FIXED PROS - Principles of Tooth Prep Flashcards
what is an indirect restoration? give 4 examples.
a restoration which is not placed directly into the patients mouth e.g. a crown, veneers, onlays or inlays
why is a crown an indirect restoration?
- take an impression
- produce restoration within the labs
what are 4 cons of indirect restorations?
more appointments
more expensive
more stages involved - time consuming
more professionals involved
why are indirect restorations needed?
aesthetics
comfort
function
stability
what 3 things need to be considered when preparing?
- room needs to be created for the restoration and cement
- needs taper - narrow at the bottom
- consider the path of insertion with proximal contact - ideal to be parallel to taper
what are the 7 principles of preparation?
- preservation of tooth tissue
- protect pulp, periodontium and prevent fracture - retention and resistance
- structural durability
- the material choice
- marginal integrity and position
- biological considerations
- aesthetics
what happens if there isn’t enough space and a crown is placed?
cause pain
opposing tooth or crown may fracture due to forces
complain due to crown being high
what if the tapering leads to a wider top and narrower bottom?
it becomes an undercut
- leaves overhand of tooth tissue
- over prepared
- weakens the tooth risking fracture or pulpal exposure
- crown will not fit properly
describe difference between retention and resistance
retention - prevents movement of vertical forces
resistance - prevents movement of lateral or apical forces
what is retention and resistance influenced by?
the taper, surface area, height and design
the greater the taper, the less the retention and resistance
the larger the surface area and height, the better the retention and resistance
design - grooves and boxes
what is the best degree of taper?
6-12 degree
what bur is used, already possessing the 6 degree angle?
long diamond bur
what is the minimum recommended height for the tooth tissue?
3mm
allows placement of crown without occlusal interference
what are the differences in cement selection?
passive vs active
- can have adhesive properties rather than passive cement
what should be the depth of a groove?
no less than half the burs diameter
what comes under structural durability?
to be able to withstand:
- occlusal forces
- changes in the oral environment
temperature, pH, mastication of food
- minimal maintenance
what are the 4 different materials to choose from?
metal ceramic
gold
non precious metal
all ceramic
why do the margins need to be accurate?
to allow the crown to fit flush onto the tooth
- prevent plaque retentive factors forming
- reduce exposed cement
what are the different types of margin design?
horizontal margin
- shoulder design - metal ceramics crowns
- requires 1.2mm margin width
- chamfer design - gold crowns
- requires 1.5mm margin width
vertical margin
- knife edge
- a thin, fine edge which fades away - metal crowns
what should be regarded in terms of biological consideration?
- preservation of the periodontium
- preservation of the pulp
- biological width
how do you preserve the periodontium?
good oral hygiene
supragingival margins
sufficient marginal reduction
how can the aesthetics of the periodontium be affected?
if there is recession and increased crown height ratio
what is the biological width?
the distance from depth of sulcus to the alveolar crest
why can biological width be difficult to manage when taking impressions and placement?
- may be gingival inflammation
- increase probing depth
- increase chance of attachment loss when extra coronal margins are placed subgingivally
how much can a extra coronal margin increase recession by?
1mm: 2.65x
…/5 teeth can become non-vital following crown preparation
1/5
how do you assess the abutment tooth?
Assessing the abutment tooth
Clinical
Caries
Quality of restoration
Pocketing
Mobility
Occlusion
Radiographs - bone levels, apical status, root form and shape
what is the unit?
a term to indicate the no of pontics or retainers associated with the bridge
also indicates the length of bridge
