Fixed I - Principles of Preparation: Mechanical Principles

What are the three categories that mechanical considerations of tooth prep can be divided into?

providing retention form, providing resistance form, preventing deformation of the restoration

What are the principles that govern preparation design?

A) preservation of tooth structure

B) retention and resistance

C) structural durability

D) marginal integrity

E) all of the above

F) none of the above

E) all of the above

What is retention form?

feature of tooth prep that resists dislodgment of the crown in a vertical direction or along path of placement

Retention form is

A) prevention of dislodgement in vertical direction or path of placement

B) prevention of dislodgment along axis other than path of placement

A) prevention of dislodgement in vertical direction or path of placement

Resistance form is

A) prevention of dislodgement in vertical direction or path of placement

B) prevention of dislodgment along axis other than path of placement

B) prevention of dislodgment along axis other than path of placement

True/False: taller teeth are more retentive than smaller teeth

True

True/False: skinnier teeth are more retentive than wider teeth

False

What are reasons why crowns fail?

A) caries

B) porcelain fracture

C) lack of retention

D) all of the above

E) none of the above

D) all of the above

True/False: Magnitude of dislodging forces are largely a function of the stickiness of foods

True

True/False: traditional luting agents are adhesive

False

True/False: some convergence is desirable to allow the crown to seat

True

What is taper?

angle formed between external wall and path of placement of a tooth prep

The recommended total occlusal convergence is

A) 5 degrees

B) 6 degrees

C) 7 degrees

D) 8 degrees

B) 6 degrees

True/False: the total occlusal convergence being 6 degrees means that both sides of the prep should be 6 degrees

False (taper on both sides is 3 degrees)

True/False: an increased taper leads to a lack of concentricity

True

True/False: retention is directly proportional to taper

False

Excess taper leads to

A) tensile stress (less friction)

B) shear stress (increase friction)

A) tensile stress (less friction)

Minimal taper leads to

A) tensile stress (less friction)

B) shear stress (increase friction)

B) shear stress (increase friction)

An undercut is a

A) divergence between opposite facing axial walls from cervical to occlusal

B) convergence between opposite facing axial walls from cervical to occlusal

A) divergence between opposite facing axial walls from cervical to occlusal

When retention goes from 5 degrees to 10 degrees, retention

A) increases significantly

B) decreases significantly

C) stays the same

B) decreases significantly

What is the recommended taper? (note: NOT asking about total occlusal convergence)

A) 1-3 degrees

B) 2-5 degrees

C) 6-10 degrees

D) 10-12 degrees

B) 2-5 degrees

True/False: larger diameter preparations are more retentive than smaller diameter preparations

True

True/False: as the surface area of the prep increases, the retention decreases

False

True/False: a smooth prep surface has better retention than a slightly rough prep surface

False

Retention is affected by

A) type of casting alloy

B) type of core or buildup

C) both A and B

D) neither A nor B

C) both A and B

True/False: reactive alloys have better adhesion

True

True/False: for core materials, composite is better than amalgam

False

True/False: adhesive cements provide more retention than non-adhesive cements

True

What is an example of a strong type of luting agent?

adhesive resin

Resistance depends on

1) magnitude and direction of dislodging forces

2) geometry of tooth prep

3) physical properties of the luting cement

A) 1 and 2

B) 2 and 3

C) 1 and 3

D) 1, 2, 3

D) 1, 2, 3

For most teeth (not including molars), the prep height should be ____ mm minimum

A) 1

B) 2

C) 3

D) 3.5-4

E) 4

C) 3

For molars, the prep height should be ___ mm

A) 1

B) 2

C) 3

D) 3.5-4

E) 4

D) 3.5-4

For good retention and resistance, the height:width ratio should be

A) 2:3

B) 3:8

C) >4:10

D) <4:10

C) >4:10

True/False: as the prep gets more tapered, there are less degrees of freedom

False

As diameter increases, resistance

A) increases

B) decreases

C) stays the same

B) decreases

As the diameter decreases, resistance

A) increases

B) decreases

C) stays the same

A) increases

As the radius of the prep increases, resistance

A) increases

B) decreases

C) stays the same

B) decreases

As taper increases, resistance

A) increases

B) decreases

C) stays the same

B) decreases

True/False: as taper increases, resistance increases

False

As height increases, resistance

A) increase

B) decreases

C) stays the same

A) increases

True/False: as height of the prep increases, resistance increases

True

Adding grooves will

A) increase resistance

B) increase retention

C) A and B

D) neither A nor B

A) increase resistance

True/False: sharp line angles concentrate stress and must be rounded

True

Why should sharp line angles be rounded?

A) easier die fabrication

B) easier investing

C) simpler removal of casting nodules

D) all of the above

E) none of the above

D) all of the above

Gold as an alloy component

A) corrosion resistance

B) hardness

C) MP and hardness

D) MP

A) corrosion resistance

Copper as an alloy component increases

A) corrosion resistance

B) hardness

C) MP and hardness

D) MP

B) hardness

Silver as an alloy component

A) counteracts orange color of copper

B) prevents oxidation during melting

A) counteracts orange color of copper

Zinc as an alloy component

A) counteracts orange color of copper

B) prevents oxidation during melting

B) prevents oxidation during melting

Palladium as an alloy component increases

A) corrosion resistance

B) hardness

C) MP and hardness

D) MP

C) MP and hardness

Platinum as an alloy component increases

A) corrosion resistance

B) hardness

C) MP and hardness

D) MP

D) MP

For metal crowns, the recommended reduction on the occlusal surface is

A) 0.5-1.0 mm

B) 1.0-1.5 mm

C) 1.0-2.0 mm

C) 1.5-2.0 mm

B) 1.0-1.5 mm

For metal-ceramic crowns, the recommended occlusal reduction is

A) 0.5-1.0 mm

B) 1.0-1.5 mm

C) 1.0-2.0 mm

C) 1.5-2.0 mm

C) 1.0-2.0 mm

For zirconia crowns, the recommended occlusal reduction is

A) 0.5-1.0 mm

B) 1.0-1.5 mm

C) 1.0-2.0 mm

C) 1.5-2.0 mm

B) 1.0-1.5 mm

For metal crowns, the recommended reduction at the margin is

A) 0.3-0.6 mm

B) 0.5-0.8 mm

C) 1.0-1.2 mm

D) 1.5-2.0 mm

A) 0.3-0.6 mm

For metal-ceramic crowns, the recommended margin reduction is

A) 0.3-0.6 mm

B) 0.5-0.8 mm

C) 1.0-1.2 mm

D) 1.5-2.0 mm

C) 1.0-1.2 mm

For zirconia crowns, the recommended margin reduction is

A) 0.3-0.6 mm

B) 0.5-0.8 mm

C) 1.0-1.2 mm

D) 1.5-2.0 mm

B) 0.5-0.8 mm

Retention and resistance form of full coverage preparations on short molars can best be enhanced by

A) using a zinc phosphate cement

B) placing several vertical grooves

C) using a full shoulder finish line

D) minimizing depth of occlusal reduction

E) placing several horizontal grooves

B) placing several vertical grooves