Lecture 3 - Tooth Preparation Principles

Question 1

Define Biologic Width

Answer 1

Biologic width can be expressed as the height between the deepest point of the gingival sulcus and the alveolar bone crest.

= 2.04 mm

Question 2

It is suggested to have how much space between the restorative margin and the crest of the alveolar bone

Answer 2

3 mm

If bone needs to be removed, it is suggested to be done

Question 3

mechanical considerations of extra-coronal tooth preparations can be divided into what 3 categories?

Answer 3

Providing retention form
Providing resistance form
Structural durability

Question 4

Retention form:

Answer 4

Quality of a preparation that prevents the restoration from becoming dislodged by forces parallel to the path of placement

Question 5

What factors must be considered when the dentist decides whether retention is adequate for a given fixed restoration:

Answer 5

1. Magnitude of the dislodging forces.
2. Geometry of the tooth preparation.
3. Roughness of the fitting surface of the restoration.
4. Materials being cemented.
5. Film thickness of the luting agent.

Question 6

How does the geometry affect a preparation

Answer 6

Minimizing taper effectively limits the number of directions in which a cast crown can be dislodged.

Question 7

For a crown to seat and have the optimal retention, all axial walls should have how much taper?

Answer 7

a 6-degree taper from cervical to occlusal

Question 8

T or F, Slight decreases in taper have a significant decrease in retention

Answer 8

False, Slight increases in taper

Question 9

Describe the correct path of insertion of a preparation

Answer 9

It must parallel the adjacent proximal contacts or it will be prevented from seating

• Must be considered in two dimensions mesio-distal and faciolingual (esthetics)

Question 10

Describe the importance of surface area in retention

Answer 10

Retention depends on the length of the path, the surface area in sliding contact.

So, crowns with tall axial walls are more retentive than those with short axial walls
and molars are more retentive than premolars because of the greater diameter of a molar.

Question 11

In the following 6 categories, name what will cause greater retention:

• Taper
• Surface Area
• Type of prep
• Surface texture
• Film thickness
• Luting agent

Answer 11

Taper: Parallel 
Surface Area: Large
Type of prep: Molar complete crown
Surface texture: Rough
Film thickness: effect uncertain
Luting agent: Adhesive resin

Question 12

Resistance form:

Answer 12

The features of a tooth preparation that enhance the stability of a restoration and resist dislodgment along an axis other than the path of placement.

Question 13

Adequate resistance depends on the following:

Answer 13

1. Magnitude and direction of the dislodging forces.
2. Geometry of the tooth preparation.
3. Physical properties of the luting agent.

Question 14

What happens to resistance form when taper or diameter increases, or preparation height is reduced?

Answer 14

It decreases

Resistance is a function of the relationship between axial wall taper, preparation diameter, and preparation height

Question 15

How can resistance form of an excessively tapered preparation be improved?

Answer 15

By adding grooves or boxes. As an alternative, pinholes can be prepared to achieve the same effect.

Question 16

Of the following categories, name which attribute of each has higher resistance:

• Disloding forces
• Taper
• Diameter
• Height
• Type of preparation
• Luting agent

Answer 16

Disloding forces: Habits? 
Taper: Minimum
Diameter: Small (premolar)
Height: Long
Type of prep: Complete coverage
Luting agent: Adhesive resin

Question 17

What 3 things correspond to structural durability of the prep

Answer 17

Occlusal reduction
Functional cusp bevel
Axial reduction

Question 18

Lack of a functional cusp bevel may result in what?

Answer 18

over contouring and poor occlusion

Question 19

Over inclination of the buccal surface will do what?

Answer 19

Destroy excessive tooth structure while lessening retention and potentially violating the pulp

Question 20

Inadequate axial reduction can cause what?

Answer 20

Thin walls and a weak restoration or a bulbous over contoured restoration

Question 21

4 esthetic considerations of a tooth preparation

Answer 21

Minimal display of metal
Adequate thickness of restorative material
Near or Sub-gingival margins
Visible surfaces are tooth colored

Question 22

Types of Finish lines

Answer 22

Bevel
Chamfer
Shoulder
Sloped shoulder
Shoulder with bevel

Question 23

Bevel finish line

Answer 23

45-60 degrees to the long axis of the tooth and .5 mm wide

For inlay/onlay margins

Question 24

Chamfer finish lines

Answer 24

Rounded axiopulpal line angle, 90 degree cavosurface line angle, .5 to 1.5 mm wide

• Full metal casting

Question 25

Shoulder finish lines

Answer 25

90 degree axiopulpal line angle
90 degree cavosurface line angle
1.2 to 1.5 mm wide
Porcelain margins

Question 26

Sloped shoulder finish lines

Answer 26

120 degrees to long axis of tooth

1.2 to 1.5 m wide

Question 27

Beveled Shoulder finish lines

Answer 27

90 degree axiopulpal line angle
135 cavosurface line angle
Bevel is 0.5 mm wide