Preformed metal crowns

Question 1

What is another name for preformed metal crowns

Answer 1

Stainless steel crowns (but they are actually made of nickel chrome)

Question 2

What are preformed metal crowns?

Answer 2

For children (deciduous and permanent teeth)
No impressions, no lab stage
Pre-contoured and pre-crimped

Question 3

How many sizes (3M ESPE)

Answer 3

6 different sizes per tooth
Sizes 2-7
Size located on buccal aspect

Question 4

When to use PMC on primary teeth

Answer 4

Teeth with large or multi-surface carious lesions (most common)
Pulp treated teeth (full seal, big hole, brittle because no fluid in dentinal tubules)
Trauma (rare: big fractures)
Enamel and dentine defects
Abutment for crown-loop space maintainer
Infraoccluded teeth (sinking) to maintain mesial/ distal space
Teeth with severe wear (if you can get crown on)

Question 5

Abutment

Answer 5

Structure built to support the lateral pressure of an arch or span

Question 6

When not to use PMC on primary teeth

Answer 6

Unrestorable tooth (too broken down or dead)
Failed pulp therapy
Soon to exfoliate
Pre-cooperative
Severe space loss
Poor motivation?
Multiple grossly carious teeth

Question 7

When to use PMC on permanent teeth

Answer 7

Hypomineralised molars
Amelo- and dentinogenesis
Temporary restoration
Severe erosion
To keep space for ortho

Question 8

Advantages of PMCs

Answer 8

Straightforward technique
Quick and cheap
Evidence of excellent longevity, low failure rates, compare well with other materials
Failure, if occurs, if easily corrected

Question 9

Disadvantages of PMCs

Answer 9

Poor aesthetics
May impede eruption of adjacent teeth if too big
May cause gingival inflammation if cement not removed completely
Theoretical nickel allergy risk

Question 10

Evidence for PMCs: Einwag and Dunninger (1996)

LEARN ONE

Answer 10

Longitudinal study of 66 pxs

• PMC paired with amalgam restorations on contralateral teeth
• 4.5 year survival rate was >90% for PMCs but <40% for amalgam
• only 6% of PMCs required replacement, but 58% of amalgams

Question 11

Evidence for PMCs: Randall, Vrijhoef and Wilson (2000)

LEARN ONE

Answer 11

SR, 10 studies from 1975-1997, duration 1.6-10 years
Failure rate 1.9-30.3% for PMCs vs 11.6-88.7% for amalgam
PMCs had greater longevity, reduced retreatment need
All studies favoured treatment with PMCs

Question 12

Barriers

Answer 12

Lack of training, esp. undergrad
Reluctance to administer LA to children
Difficulties in prep in young children
Perceived reaction by parents

Question 13

Selling them

Answer 13

Parent's often don't like the look of them
Children love them
-princess/ Barbie teeth
-tooth jewellery
-pirate tooth
-iron man tooth
-bling

Question 14

Things to tell px/ parent

Answer 14

They stay on until tooth falls out
Need to be brushed like normal teeth
Glue tastes like lemons/ salt and vinegar crisps
They feel a bit funny to bite on to start with

Question 15

Conventional technique: you will need

Answer 15

Pointy bur (Xmas tree)
Whole box of crowns
Topical/ LA
Diamond burs 
Cement
Dental tape - knotted
Maybe:
-rubber dam
-crown scissors
-crimping pliers
-ortho band seater

Question 16

Conventional technique: airway protection

Answer 16

Child sitting slightly upright
Rubber dam
Gauze
Adhesive handle

Question 17

Conventional technique

Answer 17

1. Topical / LA
2. Remove caries
3. Pulpotomy/ pulpectomy if needed
4. Prepare tooth
5. Select crown
6. Adapt crown or modeify prep
7. Cementation

Question 18

Adapt crown/ modify prep

Answer 18

Coping with:
poorly adapted crown margins - crimp
space loss - modify shape or use crown from opposite side and arch
gingival blanching - will resolve
occlusal discrepancies - will resolve

Question 19

Cementation

Answer 19

Glass ionomer (Aquacem)
Clotted cream consistency
Enough to fill crown
Remove excess with gauze and knotted floss
Apply crown from lingual to buccal

Question 20

The Hall technique

Answer 20

No tooth prep
No local analgesia
No try-in
Not for extensively carious teeth
Caries not removed, but sealed into tooth to isolate from mouth
Tooth asymptomatic
Child not at risk of endocarditis
Pre-op radiograph
\+/- separators
Airway protection
Occlusion

Question 21

Innes N, Evans DJP, Stirrups DR (2007)

Answer 21

Split mouth RCT
132 children, aged 3-10
17 GDPs in Tayside, Scotland
Hall technique vs normal 
Clinical and radiographic follow-up
Hugely in favour of Hall technique
5 year results: Major failures 3% Hall, 16.5% controls, minor failure 5% Hall, 42% controls

Question 22

Technique for Hall

Answer 22

If necessary place separators 1 week before
Topical (optional)
Choose crown
Airway protection
Try crown to contact point only
Fill crown with GIC
Push down as far as possible
Allow child to bite on band seater/ cotton wool roll
Remove excess cement with wet gauze
Get child to bite together
Remove further cement with gauze, excavator or probe
Knotted floss between contact points

Question 23

Px instructions Hall technique

Answer 23

May be a little uncomfortable afterwards
Advice about analgesia
Occlusion will be propped open but will settle