1
Q
What is a crown?
A
- full coverage extra-coronal restoration
- indirect restoration
2
Q
How is a crown attached to a tooth?
A
cemented/luted
3
Q
What can crowns be made from?
A
- gold alloy (precious metal alloy)
- ceramic
- metal bonded to ceramic
- non precious metal alloy (eg. CoCr, NiCr)
4
Q
What can a crown be used to retain?
A
a prosthesis
5
Q
What are the indications for a crown?
A
- repeated failure of a direct plastic restoration
- difficulty achieving adequate contour, contact point and occlusal contacts with direct restoration
- minimise risk of tooth fracture
- aesthetics
- to accommodate a metal-based removable prosthesis
- bridge abutment
- replacement of an existing crown
6
Q
What do inadequate occlusal contacts of a large direct restoration risk?
A
increased risk of restoration fracture and subsequent microleakage and secondary caries
7
Q
What do inadequate contact points on a large direct restoration risk?
A
contact point not achieved, increased food packing, difficulty cleaning and maintaining restoration, risk of periodontal disease and secondary caries
8
Q
What can a deficient contact point on a large direct restoration cause?
A
- food packing
- plaque trap
- risk of periodontal disease and secondary caries
9
Q
What can an inadequate contour on a large direct restoration cause?
A
- difficulty maintaining OH, increased risk of caries and periodontal disease
- poor aesthetic outcome
10
Q
What can a very long contact point and inadequate interproximal contour cause?
A
- difficulty cleaning
- increased risk of periodontal disease and secondary caries
11
Q
What are crowns made on?
A
an articulated cast
12
Q
Is a fractured cusp restorable?
A
not if it extends subgingivally
13
Q
When is a cracked tooth considered restorable?
A
when the crack is isolated to crown ONLY
14
Q
Are a split tooth or a vertical root fracture restorable?
A
No
15
Q
How is a crown beneficial to a tooth with a fractured cusp isolated to the crown only?
A
- placing a crown would direct occlusal forces down the long axis of the tooth, preventing propagational cracks as the tooth is protected
16
Q
What is the risk of a cracked tooth isolated to the crown being put under occlusal forces without a crown?
A
crack propagates further down the tooth possibly through root making it unrestorable
17
Q
Why do root treated teeth have a higher risk of experiencing fracture?
A
due to amount of tooth lost due to caries, caries removal and endo access cavity
18
Q
What type of root treated teeth have higher success rates than root treated teeth with normal direct restorations?
A
crowned root treated teeth
19
Q
What type of crown is generally used as an aesthetic option?
A
ceramic crown for improved aesthetics
20
Q
How can crowns be used as denture abutment teeth?
A
- crown prep with rest seat preparation for denture
- crown with incorporated rest seats within metal
21
Q
What is a telescopic/double crown denture?
A
removable denture that fits precisely over teeth prepared with an ‘inner crown’
- expensive, very technique sensitive, requires excellent maintenance to avoid secondary caries
22
Q
What can cause biological failure of an existing crown?
A
- secondary caries
- periodontal issues - perio disease, gingival inflammation, encroachment of biologic width
23
Q
Where should a crown margin ideally finish?
A
- supragingivally but if it is subgingival it must NOT encroach on the biological width
24
Q
What is the biological width comprised of?
A
- the junctional epithelium and the connective tissue
25
What can occur if a crown is placed which encroaches upon the biological width?
there is too short a distance between the crown margin and crest of the bone and the gingiva can reject the restoration, causing inflammation leading to loss of bony support of the tooth
26
What can cause the mechanical failure of a crown?
- ceramic fracture
- occlusal wear
- cement failure
27
What can cause the aesthetic failure of a crown?
visible margin
colour
size and shape
28
Why do we not crown everything?
- heat generation
- exposure of dentinal tubules
- potential pulp exposure
- potential to introduce bacteria into pulp of tooth
29
When should you not use a crown?
- lifestyle factors which adversely affect oral health
- active caries or periodontal disease
- inadequate crown height
- inadequate access for tooth preparation or impression taking
- when there is a more minimally invasive option
30
What lifestyle factors can influence the choice to place a crown or not?
- sugar intake
- oral hygiene
- smoking
- parafunction
31
What active disease types can influence the choice to place a crown or not?
- caries
- periodontal disease
- peri-radicular disease
- tooth wear
32
Why is a heavily worn down or heavily restored tooth not favourable for a crown?
inadequate tooth height
33
How does inadequate tooth height negatively impact crown prognosis?
- very short preparation for crown
- when rotational forces are applied, because its so short you have nothing on the opposing side when the crown is rotating
- crown can just rotate and fall off
- tooth this short cannot retain a crown on it just by mechanical means
34
What type of condition can cause inadequate access for tooth preparation or impression taking?
- sclerosis - scleroderma, post radiation changes
- post surgical changes
35
What are the options when a crown fails?
- a new crown
- a post retained crown
- extraction
36
What kind of guidance do we ideally want for placing a crown?
canine guidance
37
What is a core?
restoration placed in teeth prior to preparation for an indirect restoration (in teeth with large loss of tooth structure)
38
When is a core build up indicated?
if tooth or teeth are heavily restored or broken down
39
What materials can be used for direct cores?
- amalgam
- composite
- glass ionomer (all 3 used at DDH)
- resin modified GI
- compomer
- metal alloy - most commonly used at DDH
40
What are the advantages of amalgam as a core material?
- not particularly technique sensitive
- strong if placed in sufficient bulk (2mm or more)
- can be used as bonded amalgam
- easy to distinguish between it and tooth structure
- packable - voids avoided if packed well
41
What are the disadvantages of amalgam as a core material?
- long setting time
- low initial tensile/compressive strength - requires to leave crown till next visit
- weak in thin section
- mercury may be of concern to patients
- not adhesive unless with specific resin for bonding
- potential electrolytic action between amalgam and other metals in crowns e.g. gold
42
What are the advantages of composite resin as a core material?
- strong so can be placed in thinner section than amalgam
- immediate setting (not complete) with light cure allowing immediate preparation and impressions
- can be bonded to tooth structure
- no mercury
- tooth coloured so ideal under ceramic crowns
43
What are the disadvantages of composite resin as a core material?
- very technique sensitive - moisture contamination and polymerisation shrinkage should be avoided
- can be difficult to distinguish between composite and tooth structure when prepping margins
44
What are the advantages of GIC and RMGICs as core materials?
- adhesive
- fluoride release (controversial evidence)
- low thermal expansion coefficient
45
What are the disadvantages of GIC and RMGICs as core materials?
- low compressive and tensile strengths
- deterioration at low pH
- sensitivity to moisture during setting
- can be difficult to distinguish between GIC and tooth structure when prepping crown margins (NB fuji pink)
- not packable - danger of voids
46
How can retention of a core be gained generally in vital teeth?
- undercut preparation
- dentine pins
- adhesive materials
- elective endodontics - pulp chamber, posts
47
What are the disadvantages of a self-threading dentine pin?
- induces stresses
- dentinal crazing
- self shearing pins often do not penetrate to full depth of pin hole
- fracture resistance of core material reduced
- risk of perforation
48
What can be used instead of dentine pins for retention in vital teeth?
amalgam bonding
49
What is amalgam bonding?
- used to bond amalgam to tooth structure
- molecule present that allows bonding in MDP monomer (methacryloyloxydecyl dihydrogen phosphate) which creates long term durable bond to both dental tissue and metal oxides
50
What are 5 examples of amalgam bonding agents?
1) Panavia 21
2) Panavia F
3) Amalgam bond
4) RelyX ARC
5) Glass ionomer
51
What is the technique for amalgam bonding?
- complete cavity preparation
- place lining if necessary in extremely deep aspects
- etch enamel 20 secs, dentine 10 secs
- rinse and dry - good isolation
- dentine bonding agent on all aspects of cavity and light cure (panavia A&B, scotch bond)
- paint adhesive resin cement (dual cured e.g. panavia or RelyX ARC) on base and walls of cavity
- pack amalgam onto unset cement - wipe away excess
(make sure to place thin coat of vaseline on inner aspect of matrix band
52
What are the characteristics of a composite core?
- good bond to tooth structure
- tooth coloured crowns eg. procera (good under tooth coloured crowns)
- easy to prep/difficult to differentiate from tooth
- good coronal seal
- expansion in water - die relief required on cast before crown is prepared
53
How is a core retained in the restoration of an endodontically treated posterior tooth?
- best achieved by removing all gutta percha from pulp chamber
- place GI or RMGI over floor of pulp chamber and openings of root canals
- leaves an undercut pulp chamber providing potential for good mechanical retention
54
What material are Nayyar cores best suited to?
Amalgam (can use composite)
55
What is a Nayyar core?
retention for amalgam core derived from the remaining pulp chamber and prepared canals by extending amalgam into these areas
56
What is important for the placement of a Nayyar core?
- pulp chamber must be sufficiently undercut and of sufficient depth
57
What are the disadvantages of posts in posterior teeth?
- posts do not reinforce roots
- roots often narrow or curved
58
What can the use of posts in posterior teeth lead to?
- strip or lateral perforation
- weakened tooth
- root fracture
59
Generally what is used in a posterior tooth for fixed pros?
- generally do not use pre-fabricated posts in posterior teeth, we would use a Nayyar core
60
What are the key characteristics of posts in root filled anterior teeth?
- not needed if most coronal tooth structure present (intact marginal ridges)
- composite best over GI/RMGI coronal seal
- posts only needed to retain core if heavily broken down
- metal posts do not reinforce roots
61
Do metal posts reinforce roots?
no
62
When are posts needed in anterior root filled teeth?
only needed to retain core if tooth heavily broken down
63
How is gutta percha removed for a post space?
- soften with heat or chemicals
- mechanical with rotating instruments - preferred, usually a Gates Gliddens bur
- can be done immediately after obturation
64
What is the most efficient method of removing gutta percha for the post space?
- mechanical removal
65
How is mechanical removal of gutta percha for the post space achieved?
- use burs with blunt non-cutting tips e.g. Gates Gliddens (lateral cutting)
- start with smaller size to reduce heat generated and preferential cutting to one side of post space
66
Generally what size of Gates Gliddens bur is used to remove gutta percha for post space?
- start with size 3 (0.9mm) gates gliddens bur, 3 horizontal lines on it to indicate size
67
What are the Gates Gliddens burs matched to?
the post channel preparation burs
68
What does the size 3 Gates Gliddens bur match up with?
the thinnest parapost preparation bur
69
How much GP should be left apically before the placement of a post?
4mm
70
Why is some GP left apically before post placement?
4mm left apically to retain apical seal
71
How long should a post be?
as long as, if not longer than the crown
if short, lacks retention
72
How wide should the diameter of a post be apically?
diameter of post apically no greater than 1/3 of root
73
Where is a ferrule cut?
ferrule to crown or core - cut on natural tooth structure
74
What are the most retentive posts out of smooth, threaded and serrated?
threaded - best retention
serrated
smooth - least retentive
75
Which post is better for an anterior tooth?
parallel sided > tapered
76
How are custom made posts made?
- GP removed, impression post inserted and impression material (light bodied and heavy bodied silicone) to record an impression of the post hole space and the margins.
- impression sent to lab to be cast
77
When are cast post and cores advantageous?
advantageous when:
- unable to achieve parallel sided post
- altering angle of core to post
78
When should you avoid a cast post and core?
in crowns in tooth wear patients
79
What are the disadvantages of cast post and cores?
- poor fit - frequently shorter than length of impression post
- crown often made on 2nd impression so another impression required sometimes
- may be unsuitable under all ceramic restorations - no bond, no translucency
- frequent fracture
80
How are cast post and cores cast?
- cast in molten metal alloy
- cools from tip of post
- contracts on solidification towards tip
- sucks molten gold from core which acts as reservoir
- porosities created here
- fracture risk
81
Why do we tend to avoid threaded posts?
they induce internal pressure/stresses
82
When can preformed direct post and core build ups be used?
relevant when you have some supragingival natural tooth tissue
83
What kind of sides does a pre-formed serrated post have?
- parallel sided - better retention
84
What kind of cement is used for metal posts?
luting cement e.g. zinc phosphate or GI
85
Name two non-metallic posts
1) carbon fibre
2) quartz fibre
86
What kind of cement is used for non-metallic posts?
adhesive resin luting cements
87
What are the key characteristics of non-metallic posts?
- good flexural strength
- less rigid than metal (less chance of root fracture)
- compatible with all ceramic bonded crowns
- easier to remove if required
88
Why does the indirect technique of post placement take longer?
- involves more visits as lab requires to make post and core then perhaps take another impression once placed for the crown
89
What kind of post and core is recommended in a tooth with remaining tooth structure suitable for ferrule preparation and with sufficient structure to bond a core with help of a post?
fibre reinforced resin post
90
What kind of post and core is recommended in a tooth with insufficient tooth structure for ferrule preparation?
tooth will not provide any bracing and therefore you require a more rigid post in the form of a cast post and core
91
What can the placement of a fibre reinforced post with no ferrule result in?
could lead to flexing of post and marginal failure, which can lead to fluid ingress possibly causing delamination of the fibres within the resin post and hence failure
92
What are three examples of extra-coronal indirect restorations?
1) crowns - full/partial coverage
2) veneers
3) onlays
93
What are two examples of intra-coronal indirect restorations?
1) inlays
2) onlays
94
What materials can be used for indirect fixed prostheses?
- metal - gold, silver palladium, nickel chrome
- ceramic bonded to metal
- all ceramic
- composite
- acrylic (provisional)
95
An extra-coronal restoration has to occupy a 3D space bounded by what three sides?
1) proximal surfaces of adjacent teeth
2) occlusal surfaces of opposing teeth
3) soft tissues buccally and lingually/palatally
96
An intra-coronal restoration has to occupy a 3D space bounded by what three sides?
1) the proximal surfaces of adjacent teeth
2) occlusal surfaces of opposing teeth
3) the tooth preparation buccally and lingually/palatally
97
What are the six principles of preparation for a fixed prosthesis?
1) conservation of tooth tissue
2) resistance form
3) retention form
4) structural durability
5) marginal integrity
6) preservation of the periodontium
98
What risks are there if a tooth is over-prepped?
- risk of pulpal damage
- risk of losing retention and resistance form
- compromised strength of tooth
99
What risks are there if a tooth is under-prepped?
either:
- thin material for crown - poor aesthetics, inadequate strength
- overbuilt crown - plaque retention, poor aesthetics
100
What is retention form?
the ability of a preparation to retain a restoration in an occlusal direction
101
What is resistance form?
the ability of the preparation to prevent dislodgement of a restoration to lateral and oblique forces
102
In what situation is chemical retention using cement/lute good?
good when loaded in compression (2 surfaces pushing against eachother)
103
What do we mean by "loaded in compression"?
2 surfaces pushing against eachother
104
What are shearing forces?
when two surfaces are sliding across each other. Crown can slide across tooth due to no proper opposing force.
105
What is the ideal degree of taper when doing a crown preparation?
- should be near parallel for maximum retention and resistance
- aim for taper of 6 degrees - though clinically 10-20 is more often achieved
- too parallel = risk of undercuts
106
What does "taper" refer to?
angle of one axial wall in relation to the long axis of the tooth
107
What does "total occlusal convergence angle" refer to?
taper of one axial wall in relation to the taper of an opposing axial wall, with a reference point being the long axis of the tooth
108
What are grooves and what is their function in a crown prep?
grooves cut into preparation to stop the crown from being able to rotate round the tooth
109
In what situation would grooves be necessary?
round preparations and non full coverage restorations may require this kind of additional feature to aid with retention
110
What kind of reduction is necessary for the placement of a ceramic bonded to metal crown?
- 0.5mm reduction for metal PLUS 1.0mm for ceramic
- therefore, 1.5mm axial reduction
- 1-2mm occlusal reduction
- shoulder margin for ceramic
- chamfer for metal
111
What kind of preparation is necessary for the placement of a ceramic/composite (all ceramic) crown?
- between 0.6-1mm axial reduction
- between 1-1.5mm occlusal reduction
- chamfer margin
112
How wide should a chamfer margin be?
0.5mm
113
Where should a finishing margin be?
ideally
- on sound tooth structure
- below the contact point
- not subgingival
- allow adequate preparation height
114
What are the main 4 crown preparation stages?
1) occlusal reduction
2) axial reductions (interproximal, lingual/palatal, buccal)
3) finish line
4) smoothing
115
What is a functional cusp bevel?
- increased reduction on the functioning cusp
- generally on palatal cusp of maxillary teeth and buccal cusp of mandibular teeth
- depends on occlusal relationship
116
How does the palatal/lingual reduction of an anterior tooth differ from posterior teeth?
-anteriors have a cingulum which tapers off into incisal edge
- initial palatal reduction is just on gingival 1/3 to achieve something almost parallel to buccal side of prep
- then reduce rest of palatal surface/cingulum with rugby ball
117
What margins are there on an anterior prep?
- buccal/labial shoulder
- palatal chamfer
118
What are the indications for an all-ceramic restoration?
- porcelain (ceramic) offers potential for a highly aesthetic restoration with close approximation to natural tooth tissue
- highly biocompatible material
- some systems can be provided same day
119
What are the disadvantages of all-ceramic restorations?
- mechanical restorations historically a major drawback (prone to fracture under oral function)
- require larger reductions in tooth tissue
- cost can be high
- reduced scope for adjustment or repair
120
What are the four classifications of dental ceramic when classified by composition?
1) glass-based ceramic
2) glass-infiltrated ceramic
3) polycrystalline (non-glass) ceramic
4) resin-matrix ceramic
121
What are the three types of glass-based ceramic?
1) Feldspathic glass (filler <17%, high aesthetics, most fragile)
2) moderately filled glass ceramic (17-45% leucite based filler)
3) highly filled glass ceramic (45-70% leucite or lithium disilicate filler)
122
What type of glass-based ceramic is most fragile?
Feldspathic glass
123
What amount/type of filler is present in a moderately filled glass ceramic (glass-based ceramic)?
17-45% leucite based filler
124
What amount/type of filler is present in a highly filled glass ceramic (glass-based ceramic)?
45-70% leucite or lithium disilicate filler
125
What are glass infiltrated ceramics infiltrated with?
alumina, magnesium or zirconia infiltrated with low viscosity glass
126
What are the characteristics of a glass infiltrated ceramic?
good mechanical properties
reduced aesthetics
127
What materials are polycrystalline (non-glass) ceramics based off of?
- alumina or zirconia based
- good mechanical properties
128
What is the composition of a resin-matrix ceramic?
- analogous to composite - ceramic nanoparticles in a resin matrix
mostly limited clinical study due to novelty
129
What are the three classifications of dental ceramics based on method of manufacture?
1) sintering
2) hot pressing/injection moulding
3) machining
130
What occurs during sintering of dental ceramic?
- ceramic powder mixed with water is build to the required shape and exposure to high temperature causes partial melting and fusing of particles
131
What occurs during hot pressing/injection moulding of dental ceramic?
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
132
What occurs during machining of dental ceramic?
- 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.
133
What are the two final ways all ceramic restorations can be classified?
- monolithic
- bilayer
134
What are monolithic crowns?
crowns machined from a single block of ceramic
135
What are bilayer crowns?
analogous to MCCs, whereby a coping is made usually from tougher highly filled glass ceramic or zirconia.
More aesthetic feldspathic porcelain is then built onto this coping.
136
What tooth preparation is required for an all-ceramic restoration on an anterior tooth?
1.5-2mm occlusal reduction
1.0mm reduction cervically
1.0-1.5mm reduction more incisally
137
What tooth preparation is required for an all-ceramic restoration on a posterior tooth?
1.5-2.0mm occlusal reduction
1.0-1.5mm axial reduction
1.0mm margin
138
What can sharp angulations on preparations lead to?
stress concentrations in the restoration, initiating failure
139
Generally, what kind of luting cement will be used for the cementation of an all-ceramic restoration?
generally resin modified glass ionomer or a resin luting cement system will be ideal
dual cure system preferred
140
What acid is used to etch ceramics?
hydrofluoric acid NOT orthophosphoric acid
141
Most types of all-ceramic restoration demonstrate a five-year survival of what percentage?
around 95%
142
What are the common causes of crown failure? 11
- fracture of restoration
- apical osteitis
- loss of retention
- hypersensitivity
- pre-prosthetic core fracture
- chipping
- root fracture
- loss of implant
- secondary caries
- ceramic chipping/fracture
- endo complications
143
What are cuspal coverage indirect restorations?
cover cusps but do not go down to the gingival margin e.g. onlays, all function occurs on the indirect restorations
144
When is a cuspal coverage restoration appropriate?
- to preserve integrity of a weakened tooth against the forces of occlusion
- to correct occlusal discrepancies or be part of the restorative reorganisation of the occlusal scheme
145
Name four commonly considered cuspal coverage restorations
1) onlays
2) inlays
3) 3/4 crowns
4) 7/8 crowns
146
How does the preparation for a 3/4 crown differ from the prep for a FGC?
similar but with a proximal groove, occlusal offset and buccal level
147
Compare the advantages of intracoronal vs full coverage restorations
- full coverage protects cusps (ct intracoronal)
- intracoronal reduces sound tooth removal (ct full coverage)
- intracoronal reduces amount of restorative material required e.g. Au (ct full coverage)
- intracoronal easier to inspect margins ct subgingival full coverage
- intracoronal potentially better aesthetics buccally ct full coverage
148
What materials can be used for the construction of an indirect cuspal coverage restoration?
- gold
- all ceramic
- composite
149
What materials can be used for the construction of a direct cuspal coverage restoration?
composite
150
What materials can be used for the cementation of a cuspal coverage restoration?
- luting - e.g. resin modified GI (RelyX luting), PolyF
- bonding e.g. resin (Panavia) (MDP monomer allows bonding to metal as well as tooth structure)
151
What are the two main types of impression material?
- hydrophilic
- hydrophobic
152
What are the two sub-types of hydrophilic impression materials?
- irreversible
- reversible
153
What is an example of an irreversible hydrophilic impression material?
alginate
154
What is an example of a reversible hydrophilic impression material?
agar
155
What are the three sub-types of hydrophobic impression materials?
all elastomeric:
1) silicones
2) polysulphides
3) polyethers
156
What are the two sub-types of silicones used for impression taking and what are their key features?
1) addition cured
2) condensation cured
hydrophobic, elastomeric
157
Within what time frame must an alginate impression be poured?
<24hrs
158
What is an advantage of agar?
can be VERY accurate
159
What kind of tray and mechanism does agar used?
requires special tray with cooling mechanism
160
Silicones are hydrophobic, what does this mean for impression taking?
must have a DRY prep
161
Are condensation cured or addition cured silicones more accurate?
addition very accurate and very stable
condensation less accurate
162
How long must addition cured silicones be left following impression before pouring?
>1 hour
163
How long must condensation cured silicones be left following impression before pouring?
must leave 24 hours before pouring
164
What is an advantage of addition cured silicone impression material?
very accurate and very stable (2 years)
can be disinfected
165
What is one advantage of condensation cured silicone over addition cured silicone?
cheaper
166
What is aquasil an example of?
an addition cured silicone
167
Name two condensation cured silicones
Xantopren
Optosil
168
Name three addition cured silicones
Affinis
Aquasil
president
169
What are the key characteristics of the hydrophobic impression material polyether?
- very accurate
- rotten taste
- very stiff on removal, undercuts, perio pts
- less hydrophobic but dont store wet
170
What are the key characteristics of the hydrophobic impression material polysulphides?
- long working time
- great for big undercuts (hence use in removable pros)
- smelly
171
What are considered the gold standard impression tray but why are they not used at DDH?
Rim lock trays - can't cut them out the mouth
172
Why would you not use a special tray with polyether?
polyether too stiff
173
How do you carry out a putty wash one stage technique impression?
- 2 viscosities, usually putty (high) and wash (low)
- syringe wash around tooth
- nurse loads impression tray with putty at same time
- seat putty impression tray over wash before it starts setting
174
What are the four types of impression technique?
1) putty/wash - one stage
2) monophase
3) putty/wash - two stage (spacer/no spacer)
4) pick up technique/Mill tray
175
How do you carry out a monophase technique impression?
- 1 viscosity, polyether or medium viscosity silicone
- place some material in a syringe to syringe around tooth while nurse loads tray with same material
- insert tray with impression material over syringed material
176
How do you carry out a two-stage technique impression?
- 2 viscosities - usually putty (high) and wash (low)
- usually condensation cured silicones
- seat putty in imp tray and take putty impression either
1) before crown prep
2) using a spacer
- allow to set and remove (leaving space for wash)
- syringe wash around tooth and reseat putty impression
- ok if condensation cured silicone used as it will shrink following removal compensating for the compression
177
How do you ensure the papilla fills the interdental space?
distance from alveolar crest to the base of the prximal contact point
5mm = 98% filled
6mm = only 56% did so
178
What is the local regimen for disinfection of impressions?
10 x 1.7g actichlor tabs per 1 litre water - 3mins
179
What are the functions of a provisional restoration?
- protect pulp from thermal, mechanical, electrical and chemical trauma
- maintain position of tooth in occlusion
- maintain periodontal health of tooth
- restore aesthetics
- protects any root filling from coronal leakage
180
When are provisional restorations required in fixed prosthodontics?
- provisional crowns
- provisional bridges
- provisional dentures/overdentures
181
What are five methods of creating a provisional restoration?
1) pre-operative putty impression (+/- modification)
2) pre-formed crown - polycarbonate, cellulose acetate, composite, metal
3) pre-operative wax-up followed by duplication and vaccum-formed stent
4) free-hand bis-acryl resin
5) use old crown if there is one
182
What is the most common method of creating a provisional restoration?
pre-operative putty impression (+/- modification)
183
How does the pre-operative putty impression (+/-modification) work for the production of a provisional crown?
- if reproducing tooth in current shape, then take pre-op putty impression
- if modifying and then copy modified shape for provisional crown
- pre-op models cast up with wax registration
- wax-up duplicated in stone and vaccum formed mould made
- vaccum formed mould used to make composite additions, crown preps made and provisional crowns created using same mould
184
What goes into the pre-operative putty?
- chemically cured bis-acryl composite resin
trade name = Protemp (3M ESPE) and integrity (Dentsply)
185
How is a provisional crown made from the pre-operative putty?
take pre-op putty, fill with protemp and then seat back into the mouth and wait to set
186
How is a polycarbonate preformed crown placed? (provisional)
- directa polycarbonate provisional crowns (most common)
- only works with cold cure acrylic resin (TRIM) inside them which bonds to inside of crown
- place crown with TRIM inside onto prep, lift slightly off at initial set to avoid getting locked into undercuts (pull over undercuts) and do not fully remove until almost set
- remove and trim
- check occlusion, cement
- came in various sizes
- doesn't fall apart when trimmed, can be polished
187
How is cellulose-acetate used to place a provisional crown?
- cut to size with crown shears
- perforate incisal corner to let out trapped air
- fill with protemp
- place over prep and allow to cure
- remove from prep
- remove cellulose acetate
- polish margins
- check occlusion
- cement
188
Where can composite pre-formed crowns be utilised and how are they placed?
molars
- semi-set composite cut to size, swaiged over preparation to right shape, patient closes into position and establishes occlusion and then it will set hard
189
How would a metal provisional crown be placed and why are they no longer advocated?
- select, line with protemp, trim up margins, check occlusion, cement
- not encouraged due to horrible margins and plaque accumulation
190
When would free-hand bis-acryl resin be used for a provisional restoration?
last resort
when can get no matrix in place
191
How would you re-place a n old crown as a provisional?
fill with protemp and use as provisional
192
If there is no crown and you require a provisional bridge, what can you do?
- get some soft wax and 'mould it'
- make a putty index
- use some pro-temp
- trim it up
- check occlusion, polish and fit
193
When could a provisional post crown be indicated?
when existing root canal filling is satisfactory ie. having just obturated root canal or simple replacement of post crown only
194
Why is a provisional post crown not suitable as a provisional restoration when undertaking RCT or replacing a root canal filling?
because they leak LOTS
195
What are the diagnostic uses of provisional restorations?
- is the crown undercut? if yes, provisional will either tear or not withdraw from restoration
- have I removed sufficient tooth structure occlusally/incisally? - does prep cut through provisional crown when checking occlusion, is provisional less than 0.5mm thick
if so, can go back and modify as required
196
How can a provisional crown improve gingival/periodontal health prior to taking definitive impression?
- replacing poorly contoured restoration with a provisional of better contour allows access to cleaning and improved gingival health
197
How can a provisional crown improve speech difficulties?
- changing contours of palatal surfaces of upper anterior teeth
- copy successful provisional restoration contour for definitive restorations
198
How can a provisional crown improve the appearance of teeth?
- easier to change provisional restorations than definitive ones
- get it right with provisional and copy for definitives
199
At what stage should you make your provisional restoration?
- AFTER the tooth preparation stage - to check the tooth prep is satisfactory
- BEFORE impression stage - so you can modify the tooth prep (if required) before the definitive impression is taken
200
When should you replace missing teeth?
- poor appearance
- unstable occlusion - tilting, drifting, over-eruption
- function - speech, psychological, ortho retention/splinting (retain space), reorganised approach (increase OVD)
201
What are the options available to replace missing teeth?
- close space with orthodontics
- partial denture
- bridge - conventional or resin retained
- implant retained restorations
202
What are the possible issues or disadvantages of closing a space with ortho to replace missing teeth?
- poor compliance
- poor appearance e.g. canines moved into lateral space
- occlusion - can be unfavourable
203
What are the advantages of a partial denture to replace missing teeth?
- multiple edentulous spaces fixed with one prosthesis
- long edentulous spaces
- immediate/traditional prostheses available
- low cost - acrylic
204
What are the disadvantages of a partial denture to replace missing teeth?
- tolerance, retch, gag reflex
- psychological, decreased self confidence
- oral hygiene, gingival inflammation
205
What do resin retained bridges require to replace missing teeth?
- sound abutment teeth
- ideal spacing
206
What is an advantage of using a resin retained bridge to replace a missing tooth?
minimal preparation required
207
What are the disadvantages of using a conventional bridge to replace a missing tooth?
considerable prep of abutment teeth
- irreversible
- risk of pulp necrosis
- risk of caries and perio disease
208
What is an advantage of using a conventional bridge to replace a missing tooth?
good control over aesthetics
209
What are the requirements for a single tooth implant?
- sufficient space in 3 dimensions (careful of anatomical landmarks e.g. sinuses, nerves, unerupted teeth)
- well cared for dentition
- remaining teeth with good prognosis
- medical history - should be non-smoker so inflammatory process unimpeded (failure rate 2x in smokers)
210
What are the requirements for a single tooth implant regarding bone quantity?
- most implants around 4mm diameter (min 3.25 for adequate strength)
- must leave minimum 1mm bone (pref 2mm) between implant fixture and adjacent teeth
- more space left between implants
211
What are the requirements for a single tooth implant regarding bone quality?
- well formed cortex
- densely tuberculated medullary spaces
- good blood supply
n.b. radiation, infection, heavy smoker
212
What kind of radiographic technique is used to plan implant placement?
CBCT - 3D
213
What are the occlusal requirements for an implant retained tooth?
- adequate angulation and clearance of opposing arch
- fixed - no give, therefore, careful distribution of loads in lateral excursion, ensure initial contact on natural teeth
214
What is a conventional bridge?
- a fixed prosthesis replacing missing teeth only
- where abutments are natural teeth and the retainers are indirect restorations where adhesive is not generally recognised as the primary method of retainer retention
215
What is an abutment of a bridge?
the prepared tooth onto which the bridge fits
216
What is the retainer of a bridge?
indirect restoration on the abutment tooth
217
What is the connector of a bridge?
part of the bridge which connects the retainer to the pontic
218
What is the pontic of a bridge?
prosthetic tooth/teeth
219
What is the saddle of a bridge?
alveolar ridge after tooth loss
220
What are the four main types of conventional bridgework?
1) fixed-fixed
2) Cantilever and spring cantilever
3) Fixed-moveable
4) Complex
221
What is a fixed-fixed bridge used for and what is necessary for it?
-longer span bridgework
- anchored at both ends
-pontic can support loading
-need teeth with same long axis
222
What is a cantilever bridge?
- simplest design of conventional bridgework
- anchored on one end
- maximum two units
- generally pontic sited mesial to retainer
- very successful
223
What forms of loading cannot be exerted on the pontic of a cantilever bridge?
no excursive loading on pontic
no loading in CICP or excursion on pontic
224
What is a spring cantilever bridge?
In a spring cantilever, the pontic and retainer are remote from each other and connected by a metal bar.
225
What are the issues with spring cantilever bridges ultimately leading to their lack of use?
- often RBBs would work as well
- need first rate technical help
- expensive
226
What is a fixed-moveable bridge?
bridge where the join between the replacement teeth and the tooth/teeth retaining the bridge is not rigid.
227
When are fixed-moveable bridges used?
-used for mal-aligned teeth
- stress-breaking
- high success rate
228
How do fixed-moveable bridges break stresses?
- variation of tooth movement and degree
- prevents unfavourable torquing on retainers
229
What are the advantages of a fixed-moveable bridge?
- good track record
- solution to alignment issues
- use of different materials possible
230
What are the disadvantages of a fixed-moveable bridge?
- limited areas of use
- complicated
- expensive
- increased stress on major abutment
231
In a fixed-moveable bridge, where is the female component sited in comparison to the male and why?
ideally female component sited mesial to male component due to physiological mesial drift (teeth tend to move mesially)
232
What is a complex (hybrid) bridge?
any combination of bridge types possible
233
What is a pier abutment and why are they avoided?
- having an abutment between 2 end abutments
- middle abutment acts as a pivot
- minor retainer likely to spring
- acts a bit like see-saw
234
What roles must pontics fulfil?
- replacing function of lost tooth
- achieve aesthetic appearance
- enable adequate OH
- prevent tissue irritation
235
What is generally the pontic design of choice?
modified ridge lap
236
What pontic designs are available for anterior or posterior placement?
- anterior - modified ridge lap
- posterior - modified ridge lap or wash through/sanitary/hygienic/all gold (doesn't contact ridge at all, ideally min gap of 2mm clearance)
237
What is a disadvantage of modified ridge lap pontics?
not easily cleansable and can cause gingival irritation
238
What steps are involved in conventional bridge preparation?
- evaluate occlusion (esp teeth in guidance)
- determine long axis of each tooth (and prep)
- common long axis for both preps
- buccal depth/orientation grooves cut parallel to eachother
- prep distal of D tooth in relation to orientation groove
- prep distal of M tooth in relation to orientation groove
- complete proximal preps
- complete buccal preps
- occlusal reduction
- prep palatal to preserve cingulum where possible
239
What methods can be used to assess undercuts in conventional fixed-fixed bridge preps?
- direct monocular vision
- indirect monocular vision
- take alginate imp and cast in quick setting plaster
- paralleling mirror (in dundee)
240
What is a Rochette bridge?
Resin retained bridge that relied on countersunk holes through the metal retainers to allow mechanical retention for the resin. Thickness increased to maintain strength, composite may wear. historical
241
What is a Maryland bridge?
prosthetic tooth with thin metal “wings” on either side.
Base metal alloy retainer is electrolytically etched in bath of strong acid solution, etch pattern can be unpredictable and easily damaged
242
How are the metal retainers of current day resin retained bridges roughened before placement?
sandblasted with alumina particles of 50 micro m diameter
quick, easy and predictable so done at try-in stage
243
What resin is used for current day resin retained bridges?
Panavia resin as it chemically and micromechanically bonds to metal retainer and etched enamel
244
What are the key characteristics of panavia resin?
- dual cure
- radiopaque
- thin mixture
- insoluble
- phosphate monomer (MDP) allows effective bonding to enamel, dentine and metal alloys
245
What are the indications for a resin retained bridge?
- unrestored or minimally restored abutment teeth
- sufficient good quality enamel on abutment tooth
- sufficient interocclusal space
- good alveolar bond shape
246
What are the requirements for a resin retained bridge?
- wing retainer must be rigid - fabricated from metal alloy or fibre impregnated resin
- wing must fit closely to abutment teeth
- porcelain fused onto enamel
247
What bridge design has the best prognosis/success rate?
Cantilever
248
What is preparation of the tooth necessary for?
to introduce guide planes when the path of insertion is a problem or to enable maximal coverage when the desired extension would otherwise include enamel undercuts
249
What has the median survival rate (bridges and splints) been reported as by Eastman Dental Hospital?
7 years and 10 months
250
What is the most common cause of failure in resin bonded bridges?
debonding of the restoration (78%) followed by porcelain fracture (13%)
251
Are anterior RBBs or posterior RBBs more retentive?
anterior RBBs
252
What is an implant?
a dental implant is an artificial root that is surgically anchored into the jaw to hold a replacement tooth or teeth or a denture in place.
253
What is the benefit of an implant tooth in prosthodontics?
they don't rely on neighbouring teeth for support
254
What are the three components of an implant?
- abutment screw
- abutment
- implant
255
Where is the abutment of an implant screwed?
usually into the hollow part in the centre of the implant by an abutment screw. The restoration then sits on top of this
256
What is the process by which an implant has direct communication to the bone?
osseointegration
257
Where does an implant usually sit and what does it lack compared to natural teeth?
no PDL
sits at crest of the bone
258
You don't get periodontitis with implants, what do you get instead?
peri-implantitis
259
Where is the peri-implant mucosa?
the gum around the implant
260
Where do implant restorations usually sit?
subgingival
261
If a crown is screwed onto an implant, how many screws are there in the entire implant and what are they?
3 screws
- the implant
- the abutment screw
- restoration screw
262
What can an implant restore?
- single tooth (implant crown)
- multiple teeth (implant bridge)
- can secure a denture firmly (implant overdenture)
- eyes, ears, hearing aids and noses - implants used to secure other prostheses
263
What are the 6 stages in implant treatment sequence?
1) plan and consent
2) place
3) uncover and connect abutments
4) restorative procedures
5) restore
6) monitor and maintain
264
What social history factors can impact someones eligibility for implants?
- smoking - increased failure rate
- drug use - can be problematic
- other aspects - dental phobia, anxiety
265
What medical history factors can impact someones eligibility for implants?
- chemo/radiotherapy - osteoradionecrosis
- polypharmacies - dry mucosa
- immunosuppression - impaired healing, MRONJ
- MRONJ risks
- cardiac issues - surgery itself may require precautions
- mental health issues - capacity, consent, coping
- diabetes - increased failure rate
- thyroxine - increased failure rate
266
What dental history factors can impact someones eligibility for implants?
- oral health
- perio status
- uncontrolled caries
- status of crowns/bridges/root treatments
- dental anxiety
- pre-existing implants - success rate?
- other aspects - bruxism
267
What are the risks of implant placement?
- minor surgical risks - pain, bruising, swelling
- major surgical risks - proximity to other structures
- paraesthesia
- perforation into nasal cavities of maxillary antrum
- failure to integrate
- late failure
- bruxism and implants
- peri-implantitis
- failures of superstructures and components
268
How are implants planned?
- history and examination
- radiographs - if 2D then require in different planes
- other imaging - CBCT/CT
- surgical and radiographic templates
- CBCT allows 2D cross section view through bone and allows 3D modelling around ridges and 3D printing
269
What are the 4 types of implant?
1) system
2) tapered
3) platform
4) co-axis
270
What are the 4 main stages in placing an implant?
1) raise flap
2) place implant
3) place cover screw
4) suture
271
How long should it take for an implant to be integrated into the bone?
3 months
272
After the implant is integrated into the bone, what is done?
uncover the implant...
1) uncover implant - not a flap, just LA and tissue punch
2) place abutment
3) take impression with coping
4) choose colour/shade
5) place temp
6) cast impression with lab dummy
= cement completed crown/restoration
273
What are the disadvantages of cement retained restorations on implants (multiple teeth)?
- abutments so retentive that they can be very difficult to remove, even if stuck with temp cement
- can get cement around margins, if not removed at time of cementation, much less forgiving than a natural tooth and can lead to inflammation and bone loss around implant
274
What is an advantage of using cement retained abutments on implants rather than screw retained (multiple teeth)?
- no screw hole through the top of the restoration required
275
How are screw retained multiple teeth implants placed?
- once you've placed the bridge and placed the screws through the bridge into the holes in the abutments, you then fill the hole with something soft first and then composite over the top. This ensures access to these screw holes at a later date if required
276
What is the advantage of placing a soft material over the abutment screw before placing composite in an implant?
if a patient chips a tooth of breaks a bit of acrylic, you can just unscrew the restoration, fix it and screw it back on
277
What is a disadvantage of screw retained implants?
must be strict about placement of implants if they are to be screw retained because you want to avoid the screw hole sitting labially (negative aesthetic impact)
278
What is the most popular method of securing a denture with an implant?
Locator TM abutments
279
How do Locator TM abutments work (securing denture with implant)?
place a little abutment with internal and external components to it
- in the denture a stainless steel cap is placed over where the abutment is and you place a locator insert inside it
- denture clips into these locators by means of rubber locator insert, holds denture firmly in place
280
How does a ball abutment secure a denture in the mouth?
- ball abutments work like ball and socket
- ball is attached to implant in mouth and denture has cold-cured sucker cap with gold insert screwed inside
- little splits in gold cap grab hold of ball part of abutment in the mouth
- can adjust with little tool, 1/4 turn to tighten or loosen
281
How can a denture be secured with a gold bar?
implants joined together by a gold bar, sometimes with/without distal extensions
- in denture there are gold clips which clip to bar between the implants
282
What is the advantage of a gold bar (implant) retained denture?
- stops anti-rotation more than locators or ball and socket retention
283
What are the disadvantages of a gold bar (implant) retained denture?
- expensive
- bar can be harder to clean beneath
- solder joint = fracture risk
284
How can a CAD-CAM titanium bar be made to retain a denture (implants)?
take an impression, model scanned and out of solid piece of titanium, bar is made
285
Why is a CAD-CAM titanium bar superior to a gold bar?
no solder joint - eliminates fracture risk of gold bar
286
What are four common post implant treatment complications?
1) peri-implant mucositis
2) peri-implantitis
3) loose/fractured components
4) late implant failure
287
What are the roles of the GDP in implant patients?
- OH advice
- triage and diagnosis (if possible) of a complication
- referral of complication to implant dentist
- ensure pt informed/able to perform optimal plaque removal around implant(s)
- examine the peri-implant tissues for signs of inflammation and BOP/suppuration and remove supra/submucosal plaque and calculus deposits and excess residual cement
- perform radiographic examination only where clinically indicated
288
What are the SDCEP guidelines regarding the care of implant patients?
- ensure baseline PA radiograph of implant, aligned with long cone paralleling technique is obtained 1 year after superstructure connection to facilitate long-term implant maintenance
- OH, TIPPS, smoking cessation advice
- examine peri-implant tissues for signs of inflammation, BOP and suppuration.
- Probe gently around superstructure to feel for excess residual cement and submucosal plaque and calculus. Measure baseline probing depths
- remove supra and sub-mucosal plaque, calculus or submucosal excess residual cement if detected (LA may be required)
- assign risk level and schedule recall accordingly
289
What is peri-implant mucositis?
inflammation of the peri-implant mucosa with no evidence of crestal bone loss. Tissues will appear red and swollen and may bleed on gentle probing
290
How can peri-implant mucositis be excluded as a diagnosis?
take radiographs - assess peri-implant bone levels compared with baseline radiographs, if bone loss present then it is not peri-implant mucositis
291
What is peri-implantitis?
infection with suppuration and inflammation of the soft tissues surrounding an implant, with clinically significant loss of peri-implant crestal bone after the adaptive phase. Tissues appear red, swollen, may bleed on gentle probing and there will be suppuration
292
What are the diagnostic signs of peri-implantitis and what is done for treatment?
- take radiographs and compare to baseline radiograph
- if clinically significant progressing crestal boe loss detected, refer back to clinician that placed implant.
- arrange follow up 1-2months later to assess outcome of treatment, if no improvement, seek advice from secondary care
- if inflammation settled and stability achieved, radiographic follow-up in 6-12 months
3rd year - module 6
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