Failure

Question 1

Describe fatigue failure in dental restorations

Answer 1

Fatigue failure is a form of failure in structures that are subjected to dynamic and fluctuating stresses , and these stresses can be at much lower levels than that required to break the material under normal static loading. When these low stresses are repeated many times, the strength of the material or the bonding system may be significantly reduced, leading to failure.

Question 2

Fatigue cracks usually initiate as:

Answer 2

Micro-defects on the surface or within a material

Question 3

What is the relationship between stress and cycle number in fatigue failure?

Answer 3

The higher the stress, the lower the number of cycles for failure to occur. Hence areas of stress concentration are particularly dangerous, and any ground surfaces must be polished and reglazed

Question 4

Consideration when doing scale and clean on ceramic restorations:

Answer 4

Dont use ultrasonic on cermic restorations.

Question 5

What is corrosion fatigue?

Answer 5

A fatigue process which is initiated when defects are caused by corrosion

Question 6

What are three ways to classify failure

Answer 6

1. Biological (secondary caries, endo complication, periodontal complication)
2. Aesthetic failure
3. Mechanical failure

Question 7

In brittle materials such as ceramics, fracture will begin at the location with:

Answer 7

The highest stress state, this is usually at the largest ‘flaw’

Question 8

4 examples of machanical failure of all-ceramics

Answer 8

• Debonding of the prosthesis
• Cracking
• Chipping
• Bulk fracture