PRS02 - Lecture 2 - Crowns Flashcards
What are Crowns?
A cap that completely covers the tooth
What are Crowns used for? (7)
Severely broken down tooth
Root filled tooth (↑ prognosis)
Support bridges and partial denture (abutments)
Tooth wear
Change appearance (i.e. discoloration)
Change occlusion
Hypoplastic conditions
What are the 3 different types of Crowns?
Full gold crowns
↓ destructive (margins – 0.5-1mm)
↑ compressive strength (used posteriorly)
Poor aesthetics
Malleable (easily shaped)
All ceramic crowns
↑ destructive (margins – 1-1.5mm)
Good aesthetics (tooth colour – used anterior and posteriorly)
Expensive
Metal-ceramic crowns
Combinations of properties of metal and ceramic crowns.
Good aesthetics (visible portion = ceramic)
Why are metal ceramic crowns better than full ceramic crown? (3)
↑ Strength
↓ Invasive (palatal + lingual)
Adaptability – can be incorporated into a bridge (metal supports pontic areas -> replace missing teeth)
Explain why the verbal history is important when making a crown (3)
Medical History (1)
Allergies (i.e. alginate used for impression taking)
Intra-oral Examination -> periodontal health.(2)
Inflamed gingiva will be replicated on the impression.
If treated after crown is fitted -> exposure of the cervical part of the crown (usually covered by gingival sulcus).
Social History (2)
Determine patients motivation for oral health
Availability for multiple appointments.
Describe the process of Tooth Preparation (10)
1) Patient needs to consent -> treatment, LA, complications.
2) Prepare 2 putty matrices: one to monitor reduction depth + other to make temporary crown.
3) Administer local anaesthetic.
4) There are 2 planes of reduction:
Plane 1 - extends parallel to long axis of tooth from cervical margin -> removes undercut.
Plane 2 – follows contour of the tooth.
5) Reduction depths depends on material being used – for example:
Full gold crown -> 1mm (O) + 0.5-1mm (margin) = chamfer finish line (501 - round)
All ceramic crown -> 1.5-2mm (O) + 1-1.5mm (margin) = shoulder finish line (555 - flat)
Metal-ceramic crown -> 1.5-2mm (O) + 1-1.5mm (buccal) + 0.5-1mm (palatal)
6) Ideal taper is 6o – however this is hard to achieve thus 10-20o is acceptable.
7) Minimum height for final preparation needs to be: 3mm (premolars + anteriors) + 4mm (molars)
If it is less than this – post, core, additional grooves maybe required -> ↑ resistance.
8) Anterior teeth – cingulum is reduced using a rugby ball bur.
9) Finish lines need to be located -> supragingivally:
Advantages:
Allows access for -> preparation, finishing of margins, visibility.
Easy impression taking
Prevent iatrogenic damage (-> gingiva)
Disadvantages:
May not be sufficient crown height for retention/resistance.
Crown margin may be exposed on anterior teeth -> ↓ aesthetics
Acceptable to go 0.5mm subgingival for anterior.
10) Smooth all surface using a white stone making it even -> ↑ fit of the crown + remove lipping off margins (555)
What are the 4 common errors of tooth preparation?
Occlusal anatomy too flat
Margins too high -> bottom of the crown will be seen ↓ aesthetics
Lipping after using 555 (rounded) burr
Sharp uneven margins
What is the function of temporary and provisional crowns? (4)
Protect prepared dentine + pulp + margin
Prevent sensitivity
Avoid tilting, drifting, over-eruption.
As a guide to ensure the tooth is prepped correctly for definitive crown.
Describe the process of making Temporary Crowns (10)
1) Made from higher cold cure acrylics (i.e. bis-acryl composite, trim or pro-temp)
2) Use one of the putty matrices – ensuring it fits well and remove easily.
3) Cover prepped tooth with Vaseline + undercuts with red wax.
4) Place temporary material -> matrix (ensure no air bubbles)
5) Insert matrix onto -> prepped tooth
6) Remove the matrix + temporary crown before the material sets completely
7) Remove excess material using soflex disc+ polish.
8) Check the fit and occlusion.
9) Cementation requires balance between -> retention + ease of removal.
10) Examples of temporary cements include: ZOE or zinc polycarboxylate (poly-F)
What type of temporary cement should be avoided when the definitive cement is composite resin?
Cement containing eugenol (i.e. ZOE).
How do Provisional Crowns differ from Temporary Crowns?
1) Made from heat cured acrylic in the lab.
2) ↑ Strength of material
3) Stays on for much longer
4) Still requires a temporary crown to be placed.
5) Has diagnostic function: (6)
Appearance
Speech
Anterior guidance
Occlusion changes
Periodontal health
Sufficient tooth reduction
6) Has prognosis function: (4)
Implants
After recent extraction
RCT
Periodontal treatment
Describe the final placement of the definitive crown (9)
1) Done on the second visit after the definitive crown has been made by the lab.
2) Check the definitive crown:
Good marginal fit (william’s probe) – debris from temp cement -> ↑ occlusion.
Correct seating
Occlusion (articulating paper or occlude)
3) Clean fit surface from -> polish, wax, saliva, debris
4) Wash tooth with water + gently dry.
5) Clinician + patient need to be happy -> cement definitive crown using:
Zinc phosphate (↑ working time)
Resin based cements (does not work with eugenol temp cements)
6) Mix cement + place -> fit surface of crown.
7) Press the definitive crown down firmly (with constant pressure)
8) Once set – remove excess cement using floss/hand scaler.
9) Recall after several weeks to review:
Margins
Gingival health
Integrity of crown
What are the 5 principles that guide tooth preparation for a crown?
1) Preserve tooth structure – over prepared teeth -> pulp damage
Temperature rises of 5oC -> pulp death (15% chance)
Use water-air coolant w/ bur
High quality sharp burs
Light pressure (↓ pressure)
↓ Pulpal protection provided by dentine
↑ risk in younger population -> larger pulp
Decreases with age due to secondary dentine formation
2) Retention and resistance - achieved through:
Tapering (6o ideally – but 10-20o acceptable)
Height of the teeth should be at least 3mm (premolars) and 4mm (posteriors)
3) Structural durability (ability of tooth to withstand destruction due to external forces)
Uniform reduction should be achieved.
Line angle rounding for ceramic crowns (reduces stress)
4) Marginal integrity
Closely adapt margins to finish lines of preparation.
Finish lines should be supragingival -> allow access for prepration, clear visibility, easy impression taking, prevent iatrogenic damage (to gingiva)
However this could lead to exposure of the tooth-crown interface (so 0.5mm subgingivally is acceptable).
5) Preservation of periodontium
Use rubber dam (protects soft tissues)
Matrix band (protects adjacent teeth
Coolant used to protect the pulp.
