Principles of Tooth Preparation Flashcards
Indirect restoration
A restoration not placed directly into the tooth (like amalgam or composite) - prefabricated and then placed.
Why do we need indirect restorations?
- Aesthetics
- Function
- Comfort
- Stability
Why prepare tooth for indirect restoration?
- Create space for restoration (minimum required thickness of crown)
- Remove undercuts
- Create ideal path of insertion
Examples of indirect restorations
- Crown
- Veneer
- Inlay
- Onlay
Effects of UNDERpreparation
- 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
Effects of OVERpreparation
- 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
DEFINITION: Retention
Prevents vertical displacement of crown along path of insertion
DEFINITION: Resistance
Prevents lateral or apical displacement (rotation) of crown under occlusal load
Retention and Resistance (R/R)
- Taper
- 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
R/R
- Surface area
Increased surface area provides better R/R
Preserve as much tooth tissue as possible for increased surface area
R/R
- Height of crown prep
Higher prep provides greater retention and resistance = greater surface area for friction to act upon
R/R
- Preparation design
(Extra features of prep which contribute to better R/R?)
- Grooves
- Boxes
R/R
- Cement selection
Passive Vs Active
Material of crown
Material options
- Metal ceramic
- Gold
- Non-precious metal
- All ceramic
Marginal integrity and position
Accuracy of margin
- Accurate margins reduces exposed cement - reduced risk of leakage and crown failing.
- Should finish on sound tooth
- Above or equidistant to gingival margin
Marginal integrity and position
- Accuracy of margin
- Accurate margins reduces exposed cement - reduced risk of leakage and crown failing.
- Should finish on sound tooth
- Above or equidistant to gingival margin
Marginal integrity and position
- Adequate thickness of margin, types of margin
- Chamfer (1.2 - 1.5mm)
- Shoulder (0.5mm)
- Knife edge
Biological considerations
- Preservation of the periodontium
- 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)
Biological consideration
- Preservation of pulp
Periapical pathology in ~20% of crowns
Increasing crown height VS crown lengthening
Increasing crown height = increased R/R
Need to assess suitability for crown lengthening (considering biological width and)
DEFINITION: Biological width
Distance from depth of gingival sulcus to height of alveolar crest
Aesthetics
- 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
