Cementation of FGC

Cementation
Dr Adam Husein
2008

Lecture Outline
• Pre-cementation
• Removal of temporary crown
• Try-in
• Cements
• Review or recall appointments

Cementation Procedures
KEY ISSUES
• Inspection of restoration
• Status of temporary
restoration
• Tooth response
• Trial fitting
• Occlusal adjustments
• Selection of luting agent
• Familiarity with luting agent
• Cementation technique
• Polishing and Finishing

Pre-insertion Inspection of
Restoration
What to look for
• Have lab instructions been followed
• Is the design of restoration as prescribed
• Shape of restoration/ marginal fit/ stability on die
• Flaws in restoration (chip, crack, voids, perforations)
• Scratches on die, damage to die

Pre-cementation
• Ensure the correct crown
• Check on the model
– No distortion of the model
–Good fit
–Margins
– Stability
– Contact points
– Polish
• Disinfect with chlorhexidine

Pre-cementation
• In the mouth
–Temporary crown
–Symptoms
– Remove temporary crown
• Carver
• Crown removal or puller
– Check the prep
– Remove temporary cement
• Pumice and brush, ultrasonic scaler

Consequences of a Lost Temporary
Restoration
• Tooth sensitivity
• Bacterial ingress/ pulpitis
• Proximal tooth drift
• Over-eruption prepared tooth
• Eruption of opposing tooth
• Compromised appearance
• Prep prone to damage

Assessing Status of Temporary
Restoration
• Tooth sensitivity (post-prep, lingering, intermittent)
• Dislodgement (recent, long-term)
• Breakage
• Comfort
• Function, aesthetics
• Gingival response

Temporary Restoration Removal
• ? Place LA
• Spoon excavator
• Crown puller
• Section off
• Ultrasonic
• Patient’s nasogastric passage must be protected

Release
weight
Push down
weight
Berekally, 2003

Temporary Cement Removal
• Instrument (carver, excavator tip, scaler)
• Cotton pledget soaked in Chlorhexidine solution
• Ultrasonic tip
* If tooth is sensitive LA may be required

Trial Insertion
• Hold restoration in dry gloves
• Turn patients head to side of insertion
• Have large suction on standby
• Tight proximal contacts may prevent
seating of restoration
• Undercuts and very parallel prep walls
may prevent seating
• Flaws in restoration fitting surface may
prevent seating
• Inaccurate impression/die may have led to
construction of a tight or loose fitting
restoration

Safety Precautions
• Inhaled
– Serious medical emergency
– The patient should be rapidly inverted and
encouraged to cough
• If unsuccessful – hospital
• Swallowed
– Less dangerous
– Usually need radiograph
– Advise patient to recover the crown
• Sieve and running water (Smith, 2000)

Safety Precautions
• Dry gloves
• Isolate the tooth
• Keep a finger on the crown all the time
• High volume suction ready
• Gauze behind the crown
• Treat patient in upright position
• Rubber dam – may not be practical

Pre-cementation
• Try in the crown
–Fit
– Contact points
– Stability
–Resistance
–Margins
–Occlusion
• Ensure all fine before cementing
• No adjustment post cementation

Try-in
• Marginal fit
• Retention
• Contact Points and Axial Contours
• Shade
• Occlusion

Marginal fit
• Eye and sharp probe
• Gaps
– A uniform gap all the way round indicates that
the crown is not fully seated
• Retained temporary cement
• Trapped gingival tissue
• Contact points
• Overhang (positive ledge)
• Deficiencies (negative ledge)

Checking contact points
Rub pencil marks on teeth adjacent to crown. If the crown does not seat
fully the dark pencil marks will be seen at the points of binding on the
crown’s proximal surfaces. On removal these points are adjusted and
The trial seating process repeated until fit is accurate

Adjustment and polish

Artispot, a red vegetable dye in acetone can be used to mark the fitting surface of crowns
binding spots are coincident with spots of exposed alloy surface. The corresponding
tooth surface is also marked with red dye. Usually the crown is altered first. But if there
Is a risk of perforation it may be necessary to minimally alter the tooth

GC Fit Checker is a silicone material (mixed via a base = catalyst pastes) and applied
to the restoration fitting surface and seated on the tooth. After 60 seconds the crown
can be removed and high spots may be seen via exposed alloy. These spots are
marked with a pencil, the silicone removed and then adjustments carried out with a
small abrasive stone.

Caliper – measuring crown thickness

Retention
• A crown should not feel tight. Tight crowns may
be more difficult to cement, resulting in an open
margin
• Tilting
– Unretentive design
– Excessive use of die relief/spacer
• Pivot
– Not fully seated
– Contact points
– High spots on the fit surface

Contact Points and Axial Contours
• Dental floss
– Neither too tight nor too slack
• Buccal and lingual contours – not too bulbous
• Marginal area – in line with the tooth surface
– Reduce plaque retention
– Natural appearance
• Remove/add materials and repolishing/glazing

Shade
• Too light (too low chroma) – can be
darkened by adding stain and refiring
– Stain can also be used to add missing
characteristics such as crack lines or mottled
areas
• Wrong basic hue or too dark chroma or
wrong colour of the opaque core material
or the dentine porcelain – not possible to
correct – redo

Occlusion
• Reorganized
• Confirmative
–ICP
– Lateral, protrusive and retrusive
• Articulating paper
• Occlusal wax
• Shimstock or mylar matrix strip
• Remove/add material
• Repolish/glaze

Problems and Solutions at Trial Insertion
PROBLEM
Cannot seat crown
Occlusal contact high
Occlusal deficiency
Poor fit (margins, rocking)
Unsatisfactory shade
SOLUTIONS
Adjust proximal contacts
Alter taper of prep
Alter fitting surface of
restoration
New impression/ remake
Adjust with abrasive stones
Addition of resin/porcelain
Alloy augmentation not possible
Retake impression/remake
Remake restoration
Remake without impression
Alter shade in lab with low
fusing
ceramic addition
Alter shade with indirect resin

Choice of Cements
• Temporary Cement
• Zinc phosphate
• Zinc Polycarboxylate
• Glass Ionomer Cement
• Resin-Modified GIC
• Compomer (Polyacid-modified resin)
• Resin Cement

Zinc Phosphate Cement
• Good film thickness (< 25µ)
• Poor strength
• High solubility
• Nil chemical adhesion
• Easy to use
• Minimal sensitivity

Poly-F

Polycarboxylate Cements
• Adhesion to enamel/dentine
• Well tolerated by pulp
• Mix is sticky
• Contains fluoride (SnF 2
)
• ? Caries resistance
• ? Temporary cement if more
liquid added

Temporary Cements

Glass Ionomer Luting Cement

GIC
• PBM
• All metal crown, inlay and onlay
• Metal post
• Unsuitable for
– Non metal post
– All ceramic full and partial veneers

Resin-Modified GIC’s
•Hand mixed
•Chemical setting
•Fluoride release
•Low solubility
•? Linear expansion via water uptake

Resin Cements

•Non metal post
•All ceramic crown
•Veneers
•Maryland bridges
Resin Cement

Compomer Cements
POLYACID-MODIFIED RESIN CEMENTS

•Strontium-alumino-silicate glass
• ? Fluoride
•Opaque powder
•Translucent powder
•Phosphate-modified polymerisable monomers
•Carboxylic acid-modified macromonomers
•Reactive diluent
•Polymerisation initiator
•Stabiliser

Cementation Procedures
• LA if sensitive teeth
• Temporary restoration removal
• Temporary cement removal
• Trial insertion of restoration
• Adjustments
• Tooth isolation
• Tooth conditioning
• Sandblast/rocatec
• Cementation of restoration

Cementation
• Mix cement to correct consistency
• Coat internal surface of the crown
– Use plastic instrument to pick up the cement
• Seat the restoration correctly
– This is important
• Place a cotton roll for patient to bite on it to ensure
complete seating, then get patient to bite into centric
occlusion
• Check seating with explorer
• Remove excess cement when set
– Use carver and dental floss (inter-proximally)
• Check occlusion before discharging the patient

Cementation
Wait for the cement to set before
removing excess

Plastic instrument – cement pick up

Review
• Initial review – a week post insertion
–Signs and symptoms
– Occlusion
– Excess cement – gingival sulcus and interproximal
– Oral hygiene – plaque accumulation
• If any adjustments done – need further
review
• Six monthly or more – caries and PD
• Keep models as required

Prognosis
• Proven track record
– All metal
– PBM
• Relatively new
– All ceramic
–CR
• Good prognosis
– Good plaque control
– Motivation
– Well-designed and well-fabricated prostheses

Prognosis
• A systematic review (Torabinejad et al, 2007)
– Should a tooth be saved through RCT and
restoration, be extracted with no replacement,
FPD or implant-supported single crown
– 143 selected studies
– Success rates for ISCs were higher than for
RCTs and FPDs
– Long-term survival rates for ISCs and RCTs
were similar and superior to those for RPDs

Removal/Re-treatment
• Crown removal
• Sectioning

Shade
• Textbooks
• Terminologies
–Hue
–Chroma
–Value
– Metamerism
• Principles of shade selection
• Commercial shade guides
– Vita Lumin vacuum shade guide
– Vitapan 3D-Master Shade Guide
• Prescription

Conclusion
• A restoration that is cemented, forgotten, and
ignored is likely to fail, regardless of how
skillfully it was designed and executed.
• Restored teeth require more assiduous plaque
removal and maintenance than healthy
unrestored teeth.
• Common complications – caries, periodontal
failure, endodontc failure, loose retainers,
porcelain fracture, and root fracture.

References