Lecture - 09/23 - Finish Lines and Margin Design

Question 1

What is the definition of the biologic width?

Answer 1

• the combined height of connective tissue and epithelium that isolates the bone from the oral cavity; it is the distance considered necessary for the existence of healthy bone and tissue from the most apical extent of a dental restoration

Question 2

What is the mean biologic width?

Answer 2

2.15-2.30 mm

Question 3

How do you know whether you are encroaching on the biologic width?

Answer 3

retraction cord should be able to be below your margin without destroying the attached gingival connection

Question 4

What is visible at the margin of a crown with a sloped shoulder? With a 90 degree shoulder? With a beveled shoulder?

Answer 4

• sloped shoulder: metal just barely visible
• 90 degree shoulder: porcelain only
• beveled shoulder: metal collar

Question 5

When making a 90 degree shoulder, the shoulder is 90 degrees from what?

Answer 5

from the emergence profile, NOT the axial wall

Question 6

What are the biologic considerations to prevent damage during tooth preparation?

Answer 6

• adjacent teeth
• soft tissue (biologic width)
• pulp (temperature, chemical actions, bacterial action)

Question 7

What 2 situations will cause the temperature of the pulp to reach critical level during tooth preparation?

Answer 7

• high speed (air turbine) dry

- low speed dry

Question 8

What 2 factors cause the temperature of the pulp to rise?

Answer 8

• friction (heavy pressure, dull burs, no water)

- some provisional materials (PMMA)

Question 9

Which provisional material gets the hottest?

Answer 9

polymethyl methacrylate (Jet)

Question 10

True or false: The pulp usually recovers by itself after being exposed to chemical actions during tooth preparation.

Answer 10

true

Question 11

How are bacterial actions prevented during tooth preparation?

Answer 11

• many cements are bactericidal (ZnPO4) (acid/base cements but NOT composites)
• chlorhexidine (Concepsis) after preparation (not clinically proven; does not inhibit bonding)
• pulp capping NOT recommended under crown

Question 12

Which cements are bactericidal?

Answer 12

acid/base cements (NOT composites)