TRY-IN PROCEDURE FOR CROWNS- power point

TRY
TRY-
-IN PROCEDURE FOR CROWNS
IN PROCEDURE FOR CROWNS


A.Checking the crown on the die:


We must check the fit of the restoration on the cast model before trying it in the patient
mouth:

1.Marginal fit.
2.Esthetics and articulation can be anticipated prior to try in.
3.Fitness of the crown surface for defects and the die for damage, preferably with a good
light and under magnification.
4.Detecting these problems before try-in will allow you either to address the problem
yourself or to negotiate with your laboratory from a position of strength. It is surprising
how often clear ledges or deficiencies can be detected at this stage.
5.Subsequent stages then rely on the crown being checked in the mouth and then often
back on the die again when there is a problem with the fit.



A.
A.Seating the crown:
Seating the crown:


Having checked the crown on
Having checked the crown on
the patient mouth:
the patient mouth:

1.
1.Any temporary restoration
Any temporary restoration
is removed and the
is removed and the
preparation is carefully
preparation is carefully
cleaned of all residues of
cleaned of all residues of
temporary cement,
temporary cement,
especially in retention
especially in retention
grooves.
grooves.
2.
2.The try
The try-
-in procedure can
in procedure can
normally be accomplished
normally be accomplished
without the need for local
without the need for local
anesthetic.
anesthetic.
3.
3.The crown should be tried
The crown should be tried
in without forcing it onto
in without forcing it onto
its preparation.
its preparation.



The frailer to seat because of reasons localize problems:
The frailer to seat because of reasons localize problems:

a.
a.First, ensure there is no retained temporary cement or trapped gingival tissue.
First, ensure there is no retained temporary cement or trapped gingival tissue.
b.
b.Then check and adjust tight proximal contacts as these often prevent seating.
Then check and adjust tight proximal contacts as these often prevent seating.
c.
c.Check the original cast for damage to the stone in these contact areas.
Check the original cast for damage to the stone in these contact areas.
d.
d.Then re
Then re-
-check the crown for the most obvious laboratory errors, including casting
check the crown for the most obvious laboratory errors, including casting
blebs, damaged or chipped dies or grossly overextended margins.
blebs, damaged or chipped dies or grossly overextended margins.
e.
e.Over
Over-
-extended margins should be adjusted from the axial surface, not from
extended margins should be adjusted from the axial surface, not from
underneath by using bite
underneath by using bite-
-wing radiograph.
wing radiograph.
f.
f.Where the crown still does not seat burnish marks on the internal walls of a
Where the crown still does not seat burnish marks on the internal walls of a
sandblasted metal crown may indicate where it is binding.
sandblasted metal crown may indicate where it is binding.



Error Cause Treatment
Tight proximal contacts Imprecise die location or abrasion of
the adjacent stone contact points
Check for displacement of the dies
contacts the adjacent stone contact
points when the crown is seated on
the working cast. Identify tight
contact by interposing articulating
paper, grind and polish
Casting blebs on fit surface Air bubbles trapped during
investment
Identify under magnification and fit
surface remove with small round bur
Over-extended
crown margins
Poor impression, poor die trimming
surplus untrimmed wax or porcelain
Trim from axial surface and polish—
consider returning crown to lab
Under-extended
crown margins
Poor impression, poor die trimming,
difficulty identifying finish line
If under-extension obvious and
impression satisfactory have crown
remade. Alternatively retake
impression
Damaged dies Finish line chipped because of careless
handling or abraded when casting
reseated with blebs or overextended
margins
Always try and determine why the die
is damaged. If the crown does not fit
after adjusting blebs or over-extended
margins return it to laboratory
No die spacer (Space needed to
accommodate cement lute)
Technician not aware of technique or
forgot to apply
Lack of spacer results in a tightly
fitting crown which may not seat
during try in and may ‘lift’ further
after cementation

Assessment of the seated crown:
Assessment of the seated crown:


Assessment of the seated crown:
Assessment of the seated crown:

1.Proximal contacts:The tightness of proximal contacts can be tested with dental floss
and should offer some resistance but not make its passage too difficult. If these are too
tight they can be ground a little at a time and polished.
2.Assessment of marginal fit:A combination of clinical experience and empirical data
suggest a marginal opening of 100 .m2is at the borderline of acceptability,ill-fitting
margins will render the tooth more susceptible to cement dissolution, plaque retention
and recurrent caries. Defective sub-gingival margins compromise gingival health by an
alteration in local bacteria.



Assessment of the seated crown:
Assessment of the seated crown:

1.Assessment of esthetics:The minimal adjustment to crown may effected on shape and
shade,so that the crown can be glazed when you are patient agree with the final
appearance.
2.Assessment of the occlusion:The occlusion is the last assessment to make, but there is
no point thinking about making any adjustment to the occlusal surface until the crown is
finally seated.Posterior teeth, both restoration and adjacent teeth should hold shim
stock firmly in the intercuspal position(ICP).
3.Finishing and polishing:The final stage prior to cementation is polishing. A rough
surface, especially in porcelain, will rapidly wear the opposing tooth6 and so it is very
important to use a sequence of abrasives designed for the material in question to
achieve a smooth surface.Alternatively, a metal ceramic crown can be reglazed.



CEMENTS:

Whenthefitofthecrownisconsideredsatisfactoryandalladjustmentshavebeenmade,thecrowncanbecemented.Thereareessentiallythreetypesofhardcement:conventional,resinorahybridofthetwo.Conventionalcements(egzincphosphate,zincpolycarboxylateandglassionomer)relyonanacid-basereactionresultingintheformationofaninsolublesalt(thecement)andwater.Resincementssetbypolymerisation.
Themechanismsbywhichcementssecurerestorationtopreparedtoothincludenon-
adhesiveluting,micro-mechanicalbondingandmolecularadhesion.


Resincements:

Resincementsarecompositescomposedofaresinmatrix,
egbis-GMAorurethanedimethacrylate,andafilleroffineinorganicparticles.Theyhavebeenavailableasdirectfillingmaterialssincetheearly1950s,butitwasnotuntiltheearly1970sthatacompositeresinwasintroducedforcrownandibridgeicementation.


Advantages:

• Good compressive and tensile strengths.

• High tensile strength (relative to conventional cements).

• Resistant to water dissolution.

• Relatively resistant to acid dissolution.

• Can enhance strength of ceramic restoration if bond obtained.

Disadvantages:

• Film thickness varies substantially between materials.

• Excess material extruded at margin may be difficult to remove especially proximally.

Recommendations:

• Must be used with or incorporate an effective dentine bonding agent.

• Material of choice for porcelain veneers, ceramic onlays and resin bonded ceramic crowns

• May be used to improve retention where preparation geometry sub-optimal, but clinical
studies needed to determine long-term success.


Thank you