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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 9  |  Issue : 5  |  Page : 21-26

An in vitro study to compare glazed and polished surfaces of feldspathic porcelain and comparing three different polishing systems


1 Consultant Prosthodontist, The Tooth Place, Hospital and Research Institute, Ludhiana, Punjab, India
2 Department of Prosthodontics, Dr. R. Ahmed Dental College and Hospital, Kolkata, West Bengal, India
3 Department of Prosthodontics, Baba Jaswant Singh Dental College, Hospital and Research Institute, Ludhiana, Punjab, India

Date of Web Publication15-Sep-2017

Correspondence Address:
Harinder Kuckreja
Department of Prosthodontics, Baba Jaswant Singh Dental College, Hospital and Research Institute, Ludhiana, Punjab
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/IJDS.IJDS_87_17

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  Abstract 

Aim and Objectives: Effective finishing and polishing of dental restorations provides for oral health, function and aesthetics. There are studies which state that porcelain should be glazed after chairside adjustments, whereas, some studies advocate that polishing is equivalent or better than glazing. The main objective of this study was to compare glazing and polishing, and also, to compare three different polishing systems available in the Indian market, namely SHOFU, DFS and DIATECH. Materials and Methods: One hundred twenty six specimens of porcelain discs were prepared and divided into 3 groups with subsequent subgroups. Quantitative analysis was done using a profilometer to determine the roughness quotient (Ra value) and qualitative analysis was done using a Scanning Electron Microscope (SEM). Result: It was found out that glazing produces smoother surfaces as compared to polishing. Among the three different polishing systems used, SHOFU was found to produce the most smooth surfaces. Conclusion: The polished surface provided by the polishing kits was not comparable to the smoothness of the glazed surface and cannot substitute for glazing.

Keywords: Glazing, polishing, porcelain


How to cite this article:
Singh A, Sengupta B, Kuckreja H, Kuckreja K B. An in vitro study to compare glazed and polished surfaces of feldspathic porcelain and comparing three different polishing systems. Indian J Dent Sci 2017;9, Suppl S1:21-6

How to cite this URL:
Singh A, Sengupta B, Kuckreja H, Kuckreja K B. An in vitro study to compare glazed and polished surfaces of feldspathic porcelain and comparing three different polishing systems. Indian J Dent Sci [serial online] 2017 [cited 2017 Nov 21];9, Suppl S1:21-6. Available from: http://www.ijds.in/text.asp?2017/9/5/21/214939


  Introduction Top


Stains on teeth can be due to extrinsic causes such as excessive smoking, consumption of coffee, tea, poor oral hygiene habits or intrinsic causes such as metabolic disorders, genetic disorders, medications, infections in utero, and environmental.[1] They are esthetically displeasing and psychologically traumatizing.[2]

The extent of tooth destruction dictates the treatment plan of the dentist. Teeth might suffice with superficial fillings and may require veneers, inlays or onlays, extensive restorations, crowns, or replacement of missing teeth with fixed or removable prosthesis.

The restorative materials should possess properties such as wear resistance, insolubility in the oral environment, maintenance of marginal integrity, biocompatibility, maintenance of desired color, and maintenance of a smooth and polished surface.

Effective finishing and polishing of dental restorations provide three benefits of dental care: oral health, function, and esthetics.[3]

For dental applications, porcelain with a smooth surface is desirable to minimize the wear damage that can be produced on enamel by the porcelain surface.[4] Furthermore, surface texture and appearance of a porcelain restoration should resemble natural tooth surface.[5] When a porcelain restoration is obtained from a dental laboratory, it is in a glazed state.

Glazing reduces wear of the opposing dentition, improves oral function and mastication, and makes the restoration more esthetic.[6]

Clinically, modifications are often required to correct the occlusion and improve the shape and contour of porcelain restorations.[7],[8] When the modifications are made extraorally, the restoration can be sent to the laboratory for reglazing. Reglazing is time consuming, and it is not possible to reglaze after the restoration has been cemented in the mouth.

As a result, polishing of the adjusted restoration is performed which helps in achieving a smooth surface and increases the fracture toughness of the polished porcelain.[9],[10] This result may be obtained through an elimination of microcracks and large surface flaws formed during processing. Polishing can be accomplished extraorally as well as intraorally.[11],[12]

The specific objectives of this study are:

  1. To compare the surface roughness of overglazed and autoglazed porcelain surfaces and polished porcelain surfaces as polished with the three polishing systems (SHOFU, DFS, and DIATECH), qualitatively, using a scanning electron microscope (SEM) and quantitatively, using a profilometer.
  2. To compare the efficacy of the three polishing systems used in this study with each other, both qualitatively, using a SEM and quantitatively, using a profilometer.



  Materials and Methods Top


A total of 126 circular specimens of feldspathic porcelain (IPS Classic, Ivoclar Vivadent AG, Liechtenstein, Germany) were fabricated. The specimens were divided into three groups of 42 specimens each. The first group of specimens (Group I) was glazed on both surfaces. Half of the samples were autoglazed [Figure 1] and the other half was overglazed [Figure 2]. This group acted as the control group.
Figure 1: Autoglazed specimens

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Figure 2: Overglazed specimens

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The second group of specimens (Group II) was overglazed on both sides. One side of each specimen was left overglazed, and the other side of each specimen was grounded, glaze layer removed, and polished with the three polishing systems: SHOFU (USA), DFS (Germany), and DIATECH (The Netherlands).

The third group consisted of specimens that were autoglazed on both sides. One side of each specimen was left autoglazed and the other side of each specimen was grounded, glaze layer removed, and polished with the above-mentioned three polishing systems.

Comparison of the efficacy of glazing and polishing with the three systems and also the comparison of the efficacy of the three systems with each other were carried out qualitatively and quantitatively. Qualitative evaluation was done using a SEM, and quantitative evaluation was done using a profilometer.

The method used in this study has been described in the following order:

Preparation of the porcelain disc specimens

One hundred and twenty-six specimens with 10 mm diameter and 2 mm thickness were prepared using the same amount of porcelain and liquid. The specimens were allowed to cool and then finished with a medium-grit diamond on both sides to remove any irregularities (grit size 88–125 μ). Sixty-three samples were placed in the porcelain firing oven at 920°C for 5 min to obtain an autoglaze. On the remaining 63 samples, overglaze (IPS Classic, Ivoclar Vivadent) was applied according to the manufacturer's instructions. After application of the overglaze, the specimens were placed in the porcelain-firing oven. They were fired at 900°C for 6 min.

The specimens were divided into three groups of 42 samples each.

The Group I specimens had a glazed layer on both surfaces. Twenty-one samples (IA) were autoglazed and 21 samples (IB) were overglazed. This group acted as the control group.

The Group II consisted of specimens that were overglazed. This group of specimens was further subdivided into three groups of 14 samples each (Subgroups IIA, IIB, and IIC). One surface of each specimen in all of the three subgroups was left overglazed [Figure 3] and was marked as a side. On the other surface, the glaze layer was removed with a medium-grit diamond (grit size 88–125 μ) (DFS, Germany) under constant pressure and time (20 s) to simulate clinical chair-side adjustment. This surface of each specimen in the three subgroups was polished with the three polishing systems: subgroup IIA with SHOFU, Subgroup IIB with DFS, and Subgroup IIC with DIATECH [Figure 4]. During roughening and subsequent polishing, care was taken not to pass the diamond/polishing points on to the overglazed surface. The surface was marked as side 2. The polishing was performed until the surface appeared shiny to the naked eye, simulating clinical conditions. The manufacturer's instructions for each system were followed.
Figure 3: Scanning electron microscope overglazed surface

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Figure 4: Scanning electron microscope DIATECH polishing kit

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The Group III consisted of specimens that were autoglazed. This group was further subdivided into three groups of 14 samples each (Subgroups IIIA, IIIB, and IIIC). One surface of each specimen in all of the three subgroups was left autoglazed and was marked as side 1. On the other surface, the glaze layer was removed with a medium-grit diamond (grit size 88–125 μ) (DFS, Germany) under constant pressure and time (20 s) to simulate clinical chair-side adjustment. This surface of each specimen in the three subgroups was polished with the three polishing systems: subgroup IIIA with SHOFU, Subgroup IIIB with DFS, and Subgroup IIIC with DIATECH. During roughening and subsequent polishing, care was taken not to pass the diamond/polishing points on to the autoglazed surface. The surface was marked as side 2. The polishing was performed until the surface appeared shiny to the naked eye, simulating clinical conditions. The manufacturer's instructions for each system were followed.

Quantitative analysis using a profilometer

Surface roughness was evaluated using a profilometer (Surtronic 3P, Taylor Hobson, Leicester, UK). The process was repeated three times on both surfaces of all the specimens of Group I, II, and III. The roughness profile of each of the surfaces was obtained for each of the six passes of the specimen. A mean roughness profile (Ra) was determined for each side of each specimen to describe the overall roughness of the surface. The data were analyzed statistically to determine the statistical significance.

Qualitative analysis using a scanning electron microscope

Specimens were analyzed at the microscopic level. They were coated with a palladium coating using a coater (JEOL JFC-1600 Autofine Coater) and examined under a SEM (JEOL JEM-6360, JEOL, Tokyo, Japan). Photomicrographs were made with ×100 magnification for visual inspection.


  Results Top


The data obtained from the results were tabulated and subjected to statistical analysis [Table 1],[Table 2],[Table 3]. The results were analyzed using analysis of variance (ANOVA) and Tukey honestly significance difference test.
Table 1: Mean±standard deviation, median, and range of Ra values of overglazed sides and polished sides

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Table 2: Mean±standard deviation, median, and range of Ra values of autoglazed sides and polished sides

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Table 3: Mean±standard deviation, median, and range of Ra value of overglazed and autoglazed specimens

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Descriptive statistical analysis was performed to calculate the means with corresponding standard deviations. Furthermore, one-way ANOVA followed by Tukey's test was performed with the help of critical difference or least significant difference at 5% and 1% level of significance to compare the mean values. P< 0.05 was considered statistically significant.

The t-test showed that mean Ra values of overglazed sides were significantly lower than that of the polished sides (Subgroups IIA - SHOFU, IIB - DFS, and IIC - DIATECH) [Table 1]. Hence, the overglazed surfaces were smoother as compared to the surfaces polished with the SHOFU, DFS, and DIATECH polishing systems.

The t-test showed that mean Ra values of autoglazed sides were significantly lower than that of the polished sides (Subgroups IIIA - SHOFU, IIIB - DFS, and IIIC - DIATECH) [Table 2] [Graph 1]. Hence, the autoglazed surfaces were smoother as compared to the surfaces polished with the SHOFU, DFS, and DIATECH polishing systems.



The t-test showed that mean Ra values of overglazed specimens were significantly lower than that of autoglazed specimens (t39 = 20.25; P< 0.01) [Table 3] [Graph 2]. Hence, the overglazed surfaces were found to be smoother as compared to the autoglazed surfaces.




  Discussion Top


The esthetic appearance of ceramic restorations is attributable to the surface texture of these restorations. Rough unglazed ceramic surfaces are not desirable because of their numerous harmful effects, whereas glazed surfaces are considered ideal. However, clinically, some occlusal adjustments before or after cementation require grinding of the glazed surface. When the modifications are made extraorally, the restoration can be sent to the laboratory for reglazing. However, subjecting the porcelain material to another cycle of firing may cause structural changes in the porcelain, making it more susceptible to fractures.[13] Furthermore, reglazing is time consuming. Reglazing is not possible after the restoration has been cemented in the mouth. Hence, the only choice left is to polish the unglazed surface using porcelain polishing kits. However, before selecting any polishing kit, it is important to know its efficacy.

A number of mechanical polishing techniques have been described in literature. Many researchers have advocated that the porcelain surface should remain glazed.[6],[7],[8],[9],[10],[11],[12],[13],[14],[15],[16] However, some researchers have advocated that polishing produces surfaces comparable to that of glazing or better than glazing.[17],[18],[19],[20],[21],[22],[23],[24],[25],[26],[27],[28],[29],[30],[31],[32],[33]

In the present study, the surface roughness of feldspathic porcelain obtained after glazing and polishing with three different polishing systems was compared. Feldspathic porcelains are being used in the field of crown and bridge dentistry since the early 1900s. They provide high esthetic value and demonstrate high translucency just like natural dentition. With the advent of leucite-reinforced feldspathic porcelains, the drawback of a low flexural strength faced with traditional feldspathic porcelains was overcome. Leucite-reinforced feldspathic porcelains have a flexural strength in the range of 125–180 MPa. These porcelains were and still are highly esthetic materials for building tooth-like structures. Hence, feldspathic porcelain was used in this study.[34]

In addition, a comparison of the efficacy of the three polishing systems with each other was made, both qualitatively and quantitatively.

From the analysis of the results of this study, it was inferred that the glazed surfaces (both overglazed and autoglazed) were superior to the polished surfaces, polished with the three different polishing kits (SHOFU, DFS, and DIATECH), that is, glazing produced a surface that was smoother as compared to polishing.

The results also indicated that, among the three polishing systems used in this study, SHOFU porcelain adjustment kit produced surfaces that were the smoothest, as compared to the DFS and DIATECH kits. It was followed by the DFS porcelain adjustment kit, which produced surfaces that were smoother as compared to the DIATECH porcelain polishing kit but rougher as compared to the SHOFU porcelain adjustment kit. The DIATECH porcelain polishing kit produced the least smooth surfaces.

This study also provided a comparison between the two types of glazing: overglazing and autoglazing. Quantitative analysis of the overglazed porcelain surfaces and autoglazed porcelain surfaces of the feldspathic porcelain used in this study indicated that overglazing produced a surface that was smoother as compared to autoglazing. Qualitative analysis of the overglazed porcelain surfaces and autoglazed porcelain surfaces of the feldspathic porcelain used in this study indicated that autoglazed surfaces were comparatively smoother than the overglazed surfaces.

As with many in vitro studies, limitations and variability often exist. Limitation of this study is that the glazing and polishing procedures were performed on disc-shaped specimens, which are not identical to real restorations. Direct extrapolation of results to the clinics is not possible because of differences in pressure and time applied by different practitioners during the polishing procedures. Moreover, the use of different rotary instruments for initial grinding may vary the Ra values. These limitations reinforce the need for additional studies and standardization of methods to determine the best finishing and polishing technique for each material and the smoothness cut-off limit to predict clinical success.

Despite the limitations and variabilities encountered in this study, it was inferred that polishing porcelain can produce acceptable results. However, polishing cannot be a substitute for glazed ceramic surface.


  Summary and Conclusions Top


Out off autoglazed or overglazed, the glazed surface had least surface roughness.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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  [Full text]  


    Figures

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

  [Table 1], [Table 2], [Table 3]



 

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