Article_6_1_1
DENTAL MATERIALS
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL
Original Article
PROPERTIES OF LIGHT CURED PIT AND FISSURE SEALANTS
Maria Holroyd1a, Nicoleta Ilie1b *
1
Department of Operative Dentistry and Periodontology, University Hospital, Ludwig-Maximilians University Munich, Goethestr. 70, D-80336 Munich,
Germany
DDS, PhD Student
a
Dipl Eng, PhD, Professor
b
ABSTRACT DOI: https://doi.org/10.25241/stomaeduj.2019.6(1).art.1
Introduction: The study aimed to perform comparative measurements on the effect OPEN ACCESS This is
an Open Access article under
of exposure time and exposure distance on the micro-mechanical properties Vickers the CC BY-NC 4.0 license.
hardness (HV) and indentation modulus (E) of light cured, resin-based pit and fissure Peer-Reviewed
sealants. Article
Material and Methods: Thirteen pit and fissure sealants were selected. Combinations of Citation: Holroyd M, Ilie N. Effects
three clinically relevant exposure times (10, 20, 40 s) and two, fixed sample - light source of exposure time and exposure
exposure distances (4 and 7 mm) were tested. The HV and E of each group (n = 6) were distance on the micro-mechanical
properties of light cured pit and
measured with an automatic hardness indenter. Data were analyzed by a multi-variant fissure sealants. Stoma Edu J.
2019;6(1):9-17
analysis and partial eta-squared (ηp2) statistic.
Results: The factor “material” had the most significant influence (significance level α ≤ Received: January 21, 2019
Revised: February 12, 2019
0.05) on the measured micro-mechanical properties E and HV as shown by a ηp2 statistic Accepted: February 19, 2019
(ηp2 = 0.939 and 0.927 respectively). The factor “exposure time” had a significant but Published: February 21, 2019
moderate influence on both material properties E and HV (ηp2 = 0.297 and 0.084) whereas Corresponding author:
a smaller but significant effect of the factor “exposure distance” was only observed for E Nicoleta Ilie, Dipl Eng, PhD,
Professor at the Department
(ηp2 = 0.049). of Operative Dentistry and
Conclusions: Properties E and HV are strongly influenced by the type of sealant. On the Periodontology, University Hospital,
Ludwig-Maximilians University
other hand, the exposure distance had a low influence on these, whilst the exposure time Munich Goethestr. 70
had a greater influence. Exposure time and to a lesser extent exposure distance have a D-80336 Munich, Germany
Phone: +49-89-44005-9412
significant effect on the micro-mechanical properties of pit and fissure sealants. Fax: +49-89-44005-9302
Practical Implications: We conclude these findings indicate exposure time to be more e-mail: nilie@dent.med.uni-
muenchen.de
significant when considering clinical application of these materials.
Copyright: © 2019 the Editorial
Keywords: Pit and fissure sealants; micro-mechanical properties; pediatric dentistry; Council for the Stomatology Edu
dental materials; curing. Journal.
1. Introduction sealants come in a wide range of formulations
Initial descriptions in the applicative use of pit and which bear direct relevance in their application in
fissure sealants were published in the late 1960’s the clinical setting [8]. For example, some sealants
[1] whilst retention rates of such sealants were are transparent whilst others are opaque and have
evaluated in the 1980’s, clearly demonstrating the a distinctly different coloration to the tooth e.g.
benefits and effectiveness of the treatment [2-5]. In white. Indeed, it has been demonstrated in clinical
many cases the placement of pit and fissure sealant studies that opaque sealants allow a more reliable
in a clinical setting is not clearly indicated. An clinical assessment of retention [9] whilst facilitating
America Dental Association (ADA) report published a significantly more accurate identification of sealant
in 2008 [6] gave a number of recommendations to treated teeth [10]. Sealants also have a wide spread
help dental practitioners with their decision making. variability in the degree of filler content.
This took into account not only the type of material, Sealant failure can typically be attributed to a
but also focused on placement techniques and number of factors that include multiple aspects
emphasized the importance of periodical caries risk of their clinical application to the tooth surface.
re-evaluation. How different pit and fissure sealant For example, adequate preparations to ensure the
formulations performed in clinical retention studies exclusion of moisture (saliva) [11] or appropriate
has been analyzed by conducting a broad meta- acid etching times that create favorable, sponge-like
analysis of published works [7]. This allowed two structures with greatly increased surface area [12] full
central statements to be drawn that conclude light stop. Such precautions and clinical diligence lead to
polymerizing materials offer the better combination increased micro-mechanical adhesion of the sealant,
of performance in measures of five-year retention and reduced marginal fissures. Inappropriate control
and practical ease of use in the clinical setting. of occlusion to antagonists are also a source of sealant
Modern, commercially available pit and fissure failure especially for materials that do not contain
Stomatology Edu Journal 9
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL PROPERTIES OF LIGHT
CURED PIT AND FISSURE SEALANTS
Original Article a) b)
Figure 1. Preparation of fissure sealant samples for micro-mechanical measurements: a) specimen preparation for grinding; b) grinding procedure
and device .
filler as these readily fail due to mechanical stress detrimental effect on micromechanical properties of
and abrasional forces [13,14]. Polymerization in resin light cured materials. Current hypothetical models
based, light cured dental materials is an important suggest that if the period between attaining the gel-
factor that determines the quality, effectiveness and point and the initiation of polymerization is too short,
longevity of the clinical restorations [15] – indeed in internal stress build-up is not allowed to dissipate
this respect pit and fissure sealants are no different by a process of material “flow” [20]. Interestingly,
from their other material counterparts. Typically, earlier research suggested that irradiation time and
polymerization will be affected by a number of irradiance level follow a simple reciprocal association
aspects that are influenced by a range of interacting [21,22]. This lead to the assumption that exposure
factors. These include, for example, the irradiance times of less than 5 s are adequate to produce a cured
and spectral character of the light curing unit, material with optimal micro-mechanical properties.
material specific traits and formulation such as color, However, in the literature it is argued that such a
opacity, filler properties and monomer composition, relationship is a too simplified model to describe
the irradiation time and method such as a soft start observed material and chemical behavior under such
polymerization program, absolute intensity level at conditions [19,21]. Given that, for other materials of
the material surface, or pulsed light mode. this class, the degree of cure as a function of the
LED technology has established itself as the exposure time or exposure distance between the
medium of choice in dental curing units and curing unit light guide exit aperture and sample has
most contemporary devices use this type of light an influence on their material properties, we chose
source. Typically, the peak emission is centered at in the current study to quantify how typical micro-
a wavelength (470 nm) that has been selected for mechanical properties vary with exposure time and
the optimal activation of camphor quinone [16]. exposure distance. For this purpose, a selection
Indeed, this is the most common photo-initiator of thirteen commercially available pit and fissure
substance employed in dental sealants. For an sealants were chosen (refer to Table 1 for details) and
extensive review of dental photo-curing please refer investigated. Two exposure distances were selected
to the publication by F. A. Rueggeberg [17]. The of 4 mm and 7 mm to simulate clinical conditions. 4
characteristics and efficiency of such devices was mm was chosen to represent a typical distance that
intensively investigated [18]. Interestingly for the is achieved when the aperture of the curing unit
purposes of this current study, based on the results rests upon the cusps of the molar tooth. The 7 mm
published by Rencz et al. [18], the light curing unit position represents a no contact position when the
Elipar Freelight 2 (3M ESPE) provided approximately curing unit aperture is held above, but close to the
70 and 40% of the incident irradiance (1400 mW/ tooth. The following null hypothesis was proposed
cm2) at an exposure distance of 4 mm and 7 mm and tested: Firstly, (a) that increasing the exposure
respectively. These values correspond to ca. 1000 distance between the light guide aperture of the
mW/cm2 at the 4 mm geometry and 600 mW/cm2 at curing unit and the sample surface would not affect
the 7 mm distances employed in the present study. the micro-mechanical properties. Secondly, (b) that
An irradiance of 1000 mW/cm2 is a value that has an increased exposure time would have no influence
been previously identified as a suggested upper limit on the micro-mechanical properties attained and
for the polymerization of resin-based composites thirdly (c) that the material employed does not
(RBCs). This is in part due to the photochemistry of influence the micro-mechanical characteristics.
the activator where conversion to the excited state
is not the rate limiting process, rather its conversion
and reaction (or decay) is kinetically limited. In 2. Materials and Methods
this case increasing irradiance levels lead to its Thirteen resin-based pit and fissure sealants (refer to
rapid saturation [19]. Furthermore, high irradiance Table 1 for details) were investigated by assessing the
levels (>1000 mW/cm2) have been shown to have a micro-mechanical properties by varying irradiation
10 Stoma Edu J. 2019;6(1): 9-17. http://www.stomaeduj.com
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL PROPERTIES OF LIGHT
CURED PIT AND FISSURE SEALANTS
Original Article
Table 1. Summary of the dental pit and fissure sealants compared in this study (Manufactures specifications).
Manufacturer
Brand Composition Curing
(LOT Nr.)
Matrix: Bis-GMA/ TEGDMA
3M ESPE Filler: n/a
Clinpro Light
(N333694) Fluorid: Yes
Light yellow
Matrix: n/a
Dentsply Filler: Siliciumdioxide
Delton Light
(111003) Fluorid: No
(White)
Matrix: Bis-GMA/ TEGDMA
Dentsply Filler: 53 % wt. Barium-Aluminium-F-Br-Silica-Glass
Delton FS+ Light
(100218) Fluorid: No
(White)
Matrix: PENTA/ DMAEMA/ DEGDMA
Dentsply Filler: St-Al-Fl-Silica Glas Light/ Chemical
Dyract-seal (0908001309) Fluorid: Yes (Compomer)
(White)
Matrix: Urethandimethacrylate
Filler: 43% wt. Mixture of hydrophilic and
Embrace Pulpdent hydrophobic materials Light
Wetbond (100218) Fluorid: Yes
(Yellow/white)
Matrix: Bis-GMA, UDMA
Voco Filler: 9.5% wt. Siliciumdioxide
Fissurit-F Light
(1012227) Fluorid: Yes
(White)
Matrix: Bis-GMA, TEGDMA
Voco Filler: 70% wt.
Grandio Seal Light
(1024382) Fluorid: Yes
(Yellow/while)
Matrix: Bis-GMA, TEGDMA
Ivoclar Vivadent Filler: n/a
Helioseal Light
(P46901) Fluorid: No
(White)
Matrix: Bis-GMA, TEGDMA
Ivoclar Vivadent Filler: n/a
Helioseal Clear Light
(P83091) Fluorid: No
(Transparent)
Matrix: Bis-GMA, TEGDMA, UDMA
Filler: 20% wt. F-silica-glass,
Ivoclar Vivadent
Helioseal F 21.5 % wt. Silica Light
(P60584) Fluorid: Yes
(White)
Matrix: n/a
DMG Filler: Ionomerglass Light / Chemical
Ionosit Seal (635691) Fluorid: Yes (Compomer)
(White)
Matrix: Methacryloyloxydecyldihydrogenphosphate
Kuraray Filler: <10 % wt.
Teethmate F1 Light
(00118C) Fluorid: Yes
(Transparent)
Matrix: Bis-GMA, Diurethandimethacrylate
Ultraseal XT Ultradent Filler: 58 % wt. Light
plus (B4S8F) Fluorid: Yes
(White)
Abbreviations: BisGMA - Bisphenol A dimethacrylate, BisEMA - Bisphenol A polyetheylene glycol diether dimethacrylate,
UDMA - Urethane dimethacrylate, TEGDMA - triethyleneglycol dimethacrylate, PENTA - Dipentaerythritol penta acrylate
monophosphate, DEGDMA - Diethylene Glycol Dimethacrylate, DMAEMA - N,N-Dimethylaminoethyl Methacrylate
Stomatology Edu Journal 11
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL PROPERTIES OF LIGHT
CURED PIT AND FISSURE SEALANTS
time (10, 20, or 40 s) and spacing between the
Original Article specimen and the curing unit light guide aperture
Table 2. Summary of the influence of factors material, exposure
distance and exposure time on the micro-mechanical properties
(4 mm and 7 mm). The sealants were chosen to indentation modulus (E) and Vickers Hardness (HV). All values are ηp2*.
form a representative selection of the commercially
Factor E HV
available types and compositions currently on the
market. Material 0.939 0.927
The irradiance of the tested curing units was
determined previously [18] by means of a calibrated Exposure Distance 0.049 …
fiber optic spectrally resolving radiometer equipped Exposure Time 0.297 0.084
with an integrating sphere (S2000, Ocean Optics,
USA) by considering the dimension differences * Only statistically significant (α ≤ 0.05) values are shown for each
property. The higher the value of ηp2, the greater the influence of
between the curing unit tip and the sample. the selected factor on the measured property.
Irradiances passed through a round screen with
an inner diameter of 4 mm (= dimension of cured Table 3. Summary of the influence of factors exposure distance and
samples) positioned at the center of the curing exposure time on the micro-mechanical properties indentation
modulus (E) and Vickers Hardness (HV) for each material tested. All
unit tip was thus calculated. At the present curing
values are ηp2*.
conditions the irradiance amounted 1000 mW/cm²
at an exposure distance of 4 mm and 512 mW/cm² at Exposure distance
Exposure time ηp2
an exposure distance of 7 mm. Transferred to radiant Material ηp2
exposure values (= Irradiance x exposure time), E HV E HV
the amount of light received by the materials at an
Delton FS+ 0.570 0.517 … 0.294
exposure distance of 4 mm was 10.0 J/cm², 20.0 J/
cm², and 40.0 J/cm² and 5.15 J/cm², 10.3 J/cm² and Ultra Seal XT+ 0.196 0.189 0.272 ...
20.61 J/cm² at a distance of 7 mm. Embrace
0.218 0.280 0.348
Wetbond
2.1. Universal hardness measurement Helioseal … … 0.656 0.581
Samples from each sealant material were generated
Helioseal Clear 0.513 0.432 0.289 …
using a rod-shaped mold of 2 x 5 mm and 2 mm
depth (Fig 1). The sealant was bulk filled directly into Helioseal F … … 0.426 …
the mold and the sample was immediately cured. Fissurit-F … 0.137 0.598 0.565
The upper and lower surface was covered with a
Grandio Seal 0.387 … 0.836 …
transparent matrix strip to ensure reproducible,
smooth flat surfaces in the resulting samples. Two Clinpro … … 0.376 0.266
custom made adaptors were used to vary the spacing Teethmate F1 0.588 0.311 0.740 0.783
between the curing unit (Elipar Freelight 2, 3M ESPE, Delton 0.184 … 0.496 0.213
ca. 1,400 mW/cm2, peak wavelength 460 nm, serial
Dyract-Seal 0.163 … 0.370 …
# 939820013826) light guide aperture (diameter 8
mm) and the sample mold at a fixed distance of 4 Ionosit-seal … … 0.815 0.486
mm and 7 mm. For each product, exposure time (10, * Only statistically significant (α ≤ 0.05) values are shown for each
20, 40 s) and exposure distance (4 mm and 7 mm) property. The higher the value of ηp2, the greater the influence of
six samples were produced (n = 6). After curing the the selected factor on the measured property.
sample was immediately removed from the mold,
the upper irradiated surface marked, then stored with a microscope to ensure no air bubbles were
for 24 hrs at high humidity (distilled water, 37°C). present. The test load cycle was applied at a constant
Prior to measurement each sample was fixed to a average velocity increasing from 0.4 - 500 mN,
glass slide and mounted in an automatic grinding held constant at 500 mN for 5 s and subsequently
machine (EXAKT 400CS Micro Grinding System decreasing from 500 - 0.4 mN. During this cycle the
EXAKT Technologies, Inc. OK, USA). Specimens were load and penetration depth of the diamond indenter
wet-ground with silicon carbide sand paper (grit (square pyramid, angle of opposing faces at apex =
size p2500 and p4000, LECO Corporation, USA) 136°) were continuously monitored to follow the
and polished with a diamond suspension (mean load-unload hysteresis.
grain size: 1 µm) to remove the oxygen inhibited Universal hardness is defined as the applied test
surface layer. Therefore, the grinding process was force divided by the apparent area of indentation.
controlled electronically, comprising a pre-grinding A conversion factor between universal hardness
of 100 µm with the abrasive paper p2500 followed and Vickers hardness was calculated and
by additionally 100 µm with p4000. The following implemented into the software from a multiplicity
polishing process lasted 2-3 minutes, until the surface of measurements stored in a database supplied
was shiny. All measurements of HV and E were by the manufacturer. In doing so, the results were
performed using an automatic hardness indenter documented in the more familiar Vickers hardness
(Fischer-scope H100C, Fischer GmbH, Germany). Five units. The indentation modulus (E) was calculated
measurements were made on each of the six samples from the slope of the tangent to the indentation–
per material and condition (total of 30 measurement depth curve at maximum force.
positions per condition, 6 conditions per material, 13
materials = 2340 measurements). The measurement 2.2. Statistical analysis
positions were randomly selected and inspected The results were assessed using a Generalized Linear
12 Stoma Edu J. 2019;6(1): 9-17. http://www.stomaeduj.com
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL PROPERTIES OF LIGHT
CURED PIT AND FISSURE SEALANTS
Model (GLM). A multi-variant analysis was performed and fissure sealants (see Table 1 for details). We
Original Article
for the factors “material”, “exposure distance” and investigated their micro-mechanical properties with
“exposure time” and partial eta-squared (ηp2) values respect to parameters clinically relevant to light
determined (significance level α ≤ 0.05). In addition activated curing. All experiments were executed
for each material the factors “exposure distance” and using an automatic hardness indenter and micro-
“exposure time” were assessed using a uni-variant mechanical parameters determined from cured
analysis with a ηp2 statistic. samples from each sealant material prepared under
controlled laboratory conditions. We tested whether
the three factors “material”, “exposure time” and
3. Results “exposure distance” had any significant influence on
For each material we measured the micro-mechanical the micro-mechanical properties of the sealants.
properties HV and E for each exposure time (10, 20, The optical properties of the material in question
40 s) and exposure distance (4 & 7 mm). The results play a role in the way in which curing light
of these tests are detailed in Tables 2-4. propagates through the sealant, both initially and
The influence of the parameters “material”, “exposure as the polymerization reaction progresses. In fact,
time”, and “exposure distance” were analyzed the results of this research clearly indicated that,
statistically and compared using a GLM with multi- not surprisingly, the material has the most profound
variant analysis performed allowing partial eta effect on the measured micro-mechanical values.
squared (ηp2) values to be determined (see Table 2 However, the relationship appears to be complex
for summary of values). The significance levels of and it is difficult to see a direct correlation between
these factors were all α ≤ 0.05, indicating that the the material composition and the E & HV values in
null hypothesis - that no effect on micromechanical the materials tested - with some exceptions – for
properties E and HV would be observed - could be example Grandio Seal has the highest level of filler
rejected for all parameters with the exception of the content consistent and returns the highest HV of
values for exposure distance. The greatest influence any tested material. The results of our present study
on the measured micro-mechanical properties was indicate that, regardless of the material, increasing
displayed by the parameter “material” across all the exposure time leads in general to a small but
properties measured (consistently the highest values significant increase in the E values. Interestingly we
of ηp2). A significant effect of the “exposure time” was found that for HV values the exposure distance had
seen in both of the measured parameters – in order no significant effect, whereas exposure time did –
of descending magnitude E, HV. For the parameter albeit less so than for E. Based on previous findings
“exposure distance” a statistical significance was [18], the difference in irradiance between the 4 and
observed in one of the two parameters – namely E. 7 mm positions is on the order of approximately 400
A detailed summary of all the statistical results on a mW/cm2 lower at the more elevated position for the
material by material basis can be seen in Table 3. It hand-held curing device employed in the current
details both of the measured parameters (E and HV) study. A simple conversion of the irradiance values
per material for both the factors exposure distance (mW/cm2) employed in this study to examine the
and exposure time. The table clearly shows that total energy equivalents delivered per cm2 (radiant
exposure time has a significant and higher effect exposure, J/cm2) shows that approximately the
than exposure distance in most analyzed materials. same total “dose” of light energy was applied under
The detailed results of the measurements of E and HV the following conditions: 4 mm 10 s (10 J/cm2) ≈ 7
values for all material and conditions are summarized mm 20 s (10.3 J/cm2) and 4 mm 20 s (20 J/cm2) ≈ 7
as mean values from 6 samples tested at five mm 40 s (20.6 J/cm2). Previous findings on the exact
different positions (Table 4). The measured E values same group of sealant materials with the same set
ranged from 2.34 GPa (Embrace Wetbond at 20 s and of variables [23] revealed that for a given sealant
7 mm) at the lower end to 9.70 GPa (Grandio Seal at material the degree of cure after 5 minutes was more
40 s and 4 mm) at the upper across all experimental strongly influenced by the exposure time rather than
parameters and materials. For HV the span of values the exposure distance. The rates of curing, reached
ranged from 11.28 N/mm2 (Embrace Wetbond, at 20 a maximum after ca. 5 seconds and remained
s and 7 mm) for the lowest to 71.20 N/mm2 (Grandio constant for ca. 15 s before slowing to exhaustion
Seal, at 10 s and 4mm) for the highest. (unpublished observations). Minor differences in
Closely examining E and comparing the 10 s and 40 s the final degree of the cure were typically observed
values at both the 4 mm and 7 mm exposure distances for each material. In the current study, a similar
reveals that the average difference is 0.5 GPa at 4 observation can be made on a per material basis
mm and 1.04 GPa at 7 mm. A similar inspection of respect to the E and HV values. Thus, at face value it
the values for HV reveals that typically the values would appear that the energy dose, when equivalent,
are reduced with increasing exposure time with few leads to similar micromechanical properties for a
exceptions - only 2 or 4 of the materials showed an given material. However, this applies, only for the
increase at either 4 mm or 7 mm exposure distances materials Embrace, Teethmate F and Delton. Previous
respectively. investigations with the degree of cure measurements
also revealed similar findings in this respect [23].
Thus, it would seem for a given material that if the
4. Discussion total amount of energy supplied is constant then
For this study we selected a representative cross similar micromechanical properties and degree of
section of thirteen commercially available pit cure are observed. This is despite variations in the
Stomatology Edu Journal 13
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL PROPERTIES OF LIGHT
CURED PIT AND FISSURE SEALANTS
Original Article Table 4. Summary of the results showing the measurements of micro-mechanical properties indentation modulus (E) and Vickers Hardness (HV) for each
material tested for each exposure distance and exposure time. All values are the mean of measurements on 6 samples (for each sample 5 positions were
tested) for each material and condition. The standard deviation is indicated in brackets.
Material Time (s) E 4 mm (GPa) E 7 mm (GPa) HV 4 mm (N/mm2) HV 7 mm (N/mm2)
10 7.35 (0.72) 6.30 (0.54) 49.39 (3.51) 45.65 (4.15)
Delton FS+ 20 7.90 (0.45) 6.07 (1.03) 48.46 (3.46) 37.71 (5.74)
40 7.42 (0.36) 6.34 (0.40) 45.95 (1.63) 39.58 (2.05)
10 6.46 (1.84) 6.26 (1.21) 39.89 (11.55) 39.50 (8.22)
Ultra Seal XT 20 6.22 (0.78) 8.88 (0.53) 35.02 (4.34) 49.33 (2.91)
40 7.57 (1.32) 8.72 (1.77) 42.02 (6.80) 48.73 (9.52)
10 2.86 (0.18) 2.80 (0.25) 15.51 (2.55) 14.20 (1.99)
Embrace 20 2.82 (0.21) 2.34 (0.24) 13.52 (1.16) 11.28 (1.10)
40 2.79 (0.14) 2.77 (0.12) 13.00 (0.64) 13.65 (0.60)
10 3.18 (0.17) 2.74 (0.43) 26.43 (3.33) 29.17 (3.03)
Helioseal 20 3.55 (0.05) 3.47 (0.16) 23.59 (0.41) 23.70 (1.76)
40 3.45 (0.09) 3.59 (0.09) 22.39 (0.67) 23.42 (0.14)
10 3.74 (0.05) 3.36 (0.08) 25.60 (1.32) 21.47 (1.44)
Helioseal Clear 20 3.63 (0.15) 3.57 (0.10) 23.83 (1.64) 22.56 (1.32)
40 3.75 (0.73) 3.63 (0.11) 24.53 (0.77) 23.69 (1.17)
10 4.88 (0.29) 4.28 (0.44) 27.86 (3.39) 27.38 (4.46)
Helioseal F 20 5.04 (0.25) 5.23 (0.24) 25.90 (1.96) 27.38 (2.28)
40 4.98 (0.36) 5.23 (0.31) 24.94 (3.21) 27.38 (2.85)
10 3.78 (0.81) 3.18 (0.41) 32.43 (5.41) 38.74 (3.84)
Fissurit F 20 4.40 (0.05) 4.21 (0.05) 29.87 (0.24) 29.90 (0.83)
40 4.40 (0.07) 4.42 (0.07) 29.40 (0.43) 29.05 (0.55)
10 8.12 (0.66) 6.39 (0.58) 71.20 (9.02) 67.82 (16.99)
Grandio Seal 20 9.61 (0.28) 9.42 (0.60) 67.40 (2.94) 71.07 (5.92)
40 9.70 (0.51) 9.36 (0.40) 65.65 (4.43) 63.25 (4.44)
10 3.84 (0.09) 3.80 (0.05) 24.13 (0.52) 23.91 (0.96)
Clinpro 20 3.98 (0.13) 3.92 (0.05) 25.25 (0.33) 24.58 (0.50)
40 3.95 (0.09) 3.89 (0.04) 24.04 (1.15) 24.15 (0.64)
10 3.50 (0.04) 3.05 (0.23) 26.32 (0.77) 34.70 (3.44)
Teethmate F1 20 3.66 (0.05) 3.53 (0.04) 25.67 (0.28) 24.05 (1.32)
40 3.67 (0.04) 3.57 (0.06) 25.33 (0.11) 24.26 (0.36)
10 3.52 (0.17) 3.15 (0.52) 28.67 (0.70) 31.40 (8.99)
Delton 20 3.90 (0.14) 3.59 (0.12) 27.51 (0.59) 27.79 (1.07)
40 3.81 (0.11) 3.87 (0.64) 25.76 (0.87) 25.62 (0.83)
10 4.80 (0.40) 3.06 (0.34) 31.47 (2.18) 22.91 (1.84)
Dyract Seal 20 3.85 (0.18) 4.10 (0.29) 22.91 (2.47) 26.97 (2.53)
40 4.31 (0.41) 4.81 (0.68) 25.18 (2.60) 28.61 (4.56)
10 4.49 (0.29) 4.74 (0.17) 33.55 (0.99) 38.43 (2.88)
Ionosit Seal 20 5.29 (0.19) 5.07 (0.19) 31.45 (2.30) 33.46 (1.35)
40 5.71 (0.10) 5.31 (0.18) 34.14 (1.16) 31.01 (1.65)
Material composition codes:
with filler
without filler
with Fluoride
without Fluoride
Compomers
14 Stoma Edu J. 2019;6(1): 9-17. http://www.stomaeduj.com
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL PROPERTIES OF LIGHT
CURED PIT AND FISSURE SEALANTS
way in which this energy is delivered (exposure gap that might provide a niche to bacteria. Hence,
Original Article
time or exposure distance) under controlled material shrinkage and adhesion to the target are
laboratory conditions. In contrast, in the materials more important than absolute hardness for example.
Delton FS+, Ultra Seal XT+ and Dyract-Seal, both Typically, filled resins have a higher viscosity and a
parameters HV and E evidenced significant higher different characteristic in their ability to flow into
values when at a comparable radiant exposure, and penetrate narrow spaces which may have an
the exposure time was higher (p < 0.001). influence on retention rates [25]. However, the filler
The statement above applies only for the lower has another significant influence on these sealants.
radiant exposure (10 J/cm²) in Helioseal and Helioseal Typically, filled sealants are more resistant to abrasion
Clear, while at a higher radiant exposure (20 J/cm²) meaning that not only occlusal control but also
values were statistical similar. For materials Helioseal occlusal adjustment must be routinely employed
F, Fissurit-F, Grandio Seal, Clinpro and Ionosit the when applying a filled sealant [13]. Potentially, this
above afirmations are valid only for the property E, makes the process more time consuming whilst it
while HV was similar within one radiant exposure. also excludes unqualified auxiliaries from preforming
The effect of similar radiant exposure at different the task.
curing time or exposure distance is thus material This probably leads to a significant impact on
dependent and cannot be related to the filler content. the number patients treated in some localities. In
Moreover, in the clinical situation other factors, general checking for occlusion anomalies is very
such as patient compliance, choice and handling important in pit and fissures treatments of this
of the equipment, lead to a recommendation to type, as the materials are generally not formulated
optimize such parameters for the chosen material. to withstand high biting forces and potentially fail.
Interestingly, research into the efficiency of light For the unfilled sealants the situation is more
activated polymerization has shown that this may forgiving and poor occlusal adjustment, although
reach saturation such that higher intensities or highly undesirable, is probably short lived as
exposure times no longer have any effect on the local occlusion anomalies are quickly worn within
material properties [19]. 24-48 hours [26] (provided the sealant is not
Furthermore, it has been suggested that too high lost completely or partially during this period!).
light levels have a number of detrimental effects Of course, successful sealant application is more than
on the polymerization reaction. The creation of the just materials science. In part the skill and knowledge
excited state of the photo-initiator species reaches of the practitioner paired with the appropriate
saturation as the kinetics of its decay and conversion application protocol are just as paramount in this
are essentially rate limiting. Hence, it takes time for respect [6].
a partial steady state to be reached in which the
photo-initiator can either be converted to a radical
initiator or recycled to its ground state. Too high 5. Conclusions
rates of initiator production can lead to increased The presented data allow rejecting all specified null
probabilities of mutual annihilation that result in hypothesis. It can therefore be concluded that:
reduced polymer chain length. Hence, this reduces • Micromechanical properties are significantly
network formation within the curing material influenced be the factor “material”. On the other
leading to poorer mechanical properties. Thus, hand “exposure time” has inverse effects on E
longer exposures to high intensity light sources may and HV and “exposure distance” only a minor
be counterproductive in this respect. It might also be effect on E.
speculated that the light transmission characteristics • Within the bounds of this study exposure
of the materials change during the process of time has a more significant effect on micro-
polymerization and that such modifications can also mechanical properties in comparison to
account for or contribute to these observations. In exposure distance.
composite materials a significant contribution to • On the basis of these findings under comparable
this is assigned to the differences in the refractive clinical conditions a curing time of at least 20 s
index of the individual components and the way at 4 mm is probably to be recommended for
that this relationship changes during the course the majority of the tested materials, providing
of polymerization and curing of the resin-based clinical conditions are comparable to those in
matrix [24]. In work previously published [23] we the described study.
have investigated how the degree of cure (DC) • Material has the most significant effect on the
after a 5-minute time course varies with the same measured properties. This suggests that for
set of experimental parameters and materials a given sealant brand individually optimized
described here. Again, as in the current study the curing protocols need to be employed.
factor material had the most significant influence
on DC, but a comparative correlation between
filler content and DC, for example, does not reveal Author Contributions
a distinct pattern. Thus, this would suggest that NI: designed the study, provided the infrastructure
for a given sealant material brand an optimized (devices, materials), developed the measurement
curing protocol should be followed. In respect to
methods, supervised the experiment, performed
the clinical function of pit and fissure sealants, the
more important aspect is the ability to form a tight statistics, drafted and critically revised the
seal and plug between tooth and resin without any manuscript. MH: performed the measurements,
Stomatology Edu Journal 15
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL PROPERTIES OF LIGHT
CURED PIT AND FISSURE SEALANTS
collected data, and wrote the manuscript. 13. Stach DJ, Hatch RA, Tilliss TS, Cross-Poline GN. Change in
Original Article occlusal height resulting from placement of pit and fissure
sealants. J Prosthet Dent. 1992;68(5):750-753.
[Full text links] [PubMed] Google Scholar Scopus
14. Tilliss TS, Stach DJ, Hatch RA, Cross-Poline GN. Occlusal
Acknowledgments discrepancies after sealant therapy. J Prosthet Dent.
Not applicable. 1992;68(2):223-228.
[Full text links] [PubMed] Google Scholar Scopus
15. Aravamudhan K, Floyd CJ, Rakowski D, et al. Light-emitting
diode curing light irradiance and polymerization of resin-
based composite. J Am Dent Assoc. 2006;137(2):213-223.
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Maria HOLROYD
DDS, PhD Student
Department of Operative / Restorative Dentistry, Periodontology & Pedodontics
Faculty of Medicine , Ludwig-Maximillians University of Munich
Munich, Germany
CV
Maria Holroyd attended the Ludwig-Maximillians-University in Munich where she took her graduation examinations and
qualified as a dentist in 2012. Since then she has worked as a dental practitioner and is currently finalizing her dissertation in
the department of Operative / Restorative Dentistry, Periodontology & Pedodontics in Munich to obtain her medical doctorate.
16 Stoma Edu J. 2019;6(1): 9-17. http://www.stomaeduj.com
EFFECTS OF EXPOSURE TIME AND EXPOSURE DISTANCE ON THE MICRO-MECHANICAL PROPERTIES OF LIGHT
CURED PIT AND FISSURE SEALANTS
Original Article
Questions
1. The Following statements are valid for commercially available pit and fissure
sealants:
qa. Opaque sealants allow a more reliable clinical assessment of retention;
qb. Only transparent ones are recommended, based on esthetical considerations;
qc. No filler content is identified;
qd. Only a universal, transparent shade is available.
2. Pit and fissure sealants are subdivided with respect to following particularities:
qa. Pit and fissure sealants are a unitary material category, with less difference among individual materials;
qb. Presence of filler, Fluoride, chemical composition;
qc. Low and fast curing materials;
qd. Amount of light they need for polymerization.
3. It has been observed in pit and fissure sealants that:
qa. Exposure distance had a low influence on their mechanical properties;
qb. Exposure time has a low influence on their mechanical properties;
qc. The properties of the materials are not influenced by the way they are curing;
qd. The filler content and not the amount of light the materials receive is important.
4. What is clinically recommended for pit and fissure sealants?
qa. Optimized curing protocols need to be employed, but a curing time of at least 20 s is recommended for
the majority of the tested materials;
qb. 5 s of curing are considered sufficient, particularly in non-cooperative children;
qc. A curing time of at least 60 s;
qd. The exposure time has no influence on the final properties.
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Stomatology Edu Journal 17