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ORIGINAL ARTICLE
Year : 2013  |  Volume : 2  |  Issue : 1  |  Page : 36-41

Evaluation of shear bond strength and microleakage of two repair systems for porcelain fused metal restoration


1 Govt Medical College, Anantapur, India
2 Department of Prosthodontics, Meghna Institute of Dental Sciences, Nizamabad, Andhra Pradesh, India
3 Department of Prosthodontics, SRM Dental College, Chennai, India

Date of Web Publication13-Mar-2013

Correspondence Address:
A Kalyan Chakravarthy
Department of Prosthodontics, Meghna Institute of Dental Sciences, Mallaram Village, Warni Road, Nizamabad, Andhra Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2277-8632.108511

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  Abstract 

Aim: This study evaluated the shear bond strength and microleakage of two repair systems for porcelain fused metal restoration.
Materials and Methods: Forty cylindrical samples were fabricated in nickel-chromium alloy and 40 samples in feldspathic porcelain. Twenty samples of Ni-Cr alloy and 20 samples of porcelain disks were embedded in the acrylic resin, except its examination surface. The remaining 20 samples of Ni-Cr alloy and 20 samples of porcelain prepared for testing microleakage were covered with double-faced transparent tape on one surface and resin composite was bonded with the CoJet-3M and Ceramic Repair-Ivoclar. The samples were stored in distilled water for 24 h at 37°C before thermocycling at 5° to 55°C for 300 cycles and again stored at 37°C for 8 days. Shear bond strength test were performed in a universal testing machine with cross head speed of 1 mm/min. The data was analyzed using one way ANOVA and the Tukey honestly significant difference (HSD) test (P < 0.05). A total of 40 samples were tested. The remaining samples were prepared for testing microleakage samples. After thermocycling, the samples were placed in 0.5% basic fuchsin solution for 24 h and washed under tap water. These samples were transversely sectioned and the split samples were examined under 10 x microscopes for better evaluation of the samples. The leakage along the interface was measured under the microscope. Later, the inter-reliability of the scores was assessed using Kappa test. The data were analyzed statistically using a non-parametric Kruskal-Wallis test.
Results: Mean bond strength values for G 1 M 1 B 35.77 ± 2.52 was the highest followed by G 1 P 1 B 33.23 ± 3.24, G 2 P 2 B 32.47 ± 3.53 and the lowest showed in G 2 M 2 B 24.70 ± 2.87. Test of significant showed that the mean value was significant among the groups (P < 0.001). The bond strength of the repair systems could not be related to the degree of leakage.
Conclusion: For the metal surfaces, the greatest strengths were achieved with use of the CoJet-System. The bond strength of the repair systems could not be related to the degree of leakage.

Keywords: Microleakage, porcelain fused metal, repair systems, shear bond strength


How to cite this article:
Gasthi A, Chakravarthy A K, Kumar B M. Evaluation of shear bond strength and microleakage of two repair systems for porcelain fused metal restoration. J NTR Univ Health Sci 2013;2:36-41

How to cite this URL:
Gasthi A, Chakravarthy A K, Kumar B M. Evaluation of shear bond strength and microleakage of two repair systems for porcelain fused metal restoration. J NTR Univ Health Sci [serial online] 2013 [cited 2020 Apr 7];2:36-41. Available from: http://www.jdrntruhs.org/text.asp?2013/2/1/36/108511


  Introduction Top


Porcelain fused metal restorations are considered as a good optional procedures in fixed prosthodontics not only because of mechanical strength, as well as esthetic qualities imparted by porcelain material. The modern day dental practices utilize base metal alloys as a metal substructure [1] ever since its inception from 1960's. The copings made with Ni-Cr alloys even with less thickness develop high rigidity maintaining the structural durability of substructure of porcelain fused metal restoration.

Porcelain fused metal crowns and bridges are commonly used in fixed prosthodontics because of their excellent biocompatibility and superior esthetic qualities. [2] However, porcelain failures have been often reported due to fracture of either as material itself or exposing the metal substrate or completely debonding of porcelain. [3] In such cases, repair of porcelain fracture has been a mandatory procedure to continue the functional aspects of porcelain fused restorations intraoral. The repair of porcelain intraoral is a necessitating procedure, because manual fabrication of metal frame works and porcelain veneers is time consuming and requires high level of skill. It also develops unpleasant experience for the patient and arduous for the clinician to remove these restorations from mouth. [4] Intraoral repair of porcelain reduces clinical time and less treatment sessions for the patient. [4] Moreover, this procedure restores esthetic and function in easy, inexpensive and rapid form.

Porcelain material veneered to metal coping -has the potential to fracture due to factors such as, impact and fatigue load, occlusal forces, incompatible thermal expansion coefficients between the porcelain and metal substructure, use of metal with low-elastic modulus, seating force during trial insertion or cementation, improper tooth preparation especially cervical part, improper design, irregular laboratory work, micro-defects within the material, and trauma. [2],[3],[5],[6] These fractures may be either as fracture in porcelain (cohesive fracture) only or fracture with both porcelain and metal exposed or fracture with substantial metal exposure (adhesive fracture). [3]

Various materials have been used to meet the demands of repair metal and porcelain. [7],[8] For repair purposes, use of the hybrid composite resins was advised as the most suitable ones. [4],[9] Various methods have been introduced to repair fractured porcelain and metal with resin composite. [3],[4],[10],[11] Sandblasting was described as the most effective surface treatment for the fractured porcelain fused metal restorations, regardless of whether the fracture was at metal, porcelain and or combined exposure. [2],[4] However, compulsory use of silane together with aluminium oxide was advised in order to avoid changes in retention.

Different systems for repairing porcelain fused metal restorations have been used. [1],[12],[13] This study was conducted to evaluate the bond strength and microleakage of porcelain fused metal repair system of CoJet system with that of lower-cost Ceramic Repair-Ivoclar system.


  Materials and Methods Top


Two metal dies were made using stainless steel material in the form of a disc which was fabricated in a mechanical lathe. The dies used for the study was in the form of circular disk with diameter 14 mm and thickness 2 mm. One die was milled in the centre with an internal diameter of 9 mm and thickness 2 mm [Figure 1] which was used for preparing wax patterns and porcelain samples. The other die was milled in the center with an internal diameter of 4 mm and thickness of 2 mm, which was used for bonding of composite resin material. Metal dies were fabricated to standardize all the specimens made with metal and porcelain in this study.
Figure 1: The dies used for the study was in the form of circular disk with diameter 14 mm and thickness 2 mm. One die was milled in the centre with an internal diameter of 9 mm and thickness 2 mm (Figure 1) which was used for preparing wax patterns and porcelain samples

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Wax patterns were made as per the dimensions of metal die using crown wax (Kronenwachs, Bego Germany). Sprue was attached and placed in a silicon crucible former and invested using phosphate bonded investment material (Bellasun, Bego Germany) and casting was done using Ni-Cr alloy (Ceralloy, Dental alloy international private limited, India) in the induction casting machine. After complete bench curing the casting ring was divested and sand blasted using 110 μm aluminum oxide. Sprues were cut off using carborundum disc under high speed lathe instrument. A total of 40 samples of Ni-Cr alloy were made.

Porcelain samples were fabricated using the same metal die of an internal diameter of 9 mm and thickness 2 mm. Portions of body porcelain-mixed with build-up liquid (IPS d.SIGN, Ivoclar) and condensed in the milled area of metal die. Condensed material was placed on porcelain mat for firing (P 100 , Ivoclar). A total of 40 samples of porcelain were made.

Twenty samples of Ni-Cr alloy and 20 samples of porcelain disks were placed on the glass slab and plastic mold (12 mm diameter, 20 mm length) placed around the samples, so that the sample will be completely embedded in the acrylic resin, except its examination surface. The remaining 20 samples of Ni-Cr alloy and 20 samples of porcelain prepared for testing microleakage were covered with double-faced transparent tape on one surface to avoid contamination by the embedding medium and the other surface was kept for surface treatment. All 80 samples bonding surfaces were smoothed with silicone carbide papers of 100, 120, 400 grit. This was followed by 20 seconds surface treatment with 110 μm aluminum oxide and the specimens were ultrasonically cleaned and soaked in distilled water for 48 h before bonding.

Sample groups were arbitrarily divided for resin composite bonding with the CoJet-3M ESPE and Ceramic Repair-Ivoclar system and followed according to the manufacturers' recommendations. The composite resin material-Tetric EvoCeram was used for all samples. Composite resin material was bonded to each sample using the second metal die of 4 mm internal diameter and 2 mm thickness [Figure 2] and light cured for 40 seconds and after removal of metal die an additional 20 seconds of light curing was done. A total of 80 samples of alloy and porcelain samples were bonded.
Figure 2: Composite resin material was bonded to each sample using the second metal die of 4 mm internal diameter and 2 mm thickness (Figure 2) and light cured for 40 seconds and after removal of metal die an additional 20 seconds of light curing was done

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All samples were stored in 37°C distilled water for 24 h before being thermocycled between 5°C ± 2°C and 55°C ± 2°C for 300 cycles with 30 seconds dwell time at each temperature. After thermocycling, specimens were stored in 37°C distilled water for an additional 8 days before being subjected to a shear load and microleakage.

Shear bond strength was tested with a universal testing machine at 1 mm/min crosshead speed using chisel shaped rod. The samples were loaded until they are fractured. The data was analyzed using one way ANOVA and the Tukey honestly significant difference (HSD) test (P < 0.05). A total of 40 samples were tested.

The remaining samples which were covered with double faced transparent tape on one surface were prepared (as mentioned above) for testing microleakage. After thermocycling, specimens were stored in 37°C distilled water for an additional 8 days. Then the samples were placed in 0.5% basic fuchsin solution for 24 h. Samples were removed and washed under tap water. These samples were transversely sectioned with double faced diamond disk. Each sample was split into two and each of the split samples was examined under 10x microscope for better evaluation of the samples The dye (0.5% basic fuchsin) penetration at the composite-repair interface (composite to metal and composite to porcelain) was measured under microscope [Figure 3] according to the following scores and the score indicates the extent of dye penetration along the repair interface from the margin.
Figure 3: The dye (0.5% basic fuchsin) penetration at the compositerepair interface (composite to metal and composite to porcelain) was measured under microscope (Figure 3) according to the following scores and the score indicates the extent of dye penetration

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0 - Absence of dye penetration at repair interface

1 - Dye penetration up to ½ of repair interface

2 - Dye penetration more than ½ of repair interface, without total involvement

3 - Complete repair interface involvement

Later the inter-reliability of the scores was assessed using Kappa test. The data were analyzed statistically using a non-parametric Kruskal-Wallis test.


  Results Top


For simplicity to references in the study these samples were coded accordingly and tabulated in [Table 1] and [Table 2] shows the score for measuring the extent of dye penetration along the interface. The score indicates the extent of dye penetration. [Table 3] show the mean standard deviation and test of significance between groups. Mean shear bond strength in G 1 M 1 B (35.77 ± 2.52) was the highest followed by G 1 P 1 B (33.23 ± 3.24), G 2 P 2 B (32.47 ± 3.53) and the lowest showed in G 2 M 2 B (24.70 ± 2.87). Test of significance showed that the mean value was significant among the groups (P < 0.001). [Table 4] shows the distribution of dye penetration scores.
Table 1: Reference code for evaluation of bond strength and microleakage of metal and porcelain samples for both groups of repair system

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Table 2: Dye penetration scores

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Table 3: Mean standard deviation and test of significance

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Table 4: Distribution of dye penetration

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The highest bond strengths were achieved for the alloy surfaces with use of the CoJet-System and for porcelain surfaces bond strengths were similar in both systems [Figure 4] - The bond strength of the repair systems could not be related to the degree of leakage.
Figure 4: Shear bond strengh of both systems

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In this study the bond strength of porcelain repairs materials of CoJet System and Ceramic Repair system to alloy surface ranges from 20.74 to 39.54 Mpa. For alloy surfaces, the greatest bond strength 39.54 Mpa was achieved with use of CoJet system than that of Ceramic Repair system. The mean bond strength for Ni-Cr alloy samples treated with CoJet system was 35.77 ± 2.52 Mpa, which was significantly different than that of Ni-Cr alloy samples treated with Ceramic repair-Ivoclar was 24.70 ± 2.87 Mpa. In case of porcelain groups, there is no significant difference in the bond strength. The only significant difference of P < 0.000 was seen in Ni-Cr alloy samples treated with Ceramic repair-Ivoclar group when compared with other groups.

In the microleakage study, the inter-reliability of the scores was assessed using Kappa test and the Kappa value is 1.000, which is highly reliable of both split up samples and the data were analyzed statistically using a non-parametric Kruskal-Wallis test. Scores of all experimental groups were not significantly different from one another (P > 0.005). Results showed little or no dye penetration at the repair interface.


  Discussion Top


Tensile, flexural, and shear tests have been used to measure the resin porcelain bond strength, with the shear bond strength test being the most required test for efficient bonding. Shear bond was chosen for this study because multiple substrates were used for bonding the composite. In addition, anterior restorations are subjected primarily to shear stresses, and the shear test is considered appropriate for quantifying the strength of porcelain repairs. [14],[15] This study applied minimal thermal cycles to the bonded interface. The addition of thermal stress may have affected adhesion, but it has never been demonstrated that cyclic thermal testing is related to clinical failures. [14]

Significant higher bond strength of 35.77 ± 2.52 Mpa was achieved with use of CoJet system because CoJet-Sand (SiO 2, 30μm) has a unique surface treatment property that when applied to metal with air abrasion. [14],[16] Whereas the bond strength for Ni-Cr alloy samples treated with Ceramic repair-Ivoclar group have significantly less value 24.70 ± 2.87 Mpa because the alloy surface was treated with 110 μm aluminium oxide which has less penetrating capacity. The mean bond strength of porcelain samples treated with Ceramic repair-Ivoclar was 32.47 ± 3.53 Mpa similar to that of CoJet system 33.23 ± 3.24 Mpa and no significant difference found because of chemical etching with 37% phosphoric acid and sandblasting, as the chemical agents dissolve the glass matrix selectively and cause physical alteration to promote adhesion of composite to the porous surface of fractured porcelain.

Only one study was identified that report the bond strength of the CoJet system on base metal alloys, [1] such as the Ni-Cr alloy used in this study. For Ni-Cr alloy surface CoJet group showed statistical superiority of 25.24 ± 3.46 Mpa compared to other groups and for porcelain groups Scotch bond, CoJet, Bistite showed the highest shear bond strength. But studies were done on noble metal alloys [14],[17] and showed that CoJet System had greater bond strength than others. The mean bond strength of both CoJet system and Ceramic repair system in this study was 35.77 ± 2.52 Mpa and 24.70 ± 2.87 Mpa respectively high when compared to the others, [1],[14],[17] This may be due to decrease in number of thermal cycles because thermocycling significantly reduced the mean bond strength. [18],[19] The differences in properties of the alloys such as thermal coefficient of expansion, hardness, roughness and surface properties were responsible for this result. The effects of temperature change and water absorption of composite resin were also responsible. Moreover, the hydrolyzed silanol groups of the silane orient better towards Ni-Cr alloy sample surfaces, thus more bonding sites for silanol groups on alloy surface compared with noble metal alloy, which increased the bond strength. [20]

Masami [21] studied that the adhesive strength of Ag-Pd alloy was 19.5 Mpa and Ni-Cr alloy was 19.5 Mpa before thermocycling and after thermocycling the adhesive strength of Ag-Pd alloy was 12.7 Mpa sharply reduced than that of Ni-Cr alloy of 15.7 Mpa. The reduction was attributed to great shearing stresses at the interface of Ag-Pd alloys and composite resins than those found in Ni-Cr alloys. Moreover, because the Ag-Pd alloy is soft compared with the Ni-Cr alloy the surfaces of Ag-Pd alloy samples treated by sandblasting were abraded and rounding of the edges were also considered to be cause of diminished adhesive strength. Appeldoorn et al[22] and Pratt et al[23] evaluated the shear bond strength of composite resin bonded to porcelain with use of different repair systems after 24 and 48 h and 3 months of water storage and thermocycling of which the shear bond strength for all the systems significantly.

Microleakage at the composite and repair interface can compromise the repair procedure, as the interfacial staining damages esthetics and the leakage leads to deterioration of the interface. Therefore, repair techniques and materials chosen should be able to increase the repair strength and also to promote an adequate interfacial sealing. This study was conducted to determine the microleakage of the two systems on composite and repair interface.

There was no significant dye penetration among CoJet system and Ceramic repair system, along the repair interface in this study. Application of etching and silinization of the porcelain samples significantly reduced microleakage and greatly increased the reliability of the bond between porcelain and composite during thermocycling. [24] Air abrasion and or acid etching are adequate to prevent microleakage. [4],[25],[26] Application of silane to porcelain was found to decrease microleakage [12],[13] of composite repair material. Sinasi [27] evaluated the effects of different metal surface treatments on the marginal leakage of resin bonded non precious alloy and found that there was no statistical significant difference in leakage between the sandblasted, acid etched and sandblasted and acid etched groups. Jones [28] found that there was no direct correlation between microleakage and shear bond strength.

For the metal surfaces, the greatest strengths were achieved with use of the CoJet-system. The bond strength of the repair systems could not be related to the degree of leakage.


  Conclusion Top


In this study the mean bond strength for Ni-Cr alloy samples treated with CoJet system was significantly different than that of Ni-Cr alloy samples treated with Ceramic repair-Ivoclar. The only significant difference (P < 0.000) was seen in Ni-Cr alloy samples treated with Ceramic repair-Ivoclar group when compared with other groups. The mean bond strength for porcelain samples treated with CoJet system was not significantly different than that of porcelain samples treated with Ceramic repair-Ivoclar.

There was no significant dye penetration among CoJet system and Ceramic repair system, along the repair interface. Scores of all the groups were not significantly different from one another (P > 0.05). Results showed little or no dye penetration at the repair interface. The bond strength of the repair systems could not be related to the degree of leakage.

Considering the limitations of this in vitro study, the results of the present study should be viewed with caution regarding clinical significance. To enhance bond strength of porcelain fused metal repair systems, various surface treatments like sand-blasting, etching and silane application should be done to alloy and porcelain surfaces which creates irregularities and facilitates the penetration of repair materials. Clinically this study requires a skill for intraoral repair due to the presence of saliva and oral fluids which makes the repair difficult for clinical success.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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