Revision P.1 Flashcards
1
Q
Crowns
Indications for a dental crown:
A
- Protection of the remaining tooth structure
- Alteration of Aesthetics
- Alteration of crown form to facilitate the construction of removable partial dentures (act as abutments)
- To alter the occlusal plane
2
Q
Crowns
Most conservative to most destructive crowns:
A
- Zirconia (monolithic)
- All metal Crown
- All Ceramic Crown
- Ceramo-metal crown
- Porcelain fused to zirconia
3
Q
Tooth reductions
least to most destructive
A
4
Q
The ‘Functional Cusp Bevel’
A
- Maxillary teeth – Functional cusp is the palatal
- Mandibular Teeth – Function cusp is the buccal
- This gives space for the opposing cusp to move freely in articulation and prevents non-working side interference’s from being introduced.
- Improves the structural durability
- Under preparation can lead to a too bulky crown
- Under preparation can lead to a crown that is too thin
- Correction by over angulation will lead to loss of retention and resistance
5
Q
Convergence Angle
A
- A 6° taper or convergence angle has been recommended (El-Ebrashi et al, 1969)
- The average convergence angle was found to be 20o
- Clinically, when preparing always aim for parallel and the tapering of the bur will create the ideal 6° taper.
- Having completely parallel walls may lead to the excess cement failing to escape -> incomplete seating
6
Q
Crown preparation (steps)
A
- Take shade of crown (if you will prepare for porcelain or zirconia)
- Take two or three putty indices
- Use local anaesthetic if required
- Prepare the tooth appropriately (use indices as guides)
- Construction of temporary crown
- Placement of retraction cord with haemostatic agent
- Take impression
- Place temporary crown
- Check occlusion and adjust if needed
- Complete records and laboratory card
7
Q
Impression taking
Types of trays:
A
- Metal trays – full or quadrant
- Rigid Plastic – full or quadrant
- Flexible Plastic – Full or quadrant (to be avoided)
- Custom tray
- Triple tray
8
Q
Impression taking
Master Impression
A
There are several techniques for taking impressions for construction of fixed prosthesis. The recommended technique to have improved accuracy is known as the one step impression technique .
- The impression should be carried out using only silicone-based impression materials , such as: Polyvinyl Siloxane (PVS), Vinyl Polyvinyl Siloxane (VPS) and polyether materials.
- For a crown or bridge this involves heavy body PVS on the tray and Light body PVS on the tooth.
- In single crowns clinical putty can be used instead of heavy body silicone
9
Q
Inspection of the Quality of the Impression
A
how long do we disinfect it for? 3 mins
10
Q
Crown cementation (steps)
A
- Check your lab work – check fit of crown on die, check shade
- Remove temporary restoration
- Clean the underlying prepared tooth
- Try in the restoration
- Check marginal fit (with probe), contact points and occlusion
- Check patient is happy with fit and appearance
- Remove crown and clean both crown fit surface and fit surface of tooth . If indicated sandblast with Aluminium oxide 50μm
- Cement with appropriate cement. Check and remove any excess cement. Also recheck occlusion
11
Q
Definitive Cements
Zinc Phosphate
A
- Recommended for : Recommended for cast restorations on normal, conservatively prepared teeth.
- Primary Strength : Long clinical experience.
-
Primary Weakness :
1. Lack of chemical adhesion.
2. Low tensile strength
12
Q
Definitive Cements
Polycarboxylate
A
- Recommended for : Mainly for cast restorations on retentive preparations when minimal pulp irritation is important (eg. In patients with large pulp chambers).
- Primary Strength : Relative biocompatibility.
- Primary Weakness : Mixing can be tricky as sensitive to powder-to-liquid ratio.
13
Q
Definitive Cements
Glass Ionomer
A
- Recommended for : Cast metal and monolithic zirconia restorations mainly for posterior teeth.
- Primary Strength : Adheres to enamel and dentine and exhibits good biocompatibility. Releases Fluoride.
- Primary Weakness : During setting is susceptible to moisture contamination – marginal solubility.
14
Q
Definitive Cements
Resin Modified GIC
A
- Recommended for : Similarly to GIC but when we seek a stronger luting cement.
-
Primary Strength :
1. Less susceptible to early moisture exposure than GIC.
2. High strength similar to Resin luting cements - Primary Weakness : Swelling or linear expansion.
15
Q
Definitive Cements
Resin based
A
- Recommended for : Indicated for all-ceramic and laboratory-processed composite restorations.
- Primary Strength : High retention strength values, Aesthetics
-
Primary Weakness :
1. Highly technique sensitive.
2. Potential for post-operative sensitivity.
19
Q
Disinfection
A
