Fixed Prosthodontics Flashcards
(221 cards)
1
Q
Define, a full coverage extra-coronal indirect restoration which is cemented/luted to a prepared tooth.
A
A crown
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
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.
4
Q
What is the difference between an inlay and onlay?
A
- An inlay is placed inside a cavity (bonded within centre of tooth)
- An onlay replaces one or more cusp tips and covers entire occlusal surface
5
Q
Which indirect restoration is full coverage?
- Inlay
- Onlay
- Crown
- Veneer
A
- Crown
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
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
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
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
10
Q
What is the first-line treatment for a crack that extends into the pulp of a tooth?
A
RCT
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.
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
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
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
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
16
Q
What 3 ways can crowns fail? Give an example for each.
A
- Biological failure (e.g. secondary caries, encroachment of biologic width)
- Mechanical failure (e.g. fracture)
- Aesthetic failure (e.g. visible margin)
17
Q
What is a classic sign that crowns have invaded biologic width?
A
Inflammation around gingival margins
18
Q
What is the “biologic width”?
A
Width comprised of the junctional epithelium and connective tissue
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
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.
21
Q
What two ways can crown prep lead to pulp necrosis?
A
- Exposure of dentinal tubules or pulp can lead to potential ingress of bacteria leading to necrosis
- Heat generation causes trauma leading to necrosis
22
Q
What are the 5 contraindications of placing a crown?
A
- Lifestyle factors (e.g. poor OH)
- Active caries/periodontal disease
- Inadequate crown height
- Inadequate access to oral cavity
- When more minimally invasive option is suitable
23
Q
What are parafunctional habits?
A
Repetitive behaviour that targets the oral structure (e.g. bruxism)
24
Q
What are the 4 lifestyle factors that contraindicate crown placement as they are risk factors for active disease?
A
- High sugar intake
- Poor OH
- Smoking
- Parafunction
25
What medical conditions might cause inadequate access to the oral cavity for tooth prep or impression taking?
- Systemic sclerosis
- Post-radiation sclerosis
- Post-surgical changes
26
Why is canine guidance ideal for placement of a crown?
Because you only need to ensure that crown is fitting in ICP.
27
Why is group function less favourable in regards to placement of a crown?
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.
28
Define, a restoration placed in teeth prior to preparation for an indirect restoration.
A core
29
In what situation would a core be required prior to placement of an indirect restoration?
If the tooth is heavily restored/broken down
30
Name 6 materials that can be utilised for direct cores.
1. Amalgam
2. Composite
3. GI
4. RMGI
5. Compomer
6. Metal alloy
31
True or false?
Amalgam has high initial tensile/compressive strength and is therefore strong in thin section.
False. Amalgam has low initial tensile/compressive strength and is weak in thin section. It is only strong if placed in sufficient bulk.
32
What are the two main disadvantages of composite resin as a core material?
1. Very technique sensitive
2. Can be difficult to distinguish between composite and tooth structure when preparing crown margins
33
If a core material was to be placed in thin section, which material is better to use? Amalgam or composite resin.
Composite resin
34
What are the 5 disadvantages of using GIC and RMGIs as core materials?
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
35
What are the 4 ways that core retention can be improved?
1. Undercut preparation
2. Dentine pins
3. Adhesive materials (e.g. composite)
4. Elective endodontics (pulp chamber and post utilised)
36
What are the main disadvantages of self-threading pins for retention of a core?
- induce stress
- dentinal crazing
- perforation into Periodontium
37
Describe the amalgam bonding technique in 7 steps, from cavity prep to placing amalgam.
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
38
What is a nayyar core?
“A retentive core produced by preparing the coronal 2 to 4 mm of the root canals and slightly undercutting the pulp chamber”
39
What material is a nayyar core best made from?
Amalgam
40
What is the benefit of a nayyar core?
Avoids the use of posts
41
True or false?
It is sensible to place posts in posterior teeth to retain a core.
False, the roots are often narrow and curved in molar teeth, post placement could lead to perforation or root fracture.
42
What bur should be used for mechanical removal as part of post preparation?
Gates-glidden bur
43
When preparing space for a post, why should you initially start with the smaller size gates-glidden?
To reduce heat generated and preferential cutting to one side of the post space
44
Describe the cutting action of a gates-glidden bur?
A blunt, non-cutting tip, used in an up and down motion.
45
What is the advantage of a ferrule?
Minimises chances of root fracture upon core/crown placement
46
Give 4 requirements for success of posts.
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
47
What is the difference between active and passive posts?
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.
48
Is a threaded post active or passive?
Active
49
Are serrated and smooth posts passive or active?
Passive
50
What is the main advantage and disadvantage of threaded posts?
Advantage: very retentive
Disadvantage: higher risk of vertical root fracture
51
What aspect of a post has the most significant effect on its retention?
Length (longer the more retentive)
52
What type of post design is more retentive? Parallel-sided posts or tapered posts?
Parallel-sided post
53
What is the main disadvantage of a parallel-sided post?
More tooth structure must be removed to facilitate its placement compared to a tapered post.
54
What is the main advantage of a custom made post?
1. Good adaptation to the morphology of the prepared canal
2. Indicated for use where there is a change in angulation of the core
55
What are the 2 main advantages of pre-formed serrated posts?
1. Parallel sided so better retention
2. Less stress in root
56
Name a self-etching resin luting cement used for post placement.
Rely X Unicem
57
How would an immature apex be prepared prior to post placement? (4 steps)
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
58
What type of post should replace the luminex smooth post in immature root preparation, before a composite core is built up?
quartz fibre post (cemented with adhesive resin)
59
Why should use of RMGI cores be avoided for use under all ceramic restorations?
The material undergoes hygroscopic expansion which could lead to ceramic fracture
60
What type of core utilises the shape of an access cavity/pulp to retain a restoration, meaning that a post is not required?
Nayyar core
61
What is the main disadvantage of stainless steel and brass posts?
They can form corrosion products within the post space that can lead to discolouration of the root, compromising aesthetics.
62
What is the disadvantages of a titanium post?
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.
63
What is the minimum required height of a ferrule?
2mm
64
Name 3 indirect, extra-coronal fixed prostheses.
1. Crowns (full/partial coverage)
2. Veneers
3. Onlays
65
Name 2 indirect, intra-coronal fixed prostheses.
1. Inlays
2. Onlays
66
Name the boundaries of the three dimensional space that an extra-coronal restoration has to occupy.
- the proximal surfaces of adjacent teeth
- the occlusal surfaces of the opposing tooth/teeth
- the soft tissues buccally and lingually/palatally
67
What are the consequences of an over-contoured crown?
Risk of being difficult to clean so at higher risk of secondary caries and periodontal disease
68
What are the boundaries of the three-dimensional space that an intra-coronal restoration (inlay) must occupy?
- the proximal surfaces of adjacent teeth
- the occlusal surface of the opposing tooth/teeth
- the tooth preparation buccally and lingually/palatally
69
What are the 6 principles of tooth preparation?
1. Conservation of tooth tissue
2. Resistance form
3. Retention form
4. Structural durability
5. Marginal integrity
6. Preservation of Periodontium
70
What is the statistic for the number of vital teeth prepared for crowns that subsequently need root canal therapy due to pulpal damage?
Up to 20%
71
When preparing tooth tissue for a crown, what two things should be avoided during your preparation so that retention isn’t compromised?
1. Avoid over-tapering prep
2. Avoid cutting too much occlusally as prep will be short
72
What are the issues that can arise during tooth prep if you under-prepare tooth structure?
1. Inadequate thickness of material from crown Which can impair aesthetics
2. Inadeqaute strength of restoration when placed
73
What are the issues that can arise during tooth prep if you don’t prepare enough and overbuild the crown?
1. Crown will be large and bulbous, aesthetically displeasing
2. Over-contoured gingival margins create plaque traps
74
Define, the ability of the preparation to retain a restoration in an occlusal direction.
Retention form
75
Define, the ability of the preparation to prevent dislodgement of a restoration to lateral and oblique forces.
Resistance form
76
When is chemical retention of a crown with luting cement best achieved?
When crown has tall preparation and is loaded in compression (two surfaces pushing against each other in equal force)
77
In what scenario is chemical retention of a crown with luting cement inadequately achieved?
When tooth preparation is short/tapered so there are less compressive forces and more shearing forces (tooth surfaces slide against each other)
78
What are the two terms used to describe how tapered a tooth is?
1. Taper
2. Total occlusal convergence angle
79
For maximum retention and resistance, in what position should the ideal preparation taper be?
NEAR Parallel to the long axis of the tooth
80
What is meant by taper?
Refers to the angle of one axial wall in relation to the long axis of the tooth
81
What is meant by total occlusal convergence angle?
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.
82
If the taper is too parallel, what are the consequences?
1. Risk of undercuts
2. More difficult to place and remove crown on/off tooth
83
What is the ideal taper to be aimed for in degrees when preparing tooth?
6 degrees
84
In round preparations and non full coverage preparations, what additional feature may they require to help with retention and why?
Grooves, to help stop the crown from rotating around the tooth.
85
Why do you always need more tooth reduction occlusally in your preparation?
To help resist the occlusal forces in function of the restoration
86
What is the tooth reduction required for a metal crown, axial and occlusal?
Axial = 0.5mm
Occlusal = 1mm
87
What type of margin should be used for reduction when intending to place a metal crown?
Chamfer margin
88
What is the tooth reduction required for a metal-ceramic crown, axial and occlusal?
Axial:
Metal: 0.5mm
Ceramic: 1mm
Occlusal:
Metal: 0.5mm
Ceramic: 1-2mm
89
What type of margin should be used for reduction when intending to place a metal ceramic crown?
Use chamfer margin for metal component and shoulder margin for ceramic component
90
What is a metal-ceramic crown?
A crown that has a metal substructure with ceramic bonded over the top of it
91
What is the tooth reduction required for an all-ceramic crown, axial and occlusal?
Axial = 0.6-1.0mm
Occlusal = 1.0-1.5mm
92
What type of margin should be used for reduction when intending to place an all-ceramic crown?
Rounded Shoulder or chamfer margin
93
Why is it imperative that all line angles inside an all-ceramic crown are smooth/rounded with no sharp angles?
Because any sharp angles within the preparation can lead to propagation of cracks/fracture in ceramic.
94
What bur in the high speed hand piece is used to gut depth grooves and shoulder preparations?
Parallel sided, flat ended diamond bur
95
What bur in the high speed hand piece is used for occlusal reduction, axial reduction, proximal reduction and chamfer preparation?
Round (chamfer) ended, tapered diamond bur
96
What bur in the high speed hand piece is used for initial proximal reduction?
Long needle diamond bur
97
What bur in the high speed hand piece is used for lingual/palatal reduction of canines?
Rugby ball diamond bur
98
What bur in the high speed hand piece is used for refinement of preparation?
Smooth (red band) round ended, tapered diamond bur (has a goldish colour in appearance)
99
Explain the technique to cutting a chamfer margin?
Only put 0.5mm (half the 1mm bur) onto the tooth tissue to cut the margin
100
What is the consequence of placing the whole chamfer bur onto the tooth to cut the margin?
You will end up with J-shaped margin with a sharp edge
101
Name the four factors that identify where a finishing margin should be placed on a tooth.
1. On sound tooth structure
2. Below the contact point
3. Not subgingival
4. Allow adequate preparation height
102
When cutting margins on a tooth inter-proximally, what contour should be followed to ensure that you do not cut subgingivally?
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
Name the 4 stages of crown preparation sequence.
1. Occlusal reduction
2. Axial reductions (interproximal, lingual/palatal, buccal)
3. Finish line
4. Smoothing
104
What is the advantage of starting crown prep with occlusal reduction?
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
As part of occlusal reduction in posterior tooth preparations, what is a functional cusp bevel?
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
What is the advantage of a functional cusp bevel?
Reduces chance of crown being damaged when tooth is in function
107
What is the most common functional cusp in molars?
Generally,
Maxillary: palatal cusp
Mandibular: buccal cusp
108
Explain the two planes of buccal reduction required for crown prep?
Plane 1: Hold bur parallel to long axis of tooth
Plane 2: Hold bur to be angled on incisal third of tooth
109
For palatal/lingual reduction, how many planes of reduction are normally required?
One, the long axis of tooth.
110
What is meant by interproximal slice?
Reduction of margin below the contact point (use long needle bur)
111
Why is the long needle bur used for interproximal slicing?
Creates space for chamfer bur to fit interproximally
112
On a crown prep of a canine (or any other anterior tooth), how many reduction planes are required buccaly?
2 planes of reduction ( long axis + incisally angled)
113
Explain lingual/palatal reduction on anterior maxillary teeth.
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
What type of crown requires a “buccal shoulder” to be prepared?
Metal-ceramic crown
115
What is a silicone index?
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
How do you check for sufficient occlusal reduction?
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
What are the two main advantages of all-ceramic restorations?
1. High aesthetics
2. Highly biocompatible
118
What are the 4 main disadvantages of all-ceramic restorations?
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
How many classifications of dental ceramic by composition are there?
4
120
Name the 4 dental ceramic classifications by composition.
1. Glass-based ceramics
2. Glass infiltrated ceramics
3. Polycrystalline (non-glass) ceramics
4. Resin-matrix ceramics
121
What class of dental ceramic highly aesthetic and most prone to fracture?
Glass-based ceramics (in particular, feldspathic glass)
122
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?
Glass infiltrated ceramics
123
What class of dental ceramic is alumina or zirconia based with good mechanical properties?
Polycrystalline (non-glass) ceramics
124
What class of dental ceramics are analogues to composites?
Resin-matrix ceramics
125
What are the three different methods of manufacture of ceramics?
1. Sintering
2. Hot pressing/injection moulding
3. Machining
126
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.
Sintering
127
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.
Machining
128
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.
Hot pressing/injection moulding
129
What are monolithic crowns?
Crowns that are machined from a single block of ceramic.
130
What are the three factors that choice of luting cement for fitting and cementing all-ceramic restorations depends upon?
1. Preparation characteristics (height, taper)
2. Types of ceramic (glass vs glass infiltrated vs polycrystalline)
3. Aesthetic demands (anterior vs posterior)
131
What materials are usually ideal for fitting and cementing an all ceramic restoration?
1. RMGI
2. Resin luting cement
132
What is a dual cured system?
Involves mixing two components to chemically activate a self-cure reaction, while the photoinitiators are independently activated by light curing.
133
What type of acids are ceramics etched with?
Hydrofluoric acid
134
What is the 5 year survival rate of most types of all-ceramic restorations?
95%
135
What is a cuspal coverage restoration?
A restoration that covers all of the posterior tooth cusps (can be direct or indirect)
136
When are cuspal coverage restorations indicated for use?
To preserve the integrity of a weakened tooth against the forces of occlusion.
137
What are the 4 designs of cuspal coverage restorations most commonly considered?
1. Onlays
2. Inlays with cuspal coverage
3. 3/4 crowns
4. 7/8 crowns
138
What is the main advantage of using gold as the material for a cuspal coverage restoration?
Gold is strong in thin section and Therfore requires minimal preperation of tooth structure.
139
What is the main disadvantage of using gold as the material for a cuspal coverage restoration?
Very expensive material
140
What is a 3/4 crown?
Crown that cover all surfaces except buccal surface
141
Name the advantage of a full coverage indirect restoration that an intracoronal restoration cannot provide.
Protects cusps
142
Name the advantages of an intracoronal restoration which a full coverage indirect restoration cannot provide.
1. Reduces sound tooth removal
2. Reduces amount of restorative material required
3. Easier to inspect margins
4. Potentially better aesthetics buccaly
143
What material/s can be used for construction of an indirect cuspal coverage restoration?
1. Gold
2. All ceramic
3. Composite
144
What material/s can be used for construction of a direct cuspal coverage restoration?
Composite
145
Name the two types of materials for cementation of an indirect restoration and give an example for each.
1. Luting cement(e.g. Rely X luting cement)
2. Bonding cement (e.g. panavia)
146
Which type of cement is better for use when metal (e.g. gold) is utilised for indirect restoration?
Bonding cement (e.g. panavia) as the cement will bond onto metal as well as tooth structure.
147
Give an example of a hydrophilic irreversible hydrocolloid impression material?
Alginate
148
Give an example of a hydrophilic reversible impression material?
Agar
149
Name three types of hydrophobic elastomeric impression materials?
1. Silicones (addition or condensation cured)
2. Polysulphides (Permlastic)
3. Polyethers (Impregum)
150
What type of silicone impression material is more accurate, Addition or condensation silicone?
Additional silicone (e.g. aquasil)
151
What type of impression tray is required for fixed pros?
Rigid polycarbonate trays
152
What are the 5 main consequneces of invading biological width when preparing a crown?
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
Before impression taking, how would you temporarily displace the gingival margin?
Retraction, either by:
1. Braided cord
2. Injectable material
154
What patients cannot undergo electrosurgery?
Those with pacemakers
155
What is electrocautery? And its use in dentistry?
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
What is the regime for disinfection of impressions?
10 x1.7g actichlor tablets per 1 litre of water. Soak impressions for 3 minutes.
157
What is a pick up impression?
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
When are provisional restorations required for fixed prosthodontics?
For:
1. Provisional crowns
2. Provisional bridges
3. Provisional dentures/overdentures
159
What are the 5 different methods to create a provisional restoration?
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
What material is placed into the pre-operative putty impression to make a provisional crown?
Chemically-cured bis-acrylic composite resin
161
What are the 4 materials used for pre-operative crowns?
1. Polycarbonate
2. Cellulose-acetate
3. Composite
4. Metal
162
What type of acrylic resin must be used with preformed polycarbonate crowns?
Cold-cured acrylic resin
163
What type of composite can be used to make a preformed crown? and why?
Semi-cured composite as it is malleable and mouldable
164
When is a free-hand bis-acrylic resin technique indicated to make a provisional crown?
When a matrix can not be put in place.
165
When are provisional post crowns not suitable? And why?
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
Why is a provisional overdenture a suitable choice as a temporary restoration for a tooth undergoing RCT?
1. It is easy to access the root surface
2. Less coronal leakage during tx
3. Likely better long term result
167
What has happened if a provisional restoration will not withdraw from a tooth preparation or tears when withdrawn?
There are undercuts present in crown preparation
168
At what stage should a a provisional restoration be made during crown preparation?
AFTER tooth prep
BEFORE the impression stage
169
Why should the provisional restoration be made before impression are taken?
So you can modify the tooth prep before the impression is taken
170
What are the advantages of a fixed bridge?
1. Small prosthesis
2. No/minimal mucosal coverage
3. Good patient tolerance
4. Not removable
171
What are the disadvantages of a fixed bridge?
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
What are the 6 fixed bridge options?
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
What luting cement is used to bond resin retained cantilever bridges?
Panavia
174
What type of resin-retained bridges can you get?
1. Cantilever
2. Fixed-fixed
3. Hybrid
175
If extraction of a tooth that is part of a fixed-fixed bridge is required, how would you manage this?
Cut fixed-fixed bridge to extract tooth and this becomes a cantilever bridge
176
What are the 4 advantages of a conventional fixed-moveable bridge?
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
Why do occlusal loads need to be considered before placing an implant retained prosthesis? What type of patient should avoid this prosthesis?
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
What is “conventional bridgework”?
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
What is the anatomy of a conventional bridgework?
1. Abutment
2. Retainer
3. Connector (connects retainer to Pontic)
4. Pontic
5. Saddle (alveolar ridge after tooth loss)
180
Name 4 design types of conventional bridgework.
1. Fixed-fixed
2. Cantilever
3. Fixed-moveable
4. Complex
181
What type of conventional bridgework is most suitable for longer span bridges?
Fixed-fixed
182
What type of conventional bridgework requires teeth involved to be within the same long axis?
Fixed-fixed bridge
183
What type of conventional bridgework is described?
- generally a mesial pontic
- no excursive loading on Pontic
- simple design (max 2 units)
- very successful
Cantilever bridge
184
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
Spring cantilever bridge
185
What type of conventional bridgework is used for mal-aligned teeth, where the long axis of prepared teeth may vary?
Fixed-moveable bridge
186
What is the main advantage of fixed-moveable prosthesis?
Breaking of stress, which prevents unfavourable torquing on retainers.
187
What are the 4 main disadvantages of fixed-moveable bridgework?
1. Limited areas of use
2. Complicated
3. Expensive
4. Increased stress on major abutment
188
What is meant by “physiological mesial drift”?
Tendency of teeth to move forwards in an arch
189
Where should the female component of a fixed-moveable bridge ideally be sited in comparison with the male component?
Ideally female component sited mesial to male component
190
What is a pier abutment?
A freestanding abutment with edentulous space on both sides
191
Why are pier abutments generally avoided?
- middle abutment acts as a pivot
- minor retainer likely to spring becoming a plaque trap
192
What are the 5 main roles that Pontic’s should fulfill?
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
What is a ridge lap?
The amount of contact between a restoration and the alveolar ridge
194
If a Pontic is described as having a ridge lap design, what does this mean? what are the advantages and disadvantages?
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
What is a modified ridge lap Pontic?
Where the palatal or lingual aspect of the Pontic is removed to prevent plaque trap and allow for better hygiene to be maintained
196
What is a hygienic Pontic? What is the advantage?
A Pontic that doesn’t touch the ridge at all (almost floating) connected to abutments. Very easy to clean.
197
What design of Pontic is most appropriate for anterior bridge?
Modified ridge lap Pontic
198
What is the disadvantage of a dome Pontic design?
Food packing
199
What two Pontic designs are most commonly used in posterior bridges?
Modified ridge lap and hygienic
200
What is the Pontic design of choice?
Modified ridge lap
201
What are 4 methods to assess undercuts in conventional fixed-fixed bridge preps?
1. Direct monocular vision
2. Indirect monocular vision
3. Take an Alginate impression and cast in quick setting plaster
4. Paralleling mirror
202
Why is die hardener applied to study cast prior to inlay preparation with wax?
To help prevent chipping or flaking of the model when carving the wax
203
Why is a spacer applied prior to the wax inlay?
To create space for the luting cement
204
What type of wax is used to create inlay form?
Carnauba wax
205
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
1. If too high metal will come out of end of mould
2. If too low, gases cannot escape leading to a miscast
206
Why is the casting ring lined and placed in water prior to casting procedure with investment material?
Contributes to hygroscopic expansion of the investment material
207
What is the preferred design for a RRB?
Cantilever RRB
208
Why is cantilever RRB the preferred design over fixed-fixed RRB?
Fixed-fixed design is more likely do debond
209
What are the 4 types of RRB?
1. The Rochette bridge
2. The Maryland bridge
3. Resin-bonded and adhesive bridges
4. Fibre-reinforced Bridge (new)
210
How was the rochette bridge placed?
The metal wing retainer had countersunk holes to allow for mechanical retention of the resin cement.
211
How is a Maryland bridge placed?
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
How is the current day resin retained bridge placed?
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
Describe panavia cement used to retain RBB?
1. Dual cure
2. Radio-opaque
3. Thin mixture
4. Insoluble
214
What component of panavia allows for effective bonding to enamel, dentine and metal alloys?
Phosphate monomer
215
What can the wing retainer of RBB be made from?
Either metal alloy or fibre-impregnated resin
216
What are the indications for RRB?
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
What class of incisor relationship would not allow for placement of a RRB due to lack of inter occlusal space?
Class III incisor relationship
218
What are the three designs of RRB?
1. Cantilever
2. Fixed-fixed
3. Hybrid
219
Why might you choose to minimally prepare abutment teeth for RRB over no prep?
1. To improve retention and resistance form
2. To improve location
3. To remove undercuts
4. To create space
220
What aesthetic considerations should be made prior to RRB provision?
1. Will the material shine through teeth?
2. Is there diastema/spacing to consider?
221
According to a retrospective study in 1999 by Djamal et al, what is the median survival rate of bridges and splints?
7 years and 10 months
