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Indian Journal of Dental Sciences.December 2011 Issue:5, Vol.:3

All rights are reserved

www.ijds.in Original Article

of Dental SciencesIndian Journal

E ISSN NO. 2231-2293P ISSN NO. 0976-4003

1Katta Sridhar Chowdary

Address For Correspondence:Dr.Katta Sridhar Chowdary M.D.S.Professor, Department of Prosthodontics,Panineeya Mahavidyalaya Institute ofDental Sciences & Research Centre, HyderabadCell : 9849988815E-Mail : [email protected]

stDate of Submission : 1 November 2010

thDate of Acceptance : 12 January 2011

AbstractObjectives of the study: To study the marginal fit of artificial crowns made with two base metal alloys.To find out the effect of die-spacers on the fit of base metal alloy crowns. To evaluate comparatively theeffect of number of coats of die-spacers with respect to marginal fit of crowns made with two base metalalloys.Materials and methods: For each alloy material 20 specimens were made. A standardized die wasprepared and impressions were made with polyether elastomeric impression material and dies were

made with die stone. Wax patters were made on the dies with varying coats of die spacer. The waxpatters were invested and castings were made with 20 specimens using Ni-Cr alloy and 20 specimensusing Co-Cr alloy. The marginal fit of crowns were evaluated with optical micro scope.Results: The mean and standard deviation of the marginal fit was calculated for castings made with Ni-Cr alloy and castings made with Co-Cr alloy. It was found that maximum mean was with castings madewith Co-Cr alloy and minimum with castings made with Ni-Cr alloy.Conclusion: Co-Cr alloy copings had lesser marginal fit when compared with copings of Ni-Cr alloy.Use of paint-on die spacer has the potential to ease insertion of coping without significantly affecting itsmarginal fit

Key WordsMaster die, Stone die, Die-spacer, Inlay wax, Castings, Copings, marginal fit,

for the cement allows the casting to beseated completely during cementation. If theavailable space for cement is too narrow, thecasting will not seat properly.

Conversely, If the available space forcement is too wide, casting will be too looseon the prepared tooth, resulting in loss ofresistance. Spacer alters the dimension ofthe die by coating the occlusal surface andvertical axial walls with a thin layer ofrapidly drying paint. Seating of the crowndepends on the thickness of the coating,which in turn depends on the number ofcoats.

Materials and MethodsThe study was done to evaluate the marginalfit of cast metal crowns made with two basemetal alloys with varying coats of diespacers.Two base metal alloys have been selectedfor this study. (Photo - 1 & 2)

IntroductionBase metal alloys have been in use inProsthodontics as an alternative totraditional high gold content alloys. Thesealloys attracted the attention of the dental

professionals due to thei r superiormechanical properties as well as low cost.The success of a cast metal frame workdepends not only on selection of suitablematerial for investing procedure but also onmeticulous laboratory proceduresundertaken. Marginal fit of coping/crown isvery important factor for the success of

prosthesis/restoration to follow. Marginalintegrity ranks high for the success of a

restoration because good marginal fit isessential for maintaining gingival health andprotecting the tooth from physical ,chemical, thermal and bacterial injuries. Toobtain this, there must be a band of closeadaptation of casting with the prepared toothat the margins of tooth preparation. At thesame time, a space must exist between theinternal surface of the casting and the

prepared surface of the tooth to provideroom for the luting agent. This space meant

Indian Journal of Dental Sciences. (December 2011 Issue:5, Vol.:3) All rights are reserved.

1M.D.S., Professor, Department of Prosthodontics,

Panineeya Mahavidyalaya Institute of Dental

Sciences & Research Centre, Hyderabad

Evaluation Of Marginal Fit Of Castings Made With

Nickel-chromium And Cobalt-chromium Alloys

Using Varying Coats Of Die Spacers - A

Laboratory Study

Photo-1 Nickel - Chromium Alloy

Photo-2 Cobalt - Chromium Alloy


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Nickel-Chromium alloys were designatedas Group A

Cobalt-Chromium alloys were designatedas Group BAll the alloy pellets were selected from thesame batch to avoid variation in the valuesobtained.A standardized brass die was machined tothe following measurements: 6mm height,8mm gingival diameter, 6 degree taper and1mm chamfer margin to simulate the singletooth prepared for cast metal crown.

The brass master die was duplicated withpolyether impression material (Impregum-F, ESPE, and Germany) using custom madetrays and these were poured with type IVimproved stone (Ultra rock, India). (Photo-3, 4&5) A total number of 40 dies were

prepared. Twenty samples each wereprepared with group A and group B thus atotal number of forty samples were preparedfor this study.

In each group, samples were divided intofour sub groups. Five dies forGroup A andfive dies forGroup B were chosen for eachcoat of die spacer and thus dies with 1 to 4coats were prepared. Die surfaces weretreated with one coat of die hardener(George taub products, N.J., U.S.A.) to

preserve the integrity of stone margin duringthe preparation of wax pattern.

Application of die spacer:The stone dies were treated with die spacerwhich was painted upon the dies. A band o1mm in width at the cervical margin was lefunpainted. Die spacer coating was paintedon all dies.5 dies for group A and 5 dies forgroup B were chosen for each coat and thu1 to 4 coats of spacer samples were

prepared.(Photo-6&7)

Preparation of wax pattern:The finish line of the die was highlightedwith sharp, bright red pencil. Die lubrican(True release, George taub Ltd., U.S.A.) wasapplied with a clean brush. Wax patterns


GROUP

A

B

TYPE OF MATERIAL

NICKEL-CHROMIUM ALLOY

COBALT-CHROMIUM ALLOY

TRADE NAME

DURA BOND

WIROBOND LFC

MANUFACTURER

MATECH Ltd.U.S.A.Batch No.BMM001

BEGO,GERMANYBatch No.11738

Photo - 3 Brass Master Die

and Custom Trays

Photo - 4 Polyether Impression Material

Photo - 5 Die Stone

Photo-6 Die Spacer And Lubricant

Photo-7 Dies With Spacer Coats

1mm

6mm

8mm

Preparation of Stone Die

Number Of Coats Of Die Spacer

1

2

3

4

Sample In Group A

5A1

5A2

5A3

5A4

Sample In Group B

5B1

5B2

5B3

5B4


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were made by soft inlay wax (GC inlay wax,Japan) over the stone dies. (Photo-8)

Investing and casting:Each pattern was immediately invested aftermarginal refinement to minimize distortion.The lost-wax casting technique was used.The wax patterns were invested in graphitefree, phosphate bonded investment material(Super vest, Matech Ltd., U.S.A.).(Photo-9) Burnout of the wax patterns were carriedout. (Photo-10)

A separate ceramic crucible was used formelting each alloy and casting was carriedo u t i n a n i n d u c t i o n c a s t i n gmachine(Fornex,Bego,Germany).Thecastings were retrieved, sand blasted, allsp rues were r emoved wi th t h incarborundum disk and inspected withmagnifying glass.

Each casting was seated on its respectivestone die and secured with a spring-loaded

caliper exerting uniform for all samplesduring microscopic measurements. Opticalmicroscope was used with 100magnification to measure the gap betweenthe margins of the casting and marginalfinish line of the die. (Photo-11)

Results:

A total number of 40 crowns were made ouof which 20 were made with Ni-Cr alloy and20 were with Co-Cr alloy. The marginal fiwas determined at four predetermined siteson the dies. Hence, there were twentyreadings for different coats for Ni-Cr crown(Group A) (Table-1) and twenty readingsfor Co-Cr crowns (Group B) (Table-II).

The mean and standard deviation of themarginal fit was calculated. It was found thamaximum mean was with Co-Cr alloy group(59.8223.5) and minimum with Ni-Cralloy group (41.7223.17). (Table III).

The mean and standard deviation omarginal fit, maximum mean was with fourcoats followed by two coats, followed bythree coats and minimum with one coat(Table-IV)

The average marginal fit for different coatsfor Ni-Cr (Group A) varies, with maximum

discrepancy of 47.25 for a die with twocoats and minimum marginal discrepancy o37.55 for die with three coats.

The average marginal fit for different coatsof Co-Cr (Group B) varies, with maximumdiscrepancy of 75.90 for a die with fourcoats and minimum marginal discrepancy o46 for die with one coat.


Photo-9 Phosphate Bonded

Investment Material

Photo-10 Burnout Furnace

Nickel - Chromium Alloy Casting with

Maximum Marginal Fit (x 100)

Cobalt - Chromium Alloy Casting

with Maximum Marginal Fit (x 100)

Photo-11 Photomicrograph

Photo-8 Inlay Wax & Pkt Instruments

Coat

1

2

3

4

1

18

50

15

57

17

90

11

60

13

90

15

59

10

85

12

57

40

24

50

13

35

50

42

10

50

40

27

10

2

45

49

50

10

85

40

45

58

100

15

32

59

85

26

42

60

3

85

45

30

58

45

50

68

60

40

46

90

55

42

48

100

30

4

44

47

40

45

28

35

16

25

28

35

12

24

18

45

20

27

5

19

35

34

18

Average

42.35

47.25

37.55

39.75

Sample (Co-Cr)

Table 1 - Marginal Fit Values Of Samples Made With Ni-Cr (Group A)

50

45

40

35

30

25

20

15

10

5

0

42.35

47.25

37.5539.75

1 2 3 4COAT

Bar Chart IMARGINAL FIT VALUES OF SAMPLE MADE WITH

Ni-Cr Alloy (Group A)

FITINMICROMET

ERS


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Two-way ANOVAs was used to compare themean values in all castings made with twoalloys with different number of coats ospacer under each alloy. It was observed thathe average marginal fit differs significantly

between the two alloys (P < 0.001). It wasalso inferred that the average marginal fiwas different among different levels ocoating but statistical analysis showed that iwas not significantly different.

It was seen that there was a significaninteraction between alloys such as Ni-Cand Co-Cr and different number of coatingof die spacers (P < 0.001), i.e. As the level ocoating increases in Co-Cr, the averagemarginal discrepancy increases but it isreversed with Ni-Cr. (Table-V)

Discussion:Marginal adaptation of the crown is a cruciafactor in determining its clinicaacceptability. Crown fit as judged bymarginal seal influences the longevity of the

cast restorations to a great extent. The resultsof dental lost wax casting techniques aregreatly influenced by the expansion andcontraction of all the materials usedincluding impression materials, waxesgypsum products, plastics and the alloysused in fixed partial dentures.

Fusayama, Eames et al, Campagni et a3have demonstrated that the space betweeninner crown wall and the tooth preparationimproves seating of crowns. When nospacer is used or at low spacer thicknessesseating of the crown is arrested at the axia

walls.

As one coat of a spacer has a specificthickness, by varying the number of coatsdifferent amounts of relief can be producedon the internal portions of the wax patternsand subsequently on the resultant castings.

The findings of the present study reveal thathe marginal fit of nickel chromium alloycastings are superior to that of cobalchromium alloy castings. This is similar tothe findings of Nitkin Asgar 5who said thanickel chromium alloys produced castingswith very close fit. In terms of the number ofcoats of die spacers, nickel chromium alloycastings made with three coats of the diespacer had maximum marginal fit in the

present study. Cobalt Chromium alloycastings made with one coat of die spacerresulted in best marginal fit.

In nickel chromium castings, maximummarginal discrepancy was observed when


Coat

1

2

3

4

1 2 3 4 5 Average

Sample (Co-Cr)

Table 2 - Marginal Fit Values Of Samples Made With Co-Cr (Group B)

47

65

70

95

35

68

60

100

45

76

50

100

55

100

65

100

58

40

70

100

65

20

80

95

50

20

95

75

55

40

100

60

55

80

100

80

70

90

80

80

55

80

85

60

65

70

84

60

38

25

40

73

50

42

20

80

30

70

20

72

30

60

45

75

25

50

55

66

30

55

29

45

30

47

26

42

32

36

40

60

46.00

56.70

60.70

75.90

80

70

60

50

40

30

20

10

0

46

56.7 60.7

75.9

1 2 3 4COAT

Bar Chart II

MARGINAL FIT VALUES OF SAMPLE MADE WITHNi-Cr Alloy (Group B)

FITINMICROMETERS

70

60

50

40

30

20

10

0

1 2 3 4

COAT

Bar Chart IIIMEAN AND STANDARD DEVIATION OF MARGINAL FIT IN

DIFFERENT NUMBER OF COAT FOR Ni-Cr AND Co-Cr

FITINMICROMETERS

44.17

21.11

51.97

21.86

49.12

27.95

57.82

26.54

Mean SD

Mean

44.17

51.97

49.12

57.82*

SD

21.11

21.86

27.95

26.54

Coat

1

2

3

4

For Group A & B

Table-3Mean And Standard Deviation

Of Marginal Fit In Different

Number Of Coats For Ni-Cr And Co-Cr

Table-4Mean & Standard Deviation Of Marginal

Fit For Each Alloy With Different

Number Of Coats

Mean

42.35

47.25

37.55

39.75

SD

26.76

20.13

25.13

20.59

Coat

1

2

3

4

A(n=20)

Mean

46.00

56.70

60.70

75.90

SD

13.85

22.99

26.26

18.26

B(n=20)


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two coats of die spacer were used. In cobalchromium alloy castings more marginadiscrepancy was observed compared tonickel chromium alloy castings. While ican be inferred from the above that cobalchromium alloy castings exhibited

propor tionat ely increasing marginadiscrepancy when coats of die spacer wereincreased, it was not so with nickechromium alloy.

In the present study, nickel chromium alloyhas been found to develop minimumdiscrepancy with three coats. Since theaverage value of a single layer of spacercoating is 20 m, present results are similar tothe studies of Vermilyea et.al.12 andCampagni et.al3.

Rafael Grajower11 expressed a similarresult that for spacer thickness of upto 70 mretention of the casting was not affectedwhile lesser spacer thicknesses causeddifficulty in insertion of the castings over the

dies.

Grajower and Lewinstein concurred withthis view and opined that appropriate use odie relief made bevels superfluous. Theysugges ted that s tudies regardingcementation be done on teeth instead of ondies because mechanical properties odentine may affect results. In the presentstudy, dies were used to maintain uniformityin preparation.

Conclusion:Cobalt - Chromium alloy copings had lesser

marginal fit when compared with copings oNickel Chromium alloy.

The average marginal discrepancy of CobalChromium alloy coping was 59.8 m.

The average marginal discrepancy of NickeChromium alloy coping was 41.7 m.

Use of paint on die spacer has the potentiato ease insertion of the coping withousignificantly affecting its marginal fitWithin the parameters of the study, it may beconcluded that Nickel Chromium alloycopings produced minimal marginadiscrepancy than Cobalt Chromiumcopings and that die spacer facilitates theinsertion of casting without affecting themarginal fit significantly.

References:1. Aquira ishikiriama.cd jair de freita

oliveira,influence of some factors on thefit of cemented crowns,JPD,Vol


80

70

60

50

40

30

20

10

01 2 3 4

COAT

FITINMICROMETERS

46

13.85

56.7

22.99

60.7

26.26

75.9

18.26

Mean SD

Bar Chart VMEAN AND STANDARD DEVIATION OF MARGINAL FIT

FOR Co-Cr Alloy WITH DIFFERENT NUMBER OFCOATS

50

4030

20

10

0

1 2 3 4

COAT

Bar Chart IVMEAN AND STANDARD DEVIATION OF MARGINAL FIT

FOR Ni-Cr Alloy WITH DIFFERENT NUMBER OFCOATS

FITINMICRO

METERS

Mean SD

Factors

Main Effect

Group

Coat

Interaction Group & Coat

Residual

Total

Sum of Squres

13104.40

3897.00

6349.30

74523.20

97873.90

df

1

3

3

152

Mean Squres

13104.4

1299.00

2116.43

490.28

F-Ratio

26.73

2.649

4.317

P- Value

0.001*

0.051

0.001*

Table-5Two-Way Anova Table To Test Marginal Fit Between Alloys And

Different Number Of Coats Of Die Spacers


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45,No.4400-4,19812. Bernard G.N.Smith.,The effect of the

surface roughness of prepared dentin onretention of castings.,JPD,Vol-23,No.2,187-97,1970

3. Campagni W.V.Preston J.D andReisbick M.H.,Measurement of paint-on die spacers used for castingrelief.,JPD,Vol-47,No.6,606-11,1982

4. Chu-Jung Wang, Philip L.Millstein and

Dan Nathanson,Effect of cement,cement space, marginal design, seatingaid material, and sealing force on crowncementation.JPD,Vol-67,No.6,786-90,1992

5. D o n a l d A . N i t k i n , K a m a lAsgar.,Evaluation of alternative alloyst o t y p e I I I g o l d f o r u s e i n

pr os th odo nt ic s. JA DA,Vol -9 3, 62 2-

29,19766. Dedmon H.W.,Disparity in expert

opinion on size of acceptable marginopenings.Oper.Dent,Vol-7,97-101,1982

7. David Assif,Bracha Anatopolski,MichelHelft and Israel Kaffe.,Comparision ofmethods of clinical evaluation of themarginal fit of complete cast goldcrowns.JPD,Vol-54,No.1,20-24,1985

8. Gerald D.Woolsey et al.,Quantitative

and qualitative evaluation of themarginal fit of cast ceramic, porcelain-Shoulder and cast metal full crownmarg ins . JPD, Vol -67 , No . 2 , 198-204,1992

9. Olive R.A.,Lowe J.A.,and OzakiM.M.Film thickness measurements of a

p a in t - o n d i e s p a c e r. JP D, Vo l -60,No.2,180-84,1988

10. Ossamu Ushiwata,Joao Vieira deMoraes.Marginal fit of NickelChromium copings before and afteinternal adjustments with duplicatedstone dies and disclosing agent.JPD,Vol83,No.6,634-43,2000

11. Rafael Grajower,Yuval Zuberi and IsraeLewinstein.Improving the fit of crownwith die spacers.JPD,Vol-61,No.5,55563,1989

12. Stanley G.Vermilyea,Michael J.Kuffleand Eugene F.Huget.The effects of dierelief agent on the retention of fulc o v e r a g e c a s t i n g s . J P D , V o l50.No.2,207-10,1983


Source of Support : Nill, Conflict of Interest : None declared

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