A Comparison of the Marginal Accuracy of Metal Copings Made with Three Different Brands of Nickel-Chromium Alloys and Various Sprue Designs: An Vitro Study.

Introduction: It is important to construct the sprue in a way that ensures that the mold gets an appropriate supply of metal at the right speed. Many manufacturers now offer sprue designs that have not been advocated in textbooks or publications for their normal use. Aim: The goal of this research was to compare the sprue design's marginal fit to that of the other designs.
Methods: During this investigation, we attempted to see whether the fabrication of metal copings could be improved. Three sprue designs were used in this research for the assessment of casting accuracy: normal cylindrical, funnel-shaped, and cuboidal or flattened sprue forms.
Results: The mean marginal disparity of nickel-chromium (Ni-Cr) alloy copings made by three distinct brands was determined to be statistically insignificant.
Conclusion: Within the limitation of the study, it was concluded that the marginal accuracy of metal copings fabricated with three different brands of Ni-Cr alloy did not reveal a statistically significant result. However, out of the three different sprue designs, that is, cylindrical, cuboidal, and funnel shape, the marginal accuracy of cylindrical and cuboidal sprue designs was found to be better than that of the funnel shape sprue design because the funnel shape sprue design is narrow at the point of attachment, thereby increasing the flow pressure and decreasing the turbulence of the molten metal. Copyright:

INTRODUCTION

In the field of fixed prosthetic dentistry, casting is an essential and often performed process.[1]

Dr. D. Phil Brook of Council Bluffs, Iowa, published the first documented record of the use of investment materials in dental casting in 1897 in his writings. However, it was not until Dr. William H. Taggart of Chicago's research in 1907 that the entire significance of this process was realized.[12]

Many studies are being conducted to increase the quality of investment materials, casting metal alloys, sprue design, and casting technology through time to achieve precise and accurate casting. However, research is currently ongoing to achieve precise casting with the required properties.[345]

One of the most difficult problems has been achieving a casting with correct fitting and minimal surface roughness, both of which are critical requirements for rendering an accurate casting fit.[367]

The fit of a casted restoration's marginal fit has always been critical. The margin must match the prepared tooth's finish line as precisely as possible. Any flaw inside this zone can dramatically impair the restoration's longevity.[8]

Preston and Berger (1977) discovered that sprucing geometry is one of the major factors causing different castability and porosity effects with alloy casting. Sprues of various shapes and designs have been reported, including cylindrical sprues with and without reservoirs, conical sprues, and straight and flared sprue designs.[9]

The marginal accuracy of metal coping is dependent on the type of investment material, sprue geometry, and casting technique, according to the literature review.[10] As a result, more research is needed to assess the marginal accuracy of metal copings with various sprue designs.

MATERIALS AND METHOD

Rationale

In this study, we tried to find out the marginal accuracy of metal copings fabricated with three different brands of nickel–chromium (Ni–Cr) alloy after using three sprue designs.

METHODOLOGY

A total of 135 samples of cast metal coping were prepared using three different brands of Ni–Cr alloys with three different sprue designs.

This study was completed in the following steps:

Fabrication of sprue

Spruing of wax pattern

Investing of wax pattern

Burnout

Casting of specimens

Divesting and sandblasting

Grouping of Samples

These samples were divided into three main groups, with each group containing 45 numbers of

Group A: 45 samples of Ni–Cr alloys (NDN)

Group B: 45 samples of Ni–Cr alloys (RUBY MAX CB WHITE)

Group C: 45 samples of Ni–Cr alloys (DAM CAST)

These three main groups were further divided into three subgroups based on three different types of sprue designs.

Subgroup C (15) cylindrical sprue design (AC1 to AC15)

Subgroup S (15) funnel sprue design (BS1 to BS15)

Subgroup U (15) cuboidal sprue design (CU1 to CU15)

Testing of Samples

The samples were tested using a stereomicroscope at 100× magnification. The casting was seated on the master die manually and examined under an optical stereomicroscope at 100× magnification to measure the marginal discrepancy at the four predetermined sites.

RESULTS

To evaluate the marginal accuracy of metal coping made by three different brands (NDN, RUBY, and DAM CAST) of Ni–Cr alloys.

To evaluate the effect of various sprue designs (cylindrical, funnel, and cuboidal) on the marginal accuracy of metal coping.

To compare the marginal accuracy of metal coping made by three different brands of Ni–Cr alloys after using different sprue designs.

A total of 135 samples were fabricated. The samples were divided into three groups according to three different brands of Ni–Cr alloy, with 45 specimens in each group. These were further divided into three subgroups according to their sprue design. Thereafter, the castings were checked for their marginal discrepancy using a stereomicroscope and the readings were tabulated.

Description: The mean marginal discrepancy in the cylindrical subgroup was 0.27 ± 0.05, for funnel shape it was 0.27 ± 0.04 and for cuboidal, it was 0.22 ± 0.05. Using one-way analysis of variance (ANOVA), statistically significant variation was found in three subgroups of group A (F = 3.635, P value = 0.035). On comparing marginal discrepancies of three subgroups of group A, a statistically significant difference was found in only AC versus AS (P = 0.31) and AC versus AU (P = 0.028) of group A [Tables 1a and 1b].

Table 1a

One-way ANOVA results for group A

	Source of variation	Sum of squares	df	Mean square	F	P
Group A	Between groups	0.018	2	0.009	3.635	0.035
	Within groups	0.104	42	0.002		S, P<0.05
	Total	0.121	44

S=significant NS=non-significant

Table 1b

Multiple comparisons based on the Tukey test

Group		Mean difference (I-J)	Std. error	P	95% Confidence interval
					Lower bound	Upper bound
Cylindrical	Funnel shape	0.06	0.02	0.031, S, P<0.05	0.004	0.12
	Cuboidal	0.06	0.02	0.028, S, P<0.05	0.006	0.12
Funnel shape	Cuboidal	0.001	0.02	0.999, NS, P>0.05	-0.057	0.05

S=significant; NS=non-significant

Description: The mean marginal discrepancy in the cylindrical subgroup was 0.23 ± 0.03, for funnel shape, it was 0.20 ± 0.04 and for cuboidal, it was 0.20 ± 0.08. Using one-way ANOVA, no statistically significant variation was found in three subgroups of group B (F = 0.579, P = 0.564). On comparing marginal discrepancies of three subgroups of group B, no statistically significant difference was found between cylindrical and funnel shapes (P = 0.634), between cylindrical and cuboidal (P = 0.614), and between funnel shape and cuboidal (P = 0.999) [Table 2].

Table 2

One-way ANOVA results for group B

Source of variation group B	Sum of squares	Df	Mean square	F	P
Between groups	0.006	2	0.003	0.579	0.565
Within groups	0.213	42	0.005		NS, P>0.05
Total	0.219	44

S=significant; NS=non-significant

Description: The mean marginal discrepancy in the cylindrical subgroup was 0.21 ± 0.03, for funnel shape, it was 0.22 ± 0.07 and for cuboidal, it was 0.20 ± 0.05. Using one-way ANOVA, no statistically significant variation was found in three subgroups of group C (F = 0.242, P = 0.786). On comparing marginal discrepancies of three subgroups of group C, no statistically significant difference was found between cylindrical and funnel shapes (P = 0.877), between cylindrical and cuboidal (P = 0.981), and between funnel shape and cuboidal (P = 0.780) [Table 3].

Table 3

One-way ANOVA results for group C

Source of variation group C	Sum of squares	Df	Mean square	F	P
Between groups	0.002	2	0.001	0.242	0.786
Within groups	0.212	42	0.005		NS, P>0.05
Total	0.214	44

S=significant; NS=non-significant

Description: The mean marginal discrepancy in the cylindrical subgroup was 0.27 ± 0.05, for subgroup B, it was 0.23 ± 0.07 and for group C, it was 0.21 ± 0.07. Using one-way ANOVA, no statistically significant variation was found in cylindrical subgroups (F = 2.935, P = 0.064). On comparing marginal discrepancies of three cylindrical subgroups, no statistically significant difference was found between groups A and B (P = 0.278), between groups A and C (P = 0.055), and between groups B and C (P = 0.683) [Table 4].

Table 4

Comparison of marginal discrepancy in cylindrical shape sprue

Source of variation	Sum of squares	Df	Mean square	F	P
Between groups	0.028	2	0.014	2.935	0.064
Within groups	0.199	42	0.005		NS, P>0.05
Total	0.227	44

NS=non-significant

Description: The mean marginal discrepancy in the funnel shape subgroup was 0.27 ± 0.042, for subgroup B, it was 0.20 ± 0.045 and for group C, it was 0.22 ± 0.078. Using one-way ANOVA, statistically significant variation was found in funnel shape subgroups (F = 4.82, P = 0.013). On comparing marginal discrepancies of three funnel shape subgroups, a statistically significant difference was found between groups A and B (P = 0.013), and no significant difference was found between groups A and C (P = 0.075) and between groups B and C (P = 0.744) [Tables 5a and 5b].

Table 5a

Comparison of marginal discrepancy in funnel shapes sprue

Source of variation	Sum of squares	Df	Mean square	F	P
Between groups	0.032	2	0.016	4.82	0.013
Within groups	0.140	42	0.003		S, P<0.05
Total	0.172	44

S=significant; NS=non-significant

Table 5b

Multiple comparisons using the Tukey test

Group		Mean difference (I-J)	Std. error	P	95% Confidence interval
					Lower bound	Upper bound
Group A	Group B	0.062	0.021	0.013, S, P<0.05	0.011	0.114
	Group C	0.047	0.021	0.075, NS, P>0.05	-0.003	0.098
Group B	Group C	-0.015	0.021	0.744, NS, P>0.05	-0.066	0.035

S=significant; NS=non-significant

Description: The mean marginal discrepancy in the cuboidal subgroup was 0.22 ± 0.054, for subgroup B, it was 0.20 ± 0.084 and for group C, it was 0.20 ± 0.058. Using one-way ANOVA, no statistically significant variation was found in cuboidal subgroups (F = 0.532, P = 0.591). On comparing marginal discrepancies of three cuboidal subgroups, no statistically significant difference was found between groups A and B (P = 0.662), between groups A and C (P = 0.634), and between groups B and C (P = 0.999) [Table 6].

Table 6

Comparison of marginal discrepancy in cuboidal shape sprue

Source of variation	Sum of squares	Df	Mean square	F	P
Between groups	0.005	2	0.002	0.532	0.591
Within groups	0.190	42	0.005		NS, P>0.05
Total	0.194	44

S=significant; NS=non-significant

DISCUSSION

Because individuals are living longer, requesting more dental treatment, and being more educated about their dental health, fixed prosthodontics has become a prominent aspect of current restorative dentistry.[11] For the casting of fixed partial dentures, many alloys and procedures have been introduced.[2] In the molten state, an alloy is a mixture of one or more metals that are soluble in each other. It is possible to create an infinite number of structures with an infinite range of attributes by mixing different metals in varied ratios.

In comparison to high noble metal alloys, noble alloys have a lesser percentage of gold combined with silver, palladium, and platinum. Nickel, chromium, and cobalt alloys are the most common base metal alloys.[12]

Base metal alloy substructures can be finished thinner than noble alloy substructures, providing greater deformation resistance and hence better restoration strength.[13]

No research on the marginal accuracy of Ni–Cr complete coverage crowns produced with three brands of Ni–Cr alloy and with varied sprue designs have been published so far.[61213] As a result, the goal of this study was to compare the marginal accuracy of Ni–Cr alloys from three distinct companies and three distinct sprue designs.

The marginal disagreement of castings obtained in this investigation for Ni–Cr alloys was larger than the high noble alloy, which was consistent with previous research by J. David Duncan and Tjan et al.[1415]

CONCLUSION

The marginal discrepancy of funnel shape sprues with three different brands (i.e., between subgroups AS (NDN), BS (RUBY MAX), and CS (DAM CAST) was found to be statistically significant. Hence, it is interpreted that the marginal discrepancy of funnel shape sprues of NDN is more as compared to that of RUBY MAX and DAM CAST, whereas no significant difference was found between RUBY MAX and DAM CAST.

The marginal discrepancy of cuboidal shape sprues with three different brands (i.e., between subgroups AU (NDN), BU (RUBY MAX), and CU (DAM CAST) was found to be statistically insignificant.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.