|Year : 2009 | Volume
| Issue : 3 | Page : 139-144
A comparative study to evaluate the effect of fluoride releasing sealant cured by visible light, argon laers, and light emitting diode curing units: An in vitro study
UM Das, ST Prashanth
Department of Pedodontics and Preventive Dentistry, V. S. Dental College and Hospital, Bangalore, Karnataka, India
|Date of Web Publication||15-Oct-2009|
S T Prashanth
Department of Pedodontics and Preventive Dentistry, VS Dental College and Hospital, Bangalore
Source of Support: None, Conflict of Interest: None
| Abstract|| |
In Pediatric Dentistry, the use of pit and fissure sealant is one of the essential forms of prevention. Pit and fissure caries may be substantially decreased by obliteration of these developmental defects in occlusal, buccal and lingual surfaces with resin based dental sealants. Visible light-curing units, or LCUs, are an integral part of modern adhesive dentistry" They are used to cure resin based composite restoration materials, resin modified glass-ionomer and pit and fissure sealants, as well as to bond orthodontic teeth. Most recently, the argon laser has been approved for initiating the setting reaction with visible light cured-resins. Argon curing of resin materials has been show to enhance the physical properties and degree of polymerization of the resin, while reducing the polymerization time by 75 percent. The study is undertaken considering the inadequate research reports of regarding the comparison of curing ability using argon laser. LEDs and visible light as well as the resistant towards caries activity of the preventive fluoride releasing pit and fissure sealant cured by above mentioned curing units.
Keywords: Argon laser, pit and fissure sealants
|How to cite this article:|
Das U M, Prashanth S T. A comparative study to evaluate the effect of fluoride releasing sealant cured by visible light, argon laers, and light emitting diode curing units: An in vitro study. J Indian Soc Pedod Prev Dent 2009;27:139-44
|How to cite this URL:|
Das U M, Prashanth S T. A comparative study to evaluate the effect of fluoride releasing sealant cured by visible light, argon laers, and light emitting diode curing units: An in vitro study. J Indian Soc Pedod Prev Dent [serial online] 2009 [cited 2019 Jul 16];27:139-44. Available from: http://www.jisppd.com/text.asp?2009/27/3/139/57093
| Introduction|| |
Pit and Fissure caries remains the major portion of the caries experience in childhood and adolescence. Over the past several decades, a considerable reduction in caries experience has occurred in the Pediatric population.  In Pediatric Dentistry, the use of pit and fissure sealant is one of the essential forms of prevention. Pit and fissure caries may be substantially decreased by obliteration of these developmental defects in occlusal, buccal and lingual surfaces with resin based dental sealants. Curing of dental composites with blue light was introduced in 1970.  The source of blue light is normally a halogen bulb combined with a filter, so that blue light in the 410-500nm region of the visible spectrum is produced. Light in this range of wave length is most effectively absorbed by the Camphorquinone photo initiator that is present in the resin component of light activated dental composites".
Visible light-curing units, or LCUs, are an integral part of modern adhesive dentistry" They are used to cure resin based composite restoration materials, resin modified glass-ionomer and pit and fissure sealants, as well as to bond orthodontic teeth.
The most popular medium for delivery blue light has been halogen-based LCUs 
Adequate polymerization is a crucial factor in obtaining optimal physical properties and clinical performance of composite resin restorative materials (Bayne, Heymann and Swift, 1994; Ferracane, 1993). Problems associated with inadequate polymerization include inferior physical properties, solubility in the oral environment, and increased micro leakage with resultant recurrent decay and pulpal irritation.
Most recently, the argon laser has been approved for initiating the setting reaction with visible light cured-resins. Argon curing of resin materials has been show to enhance the physical properties and degree of polymerization of the resin, while reducing the polymerization time by 75 percent. 
A previous study examining the effect of argon laser curing of sealant material on microleakage resulted in unexpected and interesting findings. With argon laser cured sealants, the incidence of wall lesions were similar at lesion initiation, but significantly different, following lesion progression when compared with paired controls. An unexpected finding was that the lased surface of enamel adjacent to the sealant material showed significant reductions in lesion depths both at lesion initiation and progression periods, when compared with paired, control surface enamel. This apparent caries resistant phenomenon led us to present this study.
The study is undertaken considering the inadequate research reports of regarding the comparison of curing ability using argon laser. LEDs and visible light as well as the resistant towards caries activity of the preventive fluoride releasing pit and fissure sealant cured by above mentioned curing units.
| Materials and Methods|| |
Ninety sound non - carious human maxillary and mandibular premolar teeth, which were extracted for orthodontic purpose, were collected. The criteria for the tooth selection included intact buccal surface devoid of cracks from extraction Forceps, Free of caries and not subjected to any pretreatment chemical agents such as alcohol, formalin or Hydrogen peroxide. Curing lights used were Visible Light Curing Unit (3M ESPE), Argon Laser (Spectra Physics, Indian Institute Of Science) and LED Curing Unit (Bluedent LED). Other Material used are Fluoride pit and fissure sealant (FISSURIT- F), Acid resistant varnish (nail enamel), Synthetic saliva (20 mM NaHCO, 3mM NaH2 PO 4,1 mM CaC12. Ph- 7), Artificial caries medium (2.2 mM Ca, 2.2mM P04.5OmM acetic acid ph(3.95), and Polarized light microscope.
Teeth were divided into 3 groups of 30 each and Color coded
GROUP I is labeled with red color comprised of all 30 teeth that were filled with pit and fissure sealant (FISSURIT- F) and cured with conventional light cure unit (3M ESPE) for 40 seconds
GROUP II is labeled with blue color comprised of all 30 teeth that were filled with pit and fissure sealant (FISSURIT- F) and cured with L.E.D curing system (Bluedent LED) for 20 seconds.
GROUP III Is labeled with black color comprised of all 30 teeth that were filled with pit and fissure sealant (FISSURIT - F) and cured with Argon laser(Spectra Physics, Indian Institute Of Science) for 10 sec.
Curing devices used in the study
Halogen lamps are the most frequently used light sources for polymerization of dental materials. Their light is produced by an electric current flowing through an extremely thin tungsten filament. This filament functions as a resistor and is so strongly heated by the current that it emits electromagnetic radiation in the form of visible light. LED LAMPS
In contrast to halogen lamps, light emitting diodes (LEDs) do not produced Visible light by the heating of metal filaments, but by quantum-mechanical effects. In simple terms LEDs are a combination of two different semiconductors i.e. the "n-doped'" and "p-doped" semiconductors, "n-doped" semiconductors have an excess of electrons and "p-doped" semiconductors have lack of an electrons or "holes". When both types of semiconductor are combined and voltage applied, electrons from the n-doped and holes p-doped elements connect. As a result a characteristic light with specific wavelength range is emitted (450-480nm).
Argon laser has an active medium of Argon gas that is fiber optically delivered in continuous wave and gated- pulse modes. This laser has two emission wavelengths and both are visible to the human eye 488nm, which is blue in color, and 514nm, which blue-green in color.
The cavity preparation of depth 1 mm was placed without bevels on buccal surfaces of all 90 teeth [Figure 1]. This provided butt edge type of interface between enamel surface and the adjacent sealant without feather -edging of sealant material [Figure 2]. After a clean surface area was obtained, each tooth is acid etched with 37% phosphoric acid gel for 20 seconds, the solution was left undisturbed for 20 seconds, followed by 30-second water lavage to remove phosphoric acid and dried with oil and moisture free air stream. The dried surface was checked for a uniform dull frosty appearance of surface. The teeth were filled with fissure sealant (FISSURIT- F) and three groups were respectively cured with visible light (3M ESPEE), L.E.D curing system (Bluedent LED), and Argon laser (Spectra Physics, Indian Institute Of Science). An acid resistant varnish (nail enamel) was placed leaving a 1mm rim of exposed surface enamel adjacent to the sealant. The specimens were then thermo cycled (500 cycles at 5-50 C dwell time of 20 sees) in synthetic saliva, specimens were then suspended in an artificial caries medium for 14 days. Following lesions formation longitudinal sections per tooth were taken and examined with polarized light microscope. Photomicrography of the secondary caries lesions were projected on to digitized, computer interfaced tablet and the mean depths for primary lesions are determined and compared.
We used the Analysis of variance (ANOVA) to compare the values of the 3 different groups i.e. the 3 different lights used in this study. The ANOVA table gives us a p-value which is < 0.05 leading us to reject the null hypothesis Ho and conclude that there is a significant difference among the groups. Post-Hoc comparison among the groups is done using Bonferroni test. From this comparison it is evident that the mean difference is significant between the groups. There is no significant difference between conventional light and LED whereas there is a significant difference between LED and conventional light when compared with Argon Laser.
| Results|| |
There was considerable difference in lesion depth between conventional light and LED when compared with argon laser. The mean lesion depth was reduced by about one-third (p<.05) when Argon Laser polymerization was employed. The surface layer overlying the outer lesions was intact in the entire three polymerization group; these surfaces did not show erosions, cavitations or surface loss. The mean depth for the body of the lesion for Conventional Light is 139μm [Figure 3], LED is 127μm [Figure 4] and Argon Laser is 67μm [Figure 5]. The body of the lesion depth had been reduced by 51 % percent for those lesion exposed to Argon Laser irradiation when compared with the conventional light. The body of the lesion depth had been reduced by 47% percent for those lesion exposed to Argon Laser irradiation when compared with the LED [Figure 6].
| Discussion|| |
Light-curing dental materials that adhere to tooth structure have revolutionized modern restorative dentistry.  However, perfect adaptation should be obtained during the setting reaction of a material. Unfortunately materials such as resin composites do not meet this requirement, as the conversion of monomer molecules into a polymer network is accompanied with closer packing of the molecules, which leads to bulk contraction. This may lead to micro-openings developing between tooth structure and restoration. When these openings are significant and oral fluids and bacteria can penetrate, secondary caries and loss of restoration may eventually result.  As most composites contain camphorquinone as the photoinitiator, a substantial light intensity of approximately 470nm wave length is required for complete polymerization. Mills, Jandt and Ashworth found that a typical resin composite increments requires 16j/cm" of energy at a wavelength of 400-500nm for complete cure.  Therefore, an exposure for 40 seconds at 400 mw/crrT is needed. This same energy can also be achieved with an exposure of 800 mw/cm 2 for 20 sec or with 1200 mw/cm 2 for 10 seconds. The latter forms the basis of newer methods of curing, such as laser and plasma lights. Rueggerberg found that higher light intensities give rise to a greater degree of monomer conversion, resulting in improvement of physical and mechanical properties of resin composites.  The increase in conversion however associated with increase in polymerization shrinkage.
Adequate polymerization is a crucial factor in obtaining optimal physical properties and clinical performance of composite resin restorative materials (Bayne, Heymann and Swift, 1994; Ferracane, 1993).  Problems associated with inadequate polymerization include inferior physical properties, solubility in the oral environment, and increased micro leakage with resultant recurrent decay and pulpal irritation. 
Dental professionals have a variety of curing lights available to them, such as quartztungsten-halogen (QTH), plasma arc, laser and light emitting diode (LED). The relatively broad emission spectrum of QTH curing lights allows them to initiate polymerization of all known photo-activated resin based restorative materials. The principal output from these lamps is infrared energy with the generation of heat. Filters are used to reduce the heat energy to oral tissues and to provide further restriction of visible light to better correlate with narrower absorbance spectrum of photo-initiator. Finally, a sliver-coated dichroic reflector passes infrared energy out the back and reflects and focuses the light forward to provide a focal area of energy at a defined distance. Ultimately, 99.5% of the original radiation is eliminated. 
Despite their popularity, halogen technologies Light-Curing Units (LCUs) used to polymerize dental materials have several draw backs.  Halogen bulbs for example, have a limited life time (40-100hours).  Furthermore, the bulb, reflector and filter degrade over time due to high operating temperatures and the large quantity of heat which is produced during the duty cycles. This results in reduction of the LCUs curing effectiveness over time. The clinical implication is that with ageing LCU, light activated dental materials will be less well cured with poorer physical properties and an increased risk of premature failure of restorations-assuming no compensation for decreased LCU irradiance.
To overcome the problems inherent to halogen LCUs, solid state light emitting diode (LED) technology has been proposed curing dental materials. Rather than a hot filament as used in halogen bulbs, LEDs use junctions of doped semiconductors (p-n junctions) for the generation of light. Under proper forward biased conditions electrons and holes recombine at the LED's p-n junction leading, in the case of gallium nitride LEDs, to the emission of blue light  . A small polymer lens in front of the p-n junction partially collimates the light. The spectral output of gallium nitride blur LEDs falls conveniently within the absorption spectrum of the camphorquinone photo initiator (400-500nm)' present in light activated dental materials, so that no filters are required in LED LCU. Furthermore, LEDs have an expected lifetime of several thousand hours without significant degradation of light flux over time.  Due to their superior conversion rate as well as their optimum spectral emission, this small battery powered and handy devices are most likely to shape next generation of curing lights. It would be favorable to investigate and compare them with the standard curing  light.
In our study, the body of the lesion depth had been reduced by 51% for those lesion exposed to Argon Laser irradiation when compared with Conventional light. These results were almost correlating to results of similar type of study conducted in 1993 where caries like lesion initiation and progression in sound enamel following the Argon Laser irradiation showed body of the lesion depth had been reduced by 41%.  Results of our study indicate "Argon laser polymerization creates an additional level of protection against secondary caries formation in surface enamel adjacent to a restoration and along the restoration-enamel interface".
Argon laser polymerization creates an additional level of protection against secondary caries formation in surface adjacent to a restoration and along the restoration-enamel interference. Although the exact mechanism of caries resistance with Argon Laser is not known. The most likely mechanisms that may contribute to Laser induced caries resistance are:
- Alteration in the composition of mineral phases with loss of water, resulting in decreased enamel solubility. 
- Micro spaces created in the mineral structure, provides a means for trapping calcium, phosphate and fluoride ions released during mineralization, with these micropores acting as sites for re-precipitation.
- Enhanced uptake of fluoride, calcium and phosphate from endogenous and exogenous sources. In particular, the affinity for fluoride may result in redistribution of fluoride to root and enamel surfaces during demineralization. facilitating re-precipitation of the mineral phases into the tooth surface
- Decreased permeability to acids due to protein denaturation and swelling within enamel pores resulting in vitro caries inhibition''.
- Other mechanisms for caries prevention with laser treatment include reduction in organic and carbonate content of hydroxyapatite, reduction in lattice strain within hydroxyapatite 4'5,6.Laser irradiation of enamel and root surfaces allows for more reactive surface that absorbs fluoride to a greater level than nonlased tooth structure. Acid dissolution of tooth structure is affected by fluoride and laser irradiation alone, as well as the combined utilization of these two caries protective modalities.
| Conclusion|| |
Argon laser polymerization of fluoride-releasing, pit and fissure sealant provided a greater degree of protection against an artificial cariogenic challenge and resulted in significant reductions in primary surface lesion depth when compared to visible light and LED polymerization.
In vitro caries resistance may be enhanced by argon laser polymerization and would appear to appear to impart an additional level of caries protection when used in concert with fluoride releasing sealant
Due to their superior conversion as well as to their optimum spectral emission these small, battery powered and handy devices are most likely to shape the next generation of curing light.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
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