All ceramic crown Flashcards
What are the indications for a porcelain crown?
To improve appearance and function:
- heavily restored tooth
- trauma resulting in fracture
- hereditary and acquired hypoplasia
- tooth wear
- alter size and shape of tooth
- in combination with bridges and partial dentures
What are the alternative treatments to improve appearance and function?
- bleaching discoloured teeth
- restoration with tooth colour filling materials (may gradually stain and yellow with age)
- veneers
What is another word for internal bleaching?
“walking bleaching”
At which angle should the incisal reduction be done at?
Inciso-palatal angle of 45 degrees (554)
What is the reported correct amount of incisal reduction?
1-2mm
(>2mm increases incidence of labial fracture in the final restoration)
n.b. incisal corners are left unprepared to avoid damage to adjacent teeth
What does retention of the crown rely predominantly on?
Clinical height and minimal taper
How many planes is the labial surface reduced in?
2
What will the technician do if insufficient reduction of the labial surface ?
- Overbulk the labial surface making it unnecessarily bulbous
OR - Make the crown with a thin labial surface and poorer appearance
How much should the cingulum be reduced in an all ceramic crown preparation?
1 mm
Where should the shoulder be placed on the labial and aproximal surfaces be?
Just within the margin (appearance is of importance)
Where should the shoulder be placed on the palatal surface?
Just above gingival level (appearance is not of importance)
Why is a smooth surface needed?
Prevent dragging of the impression and provide a surface that will allow for a close fit for the crown
Why is the tip of the preparation rounded?
To avoid stress concentration for the overlying ceramic material and sharp angles are eliminated to facilitate the impression technique
What do undercuts result in?
Failure of the ceramic crown to seat during the try in stage or its fracture
Whats the function of the rounded shoulder in the preparation?
Provides marginal integrity and structural durability
