Effects of different surface treatments on stainability of ceramics

Effects of different surface treatments on stainability of ceramics Pelin F. Karagoz Motro, DDS, MSc,a Pınar Kursoglu, DDS, PhD,b and Ender Kazazoglu, DDS, PhDc Faculty of Dentistry, Yeditepe University, Istanbul, Turkey Statement of problem. Final adjustments may result in a loss of ceramic glaze, a situation which must be corrected by reglazing or polishing to obtain clinically successful restorations; such restorations may be susceptible to staining. Purpose. The purpose of this study was to determine the stainability of ceramics exposed to coffee after different surface treatments and to correlate the surface roughness with the color differences. Material and methods. Sixty-six ceramic (IPS e.maxCeram) disks (15 × 2 mm) were fabricated and glazed according to the manufacturer’s instructions, then assigned to 6 groups. Group Glaze (Group G), the control, was not subjected to any procedure. All the others were abraded with a diamond rotary cutting instrument. Group Reglaze (Group R) was reglazed; others were polished with different polishing materials; Group Shofu (Group S) was polished with abrasive stone (Dura-Green Stones), coarse silicon polisher (Ceramaster Coarse), silicon polisher (CeraMaster), and polishing paste (Ultra II) with polishing disks (Super-Snap Buff Disks); Group Ultradent (Group U) was polished with 1.0 and 0.5-µm polishing pastes (Ultradent Diamond) with a goat hair brush (Jiffy) and Group Bredent (Group B) was polished with an abrasive stone (Diagen turbo grinder), a round polishing brush (Abraso-fix),and polishing paste (Diamond) with felt wheels. Group Diamond rotary cutting instrument (Group D) was not treated after abrasion with a diamond rotary cutting instrument. Surface roughness was evaluated by profilometer (n=10), and 1 specimen from each group was evaluated by scanning electron microscopy (SEM). Color difference was measured by a spectrophotometer before and after 12 days of immersion in a coffee solution. Data were analyzed by 1-way ANOVA, the Tukey HSD test, and the Pearson rank correlation tests (α=.05). Results. The surface roughness (Ra) values were ordered from the highest to the lowest value, which were Group D, B, U, S, R, and G, respectively. Significant differences among groups (P<.01) were found, except for G and R. There were no significant differences between the color difference values of Groups G and R, both of which were significantly lower than the other groups (P<.01). Group D showed the highest ∆E values (>2), which is considered clinically unacceptable (P<.01). No significant differences were found among the S, U, and B groups. There was an 83% positively significant relationship between Ra and ∆E values (P<.01). Rough surfaces stained more after coffee immersion than did smooth surfaces. Conclusions. Surface treatments affected surface roughness and color stability. Smooth surfaces showed better color stability after discoloration. Ceramic staining may be related to surface texture changes after different surface treatments. (J Prosthet Dent 2012;108:231-237)

Clinical Implications

The results of this study indicate that the rough surfaces of ceramic may be prone to staining, which can cause discoloration. Surface treatments such as reglazing or polishing are recommended after adjustments to prevent future staining.

Resident, Department of Prosthodontics. Associate Professor, Department of Prosthodontics. c Head of Department and Professor, Department of Prosthodontics. a

b

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Volume 108 Issue 4 Ceramics are popular dental restorative materials because of their esthetic advantages, biocompatibility, and ability to yield smooth surfaces, which minimizes plaque adherence and subsequent periodontal inflammation.1,2 Dentists are able to achieve good esthetics because of the light transmission of ceramics, especially for anterior restorations.3 However, ceramic restorations may require postinsertion adjustments to correct occlusal interference, finish the margins, and improve the appearance.3-8 Postinsertion adjustments remove the glazed layer, thereby increasing surface roughness. Studies have been conducted to determine the most suitable surface treatment method to minimize the surface roughness of ceramics to obtain a smooth surface texture.2,5,7,9-16 A smooth surface reflects a greater amount of light than does a rough surface, and a rough or irregularly textured surface will reflect an irregular and diffuse pattern of light, which will change the color of the restoration.7,8,17 Furthermore, finishing and polishing procedures may influence the color of the porcelain.8,18,19 Rough porcelain surfaces are more susceptible to staining than are smooth porcelain surfaces.18-20 Thus, texture is important for the color of the restoration.4,7,8,17,20,21 The achievement of esthetics and color stability is important in the success of dental ceramic restorations.22-25 Studies on porcelain color evaluation26-30 and color stability31-35 have been performed. The effect on color of porcelain acceleration, porcelain thickness, porcelain surface roughness,36 and repeated firings has been investigated; however, there are fewer studies on the effect of staining on color,18-20,35,37 and these usually involved resin-based materials.38-42 There is also only a limited amount of information on the effect of surface roughness on the color of porcelain after it has been subjected to a staining solution.18-20 Thus, the purpose of this study was to evaluate the effect of surface treatment techniques on the stainability of ceramics after immer-

sion in a staining solution and to correlate the surface roughness with the color differences. The null hypothesis was that the different surface treatments which cause different surface roughness values are not correlated with the stainability of the ceramics.

MATERIAL AND METHODS Veneering ceramic (IPS e.max Ceram-A1/TI 1; Ivoclar Vivadent, Schaan, Liechtenstein) was layered on 66 pressable ceramics (IPS e.max Press-MO1; Ivoclar Vivadent) 2-mm-thick core disks. The disks were fired 3 times to compensate for porcelain shrinkage according to the manufacturer’s instructions. The surfaces of the specimens were wet ground with 220, 320, 500, 600, and 800 grit silicon carbide paper (English Abrasives & Chemicals Ltd, London, UK) on a grinding device (Phoenix Beta, Buechler, Ill). The application was performed for 15 seconds with finger pressure, and during the abrasion procedure, the specimens were frequently measured with electronic calipers (Absolute Digimatic Caliper; Mitutoyo, Kawasaki, Japan) to avoid reducing the thickness of the specimens to less than 2 mm. All specimens were glazed according to the manufacturers’ instructions with glaze material (IPS e.max Essence; Ivoclar Vivadent). Specimens were assigned to 6 groups. Group Glaze (Group G), the control, was not subjected to any procedure after glazing. All other groups were abraded with a 30-µm red ring diamond rotary cutting instrument (Komet; Brasseler GmbH & Co KG, Lemgo, Germany) with a high-speed handpiece at 20 000 rpm under water cooling to imitate clinical adjustment. Group Reglaze (Group R) was reglazed; Group Shofu (Group S) was polished with an abrasive stone (Dura-Green Stones; Shofu, Inc, Kyoto, Japan), coarse silicon polisher (Ceramaster Coarse; Shofu, Inc), silicon polisher (CeraMaster; Shofu, Inc) and polishing paste (Ultra II; Shofu, Inc)

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with polishing disks (Super-Snap Buff Disks; Shofu, Inc) in order; Group Ultradent (Group U) was polished with 1.0-µm and 0.5-µm polishing pastes (Ultradent Diamond Polish Mint, Ultradent Products Inc, South Jordan, Utah) with a goat hair brush (Jiffy; Ultradent Products, Inc), and Group Bredent (Group B) was polished with an abrasive stone (Diagen Turbo Grinder; Bredent, Senden, Germany), round polishing brush (Abraso-fix fine; Bredent), and diamond polish paste (Diamant-Polierpaste; Bredent) with felt wheels (Bredent). Group Diamond rotary cutting instrument (Group D) was left untreated after diamond rotary cutting instrument abrasion. All polishing instruments were used in a slow-speed handpiece, rotating at 10 000 rpm for approximately 20 seconds and were operated by the same investigator. All specimens were cleaned with a steam cleaner (Triton SLA Steam Cleaner; Bego, Bremen, Germany) under 0.3 MPa of pressure and then placed in the ultrasonic cleaner (CD4800 Digital Ultrasonic Cleaner; Jeken, Dongguan, China) for 180 seconds. Surface roughness (Ra) was calculated in µm with a profilometer (Mahr GmbH, Göttingen, Germany) (n=10). To evaluate the effects of polishing systems on the porcelain surfaces, 1 specimen from each group was coated with gold-palladium and examined under field emission scanning electron microscopy SEM (JSM6335F; JEOL, Tokyo, Japan). The SEM microphotographs were made with ×1000 magnification for visual inspection. The color parameters according to the CIE L*a*b* color order system of the Commission Internationale de l’Eclairage (International Commission on Illumination) of each specimen were measured with a spectrophotometer (CM-2600d; Konica Minolta Sensing Inc, Tokyo, Japan) before immersion in a coffee solution in a 37°C incubator (UM 400; Memmert GmbH, Schwabach, Germany) for 12 days, which is equivalent to 1 year of

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October 2012 Ceramic Diamond rotary cutting instrument

Group G

Group R

Group S

Group U

Profilometer

Group B +

Group D

SEM (1 specimen of each)

1. Color Measurement Coffee immersion 2. Color Measurement

1 Study design diagram. Surface Roughness (Ra)

1.6

Mean ±SD (µm)

1.4 1.2 1 0.8 0.6 0.4 0.2 0

Ga

Ra

Sb

Groups

Uc

Bd

De

2 Mean surface roughness values (Ra) among groups. Same lowercase letters indicate groups that were not statistically different (P>.05). coffee drinking.41-43 The coffee solution was prepared according to the manufacturer’s instructions. In total, 300 mL of hot water was used for 3.6 g coffee (Nescafe Classic; Nestle Turkiye, Bursa, Turkey), stirred with a stick for 10 minutes, and filtered with filter paper (Melitta; Haushaltsprodukte GmbH & Co. Kg, Minden, Germany). The solution was stirred every 12 ±1  hours. After 12 days of immersion at 37°C in the coffee solution, the specimens were washed with tap water and dried with tissue paper (Selpak; Eczacıbaşı, Istanbul, Turkey). Color differences (ΔE) were calculated with the spectrophotometer.

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A spectrophotometer (CM-2600d; Konica Minolta Sensing Inc) with software (SpectraMagic 3.1; Minolta Co, Ltd. CyberChrome, Inc, Osaka, Japan) was used, and ∆E was calculated according to the formula ∆E2-1 =([∆L]2 + [∆a]2 + [∆b]2)1/2. Some individuals perceive color differences as low as 0.5, whereas others do not see differences of 4.23 For this reason, in this study ∆E > 2 was considered to be clinically unacceptable. The study design and groups are shown in Figure 1. The evaluation of the quantitative data and comparison among groups were performed by 1-way ANOVA tests, and the Tukey HSD (Honestly

Significant Difference) test was used for any group that exhibited a significant difference. To determine the effects of polishing techniques on color variation, the relationship between these factors was evaluated with the Pearson rank correlation test. Data were tested at an alpha level of .05.

RESULTS The mean Ra values (µm) and the standard deviation (SDs) of the groups are, in order: Group G: 0.071 ±0.004; Group R: 0.101 ±0.005; Group S: 0.309 ±0.032; Group U: 0.620 ±0.063; Group B: 0.971 ±0.040; and Group D: 1.279 ±0.063. The results of 1-way ANOVA (df: 5; F: 1341.45; P: .001) indicated that the surface treatments affected the surface roughness (P<.01). Group D showed higher Ra values than the others. It was followed by Group B, U, S, R, and G from highest to lowest. Group S showed the lowest Ra values of the other unglazed polishing groups (D, B, U) (P<.01). There was no significant difference between Group G and Group R (Fig. 2). The SEM microphotographs showed that ceramics displayed the smoothest surfaces in Groups G and R (Figs. 3, 4). Polishing smoothed the diamond rotary cutting instrument scratches in Group S, U, and B (Figs. 5-7). Smoother surfaces were obtained with Shofu polishing materials and paste than with other polishing materials. Adjustment with a diamond rotary cutting instrument created the roughest surfaces, which can be seen in Group D (Fig. 8). The mean ∆E values, along with the standard deviation (SDs) of the groups are, in order: Group G: 0.596 ±0.136; Group R: 0.614 ±0.101; Group S: 1.282 ±0.449; Group U: 1.546 ±0.383; Group B: 1.551 ±0.256; and Group D: 2.293 ±0.516. The 1-way ANOVA (df: 5; F: 35.057; P: .001) results of the ∆E values and SDs of the groups after immersion in coffee solution are shown in Figure 9 (P<.01). There was no significant difference between Groups G

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3 SEM microphotograph (×1000 magnification) of Group G.

4 SEM microphotograph (×1000 magnification) of Group R.

5 SEM microphotograph (×1000 magnification) of Group S.

6 SEM microphotograph (×1000 magnification) of Group U.

7 SEM microphotograph (×1000 magnification) of Group B.

8 SEM microphotograph (×1000 magnification) of Group D.

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October 2012 Color Difference (ΔE) 3.0

Mean ±SD

2.5 2.0 1.5 1.0 0.5 0

Ga

Ra

Sb

Groups

Ub

Bb

Dc

9 Mean ΔE values among groups. Same lowercase letters indicate groups that were not statistically different (P>.05). Ra-ΔE

4.0

Color Difference (ΔE)

3.0

2.0

1.0

0

0

250

500

750

1000

1250

Surface Roughness (Ra)

10 Pearson correlation analysis of relationship between mean surface roughness and mean color change. and R; both were significantly lower than the other groups (P<.01). Group D was significantly higher than the other groups (P<.01). There was no significant difference among polishing groups (S, U, B) which were unglazed. The result of Pearson’s correlation analysis indicated an 83% positively significant relationship between Ra and ∆E values (P<.01). Rough surfaces stained more after coffee immer-

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sion than did smooth surfaces. Group D had the highest surface roughness values, and its coffee staining was noticeable and clinically unacceptable (Fig. 10).

DISCUSSION The null hypothesis was rejected because the different surface treatments which cause different surface

roughness values do correlate with the stainability of the ceramics. Postinsertion adjustments of ceramics create rough surfaces.4,7,8,17,21 For this reason, some authors have advocated reglazing or polishing the ceramic restorations after clinical adjustment.3,4,8-13,16,17 Investigators have emphasized that polishing techniques are unable to provide surfaces which are as smooth as glaze.10,16 Fuzzi et al16 demonstrated by SEM analysis that glazed surfaces were superior to all other polished surfaces. Patterson et al12 compared the effect of glaze and polishing kits, including diamond paste, on surface texture and reported that the lowest surface roughness was obtained by glazing rather than polishing. The findings of the present study indicate that glazing and reglazing procedures resulted in a smoother surface texture than either polishing techniques or diamond rotary cutting instrument abrasion. Several reports have investigated and described different polishing techniques for ceramic restorations and have supported the use of polishing as an alternative to glazing.7,9,11 Al-Wahadni and Martin7 advised a 4-stage polishing procedure, involving the use of the Shofu Porcelain Veneer kit (Shofu Inc) for polishing and a fine diamond polishing paste in conjunction with fine-grit diamonds and Dura-White Stones (Shofu, Inc) Klausner et al9 determined that the Shofu polishing kit (Shofu Inc) was capable of producing a surface as smooth as glazed porcelain. However, the findings of the current study demonstrated that surface polishing was less effective than surface glazing. Goldstein et al11 reported that Brasseler (Brasseler USA Inc, Savannah, Ga), Dedeco (Dedeco International Inc. Long Eddy, NY), Dentsply (Dentsply Intl) and Shofu porcelain polishing systems were suitable for restoring ground porcelain. MartinezGomis et al13 investigated the effects of 4 different polishing techniques and diamond paste on porcelain

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Volume 108 Issue 4 surface texture and indicated that diamond paste was not effective in reducing the surface roughness values. Saraç et al8 demonstrated that specimens polished with only diamond paste showed higher surface roughness values than specimens polished with only silicon impregnated rubber. The authors stated that polishing paste was not effective in reducing surface roughness.8 Bottino et al,15 who investigated the surface roughness of 5 different techniques, stated that silicon impregnated rubber polishing smoothed diamond rotary cutting instrument scratches and that polishing paste should be used after polishing with the silicon polishers. In the current study, when polishing groups were compared, the higher surface roughness values shown by Group U were attributed to the use of polishing paste alone. In Group S, diamond rotary cutting instrument scratches were lightened by DuraGreen Stones, then polished with Ceramaster Coarse and Ceramaster silicon polishers. Finally, polishing procedures were completed after using Ultra II polishing paste and SuperSnap Buff Disks. The smooth surface texture obtained may be due to the 2 silicon polishers that were used. Group B displayed the roughest surfaces among the polishing groups, even though a round polishing brush and paste were used, as in Group S; this was assumed to be caused by product differences. However, all polishing groups displayed significantly lower surface roughness values than those of Group D. In the present study, the Ra values obtained by profilometers were compatible with the SEM images in the report of Goldstein et al.11 While the glazed and reglazed groups displayed flat surfaces, which have low surface roughness values, Group D with the highest Ra values showed sharp diamond rotary cutting instrument scratches as expected. Because instrument measurements eliminate the subjective interpretation of visual color comparison, spectrora-

diometers, spectrophotometers, and colorimeters have been used to measure color difference in dental materials.24,26-30 The spectrophotometer was chosen because of its detailed determination of color differences and its common use.22 Douglas et al25 stated that mean color perceptibility was 2.6 ∆E units. Some individuals perceive color differences as low as 0.5, whereas others do not see differences of 4.23 In the present study, ∆E > 2 was considered to be clinically unacceptable. Esquivel et al 20 investigated glazed and unglazed porcelain groups immersed in methylene blue. Colorimetric evaluations that were compatible with visual evaluations showed that the glazed group underwent fewer color changes than the unglazed group. Additionally, Samra et al 37 stated that after immersion in 37°C coffee for 15 days, glazed IPS Empress 2 showed less color difference (∆E=1.28) than composite resins. Moreover, Gupta et al35 evaluated the effects of tea, coffee, and cola on the color of composite resins and porcelain. The authors found that porcelain color did change (∆E = 1.2 to 1.4), but it was not noticeable.35 Finishing and polishing procedures may influence the color of porcelain.8,18 Yilmaz et al18 reported that porcelain polished with polishing rubber in conjunction with polishing paste showed more color changes than did porcelain glazed after immersion in methylene blue. In another study, Atay et al19 stated that the type of surface treatment was a significant factor in color stability. In many studies, tea, coffee, and cola have been used for discoloration.19,39,41,42 In the present study, coffee was used as a colorant because of its frequent consumption in daily life.43 According to the authors, surface texture affected the stainability of the ceramic after immersion in coffee. In the present study, rough surfaces demonstrated more color changes than did smooth surfaces. With the exception of Group D, all groups displayed color difference at a

The Journal of Prosthetic Dentistry

level that would be considered clinically acceptable. The mean color difference of Group D, which had the highest surface roughness values, was clinically unacceptable according to the present study. Because the glaze layers were removed after diamond rotary cutting instrument abrasion, the surface became porous and tended to stain more, which affected the esthetics of the ceramics. In this study only 1 staining agent and 1 type of ceramic was used. Since it has been reported that different solutions affect the ceramic color differently,35 the lack of various solutions is a limitation of this study. Different results might have been obtained with different types of ceramics. Further studies using several solutions and different types of ceramics should be performed.

CONCLUSIONS Within the limitations of this in vitro study, the following conclusions were drawn: Surface texture was a significantly important factor in the stainability of ceramics. According to these findings, it may be concluded that glazed and reglazed materials showed less staining, and in the polished groups, staining was not clinically noticeable. However, Group D (Diamond rotary cutting instrument), which was not treated after abrasion with a diamond rotary cutting instrument was clinically unacceptable. Glazing or polishing after ceramic surface adjustments is recommended.

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34.Ertan AA, Sahin E. Colour stability of low fusing porcelains: an in vitro study. J Oral Rehabil 2005;32:358-61. 35.Gupta R, Parkash H, Shah N, Jain V. A spectrophotometric evaluation of color changes of various tooth colored veneering materials after exposure to commonly consumed beverages. J Indian Prosthodont Soc 2005;5:72-8. 36.Wang H, Xiong F, Zhenhua L. Influence of varied surface texture of dentin porcelain on optical properties of porcelain specimens. J Prosthet Dent 2011;105:242-8. 37.Samra AP, Pereira SK, Delgado LC, Borges CP. Color stability evaluation of aesthetic restorative materials. Braz Oral Res 2008;22:205-10. 38.Cooley RL, Burger KM. Effect of carbamide peroxide on composite resins. Quintessence Int 1991;22:817-21. 39.Ayad NM. Susceptibility of restorative materials to staining by common beverages: an in vitro study. Eur J Esthet Dent 2007;2:236-47. 40.Douglas RD. Color stability of new-generation indirect resins for prosthodontic application. J Prosthet Dent 2000;83:166-70. 41.Guler AU, Kurt S, Külünk T. Effects of various finishing procedures on the staining of provisional restorative materials. J Prosthet Dent 2005;93:453-8. 42.Guler AU, Yılmaz F, Külünk T, Guler E, Kurt S. Effects of different drinks on stainability of resin composite provisional restorative materials. J Prosthet Dent 2005;94:118-24. 43.Odioso LL, Gibb RD, Gerlach RW. Impact of demographic, behavioral, and dental care utilization parameters on tooth color and personal satisfaction. Compend Contin Educ Dent 2000;21:S35-41. Corresponding author: Dr Pınar Kursoglu Yeditepe University Faculty of Dentistry Bagdat Cad. No:238 Goztepe 34728 Istanbul TURKEY Fax: +90-216-3636211 E-mail: [email protected] Copyright © 2012 by the Editorial Council for The Journal of Prosthetic Dentistry.