Lab procedure cast partial

Lab procedures in Cast Partial Dentures

PresenterBejoy ZachariahI MDS

Department of Prosthodontics and Crown & Bridge

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Contents • Introduction• Impressions with work authorization forms• Requisites for casts• Surveying the master casts• Block and Relief Arbirary block out Parallel block out Shaped block out• Duplication• Investment materials Gypsum bonded Phosphate bonded Silica bonded • Waxing and Spruing Maxillary Mandibular• Investing Vaccum mix Hand investing

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• Wax elimination and heating• Casting• Cutting off Sprue, Finishing and Polishing• Corrected cast technique• Artificial teeth setting• Processing • Advancements • Conclusion• References

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Why lab procedure is important?

Introduction

“ G o o d t e c h n i q u e p a y s o ff .”

T h e s e w o r d s a r e n o t m e r e l y a m o tt o t o h a n g o n t h e w a l l i n t h e l a b o r a t o r y b u t w o r d s o f w i s d o m

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Possible errors in RPD

Everyone who participates in any step of the fabrication of a removable partial denture must share in the success or failure of the restoration.

Some seemingly innocuous deviations can be accumulative and cause serious problems, so

everyone should review the procedures that they use on a regular

basis.

Rudd and Rudd. A review of 243 errors possible during the fabrication of a removablepartial denture: Part I J Prosthet Dent 2001;86:251-61

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Impressions with work authorization forms

Bomberg TJ, Hatch RA, Hoffman W. impression material thickness in stock and custom tray. J Prosthet Dent. 1985;54(August).

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(1) The signature and license number of the dentist (2) The date the authorization was signed(3) The name and address of the patient(4) A description of the service or material ordered.

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Requisites for casts

voids or nodules

hard dense

denture support.

3 to 4 mm deep peripheral roll

Vertical side walls

15 mm thick

•Dental laboratory procedures vol 3;Rudd KD 2nd edition.

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Surveying the master casts

Dental laboratory procedures vol 3;Rudd KD 2nd edition.

23-01-2015 11Dental laboratory procedures vol 3;Rudd KD 2nd edition.

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Design should mimic the design on diagnostic cast

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Block out and Relief

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Arbitrary block out


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Parallel block out


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Shaped block out


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Relief


Not used in complete denture bases, bead retention, open retention

23-01-2015 19Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4 th edition.

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Duplicating procedure

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Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4 th edition.

Agar : complex polysacharide extracted from sea weed Primarily consists of 15% colloidal suspension of agar in water Borates- 0.2-0.5% Potassium sulphate- 1-2% Wax- 1% Thixotrophic material 0.5% Water- around 84%

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Investment Materials

Gypsum bondedPhosphate bonded

Silica bonded

Robert G. Craig & John M. Powers : Restorative dental materials (Tenth edition)

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Gypsum bonded

• mixed with water• composed of a mixture of silica (SiO2) and calcium sulphate

hemihydrates (gypsum product)• Three types of gypsum bonded investments can be identified

as follows: -Type 1 thermal expansion type; for casting inlays and

crowns. -Type 2 hygroscopic expansion type; for casting inlays and

crowns. -Type 3 casting complete and partial dentures.


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Phosphate bonded

• powder contains silica, magnesium oxide and ammonium phosphate

• Can be mixed with water or colloidal silica• Two types of phosphate-bonded investment can be identified

as follows: -Type 1- for inlays, crowns and other fixed restorations. -Type 2- for partial dentures and other casts. removable restorations


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Silica bonded

• consist of powdered quartz or cristobalite which is bonded together with silica gel.

• On heating, the silica gel turns into silica so that the completed mould is a tightly packed mass of silica particles.


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Investment cast

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Design transfer

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Waxing the frame work- Maxilla




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Waxing the frame work- Mandible


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Spruing

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Hamda et all. Investigation of the effect of three sprue design on the porosity and the completeness of titanium cast removable partial denture frameworks. J Prosthet Dent. 1999;82(1):15–21

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Hamdi et all. Button versus buttonless castings for removable partial denture framework. J Prosthet Dent. 1994;72(4):433–44.


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• Mechanical mixing under vacuum removes air bubbles created during mixing and evacuates any potentially harmful gases produced by the chemical reaction of the high-heat investments.

InvestingVacuum Mixing

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• For gypsum bonded investments, temperature can be either 4680 for the hygroscopic technique or 6500C for the thermal expansion technique.

• With phosphate bonded investments,

the maximum temperature setting may

range from 7000C to 8700C, depending

upon the alloy selected..

Wax elimination and heating

Monika nemet. Laboratory fabrication procedures of a metal partial denture framework. acta stomatol crot 2003;37:95-98. 55

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• It is also advisable to begin the burn out procedure while the mold is still wet.

• This process is facilitated by placing the ring with the sprue hole down over a slot in a ceramic tray in the burnout furnace.

Shah SA. Influence of time of placement of investments for burnout and the type of rings being used on the casting accuracy. J Indian Prosthodont Soc.2014 Mar;14(1):67-71.

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Casting

•Monika nemet. Laboratory fabrication procedures of a metal partial denture framework. acta stomatol crot 2003;37:95-98. 57

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co-cr alloy is a commonly used investment material for casting of partial dentures.this metal doesnot have adequate ductility

for adjustment purposes but are light in weight, strong and corrosion resistant. superheating the alloy before casting can

increase the ductility of the alloy.

superheating the alloy can cause the metal to react with the mold and a close adhering green scale is formed. this green

scale is very hard to be removed and requires a lot of machining.

Allan FC, Asgar K, Alligato RDE, Cobalt FDE, Con EC. Reaction of Cobalt-Chromium Casting Alloy with Investment. J Dent Res. 1966;45(5):1516–28.

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Sand blasting

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Pickling

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Cutting off Casting Sprues and Finishing and Polishing





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Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4 th edition.

The unit pictured in is theTi-Lectro Polisher (CMP Industries). The polishing occurs in a bath of 85% orthophosphoric acid, which is heated t o 49 ° C to 60 °C.

The anode is attached to the cast and the cast is immersed in the solution. Each square inch of metal surface area requires 2 amperes of current for 6 minutes. The average setting is 6 amperes f o r 6 mins.

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• A functional impression is generally made by adding an impression base to the removable partial denture framework.

• Functional impressions may be made by a variety of impression materials.

Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4th edition

Joanne N. Walton The corrected cast impression: An alternative technique. Quintessence Int 1993;24:779-781.69

Corrected cast impressions

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Techniques for pouring corrected cast impressions are boxing with a

• 1)Plaster pumice mix and wax, • 2)Beading and boxing with wax, • 3)Beading with wax and the two stage pour.

Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4th editionJoanne N. Walton The corrected cast impression: An alternative technique. Quintessence Int 1993;24:779-781.

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• 1. A rubber base corrected cast impression is received in the laboratory.

• 2. Outline the master cast for removal of the ridge areas •Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4th edition

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• 3. Remove the residual ridge areas from the master cast

• cut retention areas into the cast

Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4th edition 72

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• 4. Place the framework with its impression on the master cast and lute it

Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4th edition73

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• 5. Soak- the cast and framework in clear slurry water, and place it into plaster/pumice mixture.

•Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4th edition74

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• 6. After the plaster/pumice mixture has set, shape it to the outline of the cast.

• 7. Use a strip of boxing wax to complete the boxing of the impression and is seal with a wax spatula

•Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4th edition

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8. Soak the boxed impression in clear slurry water for 5 minutes in preparation for pouring

9. Pour the boxed impression in improved stone


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Artificial teeth setting

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Determining occlusal schemes

1. Class III removable partial denturea. The occlusal morphology of the artificial teeth is selected to

match that of the opposing teeth or surfaces.b. If the existing occlusion is physiologically healthy, the patient is

restored to the existing occlusal scheme, which may be group function or mutually protected.

c. A group function articulation is recommended if the patient’s natural canine is missing or periodontally compromised.

d. A balanced articulation is recommended if the restoration is to oppose a complete denture. Some clinicians believe that balanced articulation is not desirable or clinically obtainable and select a monoplane or lingualized occlusion.

Ivanhoe JR, Plummer KD. Removable partial denture occlusion. Dent Clin N Am. 2004;48:667–83

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2. Class II removable partial denture The recommendations given for class III are appropriate,

with the following exceptions:a. Group function articulation should be avoided when there

are no remaining premolars. A canine-protected articulation reduces the destructive lateral forces that are generated on the distal extension during function.

b. Except when opposing a complete denture, a balanced articulation should be avoided to prevent nonworking contacts on natural teeth.


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3. Class I removable partial dentureThe recommendations given for classes II and III

are appropriate with the following exception:a. Balanced articulation is recommended for

patients for whom canine-protected articulation is not possible to provide bilateral occlusal contacts for increased denture stability.


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4. Class IV removable partial denturea. During excursive movements the anterior artificial

teeth should either disocclude or have passive occlusal contact.

b. A balanced articulation is recommended if the restoration is to oppose a complete denture. Some clinicians believe that balanced articulation is not desirable or clinically obtainable and select a monoplane or lingualized articulation with no anterior tooth contact in function


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Processing

After the teeth arrangement has been completed the flasking, processing, deflasking and finishing steps are followed.

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Advancements In Cast Partial Denture Fabrication

3 D computer models

Valplast RPD

Milling of RPD

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References 1. Nasser KSGA. Cast partial denture : Laboratory step by step. J Indian Prosthodont Soc. 2006;6(4):170–4. 2. Knezoviê-zlatariê D. Laboratory Fabrication Procedures of a Metal Partial Denture Framework. Acta

Stomatol Croat. 2003;37:95–8. 3. Bomberg TJ, Hatch RA, Hoffman W. impression material thickness in stock and custom tray. J Prosthet

Dent. 1985;54(August). 4. Howard S, Rudd KD, Dc U, Morrow RM, Powell JM. Comparision of effects of tap water and slurry water on

gypsum casts. J Prosth Dent. 1970;24(5):563–9. 5. Hasaballa M. THE FEASIBILITY OF INDIRECT CASTING OF MAXILLARY REMOVABLE PARTIAL DENTURE. Saudi

Dent J. 1993;5(3):114–20. 6. Hamda et all. Investigation of the effect of three sprue design on the porosity and the completeness of

titanium cast removable partial denture frameworks. J Prosthet Dent. 1999;82(1):15–21. 7. Brudvik JS, Lee S, Croshaw SN, Reimers DL. Laser Welding of Removable Partial Denture Frameworks. Int J

Prosthodont. 2008;21(4):285–92. 8. Allan FC, Asgar K, Alligato RDE, Cobalt FDE, Con EC. Reaction of Cobalt-Chromium Casting Alloy with

Investment. J Dent Res. 1966;45(5):1516–28. 9. Hamdi et all. Button versus buttonless castings for removable partial denture framework. J Prosthet Dent.

1994;72(4):433–44. 10. Walton JN. The corrected cast impression : An alternative technique Prosthodontics. Quintessence Int

(Berl). 1993;24(11):779–81. 11. Ivanhoe JR, Plummer KD. Removable partial denture occlusion. Dent Clin N Am. 2004;48:667–83. 12. Williams RJ, Bibb R, Rafik T. A technique for fabricating patterns for removable partial denture

frameworks using digitized casts and electronic surveying. J Prosthet Dent. 2004;91(1):85–8.

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13. Textbook of clinical removable partial prosthodontics by Stewart, Rudd, Kuebker 2nd edition.

14. Stewart’s clinical removable partial prosthodontics. Rodney D. phoenix.4 th edition.

15. Dental laboratory procedures vol 3;Rudd KD 2nd edition.

16. Mc Cracken’s removable partial prosthodontics, ninth edition

17. Joanne N. Walton The corrected cast impression: An alternative technique. Quintessence Int 1993;24:779-781.

18. Knapp J.G Technique for recording the cast surveyer. J. Prosthet Dent 1979; 41:352-354.

19. Yilmaz. G Optical surveying of casts for removable partial dentures J. Prosthet Dent.1975; 34:292-296

20. Richard E Coy. Survey and design of diagnostic casts for removable partial dentures J. Prosthet Dent.1974; 32:103

21. Sergio Reinaldo De Fiori. Transferring the path of insertion from the diagnostic cast to multiple master casts. J. Prosthet Dent.1983; 50:733.

22. Arthur M La Vere. A simplified procedure for survey and design of diagnostic casts. J. Prosthet Dent.1977; 37:680.

23. Robert G. Craig & John M. Powers : Restorative dental materials (Tenth edition)

24. Kenneth J. Anusavice : Philips’ science of dental materials (eleventh edition)

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Lab procedure cast partial