The International Journal of Periodontics & Restorative Dentistry © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
689
Color Stability of Shade Guides After Autoclave Sterilization
Max Schmeling, DDS, MS, PhD1 Neimar Sartori, DDS, MS, PhD2 Sylvio Monteiro, Jr., DDS, MS, PhD3 Luiz Baratieri, DDS, MS, PhD3
This study evaluated the influence of 120 autoclave sterilization cycles on the color stability of two commercial shade guides (Vita Classical and Vita System 3D-Master). The specimens were evaluated by spectrophotometer before and after the sterilization cycles. The color was described using the three-dimensional CIELab system. The statistical analysis was performed in three chromaticity coordinates, before and after sterilization cycles, using the paired samples t test. All specimens became darker after autoclave sterilization cycles. However, specimens of Vita Classical became redder, while those of the Vita System 3D-Master became more yellow. Repeated cycles of autoclave sterilization caused statistically significant changes in the color coordinates of the two shade guides. However, these differences are considered clinically acceptable. (Int J Periodontics Restorative Dent 2014;34:689–693. doi: 10.11607/prd.1868)
Postgraduate Student, Department of Dentistry, Federal University of Santa Catarina, Florianopolis, Santa Catarina, Brazil. 2Assistant Professor, Division of Restorative Sciences, Ostrow School of Dentistry, University of Southern California, Los Angeles, California, USA. 3Professor, Department of Dentistry, Federal University of Santa Catarina, Florianopolis, Santa Catarina, Brazil. 1
Correspondence to: Max Schmeling, Pós graduação em Dentística Universidade Federal de Santa Catarina Centro de Ciências da Saúde, Campus Trindade s/n, Florianópolis, SC, Brazil. CEP: 88040-900 ©2014 by Quintessence Publishing Co Inc.
The visual observation method is characterized by the necessary interaction between three fundamental elements: a light source, an object, and a viewer.1 After being emitted by a light source, light energy can be transmitted or reflected by an object toward the eye of the observer, which captures the physical energy and transforms it into nerve impulses that are interpreted by the brain as color. The requirement of visualization and interpretation by the brain, however, gives this method of color perception a complex and subjective character, even with standardization of the light source and the object.1–3 Although the subjectivity of the visual method of color selection is described in several studies, visually comparing a natural tooth with shade guides is the main method for selecting tooth color in esthetic restorative procedures.4–7 Recently, the Vita Classical (VC) and Vita 3DMaster (V3DM) shade guides (Vita Zahnfabrik) were described as being among the most used.8,9 Even though they have the same manufacturer, they present some differences, mainly due to the appearance of the samples, which are arranged in groups according to the hue in VC and according to value in V3DM.8,9 When selecting the color, regardless of type or brand, the shade guides should be viewed in close proximity to the patient’s
Volume 34, Number 5, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
690 Color evaluation
Fig 1 Vita Classical shade guide.
Fig 2 Vita 3D-Master shade guide.
Table 1 Sample information Shade guide
Selected samples
Batch
Vita Classical
A1, A2, A3, A3.5, A4, B1, B2, B3, B4
B027C
Vita 3D-Master
2M1, 2M2, 3M2, 3R2.5, 4M2, 1M1, 2L1.5, 3L2.5, 3M3
B360A
tooth, which will serve as reference for color restoration.10–12 Thus, they are exposed to pathogenic microorganisms from saliva and aerosol, requiring appropriate crosscontamination control at the end of the clinical appointment. To avoid cross-contamination, various sterilization and disinfection methods are described under distinct physical and chemical types. Ultimately, sterilization is the process required to ensure that all microorganisms have been removed from or inactivated on a given surface. According to several authors,13–15 the autoclave is the mechanism recommended for sterilization of dental instruments. It applies moist heat under high pressure and has inherent advantages over other methods in that it is expedient, inexpensive, and convenient.13–15 Although shade guides are often used in esthetic restorative procedures, and sterilization by autoclave is considered the main method of cross-infection control in the dental office, no study concerning the influence of autoclave steril-
ization on the color stability of shade guides was found in the literature. The objective of this study was to evaluate the influence of 120 cycles of autoclave sterilization on the color stability of two shade guides. The null hypothesis tested is that the sterilization cycles will not cause color changes in shade guides.
Method and materials Selection of the samples
To perform the study, the shade guides VC and V3DM (Figs 1 and 2) were subjected to tests. Based on previous studies16–18 that described the hues A (brown) and B (yellow) of the VC as the most observed hues in the human dentition, they were chosen to represent this shade guide. The samples representing the V3DM corresponded to the selected samples in the VC, according to the color conversion table provided by the manufacturer. The selected samples and batch numbers for each shade guide are given in Table 1.
The color assessment was performed with an intraoral spectrophotometer (Vita Easyshade, Vita Zahnfabrik) before and after the sterilization cycles (Fig 3). The presented wavelengths, between 400 and 700 nm, were calibrated according to the manufacturer’s instructions. To exclude eventual relative inconsistencies from the device and the operator, three measurements were taken consecutively for each specimen. The color was obtained by averaging the three measurements and expressing them according to the CIELab system.19 According to this system,19 colors are expressed in three related axes that cross in order to determine the color of the object. The L* axis indicates the achromatic coordinate or the lightness of the object, with a range from 0 (absolute black) to 100 (absolute white). The a* and b* axes indicate the three-dimensional positioning of the object in color space. The a* axis represents the amount of red (positive a* value) or green (negative a* value). The b* axis represents the amount of yellow (positive b* value) or blue (negative b* value). To ensure the same location of the evaluations in all specimens and to minimize the influence of ambient light on the result, a stainless steel positioning device was specially manufactured for each shade guide used in this study. Each device had a cylindric shape and was composed of a base and a lid (Fig 4). The base had a cavity (6-mm diameter × 4-mm height) filled with heavy silicone (Virtual Putty, Ivoclar Vivadent), which was manipulated according
The International Journal of Periodontics & Restorative Dentistry © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
691 to the manufacturer’s instructions. A chromatic sample (randomly selected) from each shade guide was pressed on the molding material inserted in the base, with its labial surface exposed. After polymerization of the impression material, the reference sample was removed, yielding a perfect fit for all samples evaluated for each scale. With the samples individually positioned on the base, the cover of the device was positioned, with the center hole allowing the introduction of the optical reader of the spectrophotometer, which was inserted at the middle third of the specimen (Fig 5). This location was chosen in order to avoid the translucency of the incisal third and the low value of the cervical third.20,21
Autoclave sterilization
The sterilization cycles were performed by regulating the autoclave for sterilizing packaged instruments (121°C; 15 psi). Samples were packed (five samples per pack; 18 packs per sterilization cycle), and the packaging units were discarded at each new sterilization cycle. Each cycle lasted 40 minutes (10 minutes of heat, 20 minutes of sterilization, and 10 minutes of drying). The temperature of the autoclave was monitored on all cycles by visual inspection of the digital display and by chemical control for every 10 cycles.
Chromatic difference evaluation
Five specimens (n = 5) were used for each sample. With the aid of a
Fig 3 (left) Vita Easyshade spectrophotometer. Fig 4 (below) Stainless steel positioning device (base and lid).
Fig 5 Positioning of chromatic sample in the device.
spherical tip in the high-speed handpiece, the specimens of the same color were numbered on the back of the metal rod (from 1 to 5) to obtain individual results. For evaluation of the color differences, the measurements were analyzed by calculating the color difference ∆E*, as follows22: ∆E* = ([∆L*]2 + (∆a*)2 + (∆b*)2 )1/2
ciable by skilled operators but clinically acceptable, while values of ∆E* > 3.3 were considered appreciable by laypersons and, for that reason, not clinically acceptable.22 Each of the CIELab color coordinates of all samples were analyzed before and after sterilization cycles, using the t test for paired data.
where: ∆L* = L*1 – L*2 (difference in coordinate L* between periods 1 and 2) ∆a* = a*1 – a*2 (difference in coordinate a* between periods 1 and 2) ∆b* = b*1 – b*2 (difference in coordinate b* between periods 1 and 2) To verify the clinical significance of the obtained results, values of ∆E* < 1 were regarded as not appreciable by the human eye. Values 1 < ∆E < 3.3 were considered appre-
Results The chromatic parameters of the samples before and after 120 cycles of autoclave sterilization are described in Table 2. The chromatic differences of the samples are described in Tables 3 and 4. According to this result, all specimens showed chromatic variation after 120 cycles of sterilization. According to the t test for paired data, all specimens became darker. However, specimens of Vita Classical became redder, while the Vita 3DMaster became more yellow.
Volume 34, Number 5, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
692
Table 2 CIELab data are presented as mean (SD) Before sterilization Samples A1 A2 A3 A3.5 A4 B1 B2 B3 B4 2M1 2M2 3M2 3R2.5 4M2 1M1 2L1.5 3L2.5 3M3
After 120 cycles
L*
a*
b*
L*
a*
b*
82.5 (1.0) 78.9 (0.8) 75.4 (0.6) 75.4 (0.4) 68.5 (0.4) 81.2 (0.8) 79.9 (0.3) 74.6 (0.7) 75.8 (0.4) 80.1 (0.5) 79.8 (0.7) 75.0 (0.6) 75.1 (1.1) 70.1 (0.5) 84.3 (0.7) 80.5 (0.7) 74.9 (0.5) 74.7 (0.9)
–0.7 (0.2) 0.7 (0.1) 1.1 (0.2) 1.1 (0.2) 3.0 (0.1) –1.7 (0.1) –0.9 (0.1) 0.6 (0.1) 0.8 (0.2) 0.2 (0.1) 0.2 (0.1) 1.4 (0.1) 2.3 (0.6) 2.9 (0.2) –0.6 (0.0) –0.7 (0.1) 0.9 (0.2) 2.0 (0.4)
14.4 (0.6) 21.2 (0.6) 21.8 (1.2) 21.8 (0.4) 26.8 (0.7) 12.4 (0.6) 19.4 (0.4) 25.9 (1.4) 28.7 (0.8) 14.4 (0.9) 20.5 (0.6) 23.2 (0.6) 26.7 (1.2) 25.8 (0.8) 11.8 (0.7) 18.0 (0.3) 27.0 (1.1) 29.1 (1.7)
80.5 (0.9) 78.1 (1.1) 74.7 (0.5) 72.2 (0.3) 67.8 (0.4) 80.0 (0.7) 78.8 (0.4) 73.4 (0.5) 74.5 (0.5) 78.4 (0.3) 78.2 (0.5) 73.5 (0.4) 73.3 (0.7) 68.8 (0.6) 82.8 (0.6) 78.9 (0.4) 73.2 (0.8) 73.8 (0.8)
–0.4 (0.1) 0.9 (0.1) 1.1 (0.2) 2.1 (0.3) 3.0 (0.2) –1,4 (0.1) –0.7 (0.1) 0.7 (0.2) 1.0 (0.2) 0.3 (0.1) 0.3 (0.1) 1.5 (0.1) 2.6 (0.2) 2.9 (0.2) –0.4 (0.1) –0.5 (0.1) 1.7 (0.3) 1.7 (0.3)
15.4 (0.6) 21.5 (0.5) 21.6 (0.5) 26.8 (0.2) 26.8 (0.6) 13.1 (0.6) 19.7 (0.5) 25.9 (1.4) 28.4 (0.8) 15.0 (0.2) 20.6 (0.6) 23.6 (0.5) 27.6 (1.9) 25.7 (0.8) 12.2 (0.7) 18.0 (0.5) 27.3 (1.3) 29.6 (1.8)
Discussion According to this result, all specimens showed chromatic differences after sterilization cycles, rejecting the null hypothesis. This change can be explained by the influence of the moist heat under high pressure in each chromatic scale. While some specimen differences were imperceptible to the human eye (∆E* < 1; VC: A2, A3, A4; V3DM: 3M3) others showed detectable changes only to the trained eye (1 < ∆E < 3.3; VC: A1, A3.5, B1, B2, B3, B4; V3DM: 2M1, 2M2, 3M2, 3R2.5, 4M2, 1M1, 2L1.5, 3L2.5). None of the specimens showed chromatic differences that would be considered clinically unacceptable (∆E* > 3.3).
The color changes in shade guides after sterilization by autoclave can result in inappropriate selection of composites (direct restorative treatments) and failure in color communication with the ceramist (indirect restorative treatments). Despite the esthetic significance of this finding, cross-contamination control is inarguably a fundamental step in the color selection and reproduction procedure. The control of microorganisms and microbial growth is an important consideration in clinical situations. According to United States Occupational Safety and Health Administration (OSHA) guidelines, shade guides are considered semicritical items that can be disinfected according to intermediate-level
Environmental Protection Agency guidelines. This statement is based on the fact that shade guides contact only intact mucous membranes or in some cases broken skin.23,24 However, there may be situations in which the professional feels more secure with the use of sterilization via autoclaving. Initially, the type and amount of microorganisms must be considered. Obviously, microorganisms that have a high level of resistance and higher populations of microorganisms can present a greater challenge to disinfection and sterilization. The wide variety of chemical agents available on the market can also confuse the professional, who must ensure adequate contact times and concentrations of chemical.24 This confusion can introduce toxicity,25 cause damage to the instruments,26 and be inefficient against certain groups of microorganisms. Another important advantage of the autoclave over chemical methods is the possibility of monitoring. There are no readily available biologic tests to assess the effectiveness of chemical sterilization, but there are a number of ways of monitoring autoclave performance.14 Checking the autoclave display to ensure adequate cycle duration, temperature, and pressure are attained is a simple and reliable method, provided the autoclave has been regularly calibrated and validated. Chemical monitors may be used, eg, autoclave tapes or strips, where a color change indicates that the correct result has been achieved during the autoclave cycle.13 The number of sterilization cycles performed in this study was
The International Journal of Periodontics & Restorative Dentistry © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
693 limited by the silicone used in the positioning device. According to the manufacturer, it provides 3 weeks of dimensional stability, ensuring the correct position of the spectrophotometer optical reader. The absence of ∆E* values greater than 3.3 can be explained by the small number of sterilization cycles. These differences, however, may be observed with the increase in the number of cycles. Other studies presenting methodology for long-term periods are needed in order to make this statement.
Conclusions According to the results of this study, it is possible to conclude that the repeated cycles of autoclave sterilization caused statistically significant changes in the color of the two shade guides. However, the differences are clinically acceptable.
Acknowledgments The authors reported no conflicts of interest related to this study.
References 1. Wyszecki G, Stiles WS. Color Science. Concepts and Methods, Quantitative Data and Formulae. 2nd ed. New York: John Wiley and Sons, 2000. 2. Chu SJ, Devigus A, Mieleszko AJ. Color theory. In: Fundamentals of Color: Shade Matching and Communication in Esthetic Dentistry. Chicago: Quintessence, 2004. 3. Joiner A. Tooth color: A review of the literature. J Dent 2004;32(suppl 1):3–12. 4. Okubo SR, Kanawati A, Richards MW, Childress S. Evaluation of visual and instrumental shade matching. J Prosthet Dent 1998;80:642–648.
Table 3 Vita Classical mean chromatic differences Samples
A1
A2
A3
A3.5
A4
B1
B2
B3
B4
∆E*
1.8
0.7
0.7
1.5
0.6
1.1
1.0
1.2
1.6
Table 4 Vita 3D-Master mean chromatic differences Samples ∆E*
2M1
2M2
3M2
3R2.5
4M2
1M1
1.6
1.8
1.4
1.3
1.3
2.0
5. Chu SJ, Tarnow DP. Digital shade analysis and verification. A case report and discussion. Pract Proced Aesthet Dent 2001; 13:129–136. 6. Paul S, Peter A, Pietrobon N, Hämmerle CH. Visual and spectrophotometric shade of human teeth. J Dent Res 2002; 81:578–582. 7. van der Burgt TP, ten Bosch JJ, Borsboom PC, Kortsmit WJ. A comparison of new and conventional methods for quantification of tooth color. J Prosthet Dent 1990;63:155–162. 8. Oh WS, Koh IW, O’Brien WJ. Estimation of visual shade matching errors with 2 shade guides. Quintessence Int 2009;40:833–836. 9. Vichi A, Louca C, Corciolani G, Ferrari M. Color related to ceramic and zirconia restorations: A review. Dent Mater 2011;27:97–108. 10. Paravina RD, Powers JM. Esthetic Color Training in Dentistry. St Louis: Elsevier/ Mosby, 2004. 11. Baratieri LN, Araújo EM Jr, Monteiro S Jr. Basic fundamentals and restorative protocol for the use of composite resins in anterior teeth. In: Composite Restorations in Anterior Teeth: Fundamentals and Possibilities. Chicago: Quintessence, 2005. 12. Fondriest J. Master’s technique level: Shade matching a single maxillary central incisor. Quintessence Dent Technol 2005;28:215–225. 13. Burke FTJ, Coulter WA, Cheung SW, Palenik CJ. Autoclave performance and practitioner knowledge of autoclave use: A survey of selected UK practices. Quintessence Int 1998;29:23l–238. 14. Healy CM, Kearns HPO, Coulter WA, Stevenson WA, Burke FJT. Autoclave use in dental practice in the Republic of Ireland. Int Dent J 2004;54:182–186. 15. Bhatnagar S, Bagga DK, Sharma P, Kumar P, Rakesh S, Singh V. Infection control strategy in orthodontic office. Eur J Gen Dent 2013;2(1):1–7.
2L1.5 3L2.5 1.6
1.5
3M3 0.7
16. Yamamoto M. The value conversion system and a new concept for expressing the shades of natural teeth. Quintessence Dent Technol 1992;19:9. 17. Schwabacher WB, Goodkind RJ. Threedimensional color coordinates of natural teeth compared with three shade guides. J Prosthet Dent 2000;64:425–431. 18. Dietschi D, Ardu S, Krejci I. A new shading concept based on natural tooth color applied to direct composite restorations. Quintessence Int 2006;37:91–102. 19. Comission Internationale de L’Eclairage. Colorimetry, Official Recommendations of the International Commission on Illumination. Publication CIE No. 15 (E1.3.1). Paris: Bureau Central de la CIE, 1971. 20. Hasegawa A, Ikeda I, Kavaguchi S. Color and translucency of natural central incisors. J Prosthet Dent 2000;83:418–423. 21. Dozic A, Kleverlaan CJ, Aartman IH, Feilzer AJ. Relation in color of three regions of vital human incisors. Dent Mater 2004;20:832–838. 22. Ruyter IE, Nilner K, Moller B. Color stability of dental composite resin materials for crown and bridge veneers. Dent Mater 1987;3:246–251. 23. Pohjola RM, Hackman ST, Browning WD. Evaluation of a standard shade guide for color change after disinfection. Quintessence Int 2007;38:671–676. 24. da Silva FC, Kimpara ET, Mancini MN, Balducci I, Jorge AO, Koga-Ito CY. Effectiveness of six different disinfectants on removing five microbial species and effects on the topographic characteristics of acrylic resin. J Prosthodont 2008;17:627–633. 25. Angelillo IF, Bianco A, Nobile CG, Pavia M. Evaluation of the efficacy of glutaraldehyde and peroxygen for disinfection of dental instruments. Lett Appl Microbiol 1998;27:292–296. 26. Bell JA, Brockmann MS, Feil P, Sackuvich DA. The effectiveness of two disinfectants on denture base acrylic resin with an organic load. J Prosthet Dent 1989;61:581–589.
Volume 34, Number 5, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
689
Color Stability of Shade Guides After Autoclave Sterilization
Max Schmeling, DDS, MS, PhD1 Neimar Sartori, DDS, MS, PhD2 Sylvio Monteiro, Jr., DDS, MS, PhD3 Luiz Baratieri, DDS, MS, PhD3
This study evaluated the influence of 120 autoclave sterilization cycles on the color stability of two commercial shade guides (Vita Classical and Vita System 3D-Master). The specimens were evaluated by spectrophotometer before and after the sterilization cycles. The color was described using the three-dimensional CIELab system. The statistical analysis was performed in three chromaticity coordinates, before and after sterilization cycles, using the paired samples t test. All specimens became darker after autoclave sterilization cycles. However, specimens of Vita Classical became redder, while those of the Vita System 3D-Master became more yellow. Repeated cycles of autoclave sterilization caused statistically significant changes in the color coordinates of the two shade guides. However, these differences are considered clinically acceptable. (Int J Periodontics Restorative Dent 2014;34:689–693. doi: 10.11607/prd.1868)
Postgraduate Student, Department of Dentistry, Federal University of Santa Catarina, Florianopolis, Santa Catarina, Brazil. 2Assistant Professor, Division of Restorative Sciences, Ostrow School of Dentistry, University of Southern California, Los Angeles, California, USA. 3Professor, Department of Dentistry, Federal University of Santa Catarina, Florianopolis, Santa Catarina, Brazil. 1
Correspondence to: Max Schmeling, Pós graduação em Dentística Universidade Federal de Santa Catarina Centro de Ciências da Saúde, Campus Trindade s/n, Florianópolis, SC, Brazil. CEP: 88040-900 ©2014 by Quintessence Publishing Co Inc.
The visual observation method is characterized by the necessary interaction between three fundamental elements: a light source, an object, and a viewer.1 After being emitted by a light source, light energy can be transmitted or reflected by an object toward the eye of the observer, which captures the physical energy and transforms it into nerve impulses that are interpreted by the brain as color. The requirement of visualization and interpretation by the brain, however, gives this method of color perception a complex and subjective character, even with standardization of the light source and the object.1–3 Although the subjectivity of the visual method of color selection is described in several studies, visually comparing a natural tooth with shade guides is the main method for selecting tooth color in esthetic restorative procedures.4–7 Recently, the Vita Classical (VC) and Vita 3DMaster (V3DM) shade guides (Vita Zahnfabrik) were described as being among the most used.8,9 Even though they have the same manufacturer, they present some differences, mainly due to the appearance of the samples, which are arranged in groups according to the hue in VC and according to value in V3DM.8,9 When selecting the color, regardless of type or brand, the shade guides should be viewed in close proximity to the patient’s
Volume 34, Number 5, 2014 © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
690 Color evaluation
Fig 1 Vita Classical shade guide.
Fig 2 Vita 3D-Master shade guide.
Table 1 Sample information Shade guide
Selected samples
Batch
Vita Classical
A1, A2, A3, A3.5, A4, B1, B2, B3, B4
B027C
Vita 3D-Master
2M1, 2M2, 3M2, 3R2.5, 4M2, 1M1, 2L1.5, 3L2.5, 3M3
B360A
tooth, which will serve as reference for color restoration.10–12 Thus, they are exposed to pathogenic microorganisms from saliva and aerosol, requiring appropriate crosscontamination control at the end of the clinical appointment. To avoid cross-contamination, various sterilization and disinfection methods are described under distinct physical and chemical types. Ultimately, sterilization is the process required to ensure that all microorganisms have been removed from or inactivated on a given surface. According to several authors,13–15 the autoclave is the mechanism recommended for sterilization of dental instruments. It applies moist heat under high pressure and has inherent advantages over other methods in that it is expedient, inexpensive, and convenient.13–15 Although shade guides are often used in esthetic restorative procedures, and sterilization by autoclave is considered the main method of cross-infection control in the dental office, no study concerning the influence of autoclave steril-
ization on the color stability of shade guides was found in the literature. The objective of this study was to evaluate the influence of 120 cycles of autoclave sterilization on the color stability of two shade guides. The null hypothesis tested is that the sterilization cycles will not cause color changes in shade guides.
Method and materials Selection of the samples
To perform the study, the shade guides VC and V3DM (Figs 1 and 2) were subjected to tests. Based on previous studies16–18 that described the hues A (brown) and B (yellow) of the VC as the most observed hues in the human dentition, they were chosen to represent this shade guide. The samples representing the V3DM corresponded to the selected samples in the VC, according to the color conversion table provided by the manufacturer. The selected samples and batch numbers for each shade guide are given in Table 1.
The color assessment was performed with an intraoral spectrophotometer (Vita Easyshade, Vita Zahnfabrik) before and after the sterilization cycles (Fig 3). The presented wavelengths, between 400 and 700 nm, were calibrated according to the manufacturer’s instructions. To exclude eventual relative inconsistencies from the device and the operator, three measurements were taken consecutively for each specimen. The color was obtained by averaging the three measurements and expressing them according to the CIELab system.19 According to this system,19 colors are expressed in three related axes that cross in order to determine the color of the object. The L* axis indicates the achromatic coordinate or the lightness of the object, with a range from 0 (absolute black) to 100 (absolute white). The a* and b* axes indicate the three-dimensional positioning of the object in color space. The a* axis represents the amount of red (positive a* value) or green (negative a* value). The b* axis represents the amount of yellow (positive b* value) or blue (negative b* value). To ensure the same location of the evaluations in all specimens and to minimize the influence of ambient light on the result, a stainless steel positioning device was specially manufactured for each shade guide used in this study. Each device had a cylindric shape and was composed of a base and a lid (Fig 4). The base had a cavity (6-mm diameter × 4-mm height) filled with heavy silicone (Virtual Putty, Ivoclar Vivadent), which was manipulated according
The International Journal of Periodontics & Restorative Dentistry © 2014 BY QUINTESSENCE PUBLISHING CO, INC. PRINTING OF THIS DOCUMENT IS RESTRICTED TO PERSONAL USE ONLY. NO PART MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM WITHOUT WRITTEN PERMISSION FROM THE PUBLISHER.
691 to the manufacturer’s instructions. A chromatic sample (randomly selected) from each shade guide was pressed on the molding material inserted in the base, with its labial surface exposed. After polymerization of the impression material, the reference sample was removed, yielding a perfect fit for all samples evaluated for each scale. With the samples individually positioned on the base, the cover of the device was positioned, with the center hole allowing the introduction of the optical reader of the spectrophotometer, which was inserted at the middle third of the specimen (Fig 5). This location was chosen in order to avoid the translucency of the incisal third and the low value of the cervical third.20,21
Autoclave sterilization
The sterilization cycles were performed by regulating the autoclave for sterilizing packaged instruments (121°C; 15 psi). Samples were packed (five samples per pack; 18 packs per sterilization cycle), and the packaging units were discarded at each new sterilization cycle. Each cycle lasted 40 minutes (10 minutes of heat, 20 minutes of sterilization, and 10 minutes of drying). The temperature of the autoclave was monitored on all cycles by visual inspection of the digital display and by chemical control for every 10 cycles.
Chromatic difference evaluation
Five specimens (n = 5) were used for each sample. With the aid of a
Fig 3 (left) Vita Easyshade spectrophotometer. Fig 4 (below) Stainless steel positioning device (base and lid).
Fig 5 Positioning of chromatic sample in the device.
spherical tip in the high-speed handpiece, the specimens of the same color were numbered on the back of the metal rod (from 1 to 5) to obtain individual results. For evaluation of the color differences, the measurements were analyzed by calculating the color difference ∆E*, as follows22: ∆E* = ([∆L*]2 + (∆a*)2 + (∆b*)2 )1/2
ciable by skilled operators but clinically acceptable, while values of ∆E* > 3.3 were considered appreciable by laypersons and, for that reason, not clinically acceptable.22 Each of the CIELab color coordinates of all samples were analyzed before and after sterilization cycles, using the t test for paired data.
where: ∆L* = L*1 – L*2 (difference in coordinate L* between periods 1 and 2) ∆a* = a*1 – a*2 (difference in coordinate a* between periods 1 and 2) ∆b* = b*1 – b*2 (difference in coordinate b* between periods 1 and 2) To verify the clinical significance of the obtained results, values of ∆E* < 1 were regarded as not appreciable by the human eye. Values 1 < ∆E < 3.3 were considered appre-
Results The chromatic parameters of the samples before and after 120 cycles of autoclave sterilization are described in Table 2. The chromatic differences of the samples are described in Tables 3 and 4. According to this result, all specimens showed chromatic variation after 120 cycles of sterilization. According to the t test for paired data, all specimens became darker. However, specimens of Vita Classical became redder, while the Vita 3DMaster became more yellow.
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Table 2 CIELab data are presented as mean (SD) Before sterilization Samples A1 A2 A3 A3.5 A4 B1 B2 B3 B4 2M1 2M2 3M2 3R2.5 4M2 1M1 2L1.5 3L2.5 3M3
After 120 cycles
L*
a*
b*
L*
a*
b*
82.5 (1.0) 78.9 (0.8) 75.4 (0.6) 75.4 (0.4) 68.5 (0.4) 81.2 (0.8) 79.9 (0.3) 74.6 (0.7) 75.8 (0.4) 80.1 (0.5) 79.8 (0.7) 75.0 (0.6) 75.1 (1.1) 70.1 (0.5) 84.3 (0.7) 80.5 (0.7) 74.9 (0.5) 74.7 (0.9)
–0.7 (0.2) 0.7 (0.1) 1.1 (0.2) 1.1 (0.2) 3.0 (0.1) –1.7 (0.1) –0.9 (0.1) 0.6 (0.1) 0.8 (0.2) 0.2 (0.1) 0.2 (0.1) 1.4 (0.1) 2.3 (0.6) 2.9 (0.2) –0.6 (0.0) –0.7 (0.1) 0.9 (0.2) 2.0 (0.4)
14.4 (0.6) 21.2 (0.6) 21.8 (1.2) 21.8 (0.4) 26.8 (0.7) 12.4 (0.6) 19.4 (0.4) 25.9 (1.4) 28.7 (0.8) 14.4 (0.9) 20.5 (0.6) 23.2 (0.6) 26.7 (1.2) 25.8 (0.8) 11.8 (0.7) 18.0 (0.3) 27.0 (1.1) 29.1 (1.7)
80.5 (0.9) 78.1 (1.1) 74.7 (0.5) 72.2 (0.3) 67.8 (0.4) 80.0 (0.7) 78.8 (0.4) 73.4 (0.5) 74.5 (0.5) 78.4 (0.3) 78.2 (0.5) 73.5 (0.4) 73.3 (0.7) 68.8 (0.6) 82.8 (0.6) 78.9 (0.4) 73.2 (0.8) 73.8 (0.8)
–0.4 (0.1) 0.9 (0.1) 1.1 (0.2) 2.1 (0.3) 3.0 (0.2) –1,4 (0.1) –0.7 (0.1) 0.7 (0.2) 1.0 (0.2) 0.3 (0.1) 0.3 (0.1) 1.5 (0.1) 2.6 (0.2) 2.9 (0.2) –0.4 (0.1) –0.5 (0.1) 1.7 (0.3) 1.7 (0.3)
15.4 (0.6) 21.5 (0.5) 21.6 (0.5) 26.8 (0.2) 26.8 (0.6) 13.1 (0.6) 19.7 (0.5) 25.9 (1.4) 28.4 (0.8) 15.0 (0.2) 20.6 (0.6) 23.6 (0.5) 27.6 (1.9) 25.7 (0.8) 12.2 (0.7) 18.0 (0.5) 27.3 (1.3) 29.6 (1.8)
Discussion According to this result, all specimens showed chromatic differences after sterilization cycles, rejecting the null hypothesis. This change can be explained by the influence of the moist heat under high pressure in each chromatic scale. While some specimen differences were imperceptible to the human eye (∆E* < 1; VC: A2, A3, A4; V3DM: 3M3) others showed detectable changes only to the trained eye (1 < ∆E < 3.3; VC: A1, A3.5, B1, B2, B3, B4; V3DM: 2M1, 2M2, 3M2, 3R2.5, 4M2, 1M1, 2L1.5, 3L2.5). None of the specimens showed chromatic differences that would be considered clinically unacceptable (∆E* > 3.3).
The color changes in shade guides after sterilization by autoclave can result in inappropriate selection of composites (direct restorative treatments) and failure in color communication with the ceramist (indirect restorative treatments). Despite the esthetic significance of this finding, cross-contamination control is inarguably a fundamental step in the color selection and reproduction procedure. The control of microorganisms and microbial growth is an important consideration in clinical situations. According to United States Occupational Safety and Health Administration (OSHA) guidelines, shade guides are considered semicritical items that can be disinfected according to intermediate-level
Environmental Protection Agency guidelines. This statement is based on the fact that shade guides contact only intact mucous membranes or in some cases broken skin.23,24 However, there may be situations in which the professional feels more secure with the use of sterilization via autoclaving. Initially, the type and amount of microorganisms must be considered. Obviously, microorganisms that have a high level of resistance and higher populations of microorganisms can present a greater challenge to disinfection and sterilization. The wide variety of chemical agents available on the market can also confuse the professional, who must ensure adequate contact times and concentrations of chemical.24 This confusion can introduce toxicity,25 cause damage to the instruments,26 and be inefficient against certain groups of microorganisms. Another important advantage of the autoclave over chemical methods is the possibility of monitoring. There are no readily available biologic tests to assess the effectiveness of chemical sterilization, but there are a number of ways of monitoring autoclave performance.14 Checking the autoclave display to ensure adequate cycle duration, temperature, and pressure are attained is a simple and reliable method, provided the autoclave has been regularly calibrated and validated. Chemical monitors may be used, eg, autoclave tapes or strips, where a color change indicates that the correct result has been achieved during the autoclave cycle.13 The number of sterilization cycles performed in this study was
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693 limited by the silicone used in the positioning device. According to the manufacturer, it provides 3 weeks of dimensional stability, ensuring the correct position of the spectrophotometer optical reader. The absence of ∆E* values greater than 3.3 can be explained by the small number of sterilization cycles. These differences, however, may be observed with the increase in the number of cycles. Other studies presenting methodology for long-term periods are needed in order to make this statement.
Conclusions According to the results of this study, it is possible to conclude that the repeated cycles of autoclave sterilization caused statistically significant changes in the color of the two shade guides. However, the differences are clinically acceptable.
Acknowledgments The authors reported no conflicts of interest related to this study.
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Table 3 Vita Classical mean chromatic differences Samples
A1
A2
A3
A3.5
A4
B1
B2
B3
B4
∆E*
1.8
0.7
0.7
1.5
0.6
1.1
1.0
1.2
1.6
Table 4 Vita 3D-Master mean chromatic differences Samples ∆E*
2M1
2M2
3M2
3R2.5
4M2
1M1
1.6
1.8
1.4
1.3
1.3
2.0
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