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ORIGINAL ARTICLE
Year : 2018  |  Volume : 10  |  Issue : 1  |  Page : 31-36

Assessment of the marginal fit, ceramo-metal shear bond strength and the fractographic analysis of sinter cast gold: An In-vitro study


1 Department of Prosthodontics and Crown and Bridge, Saraswati-Dhanwantri Dental College and Hospital and Post-Graduate Research Institute, Parbhani, Maharashtra, India
2 Department of Prosthodontics and Crown and Bridge, MGM Dental College and Hospital, Navi Mumbai, India
3 Department of Prosthodontics and Crown and Bridge, Dr. D. Y. Patil Dental College and Hospital, Navi Mumbai, India
4 Department of Oral Medicine and Radiology, Saraswati-Dhanwantari Dental College and Hospital and Post-Graduate Research Institute, Parbhani, Maharashtra, India

Date of Web Publication9-Jul-2018

Correspondence Address:
Dr. Abhishek S Nayyar
Reader cum Associate Professor and PG Guide, 44, Behind Singla Nursing Home, New Friends’ Colony, Model Town, Panipat - 132 103, Haryana
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jofs.jofs_101_16

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  Abstract 


Introduction: The fractographic analysis is performed by observing, measuring, and interpreting the fracture surface topography that can determine many features of the microstructure of materials and the mechanics of the fracture. The aim of this study was to assess the marginal fit and the ceramo-metal shear bond strength of sinter cast gold, and to analyze the debonded sample by fractography. Materials and Methods: A total of five sinter cast gold copings were prepared on a stainless master die resembling a maxillary 1st pre-molar to receive a ceramo-metal restoration. Each of the copings was then assessed for the marginal fit before and after ceramic firing. In addition, a total of five ceramo-metal discs were fabricated for testing shear bond strength at the metal-ceramic interface. The samples were subjected to increasing shear load on a universal testing machine with crosshead speed of 0.002 mm/s. The load at which the samples debonded completely was noted, and the fractographic analysis of the samples was performed. Results: The mean marginal fit found in this study for sinter cast gold before ceramic firing was found to be 11.5 μm with a standard deviation of ±4.64 μm, and after ceramic firing, it was found to be 9.38 μm with a standard deviation of ±3.57 μm. The average shear bond strength at the sinter cast gold ceramic interface was 18.216 MPa. The fractographic analysis showed the globular microstructure of sinter cast gold on sintering, adhesive, and mix-mode type of fracture with the presence of both gold and ceramic. Conclusion: The marginal fit observed before and after ceramic firing was within clinically acceptable range, whereas the ceramo-metal shear bond strength between sinter cast gold and ceramic was found to be inadequate.

Keywords: Ceramo-metal restorations, fractographic analysis, shear bond strength


How to cite this article:
Turakhia H, Ram SM, Mehta A, Nayyar AS. Assessment of the marginal fit, ceramo-metal shear bond strength and the fractographic analysis of sinter cast gold: An In-vitro study . J Orofac Sci 2018;10:31-6

How to cite this URL:
Turakhia H, Ram SM, Mehta A, Nayyar AS. Assessment of the marginal fit, ceramo-metal shear bond strength and the fractographic analysis of sinter cast gold: An In-vitro study . J Orofac Sci [serial online] 2018 [cited 2018 Dec 17];10:31-6. Available from: http://www.jofs.in/text.asp?2018/10/1/31/236202




  Introduction Top


Modern science and technology in dentistry has traveled the lengths and breadths of many unimaginative firsts. Adaptation and a detailed study of our history gives birth to many such innovations. Ceramo-metal restorations, precious or nonprecious, have been popular for decades. Their success depends on many factors including the accuracy of the preparation, impression materials, techniques, laboratory procedures, type of alloys, ceramics, and also, the skill of the operator. The marginal fit is of prime importance to provide a seal at the margins and reduce the thickness of luting cement. There are many theories proposed in literature to explain the improper fit of ceramo-metal restorations when they are fabricated by the lost wax technique. There are various steps involved in the fabrication of ceramo-metal restorations. Distortion may creep in at any of the stages during the fabrication procedures, which may ultimately lead to failure in the final restoration. The ceramo-metal bond strength is also an important parameter in the success of the restoration. This is because during intra-oral function, the restoration is subjected to constant masticatory load and thermal cycling. Although many theories and concepts have been offered relative to the actual mechanism of bonding, the exact mechanism still remains uncertain. The accurate measurement of the bond strength at the metal ceramic interface is most complex, and various test methods have been used over the years. The ceramo-metal interface of debonded restorations can be visualized by fractography. It is relevant to material sciences. The fractographic analysis is performed by observing, measuring, and interpreting the fracture surface topography that can determine many features of the microstructure of materials and the mechanics of the fracture. In the existential scenario of breakthrough technology, further implication of the same has been researched, and this technology was discovered to bring foil metal technology in the form of sinter cast gold, which is 99.9% pure gold, for the field of dentistry. It has helped to eliminate the lost wax technique, which has been popular for years now. Therefore, this study was conducted to investigate the two important properties of sinter cast gold – the marginal fit and the ceramo-metal shear bond strength along with the fractographic analysis of the debonded surfaces. The aim of this study was to assess the marginal fit and the ceramo-metal shear bond strength of sinter cast gold, and to analyze the debonded sample by fractography.

Aims and objectives

The main aims and objectives for which this study was conducted were:
  1. To evaluate the marginal fit of sinter cast gold copings before ceramic firing;
  2. To evaluate the marginal fit of sinter cast gold copings after ceramic firing;
  3. To evaluate the shear bond strength at the interface of sinter cast gold and ceramic; and
  4. The fractographic analysis of the surface of the debonded samples of sinter cast gold.



  Materials and Methods Top


Ethical approval for this study (DYPDC/EC/746/2007) was provided by the Ethical Committee of D.Y.Patil Dental college, Navi Mumbai, on 12 February 2014.

The materials used for the test samples were:

Sinter cast gold sheet (Noble Metal) composition:

Gold (Au) − 99.9%.; and

Trace elements (Ir, Rh, Ta) − 0.1%.

Properties of sinter cast gold as claimed by the company were:

Color − yellow;

Density − 19.3;

Coefficient of thermal expansion − 14.2–14.6;

Vicker’s hardness − 90–95 VHN;

Melting range − 10,600–10,750; and

Thickness − 1 mm.

The materials and the instruments used for fabrication of the test samples were:
  1. Sinter cast gold for adaptation:
    1. Die lubricant − Picosep;
    2. Bard parker blade no. 15 with handle; and
    3. Titanium spatula (Noble Metal).
  2. Investing and sintering process:
    1. Refractory die material (Noble Metal);
    2. Acetone more than 99% pure (S.D. Fine-Chem Limited);
    3. Aluminum oxide;
    4. Rubber cup;
    5. Stainless steel cement spatula;
    6. Glass slab;
    7. Hemostat;
    8. Ceramic furnace plate; and
    9. Ceramic furnace (Centurion).
  3. Recovery and cleaning of sintered samples:
    1. Hemostat;
    2. Rubber bowl with cold water; and
    3. Bard parker blade no. 15 with handle; along with
    4. Ultrasonic cleaner (Electrosonic, Germany).
  4. Finishing of the test samples:
    1. Sintered diamond burs;
    2. White messy wheels; and
    3. Ball burnisher.
  5. For ceramic application and firing:
    1. Sable paint brushes (Ivoclar, Vivadent);
    2. Wash opaque ceramic (Vita VMK, Ivoclar);
    3. Dentin ceramic (Vita VMK, Ivolclar);
    4. Hemostat;
    5. Ceramic furnace plate; and
    6. Ceramic furnace (Centurion).
  6. Finishing of the ceramic surfaces:
    1. Green stones (Shofu, Japan); along with
    2. White stones (Shofu, Japan).
  7. Instruments for measurement:
    1. Electronic digital vernier caliper.
  8. Equipments for testing:
    1. For marginal fit:
      1. Clay; and
      2. Optical microscope.
    2. For bond strength:
      1. Fixture to hold the sample;
      2. Special jig assembly with rods; and
      3. Universal testing machine with load analyzer (Bliss, Bangalore).
    3. For fractography:
        Scanning electron microscope (SEM) (FEI, Quanta 2000).


Methods

Assessment of marginal fit

A Stainless steel replica of a prepared maxillary 1st premolar was prepared to receive a ceramo-metal restoration following guidelines given by Tylman. Eight vertical indentations were engraved on the base of the die approximately 1 mm from the finishing margin. These acted as reference points for the measurements of marginal fit under optical microscope. For the fabrication of the copings, sinter cast gold strips were carefully cut from the sheet and adapted to the die. The copings were, then, invested and sintering process was carried-out. The sintered copings were, then, placed on the stainless steel master die and burnished at the margins [Figure 1]. The burnishing was done using ball burnisher as pure sinter cast gold was pure gold sheet and gold is malleable and ductile. In a similar manner, the remaining 4 sinter cast gold copings were fabricated and numbered 1 to 4. Each of the copings were seated on the master die one after the other and assessed for marginal fit before ceramic firing. The fit was observed under an optical microscope at 100X magnification [Figure 2]. The observations were noted and tabulated. Ceramic build-up was done on all the 5 copings [Figure 3]. The marginal fit was assessed in the same manner as done before ceramic firing in the first case and the observations were tabulated [Figure 4].
Figure 1: Sinter cast gold coping on master die

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Figure 2: Optical micrograph showing the marginal fit of sinter cast gold before ceramic firing

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Figure 3: Sinter cast gold coping on master die after ceramic firing

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Figure 4: Optical micrograph showing the marginal fit of sinter cast gold after ceramic firing

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Assessment of ceramo-metal shear bond strength

A total of 5 sinter cast gold discs were fabricated from a circular mould with nut screw assembly for easy retrieval for testing shear bond strength at the metal-ceramic interface [Figure 5]. Ceramic build-up was done on the sintered discs. The samples were numbered 1 to 5. The samples were, then, subjected to increasing shear load on a Universal Testing Machine with crosshead speed of 0.002 mm/sec at the metal ceramic interface [Figure 6]. The loads at which, the samples debonded completely, were noted and the observations were tabulated [Figure 7].
Figure 5: Ceramo-metal shear bond strength of the test samples

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Figure 6: Sample position on universal testing machine for the shear bond strength

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Figure 7: Debonded sample

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Fractographic analysis

The sinter cast gold parts of the debonded samples were cleaned ultrasonically using acetone and examined under scanning electron microscope (SEM). The analysis was seen as images which were recorded photographically [Figure 8].
Figure 8: The fractographic analysis using scanning electron microscope (SEM) showing globular microstructure of sinter cast gold on sintering

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Statistical test used

The data obtained were subjected to statistical analysis and the values obtained were shown. The statistical test used was Student’s t-test, and P-value of 0.05 was considered to be statistically significant.


  Results Top


The mean marginal fit found in this study for sinter cast gold before ceramic firing was found to be 11.5 μm with a standard deviation of ±4.64 μm, and after ceramic firing, it was found to be 9.38 μm with a standard deviation of ±3.57 μm. The change in marginal discrepancy before and after ceramic firing was 2.12 ± 2.93 μm [Table 1]. The average shear bond strength at the sinter cast gold ceramic interface was 18.216 MPa [Table 2]. The fractographic analysis showed the globular microstructure of sinter cast gold on sintering, adhesive, and mix-mode type of fracture with presence of both gold and ceramic [Figure 9],[Figure 10],[Figure 11].
Table 1: Comparison of the mean marginal fit before and after ceramic firing

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Table 2: Mean shear bond strength, standard deviation and range

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Figure 9: The fractographic analysis showing element on the debonded surface

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Figure 10: The fractographic analysis showing ceramic constituents on debonded surface

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Figure 11: The fractographic analysis showing globular microstructure of sinter cast gold on sintering, adhesive, and mix-mode type of fracture

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  Discussion Top


Sinter cast gold, the latest entrant into the arena of foil metal techniques, was introduced with an idea to make the laboratory procedures leading to the fabrication of a ceramo-metal restoration simpler and less time consuming. Sintering process is the transformation of metal powders into a single-bonded mass without getting to the melting process. The process yields a rugged surface texture suited for mechanical interlocking with ceramic. This method produces uniform thin gold copings of 0.3 mm thickness, thus providing ample space for porcelain to be built up, which would, in turn, enhance the esthetics of the restoration. A marginal adaptation below 30 μm can be obtained consistently. The ideal cement film thickness ranged from 25 to 40 μm. The practical range for clinical acceptability of the marginal fit is around 50–75 μm. The marginal opening is almost eight times more in nonprecious alloys due to thick oxide layers. The absolute marginal discrepancy for cast restorations was found to be 64 ± 24.1 μm, and for electro-formed gold restorations, it was 36 ± 32.7 μm. Captek yielded a mean marginal fit of 68 μm, whereas for those of electro-formed crowns, it was found to be 32 μm and that of high noble alloys was 31 μm. It can, therefore, be seen from the results that sinter cast gold yielded copings with good marginal adaptation and fit. It may be due to elimination of errors as in lost wax technique and because it is burnishable. The range of the ceramo-metal shear bond strength was between 25 and 55 MPa depending on the type of porcelain, alloy, and preparation used. Captek, a similar ceramo-metal material, had a shear bond strength of 56.08 ± 9.47 MPa with a thin layer of bonding agent, whereas increase in the layer of bonding agent decreased the bond strength to 27.28 MPa. The shear bond strength of base metal alloy was 29.93 MPa, whereas for ceramic alloy and palladium base ceramic alloy, it was 21.92 and 30.49 MPa, respectively. The present study found the ceramo-metal shear bond strength of sinter cast gold as 18.216 ± 0.285 MPa, which was lesser when compared with the values of similar materials from the previous studies. It was also seen in this study that no bonding agent was used for this system. In addition, sinter cast gold, being 99.9% pure gold, did not have any oxide layer formation at the metal-ceramic interface, resulting in much weaker van der Waal’s bond. However, comparison with other types of alloys and influence of time on the clinical use must be researched.[1],[2],[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16],[17]


  Conclusion Top


Within the limitations of the present in vitro study, the conclusions drawn were:
  1. The change in the marginal fit before and after ceramic firing was minimal and statistically insignificant.
  2. The marginal fit observed before and after ceramic firing was within clinically acceptable range.
  3. The ceramo-metal shear bond strength between sinter cast gold and ceramic was found to be inadequate.
  4. The fractographic analysis showed mix mode adhesive fracture between sinter cast gold and ceramic structure.


The system, being new, requires further research and clinical trials to enhance the properties of the material.

Acknowledgements

To all the patients who contributed in the study without whom this study would not have been feasible.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Morris HF. Department of Veterans Affairs Cooperative Studies Project No. 242. Quantitative and qualitative evaluation of the marginal fit of cast ceramic, porcelain-shoulder, and cast metal full crown margins. J Prosthet Dent 1992;67:198-204.  Back to cited text no. 11
    
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Hung SH, Hung KS, Eick JD, Tirade XX, Chappel RP. Marginal fit of porcelain fused to metal and two types of ceramic crown. J Prosthet Dent 1990;63:26-31.  Back to cited text no. 13
    
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Holmes JR, Pilcher ES, Rivers JA, Stewart RM. Marginal fit of electroformed ceramometal crowns. J Prosthodont 1996;5:111-4.  Back to cited text no. 15
    
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Pettenò D, Schierano G, Bassi F, Bresciano ME, Carossa S. Comparison of marginal fit of three different metal-ceramic systems: An in vitro study. Int J Prosthodont 2000;13:403-8.  Back to cited text no. 16
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11]
 
 
    Tables

  [Table 1], [Table 2]



 

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