journal of dentistry 41 (2013) 1222–1228

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Effects of exposure time and exposure distance on the degree of cure in light-activated pit and fissure sealants Maria Holroyd, Nicoleta Ilie * Department of Restorative Dentistry, Dental School of Ludwig-Maximilians-University, Goethestr. 70, 80336 Munich, Germany

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Objectives: The study aims to measure and compare the effect of different exposure times

Received 12 July 2013

and exposure distances on the degree of cure (DC) of light hardening resin based pit and

Received in revised form

fissure sealants.

28 September 2013

Methods: A representative selection of 13 commercial sealants brands was chosen. DC of

Accepted 2 October 2013

each material (n = 6) was measured in real-time by Fourier transform infrared spectroscopy (FTIR) at three clinically relevant exposure times (10, 20, 40 s) and two fixed exposure distances (4 mm and 7 mm) between sample and light source. Data were analyzed by a


multi-variant analysis and partial eta-squared statistic.

Pit and fissure sealants

Results: Factors ‘‘material’’, ‘‘exposure time’’ and ‘‘exposure distance’’ had a significant

Degree of cure

influence on the DC across all materials (h2p ¼ 0:927; 0:774 and 0.266 respectively) with

Exposure time

‘‘material’’ and ‘‘exposure time’’ showing the strongest effect (significance level a  0.05).

Exposure distance

In general, an increased exposure time and reduced exposure distance between sample and light source led to increased DC for all the materials. Conclusions: Degree of cure is influenced significantly by the brand of sealant and by exposure time. In some cases it is found that DC is also affected significantly by the exposure distance. Clinical significance: On the basis of this study, an exposure time of at least 20 s and a maximum exposure distance of 4 mm between curing unit and material surface is recommended. # 2013 Elsevier Ltd. All rights reserved.



Pit and fissure sealants are resin based materials for which an appropriate polymerization protocol is important in determining optimal clinical performance.1 In which regard, a number of factors are relevant including the light-curing unit, (LCU, irradiance and spectrum), exposure time and method (soft start, high intensity level, pulsing, exposure distance) as well as material specific traits and

formulation (colour/opacity, filler and monomer composition). However, although pit and fissure sealant is a related class of substance to resin based composite (RBC) the former fulfil a different clinical purpose thus placing a unique set of requirements on their material properties. Typically, these relate to the structural morphology of the fissures found in the permanent dentition that has its origin in their pre-eruptive development. Anatomically these fissures are between 0.005 and 0.2 mm wide but up to 1.2 mm in depth with a variable

* Corresponding author. Tel.: +49 89 5160 9412; fax: +49 89 5160 9302. E-mail address: [email protected] (N. Ilie). 0300-5712/$ – see front matter # 2013 Elsevier Ltd. All rights reserved.

journal of dentistry 41 (2013) 1222–1228

cross sectional form (U-form, V-form, ampule-form). An ideal sealant must therefore be able to flow easily into and fill these poorly accessible apertures and upon hardening form a tight seal, perfectly plugging the fissure. No cleft should be left at the perimeter that could be populated by pathogens. Dental sealants are applied to the fissures such that there is generally no direct contact between the sealant and the opposing molars. Thus, it is not first and foremost a priority that the sealants withstand biting forces like other restorative materials. Hence, sealant viscosity and shrinkage behaviour need to be optimized to these tasks while allowing a rapid and easy application in the clinical setting. Modern dental light curing units are based on LED (light emitted diode) technology where the peak emission wavelength of the diode may have been selected to correspond with the band excitation maximum for the activation of camphorquinone.2 Rencz et al.3 recently investigated the efficiency of such devices for curing RBCs and came to the conclusion that whereas very short exposure times (5 s) might be adequate for the material surface, it is necessary to use times of 20 s when a thickness of 2 mm or more is to be treated. They also examined the relationship of irradiance (mW/cm2) as a function of distance from the light guide output of several curing units (including the model used in the current study). With the exception of one prototype design all the commercially available models displayed similar characteristics in the rate at which irradiance decreased as a function of distance. The clinical performance of pit and fissure sealants has been the subject of a number of reviews.4,5 In 2008 an American Dental Association (ADA) Council on Scientific Affairs analyzed systematic reviews on pit and fissure sealants with the aim of resolving a number of questions in regard to the clinical use of pit and fissures. The ADA panel of experts drew a number of conclusions stating that the use of resin based sealants on the permanent molars of children and adolescents is an effective method of carries reduction: Typically, in children and adolescents rates of caries reduction ranged from 86% at 1 year to 78.6% at 2 years and 58.2% at 4 years. They also comment that the retention rates for pit and fissures on primary molars is between 74% and 96.3% at 1 year and 70.6–76.5% at almost 3 years. Interestingly, Simonsen and Neal4 also comment on a number of reviews relating to material traits. For example, a clinical benefit of fluoride containing pit and fissure sealants on rates of caries incidence has not been found. Likewise, it appears that filled sealants displayed lower retention rates when compared to their unfilled counterparts, possibly as a result of the better ability of the later to flow into and penetrate the fissure system on the target tooth. The first applications of resin based materials as pit and fissure sealants were reported in 1967.6 However, it was not until the 1980s that the caries prophylactic benefits of pit and fissure sealants were demonstrated in clinical half-mouth studies. Interestingly, although there have been a number of systematic reviews of pit and fissure sealants in clinical trials7–10 none of these looked at the effectiveness of different types of such materials on the retention rates. Recently, Ku¨hnisch et al.11 have reported the results of an extensive meta-analysis of the literature, which suggests that light polymerizing and auto-polymerizing materials had the best


five-year retention rates. Under consideration of the practical aspects of dental routine, the authors concluded that the faster and less error prone application of a light-polymerizing material should make them the medium of choice. The following null hypothesis was proposed and tested: Firstly, (a) that material employed does not influence DC. Secondly, (b) that an increased exposure time would have no influence on the DC values attained and thirdly (c) that increasing the exposure distance (=distance between the light guide aperture of the curing unit and the sample surface) would not affect the DC values reached.


Materials and methods

DC was measured for 13 resin based pit and fissure sealants (Table 1) for three exposure times (10, 20, or 40 s) and two exposure distances (4 mm and 7 mm), respectively, in a (13  3  2) independent design (n = 468). Sealants were chosen to form a representative selection of the commercially available types and compositions currently on the market. Ten of these were light cured, two were dual-hardening while one was self-curing.


Degree of cure measurements

DC was investigated using a fixed geometry sample mould that simulated a sample thickness of ca. 1 mm. Two custom made adaptors were used to vary the exposure distance between the LCU (Elipar Freelight 2, 3M ESPE, 1400 mW/cm2, peak wavelength 460 nm, serial # 939820013826) light guide exit aperture (diameter 8 mm) and the sample mould at fixed distances of 4 mm and 7 mm. The adaptors also ensured that the light guide was centred directly over the sample such that the surface of the irradiated material and the face of the light guide exit aperture were parallel. Each sealant was added to fill the mould and this then covered with a transparent matrix strip – care was taken not to trap any air bubbles. For each product, exposure time and exposure distance six samples were tested (n = 6). The mould was open at the bottom such that the sealant resin sat directly on the attenuated total reflectance (ATR) accessory of a Fourier transform infrared (FTIR) spectrometer (Nexus, Thermo Nicolet, Madison, USA). DC was measured in real time over a period of 5 min1 for each of the conditions described above as follows. The absorbance peak distance ratio of the of the carbon double bond at 1634 cm1 and an internal standard (IS) peak at 1608 cm1 was determined prior to irradiation of the sample, then during the entire time course of the measurement.2 The DC was then calculated according to the formula: DC% ¼ ½1  ð1634 cm1 =ISÞ cured=ð1634 cm1 =ISÞuncured  100

1 For the compomers Dyract Seal/Ionosit Seal and self-curing Delton 20 min was used for the measurement. 2 Note that for Embrace Wetbond/Dyract-Seal DC was calculated without an internal standard, since the aromatic double bound peak at 1608 cm1 is missing.


journal of dentistry 41 (2013) 1222–1228

Table 1 – Summary of the dental pit and fissure sealants compared in this study (Manufactures specifications). Brand name




Matrix: Bis-GMA/TEGDMA Filler: None Fluoride: Yes


Light yellow




Matrix: Unknown Filler: Silicon dioxide Fluoride: No




Delton FS+


Matrix: Bis-GMA/TEGDMA Filler: 53% Wt. barium-aluminiumfluoroboro-silicate-glass Fluoride: Yes







Light/chemical (Compomer)




Curing method


LOT number

Filler: Strontium-alumino-fluoro-silicate glass Fluoride: Yes Embrace wetbond


Matrix: Urethane dimethacrylate Filler: 43% Wt. mixture of hydrophilic and hydrophobic materials Fluoride: Yes






Matrix: Bis-GMA, Hexandioldimethacrylate, 7,7,9-Trimethyl-4,13-dioxo-3,14-dioxa-5, 12-diazahexandecan-1,16-diyldimethacrylate Filler: 9.5% Wt. silicon dioxide Fluoride: Yes




Grandio Seal


Matrix: Bis-GMA/TEGDMA Filler: 70% Wt. Fluoride: Yes





Ivoclar Vivadent

Matrix: Bis-GMA/TEGDMA Filler: None Fluoride: No




Helioseal clear

Ivoclar Vivadent

Matrix: Bis-GMA/TEGDMA Filler: None Fluoride: No




Helioseal F

Ivoclar Vivadent

Matrix: Bis-GMA/TEGDMA, UDMA Filler: 20% Wt. fluorosilicate glass, 21.5% Wt. silicon dioxide Fluoride: Yes




Ionosit Seal


Matrix: Unknown

Light/chemical (Compomer)



Filler: Ionomer glass Fluoride: Yes Teethmate F1


Matrix: 10-Methacryloyloxydecyl dihydrogen phosphate Filler: 1000 mW/cm2) irradiance values could be detrimental to the polymerization process and lead to poorer micromechanical properties.12 However, on the other hand, these finding are at odds with earlier studies that propose a simple reciprocal relationship between irradiance and exposure time.13,14 It is argued that this is an oversimplification – that ignores true material behaviour/chemistry and product specific characteristics – leading to the assumption that exposure times of

Effects of exposure time and exposure distance on the degree of cure in light-activated pit and fissure sealants.

The study aims to measure and compare the effect of different exposure times and exposure distances on the degree of cure (DC) of light hardening resi...
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