Summary:
SUMMARY
In vitro evaluation of composite surface sealers
Μaria Anagnostou , DDS, MS, DrMed
PhD Candidate, Department of Operative Dentistry, University of Athens, School
of Dentistry
Objectives:
The aim of the present study was to evaluate the chemical, mechanical, surface
and biological properties of composite surface sealers (CSS) with different
monomer composition. The null hypothesis was that no statistically significant
differences exist among the CSS in the properties tested.
Representative, regarding molecular composition, products of CSS were chosen.
Products tested were Biscover LV (BC) (Bisco, Inc., Schaumburg, IL, USA),
DuraFinish (DF) (Parkell, Inc., Edgewood, NY, USA), G-Coat Plus (GC) (GC
Corporation, Tokyo, Japan) and PermaSeal (PS) (Ultradent Products, Inc., S.
Jordan, UT, USA).
Materials and methods:
In vitro evaluation included analysis of chemical composition of monomers
contained in CSS products, evaluation of curing efficiency and measurement of
the extent of oxygen-inhibited layer. In respect to mechanical properties,
Vickers hardness and wear resistance using the toothbrush abrasion method and
the OHSU oral wear simulator were evaluated. Surface roughness, color and gloss
stability due to abrasion were also tested. Finally, biological evaluation
included toxicity and estrogenicity testing.
Analysis of molecular composition and measurement of the degree of conversion
(DC%) in the irradiated specimens was performed using micro-attenuated total
reflectance Fourier transform infrared spectroscopy (micro-ATR FTIR). Spectra
acquisition was performed on an FTIR spectrometer equipped with a micro-ATR
cell operated under the following conditions: 4000-600 cm-1 range, 4 cm-1
resolution, 20 scans coaddition, 2 mm diamond minicrystal of a single internal
reflection, ZnSe lenses and 2 μm depth of analysis at 1000 cm-1. For chemical
analysis, cylindrical specimens (O:8.0mm, h:1.5mm, n=5) were fabricated without
being polymerized. The same specimens were used for the evaluation of DC% after
being exposed for 20s to a halogen light-curing unit operated in standard
irradiation mode at 750 mW/cm2 light intensity. In this case, an uncured
specimen from each CSS tested was used as control material. The DC% of the
tested surfaces was calculated by the two frequency technique using the net
peak absorbance areas of C=C stretching vibrations at 1638 cm-1 as analytical
frequency and the aromatic CC stretching vibrations at 1605 cm-1 as
reference frequency according to the equation:
DC%= 100 X [1-AM (CC) X AP (C=C) / AM (C=C) X AP (CC)],
where, AM and AP are the net peak absorbance height ratios of the uncured and
cured materials, respectively. The peak absorbance height ratios were measured
from the curve fitted spectra at the region 1675-1550 cm-1 following peak
fitting with Peak-Fit software (v 4.12, SeaSolve Software Inc., Framingham, MA,
USA) employing the Pearson IV amplitude curve fitting (standard width per
spectrum), after baseline correction (2nd derivative zero algorithm).
For measurement of the oxygen-inhibited layer, the standard film thickness
method, employing 100-μm thick spacers was used. Briefly, a 10 μl drop of
uncured CSS was placed on a microscopic glass slide, transferred on the stage
of a light-transmission microscope (DM4000B, Leica Microsystems, Wetzlar,
Germany) and covered with a glass slip with two similar slips used as spacers
placed on each side. After wetting equilibrium occurred (~10 s), an uncured
material disk was created with a diameter of ~8 mm and resin-air contact
possible only at the disk periphery. Specimens (n=5) were light-cured as
described previously. The thickness of the oxygen inhibited layer was measured
at three different locations on each specimen, 5 min after irradiation, and
averaged to obtain a single value that was reported for a given specimen.
The specimens used for the degree of conversion measurements were further
utilized sequentially to measure hardness 10 min after light-curing. Another
series of specimens was prepared as described previously and tested following
one week storage in H2O at 37οC. Measurements were made on the top and the
bottom surfaces using a Vickers hardness tester (load 1 Kp, 10 s, 70Χ).
To evaluate morphological changes on the surface of CSS products upon abrasion,
resin composite specimens were constructed (8.0mm x 3.0mm x 2.0mm, n=4), which
were covered with each product of CSS, embedded in an epoxy ring mold and
placed in the toothbrush abrasion device (25000 cycles with toothpaste and
H2O). Specimens’ surfaces were examined, before and after abrasion, under a
stereomicroscope. Resin composite surface, polished with silicon carbide papers
(300-1000 grit), was used as control surface.
OHSU oral wear simulator was also used to evaluate the wear resistance of CSS.
Specimens were fabricated, as previously described (8.0mm x 3.0mm x 2.0mm,
n=4), using two of the CSS products (GC and PS), and mounted individually in a
two part cold-setting acrylic resin to produce cylinders compatible with the
chambers of the wear testing apparatus. Prior to wear testing the specimens
were scanned using the non-contact optical profilometer. Each of the specimens
was secured into an individual wear chamber of the wear simulator and food-like
slurry was added to each chamber. The antagonist consisted of steatite spheres
which were repeatedly driven along a 7 mm path at 20 N to simulate abrasion
wear. At the end of the 7 mm path a 90 N force was applied to simulate
attrition wear for 50,000 wear cycles at a frequency of 1 Hz (equivalent to 6
months wear in the oral environment). The tear drop wear facet produced on the
surface of each specimen was analysed using optical profilometry. The total
volumetric wear, surface roughness and maximum wear depth measurements were
determined using the non-worn areas around the wear facet as a reference.
The same specimens used in the toothbrush wear testing (8.0mm x 3.0mm x 2.0mm,
n=4) were used for color measurements. Color measurements were performed,
before and after abrasion with the toothbrush method, using a colorimeter. The
CIE-L*a*b* color system was used to determine the color differences by the
equation ΔΕ*= [(ΔL*)2+(Δa*)2+(Δb*)2]1/2, where ΔΕ* represents color change and
ΔL*, Δa*, Δb* represent change of parameters L*, a*, b*, respectively.
The same specimens (8.0mm x 3.0mm x 2.0mm, n=4) were also used for surface
gloss assessment. Gloss was measured, before and after abrasion with toothbrush
abrasion method, at 60o incidence angle with a calibrated infrared
gloss-meter.
For biological testing, cylindrical CSS specimens were fabricated (O:8.0mm,
h:1.5mm, n=4), which were immersed in sterile glass tubes with 50 ml of normal
saline (NS) at 37οC for 2 weeks. Then, specimens were removed from the glass
tubes and two solutions were prepared (1% και 5% v/v). Toxicity and
estrogenicity testing was performed based on standardized procedures. NS was
used as control material.
To evaluate statistically significant differences between mean values of DC%,
extent of oxygen inhibited zone, color and gloss changes among materials
tested, one-way analysis of variance (ANOVA) and Tukey’s multiple comparison
test were used.
Statistical analysis for Vickers hardness testing was done using three-way
analysis of variance (ANOVA) and Tukey’s multiple comparison test.
Statistical analysis for total volumetric wear, surface roughness and maximum
wear depth upon abrasion was performed using t-test.
Statistical analysis for biological testing was done using two-way analysis of
variance (ANOVA) and Tukey’s multiple comparison test.
Pearson correlation coefficient was used to identify correlations between DC%,
VHN and cytotoxicity.
Statistical analysis was performed using IBM SPSS Statistics 20 software at an
α: 0.05 significance level.
Results:
- Chemical analysis showed that, in addition to the information given by the
manufacturers, products BC, DF and GC contain aromatic monomers. In addition,
GC showed the presence of N-H compounds. BC showed the greatest contribution of
-OH s peak, followed by PS.
- PS demonstrated highest conversion compared to BC, DF and GC.
- Polymerization of products BC and GC resulted in lower extent of
oxygen-inhibited zone, compared to PS and DF.
- In respect to hardness testing, 10 minutes after polymerization, product GC
presented higher values of Vickers hardness, followed by BC and DF, and
finally, by PS, which presented the lower values of Vickers hardness. After
storage in H2O, products BC and DF presented the higher values of Vickers
hardness, followed by GC, while PS showed the lower values. For both storage
conditions (10 minutes after polymerization and after 1 week storage in H2O)
and for all products tested, there was no statistically significant difference
in hardness values recorded for top and bottom surfaces. Storage in H2O
resulted in significant decrease in hardness values for all products tested, in
both top and bottom surfaces. However, the most significant decrease was
recorded for products GC and PS.
- Examination under a stereomicroscope revealed the best topography in BC and
DF before, and in PS after toothbrush abrasion. Abrasion tracks were identified
in GC and DF, whereas BC showed porosity.
- Products PS and GC did not differ in total volumetric wear values, maximum
attrition depth and mean depth of the entire wear facet upon abrasion.
- GC resulted in rougher surface upon abrasion, compared to PS.
- The only statistically significant difference was found in ΔL* values between
GC and the rest materials, with the former being much brighter after toothbrush
abrasion. The differences in hue (Δa*) and chroma (Δb*) coordinates revealed a
red/yellow color shift for DF and a yellow color shift for GC following
toothbrush abrasion. The ΔΕ* values ranged from 0.67 to 1.11. The most stable
material regarding color changes was the PS.
- All products resulted in significant gloss reduction after toothbrush wear.
Although BC and PS before abrasion, had glossier surfaces compared to DF and
GC, they presented the highest gloss reduction. After abrasion, gloss values of
PS were still higher than those recorded for DF and GC.
- Regarding toxicity testing, at 1% v/v eluent concentration, only DF showed
statistically significant toxicity. However, at 5% v/v eluent concentration,
all sealers demonstrated cytotoxicity. More specifically, at 5% v/v eluent
concentration sealers BC και DF were the most toxic, while GC and PS revealed
moderate toxicity. Toxicity at 5% v/v eluent concentration was more intense
compared to1% v/v eluent concentration for all products tested. Finally,
estrogenicity was not recorded for any of the sealers tested.
Conclusions:
- The qualitative material compositions given by the manufacturers do not
correspond to the actual monomer composition of the products.
- PS demonstrated highest conversion compared to BC, DF and GC.
- BC and GC showed significantly lower extent of oxygen-inhibited layer
compared to PS and DF.
- In respect to hardness testing, 10 minutes after polymerization, product GC
presented higher values of Vickers hardness, followed by BC, DF, and finally,
by PS. After storage in water, products BC and DF presented the higher values
of Vickers hardness, followed by GC, while PS showed the lower values. Storage
in H2O resulted in significant decrease in hardness values for all products
tested, in both top and bottom surfaces, indicating a strong plasticization
effect. However, the most significant decrease was recorded for products GC and
PS.
- Examination under a stereomicroscope revealed the best topography in BC and
DF before abrasion and in PS after toothbrush abrasion.
- Optical profilometry showed significantly increased roughness values and
similar material volume loss, mean and maximum wear depth upon abrasion, in GC
compared to PS.
- ΔΕ* values ranged from 0.67 to 1.11. The most stable material regarding color
changes was the PS.
- Prior to toothbrush wear testing, BC and PS revealed the glossiest surfaces
among the materials tested. All products resulted in significant gloss
reduction upon abrasion. BC and PS presented the highest gloss reduction.
However, PS remained glossier than DF and GC after abrasion.
- Products BC and DF revealed increased cytotoxicity compared to GC and PS,
which demonstrated moderate toxicity. None of the products revealed
estrogenicity.
Significance:
The results of the present study showed statistically significant differences
in all material properties, among all the products tested. Therefore, the null
hypothesis should be rejected. The great variations in the chemical,
mechanical, surface and biological properties among the materials tested may
influence their clinical performance. For accelerated wear testing, where only
filled (GC) and unfilled (PS) materials were evaluated, the null hypothesis
should be partially rejected, because no statistically significant difference
was found in volume loss, maximum and mean wear depth.