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
How would you prepare the palatal/lingual aspect of a crown in canines and incisors?
follow palatal contour
What should you retain during occlusal reduction?
Occlusal morphology (cusps and marginal ridges)
What anatomical structure should you avoid during buccal reduction?
Pulp horns especially in premolars
What is the most common reason for technicians being unable to construct a crown?
- insufficient occlusal clearance
