Success and failure andproblem solving in prosthodontics complact final

Scenario Impression Framework check

SUCCESS AND FAILURE Problem solving in fix prosthodontics

INTRO……. Failure means, to be unsatisfactory, and

in C&B, it’s the inevitable. Repairment is the work that is done to

get rid of the failure. Recent large surveys of bridges made in

practice and elsewhere in different countries show that about 90% of bridges last at least 10 yrs.(Smith, 2000)

1- impression

Inhibited or Slow Setting Visual

Appearance: Shiny, no detail

Result: Inadequate

surface detail on cast

Poor fitting restorations.

Inhibited or Slow Setting

For Vinyl Polysiloxane Materials

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.

CAUSE SOLUTION

Inhibited or Slow Setting

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.

CAUSE SOLUTION

Inadequate mix

Use mix tip according to manufacturer’s instruction for use.

When using hand-mix materials ensure correct mixing ratio and thorough mix of catalyst and base paste.

Visual AppearanceNon-homogeneous mix.

Result Slow setting impression material.

Lack of Impression Detail

Visual Appearance: Muted detail reproduction.

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


Impression material stored at

elevated temperature.

Store impression material at room temperature.

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.

CAUSE SOLUTION


Thick blood/saliva pooled around prep.

Remove blood and saliva prior to making impression.

Use 2-step impression technique.

CAUSE SOLUTION


Inadequate retraction of sulcus around prep.

Use good retraction technique

proper moisture control.

CAUSE SOLUTION


Exceeding the working time.

Follow manufacturer’s working time specifications.

Choose material with longer working time.

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.

CAUSE SOLUTION

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 Margin

Improper syringe technique.

Keep syringe tip immersed in wash material to

avoid entrapping air.

Wiggle and stir while syringing. Push

material forward.

CAUSE SOLUTION

Voids on the Margin

Inadequate coverage of marginal area with light body impression material.

Use wash material liberally on preparation

and abutments.

CAUSE SOLUTION

Voids on the Margin

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.

CAUSE SOLUTION

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 Margin

Expired impression material.

Inadequate mix.

Check expiration date of impression material.

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

CAUSE SOLUTION


Insufficient retraction.

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

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

Use impression material with sufficient tear resistance.

CAUSE 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.

CAUSE SOLUTION

Facial-Lingual Pulls Visual

Appearance: V-shaped void, trough-like.

Result: Failure to capture complete and accurate dentition.

Facial-Lingual Pulls




CAUSE SOLUTION


Tray movement or repositioning

after seating.

Do not move tray after seating.

CAUSE SOLUTION


Insufficient amount of impression material used.

Use more material to create back flow effect.

CAUSE SOLUTION


Impression tray does not support flow of impression material.

Use lingual stops. Use an

impression tray that supports the flow of the material.

CAUSE SOLUTION

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 Contact

Prepared teeth contact the sides or bottom of impression tray.

Use proper size tray.

Test various tray sizes to ensure proper size.

CAUSE SOLUTION

Tray-Tooth Contact

Tooth contact with the pre-set tray material when using the two-step technique.

Carve out tray material properly before applying wash.

CAUSE SOLUTION

Tray-Tooth Contact

Insufficient impression material used.

Fill tray adequately.

CAUSE SOLUTION

Delamination Visual

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

Result: Restoration will not seat or fit properly.

Delamination


Impression material stored at elevated temperature.



Store impression material at room temperature.

CAUSE SOLUTION

Delamination

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

Avoid contact with sulfur contaminants: Wear gloves proven not to

contain traces of sulfur. Avoid contact with acrylic

and methacrylic contaminants: Ensure impression

materialdoes not come into contact with methacrylate residue from acrylate temporary materials.

CAUSE SOLUTION

Poor Bond of Impression Material 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.

CAUSE SOLUTION


Incompatible tray adhesive used.

Use appropriate tray adhesive.

VPS adhesive for VPS.

Polyether adhesive for polyether materials.

CAUSE SOLUTION


Inadequate drying time for tray adhesive..

Follow manufacturer’s instructions for application, and drying time

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.

CAUSE SOLUTION

Stone Model Discrepancies

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


Tooth contact with impression tray 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


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

VPSHydrogen gas emission.

Follow manufacturer’s instruction for casting time.

Short crown

WHY C&B WORKS FAIL?

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 # Stresses are developed within PJC’s as a

result of contraction on cooling after the firing cycle. These stresses produce minute cracks, some of which originate at the fit surface & propagate to produce failure if the crown is subjected to sufficient force. These stresses are concentrated around sharp internal angles of the fit surface, so the external angles of PJC preps should be rounded to reduce them.

Porcelain # Distortion of metal-ceramic

framework invariably results in the loss of porcelain

Inadequate metal support Excessive porcelain thickness Technical flaws Normal function (occlusal forces) Trauma

Failure of solder joints A flaw or inclusion in the solder itself Failure to bond to the surface of the

metal The solder joint not being sufficiently

large for the conditions in which it is placed.

CHANGES IN ABUTMENT TOOTH….

Progression of perio disease Abutment tooth may become non-vital

(pulpal problems) Recurrent caries occurring at margins of

retainers: change in diet. lapsed oral hygiene. inadequate restoration design

Distortion May occur to all-metal bridges if pontics

are too thin or if a bridge is removed with too much force.

Framework distortion may occur during function or as a result of trauma.

Occlusal/Incisal Wear & Perforation

Crowns tend to wear down substantially over a lifetime

All restorative materials wear in use, and the rate is determined by the occlusion the diet and parafunctional (bruxing) habits

3) DESIGN FAILURES….. Abutment prep. design Inadequate bridge design Under-prescribed bridges

few abutment teeth Over-prescribed bridges

Marginal deficiencies Positive ledge (overhang) excess of crown material protruding beyond the

margin of the preparation.

Negative ledge deficiency of crown material that leaves the

margin exposed but with no major gaps between the crown and the tooth.

Often arises because the impression did not correct at the try-in stage.

Casting difficulties “External angles of crown preps for

metal castings should be rounded to prevent one of the faults that may occur in the following chain of events:”

Stone die may not flow into the impression adequately, trapping air bubbles in the sharp angles of the imp.

Casting difficulties Sharp edges may be damaged at the wax-up stage. Investment material may not flow adequately into the

wax pattern to produce rounded internal angles on the casting, preventing the casting from seating fully.

It may be difficult to remove the investment material entirely from sharp internal angles without damaging the casting.

Cement will flow less rapidly around sharp angles, increasing the likelihood of an unnecessary thick cement layer at the margins.

REPAIRMENT TIME…

Some things are really beautiful!

But nothing lasts forever!

HOW CAN WE REPAIR THESE C&B FAILURES?

TECHNIQUES FOR ADJUSTMENTS, ADAPTATIONS AND REPAIRS TO CROWNS AND BRIDGES Assessing the seriousness of the

problem

Leave it alone if not causing any serious harm

Adjusting or repairing the fault Replace the crown or bridge

Adjustments by grinding and polishing in situ

In some situations, margins of crowns with good ledges can easily be adjusted.

If margin is porcelain (or specially

designed), finishing instruments should be used, example, heatless stone or diamond point followed by various composite finishing burs and discs.

In case of metal margins diamond stone followed by green stones,

tungsten carbide stones or metal and linen strips may be used.

Interdentally, a triangular shaped diamond and an abrasive rubber instrument with special handpiece (esp overhangs).

Margins should be polished with prophylactic paste with brush/rubber cup, and interdentally with finishing strips.

Repairs by restoring in situ…….

Occlusal Repairs Occlusal effects in metal retainers can

be fixed by amalgam which usually gives good results.

A small gold inlay may also be preferred. In metal-ceramic or porcelain

restorations, composite material can be used but repair may need to be done periodically.

Repairs at the Margins Should never try to repair margins of a poorly fitting bridge

during insertion. Secondary caries/early erosion and abrasion can be

treated with composite or GIC. Cavity prep at margins should not endanger strength

although all caries should be removed. If poor access, then it is better to remove part of the crown margin rather than excessive amount of tooth structure.

In some cases, raising a full gingival flap may be justified. Retainer margins can be adjusted and restored with good

visibility. Any necessary periodontal therapy or endodontic surgery

can also be carried out.

Repairs to Porcelain Materials such as basic composite with a

separate silane coupling agent for optimum bonding can be used to modify or shape ceramic restorations.

It is not an acid etch bond to enamel and is not strong. Therefore, the use of the material is limited to sites with minimal occlusal forces.

C&B – METABOND WITH COMPOSITE TO REPAIR PORCELAIN…..

3.Ceramic facings When porcelain is lost from a metal-ceramic unit and

composite repair is not possible – often better to replace whole crown.

Sometimes possible with a pontic. A hole is drilled through the backing and an impression is taken with suitable pins for a new pin retained metal-ceramic facing.

- It could be a little bulkier than the original! Sometimes possible to fix retainers or pontics by

removing all the porcelain and reprepare the metal part using a “metal ceramic sleeve crown” which covers the skeleton of the old retainer or pontic.

Sometimes made with heat cured acrylic or laboratory light cured composite.

4.‘Unit construction’ bridge facings

Before the routine use of metal ceramic materials, bridges were often made with Separate PJC’s cemented to it.

However, they often broke as they were usually reduced approximally for connector accomodation

Patients sometimes were given a spare set when bridge was cemented

Removing and/or replacing entire sections of a bridge A good purpose for removable, telescopic crown retained

bridges and of dividing multiple unit bridges into smaller sections.

When a part of a bridge is removed, the remainder can be modified like cutting a slot for a movable joint and replacing the lost section.

Bridges can also be extended using same principles if more teeth are apparently lost

Removing C&B’s In removing any crown or bridge, in

particular posts and caries, often helpful to break up the cement by vibration of ultrasconic scaler. It works best with zinc phosphate cement.

Removing Crowns Metal crowns Good leverage at margins for either complete or

partial metal crowns. Some instruments used are; - cumine or mitchels trimmer - even a slide hammer type crown - bridge remover may be used Crown can be cut off if all else fails.

Removing Post & Cores

Using extraction forceps and using sharp twists – carefully…

Several other devices can be used

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 but are more rigid than gold and porcelain may break – usually better to cut off.

cast metal is best cut with a solid tungsten carbide bur with very fine cross cuts (beaver bur).

Eye protection is important for everyone. Vertical groove cut on buccal as metal is usually

thinner here with better vision. Diamond bur can cut porcelain favourably !

Removing Bridges (3 situations)

Abutment teeth need to be extracted Bridge is removed with crown and bridge remover Easy for cantilever Others - Dividing the bridge through pontic or connector and remove teeth individually with retainers in

place

Cont…..

2. When abutment teeth are needed to be retained either for support of partial denture or overdenture or for making a new crown. Retainers are cut and bridge removed carefully as preparations are protected.

3. Some temporary measures require removing whole bridges and making adjustments. Neither bridge nor preparation should be damaged.

Removing Bridges intact

All metal bridges and minimal preparation bridges are slightly more flexible and can be removed more easier than metal ceramic conventional bridges.

Slide hammers can fit under margins, under pontics and embrasure spaces, even in drilled holes on palatal surfaces of retainers or pontics.

Other Techniques….. Ultrasonic vibration with a scaler can loosen crowns and

bridges. Loops of soft wire and sliding hammer If no slide hammer, than heavy duty instruments like

mallet is passed through the loops well outside the mouth and sharp blows are applied. – need to warn patient beforehand ( rather dramatic approach)

Practical Points A large proportion of failures are partial, a level of

acceptability must be reached by dentist and patient (esp min prep bridges)

Periodontally affected teeth can frequently be treated. Never should be used to cover up poor design Bridge can be made with fail safe procedures

THE END

PFM EVALUATION

1. Proximal contact 2. Marginal integrity3. Stability 4. Occlusion5. Characterization and glazing

PFM evaluation

PFM evaluationProximal contact Marginal integrity/complete seating Occlusion Characterization and glazing

MARGIN CHECK / COMPLETE SEATING


Small ledge

Acceptable

Risk of caries

Overhang

Careful Adjustment

Open margin

Making new casting




CORRECTION OF COLOR MISMATCH



Success and failure andproblem solving in prosthodontics complact final

Devices & Hardware

longer working

follow working

fabricate

sharp internal

margin visual

temporary

remove air

diamond bur