Principles of Cavity Preparation

Question 1

Who is Greene Vardiman Black?

Answer 1

• In 1896, he classified cavity preparations according to size and location
• invented first foot drill
• 1st to use nitrous oxide to remove teeth without pain
• extension for prevention (incorporated more pits and fissures than carious to prevent future disease)
• advances in materials and instrumentation, alongside reliable adhesives have allowed us to be more conservative of tooth structure

Question 2

What is Blacks Classification of Cavities (1896)?

Answer 2

Class I: occlusal surfaces of molars and premolars, buccal pits of molars
Class II: approximal surfaces of molars and premolars
Class III: approximal surfaces of incisors and canines
Class IV: incisal edges of incisors and canines
Class V - cervical margins

Question 3

What are the disadvantages of Blacks Classification?

Answer 3

• was used before adhesive materials were available
• retentive cavities needed to be cut
• removes more tooth substance than necessary
• does not include root caries and secondary caries
• cavity preps nowadays are modified versions of blacks classification

Question 4

What are the principles relating to cavity prep according to G.V. Black?

Answer 4

• outline form
• resistance form
• retention form
• treatment of residual caries
• correction of enamel margins
• cavity debridement

Question 5

What is outline form?
Resistance form?

Answer 5

Outline form: Gaining access to caries
Resistance form: to resist occlusal forces
- to enable the restoration and remaining tooth structure to withstand masticatory forces
- cavity floor at right angle to the direction of the occlusal forces
- sufficient depth of material compatible with its physical properties
- no unsupported/overhanging enamel remains

Question 6

What is retention form?

Answer 6

Retention form: to retain the material in the cavity
- grooves
- undercuts and occlusal keys
- acid etch and bonding agents
- dentine pins

Question 7

What is treatment of residual caries?

Answer 7

• always remove caries from enamel/dentine junction first, then move on to the base of the cavity
• general rule of thumb - soft dentine is infected, therefore should be removed
• firm but stained dentine in the base of the cavity can be left

Question 8

What does correction of enamel margins involve?
What is cavity debridement?

Answer 8

• unsupported enamel is weak and prone to fracture
• can be splinted by adhesive materials
• remove weakened tooth substance
• facilitate placement of matrix retainers
• bevel to increase surface area for bonding
  Cavity debridement: thorough wash and dry to remove debris and bacteria

Question 9

What is the cavosurface angle?

Answer 9

• where cavity wall meets tooth surface, should be 90-110 degrees

Question 10

How long do restorations last?

Answer 10

Amalgam - 10 years
Composite - 8 years
Glass ionomer - 3 years
Several factors have a bearing on survival of restoration

Question 11

Survivability of restorations depends on…

Answer 11

• caries risk
• depth and extent of the cavity, number of surfaces involved
• operator skill and techniques employed during cavity prep and restoration placement
• other local factors

Question 12

Reasons for restoration failure:

Answer 12

• secondary caries
• NCTSL
• pulp pathology
• trauma
• fractures (restoration or tooth)
• bond failure
• ditching
• lack of retention
• defective contacts
• defective margins
• aesthetics