Crown preparation Flashcards
4 indications of extra-coronal restorations?
- To protect weakened tooth structure
- improve or restore aesthetics
- to restore tooth function
- retainer for bridges
- when indicated by RPD design
What 3 things you can include in a crown indicated for RPD design?
- Rest seats
- Clasps
- guideplanes
What are the 6 principles of tooth preparation for crowns?
- preservation of tooth structure
- retention and resistance
- marginal integrity
- structural durability
- preservation of the periodontium
- aesthetic considerations
2 reasons why to preserve tooth structure?
- to avoid weakening tooth structure
- to avoid damaging the pulp
2 things under preparation will result into?
- Poor aesthetics
- overbuilt crown leading to occlusal and periodontal consequence
what will over-preparation lead to?
Pulp and tooth strength being compromised
What is retention in crowns?
Prevents the removal of restoration along the path of insertion
What is resistance in crowns?
- prevents dislodgment of restorations by oblique or apical forces
- prevents movement of restoration under occlusal forces
What is the ideal taper of crown walls?
6 degrees
2 modifications in preparation to increase crown retention?
- Grooves
- Slots
What 3 aspects of a crown preparation contribute to its retention?
- Taper - 6 degree
- Path of insertion
- length of walls
What is the problem with short crown preparation walls?
- more prone to tipping displacement
How is retention achieved by path of insertion in crown prep?
limiting the number of paths of insertion
What 3 things achieve crown structural durability?
- occlusal redection
- functional cusp bevel
- Axial reduction
How is marginal integrity achieved?
By finish line configurations
Give 5 examples of finish line configurations?
- knife edge
- bevel
- chamfer
- shoulder
- bevelled shoulder
Give 3 features of a good margin finish to preserve the periodontium?
- smooth and fully exposed to cleansing action
- placed where the patient can clean them and the dentist can finish them
- placed at the gingival margin whenever possible
What is the biological width?
- the dimension of the junctional epithelium and connective tissue above the bone crest
- 2mm
What line should you note to achieve good aesthetics for anterior restorations?
Smile line
What 4 most common materials are crowns made of?
- Metal - gold
- Ceramic - porcelain
- Metal ceramic
- All ceramic - porcelain bonded to zirconia or alumia framework
What are the 6 stages in crown preparation?
- occlusal reduction
- separation
- buccal reduction
- palatal or lingual reduction
- shoulder and chamfer finish
- check occlusion and clearance
What degree of taper you want to achieve when separating in crown prep?
5-10
How would you prepare the buccal aspect of crown prep?
in two planes ( coronal and apical)
How would you prepare the palatal/lingual aspect of a crown in premolars and molars?
in one plane
