. Take an Alginate impression and cast in quick setting plaster
  4. Paralleling mirror
202
Q

Why is die hardener applied to study cast prior to inlay preparation with wax?

A

To help prevent chipping or flaking of the model when carving the wax

203
Q

Why is a spacer applied prior to the wax inlay?

A

To create space for the luting cement

204
Q

What type of wax is used to create inlay form?

A

Carnauba wax

205
Q

The sprued inlay has to be positioned 3/4 high in the casting ring. Why is this? What will happen if it is positioned:
1. Too high
2. Too low

A
  1. If too high metal will come out of end of mould
  2. If too low, gases cannot escape leading to a miscast
206
Q

Why is the casting ring lined and placed in water prior to casting procedure with investment material?

A

Contributes to hygroscopic expansion of the investment material

207
Q

What is the preferred design for a RRB?

A

Cantilever RRB

208
Q

Why is cantilever RRB the preferred design over fixed-fixed RRB?

A

Fixed-fixed design is more likely do debond

209
Q

What are the 4 types of RRB?

A
  1. The Rochette bridge
  2. The Maryland bridge
  3. Resin-bonded and adhesive bridges
  4. Fibre-reinforced Bridge (new)
210
Q

How was the rochette bridge placed?

A

The metal wing retainer had countersunk holes to allow for mechanical retention of the resin cement.

211
Q

How is a Maryland bridge placed?

A

The inner surface of the base metal retainer is electrolytically etched in a bath of strong acid solution. (Micro mechanical retention of material onto metal)

212
Q

How is the current day resin retained bridge placed?

A

The metal retainer is sandblasted with albumin particles of 50 micro meters diameter and panavia resin is used to chemically/micromechanically bond to the metal retainer and etched enamel.

213
Q

Describe panavia cement used to retain RBB?

A
  1. Dual cure
  2. Radio-opaque
  3. Thin mixture
  4. Insoluble
214
Q

What component of panavia allows for effective bonding to enamel, dentine and metal alloys?

A

Phosphate monomer

215
Q

What can the wing retainer of RBB be made from?

A

Either metal alloy or fibre-impregnated resin

216
Q

What are the indications for RRB?

A
  1. Unrestored or minimally restored abutment teeth
  2. Sufficient good quality enamel on abutment tooth
  3. Sufficient interocclusal space
  4. Good alveolar bone shape
217
Q

What class of incisor relationship would not allow for placement of a RRB due to lack of inter occlusal space?

A

Class III incisor relationship

218
Q

What are the three designs of RRB?

A
  1. Cantilever
  2. Fixed-fixed
  3. Hybrid
219
Q

Why might you choose to minimally prepare abutment teeth for RRB over no prep?

A
  1. To improve retention and resistance form
  2. To improve location
  3. To remove undercuts
  4. To create space
220
Q

What aesthetic considerations should be made prior to RRB provision?

A
  1. Will the material shine through teeth?
  2. Is there diastema/spacing to consider?
221
Q

According to a retrospective study in 1999 by Djamal et al, what is the median survival rate of bridges and splints?

A

7 years and 10 months

Dentistry Module 6 (15 decks)

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