|Year : 2018 | Volume
| Issue : 1 | Page : 31-38
The effect of commonly consumed beverages on colour stability and surface roughness of two metal ceramic materials: An in-vitro study
N Raja Reddy, B Indira Padmaja, G Devi, G Krishna Priya, G Hima Bindu, N Suresh Babu
Department of Prosthodontics, CKS Theja College of Dental sciences, Tirupati, Andhra Pradesh, India
|Date of Web Publication||22-Mar-2018|
Dr. N Raja Reddy
Department of Prosthodontics, CKS Theja College of Dental sciences, Tirupati, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Aims: The aim of this study was to compare color stability and surface topography of two different feldspathic porcelains, both qualitatively and quantitatively, after exposure to routinely consumed beverages over different time periods using a spectrophotometer and surface noncontact profilometer, respectively.
Materials and Methods: In this in-vitro study, a total of 120 base metal alloy discs with a thickness of 0.5 mm were made following the conventional casting technique. They were randomly divided into two categories. Category-I was built with IPS.d.Sign (Ivoclar), Category-II was built with Ceramco 3 (Dentsply) each containing 60 samples. The samples were immersed into different beverages. Color stability and surface roughness were measured by a spectrophotometer and profilometer, respectively.
Statistical Analysis: t-test between two categories and ANOVA within the same group.
Results and Conclusion: Color difference (ΔE) between different test solutions at different intervals showed clinically acceptable range (below 3.3 units). Thus, ceramics were considered color stable and resistant to external staining. Scanning electron microscope and profilometer study revealed that there were significant surface roughness changes in both IPS.d.Sign and Dentsply metal ceramic materials when immersed in soft cola drink and coffee solutions for 90 days and compared to the control group which was immersed in distilled water.
Keywords: Coffee, metal ceramic materials, profilometer, soft cola, spectrophotometer
|How to cite this article:|
Reddy N R, Padmaja B I, Devi G, Priya G K, Bindu G H, Babu N S. The effect of commonly consumed beverages on colour stability and surface roughness of two metal ceramic materials: An in-vitro study. J NTR Univ Health Sci 2018;7:31-8
|How to cite this URL:|
Reddy N R, Padmaja B I, Devi G, Priya G K, Bindu G H, Babu N S. The effect of commonly consumed beverages on colour stability and surface roughness of two metal ceramic materials: An in-vitro study. J NTR Univ Health Sci [serial online] 2018 [cited 2020 Mar 29];7:31-8. Available from: http://www.jdrntruhs.org/text.asp?2018/7/1/31/228157
| Introduction|| |
Aesthetics in dentistry is partly defined by the patients' desire for naturalness and harmony. Modern techniques in restorative dentistry include the use of ceramic materials for jacket crowns, laminates, inlays, and onlays.
Discoloration of porcelain restoration may be intrinsic or extrinsic. Intrinsic factors involve discoloration due to alteration of the resin matrix itself or the oxidation or hydrolysis in resin matrix. Extrinsic factors for discoloration include staining by the adsorption or absorption of colorants because of contamination from various exogenous sources.,
Porcelain has been established as an ultimate anterior esthetic restorative material because of its natural appearance, good wear resistance, and color stability. Though porcelain restorations are color stable, discoloration is one of the primary factors for failure of esthetic restorations.
Thus, the present study was undertaken to compare the color stability and surface topography of two different porcelains.
| Materials and Methods|| |
In this in-vitro study, a total of 120 base metal alloy discs with a thickness of 0.5 mm were prepared following the conventional casting technique. The opaque porcelain followed by dentin porcelain was applied to all specimens and were subjected to opaque and dentin firings in Singlemat ceramic furnace. They were divided into two categories, as mentioned in [Table 1].
Description of the custom-made device (depth micrometer)
Depth micrometer instrument was fabricated at RVS Machine tools, Peenya industrial estate, Bangalore. This instrument consists of an outer cylinder with an inner diameter of 10 mm, a piston which is movable inside the cylinder, and one end of this piston is attached to a rod on which main scale reading is between 0 and 20 mm with 0.5 mm interval. Over this main scale rod, a vernier scale is attached with 50 divisions on its entire circumference. The whole piston assembly moves in the cylinder with the help of thumbscrew which is on the rear end of the vernier scale. It can be rotated clockwise or anticlockwise. A lock is attached to the outer cylinder which helps to lock the piston in any position while fabricating wax pattern or during ceramic build up [Figure 1] and [Figure 2].
For one complete rotation of the thumb screw, the piston moves 0.5 mm, for each division reading on the vernier scale, it moves 0.01 mm.
Fabrication of metal backings or discs
A total of 120 wax patterns were fabricated using type II inlay wax (MDM Corporation, New Delhi) with 10 mm diameter and 0.6 mm thickness, so that 0.1 mm of metal can be utilized during finishing procedures to obtain uniformly thick 0.5 mm metal backings. The custom-made device (depth micrometer) was adjusted such that the main scale reading was at 0.5 mm and vernier scale reading was at 10. In this manner, 0.6 mm of space was created between the piston and outer sleeve of the cylinder [Figure 3]. Wax patterns thus fabricated are checked for any irregular surfaces, uneven thickness, porosities, etc. Any such patterns were discarded and again fabricated.
Wax patterns were sprued using 0.2 mm sprue wax (Yeti dental), and invested using phosphate bonded investment (Deguvest, Dentsply) in a metal ring. The invested ring was allowed to bench set for 30 min. Burnout was carried out in a muffle furnace and casting was done using Nickel Chromium alloy in an induction casting machine (Delta).
Once the invested ring was cooled, it was divested, castings were retrieved, sand blasted with aluminium oxide with particle size 110 μm to obtain clean casting, and then the sprues were cut. Metal discs were trimmed carefully to obtain uniform thickness of 0.5 mm using finishing abrasives [Figure 4]. The thickness was verified using a metal gauge [Figure 5].
Ceramic build up and firing
A total of 120 metal discs of uniform thickness were sand blasted with aluminium oxide with particle size 50 μm, ultrasonically cleansed for 3 min, and then dried [Figure 6]. They were placed in ceramic furnace (Delta) for oxidation, with a stand by temperature of 403°C and gradually increased to holding temperature of 700°C at a rate of 30°C/min and maintained for 1 min before cooling [Figure 7].
Then, the specimens were taken out of the furnace and allowed to cool to room temperature. Opaque paste (A2 shade, d sign Ivoclar, and Dentsply) was mixed with the opaque liquid and evenly applied on metal discs using sable brush [Figure 8]. Two coats of opaque paste were applied on all 120 specimens by placing 10 specimens each time on a saggar tray and transferred to furnace and subjected to opaque firing.
Dentin build up and firing
Body dentin A2 shade (Ivoclar and Dentsply) was dispensed on the glass slab and mixed with a modeling liquid using a ceramic spatula until the mix obtained was of a working consistency. Excess moisture, if present, was blotted with a tissue paper. Using a sable brush dipped in distilled water and making the tip pointed, mixed ceramic was carried out in small increments and condensed on the opaque layer of the specimen, which was kept in the custom-made device. It was adjusted such that main scale reading was 1.5 mm and vernier scale reading was 20, i.e., dentin build up was 1.2 mm, which helps in allowing 10–15% for ceramic firing shrinkage and obtaining 1 mm of dentin after firing [Figure 9].
The dentin porcelain was condensed till the rim of the outer tube and excess ceramic material was removed using ceramic spatula and smoothened. A glass plate was used to verify whether the surface was flush with a rim of outer tube and ceramic was added or removed accordingly. Then, the thumb screw was rotated to raise the specimen, and the specimen was carefully transferred from the custom-made device to the saggar tray by lifting with the mixing spatula [Figure 10] and subjected to the manufacturer-recommended firing cycle.
After firing and cooling, specimens were taken out, thickness was measured using the custom-made device, and any irregularities were trimmed. Another increment of dentin was added and subjected for a second dentin firing and trimmed until an even thickness of 1.5 mm was achieved for every specimen.
Then, glaze paste (Ivoclar, Dentsply) mixed with glaze liquid (Ivoclar, Dentsply) was applied for all specimens with a ceramic brush, and glaze firing was done according to manufacturer recommendations [Table 2].
Immersion in acidic beverages
Specimens were divided into two categories I (Made up of IPS d.sign, Ivoclar) and II (Made up of Dentsply Ceramco 3) each containing 60 samples. Each category is divided in to two groups. Group A and B containing 30 samples each. Then, they were further subdivided into three subgroups. Subgroup A (i) and B (i) acting as control, A (ii) and B (ii) were immersed in 25 ml of coffee (30 g of instant Nescafe coffee powder was added in 1ltr of boiling water simmered for 5 min and then filtered) having a pH of 5, A (iii) and B (iii) were immersed in 25 ml of soft cola drink having a pH of 2.4, and were analyzed for color change and surface roughness before and after immersing at an interval of 45 days and 90 days [Figure 11].
Color stability analysis was carried out using UV spectrophotometer [Figure 12] (MINOLTA: CM-3600d) at CIPET plastic testing centre, Guindy, Chennai.
Surface roughness analysis was done using surface noncontact profilometer [Figure 13] at IIT, Madras and using scanning electron microscope (ZEISS) at S.V. University, Tirupathi.
Color stability was analyzed statistically using comparison t-test between two categories and analysis of variance (ANOVA) within the same group. The mean, standard deviation, and P value were calculated between two categories and also within each group to determine any significant difference in color change between the variables. In the present study, P value of 0.05 is considered as the level of significance.
| Results|| |
In this study, color stability analysis was carried out using L*, a*, b* values of each specimen at different intervals. Significant difference is seen between L* values of Dentsply material samples immersed in soft cola, coffee, and water at 90 days, whereas L* value of IPS d. Sign shows significant difference at 0 and 90 days. The L* value when compared between all samples at 0, 45, and 90 days shows significant difference except for samples of IPS d. Sign immersed in soft cola (P = 0.106).
a* value mean of color change of Dentsply and IPS d. Sign showed significant difference in all three solutions at only 0 and 45 days, whereas at 90 days it showed no significance. The mean a* value of all metal ceramic samples of three solutions at different intervals showed significant difference only in Dentsply and IPS d. Sign samples immersed in coffee and water, whereas samples immersed in soft cola showed insignificant values at 0, 45, and 90 days.
Significant difference of color change was seen in b* mean value of Dentsply samples immersed in all three solutions at 0 and 45 days only, whereas at 90 days all samples in three solutions showed insignificant difference. The samples of IPS d. Sign showed significant change in all three solutions at 0 and 90 days only whereas at 45 days it was not significant. The samples of both Dentsply and IPS d. Sign immersed in soft cola, coffee, and water showed significant difference at 0, 45, and 90 days, however, Dentsply-soft cola and IPS d. Sign-coffee showed no significance.
Color stability analysis
Color change (ΔE) mathematically expresses the amount of difference between the Commission Internationale de I'Eclairage (CIE) L*a*b* coordinates of different specimens or the same specimen at different instances. The L* value is a measure of the lightness, the a* value is a measure of redness (positive a*) or greenness (negative a*), and the b* value is the measure of yellowness (positive b*) or blueness (negative b*) of an object. CIELAB color difference formula is designed to provide numeric data (ΔE) that represents the magnitude of the color difference between two objects.
ΔE = [ΔL2 + Δa2 + Δb2]1/2
ΔE values of Dentsply and IPS d. Sign samples immersed in soft cola, coffee, and water are shown in [Table 3]. [Table 3] shows ΔE values as Dentsply-control as 3.08 units, Dentsply-soft cola as 1.01 units, Dentsply-coffee as 2.63 units, IPS d. Sign-control as 2.43, IPS d. Sign-soft cola as 2.87 units, and IPS d. Sign-coffee as 1.37 units. Significant difference was observed when L*a*b* values were compared individually at different time intervals. whereas ΔE values were less than 3.3, which explained ceramics are color stable.
|Table 3: Comparison of color difference ΔE between different test solutions at 0, 45, 90 days interval of dentsply and IPS D.SIGN|
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Surface roughness analysis
Surface roughness estimated on Group B containing 30 samples for both the materials (category I- IPS d. Sign, category-II-Dentsply) were divided into three subcategories B (i) acted as control, B (ii) were immersed in coffee, B (iii) immersed in soft cola drink and were examined under profilometer and SEM.
The surface roughness was measured using BRUKER-contour GT surface profiler, which works on the principle of optical interferometry, and average surface roughness Ra values were used in the evaluation.
Ceramic samples of Dentsply and IPS d. Sign which were immersed in soft cola, coffee, and water showed significant difference in the mean surface roughness values when coffee and soft cola samples were compared with the control group [Table 4]. However, there was no statistical significant difference between samples of coffee and soft cola of both the categories when compared with each other [Figure 14]. When samples of Dentsply and IPS d. Sign of the three solutions were compared significant difference was seen in the samples of both categories immersed in soft cola and coffee whereas samples immersed in water of both categories were insignificant [Figure 15].
|Table 4: Comparison of surface roughness changes between IPS D.SIGN and dentsply after immersing in test solutions for 90 days|
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|Figure 14: SEM Photomicrograph of IPS.d.SIGN specimens at 90 days in control, soft cola and coffee respectively|
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|Figure 15: SEM Photomicrograph of DENTSPLY specimens at 90 days in control, softcola and coffee respectively|
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| Discussion|| |
In the oral cavity, ceramic restorative materials are exposed to harsh conditions arising from temperature changes and acid-base shifts. This indicates that ceramic material should be able to resist or have only minimal alterations under these circumstances. The chemical durability of ceramics is basically good, but may be influenced by its composition and microstructure of the ceramic material, the chemical character of the corrosive medium, the exposure time, the temperature, etc.
In this study, the material under degradation investigation was metal ceramics. Changes in color stability and surface roughness were evaluated in commonly consumed beverages over a period of 90 days. All specimens were immersed in solutions for 90 days, immersion time was comparable to clinical service of metal ceramics according to study conducted by Erik Asmussen by storing for 1 month in water at 60°C is well correlated with color change obtained after storing for 12 months in water at 37°C.,
The acidic agents used in this study were coffee and soft cola with pH of 5 and 2.4, respectively. Specific interest in selecting these agents was that these two are most commonly consumed soft and hot beverages. Soft cola consists of carbonic and citric acid and is a highly acidic soft drink whereas coffee consists of acidic contents and is a hot caffeinated beverage. These acids might cause elemental dissolution of ceramics due to their chelating effect.
Considering the mean staining intensity of all solutions, coffee was found to cause more discoloration than tea, soft cola, and water, as is evident by results that shows that all the test materials including porcelain discolored most in coffee. This is in general agreement with the results of previous studies on the effect of various staining agents on different resinous materials., Gross and Moser (1977) and Yannikakis (1998) found that the staining intensity of coffee was higher than tea and water. Chan et al. found that coffee caused more discoloration than tea and cola beverages.
According to a study conducted by DuyguSarac in 2006, the human eye has a limited capability to perceive colour differences. It cannot perceive ΔE values less than 1 unit. ΔE values between 1 and 3.3 represent a perceptible and clinically acceptable range. ΔE values of 3.3 and higher are reported to be unacceptable under clinical conditions.
Thus, changes in both materials are of relevance clinically as these changes would be apparent after prolonged and frequent exposure of the restorations to coffee and soft cola. From the present in-vitro study, it can be concluded, however, that the color match of aesthetic restorations can be maintained over a longer period in the oral cavity by observing some restrictions on the dietary habits.
According to a study conducted on the surface degradation of glass ceramics after exposure to acidulated phosphate fluoride by Vanessa Zulema et al., IPS.d. Sign ceramic showed the highest values of loss of mass. The reason for this could be due to the presence of 65% glass, fluorapatite crystals, and leucite in its composition. However, interestingly this ceramic did not present mean surface roughness values that were significantly different than those of the other ceramics.
Though both the two porcelains used in the present study were feldspathic and had the same composition and firing cycles, all showed different amounts of color change and surface roughness. This variation may be attributed to the difference in the percentage of basic individual composition. Hence, this study highlights the effect of commonly consumed beverages in causing surface roughness and staining of the feldspathic porcelain. Therefore, the exact role of feldspathic and glass ceramics, the compositional and structural changes occurring post firing and glazing, and their effect on the color change needs further research.
Limitations of the study
Though the study was carried out with utmost accuracy, it had some limitations:
- Only pH of the immersion liquids has been taken as the main criteria which indicated a high H+ ion concentration, but their titratability, chemical nature, and temperature should also be considered
- In the present in-vitro study, natural buffering capacity of the saliva present in the oral cavity which compensates for the acidic effect of the agents used was not considered as it also has some influence on the pH of immersion liquids
- Despite following the standard and uniform protocol while preparing the metal ceramic discs, any minor distortion of wax patterns and release of internal stresses during ceramic firing were not considered.
| Conclusion|| |
Within the limitations of this study, the following conclusions can be drawn:
- There was a significant change in L*, a* and b* values of IPS d. Sign and Dentsply metal ceramic materials when immersed in soft cola drink and coffee at various time intervals
- Color difference (ΔE) between different test solutions at different intervals showed clinically acceptable range (below 3.3 units). Thus, ceramics were considered color stable and resistant to external staining
- SEM and profilometer study revealed that there were significant surface roughness changes in both IPS d. Sign and Dentsply metal ceramic materials when immersed in soft cola drink and coffee solutions for 90 days when compared to the control group, which was immersed in distilled water.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15]
[Table 1], [Table 2], [Table 3], [Table 4]