Fixed Pros Flashcards
1
Q
What are examples of complex conservative dentistry in fixed prosthodontics?
A
- Inlays
- Onlays
- Veneers
- Posts
- Cores
2
Q
What are the main types of fixed pros
A
- Complex Conservative Dentistry
- Crown and Bridge
3
Q
What is meant by an indirect restoration?
A
A rigid restoration that is constructed outside the mouth and then fitted
4
Q
What are materials used in indirect restorations?
A
- Porcelain
- Gold
- Base Metals
- Porcelain fused to gold
5
Q
What is a fixed crown?
A
An artificial extra-coronal coverage replacement that restores missing tooth structure by surrounding part or all of the remaining structure with a material such as cast metal, porcelain or a combination of materials such as metal and porcelain
6
Q
What are different types of crown?
A
Full Crown
Partial Crown: 3/4 Crowns, Onlays
7
Q
What is a pontic?
A
An artificial tooth/teeth on a prosthesis that replaces a missing natural tooth
8
Q
What is an abutment?
A
A tooth that serves to support or retain a bridge
9
Q
What is a retainer?
A
Component of a restoration that is cemented to the abutment teeth to retain a bridge
10
Q
What is an inlay?
A
A intra coronal restoration that is within the internal boundary of the tooth
11
Q
What is an onlay?
A
An intracoronal restoration that covers a cusp or external boundary of the tooth
12
Q
What are indications for crowns?
A
- Protection of weak tooth structure
- Re-establish occlusion
- Modification of tooth shape
- Replacement of missing tooth structure/tooth/teeth
- As retainers: e.g. to help retain a partial denture
- Aesthetics (minor reason)
13
Q
What are contraindications for crowns?
A
- Poor Oral Hygiene / Active Dental Disease
- Cost
- Age / Ill Health
- Excessive Removal of Tooth Structure
14
Q
What is the main reason for crown failure?
A
Recurrent Caries
15
Q
What is the longevity for crowns at 10 years?
A
96%
16
Q
What is the problem with placing crowns in younger patients?
A
- Inadequate secondary dentine increases the risk of pulp exposures
- Passive Eruption after 14 exposes crown margins if not subgingivally placed
17
Q
What is the problem with placing crowns in old patients?
A
Mobility issues for complex work
18
Q
What are indications for veneers?
A
Diastema Closure
Alter Shape, Contour, Position
Alter Tooth Colour
Mask Surface Anomalies (tetracycline staining, hypomin, hypoplasia))
19
Q
What are advantages of veneers?
A
- Excellent aesthetics
- Alloy free (No Sensitivity issues)
- Good clinical record
- Conservative restoration
- Very good colour stability
- Good Biocompatibility
- Cheaper than full crown
- Very thin
- Minimal/no prep on teeth, in enamel only (Good bond)
20
Q
What are the 3 functions of a post?
A
- Retain the core (foundation restoration)
- Stabilise the core (primary function is supporting the core)
- Obturation of the post canal
21
Q
How can a post provide additional support to a tooth
A
1) Resistance of filling against fracture
2) Retention of filling against dislodgement
22
Q
What are the functions of a core?
A
- Foundation for coronal restoration
- Retention and stabilisation of coronal restoration
- To perform as an interim restoration
23
Q
What are the 5 governing principles of a crown preparation?
A
- Preservation of tooth structure
- Retention and resistance form
- Structural Durability
- Marginal Integrity
- Preservation of periodontium
24
Q
What is retention form?
A
Prevents removal of the restoration along the path of insertion or long axis of the tooth preparation
25
What is resistance form?
Prevents dislodgement of the restoration by forces directed in an horizontal or oblique direction
26
What is the purpose of a taper?
Allows the restoration to be seated
27
What is the ideal taper angle?
The angle of the opposing walls meet at 6-10 degrees
28
What is the issue with having an idealised taper of 0 degrees? (Parallel)
Likely to get it wrong (angle is converged and an undercut created) and the restoration can't be seated
29
What is the perfect taper angle?
0 degrees (Parallel)
30
Do taper angles apply for both intracoronal and extracoronal restorations?
Yes, but require tapering to seat and attach indirect restorations
31
What is the issue with short-walled preparation of a large tooth?
Prone to tipping displacement
32
How can you overcome displacement issues with a short walled preparation
Increase resistance by placing grooves (increased surface area)
33
What are issues that can occur with the path of insertion?
Crown seating can be locked out by interference from a neighbouring tooth
34
What are 5 rules to ensure structural durability for a crown?
1. Restoration must contain adequate material to withstand occlusion
2. Follow Anatomical Form during preps
3. Ensure adequate height to length ratio
4. Adequate Occlusal Thickness
5. Small diameter of crow prep resists tipping
35
Why is a subgingival margin problematic?
- Affects gingival health - biofilm accumulation + gingivitis
- Harder for patients to clean
36
T/F: Dental Ceramics have good tensile strength
False, they have good compressive strength
37
What is the Teknik 847-012 bur used for?
Medium grit tapered diamond with a flat end for:
- Cuts flat butt shoulder finish
- PJC + PBM preparations
38
What is the Komet 8877-010 bur used for?
Torpedo shaped fine grit parallel diamond for:
- Cutting fine chamfer margins
- Axial reduction for crowns, gold, PBM
- Finishing margins, proximal flares
39
What is the Teknik 856-014 bur used for?
Long 9mm medium grit tapered diamond with a round end for:
1. Cuts flat shoulder with rounded internal line angle
2. Axial reduction - FGC/PBM/Porcelain Veneer Preps
40
What is the Horico 239-018 bur used for?
Coarse grit pear shared for:
- Concave reduction on palatal and occlusal
41
Why are non-vinyl gloves used for mixing PVS putty?
Sulphur content in some latex gloves inhibits the putty set
42
Which burs are suitable for clearing interproximal contacts?
L10 or TC 169L
43
Which bur would you use for a flat shoulder finish?
Teknik 847-012
| L20
44
Which bur would you use for a chamfer finish?
Komet 8877-010
45
What are 6 main reasons for making a Temporary Crown from a Dentist's perspective?
1. Pulpal Protection (from dentinal sensitivity, decay and fracture)
2. Positional Stability (horizontal drift or overerruption)
3. Restoring Function
4. Restoring Aesthetics
5. Maintain Periodontium
6. Protect Underlying Tooth Structure and Core Structure
46
What are 5 requirements that a patient might have for a temporary crown?
1. Should look like natural tooth - matching shape and colour
2. No pain or discomfort
3. Comfortable when chewing and speaking
4. No food impaction
5. Doesn’t break or fall off
47
What are Anterior Prefabricated Crown Forms made of?
Polycarbonate - in order to be tooth coloured
48
What are Posterior Prefabricated Crown Forms made of?
Aluminium - in order to be functional on occlusal load areas
49
What are some composite materials that can be used for direct temporary crowns?
Bis-acryl (Bis-GMA) Composite Resins (Protemp 4)
Methyl Methacrylate (Duralay, Jet)
Vinyl Ethyl Methacrylate (Trim)
50
What were some issues with earlier generation temporary crown materials?
Very heavy resin smell - unpalatable to patients
Highly Exothermic
High Shrinkage
51
What are some properties of 4th generation Bis-acryl (Bis-GMA) Composite Resins (Protemp 4)?
1. Low shrinkage
2. High dimensional stability
3. Low exothermic reaction
4. Brittle in thin sections
5. Irritative to Skin Contact
52
Where might Vinyl Ethyl Methacrylate (Trim) be more suitable than Bis-acryl (Bis-GMA) Composite Resins (Protemp 4) for temp crowns?
Higher strength and hardness - suitable for long span temp bridges
53
Why might Methyl Methacrylate (Duralay, Jet) be less suitable than Bis-acryl (Bis-GMA) Composite Resins (Protemp 4) for temp crowns?
Less suitable due to high shrinkage, high exothermic reaction and high pulp toxicity due to free monomer
54
What are the 10 steps for making a custom-made temporary crown?
1. Make a pre-operative impression of the tooth
2. Complete the crown preparation
3. Make temporary crown - fill the pre-op impression with Protemp and place onto prepared tooth
4. Remove temporary crown from tooth before resin has fully set
5. Leave to harden outside mouth
6. Take secondary impression of crown preparation
7. Trim margins of temporary crown to the prepared finishing line
8. Adjust occlusion
9. Cement with suitable temporary cement
10. Remove excess cement at margins and re-check occlusion before dismissing patient
55
What are the 5 defects that can occur with temp crowns?
1. Open margins
2. Bulky or overextended margins
3. Open proximal contacts
4. “High” or supra-occlusion
5. Infra-occlusion
56
What are potential complications from a temporary crown with open margins?
1. Microleakage
2. Dentinal Hypersensitivity
3. Pulpitis
4. Caries (long term)
57
What are potential complications from a temporary crown with bulky/overextended margins?
1. Plaque Retention
2. Marginal Gingivitis
3. Gingival Recession
58
What are potential complications from a temporary crown with open proximal contacts
1. Gingivitis from Food Impaction
2. Drift of adjacent teeth
3. Contacts become too tight for permanent crown
59
What are potential complications from a temporary crown with high/supra-occlusion?
1. Pain on biting
| 2. Fracture of Temp Crown
60
What are potential complications from a temporary crown with infra-occlusion?
1. Over-eruption of opposing tooth
| 2. Final Crown will requires extensive occlusal adjustment
61
What are some desirable properties of temporary cements?
1. Thin film thickness - 30-50 microns
2. Non-irritating to soft tissue
3. Fast setting with adequate strength
4. Easy to remove set cement
5. Compatible with composite resin luting cement
62
What are 3 different types of Temporary Cements
1. Modified ZnO eugenol cement (Tempbond)
2. Eugenol free temporary cements (Tempbond NE, RelyX TempNE)
3. Polycarboxylate Cement (Poly-F cement)
63
What are the issues with the use of Modified ZnO eugenol cement (Tempbond)?
1. Forms a poor bonding substrate against CR
| 2. Can cause hypersensitivity reaction / stomatitis on soft tissue
64
What are the benefits of a Eugenol free temporary cements such as Tempbond NE
1. Better bonding to CR cores/restorations
| 2. Lower hypersensitivity to soft tissue around margins
65
When would a Polycarboxylate cement (Poly-F cement) be used?
When a stronger "temporary" cement needs to be in place - for example if the temp crown needs to be held for over 4 weeks because the patient is going away.
Polycarboxylate is actually an old permanent cement but has since been superceded so is ideal for this purpose
66
What are the steps for preparing a polycarbonate crown?
1. Select the correct crown size: based on Mesio-distal width (Wide > Medium > Narrow)
2. Shorten length to match adjacent teeth
3. Leave tab for handle
4. Roughen inside to improve bond
5. Fill crown form with Protemp and seat on tooth
6. Remove from tooth when “rubbery”
7. Use soflex discs to trim until margin coincides with imprint of finish line on tooth
67
What are the steps for preparing an aluminium crown?
1. Select crown size from mesio-distal width
2. Shorten crown using crown and collar shears. occlusally level with adjacent teeth and margins just cover finish line on prepared tooth
3. Ask the patient to bite down to contour occlusal surface of crown
4. Make two holes using a Jet 330 but on buccal and lingual surfaces for resin retention
5. Fill the crown with Protemp and seat on lubricated tooth
6. Remove the crown before Protemp sets hard
7. Trim margins to imprint of finishing line in Protemp using black coarse soflex disc
8. Check and adjust occlusion
9. Smooth with brown soflex discs
10. Cement with temporary cement
68
What is a connector?
A Connector: The join between the Pontic and the retainer
69
How do direct and indirect restorations vary?
Material: Rigid (Indirect) vs Direct (Malleable)
Design: Must fit by insertion via long axis of tooth (Indirect) vs Retentive Design (Direct)
Clinical: Direct can be done in one appointment
Materials: Resins/Amalgam/GIC vs Ceramics/Metals
70
What are 6 considerations when planning to do an indirect restoration?
1. Occlusion
2. Endodontic Status/Vitality
3. Other teeth requiring treatment (Strategic Value, Active Disease)
4. Future Outlook for Tooth
5. Future Outlook for Whole Dentition
6. Restorability of the Tooth
71
If a patient has very darkly stained teeth and wants veneers, what aesthetic considerations would you have?
Veneers are semi-translucent, so teeth bleaching might be indicated if the patient is concerned about the current shade being too dark/stained
72
T/F: Veneers are the most conservative option for indirect restorations
Yes, as they require the least amount of prep removing healthy tooth structure
73
What materials are typically used for posts?
Titanium Posts
74
When would an elective post be considered?
If there was insufficient coronal tooth structure for a crown, an elective RCT could be performed to insert a titanium post, with a composite core created over it to support the crown
75
What are the risks of a core?
Vertical Root Fracture
76
T/F: Increasing crown height aids in increasing retention
True, because there is more surface area
77
Given a molar and pre-molar tooth of the same height, which has more retention and why?
Molar has more surface area = Greater retention
Pre-Molar has less width = less likely to for tipping displacement
78
Clinical, how would you ensure that a crown prep has an adequate path of insertion
By viewing the tooth directly at the long axis of the tooth, if all aspects of the crown prep can be seen, then the path of insertion will be successful.
If any aspect can not be seen, an undercut has been created and the crown will not seat adequately
79
What obstacles can occur when seating a crown, when consider the path of draw in the mesial/distal dimension
That an interproximal contact from adjacent teeth will "lock out" the crown and prevent adequate seating
80
What broader context consideration will a clinician need to consider with path of insertion
Whether the tooth is tilted or crowded, that the long axis of the tooth might need to be altered to allow for a path of draw that can fit despite interference from other teeth
81
What structural durability aspects does a clinician need to consider for a crown?
1. Adequate thickness of material in all directions
2. Following anatomical form
3. Adequate height/length ratio
4. Smaller diameter to resist tipping
82
What is the minimum occlusal reduction needed?
1.5-2mm
83
What is the minimum labial reduction needed at the gingival 1/3rd for an Mx anterior PFM?
1mm
84
What is the minimum labial reduction needed at the coronal 2/3rd for an Mx anterior PFM?
1.5mm
85
What is the minimum reduction needed at the lingual for an Mx anterior PFM?
0.5mm - as the lingual is metal only
86
What is the minimum reduction needed at the proximal for an Mx anterior PFM?
A transition between the 1mm on the labial, to the 0.5mm on the lingual
87
What is the Cavosurface finish line
The interface between the cavity prep and the finished restoration. The margin should transition seamlessly, without excess or deficiencies
88
On what material can a feather edge or chisel finish be considered?
Full/Partial Gold Crowns only
89
What is a chamfer?
A rounded crown prep margin created by a rounded bur tip
90
When can Chamfer margin be used?
Full Gold Crowns
Porcelain Crowns
Metal Crowns
PBM Crowns
91
When can a shoulder with bevel margin be used?
- Proximal box of gold inlay/onlay
| - PFM where aesthetics not important
92
What is biologic width?
Length between the base of the sulcus and the height of the alveolar crest. It covers the junctional epithelium and CT.
93
Why is having the crown margin above the biological width important
1) Aesthethics - the finishing line is not visible
2) Biocompatibility - if margin is into biological width (aka Junctional Epithelium), irritation and inflammation with bonding cements and plaque traps may occur
94
When would you consider subgingival margins for a crown prep?
When aesthetics is important - patient has a high smile line, tooth is in the aesthetic 5-5 zone
95
What are the steps involved with creating a crown for a patient over 2 appointments
Appointment 1
- Consultation appointment
- Impression to facilitate construction of temporary crown (e.g. pvs putty)
- Tooth preparation
- Soft tissue management
- Impression of preparation + Bite registration/facebow => Send to Lab
- Construct/fit temporary crown
- Check occlusion
Appointment 2
- Remove temporary crown
- “Try-in” Casting: check for fit
- Permanent cementation
96
What are 3 objectives for gingival retractions when doing a crown prep?
1. Retract soft tissues to allow impression material to flow to the margins of the preparation
2. Control Bleeding
3. Moisture Control
97
What 3 forms of gingival retraction are available?
Chemical (Astringents)
Mechanical (Retraction Cords)
Electrosurgery
98
What is the technique for placing a retraction code prior to taking a crown prep impression?
1. Place smaller retraction cord
2. Place larger retraction cord, leave for 4 minutes
3. Remove second cord prior to taking impression
99
What should an operator do if the primary retraction cord comes off with the impression
Leave it. Let the dental lab technician remove it.
100
What materials are possible to use for secondary impressions?
1. Polysulphide
2. Condensation reaction silicone
3. Polyvinyl siloxane e.g. imprint III, honigum (used in ADH)
4. Polyether e.g. Impregum (used in ADH)
Reversible hydrocolloids such as Alginates should not be used due to imbibition/syneresis
101
What are the limitations of using a heavily hydrophobic impression material?
The mouth needs to be very dry before impression is taken
102
What are the limitations of using a heavily hydrophilic impression material?
Excessive moisture leads to imbibition (swelling of the material from absorption of excess moisture)
103
What are the steps for taking a secondary impression
1. Place primary and secondary retraction cords
2. Remove secondary retraction cord after 4 minutes
3. Syringe Light Body Impression Material onto tooth preparation, ensuring flow into sulcus. Wait 4-5 minutes
4. Place Heavy Body material into special impression tray. Allow to set. Remove from mouth
104
What is the purpose of a temporary crown?
1. Pulpal Protection: due to exposed dentine
2. Prevent sensitivity : cover up exposed dentine
3. Protect the preparation (e.g. margins)
4. Stops teeth from drifting
5. Stops opposing teeth from over-erupting
6. Aesthetics
7. Function
105
What are 3 types of temporary crowns?
1. Pre-formed
2. Custom Direct (taken from alginate impressions)
3. Custom Indirect (PVS Putty Keys)
106
What are 3 different types of temp crown materials that can be used?
1. Composite resin (biis-acrylic composite)
e. g. Protemp 4 (used in ADH)
2. Methyl methacrylate : e.g. Duralay, Jet
3. Vinyl ethyl methacrylate: e.g. trim
107
What are the stages for making a direct temporary crown?
1. Mix
2. Place in the impression (correct tooth)
3. When rubbery (initial set) → remove temp crown
4. Trim margins and excess → for easy seating
5. Trim margins and excess (try-in) and check occlusion + polish the temp crown
6. Cement
108
What are the stages for making an indirect temporary crown?
1. Alginate impression (full arch)
2. Pour up model – Yellowstone
3. Wax-up tooth (36) to ideal anatomy
4. Construct “lab putty” key
5. Fit Putty Key
6. Adjust Temporary Crown
7. Cement in Place
109
What are the stages for fitting a preformed crown?
1. Choose the correct width of crown (S/M/L, LHS vs RHS)
2. Fill the anterior with temporary material and cement on
May need to rough the inside if not already lined with protemp
3. Remove and adjust margins
4. Check occlusion
5. Cement in place
110
What are the stages for doing a permanent crown cementation?
1. Remove temporary crown
2. Remove remnants of temporary cement from preparation using pumice and brush
3. “Try-in” permanent crown and check: Marginal fit, Occlusion, Proximal contacts
Shade (aesthetics)
4. Ensure to get 100% pt consent on fit and appearance
5. Cement crown (Permanent cement)
111
What are 9 desirable properties of a cement?
1. Adhesion to enamel and dentine
2. Adhesion to crown
3. Biocompatibility (pulp/soft tissues)
4. Adequate compressive strength (15,000 psi)
5. Thin film thickness
6. Rapid setting time
7. Insoluble in oral fluids
8. Colour (transparent)
9. Anticariogenic
112
What are the lab steps for a full gold crown?
1. Master Cast Created from Impression
2. Removable die of tooth cut out of master cast
3. Wax Pattern of Crown designed on die
4. Sprue added to die
5. Negative of Wax Pattern created using investment material
6. Hot water dissolves Wax Pattern
7. Casting occurs with molten gold alloy poured through the sprue void
8. Investment material broken after set
9. Restoration checked for fit
10. Sprue Removed
11. Final Polishing
113
What are the 6 evaluation criteria for a secondary impression?
1. Clear recording of crown prep
2. Absence of defects from contaminants
3. Absence of air bubbles in critical areas
4. Absence of voids
5. Absence of drag lines
6. No contact between teeth and tray except at occlusal stops
114
What features should be evident on a satisfactory secondary impression?
1. Vertical drop for core with no undercuts
2. Circular band representing the finish line margin - appearing as a positive horizontal line
3. Small circular fin - the interface between the gingival sulcus and the finishing line
4. Any retentive features - post holes, grooves, pinholes
115
What non crown prep features need to be taken in a secondary impression?
1. Occlusal Stops - for articulation of upper and lower models
2. Edentulous ridge for bridge work
116
What are chemical contaminants for polyethers and how does this affect the secondary impression?
pH < 4 in hemostatics
Affects setting of polyether
117
What are chemical contaminants for silicones and how does this affect the secondary impression?
```
Sulphur Groups
Latex Gloves
Astringedent Haemostatic Agent
Freshly placed Composite Resin
Protemp
Eugenol
```
Contaminants “poison” chloroplatinic catalyst thus preventing full setting. Silicone becomes sticky and unset
118
What are physical contaminants and how does this affect the secondary impression?
Contaminants like tooth debris, plaque, protemp cause distortion of the impression.
- Surfaces should be smooth and cleaned with pumice prior to impression
- CR should be wiped with alcohol
- Dry working field and moisture control maintained
119
What are drag lines in a secondary impression potentially a sign of?
Heavy and Light body failure to bond
120
What are 2 indications for subgingival margins?
1. Aesthetics - to hide visible faial crown margins in a high smile line
2. Existing CR margins - removal of existing CR requires sub gingival prep to ensure bonding to sound tooth structure
121
Which gingival retraction cord is impregnated with haemostatic aluminium potassium sulphate?
Gingibraid (not used in ADH)
Ultrapak is plain and requires dipping in a separate hemostatic agent
122
Which is a knitted polycotton gingival retraction cord: Ultrapak or Gingibraid?
Ultrapak
123
What are 3 haemostatic agents that can be used?
1. Hemodent liquid (colourless aluminium chloride)
2. Astringedent liquid (brown ferric sulphate)
3. Atringedent liquid (colourless aluminium chloride)
124
Which haemostatic agent can interfere with PVS setting with secondary impressions
Brown astringedent liquid due to it's sulphate content
125
What does the Primary Retraction Cord achieve?
1. Vertical displacement of gingiva
2. Improves vision and access to subgingival crown margins
3. Protects epithelium and sulcus from burs
4. Moisture Control
126
What does the Secondary Retraction Cord achieve?
1. Vertical and lateral displacement of gingiva away from crown margins
2. Moisture control prior to secondary impression
3. Sulcus widened sufficiently so secondary impression is thick enough to resist tear on removal
127
If the sulcus is more than 2mm, what retraction cord should be used?
Primary: Size 1
Secondary: Same as primary or larger
128
If the sulcus is less than 2mm, what retraction cord should be used?
Primary: Size 0 / 00
Secondary: Usually one size larger than primary
129
What clinical materials are needed for gingival retraction cords?
1. Cord lengths - order 3cm for anteriors, 4cm for posteriors
2. Sharp scissors
3. Large plastic (Size 6) or Cord Packer (like a flat plastic with serrated edge to push cord)
4. Hemodent or astringent to dampen primary cord only
5. Moisture control
Cotton rolls, dry guard shields, gauze
130
T/F: The primary retraction cord can still be seen in the sulcus
False
131
Which aspect of the tooth should you start/end placement of a gingival retraction cord?
Mid Labially
132
How long is a secondary retraction cord left and when is it removed
Left for 5 minutes whilst setting up for secondary impression
Remove once the DA starts dispensing heavy body material
133
What materials can be used with custom trays?
PVS or Polyether
134
What are benefits of custom trays for secondary impressions?
Already has occlusal stops
| Can overcome issues with shape/size of dental arch
135
What are disadvantages of custom trays for secondary impressions?
No mechanical retention around rim so adhesive is needed
| Extra fabrication time/cost
136
How long is the drying time for tray adhesives?
10 minutes
137
What is the ideal clearance between teeth and tray when taking a secondary impression?
3-4mm
138
What are the 10 steps for administering the dual viscosity technique for secondary impression
1. Syringe light body around crown prep using tipe/syringe
2. When tray half filled with heavy body, the Dental Assistant informs the operator
3. Gently remove secondary cord with tweezers. Discard first 5mm of light body from mixing tip onto bracket tray and quickly syringe light body around the margins then over the tooth and adjacent teeth
4. Keep tip below surface to avoid air bubble entrapment
5. Seat the tray: avoid pressing down forcefully if using stock tray with no occlusal stops
6. Allow to set in mouth for 5 minutes
7. Remove tray – “snap removal” to minimise permanent distortion
8. Immediately wash with water and detergent to remove blood and saliva
9. Dry impression and check for defects
10. If impression satisfactory, place in infection control bag
139
What is a PBM crown indicated?
1. When restoration of natural tooth appearance is required
2. Maximum protection by full coverage for worn, broken down teeth
3. When more conservative restorations are inappropriate and lack sufficient structural durability
140
What are some clinical applications for PBM crowns?
Full coverage for fractures/cracked teeth
Protection for fractured/cracked teeth
Protection of posterior root filled teeth
High stress situations, deep overbite, bruxism
Anterior and posterior teeth as single crowns
Retainers and pontics for fixed bridgework
Splinting periodontally weakened teeth
Reshaping abutment teeth for removable partial denture
141
What are the roles for both metal and ceramic in a PBM crown?
Metal: adequate thickness for strength
Ceramic: adequate thickness for aesthetics
142
What is the minimum thickness of metal coping for noble alloys in a PBM crown?
0.3-0.5mm
143
What is the minimum thickness of metal coping for base alloys in a PBM crown?
0.2mm
144
T/F: High Noble Metal Allows have increased hardness (65% precious metal, gold, silver, platinum, palladium)
True - harder than semi-precious or base metal
145
T/F: Enamel Porcelain provides translucence not main colour
True
```
Dentine Porcelain (body) provides main colour
Enamel Porcelain (incisal) provides translucence
```
146
What is the minimum thickness for body porcelain?
Minimum 0.7mm
| Optimum 1.0mm
147
Why do palatal surfaces have unveneered metal?
1. Aesthetics not important
| 2. Prep for just metal is more conservative
148
When does Porcelain change to have compression forces that aid in Metal Ceramic Bonding Mechanisms
During furnacing, different thermal coefficients result in slight compression of ceramic to grasp the inner metal layer to increasing bonding strength
149
What are the 4 bonding mechanisms for Metal Ceramic Bonding
1. Micromechanical: air abrasion to roughen metal surface
2. Compressive: ceramic shrinks into the metal during furnacing due to different thermal coefficients
3. Molecular: attractional van der waal provide weak bonds
4. Chemical: moderate metal oxides provide dissolve and bond to the glass phase of porcelain
150
What is the risk of too much oxide formation in base metals?
Weak Bond due to thickness of oxide layer. This is a risk with base metals which are more unpredictable in metal oxide formation
151
What is the risk of too little oxide formation in noble metals
Inadequate bonding between metal and ceramic
This is why noble metals must have a percentage of base metals to create an alloy that can result in oxide formation
152
How do you create the metal oxide layer?
Metal coping is fired before adding ceramic layer
153
What is the gold and palladium composition that is optimal for bonding to porcelain
Gold (44-55%) + Palladium (35-45%)
154
What is cohesive failure in a metal / ceramic crown?
Fracture in the porcelain/oxide/metal layer itself
155
What is adhesive failure in a metal / ceramic crown?
Fracture at the interface between layers
156
What base metal must be there be consideration for hypersensitivity reactions?
Nickel
157
What are the clinical and lab steps to construct a PBM crown?
1. Prepare tooth, take impression and construct die
2. Wax up and cast metal coping and oxidise surface at high temperature
3. Apply opaque porcelain to hide grey metal colour : Powder + Water => Brush onto metal. Then Sintering in the furnace
4. Sequentially build up dentine and enamel and porcelains and further sintering
158
What occurs to porcelain when furnacing?
1. Porcelain particles melt and coalesce fusing into a composite structure of crystals within a glass matrix
2. Vacuum removes air bubbles that reduce translucence
3. Material shrinks by 2%
159
Why are PBM crowns aesthetically inferior to all-ceramic crowns?
Speculance: high light reflection due to white opaque layer
160
What are disadvantages of PBM crowns?
1. Non-Minimum Intervention
2. Expensive
3. Poorer aesthetics than all-ceramic crowns
4. Requires thicker reduction in prep
5. Brittle and can Fracture
6. Increase wear of opposing teeth
7. Inability to repair PBM
161
What are alternatives to PBM crowns?
1. Porcelain bonded to zirconium crowns (PBZ)
(Digitally Designed, Excellent aesthetics, Less conservative
2. Full contour zirconia crowns
3. E. Max crowns (aluminium oxide infiltrated with ceramic, not as nice aesthetically)
4. Full gold crowns (FGC’s)
162
What are some conservative principles for Crown Prep designs?
1. Minimum Reduction where aesthetics not required
2. Supra-gingival / Equ-gingival margins
3. Retention/Resistance Form
4. Structural Durability through adequate thickness
5. Marginal Integrity
163
What are design considerations for Retention and Resistance form for Crown Prep
1. Satisfactory Taper (6-10 degrees)
2. Path of Insertion via Long Axis of tooth is unobstructed and without undercuts
3. Use of Supplementary Retention
4. Adequate height of prep
164
What is the minimum tooth reduction needed for PBM crowns?
1. Incisal: 2mm
2. Labial
Gingival 1/3 (1-1.3mm)
Incisal 2/3 (1.5mm)
3. Proximal
Gingival 1/3 (0.5mm)
Incisal Tip (1.5mm)
```
4. Lingual:
Gingival cingulum wall = 0.5mm
Concave surface
If metal + ceramic = 1.0mm
If metal only = 0.5-0.8mm
```
165
What should be checked at the end of a crown prep?
1. No undercuts on axial walls
2. Check for continuous, flowing cavosurface margin
3. Check for adequate occlusal clearance with opposing teeth
4. Check labial margin hidden in gingival sulcus
166
Which labial/buccal margin designs are best for aesthetics?
Ceramic radial shoulder
| Ceramic heavy chamfer
167
Which labial/buccal margin designs are best for conservative design?
Ceramic heavy chamfer
| Heavy chamfer with gold collar (1.0mm)
168
Which labial/buccal margin designs are best for structural durability?
Heavy chamfer with gold collar (1.0mm)
| 45 ° bevelled shoulder with gold collar (bevel = 0.5mm)
169
Which labial/buccal margin designs are best for marginal adaptation?
Heavy chamfer with gold collar (1.0mm)
| 45 ° bevelled shoulder with gold collar (bevel = 0.5mm)
170
What are 4 physical properties of ceramics?
Strong (Compression Strength)
Hard (Wear Resistance)
Brittle (Poor Tensile Strength)
Inert Thermal/Electrical non-conductors
171
What are the basic components of dental porcelain?
1. Feldspar: ceramic binder (75-85% weight)
2. Silica Quartz: strength and optical qualities (15% weight)
3. Kaolin: binder and opacity
4. Metal Oxides: Colour Pigments
5. Leucite: provides toughness (equalises thermal expansion coefficients)
6. Spinel: limits crack propagation
172
What are advantages of dental ceramics?
```
Dimensional stability
Aesthetics
Good tissue tolerance
High wear resistance
High compressive strength
```
173
What are disadvantages of dental ceramics?
```
Abrasive when glaze lost
Complex fabrication
Adjustment and polish chairside difficult
Low fracture resistance
Low tensile strength
If broken in mouth impossible to repair
```
174
What are the 4 ways ceramics can be classified?
1. Type (Composition)
2. Processing Method
3. Substructure/Foundation Metal
4. Fusing Temperature
175
What are the 2 types of fusing temperature for dental ceramics?
```
High fusing (850-1100 ° C)
Low fusing (<850 ° C)
```
176
What are the 5 types of Substructure/foundation materials for dental ceramics?
```
Cast metal (high noble, noble, base metal)
Swaged metal (platinum foil)
Glass ceramic
CAD/CAM
Glass infused ceramic core
```
177
What are the 3 types of Processing Methods for dental ceramics?
Sintering
Casting
Machining
178
What are the 8 types of composition types for dental ceramics?
```
Feldspathic (SiO2)
Leucite reinforced
Lithium di-silicate
Alumina-oxide based
Glass infiltrated alumina
Glass infiltrated spinel
Fluoro-apatite ceramic
Zirconia ceramic
```
179
What is sintering?
When ceramic particles fuse under intense furnace temperature (950-980 degrees)
180
How can interfacial stress be minimised when selecting compatible metal and ceramicss?
The thermal expansion coefficients need to be broadly compatible
181
What are some properties of High Gold Ceramo-Metal Alloys?
```
Good biocompatibility
Good adhesion between alloy and ceramic
Good casting accuracy for margins
Less creep at high temperature
Good physical properties
Firing temperature close to ceramics
More costly than less noble and base alloys
```
182
What are some properties of Base-Metal Alloys?
```
Cheaper than noble alloys
Better strength than noble alloys
More chemically reactive
Hypersensitivity potential
Higher shrinkage on cooling
Thicker oxide layer so adhesion of ceramic may be weaker if not processed correctly
```
183
What is Hue?
Basic Colour Group
184
What is Chroma?
The intensity of colour
185
What is Colour Value?
Lightness vs Darkness
186
What is Opalescence and why is this important?
Opalescence is the way light is reflected and refracted through the crystalline structures of the various tooth layers which have different moisture contents.
This determines the translucency/transparancy and aids in the "vital" appearance of natural / crowned teeth
187
What is Metamerism?
Particular colour groups may appear different to the observer if viewed under altered lighting conditions
e.g. Natural sunlight, incandescent light, fluorescent light
188
What is Fluorescence ?
The light emitted from a substance that has absorbed/reflected light
Natural teeth emit bluish-white light when exposed to UV illumination
Fluorescence gives tooth a “vital” appearance
189
What is the halo effect (Rayleigh Scatter)?
The light scattered by passing through teeth/ceramics causing a different wavelength (colour) being transmitted to neighbouring teeth. This can affect how natural a restorative material can appear in context of natural dentition.
190
What are methods to strengthen ceramics?
```
Development of residual compressive stresses
Ion exchange
Thermal tempering
Disruption to crack propagation
Dispersion of crystalline phase
Transformation toughening
Design of dental restoration
Minimising tensile stress
Reducing stress raisers
```
191
What is the rationale behind posts?
Endodontically treated teeth that have insufficient sound coronal tooth structure remaining to retain the final restoration.
Post provide sufficient retention and stability for placement of a core
192
When are direct posts contraindicated?
1. Inadequate Tooth Structure
2. Non-Restorable Tooth
3. Short, Thin or Carious Roots
4. Bends/Blockages in root canal
5. Root Pathology
6. Poor Periodontal Support
193
When are direct posts indicated?
1. Tooth is restorable
2. Is remaining tooth structure sound
3. Good periodontal support
4. Good apical seal
5. No apical/radicular pathology
6. Sufficient root length
7. No anatomical barriers/retained instruments in canal
8. Good access + isolation possible
9. Adequate preoperative radiographs
194
What are the different post shapes?
Tapered
Parallel
Parallel > Tapered
Tiered
195
What are the different post surfaces?
Smooth
| Serrated
196
What are the 2 types of posts?
Direct Posts: prefabricated and placed at one chair side visit
Indirect Posts: fabricated in the dental laboratory prior to placement
197
What materials can be used for posts?
```
Stainless Steel
Titanium Alloy
Gold Alloy
No-Ox (Noble Alloy)
Carbon, Quartz and Glass Fibre
Mineral-coated carbon fibre
Zirconium oxide
Fibre-reinforced resin composite (non-impregnated)
Fibre-reinforced resin composite (impregnated)
```
198
What are the 2 types of post placement techniques?
Passive: post placed without it actively cutting into dentine surface inside post canal
Active: placed and cemented with post actively engaging dentine
199
What are complications that can occur from post placement?
```
Aspiration-ingestion of drill
Eye injury/needlestick injury
Spillage or leakage of irrigant
Drill breaking
Over-preparation of length
Over-preparation canal width
Lateral or furcal perforation
Depth of cut not clear on radiograph
Drill not removing GP
```
200
What drills are used to prepare a post hole?
Gates-glidden drills: cut sideways
Peeso drills: post preparation
Parapost drills: end cutting drill
201
What are the steps for tooth preparation for a post?
1. Preoperative radiograph
2. Tooth isolation
3. Access hole preparation
4. Gates-Glidden Drills to access 4-5mm to apex
5. Check radiograph
6. Parapost Drill to cut and prepare end
7. Cleaning of root canal/irrigation (Miltons + Paper Points)
8. Post selection and Try-in
9. Cementation with GIC/Resin Cement
202
What are the functions of a core?
Foundations for coronal restoration
Retention and stabilisation of coronal restoration
To perform as in interim restoration
203
What are the 2 types of cores?
Direct: placed with/out posts. Can be Amalgam, CR, GIC
Indirect: Fabricated in lab, usually Gold Alloys
204
What are the 4 classes of dental impression materials?
1. Non-Elastomeric materials
2. Aqueous elastomers
3. Non-Aqueous elastomers
4. Optical Impressions + Virtual Models
205
Why are non-elastomeric materials unsuitable for fixed pros impressions?
Material doesn’t have elastic qualities to get around undercuts
206
Why are Aqueous elastomers not used for secondary impressions?
Dimensionally unstable due to imbibition (swelling), syneresis (liquid formation out of gel) and evaporation
207
What is meant by wetting properties?
Contact angle when moisture is contact with the surface of a material.
A material with good wetting properties will allow moisture to spread and adapt to the surface, therefore reducing clumping and liquid bubble distortions in the impression.
208
Why should an impression material have good wetting properties
The oral cavity is inherently moist and so the material needs to minimise distortion and defects in this environment
209
How can wetting be improved?
By the introduction of a surfactant that reduces surface tension
Examples
Sorbitan mono/trilaureate
Polyoxyethylene sorbitan mono/trioleate
210
What are desirable properties for a impression material?
```
Easy to mix and dispense
Dimensionally stable
Good wetting
Accuracy in detail
Accuracy after cold sterilisation
Good odour and taste neutral
Good elastic recovery around undercuts
Good tear strength
Compatibility with die materials
Long shelf life
Reasonable Setting Time / Adequate working time
No irritation to tissues
Retention of Accuracy during transportation to lab
```
211
Why are Polysulfides not generally used anymore?
Poor dimensional stability due to water loss in condensation reaction
Offensive odour and smell
Long setting time
Low elastic recovery compared to more modern materials
Irritation/Allergy Reaction
212
What are examples of Polysulfides?
Permlastic (Kerr)
| Omniflex (GC)
213
What is the broad reaction for Polysulfides?
By mixing Base and Catalyst pastes
Base (Polysulfide Polymer reactant) + Catalyst (Lead Dioxide + Sulfur) => Condensation Reaction with lead dioxide and sulphur groups => di-sulphide links formed between groups + water released as bi-product
214
How can Polysulfides setting times be accelerated
Adding more water
| High room temperature
215
What are the reasons for dimensional instability during polysulfide reaction?
Temperature transition upon removal from mouth
Water loss which is a setting reaction by-product
Shrinkage from continued polymerisation
216
What are advantages of Condensation Silicones?
More stable than polysulfides
Good tear strength
Good working and setting time (approx. 9 minutes)
217
What are disadvantages of Condensation Silicones?
Odour from alcohol byproduct
Dimensional stability: Poor once the impression is taken out
Bitter taste
218
What is the broad reaction for Condensation Silicone?
Mixing Dimethyl Polysiloxane (Base) + Stannous Octoate (Catalyst) => Cross-linking of a hydroxyl terminated dimethyl polysiloxane by an alkyl silicate.
Alcohol is released as a by-product
219
What issue does Polyvinyl SIloxanes (Addition-curing silicones) overcome as an impression material?
Different reaction to condensation reactions to overcome shrinkage issues from Polysulfides/Condensation Silicones
220
What is the broad reaction for Polyvinyl SIloxanes?
Cross linking reaction of a vinyl terminated di-methyl polysiloxane
```
Base Paste (Dimethyl Sioxane)
Catalyst Paste (Chloroplatinic Acid)
Reactant (Siloxane prepolymer)
```
The reactive undergoes a cross linking reaction:
1. Substitutes 2 separate hydrogen groups on the sioxane chain
2. Producing 2x crossed linked polymers
3. Catalysed by chloroplantinic acid
4. Releasing Hydrogen gas as a by product
5. Additives can scavenge Hydrogen gas
221
What are examples of PVS impression material?
```
Honigum: initially no change in viscosity, with pressure applied viscosity rapidly decreases
Imprint 3 (3M)
```
222
What are advantages of PVS materials?
```
Very stable dimensionally
Impression re-pours possible
Odour and taste neutral
Good elastic recovery
Good tear strength
Good wetting of prep surface
Good working and setting times
Excellent delivery systems
```
223
What are disadvantages of PVS materials?
Setting retardation via sulphur in latex gloves
Setting retardation from sulphur in Astringedent solution
Tearing of wash material away from tray material
Material is hydrophobic - so won’t deal well with moisture
Locking into undercuts and open embrasures
Porosities
May sometimes get an orange skin on the surface of the impression
Some dimensional change (H2 gas release)
Very expensive
224
What materials can interfere with PVS setting reactions?
1. Setting reaction can be inhibited via zinc diethyl dithiocarbonate, which interferes with the catalyst agent. This can be found in some latex gloves, haemostatic/coagulation agents
2. Oxygen inhibition layer on resin composites
225
What are delivery systems for PVS?
Automix Guns
| Pentamix Machines
226
How much stock trays be prepared before administering heavy body PVS?
Adhesive must be applied to the occlusal surface of the tray with a dispensing brush
227
What sort of trays can be used to take secondary impressions?
1. Stock Trays
2. Position Trays (Adhesive Free)
3. Custom Trays
4. Triple Trays
228
Why is polyether more dimensionally stable than alginates or PVS?
Because there are no by-products of the cross-linking reaction
229
What is the composition of a polyether?
1. Base
Polyether polymer
Colloidal silica filler
Glycol ether or phthalate plasticizer
2. Catalyst
Alkyl aromatic sulfonate
Plasticisers and fillers as above
230
What are the broad steps of a polyether reaction
Base: Polyether polymer base
- Main branch that consists of a copolymer of ethylene oxide + tetahydrofuran
- Side branches: aziridine rings
Aromatic ester Catalyst (Alkyl aromatic sulfonate) initiates polymerisation cross linking of polymers of imine end groups located on the aziridine rings
No bi-products of reaction = therefore dimensionally stable
231
How is polyether mixed?
Polyether is difficult to mix by hand (highly viscous), so is mixed either by applicator gun or pentamix
232
What are advantages of Polyether?
Excellent accuracy and wetting
More hydrophilic than PVS: more moisture tolerant
Good dimensional stability
Good Elastic Properties
Very good shelf life (~5 years, less in warm conditions)
233
What are disadvantages of Polyether?
Handling issues: very stiff when set/problem in undercuts, embrasures (contraindication)
Very sticky: very hard to get off soft tissue
Cold disinfection
Tear strength less than PVS
Odour unpleasant
Difficult to manually mix
Shorter working time than PVS silicones
Sensitivity to aromatic sulfonate (catalyst) may occur
Water condensation on chilled mixes
Poor Storage after mixed: Polyether degradation common
Type IV hypersensitivity reactions
234
Rank elastomers by dimensional stability
1. Addition Curing (PVS): 0.15% Shrinkage (Good)
2. Polyethers: 0.2%
3. Polysulphides: 0.4%
4. Condensation Silicones: 0.6% (Poor)
235
What are common reasons for failure of Nonaqueous Elastomeric Impression Materials?
1. Rough/Uneven Surface on Impression
2. Air Bubbles
3. Irregularly Shaped Voids from debris/excess moisture
4. Rough/Chalky Stone Cast
5. Distortion
236
What could be causes of distortions in Nonaqueous Elastomeric Impression Materials?
Continuing Polymerisation shrinkage of tray caused by inadequate aging
Lack of Rubber Adhesion to tray caused by too few coats of adhesive
Filling Tray with material too soon after applying adhesive
Using wrong adhesive
Lack of mechanical retention where adhesive in ineffective
Excessive Bulk Material
Insufficient Relief for reline material (if used)
Continued pressure against impression material that has elastic properties
Movement of tray during polymerisation
Premature removal from mouth
Improper Removal from mouth
Delayed pouring of polysulfide/condensation silicone impression
237
What 6 things can you look out for when troubleshooting a PVS secondary impressions?
Delamination - light + heavy body don’t bond due to blood/saliva contamination
Irregularities - when placed in the mouth too quickly and can not flow
Repositioning - not correctly seated then moved
Poor Timing - higher room temperature means seating was too slow
Glove Contamination - use of latex gloves inhibits catalysts/accerlators
Pressure Release Channel Technique - light body not pressed thinly enough - abutments become too smore
238
What does Vinyl Siloxanethers aim to overcome?
Clinical aims: combine excellent genuine hydrophilicity of polyethers with good mechanical and flow properties of poly vinyl siloxanes (PVS)
Example: Indentium (Kettenbach Gmbh)
239
How are ROMP (Ring Opening Metathesis Polymer) reversible in nature?
Olefin Metathesis Reaction: the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon double bonds
