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Effect of time on tooth dehydration and rehydration
Article in Journal of Esthetic and Restorative Dentistry · February 2019
DOI: 10.1111/jerd.12461
6 authors, including:
Taiseer A. Sulaiman
Vilhelm G Olafsson
University of North Carolina at Chapel Hill
University of Iceland
Alex J. Delgado
University of Florida
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Received: 3 February 2019
Revised: 7 February 2019
Accepted: 10 February 2019
DOI: 10.1111/jerd.12461
Effect of time on tooth dehydration and rehydration
Sama Suliman DDS1 | Taiseer A. Sulaiman BDS, PhD1
| Vilhelm G. Olafsson DDS, MS2
Alex J. Delgado DDS MS3 | Terence E. Donovan DDS1 | Harald O. Heymann DDS1
Division of Operative Dentistry and
Biomaterials, Department of Restorative
Sciences, University of North Carolina School
of Dentistry, Chapel Hill, North Carolina
Objective: To estimate the time required for teeth to dehydrate and rehydrate and its relation
to the accuracy of tooth shade selection.
Operative Dentistry and Cariology, Faculty of
Odontology, Division of Health Sciences,
University of Iceland, Reykjavic, Iceland
Division of Operative Dentistry, Department
of Restorative Dentistry, University of Florida
School of Dentistry, Gainesville, Florida
Taiseer A. Sulaiman, Division of Operative
Dentistry and Biomaterials, Department of
Restorative Sciences, UNC School of
Dentistry, 440 Brauer Hall, CB 7450, Chapel
Hill, NC 27599.
Email: [email protected]
Materials and Methods: Thirty-two participants were recruited, and color measurements were
conducted using a spectrophotometer placed with a custom jig. After isolation, baseline measurements were made at 1, 2, 3, 5, 7, 10, and 15 min intervals to determine dehydration time.
After mouth rinsing, measurements were made to determine rehydration time. CIEDE2000
values were obtained for color change between the baseline recordings and all intervals and
compared to the 50:50% perceptibility and acceptability thresholds. Analysis of variance (ANOVA)
and Tukey test was used for multiple comparisons.
Result: The tooth color changes were beyond the ΔE00 perceptibility threshold (0.8) within the
first minute of dehydration (P > 0.0001). After the first minute, 87% of the teeth were beyond
the ΔE00 perceptibility threshold (0.8), and 72% of the teeth were beyond the ΔE00 acceptability
threshold (1.8). After 15 min of rehydration, 90% of the teeth were beyond the perceptibility
Funding information
University of North Carolina at Chapel Hill.
threshold, and 65% were beyond the acceptability threshold.
Conclusions: Shade selection procedures should be carried out within the first minute and before
teeth dehydrate by means of isolation. Teeth do not rehydrate within 15 min after rehydration.
Clinical Significance: Teeth dehydration has a negative impact on shade selection, which can
affect the final esthetic outcome. Shade selection should be performed at the beginning of any
restorative procedure.
operative dentistry, prosthodontics, shade selection, teeth dehydration, teeth rehydration
1 | I N T RO D UC T I O N
Eclairage (CIE) L*a*b* color space. The three coordinates that determine color are L* coordinate represents lightness, while a* represents
Shade selection for direct and indirect restorations is one of the most
green-red, and b* represents blue-yellow coordinate. This system is the
challenging components of esthetic dentistry.1 Clark in 1931, the first
basis for transforming spectral energy data into meaningful color data.6,7
to address the problem of color in dentistry, stated that “we as den-
Recently, the CIE published a new CIEDE2000 formula model which is
extended to the CIE 1976 (L*a*b*) color-difference model with correc-
This statement applies to this day despite numerous advances in
tions for variation in color-difference perception dependent on Light-
shade matching techniques in recent decades. Based on current pro-
ness, Chroma, Hue and Chroma-Hue interaction. Additionally, the CIE
spective and retrospective clinical studies, 50% of cemented ceramic
investigated the nonuniformity of the CIELAB space and developed this
tists are not educationally equipped to approach a color problem”.
empirical correction to improve agreement between perceived visual
crowns exhibit incorrect color matches.
The CIELAB system is frequently used to measure color and color
differences, which is based on the 1976 Commision Internationale de l´
color difference and numerical color difference.8
In the CIELAB system, Delta E (ΔEab) is the color difference, or
the distance separating two points of color. It is defined by the follow-
Abstract presented at the 96th General Session of the IADR, London, July,
J Esthet Restor Dent. 2019;1–6.
ing equation: ΔE = √(L1-L2)2 + (a1-a2)2 + (b1-b2)2.9 In the CIEDE2000
system, Delta E (ΔE00) is the total color-difference between two color
© 2019 Wiley Periodicals, Inc.
samples with Lightness (L), Chroma (C), and Hue (H) differences. It is
determined by the following equation:
0 2 0 2 2
+ RT
k c Sc
k H SH
before, and 10, 20, and 30 min after application. The levels of ΔE
obtained after relatively short intervals of rubber dam isolation
are well above the acceptability thresholds for incorrect shade match
(ΔE = 2.7)10. Further studies are warranted to examine how fast perceptibility and acceptability thresholds of shade mismatch are reached.
Where ΔL’, ΔC’, and ΔH’ are the differences in Lightness,
In a typical clinical scenario, shade determination for direct and
Chroma, and Hue for a pair of specimens, and RT is a function that
indirect restorative work is usually not performed with a rubber dam
accounts for the interaction between Chroma and Hue differences in
in place. Retraction methods are commonly used which provide rela-
the blue region. Weighting functions SL, SC, and SH adjust the total
tive levels of isolation by relieving the tooth of contact with wet soft
color difference for variation in the location of the color difference
tissues, while keeping the tooth within the confines of the oral cavity,
pair and KL, KC, KH are empirical terms used for correcting (weight-
which facilitate placement of shade guides or shade determination
ing) the metric differences to the CIEDE2000 differences for each
devices. Regardless of the means of isolation, the degree of dehydra-
coordinate. When the color difference between two compared objects
tion that occurs and how rapidly it manifests is of great importance
can be seen by 50% of the observers, it is a 50:50% perceptibility
with regard to the timing and length of the shade selection procedure.
threshold. Similarly, a 50:50% acceptability threshold has been defined
An accurate color match of the final restoration can only be expected
when a color difference is considered acceptable by 50% of the
if the shade was registered with the tooth in a hydrated state.
observers. A prospective multicenter study10 concluded that the
The purpose of the present study was to estimate the time
CIELAB 50:50% perceptibility threshold was ΔEab = 1.2, whereas the
required for teeth to dehydrate to perceivable and acceptable thresh-
50:50% acceptability threshold was ΔEab = 2.7. The corresponding
olds of color change using methods of relative isolation, and to deter-
CIEDE2000 (ΔE00) values were 0.8 and 1.8, respectively, for under
mine the time required for the color change to return to a normal
simulated clinical settings.
level after isolation removal. The null hypothesis is that there is no
Color determination is an interplay where color perception and
matching abilities need to meet in the best of conditions. Color
perception occurs when light from a particular source is reflected by
perceivable difference between tooth shade before and after dehydration, and the time required to rehydrate the tooth is not proportional to the tooth's original shade.
the object and observed by the viewer. Hence, color perception is
influenced by a triad of events: the light source, the optical properties
of the object observed and the color interpretation ability of the
observer himself.1 The light source should be spectrally balanced in
2 | M A T E R I A L S A N D M ET H O D S
the visible range (370-780 nm), have a color temperature of approximately 5500 K and a color rendering index of >90, so that the light
source itself does not become a limiting factor.11 Among optical properties of the object itself, translucency and light scattering impact
color perception. Translucency is the amount of incident light transmitted and scattered. Scattering makes the object opaque and is
dependent on the size, shape, number of the scattering centers and
refractive index.11 The color matching ability of the operator is influ-
2.1 | Participant selection
Thirty-two participants were recruited for this clinical study that was conducted after approval of the institutional review board (IRB) (XX-XXXX).
These participants were selected among students and staff members at
the School of Dentistry at University of XXXX based on the following
Inclusion criteria:
enced by viewing conditions, color fatigue of the eye, age, experience,
and presence or absence of color blindness.7
Tooth dehydration makes teeth appear whiter due to increasing
enamel opacity. The inter-prism spaces become filled with air instead of
water so light can no longer scatter from crystal to crystal. Loss of translucency due to dehydration therefore causes more reflection, which
masks the underlying color of dentin, making the tooth appear lighter.6,11
Color determination therefore must be carried out in controlled
circumstances before the tooth dehydrates, if a successful match is to
• Adult participants, 18-45 years of age.
• Participants have no adverse medical condition and are not on any
medication. Unstimulated salivary flow was measured volumetrically to ensure that it is within normal limits (0.3-0.4 mL/min).
• The tooth to be observed (central incisor) should be a sound natural tooth with no restorations, wear, recent bleaching or severe
discolorations, with a healthy periodontal condition.
be obtained. Few clinical studies have examined how rapidly teeth
dehydrate to a perceivable color difference. One study made measure-
Exclusion criteria:
ments with a reflectance spectrophotometer on a single central incisor
before and after 15 min of rubber dam isolation.12 The purpose of their
• Participants have adverse medical condition and are on medication.
study was to determine the changes in the ΔE after 15 min of rubber
• Presence of a restoration.
dam application and the time for tooth color to return to original values.
• Presence of an orthodontic fixed appliance including the central
Another study conducted an in vivo study to assess the effects of
dehydration on tooth color.
They isolated a central incisor with a
rubber dam. They made measurements with a spectrophotometer
• Recent bleaching.
• Dry mouth, or low unstimulated salivary flow levels.
patient to close and waiting a few minutes, to ensure no pretesting
dehydration. The custom-made jig was seated in place, and three measurements per time interval were made using the calibrated VITA
Easyshade spectrophotometer determining mean L, C, H values in
accordance with the Commission Internationale de l'eclairage
(CIEDE2000) system (Figure 2C). Time intervals were: 0 (baseline),
2, 3, 5, 7, 10, and 15 min.
All participants wore a nose clip during measurements to ensure
that the same mode of breathing was used (mouth vs nose breathing),
ensuring similar air flow in all study subjects.
For rehydration time determination, the Optragate isolation device
was removed from the mouth, and a full-mouth rinse for 30 s with
water was done. Then participants were asked to close their mouth for
5 min. Color measurements to determine the extent of tooth rehydration were performed according to the same intervals as in the dehydration phase of the study.
The L, C, and H values obtained were used to calculate CIEDE2000
color differences (ΔE00) between baseline and other intervals for dehydration and rehydration. These values were compared to the perceptiFIGURE 1
The VITA Easyshade spectrophotometer
bility and acceptability thresholds as determined by Paravina et al.10 to
evaluate the time clinicians have to determine a shade under relative
2.2 | Instruments used
The VITA Easyshade spectrophotometer (VITA Zahnfabrik, Bad
levels of isolation before dehydration causes perceptible levels of color
Säckingen, Germany) was used in this clinical study for color measurements (Figure 1). A custom-made jig was made for the central incisor
2.4 | Data management and statistical analysis
of each participant from a clear silicone impression material (Affinity
The data were analyzed for color differences (ΔE00) over time using
Crystal Clear, Clinician's Choice New Milford, CT) to ensure consistency
an analysis of variance (ANOVA). Post-ANOVA contrasts were made
in the positioning of the Easyshade tip. The clear jig allowed visualiza-
between baseline and each time interval (baseline and, 1, 2, 3, 5, 7, 10,
tion of the entire facial surface, where an access opening of 6 mm
15 min) by using Tukey test with P-values adjusted for multiple com-
diameter was made in the middle third using a disposable tissue punch,
parisons (P < 0.0001). Percentage changes between baseline and each
to accommodate the Easyshade tip (Figure 2AB).
time interval were assessed for color differences by using ClopperPearson (Exact) test with a 95% confidence level. Additionally, this
2.3 | Color measurements
All participants were seated and reclined to a 45 position relative to
test was used to assess the proportion of the population that
exceeded the ΔE00 perceptibility threshold of 0.8 or acceptability
threshold of 1.8 at each time interval of dehydration and rehydration.
the floor, to eliminate any shadowing effects from the nose or lips.
Color measurements were conducted under controlled light settings
(color temperature 5500 K and a Color Rendering Index [CRI] of 95)
3 | RE SU LT S
with neutral color surroundings. Lips were retracted by using an
Optragate (Ivoclar Vivadent, Amherst, NY). Optragate placement was
The values for the mean, SD, and 95% confidence interval of the color
accomplished within 15 s, otherwise it was repeated allowing the
differences, expressed by ΔE00 at baseline, 1, 2, 3, 5, 7, 10, and
Jig fabrication: A, Disposable tissue punches used to make a 6 mm hole through the clear polyvinyl siloxane impression
material. B, Easyshade tip fitting through the 6 mm hole. C, Positioning of the Easyshade through the custom-made jig in the middle third of
the central incisor
Mean and SD of change in color (ΔE00) of dehydration with
95% confidence level
Lower 95%
CL for Mean
Upper 95%
CL for Mean
15 min time intervals of dehydration and rehydration can be seen in
Tables 1–2 and Figure 3.
Analysis of variance (ANOVA) indicated that there was statistically
significant change in color over time in the mean ΔE00 for both dehy-
Color change (ΔE00) after tooth dehydration and
rehydration with different time intervals
dration and rehydration procedure (P < 0.0001). As time increases, the
mean ΔE00 increases as well within the dehydration procedure. The
While 65% of the participants were beyond the ΔE00 acceptability
values were compared to the 50:50% perceptibility and acceptability
threshold after 15 min of rehydration (Figure 6).
thresholds at ΔE00 of 0.8 and 1.8 respectively.
Within the first
minute there was a statistically significant change in ΔE00, already
beyond the acceptability threshold.
Average change in L, C, and H values are displayed in Figure 4
(A-C). Mean L value showed a significant spike within the first minute
of dehydration, while it returned to its original value after 15 min of
rehydration. Mean C value remained increasing until 15 min of
dehydration and did not return to its original value after 15 min
rehydration. The mean H value continued decreasing until 15 min of
dehydration and did not return to its original value after 15 min of
rehydration. Therefore, continued increase in ΔE to 15 min is not only
attributed to the change in L values, but also due to the changes in C
and H values.
Clopper-Pearson (Exact) test with 95% confidence interval was
used to assess the proportion of the population that exceeded the
ΔE00 perceptibility threshold of 0.8 or the ΔE00 acceptability threshold of 1.8 at each time interval of dehydration and rehydration. 87%
of teeth were beyond the ΔE00 perceptibility threshold (0.8) within
The present study revealed statistically significant and visually perceptible differences in tooth color measurements after dehydration
and rehydration within the defined time intervals, rejecting the null
ΔE00 values were calculated to assess the changes in tooth color
by using a hand-held spectrophotometer (VITA Easyshade). ΔE00
values were compared to 50:50% ΔE00 perceptibly (0.8) and acceptability (1.8) thresholds. Within the first minute of dehydration there
was a significant change in the ΔE00 (3.9) beyond the perceptibility
threshold (87% of the participants) and acceptability threshold
(72% of the participants). The ΔE00 increased constantly during the
15 min (ΔE00 = 5.1). Thereafter, participants were asked to rinse
with water and close for 5 min to allow for teeth to rehydrate. ΔE00
measurements were calculated at the defined intervals. Tooth color
the first minute of dehydration. While 90% of teeth were beyond
did not return to its original value after 15 min of rehydration. ΔE00
the perceptibility threshold after 15 min of rehydration as shown in
decreased from 4.1 to 2.7, with 65% of the participants still being
Figure 5.
beyond the acceptability threshold after the rehydration phase. Fur-
Furthermore, 72% of the participants were beyond the ΔE00
thermore, the L (Lightness) returned to its original value after rehy-
acceptability threshold (1.8) within the first minute of dehydration.
dration, while the C (Chroma) retained a higher value and a lower H
(Hue) value after rehydration. Therefore, tooth color determination
Mean and SD of change in color (ΔE00) of rehydration with
95% confidence level
should be carried out prior to the start of any treatment, before the
tooth dehydrates if a successful color match is to be achieved. In a typi-
Upper 95%
CL for Mean
cal clinical setting one cannot expect to determine a shade shortly after
matched dehydrated.
Lower 95%
CL for Mean
To understand the change in tooth color due to dehydration, the
tooth's enamel and dentin have a defined refractive index (RI) when
light passes through the tooth structure. The refractive index is the
a clinical procedure has been performed during which the tooth to be
change in the light's direction when the transmitting medium changes.
Air and water have refractive indices of 1.00 and 1.33, respectively.14
When light passes through enamel (RI = 1.63) and then through dentin (RI = 1.54) the light refracts in a certain direction.15 When the
A, Change in L (Lightness) value (A). B, C (Chroma) value (B). C, H (Hue) value (C) after tooth dehydration and rehydration
tooth is moist, the inter-prism space is filled with saliva, and light will
In the literature, little is known about how long it takes for teeth
refract in a defined path. When the tooth dehydrates, the inter-prism
to dehydrate/rehydrate and the effect time has on the shade selection
space will be replaced with air, and the light will refract differently
process. A few clinical studies have been published where the effect
due to the difference in RI. The increased light refraction reduces the
of dehydration and rehydration on color change was examined. An
tooth's translucency and increases its luminosity, giving the tooth a
in vivo study to determine the changes in color measurements of nat-
whiter appearance. When the tooth is rehydrated, it may require a
urel teeth in seven subjects before and after isolation by using rubber
longer period, more than 15 min, for the saliva to refill the inter-prism
dam for 15 min, also estimating the time taken for the tooth color to
spaces and restoring the original path of light refraction through the
return to its original color.12 Color measurements were made by using
tooth, and finally restoring the tooth's original color.
a spectrophotometer with no mentioning of using a positioning jig,
Isolation is considered one of the pillars to the success of most
and CIELab coordinates were calculated. The authors concluded that
restorative procedures. Although the use of rubber dam is essential
teeth become brighter and less saturated after 15 min of rubber dam
toward this success, it is unfortunately becoming an uncommon
application, which agrees with the present study. They also found that
practice. Other method of isolation have been introduced and offer
baseline values of the tooth's color were regained after 30 min of
relative isolation. The rationale for using the Optragate isolation
rehydration whereas the baseline values were not regained after
device in the present study instead of the rubber dam, for docu-
15 min of rehydration in the present study.
menting the dehydration process, is due to that rubber dam applica-
In a more recent studyl,13 color change due to dehydration was
tion can be time-consuming and would have precluded timely
investigated in 20 subjects. For each subject a left or right maxillary cen-
measurements of the tooth dehydration process. According to a previ-
tral incisor was used with a positioning jig made for placement of the
ous study, rubber dam application took an average time between
VITA Easyshade spectrophotometer. Baseline measurements were col-
Consequently, the color measurement process will be
lected followed by rubber dam isolation. Measurements were obtained
adversely affected. In this study, a single operator (SS) was trained on
at 10-min intervals for 30 min. The rubber dam was removed and sub-
the Optragate application in a timely manner (less than 15 s) to ensure
jects were instructed to drink a glass of water followed by additional
consistency of the results.
color measurements for rehydration with same time intervals. They
3-5 min.
Percentage of participants with perceivable color changes
during dehydration and rehydration
Percentage of participants with acceptable color changes
during dehydration and rehydration
concluded significant changes in the color of teeth occur after 10 min of
dehydration. Additionally, the tooth's original color had not returned to
The authors have no financial interest in any of the companies whose
baseline color within 30 min of rehydration, contrasting previous finding
products are used in this study.
and in agreement with the findings of the present study.
Deficiencies of the previously mentioned studies include long
time intervals. Ten-minutes intervals were used without the ability to
specify exactly color change in a timely manner. Moreover, small sample sizes were used which may have significant effects on the outcome. A larger sample size, with greater diversity of age and gender,
Taiseer A. Sulaiman
Vilhelm G. Olafsson
could reveal a more complete picture regarding the dehydration/rehydration patterns. Senior patients may have reduced salivary flow,
enhancing the dehydration effects on color and time, and also requir-
ing longer time for the tooth to rehydrate and return to its original
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color. Rubber dam isolation was used in both studies for the dehydration process. As specified earlier, the time required for rubber dam
placement may adversely affect the results.
Ideally, longer time intervals for the rehydration color measurements
would precisely predict when tooth rehydration would occur. This information is important for the clinician when missing the initial shade selection opportunity and would be suggested for further research. Another
potential limitation of this study relates to the accuracy of the VITA Easyshade device. A positioning jig was fabricated ensuring repeatability
when measurements are collected. In addition, the mean of three
measurements per interval was calculated ensuring reliability.
Within the limitations of this clinical study, the following conclusions
were drawn:
• Tooth dehydration within the first minute led to perceivable
changes in the tooth's color, adversely affecting the shade selection process.
• Teeth required more than 15 min of rehydration, in order to
regain their original shade after dehydrating.
• It is highly recommended to performing shade selection at the
beginning of the appointment.
The authors are sincerely grateful to Mr. Brandon Rodgers, Ms. Safa
Aldali and Dr. Tariq Alsahafi for their laboratory support. We are also
very thankful to Drs. Ceib Phillips and William Johnston for their statistical support. Thirty-two participants were recruited for this clini-
cal study that was conducted after approval of the institutional
Olafsson VG, Delgado AJ, Donovan TE, Heymann HO. Effect
review board (IRB) (16-1620). These Participants were selected
of time on tooth dehydration and rehydration. J Esthet Restor
among students and staff members at the School of Dentistry at Uni-
Dent. 2019;1–6.
versity of North Carolina at Chapel Hill.
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