Treatment of various degrees of white spot lesions using resin infiltration—in vitro study
Abbas et al. Progress in Orthodontics
Treatment of various degrees of white spot lesions using resin infiltration-in vitro study
Bassant A. Abbas 0
Eiman S. Marzouk 0
Abbas R. Zaher 0
0 Department of Orthodontics, Faculty of Dentistry, Alexandria University , Azarita, Alexandria , Egypt
Background: This study was conducted to evaluate the efficiency of resin infiltration to improve the color of white spot lesions (WSLs) and to estimate the effect of different numbers of etching and resin infiltrant applications on the color change of WSLs with various depths. Ninety-six sound extracted premolars were subjected to acid attack inducing different depths of WSLs. Using a DIAGNOdent, teeth were divided into four main groups according to the depth of the WSLs: shallow enamel, deep enamel, shallow dentine, and deep dentine without cavitation. Then each of the main groups was subdivided into four groups: six teeth each with different protocols of resin infiltration as follows: 1 etching + 1 infiltrant application (EA), 1 etching + 2 infiltrant applications (EAA), 2 etchings + 1 infiltrant application (EEA), 2 etchings + 2 infiltrant applications (EEAA). Spectrophotometric analysis was measured at baseline (T0), after inducing the WSLs (T1), and following resin infiltration application (T2) for each group. Results: In shallow enamel, EA produced the least mean color difference (1.62 ± 0.85), with high significant difference (P < 0.001), when compared with the clinically detectable threshold (ΔE = 3.7). While in deep enamel, EAA showed the least mean color change (1.95 ± 0.4), with P < 0.001 when compared with the critical value. Also, in shallow dentine, the least mean change was noticed with EAA (3.0 ± 0.45), with P < 0.001 when compared with the clinical color detection threshold. Furthermore, in deep dentine, EAA had the least mean difference (3.76 ± 0.6) but with no significant difference, when compared with the clinically detectable threshold. Conclusions: As the WSL got deeper, the color of the lesion became more clinically visible. In shallow enamel, the best treatment option was one etching with one resin infiltrant application. For deep enamel and shallow dentine, one etching with two applications of infiltrant gave the best lesion masking. In deep dentine, it is advisable to perform one etching with two infiltration steps, taking in consideration that all deep dentine lesions without cavitation were partially masked, remained clinically detectable, and might require more invasive restorative procedures.
White spot lesions; Resin infiltration; Color change; Decalcification
A beautiful smile, the most interactive communication
skill of a person, is created with pleasing inherent
proportions to one another and a pleasing tooth
arrangement in harmony with the gums, lips, and face of the
]. Early enamel decalcification, one of the most
common side effects of fixed orthodontic treatment,
manifests itself as white spot lesions (WSLs) [
Initially, a WSL shows an apparently intact surface layer,
followed underneath by the more porous lesion body,
giving a chalky opaque appearance, as light is scattered
mainly within the lesion body [
]. Scattering is caused
at interfaces between substances with different refractive
indices as enamel, water, and air [
]. Generally, WSLs
could appear as early as 1 month after bracket
placement; meanwhile, the formation of dental cavitation
might require up to 6 months [
]. WSLs are frequently
perceived on the dental buccal surfaces, around the
brackets, mainly in the gingival area [
Prompt diagnosis and treatment are essential to avoid
these lesions from turning into cavities [
]. The early
detection of WSL is important as these lesions have the
potential to be remineralized and monitored over time
]. The DIAGNOdent 2190, known as DIAGNOdent
Pen (DDPen, KaVo, Biberach, Germany), is a diagnostic
device in which pulsed laser irradiation of a carious
lesion causes the emission of reflected fluorescent light at
700–800 nm [
]. Values between 10 and 25 indicate
initial enamel carious lesion, values between 25 and 35
indicate superficial dentinal caries, and values over 35
indicate deep dentinal caries . Several studies
] evaluated its reliability and validity at
quantification of smooth surface caries and WSLs.
Spectrophotometry aims to specify color by taking
accurate measurements expressed either quantitatively or
graphically. The Commission Internationale de
l’Eclairage (CIE) developed a system that calculates the difference
between two colors using a formula (ΔE = [(ΔL*)2 + (Δa*)2
+ (Δb*)2]1/2, giving a single number as a value for color
difference (ΔE) [
]. Most studies set the proposed acceptance
for color matching to be 3.7 units, above which the
differences are clinically visible [
]. Previously in
], the spectrophotometer proved to
have precise measurement and high accuracy.
Recently, with the advancing of materials, the
infiltration concept was introduced in the field of dentistry.
The purpose of the resin infiltration technique is to
micro-invasively infiltrate the inter-crystalline spaces of
enamel with polymerizable low viscous resin to arrest
enamel lesions. Before a WSL can be infiltrated, it must be
acid-etched to remove the hypermineralized pseudo-intact
surface layer of enamel and thus permits resin infiltration
into the body of the lesion [
]. Since resin infiltration
has a refractive index (1.48) that is comparable to that of
enamel (1.65), thus, resin infiltration can completely mask
the opaque color of less severe inactive WSLs and partially
mask the appearance of moderate to severe WSLs .
In the 70s, Robinson et al. [
] investigated the concept
of infiltrating a carious lesion with resorcinol-formaldehyde
resin. The authors detected that in later experiments, the
penetration of the resin was improved when the tooth
surface was first etched with hydrochloric acid for 5–10 s.
Gray and Shellis [
] concluded that as the time of etching
and number of applications of resin increased, the
percentage penetration of the resin material also increased. To
clinically improve esthetic outcomes, Knösel and associates
] recommended etching time of more than 120 s in
WSLs that have been existent for a longer period of time
and deeper lesions with a thicker intact surface layer.
Arnold et al. [
] concluded that repeated conditioning with
15% hydrochloric acid resulted in reduction of surface
roughness and increased the depth of the etched surface
erosion. Nevertheless, the total erosion depth is rather
shallow and hence negligible. Neuhaus and coworkers [
showed that surface conditioning with hydrochloric acid
proved to be superior for the penetration of the infiltrant,
while etching with phosphoric acid only penetrates
superficially into non-cavitated fissure caries lesion.
Meyer-Lueckel and Paris [
] and Liu et al. [
showed that resin infiltration is capable of penetrating
almost completely into caries lesions. Kim et al. [
noted that the lesion depth and shade improvement
were correlated. It was concluded that lesions deeper
than the infiltration capacity of resin infiltrants might
demonstrate insufficient esthetic improvement. Ou et al.
] examined the treatment effect of resin infiltration
on different degrees of enamel demineralization. The
results indicated that treatment of high and low
demineralization of enamel had a similar masking effect.
Up to our knowledge, this study was the first in the
literature to evaluate the effect of different numbers of
etching and resin infiltrant applications on the color
change of WSLs with various depths. The null
hypothesis was that different depths of WSL will have the same
response of color change when using different times of
etching and infiltrant applications.
A sample size of 96 human premolars, with six teeth per
group, was required to estimate clinical average change
of color at various WSL depths, with a power of 80%
and α = 0.05 using G-power software [
Ninety-six human premolars extracted for orthodontic
purpose were collected from subjects treated in the
Department of Orthodontics, Faculty of Dentistry,
Alexandria University. Teeth were divided into four main
groups according to the depth of the induced WSL:
shallow enamel (SE), deep enamel (DE), shallow dentine (SD),
and deep dentine (DD) without cavitation. Then each of
the main groups was further subdivided into four groups,
six teeth each according to the resin infiltration protocol
applied. The different infiltration protocols used were one
etching with one infiltrant application (EA), one etching
with two infiltrant applications (EAA), two etchings with
one infiltrant application (EEA), and two etchings with
two infiltrant applications (EEAA).
Criteria for selection: 1—sound teeth free from caries,
2—intact buccal surface with no visible cracks, stains, or
hypoplastic areas, 3—no pretreatment with chemical
Following extraction, all teeth were cleaned with tap
water and stored in artificial saliva solution (20 mmol/l
NaHCO3, 3 mmol/l NaH2PO4, and 1 mmol/l CaCl2) at
37 °C and pH 7 to simulate the oral environment [
The solution was changed every day.
1. At the beginning of the study, all teeth roots were
removed at the cemento-enamel junction with a
2. In order to facilitate examination of the buccal
surface, the lingual surfaces of the teeth were
embedded down in self-curing acrylic resin held by
a metal mold so that the buccal surface aligned
parallel with the base of the mold (Fig. 1).
3. Prior to color measurement, all teeth were polished
with rubber prophylaxis cup at a low-speed
handpiece with a mixture of non-fluoridated oil-free
pumice and water and then rinsed with running
4. A black painted metallic mold was fabricated to
help hold the teeth in a standard position during
color measurement (Fig. 2). The mold had the
same dimensions of the spectrophotometer tip
from one side.
5. Base line (T0) colorimetric analysis was carried out
on all teeth by means of a spectrophotometer (Vita
easy Shade ®spectrophotometer, Model# DEASY
CHP, CBU, H013015. USA), according to the
Commission Internationale de L’Eclairage (CIE)
L*a*b* system (Fig. 3)
6. Before inducing caries lesion, the working area
under testing was demarcated by a 4 mm × 4 mm
white sticker representing the area of the acid
attack. The rest of the tooth was covered by a black
matte acid-resistant nail varnish.
7. All teeth were then immersed in a solution that
contains 200 ml artificial caries solution (2.2 mmol/l
KH2PO4, 2.2 mmol/l CaCl2, 50 mmol/l acetic acid)
at pH 5 for a whole day [
]. The solution was
changed daily till the appearance of the frosty white
8. The extent of white spot lesion was evaluated using
a DIAGNOdent™ (KaVo, Bibberach, Germany)
every day. Teeth were immersed again in an
artificial caries solution if the extent of the lesion
was not enough.
9. According to the readings of the DIAGNOdent™
] teeth were divided into four main groups 24
teeth each. The teeth were numbered and labeled. It
took 15 days to produce the first white spot lesion.
The readings of induced WSLs in the outer
and inner half of the enamel ranged between
10 and 25.
The readings of induced WSLs present in the
outer and middle of the dentine without any
signs of cavitation ranged between 26 and 37.
10. The color of the teeth in each group was
spectrophotometrically measured after induction of
the white spot lesions (T1).
11. Each of the main groups was subdivided into four
groups, six teeth each according to the resin
infiltration protocol used:
(a) 1 etching + 1 infiltrant application (EA).
(b) 1 etching + 2 infiltrant applications (EAA).
(c) 2 etchings + 1 infiltrant application (EEA).
(d) 2 etchings + 2 infiltrant applications (EEAA).
12. ICON® (DMG, Hamburg, Germany) resin
infiltration was applied on the induced white spot
lesions according to the manufacturer’s
(a) 15% HCL (ICON-Etch) was applied for 2 min,
then rinsed off with water spray for 30 s and
dried. The number of etching applications was
determined according to the group assigned.
(b) Ethanol (ICON-Dry) was applied for 30 s
followed by air-drying.
(c) ICON-Infiltrant was applied and left on the
tooth surface for 3 min. Excess resin was wiped
away by a cotton roll and then light-cured for
40 s. In the groups with double resin infiltrant
application, the application of infiltrant resin
was repeated for 1 min and then light-cured for
40 s. Finally, the roughened enamel surface was
polished using composite resin polishing discs
and polishing cups.
13. The color of the teeth in each group was again
spectrophotometrically measured after application
of ICON® (T2).
The steps of the study are illustrated in Fig. 4.
To reduce the measuring error, two readings per tooth
were taken for each time point. The reading was verified
when the color difference between the readings obtained
did not exceed the threshold of 1 ΔE unit. Readings with
a difference of ΔE more than 1 unit were rejected and
new readings were taken. An average of the two
measurements was used when a difference of ΔE more than
1 unit persisted.
The data was collected and entered into the personal
computer. Statistical analysis was done using Statistical
Package for Social Science Version 20 (SSPS Inc., Chicago,
III) software. After the data was tested for normality, it
was decided to use one sample t test to compare the mean
color difference ΔE to the threshold of clinical detection
ΔE = 3.7. In order to compare the mean ΔE between the
groups, one-way analysis of variance (ANOVA) was
performed followed by post hoc test. The significance level
was set at P < 0.05.
Color change comparisons after WSL formation
Table 1 shows the mean color difference ΔE between the
T0 (baseline) and T1 (after inducing the WSLs) in shallow
enamel, deep enamel, shallow dentine, and deep dentine
(3.84 ± 0.81, 4.81 ± 1.59, 5.11 ± 1.68, and 6.92 ± 0.86,
respectively). The shallow enamel group did not show
statistical difference when compared with the clinically
detectable threshold (ΔE = 3.7); however, the deep enamel
and shallow dentine groups showed significant difference
(P < 0.05), while the deep dentine group showed high
significant difference (P < 0.001).
There was clinically detectable WSLs in all of the
groups, as all of them exceeded the threshold of clinical
detection ΔE = 3.7 as shown in Fig. 5.
Color change comparisons following the various protocols of resin infiltration
Table 2 displays the mean color difference ΔE between
the baseline T0 and T2 following various resin
infiltration protocols in shallow enamel. EA gave the least
mean value 1.62 ± 0.85 followed by EAA, EEA and
EEAA with means of 2.40 ± 0.63, 2.47 ± 0.8 and 2.99 ±
1.33, respectively. All groups were clinically not
detectable as they did not exceed the clinically detectable
threshold of ΔE = 3.7. All treatments demonstrated high
significant difference (P < 0.001), when compared with
the critical value, except for EEAA.
In addition, Table 2 illustrates the mean color
difference ΔE between the baseline T0 and T2 following the
different resin infiltration protocols in deep enamel.
EAA gave the least mean value of 1.95 ± 0.4 followed by
EA, EEA, and EEAA with means of 2.41 ± 0.31, 2.98 ±
0.81, and 3.15 ± 0.93, respectively. All groups were
clinically not detectable as they did not exceed the clinically
detectable threshold of ΔE = 3.7. EA and EAA showed
*Significant at a P value < 0.05; **significant at a P value < 0.001; (n)
Critical value ΔE t
high significant difference (P < 0.001), EEA showed
significant difference (P < 0.05), and lastly, EEAA revealed
no significant difference, when compared with the
clinically detectable threshold.
Table 3 presents the mean color difference ΔE between
the baseline T0 and T2 following the different resin
infiltration protocols in shallow dentine. The least mean
value 3.0 ± 0.45 was observed with EAA followed by EA,
EEA, and EEAA with means of 3.55 ± 0.32, 3.83 ± 0.36,
and 4.19 ± 0.34, respectively. Only two groups were
clinically detectable (EEA, EEAA) as they exceeded the
clinically detectable threshold of ΔE = 3.7. EEAA showed
significant difference (P < 0.05) and EAA revealed high
significant difference (P < 0.001), when compared with
the critical value ΔE = 3.7.
Table 3 also demonstrates the mean color difference
ΔE between the baseline T0 and T2 following various
resin infiltration modalities in deep dentine. EAA had
the least mean value of 3.76 ± 0.6, followed by EA, EEA,
and EEAA with means of 4.03 ± 0.54, 4.73 ± 0.77, and
5.96 ± 0.57, respectively. All groups displayed clinical
detection, i.e., exceeded ΔE = 3.7. EEA showed significant
difference (P < 0.05) and EEAA showed high significant
difference (P < 0.001), when compared with the clinical
Table 4 shows multiple comparisons of the mean color
difference ΔE (T2-T0) between the different resin
infiltration protocols in shallow enamel. It was found that
EA significantly differ from the other groups: highly
significant (P < 0.001) when compared with EEAA
with a mean difference of 1.374 and significantly
different (P < 0.05) when compared with EAA and EEA
with mean differences of 0.785 and 0.853, respectively.
Those mean differences were obtained from
subtraction of the respective means presented in Table 2.
When comparing the other groups with each other,
there was no significant difference.
While in deep enamel, it was found that all the
comparisons were significant except for EEA with EEAA.
EAA gave high significant difference (P < 0.001) when
compared with EEA and EEAA with mean differences of
1.027 and 1.194, respectively. Upon comparing EA with
the rest of the modalities, significant difference (P < 0.05)
was found between them.
Table 5 shows multiple comparisons of the mean color
difference ΔE (T2-T0) between the different resin
infiltration protocols in shallow dentine. It was found that
all the comparisons are significant except for EEA with
EEAA. High significant difference (P < 0.001) was found
when comparing EA with EEA and EEAA with mean
differences of 0.274 and 0.638, respectively. Also, high
significant difference (P < 0.001) was found when
comparing EAA with EEA and EEAA with mean differences
of 0.824 and 1.188, respectively.
Whereas in deep dentine, it was found that all the resin
infiltration protocols show significant difference when
compared with each other. When comparing EEAA with
EA, EAA, and EEA, there was a high significant difference
(P < 0.001) with mean differences of 1.935, 2.201, and 1.232,
respectively. Also, high significant difference (P < 0.001) was
found upon comparing EA with EEA with mean difference
of 0.703. Furthermore, significant difference (P < 0.05) is
shown when comparing EA with EAA with a mean
difference of 0.266 and when comparing EAA with
EEA with a mean difference of 0.969. The best resin
infiltration protocols in the different depths of WSLs
are demonstrated in Fig. 6.
Results in this study showed that there was a difference
between the initial color of the tooth and its color after
the induction of the WSL. The deeper the WSL, the
more clinically apparent it was. Also, as mean ΔE
exceeded 3.7 units, the lesion got deeper. Shallow
enamel lesions were clinically detectable although they
were insignificant when compared with the critical value.
When the four groups were compared
spectrophotometrically, deep dentine showed the highest color difference.
A previous study by Gray and Shellis [
increased penetration depth with increased number of
etching; however, the depths of the lesion were not taken
in consideration. Knösel and colleagues [
recommended more etching in long-standing deep WSLs.
Moreover, Arnold et al. [
] concluded that repeated
conditioning with 15% hydrochloric acid increased the
depth of the etched surface erosion. Therefore, in the
current study, eight groups were assigned for double
etching with 15% HCL for 120 s each, to evaluate the
effect of increased etching prior to resin infiltration, on
the color change of different depths of WSLs.
Also, eight groups were assigned for double infiltrant
application: 3 min for the first step and further 1 min
*Significant at a P value < 0.05; **significant at a P value < 0.001; (n) sample size
Critical value ΔE
for the second step according to manufacturer’s
instructions. This was suggested by two studies [
noticed decreased lesion pore volume after double resin
infiltrant application. Also, the resin infiltrant was
recommended to be applied twice by Robinson et al. 
because of the shrinkage of the material following the
first application resulting in the generation of space that
can then be occluded by a second application.
Two studies by Kim et al. [
] and Ou et al. [
examined the association between the depth of WSLs
and the effect of resin infiltration, but no evidence was
given about the number of etching and infiltrant
applications needed for each depth.
The main goal of treatment of the WSL is to arrest the
progression of non-cavitated lesions and to improve the
esthetics by diminishing their opacity. Starting with
lesions in the outer enamel, the depth of the WSLs was
shallow and one etching with one infiltrant application
gave the least mean color difference when compared to
the baseline color, providing the best result, as it nearly
completely camouflaged the WSL. Therefore, it is
advisable to use single etching with one infiltrant application
to save time and material. However, double infiltrant
application with double etching gave the highest mean
color difference, statistically insignificant when compared
with the threshold of clinical detection. This might be
related to surface roughness produced by the resin. It was
postulated that the average value of the resin color
difference was related to the surface roughness, which might be
decreased by polishing [
4, 40, 41
Similarly, in deep enamel, the results showed that
various resin infiltration protocols displayed no clinical
detection of the WSLs as they did not exceed the
clinically detectable threshold; the WSLs were well masked.
The least mean color difference was noticed with one
etching and double infiltration modality when compared
to the initial teeth color. When comparing the four
modalities, double etching with double infiltrant application
improved the color but not efficiently, as the mean ΔE
approached the clinical detectable threshold. This might
be due to the double etching step that could have led to
differences in enamel prism morphology. This was
proved previously by Arnold et al. [
] but not in
accordance to a certain depth.
However, going deeper to the lesions reaching shallow
dentine where the WSLs were deeper than the previous
two groups of enamel lesions, larger differences in color
were found when compared with teeth color at baseline.
*Significant at a P value < 0.05; **significant at a P value < 0.001
*Significant at a P value < 0.05; **significant at a P value < 0.001
Only two groups gave the best color match to the
baseline; one etching step with either one or two infiltrant
applications, their values did not exceed the clinical
detectable threshold of ΔE. This might suggest that one
etching step is preferable for lesions reaching the outer
layers of dentine regardless of the number of infiltrant
applications that will be done. To be more precise when
four groups were compared, one etching with two
infiltrant applications camouflaged the WSL giving the least
mean value implicating the best combination of
treatment for this depth of WSL. On the other hand, double
etching with double infiltrant applications gave a mean
value that exceeded the critical value of ΔE, presenting
the worst treatment modality.
Progressing in deep dentine lesions, the WSLs were
the deepest reached in this study. All the treatment
modalities showed clinical detection after resin infiltration,
i.e., different resin infiltration protocols were not
successful in completely masking the WSLs. Furthermore,
the worst result was found in double etching with
double infiltrant application and the best was found in
one etching with a double infiltrant application. One
etching was found to be enough to open the lesion pores
without weakening of the tooth, while double etching
resulted in exfoliation of enamel surface in some of the
samples. This finding was in accordance with that of
Hammad et al. [
] who postulated that removal of the
hypermineralized surface layer by 15% HCL might
additionally weaken the lesion structure. Thus, in deep
dentine WSLs, one etching was found to be enough to
remove the hypermineralized layer without losing any
enamel tissues besides improving the color.
It is preferable in deep dentine lesions to first try using
the infiltration resin technique in an attempt to improve
the color. However, according to the results of this
study, we cannot anticipate the full masking of the
lesions once it reach the deep layers of the dentine. If
the gained result was not satisfactory and the WSL was
still clinically visible, unfortunately, the treatment mean
will be diverted to more invasive restorative procedures.
Based on the results of the current study, it can be
1. As the WSL got deeper, the color of the lesion
became more opaque and clinically visible.
2. Resin infiltration concept is a good technique for its
chameleon effect used for different depths of WSLs.
3. With shallow enamel, the best treatment option is
to perform one etching step with one application of
4. For deep enamel and shallow dentine, the best
treatment modality is one etching step and two
applications of the resin infiltrant.
5. In deep dentine without cavitation, lesions were
partially masked in all the treatment modalities and
remained clinically detectable.
6. It is not advisable to perform two etching steps as
enamel exfoliation, in some of the samples, was
observed especially in deeper dentine lesions.
CIE: Commission Internationale de l’Eclairage; DD: Deep dentine; DE: Deep
enamel; EA: 1 etching + 1 application; EAA: 1 etching + 2 applications; EEA: 2
etchings + 1 application; EEAA: 2 etchings + 2 applications;
HCL: Hydrochloric acid; ICON: Infiltration concept; RI: Resin infiltration;
SD: Shallow dentine; SE: Shallow enamel; TEGDMA: Tetraethylene glycol
dimethacrylate; WSL: White spot lesions
The research was not funded by any organization or association.
Availability of data and materials
Tables and figures are escorted available within the manuscript.
BAM wrote the manuscript, did the practical work, and revised the statistics.
ESM revised the manuscript and revised the statistics. ARZ revised the
manuscript and revised the statistics. All authors read and approved the final
Ethics approval and consent to participate
The research was approved by the ethical comity in Alexandria University.
Consent for publication
The authors declare that they have no competing interests.
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
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