Principles of Tooth Preparation

Question 1

Indirect restoration

Answer 1

A restoration not placed directly into the tooth (like amalgam or composite) - prefabricated and then placed.

Question 2

Why do we need indirect restorations?

Answer 2

• Aesthetics
• Function
• Comfort
• Stability

Question 3

Why prepare tooth for indirect restoration?

Answer 3

• Create space for restoration (minimum required thickness of crown)
• Remove undercuts
• Create ideal path of insertion

Question 4

Examples of indirect restorations

Answer 4

• Crown
• Veneer
• Inlay
• Onlay

Question 5

Effects of UNDERpreparation

Answer 5

• Bulky crown (to achieve sufficient thickness/strength)
• Crown too thin in section (from lab/after reducing to fit pt.)
• High crown causing pain and occlusal interference

Question 6

Effects of OVERpreparation

Answer 6

• Excessive loss of tooth tissue
• Risk of pulpal exposure
• Short crown preparation = reduced retention
• Weaker tooth = increased risk of fracture
• possible subginigival margins = inability to cleanse crown margin

Question 7

DEFINITION: Retention

Answer 7

Prevents vertical displacement of crown along path of insertion

Question 8

DEFINITION: Resistance

Answer 8

Prevents lateral or apical displacement (rotation) of crown under occlusal load

Question 9

Retention and Resistance (R/R)

- Taper

Answer 9

• Opposing external/internal surfaces provide retention (parallel walls)
• Optimal taper should preserve tooth tissue
• Provide good retention and resistance
• Allow visible finish line
• Allow adequate seating of indirect restoration (no undercuts)
• Aim for between 6 and 12 degrees

Question 10

R/R

- Surface area

Answer 10

Increased surface area provides better R/R

Preserve as much tooth tissue as possible for increased surface area

Question 11

R/R

- Height of crown prep

Answer 11

Higher prep provides greater retention and resistance = greater surface area for friction to act upon

Question 12

R/R
- Preparation design
(Extra features of prep which contribute to better R/R?)

Answer 12

• Grooves

- Boxes

Question 13

R/R

- Cement selection

Answer 13

Passive Vs Active

Question 14

Material of crown

Material options

Answer 14

• Metal ceramic
• Gold
• Non-precious metal
• All ceramic

Question 15

Marginal integrity and position

Accuracy of margin

Answer 15

• Accurate margins reduces exposed cement - reduced risk of leakage and crown failing.
• Should finish on sound tooth
• Above or equidistant to gingival margin

Question 16

Marginal integrity and position

- Accuracy of margin

Answer 16

• Accurate margins reduces exposed cement - reduced risk of leakage and crown failing.
• Should finish on sound tooth
• Above or equidistant to gingival margin

Question 17

Marginal integrity and position

- Adequate thickness of margin, types of margin

Answer 17

• Chamfer (1.2 - 1.5mm)
• Shoulder (0.5mm)
• Knife edge

Question 18

Biological considerations

- Preservation of the periodontium

Answer 18

• Good oral hygiene
• Supraginigval margins where possible for more efficient cleansing
• Subgingival margins for better aesthetics
• Sufficient marginal reduction
• Increasing crown height by managing gingivae (increase R/R)
• Careful soft tissue management (consider persistent gingival inflammation as it makes management for impressions difficult)
• Maintain and do not encroach into biological width (distance from depth of gingival sulcus to alveolar crest)

Question 19

Biological consideration

- Preservation of pulp

Answer 19

Periapical pathology in ~20% of crowns

Question 20

Increasing crown height VS crown lengthening

Answer 20

Increasing crown height = increased R/R

Need to assess suitability for crown lengthening (considering biological width and)

Question 21

DEFINITION: Biological width

Answer 21

Distance from depth of gingival sulcus to height of alveolar crest

Question 22

Aesthetics

Answer 22

• Margin position (subgingival better for aesthetics)
• Material of crown (metal is opaque so looks less natural than porcelain but is stronger)
• Shade selection
• Adequate prep to avoid bulky crown