Inlays and onlays Flashcards
What are some of the negative consequences 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 posterior teeth fracturing
- If the height to base ratio of the tooth is more than 1 (height>base)
- Root treated teeth
- A group function occlusion
- Clenching or grinding
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
- Cusps coverage
What are the challenges of bonding and direct composites
- Polymerisation shrinkage
- Achieving good contact point
What do we need to think about when looking at polymerisation shrinkage
The stress that it applies to the tooth composite interface
How can we try and reduce the stress on a tooth
Look t eat configuration factor of a cavity
What do we mean by configuration factor
(Number of bonded surfaces) / (number of unbounded surfaces)
What is the relationship between configuration factor and stress on the tooth
As the configuration fact increase so does the stress on the tooth increasing risk of polymerisation shrinkage
What problem can occur if we create an insufficient contact point
Food packing can occur and it can be hard 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
Define what an inlay is
An extra coronal restoration made in the lab and cemented into the tooth
What problems can arise when using inlays
- They require taper which can create a weeding effect wearing the cusps
- They down cover the cusps so can’t provide cuspal coverage
Why do inlays need to be tapered
As they are placed into the tooth so they need to be able to sit there properly
What is the tissue with an inlay needing to have a taper
Risk of having a wedging effect which will direct forces downward putting stress on the cusps leading to fracture
What shoddy the height to base ratio be for an inlay to be successful
heigh tot base ratio of lead than or equal to 1q
Talk through the indications of an inlay
- Small to medium cavity eg MO or DO
- Conservative MOD in molars
- Low caries risk
- Good support for cusps from the remaining tooth tissue
- About 1/3rd buccal lingual width
- Height base ratio < 1:1
- Canine guidance
When are inlays most useful
When you have a large gap between adjacent teeth to achieve good contact points
Give examples of restoration we can use that offer good cuspal protection
- Full coverage crowns
- Onlays
List the principles of preparation
- Preservation of tooth tissue
- Retention and resistance form
- Structural durability of restoration
- Marginal integrity and position
- Biological
- Aesthetic
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%
What is an onlay
A restoration constructed in the lap and cemented into a tooth that may contain an intra coronal aspect but also covers one or more cusps
Give some indications for onlays
- Teeth with larger restorations but sound buccal and lingual walls needing cuspal protection
2, Low caries risk - 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 ceramic inlay?
80% for 8 years
List some factors that govern the choice of material we use to make our inlay or onlay
- Preservation of tooth tissue
- Retention and resistance form
- Structural durability of restoration
- Marginal integrity and position
- Biological consideration
- Aesthetics
Which Material is best to use if we want to preserve tooth tissue
Gold or full coverage crown is best
Which Materia requires the most tooth preparation
porcelain
Which Materia offers the best aesthetic finish
Ceramic or composite
List some general preparation guidelines
- No undercuts
- Limited paths of insertion
- Resistance to occlusal forces
How is retention achieved for inlays and onlays to sit in the cavity
As a result of friction between opposing intra coronal walls (this means the walls need to diverge)
How can we remove undercuts from our cavity prep
- Make the cavity bigger (not preferred)
- We can restore the intra coronal aspect with composite and block out the undercuts created naturally when prepping
How much taper do we want to create when creating a cavity for a gold onlay
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
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 out cavity what should we make sure in regards to preparation margins
Need to make Sur they are not located in a areas of static or dynamic antagonise 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 dislocate 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 top s 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
1mm 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 one tapered clinical crown
- Patients with amelogenesis
Give some contra indication 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
Must be sandblasted on its fit surface
What can be added to composite onlays to help improve bonding
A primer can be added onto the fit surface
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 use cements like:
1. Zinc phosphate
2. Glass ionomer luting cement
