Key concepts of cavity design Flashcards
2 reasons why we drill holes in teeth
To remove caries
To help make a restoration
Why is it important to remove caries?
Debride an infected tissue - remove bacteria
Why make a restoration? (3)
Restorations restore function and reduce pain
A well-formed cavity aids retention of restoration
Restoration may protect damaged residual tooth structure
Why not cut a cavity? (5)
Natural tooth tissue is finite (ageing population expecting to keep teeth)
No restorative material is adequate to truly replace it
Rebuilding tooth is complex & time-consuming
Cavity weakens a tooth
Replacing a restoration always enlarges cavity
What is the main difference in cavity design now and in the past?
Past: remove all bacteria
Now: remove most bacteria
What are the basic objectives of cavity design? (5)
Remove all bacteria whilst removing minimal tooth tissue
Stop marginal fracture of tooth or material
Resist displacement of material
Retain material in tooth
Prevent further decay
Which approach did dentists take to cavity design 1890s-1980s?
Mechanical approach
4 properties of amalgam as restorative material
Does not bond to tooth tissue (fair marginal seal)
Relatively rigid
Not antibacterial
Brittle
What is the cavosurface angle?
Angle of tooth structure formed by junction of prepared cavity wall and external surface of tooth
What happens if the cavosurface angle is less than 90 degrees?
Marginal enamel prisms are unsupported = unsupported enamel
What happens when the cavosurface angle is more than 90 degrees?
Incomplete enamel prisms supported by dentine and not exposed to direct pressure
What is more likely to not be displaced in an amalgam restoration: a hemospherical cavity or parallel-sided cavity?
Parallel-sided cavity could only be removed by destruction of the filling or tooth
Why do we undercut dentinal walls?
Retention for simple restoration
What do we use to position margins and where do we position them?
To allow placement of matrix
To place margins in cleansable areas
What was distinct about the shape of cavities from 1890s - 1980s?
All looked the same - not px / case dependent
Name 3 instrument types used 1890s-1980s
Burs (diamond and TC)
Excavators
Chisels, marginal trimmers
What approach did dentists take to cavity design in 1980s - 2000s?
Preservation of tooth structure
What key principles about cavity design changed in 1980s? (4)
Margins must be caries free
Follow caries rather than rigid design principles
Use properties of contemporary materials
Use prevention to reduce caries
How did amalgam restorations change in 1980s? (3)
Smaller cavities (modern high copper alloys stronger) Rounded internal angles Bonding (enhance marginal seal and increase retention)
Give an advantage and disadvantage of GIC
+ Good bond to dentine (retained without mechanical features, accept dished cavitites)
- Mechanically weak (wear and fracture)
What is ART?
Atraumatic restorative treatment is where caries is removed with hand instruments only, and unsupported enamel removed. Restored with GIC. Came in in 1980s-2000s
Is ART a good technique to use?
Good in developing countries with no electricity
Morally dubious - not completely removing caries, just removing it from ADJ
How well does composite bond to enamel and dentine? When did it come into use?
Excellent bond to enamel (marginal seal established, retention)
Fair bond to dentine (retention)
Cutting retentive features not usually needed
1980s - 2000s
When did fissure sealants come into use? Why advantageous?
1980s- 2000s.
Prevention - no cavity prep
Why does a cavity for composite look like? (3)
Outline dictated by spread at ADJ
No minimum depth
Retention provided largely by adhesion
What is tunnel preparation? Is it still used?
Conservative approach to cavity design, where handpiece is used to drill diagonally to caries, and cavity is filled using matrix band
Very difficult access makes clearing caries at ADJ difficult & time-consuming so rarely used
What was the opinion towards unsupported enamel 1980s - 2000s?
Less of a concern but must be considered in view of occlusal loading
Support with GIC base optional
Bond with composite
What is the basis of stepwise excavation? How has it changed in its use from 1980s - now?
Bacteria beneath restoration become quiescent and dentine remineralises
Used to re-enter 6 months later, now not needed - bacteria shouldn’t come back
Process of stepwise excavation
Prepare ADJ
Prepare dentine pulpally but leave some softened caries
Restore with GIC
Re-enter 6 months later and restore
How did instrumentation change 1980s - 2000s?
Burs rounded & sometimes smaller, containing microfine diamond
Air abrasion, laser, chemomechanical (minimal invasive)
What approach have dentists taken towards cavity design since 2000?
Minimal intervention
Do we need to excavate? Good marginal seal and caries arrested over soft infected dentine if sound marginal seal at 10 years
Reduces risk of exposure of pulp and should arrest lesion progression
Advantages of minimal intervention (5)
Ensure true cause of caries is addressed
Selective caries removal to not expose pulp
Minimises iatrogenic (operator’s fault) damage
Sound margins at ADJ with enamel
Can use magnification
What instrumentation has been used for cavity design since 2000? (3)
Burs (round & pear-shaped diamond; round rosehead in slow handpiece)
Hand excavator
Air abrasion
