fixed prosthodontics problems and solutions

Problem solving in fix prosthodontics

INTRO……. Failure

Repairment

About 90% of bridges last at least 10 yrs.(Smith, 2000)

WHY C&B WORKS FAIL? MECANICAL FAILURE

CHANGES IN ABUTMENT TOOTH

DESIGN FAILURES

INADEQUATE CLINICAL OR LAB TECHNIQUE

Mechanical Failures…. Porcelain/PJC

Failure of solder joints

Distortion

Occlusal/Incisal wear & perforation

Lost facings

Porcelain fused to metal Distortion of metal-ceramic framework

Inadequate metal support

Excessive porcelain thickness

Technical flaws

Normal function (occlusal forces)

Trauma

Failure of solder joints Inclusion

Failure to bond

Small solder joint

CHANGES IN ABUTMENT TOOTH…. Perio disease

Pulpal problems

Recurrent caries

Mutiple aboutment better to index and solder

Mutiple aboutment better to index and solder

Distortion Pontics are too thin

Bridge is removed with too much force.

Trauma.

Occlusal/incisal wear & perforation Composite crowns

Belle glass

Targis vectris

Wear down substantially over a lifetime

Rate

Occlusion

Diet

Para functional (bruxing) habits

3) DESIGN FAILURES….. Abutment prep. design

Inadequate bridge design

Under-prescribed bridges

Inadequate clinical/lab technique Problems to 1 of 3 groups:

1. Minor problems

2. Can be corrected in situ.

3. Those that cannot.

Marginal deficiencies Positive ledge (overhang)

Negative ledge

Casting difficulties External angles of crown

should be rounded

Sharp edges Stone die

wax-up stage.

investment material flow

difficult to remove the investment material

Cement thickness

REPAIRMENT TIME…

Some things are really beautiful!

But nothing lasts forever!

HOW CAN WE REPAIR THESE C&B FAILURES?

Seriousness of the problem1. Leave it alone if not causing any serious harm

2. Adjusting or repairing the fault

3. Replace the crown or bridge

fit checker

Grinding and polishing in situ Metal margins of crowns with positive ledges

Porcelain margin

Heatless stone

Diamond point

Followed by various composite finishing burs and discs.

Metal margins1. Diamond stone

1. Green stones

2. Tungsten carbide stones

3. Metal and linen strips

2. Interdentally,

1. Triangular shaped diamond

2. Abrasive rubber instrument with special handpiece

3. Margins should be polished

Repairs by restoring in situ……. Occlusal Repairs

1. Amalgam

2. gold inlay

3. composite material

Repairs at the Margins margins of a poorly fitting bridge

Secondary caries/early erosion and abrasion composite or GIC

Cavity prep at margins poor access >>> remove part of the crown margin

raising a full gingival flap good visibility

Repairs to porcelain Ceramic restorations

Composite

Separate silane coupling agent

Limited to sites with minimal occlusal forces.

Ceramic facings Porcelain is lost and

composite repair is not possible Often better to replace

whole crown

Pontic. Drilled through New pin retained metal-

ceramic facing

Removing all the porcelain Metal ceramic sleeve

crown

Removing c&b’s1. Vibration of

ultrasonic scaler.

2. Good leverage at margins

3. A slide hammer Bridge remover

4. Crown can be cut off

Removing post & cores Using extraction forceps and using sharp twists –

carefully…

Files

Ultrasonic

Removing PJC’s Cannot be removed intact

and should be cut off.

A vertical groove is made with a diamond bur in the buccal surface just through to cement.

Then Removed with suitable heavy duty instrument.

Removing Metal – Ceramic Crowns Possible to remove with

normal devices usually better to cut off.

cast metal solid tungsten carbide bur

with very fine cross cuts

Eye protection!!!

Vertical groove cut on buccal metal is usually thinner here

with better vision.

Diamond bur can cut porcelain favourably !

Cutting

How to cut a pfm

Removing Bridges (3 situations) 1. Abutment teeth need to be

extracted Bridge is removed Intact Dividing the bridge

2. abutment needed to be retained Retainers are cut and bridge

removed carefully

3. temporary measures removing whole bridges and

making adjustments.

Inhibited or Slow SettingVisual Appearance: Shiny, no detail

Result:

Inadequate surface detail on cast, poor fitting restorations.

S ulfur inhibition For Vinyl Polysiloxane Materials

latex gloves .

Residues

custom temporary

provisional cements

Inhibited orSlow Setting

CAUSE SOLUTION

For Vinyl PolysiloxaneMaterials

Sulfur inhibition due to

contact of latex gloves with tissue/tooth/retraction

material or impression material.

Wear gloves proven not to contain traces

of sulfur.

If contamination is suspected, scrub affected

area with diluted hydrogen peroxide.

Inhibited or Slow SettingCAUSE SOLUTION

Residues from custom temporary or

provisional cements (acrylics) present.

Do not use impressions already used to

fabricate the temporary restoration.

Fabricate the temporary crown or bridge

after final impression has been made.

Remove air-inhibited layer on the exposed

surface with an alcohol wipe before making

final impression.

Expired impression material

Inadequate mix.

Lack of Impression Detail

Visual Appearance: Muted detail reproduction.

Result: Crowns may be too tight, or loose, and not fit correctly.

Lack of Impression Detail

CAUSE SOLUTION

Impression material stored at

elevated temperature.

Store impression material at room temperature.

Lack of Impression Detail

CAUSE SOLUTION

Impression material stored at too low a temperature

(prolongs the setting reactions,

changes viscosity and requires exceptionally

high extrusion forces for automix materials).

Keep impression material at a temperature of

18°C/64°F at least one day prior use.

Lack of Impression Detail

CAUSE SOLUTION

Thick blood/saliva pooled around prep.

Remove blood and saliva prior to

making impression.

Use 2-step impression technique.

Lack of Impression Detail

CAUSE SOLUTION

Inadequate retraction of sulcus around prep.

Use good retraction technique, with proper

moisture control.

Lack of Impression Detail

CAUSE SOLUTION

Exceeding the working time. Follow manufacturer’s working

time specifications.

Choose material with longer working time.

Lack of Impression Detail

CAUSE SOLUTION

Inadequate disinfection effects

surface quality (detail reproduction) and

dimensional stability.

Use water based disinfectants according to

FDA guidelines.

Follow manufacturer’s instructions for use.

Voids on the Margin Visual Appearance:

Voids/holes on margin of the prepared teeth. Incomplete margin.

Result: The fit and function of the final restoration may be compromised. Short crown margins

and/or open margins.

Voids on the MarginCAUSE SOLUTION

Improper syringe technique. Keep syringe tip immersed in wash material to

avoid entrapping air.

Wiggle and stir while syringing. Push

material forward.

Voids on the MarginCAUSE SOLUTION

Inadequate coverage of marginal area with light body impression material.

Use wash material liberally on preparation

and abutments.

Blood and saliva contamination around prep.

Use good moisture control technique. Rinse and dry prep area before taking the impression. Stop bleeding by using appropriate

retraction technique and hemostatic agent.

Leave cord in sulcus until no blood or saliva are

present before syringing the light body

impression material. Consider two-cord retraction

to displace tissue and control fluids.

Voids on the MarginCAUSE SOLUTION

Tray not seated straight. Insert impression tray straight.

Tearing at the Margin Visual Appearance:

Rip, or visible tearing on the margin of the preparation.

Result: Short crown margins and/or open margins.

Tearing at the MarginCAUSE SOLUTION

Check expiration date of impression material.

Ensure mixing instructions are followed and materials have a streak-free appearance.

Expired impression material.

Inadequate mix.

Tearing at the MarginCAUSE SOLUTION

Displace tissue to allow the impression material to access prepared area.

Consider two-cord retraction. Leave pilot cord in the sulcuswhen taking the impression.

Use impression material with sufficient tear resistance.

Insufficient retraction.

Tearing at the MarginCAUSE SOLUTION

Do not use impressions already used to fabricate the temporary restoration.

Fabricate the temporary crown or bridge after final impression has been made.

Remove air-inhibited layer on the exposed surface with an alcohol wipe before making

final impression.

Residues from custom temporary or provisional cements (acrylics) present.

Facial-Lingual Pulls Visual Appearance: V-

shaped void, trough-like.

Result: Failure to capture complete and accurate dentition.

Facial-Lingual PullsCAUSE SOLUTION

Follow manufacturer’s working time specifications.

Choose material with longer working time.

Exceeding the working time.

Facial-Lingual PullsCAUSE SOLUTION

Do not move tray after seating.

Tray movement or repositioning

after seating.

Facial-Lingual PullsCAUSE SOLUTION

Use more material to create back flow effect.

Insufficient amount of impression

material used.

Facial-Lingual PullsCAUSE SOLUTION

Use lingual stops.

Use an impression tray that supports the flow

of the material.

Impression tray does not support flow of

impression material.

Tray-Tooth Contact Result: Restoration

may have slight distortion at marginal area, or rocks.

Visual Appearance: Show-through of tray. Impression tray exposed.

Tray-Tooth ContactCAUSE SOLUTION

Use proper size tray.

Test various tray sizes to ensure proper size.

Prepared teeth contact the sides or bottom

of impression tray.

Tray-Tooth ContactCAUSE SOLUTION

Carve out tray material properly before

applying wash.

Tooth contact with the pre-set tray material

when using the two-step technique.

Tray-Tooth ContactCAUSE SOLUTION

Fill tray adequately. Insufficient impression material used.

Delamination Visual Appearance:

Heavy body and light body materials not blended, or mixed together.

Result: Restoration will not seat or fit properly.

DelaminationCAUSE SOLUTION

Follow manufacturer’s working time specifications.

Choose material with longer working time.

Store impression material at room temperature.

Exceeding the working time.

Impression material stored at elevated temperature.

DelaminationCAUSE SOLUTION

Avoid contact with sulfur contaminants: Wear gloves proven not to

contain traces of sulfur.

Avoid contact with acrylic and methacryliccontaminants: Ensure impression

materialdoes not come into contact with methacrylateresidue from acrylatetemporary materials.

Sulfur or acrylic contamination of pre-set heavy body material in two-step technique.

Poor Bond of ImpressionMaterial to the Tray Visual Appearance:

Impression pulling away from the sides/bottom of tray.

Result: Crown(s) may be tight and not seat fully, or require excessive internal adjustment.

No tray adhesive used. Use tray adhesive.

Poor Bond of ImpressionMaterial to the Tray

CAUSE SOLUTION

Incompatible tray adhesive used.

Use appropriate tray adhesive.

VPS adhesive for VPS.

Polyether adhesive for polyether materials.

Poor Bond of ImpressionMaterial to the Tray

CAUSE SOLUTION

Inadequate drying time for tray adhesive..

Follow manufacturer’s instructions for application, and drying time

Poor Bond of ImpressionMaterial to the Tray

CAUSE SOLUTION

Thin plastic trays allow deflection, which can cause rebound upon removal.

Use a tray that fits better, and is stiffer and more rigid.

Poor Bond of ImpressionMaterial to the Tray

CAUSE SOLUTION

Stone ModelDiscrepancies Visual Appearance:

Voids on margin, powdery cusp tips on incisal edges on prepared tooth. “Golf-ball” appearance of stone model.

Result: Incomplete seating of indirect restorations

CAUSE SOLUTION

Stone ModelDiscrepancies

Tooth contact with impression tray, or gauze of double bite tray causes water to leach out of the tray, dehydrating the stone.

Instruct patient to bite passively in centric occlusion when using dual arch trays.

Fill tray with sufficient amount of material.

CAUSE SOLUTION

Stone ModelDiscrepancies

Cast not made according to model preparation guidelines

and lacks detail.

Provide as much information as possible to the lab. Indicate

type of impression material (polyether or VPS) and whether

or not the impression has been disinfected.

CAUSE SOLUTION

Stone ModelDiscrepancies

VPS

Hydrogen gas emission.

Follow manufacturer’s instruction for casting time.

CAUSE SOLUTION

Stone ModelDiscrepancies