Inlays and Onlays Flashcards
How do we treat caries in a tooth?
We remove the caries using a handpick
Then we place a restoration to fill the cavity
What are some of the negative consequence of removing tooth tissue when treating caries
Weakening of the walls and cusps of the tooth which can lead to fractures and cracks
Give examples of factors that can increase the risk of a posterior teeth fracturing
- If the height to base ratio is more than 1 (ie the height is more than the base)
- Root treated teeth
- A group function occlusion
- Clenching or grinding
Are rooted treated teeth more or less likely to fracture in comparison to normally restored teeth
Root treated teeth
Which root filled tooth is more likely to fracture : crowned or uncrowned
Uncrowned is at a 6 times greater risk of fracturing
How can we manage weakened cusps?
- Bonding
2. Cuspal coverage
Is bonding useful for managing weekend cusps?
Yes it is seen to have improved the fracture resistance of teeth by bonding on natural premolars
What are the challenges of bonding and direct composites
- Polymerisation shrinkage
2. Achieving good contact points
What do we need to think about when looking at polymerisation shrinkage
The stress that it applies to the tooth composite interface
How much stress does polymerisation shrinkage apply to the tooth surface interface?
3-8MPa typically
How can we try and reduce the stress on a tooth
Look at the configuration factor of a cavity
What is the configuration factor of a cavity
(Number of bonded) divided by (number of unbonded surfaces)
What is the relationship between configuration fact and stress on the tooth?
As the configuration factor increases so does the stress on the tooth and leads to increased risk of polymerisation shrinkage
State the average percentage of shrinkage a typical composite restoration goes through
1.4-2%
What problems can arise if we create an insufficient contact point
Food packing can occur and it can be harder for the patient to clean the site
What can we do instead of placing a direct restoration to avoid polymerisation shrinkage and poor contact points
We can place an inlay
Is an inlay a direct or indirect restoration
Indirect
Define what an inlay is
An intra coronal restoration contracted in the lab and cemented into the tooth
How are good contact points achieved in an inlay?
The lab determines the fit and contours of the inlay
What problems can arise when using inlays?
- They require a taper which can create a wedging effect wearing the cusps
- Don’t cover the cusps so can’t provide cuspal protection
Why do inlays need to be tapered?
As they are placed into the tooth so need to be able to sit there properly
What is the issue with an inlay needing to have a taper
Risk of it having wedging affect so there might be forces directing downwards which can put stress and strain on the cusps (or even fracturing)
What should the height to base ratio be for an inlay to be successful?
Height to base less than or equal to 1
Talk through the indications for an inlay
- Small to medium cavity eg Small MO or DO cavities in molars and premoalrs
- Conservative MOD in molars
- Low caries rate
- Good support for cusps from remaining tooth tissue
- About 1/3rd buccal lingual width
- Height:base < 1:1
- Canine guidance
Are inlays commonly used in routine dentistry
No
When are inlays most useful?
When you have a large gap between adjacent teeth to achieve a good contact point
Give examples of restoration we can use that offer good cuspal protection
- Full coverage crowns
2. Onlays
List the principles of preparation
- Preservation of tooth tissue
- Retention and resistance form
- Structural durability of restoration
- Marginal integrity and position
- Biological
- Aesthetics
How much tooth tissue is removed when we place a full coverage crown?
67.5-75.6%
How much tooth tissue is removed when we place an onlay
39%
Do full coverage crowns or onlays achieve better retention and resistance
Full coverage crowns
Define what an onlay is
A restoration constructed in the lab and cemented into a tooth that may contain an intracoronal aspect but also cabers one or more cusps
Give some of the indications for onlays
- Teeth with larger restorations but sound buccal and lingual walls needing cuspal protection
- Low caries rate
- Weakened cusps
- Over 1/2 buccal lingual width
- Parafunciton
- Excessive cusp wear
- Group function
Give examples of teeth that may need large restoration but have sound buccal and lingual walls that need cuspal protection
- Endodontically treated teeth
- Wider MODs
- MODs in premolars
What materials can inlays and onlays be made up of?
- Gold
- Ceramic
- Composite
What is the survival rate for a gold inlay or gold onlay
96% for 10 years
What is the survival rate for a lithium dislocate onlay for 8 years??
100% for 8 years
What is the survival rate for a ceramic inlay?
80% for 8 years
Other than the lab where can ceramic inlays be made?
Using a CAD-CAM machine
What are some problems associated with CAD-CAM inlays?
There have been instances of submargination and hypersensitivity
List some of the factors that govern the choice of material we use to make our inlay/onlay
- Preservation of tooth tissue
- Retention and resistance form
- Structural durability of restoration
- Marginal integrity and position
- Biological considerations
- Aesthetics
Which material is best to use if we want to preserve tooth tissue
Gold or a full coverage crown is best
Porcelain requires the most preparation
Which material is best to use if we want to minimise damage to opposing enamel
Composite and gold have the least affect on opposing enamel
Which material offers the best aesthetic finish
Ceramic or composite
List some of the general preparation guidelines
- No undercuts
- Limited paths of insertion
- Resistance to occlusal forces
How is retention achieved for inlays OR onlays to sit in the cavity?
As a result of friction between opposing intra coronal walls (this means the walls need to diverge)
When we are creating a cavity what can naturally form?
An undercut
We DO NOT want his when placing an inlay or onlay
How can we remove undercuts from out cavity prep
- Make our cavity bigger (NOT PREFERRED)
- We can restore the intracoronal aspect with composite and clock out the undercuts created naturally duding preparation
How much taper do we want to achieve when creating a cavity for gold onlays
6 degree taper
State the idea marginal width we want to achieve when creating a cavity for gold onlays
Chamfer of 0.5mm
How much occlusal reduction do we need to do for a gold onlay?
1mm occlusal reduction for gold
1.5mm functional cusp bevel
Talk through the preparation requirements needed for a gold onlay
Taper: 6degree
Marginal chamfer of 0.5mm
1mm occlusal reduction
1.5mm functional cusp bevel
State the minimum width space requirement for a porcelain inlay/onlay
- 1.5-2mm width isthmus (1/3rd intercuspal width)
- 1.5-2mm depth
- 2mm occlusal coverage
State the margin angles and chamfer needed for a composite or ceramic inlay/onlay
90-120 degree Cavo surface margin
Heavy chamfer/ rounded 1mm shoulder
State the taper we need for a composite or ceramic inlay/onlay
15-20 degree taper
Talk through the preparation requirements needed for a composite or ceramic inlay/onlay
- 1.5-2mm width isthmus
- 1.5-2mm depth
- 90-120 degree Cavo surface margins
- Heavy chamfer/ rounded 1mm shoulder
- 15-20 degree taper
- Rounded internal angles
When creating our cavity what should we make sure in regards to preparation margins
Need to make sure they are not located in areas of static or dynamic antagonist contact
How much taper an a lithium disilicate restoration have?
Upto 12 degrees
What is the minimal width and occlusal reduction needed for a lithium disilicate restoration?
1mm minimal width and 1mm occlusal reduction
What should the Cavo surface angle be for a lithium disilicate restoration?
100-120 degrees
What is another name for adhesive onlays?
Table tops or occlusal veneers
What materials are adhesive onlays usually made from?
Gold or lithium disilicate
Describe the preparation needed for an adhesive onlay
- 0.5mm chamfer
2. 1.0 occlusal reduction
How do adhesive onlays adhere to the tooth?
By a cement
What is the benefit of adhesive onlays retaining onto the tooth via a cement?
Can achieve a more conservative preparation as the restoration doesn’t require any sort of intra coronal retention tool
Give some indications for adhesive onlays
- Cuspal coverage for cracked tooth syndrome or protection
- Erosion or attrition
- Short or over tapered clinical crowns
- Patients with amelogenesis
Give some of the contra indications of adhesive onlays
- Poor oral hygiene
- Subgingival margins
- Inability to gain good moisture isolation
- Lack of enamel margins
- Parafunction
Before placing a metal adhesive onlay onto a tooth what must be done to it
It must be sandblasted on its fit surface
What can be added to composite onlays to help improve the bonding?
A primer can be added onto the fit surface
What can be added to ceramic onlays to help improve the bonding?
A silane coupler can be added onto the fit surface
While the onlay or inlay is being prepared what do we need to do to the prepared tooth
We need to temporise the tooth with a temporary restoration
After preparing your cavity for an inlay or onlay what do you need to do?
Take an impression of the preparation
After your inlay or onlay has been created what do you need to do?
Cement it onto the tooth
How are cast metal onlays and inlays retained in the tooth and name the cements you’d expect to use with these metals
Mechanical retention
Would see cements like:
1. Zinc phosphate
2. Glass ionomer luting cement
Name the more modern way to adhere inlays or onlays to teeth
Adhesive retention is more modern
Give examples of some adhesive cements
- Panavia F 2.0
2. Rely X ultimate
