USE OF PREFORMED METAL CROWNS IN PAEDIATRIC DENTISTRY

outline preformed metal crowns

• 3M ESPE surgical grade stainless steel primary molar crowns

• 6 different sizes per tooth (sizes 2-7)

• pre-contoured and pre-crimped

when placing a preformed metal crown, where should the text on the crown be

• size and location text should be on the buccal aspect when placed on tooth

how does the text on the PMC come off

via rubbing and toothbrushing overtime

what are indications for the use of PMCs in primary teeth

• teeth with large or multi-surface carious lesions

• pulp treated teeth

• trauma

• enamel and dentine defects

• abutment for crown-loop space maintainer

• infraoccluded teeth to maintain mesial/ distal space

what are infraoccluded teeth

premature stop of eruption so the tooth sits below the occlusal plane compared to adjacent teeth

pulpotomy VS pulpectomy

• pulpotomy = partial

• pulpectomy = complete

what are contraindications for the use of PMCs in primary teeth

• unrestorable tooth

• failed pulp therapy

• soon to exfoliate teeth

• cautions: severe wear/ space loss, pre-cooperative, poor motivation, multiple grossly carious teeth

  • space loss - 1° teeth often have large contact areas so it may be challenging to get a crown to fit

what are indications for the use of PMCs in permanent teeth

• hypomineralised molars e.g. in MIH

• amelogenesis imperfecta

• dentinogenesis imperfecta

• temporary restoration

• severe erosion

what are advantages of PMCs

• straightforward technique

• quick and cheap

• evidence of excellent longevity, low failure rates, compare well with other materials

• failure - if it occurs - is easily corrected

what are disadvantages of PMCs

• poor aesthetics

• may impede eruption of adjacent teeth if too big

• may cause gingival inflammation if cement is not removed completely

• theoretical nickel allergy risk - most modern crowns do not have nickel in them

comment on this PMC

the crown is slightly too big

comment on these PMCs

the erupting 6s will get stuck on the PMCs so they will need to be removed

how are PMCs removed

need to drill them off

evidence for PMCs

Cochrane Review (2015)

• six studies included

• teeth with PMCs were less likely to develop abscesses or cause pain in the long term compared to a conventional restoration

• PMC on teeth with caries/ that have had pulp treatment are likely to reduce the risk of major failure or pain in the long term compared to conventional restorations

what are barriers to placing PMCs in children

• lack of training esp. at undergraduate level

• reluctance to administer LA to children

• difficulties in preparation in young children

how can you sell PMCs to children

• parents often do not like the look of them

• children love them

  • princess/ barbie teeth

  • tooth jewellery

  • pirate tooth

  • iron man tooth

points to inform the patient/ parent about PMCs

• they stay on until the tooth falls out (sometimes reported that the crown feels loose but in reality it is the tooth starting to exfoliate)

• they need to be brushed just like normal teeth

• the glue (glass ionomer) tastes a bit like lemons/ salt and vinegar crisps

• they feel a bit funny to bite on to start with (bigger/ slidey)

parent’s opinion on PMCs

conventional PMC technique: essential materials

• whole box of crowns

• topical/ LA

• diamond burs

• cement

• dental tape - knotted

conventional PMC technique: optional materials

• rubber dam

• crown scissors

• crimping pliers

• orthodontic band seater

what instrument is this

crown scissors (try to use as little as possible)

what instrument is this

orthodontic band seater

what instrument is this

crimping pliers

outline airway protection when placing a PMC

• child sitting slightly upright

• rubber dam

• gauze

• adhesive handle

• elastoplast tape

conventional PMC technique step-by-step

1. topical/ LA

2. remove caries

3. pulpotomy/ pulpectomy if needed

4. AIRWAY PROTECTION

5. prepare tooth

6. select crown

7. adapt crown or modify prep

8. cementation of crown

9. push down as far as possible

10. remove excess cement with wet gauze

11. allow child to bite on band seater/ cotton wool roll

12. remove further cement with gauze, excavator or probe

13. floss contact points with knotted floss

outline how the tooth should be prepared using the conventional PMC technique

1. occlusal reduction: remove about 1mm off occlusal surface following the contours of the tooth

2. mesial and distal reduction: use a pointy bur and remove tooth tissue mesially and distally, leaving no ledges and ensuring they are parallel

mesial/ distal reduction with ledge

finished tooth preparation

how should a PMC be selected

• want it to cover the entire crown of the tooth down to the gingival margin

• best way to try on crown size: roll from lingual to buccal, should click into place

why may a crown need to be modified/ adapted

coping with:

• poorly adapted crown margins » crimp

• space loss » modify shape or use a crown from the opposite side and arch

• gingival blanching » will resolve itself

• occlusal discrepancies » will resolve

outline PMC cementation

• glass ionomer (Aquacem on clinic)

• clotted cream consistency

• enough to fill the crown (there should be excess)

• fit crown on tooth

• remove excess with wet gauze and knotted floss

• get child to bite down on cotton wool until glue has set

outline the history of the Hall Technique

differences between the conventional technique and the Hall Technique

• no tooth preparation

• no local analgesia

• no full try-in (partial try in done)

• caries not removed but sealed into the tooth to isolate it from the mouth

• (?) not for extensively carious teeth

what are indications of the Hall Technique

• tooth has to be asymptomatic

• child not at risk of endocarditis

• pre-operative radiograph

  • must shown no inter-radicular pathology

  • must be a clear band of dentine between caries and pulp

what may be needed more when using a Hall Technique VS conventional

orthodontic separators

evidence for the Hall Technique (Innes, Evans & Stirrups, 2007)

evidence for the Hall Technique (Innes, Evans & Stirrups, 2007)

evidence for the Hall Technique (Innes, Evans & Stirrups, 2007)

what is perforation of PMCs

• if a child has had PMCs on for a long time it can get worn occlusally esp. if it is contacting enamel

• the exposed layer underneath is a layer of glass ionomer

• as long as the perforated area is not sharp or annoying, they can be left on until exfoliation

outline the Hall Technique

1. if necessary place separators 1 week prior (tell patient it will feel like food stuck between teeth)

2. topical anaesthetic (optional)

3. choose crown

4. AIRWAY PROTECTION

5. try crown to contact point only

6. cementation of crown

7. push down as far as possible

8. remove excess cement with wet gauze

9. allow child to bite on band seater/ cotton wool roll

10. remove further cement with gauze, excavator or probe

11. floss contact points with knotted floss

image of band seater being used to fit crown

patient instructions after PMCs

• may be a little uncomfortable afterwards - can be tender around gingivae

  • Calpol/ paracetamol

• advice about analgesia

• occlusion will be propped open but will settle

• gingival blanching is normal and should resolve itself in 3-4h

image showing gingival blanching after PMC placement