26. Principles of tooth preparations. 51. Tooth preparation forms and different kinds of finish lines. 52. Requirements of tooth preparation.

Question 1

0. Definition of tooth preparation

Answer 1

Preparing the clinical crown of the tooth with rotary instruments (burs)

Question 2

1. Characteristics of tooth preparation

Answer 2

1/ The selected form given to a natural tooth when it is reduced by instrumentation to receive a prosthesis (e.g. artificial crown or a retainer for a fixed or removable prosthesis)
2/ The selection of the form is guided by clinical circumstances and physical properties of the materials that make up the prosthesis.

Question 3

2. When do we prepare a tooth?

Answer 3

1. Fixed appliances
   - Full veneer crown
   - Partial veneer crown
   - Laminate veneer
   - Fixed bridges, splints
   - Inlay, onlay, overlay
   - Dowelcore
2. Complex partial dentures (fixed + removable)

Question 4

3. What are indications for full veneer crowns?

Answer 4

1/ Protect weekend tooth structure
2/ Improve or restore esthetics
3/ Restore the tooth to function
4/ Use as a retainer for fixed bridgework

Question 5

4. Principles of crown preparation described by Schillingburg
   a/ What are principles of crown preparation described by Schillingburg?

Answer 5

1/ Preservation of tooth structure (minimize the tooth structure)
2/ Retention and resistance form (appropriate length)
3/ Structural durability of the restoration (appropriate, uniform thickness)
4/ Marginal integrity (proper finishing line)
5/ Preservation of the periodontium (supra-, para-, subingival-)

Question 6

4. Principles of crown preparation described by Schillingburg
   b/ How do we preserve the tooth structure

Answer 6

• Remove as less tooth material as possible according to the crown material
• Protection of the pulp
• Protection from heat
  => crown aims to protect the rest of the dentin and enamel

Question 7

4. Principles of crown preparation described by Schillingburg
   c/ What are definitions of retention and resistance?

Answer 7

• Retention: stability against vertical forces
• Resistance: stability against oblique forces

Question 8

4. Principles of crown preparation described by Schillingburg
   d/ What are geometric configurations of retention and resistance?

Answer 8

• 6-8° taper
• Min. 4mm coronal length
• Rounded angles

Question 9

4. Principles of crown preparation described by Schillingburg
   e/ How do we maintain structural durability?

Answer 9

1. Uniform thickness of the crown
2. Thinner parts -> tend to get injured

Question 10

4. Principles of crown preparation described by Schillingburg
   e/ STRUCTURAL DURABILITY
   -> How do we reduce the functional and guiding cusps prepare for metal crown application?

Answer 10

Functional - 1.5 mm
Guiding - 1mm

Question 11

4. Principles of crown preparation described by Schillingburg
   e/ STRUCTURAL DURABILITY
   -> How do we reduce the functional and guiding cusps prepare for PORCELAIN FUSED TO METAL application?

Answer 11

Functional: 1.5 - 2 mm
Guiding: 1 - 1.5 mm

Question 12

4. Principles of crown preparation described by Schillingburg
   e/ STRUCTURAL DURABILITY
   -> How do we reduce the functional and guiding cusps prepare for PORCELAIN JACKET CROWN application?

Answer 12

Both cusps: 2 mm
Incisal edge: 2.5 mm

Question 13

4. Principles of crown preparation described by Schillingburg
   f/ What does it mean when we need marginal integrity?

Answer 13

1. Clear, simple finishing line
2. Visible line separates the prepared and unprepared surfaces
3. All prepared surfaces will be covered by the crown
4. Appropriate width or shoulder

Question 14

5. What are the rules of tooth preparation?

Answer 14

◦ Painless
◦ Protection against heat damage
◦ protection of the soft tissues
◦ Avoid pulp damage
◦ Follow the anatomical shape of the tooth
◦ 5-8 degrees convergent angle needed
◦ Parallel axis of abutments

Question 15

6. Identify this finish line configuration

Answer 15

1: radial shoulder
2: Shamfer
3: Bevel
4: Shoulder (90°)
5: Reverse bevels
6: Shoulder with bevel

7: Without shoulder, can be
- 7A: Tangential
- 7B: Knife edge

Question 16

7. Characteristics of tangential preparation

Answer 16

1/ Least reduction of tooth structure
2/ No exact finishing line, difficult to follow
3/ Thinner marginal area on the crown -> difficult to cast
4/ Results in an overdimensioned restaurant
5/ Only indicated at tilted teeth, to save tooth material

Question 17

8. Characteristics of shoulder preparation

Answer 17

1/ Indication: porcelain jacket crowns only
2/ we cannot cast 90 ̊ angle from metal(concentrate stress -> fracture)
3/ Appropriate width at the finishing line
4/ More loss of tooth structure
5/ Flat ended fissure burr

Question 18

9. Characteristics of chamfer preparation

Answer 18

1/ Indication: porcelain fused to metal crowns
2/ Exact finishing line
3/ Enough width for crown material
4/ Easy to pattern and casting or scanning
5/ rounded -> less stress
6/ chamfer diamond burr

Question 19

10. How do we preserve periodontium during tooth preparation?

Answer 19

1/ Exact fit -> cleanability
2/ Shoulder - gum relation
- Supra-gingival (above marginal gum)
- Para-gingival (at the level of marginal gum)
- Subgingival (max. 1 mm under marginal gum)
3/ Finishing line in the enamel, of possible
4/ Able to reproduce by impression taking

Question 20

11. Characteristics of porcelain fused to metal (PFM) crowns

Answer 20

1/ Widespread usage
2/ Aesthetic
3/ Mechanical resistance
4/ Chamfer preparation -> enough space (1.5 mm) for metal frame and veneering ceramic (1 mm)