Two years survivability of VITA 3D master shade matching guides after disinfection with isopropyl alcohol: An in vitro study.

BACKGROUND: Dental shade guides are used before restorative and prosthodontic procedures for the evaluation of tooth color. The spectral coverage of the specific shaded guide and a clinician's experience in shade matching are the two most important factors for a clinically viable shade match of the restoration to the given tooth. Repeated disinfection of the shade guide with disinfectant lead to a clinically significant difference of the shade to be matched, finally resulting in a clinically unacceptable prosthesis. The purpose of this study is to evaluate the effects of disinfection on various shade tabs of VITA 3D Master Shade guide after being subjected to 2 years of simulated disinfection with 70% isopropyl alcohol.
METHODOLOGY: Two sets of VITA 3-D Master Shade Guides were used. One set of each shade guide was assessed after simulated use and surface disinfection with 70% isopropyl alcohol (test group), while the other full set was subjected to cleansing with distilled water (control group). Spectrophotometer was used to measure each of the shade tabs. Readings were recorded at regular intervals of 120, 240, 360, 480, 600, 720, 840, and 960 disinfection cycles. The ΔE values obtained were used to examine the color difference.
RESULTS: There was a significant difference in terms of ΔE between the shade tabs of control and test groups of VITA 3D Master shade guides after 960 cycles of disinfection. The change in mean ΔE was more in the test specimens in the shade tabs of VITA 3D Master Shade Guide tabs than the control specimens. These results are of statistical significance, but they might not be of any clinical significance.
CONCLUSION: There was a statistically significant but clinically nonsignificant color change in the shade tabs of VITA 3D Master shade guides after 2 years of simulated use and disinfection with 70% isopropyl alcohol.

INTRODUCTION

A viewer, a light source, and an object are the trio of essential components whose interaction characterizes the visual observation method. The interpretation of color by the brain follows a sequence in which the light after being emitted from a source gets transmitted or reflected by an object toward the observer's eye which converts it into nerve impulses for the interpretation as color. The requisite of visualization and interpretation by the brain, conversely, gives this technique of color perception a multifaceted and subjective character, even with standardization of the light source and the object.[1]

The reflectance from the dentin altered by the absorption, scattering, and thickness of the enamel result for the actual color of natural teeth.[2] Hence, recognition of the optical properties of teeth is imperative for precise and harmonious color reproduction. Esthetics of dental restoration is shaped by color and its elements, such as hue, value, and chroma; translucency and opacity; light transmission and scattering; and metamerism and fluorescence.[3]

Color measurement has been categorized and quantified in numerous ways. The Munsell System and the International Commission on Illumination (CIE) color/order system are two of the most extensively used systems for depicting color.[4]

Appraisal of tooth color is classically accomplished using dental shade guides preceding to restorative and prosthodontic procedures. Successful achievement of the clinically acceptable color match is closely related to the spectral coverage of the shade guide, clinician experience, and the viewing. Nevertheless, shade guides themselves have demonstrated inconsistent color and do not satisfactorily denote the color of natural teeth, which escalates the challenge of color matching.[5]

Of late, the VITA classic and VITA 3D-Master shade guides were described as being among the most commonly used. Although they have the same manufacturer, they present some variances, mostly due to the appearance of the samples, which are organized in groups rendering to the hue in VITA classic and according to value in VITA 3D-Master. A number of studies have shown that the dependability of the VITA 3D-Master shade guide to be superior to that of VITA classic among general dentists, even though the two systems displayed one and the same consistency amid prosthodontists.[6]

Being categorized as noncritical instruments since they should only come into contact with intact skin and hence, their risk category may be presumed to be low. Conferring to the Occupational Safety and Health Administration (OSHA) recommendations, it should be cleaned or if contaminated, cleaned and then disinfected with a hospital-grade tuberculocidal intermediate-level disinfectant.[7] Contamination with saliva must be expected while using shade guides. Disinfection of shade guides is usually carried out with solutions that are considered to be the most convenient, frequently without the following manufacturer's guidelines. In the manufacturer's specifications, disinfectants comprising phenol, methyl ethyl ketone, or iodine are detrimental to the shade guide.[8]

Earlier studies have presented that the color change of shade tabs was noteworthy both after disinfection by a chemical solution and by sterilization through autoclaving (140°C or 284°F).[9] It is not clear whether disinfection of shade guides result in a substantial alteration in the shade selection practice leading to pointless miscommunication and misunderstanding between the clinicians and dental laboratories resulting in the sub-standard finished prosthesis.[10]

The significance of such effects should not be disregarded and at the same time, it is sensible that disinfection is carried out properly without having to compromise the color or surface stability of the shade guide.

The purpose of this study is to evaluate the effects of disinfection on various shade tabs. Changes in color of the shade tabs will be studied after being subjected to 2 years of simulated disinfection.

METHODOLOGY

An ethical consent was obtained from the educational institution before collection of data and nature of the investigation was fully informed.

The materials that were used in the analysis were prepared and handled in harmony with the manufacturer's guidelines.

One set of VITA 3-D Master Shade guides [Figure 1a] was used as control, whereas the other set of VITA 3D-Master Shade guides was used as test sample. They were stored at room temperature.

Figure 1

(a) VITA 3D-Master shade guide. (b) Fabrication of acrylic jig. (c) Disinfection of shade guides with isopropyl alcohol

Fabrication of acrylic jig

The central 1/3 area of each shade tab was measured as it best signifies the color of the tooth material. With the intention of ensuring constancy of the areas to measure, an acrylic jig was fabricated to firmly mount each shade tab. The base and the cover of the jig were made from clear acrylic and die pins [Figure 1b]. This allowed readings to be taken from the same central 1/3 area on all the shade tabs. The acrylic jig allowed only the central third of the shade tab to be visible.

Disinfection of shade guides

One full brand new set of VITA 3D-Master shade guides was treated with distilled water (control group), while the other brand new set was treated with 70% isopropyl alcohol [Figure 1c] which was used as test sample. All possible shade tabs of vita 3d master shade guides (0M1, 0M2, 0M3, 1M1, 1M2, 2 L1.5, 2 L2.5, 3 L1.5.3 L2.5, 4 L1.5, and 4 L2.5 - 2M1, 2M2, 3M1, 3M2, 4M1 and 4M3 - 2R1.5, 2R2.5, 3R1.5, 3R2.5, 4R1.5, and 4R2.5) were included. Shade Tabs were sprayed until wet. Roughly six sprays were used each time, which is corresponding to 6 mL of solution. After 3 min, shade tabs were then wiped until visibly dry with 3 × 3 gauzes. To ensure consistency between testing cycles and to reproduce clinical conditions, single operator did all of the testings using gauze of the similar roughness and manufacturer.

The testing process was repeated for 960 cycles to simulate 2-year usage. Dental shade guides may be used twice a day, five times a week, and 48 weeks per year. Shade tabs were measured every 120 cycles, corresponding to 3 month's usage.

Shade measurement with spectrophotometer

Each shade tabs was secured in place in the acrylic jig, spectrophotometer was used to measure and the L*a*b values were recorded from the computer screen. One initial recording of each shade tab of brand new shade guide was taken. Records were taken for each shade tab after every 120 cycles the jig was used for every measurement to ensure constancy and to eliminate the jig as a potential confounding factor.

Data analysis

The CIE system is the international standard for color measurements. To calculate the change in color (Δe), the following formula set by the CIE was used:

Δe = √([L*2 − L*1]2 + [a*2 − a*1]2 + [b*2 − b*1]2)

L* 2, a*2, and b*2 were the recordings after 2 years of simulated usage.

L*1, a*1, and b*1 were the initial recordings.

Statistical analysis of data

Paired t-test was employed in statistical analysis.

RESULTS

There was noteworthy alteration in terms of ΔE amid the shade tabs of control and test groups of VITA 3D-Master shade guides after 960 cycles of disinfection [Graph 1].

Graph 1

ΔE difference between control and test tabs of VITA 3D Master shade guide

There was noteworthy difference in terms of ΔE amid the shade tabs of the control group. Maximal variation was seen in the 2M2 shade tab. Minimal ΔE variations were seen in 3M2 shade tab [Graph 2].

Graph 2

ΔE changes in the shade tabs of VITA 3D-Master control group

There was significant difference in terms of ΔE between the shade tabs of the test group. Maximal variation was seen in the 2L 2.5 shade tab. Minimal ΔE alterations were seen in 3M2 shade tab [Graph 3]. The mean ΔE for the control group is 0.98 and for the test group, it is 1.79.

Graph 3

ΔE changes in the shade tabs of VITA 3D-Master test group

There was a 0.965% increase in the mean ΔE between the test group after simulated use and disinfection after 1 year and 2 years usage, respectively.

There was 2.2% decrease in the mean ΔE between the control group after 1 year and 2 years usage, respectively.

As the value of P < 0.05 (i.e., P < 0.05), it can be concluded that there is a statistically significant difference between the control and test group.

DISCUSSION

To attain esthetics, four basic elements are required in sequence, namely position, contour, texture, and color.[1] For this reason that esthetic dentistry levies several demands on the artistic skills of the dentist and the technician, knowledge of the fundamental scientific principles of color are vital. Precise shade matching not only improves esthetics but also makes the restoration look natural and attractive.[11]

Individuals show discrepancy in their skill to select color matches. Culpepper found disparities amid dentists in the shade matching the same tooth, and he demonstrated the lack of ability of individuals to replicate their shade selection on different days. Moreover, changes in the lighting conditions can cause variations in the perceived color.[12]

One of the variables to be considered for the choice of color is the light source used. The best light source is natural light occurring between mid-day and 3 PM for precise color judgment. This can be referred to as standard daylight, which occurs at about 5500 K. The time of day, time of year, and weather conditions affect the color of sunlight; consequently, standard daylight is rarely available. Early morning and evening light is more reddish compared with daytime. If the light source changes, then the light reflected from an object changes too, in which case a dissimilar color is perceived. The lack of ideal conditions has led to the use of artificial lighting for color matching. The light source is selected mainly for its ability to approximate standard daylight.[1314]

Finally, the range of shades available do not cover the widespread color space of natural teeth, the shade guide tabs are not methodically distributed in their color space, and any change in lighting conditions can cause disparities in perceived color.[11]

In the shade matching process, the shade tabs are positioned underneath the lip straight next to the tooth being matched. First, the shade is matched with the patient smiling habitually and only the incisal third is noticeable and the shade tab is placed next to it. Second, the patient is asked to present an exaggerated smile with the central third, and cervical third of the tooth observable and the shade guide placed next to it. Thus, contamination with saliva must be expected throughout this process and disinfection of the shade guides becomes unavoidable. Most dental offices use various shade guides at best twice a day, 5 days a week, and 48 weeks a year.[15]

As shade guides are categorized noncritical instruments by the 2005 OSHA Guidelines, it is obligatory to disinfect the shade guides with a hospital grade intermediate level tuberculocidal disinfectant on a regular basis.[7] The use of chemical solutions and autoclave for shade guide disinfection and sterilization have been used formerly due to their efficacy in reducing microorganisms. As per the manufacturer's recommendations plastic parts of shade guides comprise of a high-quality, temperature resilient and easy care material making it possible to sterilize the entire tooth guide in the autoclave at a maximum temperature of 140°C or 284°F. Nonetheless, sterilization with autoclaves have shown harmful and long-lasting color changes in shade guide tabs.[16] The manufacturer also mentions that shade guides can be disinfected by the surface disinfectants, but disinfectants comprising phenol or compounds with phenol groups, and methyl ethyl ketone, are detrimental to the shade guide. More aggressive approaches of disinfection have been seen to harm portions of shade guides. Hence, surface disinfection is generally preferred to clean and disinfect shade guides.[8]

When sprayed, solutions can interfere with the optical and mechanical properties of the shade guide materials. Therefore, the color stability of shade guides should be checked on a regular basis.[14] There are inadequate long-term studies available about the effect of chemical disinfection on the color stability of shade guides, and this effect is vital for the aesthetic result of the final prosthesis.[17]

This study was conducted to study the effect of disinfection using 70% iso-propyl alcohol on the color stability of shade guides. An average shade guide will go through 960 disinfection cycles in 2 years.[18]

Color changes in shade guides were best measured by spectrophotometer.[19] This removed the subjective interpretation of visual color alteration as it has been seen to be undependable and erratic.[1219] The CIE L*a*b* system for measuring chromaticity was chosen to record color changes, as it is well suited for determining small color variances. The ΔE values obtained was used to examine the color difference.[20]

There was noteworthy variance in terms of ΔE between the shade tabs of control and test groups of VITA 3D-Master shade guides after 960 cycles of disinfection. The change in mean ΔE was more in the test specimens in the shade tabs of VITA 3D-Master Shade Guide Tabs than the control specimens.

Maximal ΔE variations were seen in the VITA 3D Master it was seen in the 2M2 shade tab for control specimen and for test specimen in 2L 2.5 shade tab. Minimal ΔE variations were seen in 3M2 shade tabs of both control and test specimens of VITA 3D Master [Tables 1 and 2].

Table 1

ΔE values of shade tabs of VITA 3D Master Shade Guide (control) after 960 cycles

V3DC	L2	L1	a2	a1	b2	b1	ΔE
0M1	17.65	17.34	0.12	0.22	1.46	1.14	0.46
0M2	17.71	17.83	0.23	0.21	1.12	0.82	0.32
0M3	17.13	17.64	0.30	0.07	1.30	1.48	0.57
1M1	16.42	16.93	0.26	0.07	1.60	1.67	0.53
1M2	16.44	17.14	0.13	-0.04	2.26	2.32	0.67
2L1.5	17.10	15.89	0.05	0.19	2.79	1.45	1.47
2L2.5	15.94	16.69	0.26	0.13	2.77	3.56	1.01
2M1	16.44	16.51	0.36	0.17	2.04	1.77	0.51
2M2	18.59	16.27	0.02	0.19	1.86	2.25	2.38
2M3	17.64	17.23	0.13	0.20	2.93	2.53	0.55
2R1.5	16.38	17.59	0.33	0.00	2.14	1.81	1.33
2R2.5	16.56	16.57	0.24	0.24	2.23	3.72	1.44
3L1.5	16.98	16.36	0.18	0.24	1.89	2.06	0.66
3L2.5	16.91	16.23	0.28	0.23	2.16	2.93	1.01
3M1	16.21	13.85	0.27	0.028	1.81	2.17	0.51
3M2	15.90	16.08	0.44	0.40	2.57	2.63	0.18
3M3	15.63	16.48	0.49	0.38	2.73	2.72	0.87
3R1.5	15.85	16.37	0.51	0.39	1.45	2.29	0.62
3R2.5	16.26	16.18	0.66	0.48	2.96	4.09	1.61
4L1.5	17.20	15.40	0.27	0.40	2.11	2.72	1.92
4L2.5	15.88	15.73	0.42	0.50	2.81	2.86	0.20
4M1	14.91	15.80	0.61	0.30	1.90	1.73	0.96
4M2	14.64	15.30	0.81	0.63	2.82	2.21	0.92
4M3	16.45	15.58	0.49	0.75	2.48	2.96	1.06
4R1.5	17.11	15.04	0.36	0.67	1.60	2.23	2.21
4R2.5	16.25	15.29	0.44	0.89	2.43	3.04	1.27
5M1	14.98	14.34	0.61	0.67	1.78	1.89	0.67
5M2	14.65	15.38	0.80	0.56	2.54	2.42	0.77
5M3	16.05	14.68	0.74	1.10	2.66	3.94	1.94

Table 2

ΔE values of shade tabs of VITA 3D Master Shade Guide (test) after 960 cycles

V3DT	L2	L1	a2	a1	b2	b1	ΔE
0M1	17.93	17.33	−0.21	0.25	1.85	1.14	0.94
0M2	20.09	17.81	0.01	0.21	1.15	0.81	2.32
0M3	17.23	17.64	−0.07	0.07	2.22	1.48	0.85
1M1	18.98	16.93	−0.35	0.07	2.08	1.47	2.13
1M2	17.09	17.14	−0.16	-0.06	3.13	2.33	0.77
2L1.5	17.63	15.89	−0.29	0.19	3.37	1.96	2.24
2L2.5	18.97	16.69	−0.16	0.13	1.94	3.56	2.84
2M1	19.31	16.52	−0.13	0.15	1.56	1.79	2.83
2M2	17.97	16.27	−0.11	0.20	3.75	2.51	2.23
2M3	16.31	17.21	−0.04	0.23	3.88	2.51	1.60
2R1.5	18.67	17.60	−0.24	0.01	2.27	1.79	1.44
2R2.5	19.21	16.57	−0.41	0.24	3.16	3.71	2.78
3L1.5	18.84	16.36	−0.20	0.24	2.95	2.04	1.04
3L2.5	15.80	16.28	−0.01	0.18	3.73	2.91	0.90
3M1	21.90	15.85	−0.53	0.29	1.35	2.13	1.21
3M2	15.96	16.06	0.24	0.42	3.29	2.62	0.18
3M3	16.63	16.48	0.67	0.38	4.33	2.71	1.62
3R1.5	17.73	16.36	0.01	0.42	2.43	2.23	1.44
3R2.5	16.20	16.19	0.12	0.46	3.16	4.07	1.00
4L1.5	16.20	15.39	0.11	0.41	2.74	2.71	0.86
4L2.5	16.61	15.72	−0.14	0.51	5.13	2.87	2.42
4M1	19.03	15.81	−0.11	0.29	1.58	1.69	2.27
4M2	16.52	15.33	0.07	0.63	2.96	2.18	1.49
4M3	17.57	15.60	−0.01	0.77	3.27	2.92	2.13
4R1.5	16.55	15.04	0.16	0.67	4.32	2.22	2.53
4R2.5	19.10	15.30	0.04	0.91	1.94	2.99	2.11
5M1	16.88	14.34	0.11	0.69	2.36	1.86	2.63
5M2	17.26	15.38	0.04	0.57	2.56	2.41	1.94
5M3	17.89	14.68	0.11	1.11	2.27	3.95	2.81

The humanoid perceptibility of color change under standardized lab conditions is 1 ΔE unit.[21] In the oral cavity, conversely, an average change of 3.7 ΔE units could still allow teeth to be perceived as having the equivalent color.[22] As ΔE changes in each of the shade tabs of both test and control specimens of both shade guides were under 3.7 after simulated usage of 2 years or 960 cycles, the variance is clinically acceptable. Hence, the results are of statistical importance, but they might not be of any clinical importance.[17]

For determining the significance of the color change in the shade tabs of test and control specimens of VITA 3D-Master after 960 cycles, a paired t-test was performed using the ΔE values. In VITA 3D-Master Shade guide P = 0.00 was obtained which is extremely significant. Hence, there is an out-and-out change in color of the shade tabs of VITA 3D Master shade tabs both with distilled water as control and 70% isopropyl alcohol as test specimens. These numbers reject the null hypothesis that no substantial alteration would be found after repetitive disinfection with 70% isopropyl alcohol.

ArRejaie studied the effect of disinfection on shade tabs for a simulated three year period and presented no major change amid the studied samples in relation to time. These findings were constant with the results of the current study in the disinfectant group.[23] The amount of ΔE was under the perceptible level (ΔE = 1) and the clinically acceptable level (ΔE = 3.7).[23] In the current study, the variation was greater than the perceptible level and lower than the clinically acceptable level in the test specimens, while it was lower than perceptible level as well as the clinically acceptable level in the control specimens.

Rendering Pohjola's study, two aspects might have affected the color of shade tabs after repetitive disinfection: abrasion of surface characterization by wiping with gauze and surface disinfectant could have left the surface residue on the shade tabs after several disinfection cycles. Hence, these two aspects might have played a part owing to which there is noteworthy color difference. Nonetheless even the control group of shade tabs have shown color variation which might be attributed to abrasion of surface characterization by wiping with gauze.[15]

After 2 years of usage, mean ΔE for the 70% iso-propyl disinfected shade tabs was 1.79 for VITA 3D-Master [Table 3]. Even though this is statistically important but as it is below 3.7, it is clinically acceptable. Hence as the color perception is of subjective value and differs from person to person, sustained usage of shade guides for >2 years and disinfection with 70% iso-propyl alcohol may lead to imprecise shade matching. The numbers of this study shows that 70% isopropyl alcohol causes damage to the shade tabs of the shade guide. Even with ⊗E values obtained suggesting color change in the shade tabs caused by 70% isopropyl alcohol, shade guides may carry on to be clinically acceptable even after 2 years. However, it appears fairly practical that the shade tabs have proven their durability and are due for replacement. Instead to prevent the abrasion of surface characterization through gauze and prolong the longevity of shade tabs air drying can be preferred instead wiping.

Table 3

Paired t-test to determine significance of color change in VITA 3D Master Shade Guide after 960 cycles

Vita 3D Master	n	Mean	SD	t	P	Comments
V3DC	29	0.98	0.59	−5.31	0.000	Highly significant
V3DT	29	1.79	0.72

SD: Standard deviation

Few limitations exist within this study. First, the shade tabs are not made out of porcelain, but rather layered acrylic has been used intending to denote the available dental porcelain shades. This causes complications such as imprecise shade match and the possibility of metamerism display. Furthermore, these shade tabs may not present a constant change in ΔE values as they have also been seen not to be substitutable between similar types of shade guides.

Similarly, it has been seen that the ΔE does not show the direction of the change in the color space specifying whether the shade tabs gets darker or lighter. Hence, additional evaluation into the L*a*b* is necessary. Finally, the storage of shade guides under natural light augmented the chromaticity of the shade tabs.[14]

Supplementary studies are vital for a better understanding of the process of color change in shade guides. As well evaluation of the effect of other disinfection solutions has to be investigated. Alternate methods of sterilization like gas sterilization can be tried to overcome the result of autoclave and disinfection solutions on shade guides.[15] Furthermore, one shade guide should be retained as control and periodically compared with the shade guide in use to determine when the shade tabs in use should be replaced or discarded.[24] Even other shade guides available in the market like VITA linear guide shade guide, the VITA bleached guide shade guide, Chromascope Shade Guide, etc., should be tried out for their color stability in the long run.[17]

CONCLUSION

It was evaluated that after surface disinfection with 70% isopropyl alcohol for a simulated 2 years usage, there was a statistically noteworthy but clinically nonsignificant color change in the shade tabs of VITA 3D-Master shade guides.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.