W3. Fundamentals of periodontal preparation, tooth aspects

Question 1

I. Tooth preparation
1. What is the tooth preparation?

Answer 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)

Question 2

I. Tooth preparation
2. How is the selection of form guided?

Answer 2

The selection of the form is guided by clinical circumstances and physical properties of the materials that make up the prosthesis.

Question 3

II. Fixed Prosthodontics Terminology
1. What are the 6 examples of Fixed Prosthodontics?

Answer 3

1. Full veneer crown
2. Partial veneer crown
3. Laminate veneer
4. Inlay
5. Onlay
6. Fixed partial denture

Question 4

II. Fixed Prosthodontics Terminology
2A. What is full veneer crown?

Answer 4

Cemented extracoronal restoration covers outer surface of clinical crown

Question 5

II. Fixed Prosthodontics Terminology
2B. What are indications for full veneer crown?

Answer 5

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

Question 6

II. Fixed Prosthodontics Terminology
2C. What is FPD retainer for full veneer crown?

Answer 6

extracoronal restoration that is cemented to the prepared abutment tooth

Question 7

II. Fixed Prosthodontics Terminology
3. What are the 5 Principles of crown preparation described by Schillingburg?

Answer 7

1. Preservation of tooth structure
2. Retention and resistance form
3. Structural durability of the restoration
4. Marginal integrity
5. Preservation of the periodontium

Question 8

II. Fixed Prosthodontics Terminology
3A. How should we preserve tooth structure?

Answer 8

1. Avoide excessive destruction
2. Design restoration to reinforce and protect remaining enamel and dentin
3. Overtapered or shortened too much:
   - no retention and reistance
   - thermal hypersensitivity
   - pulpal inflammation
   - Necrosis

Question 9

II. Fixed Prosthodontics Terminology
3B. Why are retention and resistance forms important in crown preparation?

Answer 9

1. Geometric configuration of tooth preparation
2. Retention prevents removal along the path of insertion or long axis
3. Resistance prevents dislodgement of oblique forces
4. Retention and resistance are interrelated and inseperable qualities

Question 10

II. Fixed Prosthodontics Terminology
3C1. How do we use taper in crown preparation?

Answer 10

1. Axial walls of a preparation must taper slightly to permit the restoration to seat
2. Two opposing surfaces, each with a 3degree inclination (diamond held paralell to the intended path of insertion) 6 degree taper
3. The more nearly paralell the opposing walls of a preparation, the greater should be the retention

Question 11

II. Fixed Prosthodontics Terminology
3C2. Why are walls tapered?

Answer 11

• visualize preparation walls
• prevent undercuts
• compensate fabrication inaccuracies
• permit complete seating during cementation

Question 12

II. Fixed Prosthodontics Terminology
4. Explain this picture

Answer 12

• CA:convergence angle - Total occlusal convergence of a preparation
• AI:axial inclination - Angle of the preparation wall relative to the line of draw of the preparation
• Sum of the axial inclination of two opposing walls equals the convergence angle. Symmetrical preparation: CA is twice the value of the axial inclination

Question 13

II. Fixed Prosthodontics Terminology
5. What is the angle of convergence?

Answer 13

Respective relationship between 2 opposing walls

Question 14

II. Fixed Prosthodontics Terminology
6. What is inclination of wall?

Answer 14

Relationship of 1 wall to the long axis of preparation

Question 15

II. Fixed Prosthodontics Terminology
7. What is Angle between the hour and minute

Answer 15

Angle between the hour and minute hand at 12:01 is 5.5 degree

Question 16

II. Fixed Prosthodontics Terminology
8. How do we hold Diamond rotary cutting instrument?

Answer 16

Diamond rotary cutting instrument held parallel to the path of insertion when preparing the axial surfaces:
- AI equals to that of the diamond being used 12 degree to insure absence of undercuts
- Overall target: 10 - 22 degree

Question 17

II. Fixed Prosthodontics Terminology - Retention and resistance
10. Why is occlusogingival a factor of retention and resistance?

Answer 17

1. Occlusogingival length: factor of retention and resistance!
2. Greater the surface area of preparation (longer preparation), the greater its retention= preparations on large teeth are more retentive than preparations on small teeth
   - Cement creats mechanical interlocks between inner surface of restoration and axial wall of preparation
   - Surface area can be increased by adding boxes and grooves
3. The shorter the wall the more important its inclination
   - shorter preparations: as little taper as possible to increase resistance

Question 18

II. Fixed Prosthodontics Terminology - Retention and resistance
11. What are good retention and resistance forms?

Answer 18

1/ Limit the pathes of withdrawal=retention!
- long, parallel axial walls and grooves=good retention
- short, overtapered preparation= restoration easy to remove, less retention
2/ Limiting freedom of displacement from torquing or twisting forces in a horizontal plane=resistance!
3/ Additional internal features: boxes, grooves!

Question 19

II. Fixed Prosthodontics Terminology
12. Why is structural durability important in crown preparation?

Answer 19

1. Adequate space created by tooth preparation
2. Occlusal reduction:
   - Material of restoration withstand occlusal forces and create harmonious occlusion
3. Axial reduction:
   - Normal axial contours preventing periodontal problems

Question 20

II. Fixed Prosthodontics Terminology
13A. What should occlusal reduction of functional cusp?

Answer 20

buccal of mandibular molars and premolars

Question 21

II. Fixed Prosthodontics Terminology
13B. What should occlusal reduction of non-functional cusp?

Answer 21

lingual of mandibular molars and premolars

Question 22

II. Fixed Prosthodontics Terminology
13C. What should occlusal reduction for full metal crown be?

Answer 22

1.5 mm functional cusp
1.0 mm nonfunctional cusp

Question 23

II. Fixed Prosthodontics Terminology
13D. What should occlusal reduction for Metal-ceramic be?

Answer 23

1.5-2.0 mm functional cusp
1.0-1.5 mm nonfunctional cusp

Question 24

II. Fixed Prosthodontics Terminology
13E. What should occlusal reduction for All-ceramic be?

Answer 24

2.0 mm of clearance
- Provides space for a cast restoration of adequate thickness in an area of heavy occlusal contact
- Prevents thin casting and perforation
- Prevents overcontoured restoration and poor occlusion
- Prevents overinclination (destroy tooth structure, less retention)

Question 25

II. Fixed Prosthodontics Terminology 14. How should axial reduction be?

Answer 25

- Space for adequate thickness of restorative material - Prevent thin walls and weak restoration - Prevent overcontoured restoration

Question 26

II. Fixed Prosthodontics Terminology 15. How should Marginal integrity be?

Answer 26

1. Margins of restoration must be closely adapted to finish line of preparation 2. Configuration of the preparation finish line dictates the shape of restorative material in the margin of the restoration 3. Finish line configurations: knife edge, slice, shoulder, (radial shoulder, shoulder with a bevel),chamfer (heavy chamfer, chamfer with a bevel)

Question 27

II. Fixed Prosthodontics Terminology 16. What are the 5 Finish line configurations?

Answer 27

1. Slice-Knife-edge 2. Bevel 3. Chamfer/ shoulder with a bevel 4. Shoulder 5. Chamfer

Question 28

II. Fixed Prosthodontics Terminology 17. What are the features of Knife edge and slice finishing configure line?

Answer 28

1. Less destruction of tooth structure 2. Difficult to follow both on tooth and die, axial reduction fade out instead of terminating a definite finish line 3. Thin margin that fits finish line difficult to wax and cast 4. Overcontoured restorations 5. Indicated only on axial wall toward tooth is tipped-preservation of tooth structure!

Question 29

II. Fixed Prosthodontics Terminology 18. What are the features of Shoulder finishing configure line?

Answer 29

1. Recommended for all-ceramic restorations only 2. Resistance to occlusal forces and minimize stress that might lead to porcelain fracture 3. Adequate bulk of material at the margin 4. Require much tooth structure destruction 5. 90 degree internal line concentrates stress-coronal fracture! 6. Radial shoulder: rounded internal angle 7. Shoulder with a bevel:adding a bevel to a shoulder creates acute edge of metal at the margin

Question 30

II. Fixed Prosthodontics Terminology 19. What are the features of Chamfer finishing configure line?

Answer 30

1. Cast metal restorations: acute margin,sufficient thickness and strength 2. Rounded concavity, lower stress concentration within cement film 3. Cut with the tip of a round- end tapered diamond, axial reduction with side of instrument 4. Heavy chamfer-large radius internal angle 90 degree surface: ceramic restorations! 5. Chamfer with a bevel: bevel added for use with a metal restoration

Question 31

II. Fixed Prosthodontics Terminology 20. How should we preserve periodontium?

Answer 31

1. Margins as smooth as possible 2. Kept clean by the patient 3. Duplicated by the impression 4. Placed in enamel if possible 5. Supragingival placement of finish lines whenever possible! 6. Subgingival finish lines 2.0 mm from alveolar crest (combined dimension of epithelial and connective tissue attachments)

Question 32

III. 4 main categories of crown: „ Crown selection” 1. What are the materials of 4 main categories of crown

Answer 32

1. Metal 2. Metal-ceramic PFM 3. All ceramic: PJC, HSPC, RBPC 4. Composite (e.g..:PPF composite-BelleGlass;MFR composite-Gradia: newly developed laboratory materials have not been fully evaluated)

Question 33

III. 4 main categories of crown: „ Crown selection” 2. What are the 2 material requirements of crown?

Answer 33

1. Amount of space needed to accomodate the crown 2. And its marginal configuration

Question 34

III. 4 main categories of crown: „ Crown selection” 3. How should we Select most suitable type of crown?

Answer 34

1. Major factor to be considered : amount of tooth destruction you are willing to allow in order to give the esthetics you want 2. Tooth preparation: - Balance between conserving tooth structure on the one hand , achieving an aesthetic and strong crown on the other!

Question 35

III. 4 main categories of crown: „ Crown selection” 4. What are advantage and disadvantage of Full veneer metal crown VMC when it comes to crown selection?

Answer 35

1. Advantage: require little tooth prep! 2. Disadvantage: aesthetics!

Question 36

III. 4 main categories of crown: „ Crown selection” 5. What are advantage and disadvantage of Porcelain fused to metal crown PFM when it comes to crown selection?

Answer 36

1. Strength & aesthetics 2. Prep to accomodote both porcelain & metal destructive!

Question 37

III. 4 main categories of crown: „ Crown selection” 6A. What are the 2 examples of improved ceramic materials?

Answer 37

1. Resin bonded porcelain crowns (RBPC) 2. Resin Bonded Pressed Crown

Question 38

III. 4 main categories of crown: „ Crown selection” 6B1. What are the characteristics of Resin bonded porcelain crowns (RBPC)?

Answer 38

1. Glass Ceramic - IPS Empress-pressed leucite system - IPS E.max 2. advanced functional and aesthetic features 3. laboratory process casting, pressing, CAD/CAM 4. “bonded” to the remaining tooth structure using a dental BisGMA based composite resin

Question 39

III. 4 main categories of crown: „ Crown selection” 6B2. How should preparation Resin bonded porcelain crowns (RBPC) be?

Answer 39

Question 40

III. 4 main categories of crown: „ Crown selection” 6C1. What are the structures of High strength porcelain crowns?

Answer 40

Oxide ceramics: - Aluminium-oxide - Zircon-oxide: ZrO295%+ 5% Yttrium

Question 41

III. 4 main categories of crown: „ Crown selection” 6C2. What are the characteristics of High strength porcelain crowns?

Answer 41

1. High strength underlying core to support veneering porcelain which gives the final shape and aesthetic attributes required for the restoration. 2. ceramic substructure 3. CAD/CAM systems 4. Deep chamfer at the finish line to allow the profile of the die to be scanned 5. Corners, line angles rounded 6. Enough tooth tissue to be removed for adequate thickness of porcelain