Keywords silver diamine fluoride (SDF) - potassium iodide (KI) - tensile strength
Introduction
Silver diamine fluoride (SDF) is a cost-effective caries-prevention agent. It is among
the preventive agents commonly used in minimally invasive dentistry. It has been authorized
for use as a therapeutic medication to arrest caries. SDF possesses antimicrobial
properties and remineralizing ability of dental tissue.[1 ]
[2 ]
According to multiple laboratory investigations, SDF produces a dark silver precipitate
of Ag(s) that discolors dentin in addition to the free fluoride ions and CaF2 required
to remineralize dental tissues.[3 ]
[4 ]
However, one of the main drawbacks of applying SDF alone to tooth structure is discoloration.
As previously documented, sound tooth structure and carious tissues are discolored
dark brown or black following SDF. Silver ion staining increased with the amount of
demineralized region. The stain persists over time and can only be removed by physical
means.[5 ]
The combination of SDF and potassium iodide (KI) was proposed as a discoloration treatment.
As KI minimizes the discoloration caused by SDF without affecting its effectiveness
in preventing caries.[6 ]
Another proposal to solve the discoloration of SDF/KI is to cover the lesion with
restorative material. However, the risk of discoloration is still considered.[7 ]
Previous investigations focused on the influence of glass ionomer restoration on covering
the color of SDF.[5 ] However, no study has been conducted to assess the effect of delayed application
of composite restoration on concealing the color of SDF/KI and its effect on bonding
strength. Placing SDF/KI in the cavity after partial caries removal acts as an inhibitor
for residual carious progression; however, adding SDF/KI to dentin may affect the
bond strength of composite restoration.[8 ]
Our primary objective of this investigation was to evaluate microtensile bond strength
and mode of failure of delayed application of composite restoration (self-etch adhesive
mode) to artificial carious dentin with and without SDF and KI in primary and permanent
teeth.
Our secondary objective was to evaluate the difference in shade between the composite
on nontreated dentin and the composite on SDF/KI-treated dentin.
Materials and Methods
Sample size was determined using the G power statistical power analysis program (version
3.1.9.4) for sample size determination; a total sample size of n = 48 (subdivided to 24 in each group; further subdivided to 12 in each subgroup)
will be sufficient to detect a large effect size (d ) = 1.06, with an actual power (1–β error) of 0.9 (95%) and a significance level of (α error) 0.05 (5%) for two-sided hypothesis test.[9 ]
Forty-eight human teeth were utilized in the study; 24 freshly erupted sound premolar
teeth were extracted in the pedodontics department for orthodontic purposes as part
of a treatment plan. The pedodontics department provided 24 noncarious deciduous molars,
which were extracted as part of a treatment plan. The ethical committee gave its approval
for the study's use of human teeth, which were distributed at random among four experimental
groups (n = 12). The clearance reference was from the ethical committee, and they followed
their guidelines.
Variables
G1: composite (self-etch adhesive mode) restoration of primary teeth without use of
SDF/KI on artificial carious dentin
G2: composite (self-etch adhesive mode) restoration of primary teeth with SDF/KI applied
on artificial carious dentin
G3: composite (self-etch adhesive mode) restorations for permanent teeth without the
use of SDF/KI on artificial carious dentin
G4: composite (self-etch adhesive mode) permanent teeth restored with SDF/KI on artificial
carious dentin
Specimen Preparation
The teeth were properly cleaned with running water to remove blood. The teeth were
scaled to remove calculus and periodontal ligament remains, then polished with fine
pumice and soft rubber cups at a standard speed. A magnifying lens was used to examine
the teeth for fissures. The teeth with evidence of caries, microcracks, or other faulty
structures were eliminated. All samples have been kept in deionized (DI) water containing
0.02% thymol immediately after extraction and used in this study within 1 month.
Each tooth was prepared by removing the roots below the cementoenamel junction using
a diamond disc with a high-speed handpiece and DI water irrigation. The remaining
coronal tooth structure was vertically impeded in self-curing acrylic resin blocks
(Acrostone Dental Factor, England). Acrylic blocks were made with a specially designed
cylindrical, split Teflon mold for retaining teeth (4 cm vertically and horizontally).
A low-speed diamond blade was used to remove 3 mm of tooth structure from the cusp
tip to the middle of the tooth structure, exposing a consistent layer of midcoronal
dentin.
Formation of Artificial-Like Caries Lesion
A coat of varnish was applied to all surfaces of the specimen except the occlusal
surface. After that, the collected specimens were submerged for 4 days at 25°C in
a demineralizing solution (pH 4.4, 50 mm acetate, 2.2 mm KH2PO4, and 2.2 mm CaCl2).[8 ]
For Control Group (Nontreated Dentin)
In G1 and G3, DI water was applied to prepared tooth surfaces using a microbrush applicator
for 10 seconds and air-dried for 5 seconds. Exposed dentin surfaces were immediately
kept in artificial saliva (pH 7.4) containing 5 mM HEPES, 2.5 mM CaCl2•H2O, 0.05 mM
ZnCl2, and 0.3 mM NaN3 at 37°C for 14 days.[7 ]
Application of SDF/KI
In G2 and G4, a drop of SDF solution (Advantage Arrest, Elevate Oral Care) was dispensed
into a disposable plastic dish, and a microbrush applicator was utilized to apply
SDF to prepared tooth surfaces. The material was then transferred to the dentin surface
and actively rubbed for 10 seconds.
Each specimen was thoroughly dried with an air syringe for 5 seconds; the material
was left untouched for 1 minute to be absorbed by the tooth. The excess substance
was removed with a cotton Q-tip. Using the triple syringe, the specimen was washed
with water for 15 seconds.[6 ]
KI (Riva Star, SDI; Bayswater, Australia) was immediately applied for 1 minute till
the creamy white became transparent. Distilled water was used to clean all affected
surfaces properly. Following SDF/KI treatments per the manufacturer's recommendations,
exposed dentin surfaces were immediately kept in artificial saliva (pH 7.4) containing
5 mM HEPES, 2.5 mM CaCl2•H2O, 0.05 mM ZnCl2, and 0.3 mM NaN3 at 37°C for 14 days.[7 ]
[10 ]
Bonding Procedures and Resin Composite Application
The bonding system (3M Scotch bond Universal adhesive) was used for four groups in
the self-etch technique (Scotch bond Universal (SBU)). One drop of universal bonding
agent was placed on the dentin surface as an active adhesive for 20 seconds. Gentle
solvent evaporation with an air syringe was applied for 10 seconds to provide a uniform
thin layer. Three successful adhesive layers were softly blasted thin using oil-free
compressed air for 10 seconds to provide a homogenous coating of material. Light curing
(Elipar DeepCure-S LED Curing Light, 1200 mW/cm2 ) was administered for 10 seconds.[10 ]
To standardize the bonding area, a 6 × 6 mm in diameter and 4 mm height plastic cylindrical-shaped
mold was placed on the flat dentin surface in each group. The ring was filled with
A3 composite resin from Filtek bulk-fill posterior (3M ESPE, St. Paul, Minnesota,
United States). A polyester strip was applied to the top of the filled mold.
The composite restoration was made to a thickness of 4 mm to provide support and attachment
to the jig. A glass slip was put over the celluloid strip to create a flat surface
and remove the remaining composite resin. The samples were then light-cured from the
occlusal surface for 40 seconds using the light-emitting diode light cure system from
Dentsply Caulk (Milford, Delaware, United States).
Using a slow-speed handpiece in dry conditions, all specimens' occlusal surfaces and
sides were polished utilizing fine, superfine (24 μm), and superfine (8 μm) aluminum
oxide polishing disks (Sof-lex, 3M ESPE).
Evaluation of Shade Matching
The spectrophotometer (VITA Easyshade V, VITA Zahnfabrik, Bad Sackingen, Germany)
was used to measure the color of each composite restoration. The following formula
was used to determine the shade difference (ΔE ) between the restoration and the tooth:
ΔE = [(ΔL ∗)2 + (Δa ∗)2 + (Δb ∗)2]1/2
where L * denotes the color's lightness, a *, b *, and c * stand for the color's redness, greenness, and yellowness, respectively.[11 ]
Microtensile Bond Strength Test
Forty-eight beams were yielded from each restored specimen. Each beam's bonded surface
area was measured using a digital caliper. The ends of the adhesive-dentin bonded
beams were attached to a jig through cyanoacrylate adhesive and tested under tension
using a universal testing machine (Model 2519-104; Instron, United States). The force
in Newton (N) required to displace the restoration was measured. The microtensile
bond strength (µTBS) was calculated by dividing the load at failure (N) by the cross-sectional
bonding area (1 mm2 ). The readings are expressed in mega Pascal (MPa)[12 ]
[13 ] ([Fig. 1 ]).
Fig. 1 Microtensile bond strength beams selected from coronal parts.
Failure Mode Analysis
After undergoing microtensile testing, the fracture patterns of all the debonded specimens
were examined using a stereo microscope at a magnification of 40 × . Four groups were
created based on the nature and location of the failure modes:
Type 1: adhesive fracture between adhesive agent and dentin (adhesive failure)
Type 2: adhesive fracture between dentin and adhesive agent plus partial cohesive
fracture in the composite restoration or dentin (mixed fracture)
Type 3: cohesive fracture in dentin
Type 4: cohesive fracture in the composite restoration ([Fig. 2 ])
Fig. 2 Representative images for the failure mode analysis (A ) Cohesive fracture in dentin. (B ) Cohesive fracture in composite. (C ) Adhesive failure in primary dentition. (D ) Mixed failure in permanent dentition.
Statistical Analysis
Data management and statistical analysis were carried out with the Statistical Package
for Social Sciences (SPSS) version 20. The one-way analysis of variance (ANOVA) test
was used to compare groups based on normally distributed numeric variables, followed
by Bonferroni's post hoc test for pairwise comparisons. A two-way ANOVA test was employed
to investigate the influence of factors and their interaction. The chi-squared test
was designed to analyze qualitative data provided as counts and percentages. Each
p -value is two-sided. p -Values of < 0.05 were considered significant.
Result
[Table 1 ] and [Fig. 3 ] represent the data of the different shades between the groups. The highest mean
value was recorded in G4 (composite with SDF/KI, permanent teeth group) (3.763 ± 0.177),
followed by G3 (composite without SDF/KI, permanent teeth group) (3.608 ± 0.13), then
G2 (composite with SDF/KI, primary teeth group) (3.512 ± 0.236), with the least mean
value recorded in G1 (composite without SDF/KI, primary teeth group) (3.299 ± 0.097).
The difference between groups was statistically significant (p = 0.000). The post hoc test revealed that G3 was not significantly different from
G2 and G4.
Fig. 3 Mean chart illustrating the different modes of failure in different groups.
Table 1
Descriptive statistics and comparison between groups regarding shade difference [∆E ] (ANOVA test)
Groups
Mean
Standard deviation
Standard error
95% confidence interval for mean
Min
Max
F -value
p -Value
Lower bound
Upper bound
G1
3.299c
0.097
0.028
3.24
3.36
3.15
3.53
16.08
0.000
d
G2
3.512b
0.236
0.068
3.36
3.66
3.24
3.91
G3
3.608a,b
0.130
0.037
3.53
3.69
3.46
3.92
G4
3.763a
0.177
0.051
3.65
3.88
3.45
3.98
Abbreviation: ANOVA, analysis of variance.
Note: Significance level p ≤ 0.05. Post hoc test: Within the same comparison means with different superscript
letter are significantly different.
[Table 2 ] provides a summary of the findings. In deciduous teeth, the mean value in G1 was
23.96 ± 4.09, whereas G2 was 23.83 ± 7.16. The change was not statistically significant
(p = 0.941). In permanent teeth, the mean value in G3 was 37.97 ± 5, whereas in G4 was
37.97 ± 5.29. The change was not statistically significant (p = 0.988).
Table 2
Descriptive statistics and comparison of microtensile stress at maximum load (MPa)
(one-way ANOVA test)
Mean
Standard deviation
95% confidence interval for mean
Min
Max
p -Value within the same dentition
p -Value between all subgroups
Lower bound
Upper bound
G1
23.96b
4.09
22.27
25.64
18.76
32.43
0.941 ns
G2
23.83b
7.16
20.88
26.79
19.43
46.34
0.000*
G3
37.97a
5.00
35.91
40.03
32.10
49.15
0.988 ns
G4
37.97a
5.29
35.79
40.15
32.10
47.35
Abbreviations: ANOVA, analysis of variance; ns, non significant.
Note: Significance level p ≤ 0.05, sharing the same superscript letter are not significantly different.
* Significant, post hoc test.
The results are summarized in [Fig. 4 ].
Fig. 4 Mean chart illustrating the different modes of failure in different groups.
In deciduous dentition, G1 recorded 20% in types 1, 2, and 3, and 40% in type 4, compared
to G2's 0, 40, 0, and 60%. A statistically significant difference was detected (p = 0.005).
In permanent dentition, G3 reported 20% in each of types 1, 2, and 4 and 40% in type
3, compared to 0, 40, 60, and 0% in G4. The result showed a statistically significant
difference (p = 0.005).
Discussion
The current study examined the effect of composite restoration color after 2 weeks
of different dentin pretreatments (with or without SDF/KI) in primary and permanent
dentations.
In our study, we applied SDF/KI on artificial carious dentin. SDF can be very useful
in partial caries removal techniques due to its antibacterial activity in disinfecting
the cavity and inhibiting carious propagation and recurrent caries. Also, it was concluded
that SDF has the ability to remineralize the demineralized carious dentin.[8 ]
[14 ]
[15 ]
Also, 14 days were the period of storage of the specimen before applying composite
restoration to examine the delayed application of composite on SDF-treated dentin
and its effect on bond strength and color of the restoration.[16 ]
[17 ]
Moreover, the self-etch adhesive mode was selected in this study due to its mild acidity
to avoid the removal of silver ions in SDF with strong acid as in the etch rinse mode.
Also, the presence of 10-Methacryloyloxydecyl dihydrogen phosphate (MDP) enhances
the bond's strength and durability.[18 ]
The VITA, easy shade spectrophotometer, was used to analyze color because it uses
low light intensity to provide great data consistency and strong repeatability for
the whole visible spectrum of the laboratory system.[19 ]
The ΔE value of composite with SDF/KI indicates its ability to mask color, as there is no
significant difference between the control and SDF/KI-treated groups. However, the
primary teeth groups were less able to cover color than the permanent teeth groups,
which may be explained by the shorter clinical crown of primary teeth compared to
permanent teeth, which decreases the ability to mask the color of conditioning.[20 ]
The filler inside the composite, which improves color reflection and covers the color
of SDF/KI, may be the primary reason for the good masking effect ability observed
in the comparison of conditions between the composite restorations applied in this
study after SDF/KI and without SDF/KI.[11 ]
The second reason is that KI reacts with excess silver ions to generate silver iodide,
which is easily removed with water and has a yellowish-cream hue, which reverses the
staining effect of SDF.[21 ]
[22 ]
Moreover, the exposure to the light-curing system in the composite restoration group
minimized the creation of the dark metallic silver ions. The results of the present
investigation were consistent with those of Raafat et al, who suggested that zirconia-reinforced
glass ionomer may effectively cover SDF-induced discoloration.[21 ]
Regarding Microtensile Bond Strength
The primary goal of our current study was to evaluate the microtensile bond strength
and mode of failure of composite on two carious distinct dentitions with and without
SDF/KI-treated dentin.
There was no significant difference in delayed self-etch bonding after 14 days with
SDF/KI treatment versus untreated artificial carious dentin groups in both dentitions.
There are several possible explanations for this. The first explanation is that using
a saturated KI solution could improve dentin bonding. Several investigations revealed
that KI could react with residual silver ions and improve the bonding.[23 ]
Another explanation is that delayed self-etches bonding can restore bond strengths,
resulting in values comparable to those of untreated dentin. That may be due to delayed
bonding having improved Ag stability of SDF particles and remineralization of weak
demineralized dentin, which has significant consequences on bonding efficiency. Also,
artificial saliva gradually washed away alkaline compounds during storage, lowering
the negative buffering effect on functional acidic monomers. So, delayed bonding procedures
may be considered an approach to minimize the adverse impacts of SDF/KI treatment.[7 ]
[10 ]
[24 ]
Several researches have supported our findings, demonstrating that SDF does not affect
bond strength while increasing dentin microhardness. It has the potential to reduce
ion exchange during acid-base interactions.[23 ]
[24 ] However, Knight et al's investigation showed that leaving SDF/KI precipitates on
the dentin surface significantly lowered bonding strength.[6 ]
In this study, permanent teeth demonstrated greater microtensile bond strength than
deciduous teeth. Composites applied to permanent teeth have a greater μTBS compared
to primary teeth. That could be attributed to dentin's mineral content, as lower concentrations
of calcium and phosphorus were measured for primary teeth than permanent teeth.[25 ]
Regarding the Mode of Failure
Cohesive failure in resin composites exhibited the greatest failure score in the SDF/KI-treated
permanent dentin group; however, adhesive failure was absent from this group. Nevertheless,
considering that the adhesive layer is still intact, this suggests effective bonding.
Additionally, cohesive failure in dentin demonstrated the greatest failure score in
the SDF/KI-treated deciduous dentin group; however, adhesive failure was absent from
this group. The bond between the composite and the demineralized dentin was not weakened
by the SDF/KI application.[26 ] These findings coincided with the result of microtensile bond strength.
Our current study limitation is that it was performed in vitro using extracted teeth without stimulating the oral condition. Also, the dryness of
extracted teeth after the loss of pulp fluid pressure may collapse collagen fibers,
decreasing the bond strength, which may affect the accuracy of the result.
Conclusion
Within the limitation of this study, we conclude that,
Composite restoration has a positive effect in covering the color of dentin after
the application of the SDF/KI treatments.
Postponing the application of composite restoration for 14 days after SDF/KI treatments
can improve the bond strength
