posterior full coverage crowns Flashcards
How do PFMs provide support and retention for RPDs?
1. Metal occlusal and lingual for support and to avoid damage
2. Lingual metal vertical walls are milled for a single path insertion
3. Cervical shoulder on lingual surface for rest seat and tooth borne support
4. Buccal undercut w porcelain for clasp retention
What is the rationale for provision of posterior crowns?
1. Restore function
2. Restore aesthetics (maxillary premolars)
Restore structural integrity and resist fracture
Integrate w other prosthesis
What is the problem w root treated teeth?
Weakened tooth due to access cavity prep
Loss of structural integrity- loss of roof of pulp chamber
Loss of dentine elasticity (loss of collagen making it brittle)
How do you treat a compromised tooth?
May need cuspal protection if-
-loss of marginal ridges
-loss of substantial tooth structure inc. cusps
-large restoration inv. above
Adhesive direct composite
Adhesive indirect resin bonded
Cusp coverage cast
Full coverage
What are design considerations?
Disease status
Restorative status
Retention and resistance form
Occlusal considerations
Position in arch
Aesthetics
Adjacent teeth
Optimal materials
How do crowns compromise pulpal health?
Aggressive insult to tooth, dentine and odontoblasts
Thermal damage
LA
Desiccation
Bacterial contamination
What challenges are dentine tubules exposed to during prep?
Desiccation
Thermal
Chemical
Osmotic
Bacterial toxins
What are the prep principles of posterior crowns?
Preserve tooth structure
Retention (prevents dislodgement in AXIAL direction)
Resistance (prevents dislodgement from LATERAL LOAD)
Structural durability
Marginal integrity
What are key concepts of a good tooth prep?
Well defined and finished
Clear finish line visible
Ceramic margins- butt-joint rounded shoulder
Metal margins- chamfer
All prep line and point angles- best rounded
How do you prep for an FGC?
Conservative
Thin layer of gold (so usually mandibular posteriors or maxillary second molars)
Can be adjusted and polished intra orally after cementation
What are the types of gold alloys for crowns?
Type I—>IV= soft—>extra hard
TYPE I- can stand up to biting forces but can be burnished against margins
TYPE II- can stand up in small, multiple surface inlays not inc. buccal/lingual
TYPE III*- gold 75%, silver 10%, copper 10%, palladium 3%, zinc 2%
TYPE IV- for some RPD frameworks but not in fixed
*most commonly used
How do you prep for a PFM?
Metal core and ceramic veneer
Deep buccal reduction (1.5mm shoulder)
Shallow palatal (0.7mm chamfer)
Aesthetic porcelain window
Exposed occlusal, proximal, palatal metal (for adjustment/polishing)
What is an all ceramic crown?
High strength ceramic core
Most aesthetic
Low edge strength
Extensive reduction
Intra oral adjustment not possible
CADCAM milled from single block of porcelain (chair side available)
Reduces human error
Standardised restoration shaping processes
Higher and more uniform quality material
Compatible w intra oral scanners
Can use difficult materials eg. Zirconia, titanium
How do you prep for an all ceramic?
Rounded shoulder margin
Occlusal reduction 1.5mm or 2+ in areas of excessive occlusal force
5 degree taper w no undercut providing retention
More extensive taper limited to coronal cusp 1/3
What are the clinical stages of posterior crowns?
Stabilise
Preop assessment
Further investigations
Treatment plan
Informed consent
Tooth build up in necessary and prep
Impressions
Shade selection
Occlusal record
Temporisation
Fabrication (lab stage)
Remove temp crown
Try in definitive crown
Cementation
Occlusal check
Review
