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
16
Q
Explain the Hall technique
A
- quick and non-invasive method
- crown seated over tooth without caries removal or prep and no local anaesthesia
- manipulates the plaque environment by sealing it into tooth, separating it from substrates it’d normally recieve
- plaque may continue to recieve some nutrition from dentinal tubule perfusion but if carious lesions sealed effectively, good evidence that bacterial profile in cariogenic biofilm changes to a less cariogenic community and lesion progress halts
17
Q
Steps of Hall technique
A
- assess the shape of primary molar and occlusion
- protect the airway
- size a crown
- load the crown with cement
- fit the crown - first stage seating
- wipe the excess away
- check fit and second stage seating
- final clearance of cement and discharge
18
Q
How to use separators at tight contact points?
A
- thread 2 long pieces of floss through an orthodontic separator
- pull taught, stretching separator
- floss half of sep through contact point
- OR floss through contact point, pull sep under contact point and then pull half through contact point
- leave for 15 mins - 2 weeks
19
Q
Explain modified Hall prep
A
- sometimes the shape of the cavity means there is insufficient space for the crown and yet separators won’t work
- lead to use skills of prep from OAP technique to adjust interproximal surface with high speed but but allow crown to seat
20
Q
Tips for modified Hall prep
A
- don’t crown opposing teeth at the same visit as it increases vertical dimesnion too much (need occlusion to settle) and not enough interproximal space
- have a tidy clinic, everything to hand and be slick
- sell them to patients and parents
- know evidence - explain why it’s good
21
Q
Compare key differences in OAP and Hall technique
A
- caries removal vs no caries removal
- tooth tissue removal vs none
- PFMC modification vs none
- LA required - none
- no increase in vertical dimension - increased vertical dimension (resolves naturally)
22
Q
What would be considered a poorly fitting crowns?
A
- occlusion altered by more than 2mm
- crown margins supragingival
- occlusal interferance
- impeding eruption
23
Q
How to fix a poorly fitting PFMC
A
- needs to be sectioned with a high speed bur and removed
- cut through buccal surface completely and onto occlusal surface
- peel open with spoon excavator
- attach airway protection and remove crown
24
Q
How to follow up on PFMC?
A
- mobility of PFMC (poor cementation, incorrect size)
- mobility of tooth (natural exfoliation, pathological root resorption)
- sinus/interradicular pathology/periapical pathology
- impaction of perm dentition
- occlusal wear through PFMC
25
Action taken if pathology of crown is wrong
extract tooth
26
Action taken if mobility due to exfoliation of crown is wrong
await exfoliation
27
Action taken if mobility due to poor fit of crown is wrong
remove crown and replace
28
Action taken if impaction of crown is wrong
- disimpact with seps
- remove crown until eruption complete
- extract crowned tooth
29
Action taken if occlusal wearof crown is wrong
- seal with composite
- remove and replace
