FIXED PROSTHETICS
1. In the appointment for bridge preparation, what else do you do in the same
appointment?
Take an impression of the unprepared teeth or of the wax up in a silicone putty or
alginate and save it for later. Before making the preparation, replace or adjust any
damaged restoration.
LA, Make the preparation, check parallelism, place retraction cords impregnated
with epinephrine or aluminium chloride solution, and take impressions using an
elastomeric material, make an occlusal registration (blue-mousse or jet bite).
Make the temporary bridge using the impression taken before of the wax up or
unprepared teeth, use a bis – acryl resin (luxatemp) and seat it over the
preparation. After initial set, remove it, let it finish curing, trim it, polish it and
cement it with temporary cement (temp bond). Take the shade, make the lab sheet
and send it off and give another appointment to the patient.
2. How do you prepare a temporary bridge?
Using a good alginate impression material or PVS putty of the unprepared teeth,
place Bis acryl composite resin material such as luxatemp or protemp. Place it on
the prepared teeth, when the initial set has been reached the impression is removed
and the provisional left to finish curing, remove it, trim it, check occlusion and
polish it.
It can also be done with an over-impression taken of the diagnostic cast
(diagnostic waxing). Placing resin in the over-impression and then seating the cast
into the over-impression. After it has cured it is removed and trimmed, the
occlusion adjusted and polished (useful for multiple crowns).
Prefabricated provisional restorations can be use as well (prefabricated
polycarbonate crowns, preformed anatomic metal crown). These can be trimmed
to fit, lined with resin and joined together.
3. How is it prepared in the lab?
Advisable if preparing multiple crowns or if temporary crown needs to last for
several months, preferred for its accuracy, protection to the pulp.
By taking an over-impression on the diagnostic cast (diagnostic waxing). An
acrylic template can also be used, shaped on a diagnostic cast, using a vacuum
forming machine. Then, filled with resin and after it has finish curing, the
provisional is removed, trimmed and polished. Any defects on the tooth should be
filled and smooth over with red utility wax, before the over-impression is taken.
The provisional is relined and adjusted at the chairside.
4. Why would not let the acrylic completely cure in the mouth? (at least 2
reasons)
It may bind in the undercuts and be impossible to remove.
It may cause a thermal injury from the exothermic setting reaction (poly-n-butyl
methacrylate), a chemical injury from the presence of free monomer, and
mechanical injury caused by volume changes or pressure arising from
polimeratization shrinkage.
Neither poly methyl methacrylate PMMA, nor poly ethyl methacrylate PEMA, are
considered strong enough these days for provisional bridge construction. They
Have been replaced by the use of Bis GMA composite resin material such as
Protemp or Luxatemp.
5. What characteristics would you be looking for when choosing an impression
material?
Accuracy, long term dimensional stability, use characteristics (handling
properties), taste or smell, elastic recovery, tear resistance, hydrophilicity
(wettability), bond to tray, cost.
6. What would you do in the next appointment?
Try in stage: If porcelain fused to metal bridge is being constructed it is advisable
to try in the metal work before the porcelain is added to it. The fit of the metal
framework is evaluated and the occlusion adjusted. Check contacts, proximal,
centric and excursive-lateral and protrusive. If ceramic crowns, use try in paste to
hydrate the porcelain, protecting it from breaking, check marginal fit, contact
points, and occlusion, if any adjustments are required polish with porcelain
polishing wheels. Make sure patient is happy before you cement the crown.
7. Would you try the metal framework with the biscuit bake or only the metal
framework and why?
Only for big cases to try aesthetics, speech, length, seating on the lip. If you only
try the biscuit bake you wont be able to see the metal framework. You try both
with the metal framework you check the margins and with the biscuit bake
occlusion.
8. What do you do when first trying the metal framework and it does not seat?
The bridge can be sectioned, and hopefully both retainers will then seat. The two
parts are then secured in the new position with acrylic resin (duralay) and sent
back to the lab to be soldered. Or take a new impression and secure good
provisional to make sure teeth stay stable. Make sure of good contacts.
9. What are the possible reasons for that?
This can occur if there has been some minor movement of the abutments since the
impression was taken.
10. What could have gone wrong if the metal framework is perfect on the dies but
only seats in one abutment in the mouth? (give at least 2 reasons)
Temporary cement left in the preparation, too tight proximal contacts, distorted
impression, die over trimmed leading to over extension of margin, movement of
the abutments.
11. What cement do you use to porcelain fused to metal bridge and why?
Any is good, Zinc phosphate (standard and has been extremely successful,
disadvantages is solubility in oral fluids and lack of adhesion), Polycarboxylate
(week chemical bond to dentin, undergo plastic deformation after loading, less
retentive than Zinc phosphate and GI cements), GI (weak chemical bond to dentin,
release fluoride), resin modified glass ionomer cements (release fluoride, are
insoluble and provide better retention, imbibes water and expands with time),
resin cements (greater retention, care with eugenol contamination of dentin,
difficulty in manipulating).
I will choose GI cement. They are easy to handle, may be polished after light
curing, good aesthetic, fluoride release, improve mechanical strength.
12. What is your favourite brand name?
Fuji (plus), encapsulated system ensure optimal mixing and allow placement via
syringe tip
13. What would it be your second option and why?
Zinc phosphate because has been the traditional cement to lute dental restorations
and has been extremely successful, has good strength properties.
14. What causes postoperative sensitivity and what is the management?
Over reduction, overheating while preparing, chemical reaction of provisional
cement, bacterial contamination of the pulp, exposure, high contact.
Postpone cementation of the crown, make sure the provisional restoration is not in
hyperocclusion and it covers all prepared tooth surfaces, recement for several
days. If pulpitis persists, endodontic therapy will be necessary before the
permanent restoration can be cemented. Never cement a crown permanently over
a symptomatic tooth.
15. Bridge 13-11: All the procedure from case selection to cementation, follow
up?
Take a history. Clinical exam (extra oral-sings TMJ dysfunction and intraoral-oral
hygiene, periodontal condition, general condition, length edentulous span,
condition and position abutments, occlusion).Radiographs, diagnostic mounting in
ICP. Diagnostic waxing. Treatment planning. Before tooth preparation, remove
caries, place core and post. Preparations. Soft tissue management. Impressions.
Occlusal registration. Temporary bridge. Metal work try in. Trial cementation(if
any further adjustments need to be done). Instructions of how to clean the bridge.
Permanent cementation. Adjust contacts and polish. Follow up (to check if bridge
still functioning satisfactory, check fit, contacts, comfort and sensitivity, gingival
response). Maintenance.
16. In which case a wax up is not needed
When the destruction of the teeth is minimal, when the occlusion is not a problem,
in anterior when a denture tooth can be use for the same purpose (simulation of
final restoration and occlusion). When it is straight forward, easy case.
When the shape is not going to change or when aesthetic is not an issue for a
posterior tooth.
17. Gingival tissue management? Horizontal and vertical displacement? Why is
horizontal displacement required? How would you retract the gingiva prior to
taking the impression for the fabrication of a bridge?
Gingival retraction is performed to decrease gingival exudates’ and expose sub
gingival preparation prior to polishing the margins and impression taking.
Impregnating the retraction cord in substances such as adrenaline-8% epinephrine
(could induce cardiac reactions), ferric sulphate (kinder to the gingival tissue) or
aluminium chloride to decrease bleeding. The cord should be gently placed into
the gingival crevice with a flat plastic or cord packer prior to impression taking
and temporization.
Placement of retraction cord prior to tooth reduction around the cervical area,
results in minimal damage to the gingival complex. The cord shields the soft
tissues from the bur.
A retraction material such as Expasyl can be used as well to access the cervical
margins. It is the only sulcus opening method that guarantees the integrity of the
epithelial attachment, unlike the double cord technique. No anaesthesia required.
Electrosurgery may be indicated where a margin extends subgingivally and
gingival overgrowth is hampering restoration placement or impression taking.
18. Case of patient with severe pain in third quadrant, wear facets, no dental
problems, stressful job. Differential diagnosis, other tests needed for
diagnosis, definitive diagnosis and treatment plan?
More x rays (PA, OPG), vitality test, check for fractures, check occlusion, Palpate
muscles.
It could be crack tooth syndrome, referred pain, cyst or tumour.
It can also be grinding or clenching teeth (Bruxism), TMJ problems, muscular
spasm.
Stress management, local heat on face (heat packs), occlusal splint to protect
teeth.
19. What is bilateral balanced occlusion?
Balancing contacts in all excursions of the mandible to increase stability of full
dentures. Not applicable to natural dentition.
20. Preparation of 21 and 23 for full coverage PFM bridge. Impression material
that I would choose and reason? What records are to be sent to the lab? What
type of occlusion would be ideal for this case, would be better canine guidance
or group functions, why?
Elastomers, addition cured silicone preferred because are very stable.
Lab sheet wit explanation, date to be return, impression in silicone of upper arch,
impression in alginate or cast of lower arch, occlusal registration, shade.
Group function occlusion because multiple tooth contact and the load wont be
only in the canine. I think, as it is already supporting the bridge.
21. Prepare 12, 11 CR veneer, tetracycline staining, CR bonding to enamel and
dentine, dentin exposed during prep, thickness, finishing line, traumatic
occlusion, porcelain veneer?
Tetracycline staining (mild discoloration) is an indication for porcelain veneer.
Avoid in edge to edge occlusion.
There should ideally be enamel around the entire periphery, which is necessary for
adhesion and seal the veneer to the surface. There should be enough available
enamel for bonding, because bonding in dentin is not as reliable as enamel
bonding.
Veneers are usually 0.5-0.7 mm thick, 0.3 for small teeth. The finish line should
be a chamfer. If the tooth is discoloured the margin should be subgingival (but
still in enamel), otherwise keep it slightly supragingival (right at the gingival
margin).
Porcelain veneers have better performance aesthetics than resin composite.
Porcelain is less plaque retentive.
22. Types of impressions techniques?
Monophase (polyeter) The same mix of regular viscosity material is used for both
a stock tray and syringe.
Double mix technique (polysulfite, addition cured silicone) a single stage
technique necessitating the mixing of heavy and light body materials at the same
time, and use of a special or stock tray.
Apply adhesive to the tray, mix heavy and light body for 45-60 seconds, remove
retraction cord or leave it in place and dry preparation. Apply light body mix
around preparation and gently stream air to direct material into crevice. Position
tray containing heavy bodied material, support the tray with light pressure until 2
min after apparent set.
Putty and wash technique (silicone). The putty and light body can be used with a
stock tray, either single stage (as described above) or two stage.
23. Implants. 65 years patient advice for implant? Explain about osteoporosis.
Implants are based on the concept of osseointegration. Made of titanium or
hydroxyapatite coated titanium. Indicated in edentulous mouth unable to retain
dentures, partially dentate for bridges abutments, single anterior tooth
replacement, and maxillofacial prostheses post cancer surgery or trauma. Good
oral hygiene is mandatory. Joint planning between oral surgeon and restorative
dentist is essential for success.
It is performed by raising a mucosal flap and preparing a channel in bone, using
matched spiral drills. The entrance is counter sunk and then it is either pressed
into place or screwed in. In two stage procedure the implant is covered by the flap
at the end of the procedure and left to heal for 4 to 6 months. After healing;
excision of the mucosa overlying the implants is performed and insertion of the
abutments. Prosthetic procedures can start after two weeks. I one stage procedure,
insertion of the abutment at the end of implant placement.
Age is not a major impactor. Osteoporosis can be a risk factor for implant not to
work, as well as diabetes, smokers and patients taking Bio- phosphates (fosamas);
calcium related medicament-danger osteonecrosis. This medicament is given to
people with osteoporosis to stop the metabolism of the bone.
24. What is benefit of condylar guidance
????Reproducing (simulates) the real mandibular movements on the articulator,
which minimize the amount of time spent adjusting the restoration at the try in
stage and allows changes to the patient’ occlusion to be planned.
This question should be about anterior guidance, in that case it protects the
posterior tooth in protrusive movements.
If adjustable articulator, you could program it to help you achieve the anterior
guidance.
25. What would happen if there is uneven thickness of metal coping?
The metal will show through the crown or there will be over contouring in some areas
restoration (either opaque or over contoured). It could have deficient strength,
deficient margins, and induce casting errors.
26. Is the upper lateral incisor an adequate abutment for a missing upper canine?
The upper lateral incisor has the poorest amount of support and retention. If a
canine is to be replaced with a bridge the occlusal scheme should be designed to
provide group function in lateral excursions. The two premolars and lateral can be
use as abutments.
27. What do you understand by the concept of biological width?
It extends approximately 2 mm from the bottom of the gingival sulcus to the
alveolar crest. 1 mm is junctional epithelium and 1 mm is connective tissue. A 3
mm distance is recommended between the finish line of the preparation or final
margin of a restoration and the alveolar bone.
28. If the patient presents with a lost upper anterior as an emergency. What are the
treatment options that you have to offer?
Direct bonded resin bridge, temporary denture. Depending on the patient urgency,
the time.
29. How would you manage gingival bleeding prior to taking impressions?
Astringent, retraction cord, electrosurgery, TCA.
30. What is the best material to make impressions for crown and bridge? Why?
Polyvinyl siloxane (PVS) or addition reaction silicone. It has good physical
properties:
Accuracy unsurpassed, can record fine detail, best elastic recovery, dimensional
stable and can be poured the convenience of the operator, permits second pour,
handling properties very favourable, supplied in number of viscosities, clean,
odourless and tasteless, minimal material specially in custom tray.
Polyether as PVS are the most acceptable impression materials, have excellent
accuracy, long term stability, less accurate after 2 weeks, poor taste, elastic
recover good but not as good as PVS, good tear resistant, hydrophilic, less
expensive.
31. What do you do if the patient is complaining of pain on the night after you
cement the temporary bridge?
Reassure the patient, explain the possible causes, and tell it could be an initial
symptom. Make sure the temporary bridge is well cemented covering the margins,
check occlusion; it could be a high contact. Keep in observation until symptoms
disappear.
32. What do you do if you discover that during the preparation there was a pulp
exposure?
If traumatic exposure, small, and uncontaminated, perform direct pulp cap with
hard setting calcium hydroxide and restore.
If carious exposure, and continued pulp vitality is doubtful, RCT will be required.
If time is short, can dress tooth with ledermix and a traditional GI cement, and
extirpate pulp at next visit.
33. How can you improve the retention if you have a short crown?
Crown lengthening, forced eruption, addition of grooves or boxes in the
preparation.
A minimum of 4.0 mm oclusocervical is necessary for molar preparations and 3.0
mm for premolar preparations.
34. Bennet movement, angle, how much?
Bennet movement is the lateral shift of the mandible. Bennet angle is formed by
the balancing condyle when moves down forward and inward with the median
plane when projected perpendicularly on the horizontal plane.