Principles of Tooth Preparation Flashcards
What do we mean by indirect restoration
A restoration is a restoration which is not placed directly into the patients mouth
Are amalgam and composites a direct or indirect restoration?
Direct as they are placed directing into the mouth
Are crowns direct or indirect restorations?
Indirect
Why are crowns considered as indirect restoration
As their are multiple steps to make the restoration OUTSIDE the patients mouth before the restoration is finished and fitted for the patient
Give some examples of indirect restorations
- Crown
- Porcelain veneer
- Onlay
- Gold inlay
Why are indirect restorations important?
- Improve aesthetics
- Comfort
- Improved function
- Increased stability
What are some of the disadvantages of an indirect restorations
- Tooth needs more prep
- Takes more
- Patient needs to come in for more appointment
Why do we need to prepare teeth before placing an indirect restoration?
To create space
If there was no preparation then there would be inadequate room to place the materials needed to create an pathetic result
What do we NOT want to create when preparing a tooth
An undercut
What is an undercut
When the top of the tooth is wider than the bottom
Why do we not want to create an undercut?
As to results in over preparation and weakeaning of the tooth
This puts th teeth at higher risk of fracture and also increases risk of locking impression materials
What do we aim to create when preparing teeth?
A slight taper ensuring that the widest portion of the tooth is at the bottom and the narrowest at the top
This allows the restoration to slide on and off the tooth
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 we 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 relating as much as possible to protect the pulp and periodontium to reduce fracture risk
What can happen if a tooth is underprepared?
- Inadequate space for the restoration
- Need to use thinner restorative material increasing risk of fracture and perforation
- If thicker material is used conforming with the occlusal scheme may be difficult resulting gin a high spot on the restoration
What will happen if there is under preparing of the shoulder/ chamfer near the cervical margin of a tooth?
Material may chip or fracture exposing tooth tissue
what are the problems associated with over preparation
- Working closer to the pulp which can lead to loss of vitality
- Increased risk of tooth fracture
State the 2 Rs of preparation
Resistance
Retention
What is retention?
Preventing the removal of an extra corona restoration alone the path of insertion
What is resistance
Preventing dislodgment 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 retention and resistance
The greater the taper the less retention and resistance
How can internal surfaces be used to offer retention
Opposing surfaces contribute and the 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 of the cavity
What is the acceptable degree of taper on clinic?
6-12 degrees
What does a taper of 6-12 degrees 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 indirect restoration
- Aim for between 6-12 degrees
On top of taper what else do we need to consider with retention and resistance
Surface area
height
What is the relationship between surface area and resistance 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 and resistance
What preparation designs can we add to aid retention and resistance
Grooves
Boxes
Where are grooves placed?
They are placed along the path of insertion and may change the arc of displacement
Do grooves aid retention of resistance?
Resistance
Name the 2 categories of cements we can choose from
Passive and aggressive
What does the structure of the restoration need to be able to withstand?
Needs to be able to withstand:
- occlusal forces
- the oral environment and changes in temperature, pH
- Mastication of caretity of foods
What are the problems associated with using thin porcelain?
It is prone to cracks and fracture
What are the problems associated with using thin metal?
May perforate
List some materials we can use to make an indirect restoration
- Metal ceramic
- Gold
- Non precious metal
- All ceramic
Why does the marginal integrity and portion need to be accurate before you place an indirect restoration?
The more accurate a margin is the less exposed cement there is and this is good to avoid washing the cement away
What can happen if a reduced to excessive dimension for the margin is used?
Can lead to failure in the materials such as cracks or fracture
Name the 3 types of margin designs we can make
- Chamfer
- Shoulder
- Knife edge
When is a shoulder used?
Often used for metal ceramic crowns
What thickness do shoulders need?
At least 1.2mm
When is a chamfer used?
For cold crowns
What thickness do chamfers require?
Only require a reduction of 0.5mm
What is a knife edged margin and when is it used?
It is a very fine edge which fades away and is sally made of metal
When preparing palatal chamfer what isn’t a concern?
Aesthetics aren’t a concern as you cannot see the margin and so you can finish the margin sub gingival
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
Where 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 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 the patient has good oral hygiene
- Make a supra gingival margin
- Make sure there’s sufficient marginal reduction (no overhangs 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 can we increase the height of the crown
With crown lengthening surgery
What biological considerations must be make when preparing an indirect restoration?
- Preserve the periodontium
- Preserve the pulp
- Protect soft tissues
- Consider crown length
How many teeth become non vital after crown prep
1 in 5
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
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
