Effect of Different Chemical Disinfectants on Color Stability of Acrylic Denture Teeth Bulent Piskin, DDS, PhD,1 Cumhur Sipahi, DDS, PhD,1 & Hakan Akin, DDS, PhD2 1 2
Associate Professor, Department of Prosthodontics, Gulhane Military Medical Academy, Ankara, Turkey Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Cumhuriyet University, Sivas, Turkey
Keywords Denture teeth; color stability; disinfectant; spectrophotometry. Correspondence Dr. Hakan Akin, Department of Prosthodontics, Faculty of Dentistry, Cumhuriyet University, 58140 Sivas, Turkey. E-mail: [email protected] The authors deny any conflicts of interest. Accepted September 15, 2013 doi: 10.1111/jopr.12131
Abstract Purpose: The purpose of this study was to evaluate the effects of chemical disinfectants on the color stability of acrylic denture teeth (ADT) via spectrophotometric analysis. Materials and Methods: A total of 120 central ADT specimens were randomly assigned to eight experimental groups and immersed in the following solutions (n = 15). Tap water/control group (CON), neutral soap (NTS), 2% sodium hypochlorite (SHC1), 5.25% sodium hypochlorite (SHC2), sodium perborate (SPB), povidone-iodine (PVI), chlorhexidine gluconate (CHG), and glutaraldehyde (GTA). Color measurements of teeth were performed by spectrophotometry after 10, 30, 48, 72, 144, and 960 immersion cycles in each tested solution. Color differences (E* ) were then evaluated using the Commission Internationale D’Eclairage (CIE) L* a* b* color system. Furthermore, Kruskal-Wallis, Mann-Whitney U, and Friedman comparison tests (α = 0.05) were performed on all data. Results: There were significant differences in E* values (p < 0.05) among the eight experimental groups. In addition, the highest E* values were obtained in group SHC2, followed, respectively, by the SHC1, CHG, SPB, PVI, NTS, and CON groups. Conclusion: All the chemical disinfectants used in the study affected the color values of ADTs. Furthermore, E* values increased along with the number of immersion cycles and total immersion time.
Removable prosthesis fabrication requires the use of numerous materials and large pieces of equipment that are not easily disinfected or sterilized.1-3 Dentures can become contaminated during any stage of the fabrication process, creating the risk of cross-contamination between dental personnel and patients.4 Impression materials, stone casts, dental pumice, polishing wheels, and other dental materials might be responsible for major bacterial deposits in dental clinics and laboratories.4-10 Microorganisms existing on the surfaces of intraorally used dental materials or dentures could cause denture-related stomatitis, airway infection, or cross-contamination.4,11-13 The increasing prevalence of life-threatening infectious diseases has led to a more widespread interest in the control of crossinfectious diseases,6,14,15 and the effective disinfection of dentures has become an indispensable procedure to prevent crosscontamination and protect patients’ health.13 Existing disinfection methods proven to be effective can be divided into two main categories: chemical and physical. Two of the most valuable features of chemical disinfectants are their low cost and ease of use.16 Unfortunately, the main drawback of resinbased materials is their affinity to adsorbtion (or absorbtion)
into an aquous media.17 It has been reported that water sorption could negatively affect the physical and mechanical properties of resin-based materials.18 In addition, if the resin material is in contact with a liquid containing colorant agents, the situation may worsen, and a discoloration may be unavoidable.19 Numerous studies have thoroughly investigated the effects of different chemical disinfectants on the dimensional stability, hardness, wettability, and flexural strength of various dental materials.1,6,20-23 The effects of chemical disinfectants or various denture cleansers on the surface properties and color stability of denture base resins have also been well documented.1 It is believed that some of the chemical disinfectants and denture cleansers could have a bleaching or whitening effect on resin-based materials. Furthermore, it was assumed that even distilled water could affect the color of these materials after a long immersion period.18,23 The dissolution of some chemical constituents and the leaching of residual monomer could also contribute to the complex degradation process of the resin material.18 Besides denture base materials, studies also report color changes in relined dentures, maxillofacial elastomers, and
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 00 (2014) 1–8
1
Color Stability of Acrylic Teeth
Piskin et al
Table 1 Test liquids used
Table 2 Repeated immersion cycle and total immersion time of each protocol
Liquids
Dilution
Tap water (control group) Neutral soap
(CON)
–
(NTS)
–
Sodium hypochlorite
(SHC1)
2%
Sodium hypochlorite
(SHC2)
5.25%
Sodium perborate
(SPB)
4%
Povidone-iodine
(PVI)
10%
Chlorhexidine gluconate Glutaraldehyde
(CHG)
4%
(GTA)
2%
Manufacturer Immersion protocols Sonett, Ekoorganik, Istanbul, Turkey Aklar Kimya, Ankara, Turkey Aklar Kimya, Ankara, Turkey Aklar Kimya, Ankara, Turkey Ortikon, MSB ˙IF, Ankara, Turkey Drogsan, Ankara, Turkey Aklar Kimya, Ankara, Turkey
artificial irises after immersion in chemical disinfectants.24-26 However, there are sparse data about the color stability of denture teeth. Therefore, the aim of this in vitro study was to determine the effects of commonly used chemical disinfectants on the color stability of acrylic denture teeth (ADT) via spectrophotometric analysis. The null hypothesis was that color stability of ADT could be negatively affected with the use of chemical disinfectants.
Materials and methods This study was conducted in five stages: selection of chemical disinfectants, arrangement of the ADT (Ultraplus; Ostim, Ankara, Turkey), determination and application of immersion protocols (IPs), fabrication of a custom acrylic resin holder with spectrophotometric measurements, and statistical analysis. Selection of chemical disinfectants
This study used six chemical disinfectants widely used in medical practice and a neutral soap (NTS), which is the most commonly used hygienic material in daily life. Tap water was used as the control (CON). Eight experimental groups were created. The control group, chemical disinfectants, and the dilutions used in this study are listed in Table 1. Arranging of acrylic resin denture teeth
The cross-linking agent used in the poly(methyl methacylate) structure of ADT specimens was ethylene glycol dimethacrylate. Dimensions of ADT specimens were as follows: 13.15 mm inciso-gingival lengths, 8.74 mm mesio-distal lengths, and 7.66 mm bucco-palatinal lengths. In total, 120 right first central incisor ADT specimens were randomly assigned to eight experimental groups according to the test liquids used (n = 15). Each ADT was preserved in high-density polyethylene (HDPE) containers labeled with the name of the group and numbered from 1 to 15. The ADTs were kept in the same container throughout the study. 2
IP 1 IP 2 IP 3 IP 4 IP 5 IP 6
Immersion cycle time (minutes)
Number of repeated immersion cycles
Total immersion time
15 15 15 15 15 15
10 30 48 72 144 960
2.5 hour 7.5 hour 12 hour 18 hour 36 hour 10 days
Determination and application of IPs
The ADT specimens were subjected to six IPs according to the number of repeated immersion cycles. The immersion period of each cycle lasted 15 minutes. The number of repeated immersion cycles and total immersion time for each IP are given in Table 2 Before immersion, the HDPE containers of each group were filled with 20 ml of an experimental liquid at room temperature (23 ± 2◦ C), and all the liquids were renewed after each IP. After each IP, the ADTs were kept in distilled water at room temperature (23 ± 2◦ C) for 10 minutes and dried with absorbent paper. Spectrophotometric measurements were then performed. Fabrication of a custom acrylic holder and spectrophototmetric measurements
All of the ADTs were subjected to an initial spectrophotometric analysis before IPs. Spectrophotometric measurements were performed with a ColorFlex EZ spectrophotometer (HunterLab Inc., Reston, VA), and a custom acrylic holder was used during spectrophotometic measurements. Fabrication of a custom acrylic holder
Because the optic detector was located in a deep cavity in the spectrophotometer, preventing the accurate measurement of ADT specimens, the fabrication of a custom-made acrylic holder that would precisely fit into this cavity and would serve to carry the test specimens into the device, was required. The ADT specimens were located in this holder so that their palatinal surfaces were located at the bottom, and the buccal surfaces were positioned at the top. The custom-made acrylic holder also served to prevent movement of the ADT during spectrophotometric measurements and to provide a standard measurement for each ADT. The diameter and height of the cylindrical acrylic holder were designed to fit into the optical cavity of the spectrophotometer. To create the holder, an open-ended polyvinyl cylinder (PVC), with a diameter of 53 mm and height of 14 mm, was positioned on a sheet of modeling wax (Cavex, Haarlem, The Netherlands) so the median third of the labial surface was at the cylinder’s center, allowing for accurate measurement by the spectrophotometer. The lingual and proximal surfaces of the ADT specimen were covered with a thin modeling wax layer to provide isolation, and a vibrator (Degussa R2, Frankfurt, Germany) was used to mix and pour autopolymerizing clear acrylic resin (Meliodent; HeraeusKulzer, Hanau, Germany) into
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 00 (2014) 1–8
Piskin et al
Color Stability of Acrylic Teeth
Table 3 Spectrophotometric measurement steps, labeling of obtained L∗ a∗ b∗ values, measurement steps of E∗ values and labeling of obtained E∗ values Steps of spectrophotometric measurements Initial measurements Measurements after IP1 Measurements after IP2 Measurements after IP3 Measurements after IP4 Measurements after IP5 Measurements after IP6
Steps of E measurements
Labeling of L∗ a∗ b∗ values L∗ 1 a∗ 1 b∗ 1 L∗ 2 a∗ 2 b∗ 2 L∗ 3 a∗ 3 b∗ 3 L∗ 4 a∗ 4 b∗ 4 L∗ 5 a∗ 5 b∗ 5 L∗ 6 a∗ 6 b∗ 6 L∗ 7 a∗ 7 b∗ 7
the PVC ring. After the autopolymerizing clear acrylic resin set, the PVC ring was removed from the cylindrical resin substrate, completing the fabrication of the acrylic holder. This procedure produced a negative copy of ADT specimens’ palatinal surfaces on the acrylic holder. This negative cavity provided the retention of the ADT specimens to the acrylic holder while being transferred into the optical cavity of the spectrophotometer. In this manner, similar and stable positioning of ADT specimens was provided for a standard colorimetric measurement. Spectrophotometric measurements
For spectrophotometric measurements of the ADTs and calculation of color value differences, the CIE L* a* b* color space (in which the brightness is shown with L* , red-green chromacy with a* , and yellow-blue chromacy with b* ) was used. Before spectrophotometric measurements, a pilot study was performed with various color measurement devices. Because the color characteristics of a material are directly related to its entire surface, devices that perform measurements in a limited area or those making point type measurments were not prefered. Thus, in the end of the pilot study, the authors decided to use the ColorFlex EZ spectrophotometer device having the ability to give the mean L* a* b* value of the material by analyzing its color from the entire surface in three consequent measurements in one trial. The optic detector located in an isolated cavity, preventing external light penetration by use of a “sample cup opaque cover,” was an additional advantage of the device. Because the optic detector had a wider surface area than those of ADT specimens, the cavity floor of the device was covered with a grayscale sheet (400 Series Gray Scale Pads; Strathmore, Appleton, WI) having at the center an opened area equal to the buccal surface boundaries of ADT specimens. ADT specimens fixed on the acrylic holder from their palatinal surfaces were precisely seated on the opened area formed on the grayscale sheet. This process was followed by the calibration of the spectrophotometer according to the instructions of the manufacturer using calibration tiles. Each ADT specimen was dried with absorbant paper before each measurement. Spectrophotometric measurements were repeated after each IP, and L* a* b* values were also measured. The spectrophotometer was set to give mean L* a* b* values after three consecutive readings. A total of seven L* a* b* values were obtained for each ADT specimen (the initial L* a* b* values and the L* a* b* val-
L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1
and L∗ 2 a∗ 2 b∗ 2 and L∗ 3 a∗ 3 b∗ 3 and L∗ 4 a∗ 4 b∗ 4 and L∗ 5 a∗ 5 b∗ 5 and L∗ 6 a∗ 6 b∗ 6 and L∗ 7 a∗ 7 b∗ 7
Labeling of obtained E values E1 E2 E3 E4 E5 E6
ues obtained after six IPs). The differences between the initial L* a* b* values and those obtained after IPs were calculated with the formula: E = [(L ∗2 − L∗1 )2 + (a2∗ − a∗1 )2 + (b2∗ − b∗1 )2 ]1/2 A total of six E values for each ADT specimen were obtained after measurements. Table 3 shows the spectrophotometric measurement steps for the eight experimental groups, the labeling of the obtained L* a* b* values, and the measurement steps and labeling of the E values. The obtained E* values have been quantified by National Bureau of Standards (NBS) units to match the color differences for the clinical conditions (NBS units-clinically acceptable level
Associate Professor, Department of Prosthodontics, Gulhane Military Medical Academy, Ankara, Turkey Associate Professor, Department of Prosthodontics, Faculty of Dentistry, Cumhuriyet University, Sivas, Turkey
Keywords Denture teeth; color stability; disinfectant; spectrophotometry. Correspondence Dr. Hakan Akin, Department of Prosthodontics, Faculty of Dentistry, Cumhuriyet University, 58140 Sivas, Turkey. E-mail: [email protected] The authors deny any conflicts of interest. Accepted September 15, 2013 doi: 10.1111/jopr.12131
Abstract Purpose: The purpose of this study was to evaluate the effects of chemical disinfectants on the color stability of acrylic denture teeth (ADT) via spectrophotometric analysis. Materials and Methods: A total of 120 central ADT specimens were randomly assigned to eight experimental groups and immersed in the following solutions (n = 15). Tap water/control group (CON), neutral soap (NTS), 2% sodium hypochlorite (SHC1), 5.25% sodium hypochlorite (SHC2), sodium perborate (SPB), povidone-iodine (PVI), chlorhexidine gluconate (CHG), and glutaraldehyde (GTA). Color measurements of teeth were performed by spectrophotometry after 10, 30, 48, 72, 144, and 960 immersion cycles in each tested solution. Color differences (E* ) were then evaluated using the Commission Internationale D’Eclairage (CIE) L* a* b* color system. Furthermore, Kruskal-Wallis, Mann-Whitney U, and Friedman comparison tests (α = 0.05) were performed on all data. Results: There were significant differences in E* values (p < 0.05) among the eight experimental groups. In addition, the highest E* values were obtained in group SHC2, followed, respectively, by the SHC1, CHG, SPB, PVI, NTS, and CON groups. Conclusion: All the chemical disinfectants used in the study affected the color values of ADTs. Furthermore, E* values increased along with the number of immersion cycles and total immersion time.
Removable prosthesis fabrication requires the use of numerous materials and large pieces of equipment that are not easily disinfected or sterilized.1-3 Dentures can become contaminated during any stage of the fabrication process, creating the risk of cross-contamination between dental personnel and patients.4 Impression materials, stone casts, dental pumice, polishing wheels, and other dental materials might be responsible for major bacterial deposits in dental clinics and laboratories.4-10 Microorganisms existing on the surfaces of intraorally used dental materials or dentures could cause denture-related stomatitis, airway infection, or cross-contamination.4,11-13 The increasing prevalence of life-threatening infectious diseases has led to a more widespread interest in the control of crossinfectious diseases,6,14,15 and the effective disinfection of dentures has become an indispensable procedure to prevent crosscontamination and protect patients’ health.13 Existing disinfection methods proven to be effective can be divided into two main categories: chemical and physical. Two of the most valuable features of chemical disinfectants are their low cost and ease of use.16 Unfortunately, the main drawback of resinbased materials is their affinity to adsorbtion (or absorbtion)
into an aquous media.17 It has been reported that water sorption could negatively affect the physical and mechanical properties of resin-based materials.18 In addition, if the resin material is in contact with a liquid containing colorant agents, the situation may worsen, and a discoloration may be unavoidable.19 Numerous studies have thoroughly investigated the effects of different chemical disinfectants on the dimensional stability, hardness, wettability, and flexural strength of various dental materials.1,6,20-23 The effects of chemical disinfectants or various denture cleansers on the surface properties and color stability of denture base resins have also been well documented.1 It is believed that some of the chemical disinfectants and denture cleansers could have a bleaching or whitening effect on resin-based materials. Furthermore, it was assumed that even distilled water could affect the color of these materials after a long immersion period.18,23 The dissolution of some chemical constituents and the leaching of residual monomer could also contribute to the complex degradation process of the resin material.18 Besides denture base materials, studies also report color changes in relined dentures, maxillofacial elastomers, and
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 00 (2014) 1–8
1
Color Stability of Acrylic Teeth
Piskin et al
Table 1 Test liquids used
Table 2 Repeated immersion cycle and total immersion time of each protocol
Liquids
Dilution
Tap water (control group) Neutral soap
(CON)
–
(NTS)
–
Sodium hypochlorite
(SHC1)
2%
Sodium hypochlorite
(SHC2)
5.25%
Sodium perborate
(SPB)
4%
Povidone-iodine
(PVI)
10%
Chlorhexidine gluconate Glutaraldehyde
(CHG)
4%
(GTA)
2%
Manufacturer Immersion protocols Sonett, Ekoorganik, Istanbul, Turkey Aklar Kimya, Ankara, Turkey Aklar Kimya, Ankara, Turkey Aklar Kimya, Ankara, Turkey Ortikon, MSB ˙IF, Ankara, Turkey Drogsan, Ankara, Turkey Aklar Kimya, Ankara, Turkey
artificial irises after immersion in chemical disinfectants.24-26 However, there are sparse data about the color stability of denture teeth. Therefore, the aim of this in vitro study was to determine the effects of commonly used chemical disinfectants on the color stability of acrylic denture teeth (ADT) via spectrophotometric analysis. The null hypothesis was that color stability of ADT could be negatively affected with the use of chemical disinfectants.
Materials and methods This study was conducted in five stages: selection of chemical disinfectants, arrangement of the ADT (Ultraplus; Ostim, Ankara, Turkey), determination and application of immersion protocols (IPs), fabrication of a custom acrylic resin holder with spectrophotometric measurements, and statistical analysis. Selection of chemical disinfectants
This study used six chemical disinfectants widely used in medical practice and a neutral soap (NTS), which is the most commonly used hygienic material in daily life. Tap water was used as the control (CON). Eight experimental groups were created. The control group, chemical disinfectants, and the dilutions used in this study are listed in Table 1. Arranging of acrylic resin denture teeth
The cross-linking agent used in the poly(methyl methacylate) structure of ADT specimens was ethylene glycol dimethacrylate. Dimensions of ADT specimens were as follows: 13.15 mm inciso-gingival lengths, 8.74 mm mesio-distal lengths, and 7.66 mm bucco-palatinal lengths. In total, 120 right first central incisor ADT specimens were randomly assigned to eight experimental groups according to the test liquids used (n = 15). Each ADT was preserved in high-density polyethylene (HDPE) containers labeled with the name of the group and numbered from 1 to 15. The ADTs were kept in the same container throughout the study. 2
IP 1 IP 2 IP 3 IP 4 IP 5 IP 6
Immersion cycle time (minutes)
Number of repeated immersion cycles
Total immersion time
15 15 15 15 15 15
10 30 48 72 144 960
2.5 hour 7.5 hour 12 hour 18 hour 36 hour 10 days
Determination and application of IPs
The ADT specimens were subjected to six IPs according to the number of repeated immersion cycles. The immersion period of each cycle lasted 15 minutes. The number of repeated immersion cycles and total immersion time for each IP are given in Table 2 Before immersion, the HDPE containers of each group were filled with 20 ml of an experimental liquid at room temperature (23 ± 2◦ C), and all the liquids were renewed after each IP. After each IP, the ADTs were kept in distilled water at room temperature (23 ± 2◦ C) for 10 minutes and dried with absorbent paper. Spectrophotometric measurements were then performed. Fabrication of a custom acrylic holder and spectrophototmetric measurements
All of the ADTs were subjected to an initial spectrophotometric analysis before IPs. Spectrophotometric measurements were performed with a ColorFlex EZ spectrophotometer (HunterLab Inc., Reston, VA), and a custom acrylic holder was used during spectrophotometic measurements. Fabrication of a custom acrylic holder
Because the optic detector was located in a deep cavity in the spectrophotometer, preventing the accurate measurement of ADT specimens, the fabrication of a custom-made acrylic holder that would precisely fit into this cavity and would serve to carry the test specimens into the device, was required. The ADT specimens were located in this holder so that their palatinal surfaces were located at the bottom, and the buccal surfaces were positioned at the top. The custom-made acrylic holder also served to prevent movement of the ADT during spectrophotometric measurements and to provide a standard measurement for each ADT. The diameter and height of the cylindrical acrylic holder were designed to fit into the optical cavity of the spectrophotometer. To create the holder, an open-ended polyvinyl cylinder (PVC), with a diameter of 53 mm and height of 14 mm, was positioned on a sheet of modeling wax (Cavex, Haarlem, The Netherlands) so the median third of the labial surface was at the cylinder’s center, allowing for accurate measurement by the spectrophotometer. The lingual and proximal surfaces of the ADT specimen were covered with a thin modeling wax layer to provide isolation, and a vibrator (Degussa R2, Frankfurt, Germany) was used to mix and pour autopolymerizing clear acrylic resin (Meliodent; HeraeusKulzer, Hanau, Germany) into
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 00 (2014) 1–8
Piskin et al
Color Stability of Acrylic Teeth
Table 3 Spectrophotometric measurement steps, labeling of obtained L∗ a∗ b∗ values, measurement steps of E∗ values and labeling of obtained E∗ values Steps of spectrophotometric measurements Initial measurements Measurements after IP1 Measurements after IP2 Measurements after IP3 Measurements after IP4 Measurements after IP5 Measurements after IP6
Steps of E measurements
Labeling of L∗ a∗ b∗ values L∗ 1 a∗ 1 b∗ 1 L∗ 2 a∗ 2 b∗ 2 L∗ 3 a∗ 3 b∗ 3 L∗ 4 a∗ 4 b∗ 4 L∗ 5 a∗ 5 b∗ 5 L∗ 6 a∗ 6 b∗ 6 L∗ 7 a∗ 7 b∗ 7
the PVC ring. After the autopolymerizing clear acrylic resin set, the PVC ring was removed from the cylindrical resin substrate, completing the fabrication of the acrylic holder. This procedure produced a negative copy of ADT specimens’ palatinal surfaces on the acrylic holder. This negative cavity provided the retention of the ADT specimens to the acrylic holder while being transferred into the optical cavity of the spectrophotometer. In this manner, similar and stable positioning of ADT specimens was provided for a standard colorimetric measurement. Spectrophotometric measurements
For spectrophotometric measurements of the ADTs and calculation of color value differences, the CIE L* a* b* color space (in which the brightness is shown with L* , red-green chromacy with a* , and yellow-blue chromacy with b* ) was used. Before spectrophotometric measurements, a pilot study was performed with various color measurement devices. Because the color characteristics of a material are directly related to its entire surface, devices that perform measurements in a limited area or those making point type measurments were not prefered. Thus, in the end of the pilot study, the authors decided to use the ColorFlex EZ spectrophotometer device having the ability to give the mean L* a* b* value of the material by analyzing its color from the entire surface in three consequent measurements in one trial. The optic detector located in an isolated cavity, preventing external light penetration by use of a “sample cup opaque cover,” was an additional advantage of the device. Because the optic detector had a wider surface area than those of ADT specimens, the cavity floor of the device was covered with a grayscale sheet (400 Series Gray Scale Pads; Strathmore, Appleton, WI) having at the center an opened area equal to the buccal surface boundaries of ADT specimens. ADT specimens fixed on the acrylic holder from their palatinal surfaces were precisely seated on the opened area formed on the grayscale sheet. This process was followed by the calibration of the spectrophotometer according to the instructions of the manufacturer using calibration tiles. Each ADT specimen was dried with absorbant paper before each measurement. Spectrophotometric measurements were repeated after each IP, and L* a* b* values were also measured. The spectrophotometer was set to give mean L* a* b* values after three consecutive readings. A total of seven L* a* b* values were obtained for each ADT specimen (the initial L* a* b* values and the L* a* b* val-
L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1 L∗ 1 a∗ 1 b∗ 1
and L∗ 2 a∗ 2 b∗ 2 and L∗ 3 a∗ 3 b∗ 3 and L∗ 4 a∗ 4 b∗ 4 and L∗ 5 a∗ 5 b∗ 5 and L∗ 6 a∗ 6 b∗ 6 and L∗ 7 a∗ 7 b∗ 7
Labeling of obtained E values E1 E2 E3 E4 E5 E6
ues obtained after six IPs). The differences between the initial L* a* b* values and those obtained after IPs were calculated with the formula: E = [(L ∗2 − L∗1 )2 + (a2∗ − a∗1 )2 + (b2∗ − b∗1 )2 ]1/2 A total of six E values for each ADT specimen were obtained after measurements. Table 3 shows the spectrophotometric measurement steps for the eight experimental groups, the labeling of the obtained L* a* b* values, and the measurement steps and labeling of the E values. The obtained E* values have been quantified by National Bureau of Standards (NBS) units to match the color differences for the clinical conditions (NBS units-clinically acceptable level
