metallic denture base materials-new1

8/13/2019 Metallic Denture Base Materials-new1

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METALLIC DENTURE BASE

MATERIALS


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Introduction

Definitions

Brief History.

Classification ofdenture base materials

Ideal requirements

Advantages and disadvantages of metallic denture bases .

Different metallic denture bases


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Review of literature

Summary andconclusion

References


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introduction

In the space age , there is a belief prevalent that

modern technology can be put to use to solve anyscientific problem, if the problem can be clearly

defined .

All through the history of making dentures we find a

constant struggle of the dentist to find a suitable

denture base.


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DEFINITIONS

Denture base :

That part of a complete or removable partial denturewhich rests upon thebasal seat and to which the teethare attached. - GPT

METAL BASE :

The metallic portion of the denture base forming a

part or all of the basal surface of the denture .It servesas a base for the attachment of the resin portion of the

denture base and the teeth.


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Brief history of denture base

materials

Various types of materials have been used in the past

for fabrication of denture bases. Wood, ivory, baked porcelain, gold,silver, cheoplastic

metal and celluloid were used.

Of the metals used gold and silver were the best , but

their cost was too great for the average patient.


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Brief history of denture base

materials

In 1839, Charles Goodyear discovereda method of

producing rubber, and in 1851,Nelson Goodyear

invented a process for making hard rubber or

vulcanite.

In 1937, methyl methacrylate was found to be useful

as a denture base.

The first know casting of an aluminium completedenture base in the United States was done in 1867 by

BEAN.


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Chromium-cobalt base alloys were

introduced for use in dentistry in 1933 by

Erdle and Prange.


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CLASSIFICATION OF DENTURE BASE

MATERIALS

1.Metallic denture base materials

example : Cobalt-chromium

Gold, titanium

2. Non Metallic denture base materials :

example :Acrylic resins

3.COMBINATION


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Bio-compatible

Adequate physical and mechanical properties:

- High flexure and impact strength- Long fatigue life

- High abrasion resistance

- High thermal conductivity- Low density

- Low solubility and sorption to oral fluids

Ideal requirements of a denture

base material


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- Dimensionally stable and accurate

- Superior esthetics and color stability

- Radio-opacity- Good adhesion with denture teeth and liners

- Ease of fabrication with minimum expense

- Easy To repair- Readily cleansable


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Advantages of cast metal denture bases over

acrylic bases

Lack of bulk with more strength

The metal base prevents warpage during processing.

Stronger and are less subject to breakabge.

More accurate fit and more faithful reproduction oftissue details.

Less tissue changes occur under metal bases.

Dimesional accuracy.

Less porous.

Better thermal conductivity

Show less lateral deformation in function.


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Disadvatages of metal bases

Greater technical costs.

Difficulty of rebasing and relining

Less margin for errorpermissible in the

posterior palate seal area

Increased weight for a maxillary denture


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Despite the popularity of PMMA as a denture

base there are various situations where a

metallic denture base can be used :

- Single maxillarycomplete denture opposing a

natural mandibular dentition

- Unfavourable occlusal plane

- Heavy anterior contacts

- Heavy masticatory forces


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Different metallic denture base materials:

Cobalt-chromium alloys :

As early as 1949 it was estimated that nearly 80% of

all partial denture appliances were cast from co-cr

alloys.

composition :

Principle elements(approx. 90%)

Cobalt 60%

Chromium 25% to 30%


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Other components

:Molybdenum silicone

Aluminium nitrogen

Berylium carbon & manganese

Nickel chromium alloys :

Nickel 70% Chromium 16%

Other constituents


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1.Chromium :

Responsible for the tarnish resistance and stainlessproperties.

When the chromium content of an alloy is more than

30% it is more difficult to cast ; and therefore dentalalloys should not contain more than 28% or 29%

chromium.

These alloys are considered to be technique

sensitive


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Cobalt and nickel :

In general cobalt and nickel are

interchangeable .

Cobalt increases the elastic modulus ,strength

and hardness more than Nickel does.


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Other alloying components :

CARBON : Increase in carbon content increases the

hardness of Co-based alloys

If the carbon content is increased by 0.2% more thanthe desired amount results in a too hard and too

brittle alloy not suitable for dental appliances .

whereas a decrease of 0.2% will decrease the tensile

and the yield strength


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MOLYBDENUM :(3% to 6% )

-Contributes to the strengthof the alloy.

-Initially tungsten was used , but it reduced the

elongation ,was therefore replaced by other hardening

elements like molybdenum .

ALUMINIUM :

-Forms a compound with Ni and Al (Ni3Al) whichincreases the tensile and the yield strength of the

alloys


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BERYLIUM :

About 1% lowers the fusion temperature range of the

alloy by about 100 degrees C.

SILICONE AND MANGANESE:Increase the fluidity and castability of these alloys.

NITROGEN :

If present contributes to the brittle qualities of these

alloys .


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titanium

Ti was developed by William Gregor of Englandin 1791,and was named by Martin H. Kalproth ofGermany in 1795.

Welhelm Kroll1930 invented useful metallurgicalprocesses for Ti and is considered to be theFATHER of Ti dentistry.

In the recent years ,the attention of Ti has switchedfrom its previous attention with jet engines,mammoth aircraft frames to prosthetic limbs ,dentalimplants.


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Ores of Ti: Rutile

Ilmenite

Ti processing:

1.Reduction process

2.Melting the sponge

3.Primary ingot formation

4.Secondary ingot formation


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Types of Ti :

Ti and Ti alloys exist in 3 major categoriesaccordingto predominant phases present as :alpha

- Beta and

- Alpha-beta forms

When pure Ti is heated at 882+/- 2degrees C themetal exhibits an allotrophic phase transformation inwhich a hexagonal close-packed alpha phasestructure is transformed into a body centered cubicstructure as the temperature is raised above that

temperature. Even a rapid quenching does not suppress the alpha

beta phase transformation .Thus a pure Ti casting hasa alpha hcp structure near room temperature .


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Forms and sizes :Alloyed and unalloyed Ti

is available in different formsand sizes like :

plates , bar ,rod, wire, sheet, strip, powder..

Commercially pure Ti: available in 4

different grades(ASTM-Grade1-4)


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Dental Ti casting:

Because of the inherent properties of Ti that made it

difficult to melt and cast, traditional casting machines

that cast in air with conventional ceramic crucible and

investment materials could not be used .

More specialized casting equipment and mold

materials developed solely for this purpose were

developed.


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Casting problems were due to-1. The high melting point of Ti (1670 degrees

C),Murray 1987.

2. The strong chemical affinity of Ti with

gases viz. O2,H2,N2..

3. High reducing ability of Ti

4. High solubility of the same gases in Ti

5. Low density of Ti


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Thus, improvements in the conventional castingmethods were required viz:

1. Selecting heat sources high enoughfor fusing Ti.

2. Isolating the molten metal from air.3. Developing a container which reacts with very little

or does not react at all with the molten Ti.

4. Finding new ideas for delivering the molten metal in

the mold at desired velocity .


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Ti casting equipment :

Inorder to cope with the high fusion temperature of Ti

alloys , 2 melting methods are used -

1. Argon/arc melting with a non-consumable tungsten

electrode.

2.High frequency induction melting


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Melting Casting Equipment

1.Electric arc A. Gas Pressure

B. Centrifugal Force

Casmatic (Iwatani, Osaka, Japan)

Cyclarc Manita ( Tokyo , Japan)

Titaniumer Ohera (Osaka,Japan)Ti cast Super C (Selec , Japan)

2.High frequency A. Gas pressure

B. Centrifugal force

Arvatroa (Kyato , Japan)

Titanus (Bego, Germany)


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ALUMINIUM

Basically produced by the electrolysis of bauxite ore

in a molten cryolite bath.

BACKGROUND The first know casting of an aluminium complete

denture base in the US was done in 1867.

Carroll presented a method for casting the aluminium

bases under pressure.


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ALUMINIUM

Prothero detailed some of the advantages of

Aluminium as thermal conductivity, malleability, and

rigidity; and disadvantages as warpage and imperfect

density of the casting

Campbell suggested that aluminiums thermal

conductivity not only elicits a favourable patientresponse , but also promotes a normal pink,

physiologic condition of the mouth.


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Sizeland Coe was the first to discuss the use of a

super pure alluminium alloy for the construction of

denture bases, as it eliminated much of the intra-oral

corrosion that existed.

Lundquist felt that the primary dis -advantage of the

alloy was its discoloration .

Barsoum et al evaluated the accuracy of fit of Al

bases as compared to heat and cold cured resins-Alhad a better fit.


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Indicationsof an aluminium denture base:

1. Is an excellent choice when the natural mandibular

dentition opposes the edentulous maxillary arch.

2.patients who have undergone maxillary and

mandibular atrophy through years of CD use will

benefit .3. Patients who have had fracture problems with resin

denture bases.

Contraindications :

1.Following recent extractions.

2.Systemic problems

3.Severe undercuts


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Advantages :

1.Accurate fit .

2.Greater accuracy and added retention

3.Good thermal conductivity, malleability.

4.Interocclusal record making is more accurately

reproduced.

5.Less bulk with more strength.6.Inexpensive


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Technique for casting aluminium

1. Duplicate master cast

with reversible

hydrocolloid.

2. Pour refractory cast,

remove and place in a

drying oven at 190degree C for 30min .


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3. Trim the refractory cast

4. Immerse the refractory cast in bees wax at 290

degrees F

5. Place one thickness baseplate wax over entire

tissue bearing surface of the cast.

6. Coat the cast with Ti seal. Place retention beads

7. Place the main sprue as well as the auxillary

sprue.


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Induction casting is recommended for

aluminium denture base.

Fill the crucible with Al pellets & push the

start button.

Keep the arm spinning for 4 minutes non stop.

Alloy the casting to bench cure for atleast 45

minutes

Final cleaning and anodization may be done if

required.


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STAINLESS STEEL DENTURE BASE

When approximately 12% to 30% chromium is added

to iron ,the alloy is called STAINLESS-STEEL .

Types of stainless steel

(crystal structure formed

by iron atoms )

chromium nickel carbon

Ferritic 11.5-27 0 0.20max

Austentic16-26 7-22 0.25max

Martensitic 11.5-17 0-2.5 0.15-120


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PROPERTIES :

Despite the difficulties in swaging ,stainless steel

has some merits as a denture base material :

1.Very thin denture base can be producedfigures as

low as as 0.11mm

2. The steel is fracture resistant.

3. Not heavy due to the thinness .

4.The corrosion resistance is good .

5. Good thermal conductivity.


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Methods of swaging :

1.Conventional method

2.Newer methods :

a. Explosion forming

b. Explosion hydraulic formingc. Hydraulic forming


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Gold alloys

Gold alloys of types 3 and 4 are

sufficiently rigid for use as a cast metal

base.

casting with gypsum bonded investments

with a uniform thickness as thin as 28

gauge is easy.


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TYPE %Au %Cu %Ag %Pd %Pt %In,Sn,Fe,Zn,Ga

I 83 6 10 0.5 - Balance

II 77 7 14 1 - Balance

III 75 9 11 3.5 - Balance

IV 69 10 12.5 3.5 3 Balance


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Procedure for gold alloy cast base :

Wax block out of the master cast is done.

Place the cast in a slurry water preheated to

38degrees C for 20 min.

Duplicate the cast using a duplicating colloid.

Dry the refractory cast ,then pour and trim the

cast.

Selection of he size of the plastic pattern us a

clinical decision (18 gauge generally)


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Add retention beads for the resin.

Attach the sprues.

Invest the cast.

Burn out the wax.

Induction casting may be used .


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Metal Type Yeild

Strength

(Mpa/Ksi)

Tensile

Strength

(Mpa/Ksi)

Elongation

(%)

Hardness

(HV)

Elastic

Modulus

(GPa/Ksi x

103

)Co- Cr (A ) 710/103 870/120 1.6 432 224/32.4

NiCr (B) 690/100 800/116 3.8 300 182/26.4

Co

Cr

Ni (c) 470/68 685/99 8.0 264 198/28.7

FeCr ( D) 703/102 841/122 9 309 202/29.3

Type IV Gold 493/71.5 776/112 7 264 90/13

CP Ti 344/50 345/50 13 210 103/14.9

Ti6V- 4 Al 870/126 925/134 5 320 117/17


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REVIEW OF LITERATURE

1. WATANABE et al in 1997 tested the

hypothesis that differences in pressure

produce castings with various amounts ofporosities values. This study suggested

castings which have adequate mechanical

properties and low porosities can beobtained by choosing an argon pressure

difference.


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Hamda et al in 1999 conducted a study with

an objective to produce complete, void free

castings of removable partial dentureframeworks made from commercially pure Ti.

The ball sprue design produced the most

complete castings for the removable partial

denture denture Ti frameworks.


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Moore and White K.C. in 1986 described

materials and technique for applying gingival

color to aluminium when it is used as a denturebase.

They concluded that abrasion of anodized

surface may release dye inclusions.


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Anthony De Furio and Daniel H. Gehl (1970)

conducted a study to determine the amount of force

required to dislodge maxillary dentures made from

aluminium , gold and acrylic resin. He used aprecision machine to measurethe force necessary todislodge a maxillary denture base from its basal seat.

He concluded that the chrome cobalt and aluminium

alloy bases gave retention values which weresignificantly higher than those obtained with the

acrylic resins and gold alloy bases .


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A study which was conducted in dept of

prosthodontics by Dr.Gautam Shetty under the

guidance of DR. N.P.PATIL in sdm dental

college.

The main objective of the study were :

1. To compare the fit of Al alloy (7010)denture base

with acrylic denture base and base metal alloy

denture base.

2. To study the effect of anodization andelectroplating on the resistance to corrosion.

3. To compare the flexure strenght of aluminium

alloy wih that of resin and base metal alloy .


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RESULTS :

The results indicated the accuracy of fit of aluminium

was better than base metal alloy and superior than

acrylic resin

Anodized Al showed better resistance to corrosion

resistance than that electroplated and that without anysurface treatment.


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SUMMARY AND CONCLUSION

The dentist should possess sufficient

knowledge of the properties of different

Prosthodontics materials they deal with ,so thatthey can exercise prudent judgment in their

selection, which in turn will ensure treatment

efficacy and effectiveness.


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REFERENCES

Anusavice Kenneith. J :Philips science of Dental

materials .11thedition 2003

Atwood D.A : Final report on the clinical

requirement of ideal denture base materials .JPD1968,20 :101

Baraco M.T and Dember M.L:Cast Aluminium

denture base,JPD 1987,58:179 Combe E.C : Notes on dental materials 6th edition

1992 Churchill Livingstone


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REFERENCES

Craig R.G :Restorative dental materials 8th edition

De Furio A. and Gehl. DH : Clinical study of the

retention of maxillary complete denture with different

DBM . JPD 1970 ,23:374 Faber B. L: Lower cast metal base JPD1957 51 :7

Grundwald A.H:Gold base lower denture ,JPD 1964,

14:432

Johnson W.W :The history of Prosthetic

dentistry,JPD 1959,9:841

Lundquist Do :An Al alloy as a denture base, JPD

1963,13:102


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Moore F.D :Organic or metal bases for dentures , JPD

1967,17:227

Morrow R.M RUDD K.D :Dental Lab procedures CD

Vol 1 2ndedition

Wang Russel .R : Titanium for complete denture

application,Quintessence Int.1996,27:401

Winkler Sheldon : EsssentialsOf Complete DentureProsthodontics 2ndedition 2000

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