30. Preformed Metal Crowns Flashcards
1
Q
What is a preformed metal crown?
A
- used to restore primary and perm teeth in children and adolescents
- where intracoronal restorations would fail
2
Q
Composition of preformed metal crowns
A
- 76% nickel
- 15% chromium
- 8% iron
- 0.08% carbon
- 0.35% mangenese
- 0.2% silicon
3
Q
Indications for preformed metal crowns
A
- restorations of primary molars with caries on 2 or more surfaces
- those with caries on 1 surface but no coop for composite
- those that have undergone pulpotomy or pulpectomy
- those affected by developmental problems (hypoplasia, AI)
- those affected by tooth surface loss
- or perm molars with post-eruptive breakdown
4
Q
Contraindications for preformed metal crowns
A
- teeth with irreversible pulpitis
- teeth with interradicular or periapical infection
- teeth where clear dentine barrier between caries and pulp can’t be seen
- teeth with less than 2/3 root length
- teeth with insufficient coronal tissue to retain PFMC
- patient at risk of infection (immunosuppressed, bacterial endocarditis)
- patient/parent unhappy with anaesthetics
5
Q
3 PFMC techniques
A
- OAP
- Hall
- modified Hall
6
Q
What does OAP technique stand for?
A
occlusal approximal peripheral
7
Q
What happens in OAP technique?
A
- Occlusal retention - 1.5mm, maintain occlusal contour
- Approximal reduction - 10-15 degrees angulation, no shoulder
- Peripheral reduction - increase area of occlusal table, bevel to remove sharp angles
8
Q
Features of OAP technique
A
- restores function
- maintain form and tooth tissue
- no pulp damage
- occlusal reduction 1-1.5 mm
- approximal reduction 10-15 degrees, no shoulder
- peripheral reduction - bevel edges
- no preparation of buccal or lingual surfaces
- smooth edges
9
Q
How to choose the correct crown?
A
- sizes 2-7
- measure mesio-distal size of tooth - use perio probe
- don’t encroach on distal space behind an E especially if 6 is unerupted
- try the crown on tooth - should cover tooth completely, margins in gingival crevice
- but should also engage with buccal and lingual undercuts to aid retention
10
Q
How to protect airway in PFMC
A
- before fitting ensure no danger of child inhaling or swallowing loose crown
- sit child upright (but does compromise working position for uppers) - ideal in lower teeth, just move round
- gauze swab square placed between tongue and tooth where crown is being fitted
- piece of Elastoplast tape on crown
- Micro-Stix applicator attached to crown
11
Q
Explain crown trimming
A
- margins of crown must be in gingival crevice
- in excessive gingival blanching, remove crwon with excavator
- trim with Bee Bee scissors or polishing stone
- follow the contour already there
- keep to minimum
- loss of cervical construction will occur
- polish rough areas with stone/Sof-lex
- re-contour with contouring pliers to re-enter gingival margin and engage undercut
12
Q
You engage the undercut for a …
A
snap fit
13
Q
Explain cementation
A
- GIC or polycarboxylate cement
- mix enough cement to fill crown
- should flow off spatula - consistency of PVA glue
- wash and dry tooth
- seat crown from lingual to buccal
- patient to bite on cotton wool roll or bite stick
- remove excess using spoon excavator and knotted floss interdentally if needed
14
Q
How to check the occlusion
A
- ensure crown is fully seated with margins sitting subgingivally
- ensure marginal ridges are level
- children can tolerate 1-2 mm of increased opening - settles over 2-3 weeks
15
Q
Issues with placing PFMC
A
- can be difficult to fit using conventional approach as it needs injections and extensive tooth prep, high level of child coop
- high risk of damaging adjacent first perm molar when on 5s
