Principles of tooth prep Flashcards
What do we mean by indirect restoration
A restoration which is not placed directly into the patients mouth but crafted outside of the mouth
Give examples of indirect restorations
- Crown
- Porcelain veneer
- Only
- Inlay
What are indirect restorations important
- Improve aesthetics
- Comfort
- Improved function
- Increased stability
What are some fo the disadvantages of an indirect restoration
1 More tooth prep required
2. Take more Time
3. Multiple appointments
Why do we need to prepare teeth for an indirect restoration
To create space to create the restoration
What do we not want to create when preparing a tooth and why
An undercut as it results in over preparation and weakening of the tooth
this cute the teeth at higher risk of fracture an increase risk of locking impression material
What is an undercut
When the top of the tooth is wider than the bottom
What do we aim to create when preparing teeth
A single taper ensuring the widest portion of the tooth is at the bottom and the narrowest at the top
As well as the tooth you are preparing what else do you need to keep in mind and why
The adjacent teeth and the proximal contacts for the tooth you are preparing
This is t ensure you have an easy path of entry
What are we aiming for when considering the proximal contacts of the tooth we are preparing?
Ideally the proximal contacts should be parallel to the path of insertion
List the 7 principles of preparation
- Preservation of tooth tissue
- Retention and resistance
- Structural durability of the restoration
- Material choice
- Marginal integrity and position
- Biological considerations
- Aesthetics
What balance do we need to maintain when preparing a tooth
Need to balance taking enough tooth tissue to allow space for the restoration while also retaining as much as possible to protect the pulp to reduce fracture risk
What can happen if a tooth is under prepared
- Inadequate space for restoration
- Need to use thinner restorative material increasing risk of fracture and perforation
- If thicker material is used conforming to occlusion may be difficult resulting in a high spot on the restoration
What will happen if there is under peroration of the should/ chamfer near the cervical margin of a tooth
Material may chip or fracture scooping tooth tissue
What are the problems associated with over preparation
- Working closer to the pulp increasing risk of loss of vitality
- Increased risk of tooth fracture
State the 2 Rs of preparation
Resistance and retention
What is retention
Prevention the removal of an extra coronal restoration along the path of insertion
What is resistance
Preventing dislodgement by lateral or apical forces under occlusal load
What are the properties of retention and resistance influenced by
- Taper
- Surface area
- Height
- Preparation design
- Cement selection
What is the relationship between taper and resistance and retention
The greater the taper the less retention and resistance
How an internal surfaces be used to offer retention
Opposing surfaces contribute and the more parallel sided they are the greater the retention
What do we need to keep in mind when creating a taper
We need to be able to get the restoration in and out the cavity
What is the acceptable degree of taper on clinic
6-12 degrees
What does a taper of 6-12 mean
It means there is a reduction of between 3 and 6 on the circumference of the tooth
List the characteristics of an optimal taper
- Preserve tooth tissue
- Provide good resistance and retention
- Allow visible finish line
- Allow adequate seating of an indirect restoration
- Aim for taper between 6-12 degrees
Other than taper what else do we need to consider
Surface area
Height
What is the relationship between surface area and resistence and retention
The greater the surface area the greater the retention and resistance
What is the relationship between height retention and resistance
The greater the height the greater the retention dn resistance
What preparation designs can we add to aid retention and resistance
Grooves and boxes
Where are grooves placed and what do they aid
They are placed along the path of insertion aiding resistance
Name the 2 categories of cement we can choose from to cement an indirect restoration
passive and agressive
What does the structure of an indirect restoration need to be able to withstand
- Occlusal forces
- Oral environment and changes in temp and pH
- Mastication of food
What are the problems associated with using thin porcelain
It is prone to cracks and fractures
What are the problems associated with using thin metal
May perforate
List some materials we cause to make an indirect restoration
- Metal ceramic
- Gold
- Non precious metals
- All ceramic
Name the three types of margin designs we can make
- Chamfer
- shoulder
- Kinfe edge
When is a shoulder margin used
For metal ceramic crowns
What thickness shoulder do we need for an MCC
At least 1.2mm
When is a chamfer margin used
For gold crowns
What thickness do we require our chamfer margins to be
0.5mm
What thickness do we require our chamfer margins to be
0.5mm
Where is the margin placed on the labial side of a tooth?
As aesthetics are key often placed level with the gingiva or slightly into the gingival sulcus
What is the problem with placing a margin level with the gingiva and how do we overcome this problem?
Makes maintenance difficult and so impression may require a retraction cord
What is the ideal position to finish a margin
On sound tooth tissue if feasible
What are the problems with taking a margin sub gingival
Can compromise the gingival health
What are the problems with the margin being inline with the gingiva
Can compromise aesthetics
What are the problems with the margin being supra gingival
Can compromise aesthetics
What do we NEED to preserve when preparing a tooth for an indirect restoration?
NEED to persevere the periodontium
What can we do to persevere the periodontium ?
- Make sure patient has good oral hygiene
- Make a supra gingival margin
- Make sure there’s a sufficient marginal reduction with no over hangs or PRF
On top of the periodontium what else do we need to take of when placing an indirect restoration?
Need to protect the soft tissues and look at the biological width
What is the biological width
The distance from the depth of the sulcus to the crest of alveolar bone
What does the biological width include
The junctional epithelium and the connective tissue attachment
What effect can impressions and indirect restoration placement have on the soft tissues
Can lead to persistent gingival inflammation
How many teeth become non vital after crown prep
1 in 5
What biological consideration must be made when preparing indirect restoration
- Preserve the periodontium
- Preserve the pulp
- Protect soft tissues
- Consider crown length
How can we protect the pulp when carrying out preparations
Retain as much mineralised tissue as possible and avoid excessive reduction which approaches the pulp tissue
