Vol. 12, No. 1 - Jan - June 2009 J. Baqai Med. Univ.

REVIEW ARTICLE Use of Different Light-Curing Units in Setting of Dental Restorative Materials 1 2 2 2 Kefi lqbal , Iqbal Ahmad , Muhammad Ali Sheraz , Sofia Ahmed , Mohammad Aminuddin2 and Tania Mirza2

ABSTRACT The resin based filling materials were introduced in dentistry at the end of the 1940s. Poor color stability, low stiffness, lack of adhesion to tooth structure were the major drawback of this class of restorative material. Polymerization shrinkage is one of the challenges wh1th needs improvement of this material to many methods were developed. Light curing units which were the major breakthrough and the energy efficiency of the different light sources have also been discussed.

KEYWORDS: Dental light curing units, Light emitting diodes, Resin composites, UV light, Quartz Tungsten Halogen light units.

INTRODUCTION benzoin methyl ether into free radicals, without the The restorative materials have been used in dentistry incorporation of tertiary amines, thus responsible for 5 for a very long time. One of the first aesthetic restorative the polymerization of composite resin • In this way, material introduced in 1873 by Thomas Fletcher was only one paste of composite was necessary and 1 silicate cement . This cement did not become popular polymerization did not start until it was activated by until the early 1900s. The main advantage of silicate the UV light. Along with the advantages of UV light, cements as it superior aesthetic properties and the there were some serious drawbacks associated with release of fluoride, however, it was only partly soluble the UV light-curing systems. The spectral distribution 2 in the oral cavity • Resin-based materials were of UV light it may cause damage to the eye and may introduced in dentistry at the end of the 1940s. Besides burns soft tissue. The depth of cure was limited because 5 with their popularity, the disadvantages were also of high light absorption in the dental resin composite • associated with this class of direct restorative materials, such as, polymerization shrinkage up to 20 - 25%, Glass-Poly (alkenoate) dental cements, commonly poor color stability, low stiffness and lack of adhesion known as glass ionomer cements (GICs) are set by an 3 to the tooth structure • acid-base reaction between polymeric acid typically a polyacrylic acid (PAA), and an acid degradable glass The activation of resin restorative materials, several known as "Bioactive glass". It is a generic term for a types and designs of light activation unit are available group of silicate glasses which have a highly disrupted

for initiating the polymerization of light-activated structure (consisting of SiO2 silica chains with a large materials. The conventional type of blue visible light number of non-bridging oxygens - two per activation unit was introduced around 1970s. It is silicontetrahedron)6. Control over the reaction rate is' 7 based on light produced by quartz tungsten halogen often achieved by the addition of tartaric acid • In 4 bulb (QTH) • For the early dental resin composites, more recent developed resin-modified glass-ionomer polymerization was initiated by mixing of the two cements there is also a light-catalyzed free radical pastes of different component, in which one paste polymerization reaction of a hydrophilic methacrylate­ 9 contained an activator, such as a tertiary amine. This based monomer8· . was used to split the initiator, usually benzoyl peroxide, which was found in the second paste. The UV light, Literature Review with a wavelength of approximately 365 nm, splits Different types of light curing units are used in 1: Baqai Dental College and 2: Baqai Institute of Pharmaceutical Sciences, Baqai Medical University, Toll Plaza, Super Highway, Gadap Road, Karafhi, Pakistan • Vol. 12, No. 1 - Jan - June 2009 J. Baqai Med. Univ. dentistry. It can be divided according to the light source device play an important role to facilitate the cross and/ or curing mode used. The first light source used infection control; It may also reduce the thermal 4 for the polymerization was. UV light, which was changes because it emits no heat during use • They produced from a mercury discharge lamps. have a limited and sp~cific spectrum of light output, which is responsible for the activation of initiators 4 Quartz Tungsten Halogen light units (QTH). In this in a resin composite curi~g • curing unit the bulb is filled with the mixture of gases like halogen, iodine or bromine. It also contains a Factors affecting the degree of cure tungsten filament which glows and produces a very The irradiance of the curing unit, the exposure time, powerful white light when it is attached to an electrical the resin shade, the filler size, the filler load and the source, which is filtered to the range of blue light (400- distance between the light-tip and the resin composite, 10 18 500 nm) . The major demerits are the production of all affect the extent of cure . As light passes through heat, short life of the bulb, deterioration of the reflector the bulk of the restoration, its intensity decreases 11 12 and a filter, over the period of time • . The greatly, thus decreasing the curing efficacy and limiting 2 19 recommended density of QTH was 300400 mW/ cm the depth of cure . Inadequate cure hampers physical which were adequately enough to cure a 2 mm and biological properties of the resin composite 20 22 increment of dental resin composite during a 40 restoration - . In certain clinical situations there is 13 second light cure . unavoidable a distance between the light-tip and the surface of the composite. It has been shown that the High intensity light-curing unit was introduced in mean distance of the light-tip to the gingival floor of 23 1990s in which the light is generated by high voltage a Class II molar cavity is 6.3 mm . between two tungsten electrodes, separated by a small gap. This produced the gaseous environment (Xenon) DISCUSSION and created a conductive gas known as plasma, as Most of the dentists preferred visible-light activated plasma arc (PAC) light unit. The curing unit was resins adhesive for decades. However due to new responsible to produce densities more than 2000 development in recent years the resin cements are mW/cm 2 and was marketed with recommended curing utilized in luting cast ceramics, full por~elain, and 14 times of 3 seconds per increment of resin composite . veneer restorations that are thin or translucent to Only 2 or 3 seconds of exposure is required with permit visible light penetration and thus polymerize plasma arc lamps to achieve the same depth of cure the cement. Light-activated cements may be radiolucent obtained with a 30 second exposure to a typical QTH and are usually provided in various shades since they 24 lamps. The Argon Laser is recommended as a device are utilized in esthetically demanding situations . for the curing of composite resin at 2-mm depth for five second argon laser exposure1s. There are two Quartz-tungsten-halogen lights (QTH) are the most potential advantages of the laser light, firstly that the frequently used curing units to photoactivate resin­ 24 26 radiation is produced in a narrow wavelength based dental materials - . Since the introduction of distribution and secondly that the lasers are capable LED, studies have been made on the influence of these of emitting a collimated beam of radiation which may lights on the mechanical properties of resin-based 27 31 travel a large distance without dispersing. This device restorative materials - . However, few studies are is costly4. known in literature regarding the influence of LED lights on the mechanical properties of resin-modified 32 33 Light emitting diodes unit (LED) was intro4uce in the glass ionomer cements (RMGIC) and compomers , . late 1990s. LED has a narrower wavelength spectrum and requires no filters 16 as compared to the quartz Conventional halogen bulbs, argon laser and xenon tungsten halogen light units. It has therefore; many arc lights are currently used in clinical practice. A new advantages over the QTH, as it produces less heat technological approach for curing light activated oral and more appropriate power densities to cure the biomaterials has been presented. The new light curing resin composites. This is more energy efficient and unit (LCU) is based on blue light-emitting diode the power densities are now available up to (LED). The main potential benefits of LED LCU 21 7 900mW / cm . The advancement of a design in a technology such as, long lifetime of LED LCU (several Vol. 12, No. 1 - Jan - June 2009 J. Baqai Med. Univ. thousand hours), lack of filters or cooling fan no 10. Meyer, G.R., Ernst, C.P., Willershausen, B. decrease of light output over lifetime with resulting Decrease in power output of new light-emitting consistent and high quality of material curing is diode (LED) curing devices with increasing required. Simple depth of cure experiments of dental distance to filling -surface. J. Adhes. Dent., 2002; composites cured with LED technology show 3:197-204. promising results. The comparison of em:rgy efficiency 11. Shortall, A.C, Harrington, E. Temperature rise among different light sources depends on the relation during polymerization of light-activated resin between power input and light output. For QTH the composites. J. Oral. Rehab., 1998; 25: 908-913. energy efficiency is 0.7%, for PAC 0.2%, for Laser 12. Tarle, Z., Meniga, A ., Kne evic, A., Sutalo, J., 34 0.02% and for LED 13% . The reaction acceleration, Ristic, M., Pichler, G. Composite conversion and deceleration, and maximum rate were dependent upon temperature rise using a conventional, plasma arc, 35 the irradiance of the curing light source • Because of and an experimental blue LED curing unit. J. this high energy efficiency of the LED and the absence Oral. Rehab., 2002; 29: 662-667. of a fan, the LED units are not as energy consuming 13. Rueggeberg, F.A., Caughman, W.F, Curtis, J.W as QTH units. The microhardness values, when a Jr. Effect of light intensity and exposure duration LED light was used, varied depending on the on cu.re of resin composite. Oper. Dent., 1994; 36 restorative material tested . 19: 26-32. 14. Peutzfeldt, A., Sahafi, A., Asmussen, E. CONCLUSION Characterization of resin composites polymerized The latest generations of LED curing units were able with plasma arc curing units. Dent. Mater., 2000; to cure resin composites to a higher degree of 16: 330-336. conversion than the control QTH unit. 15. Rueggeberg, F.A., Ergle, J.W., Mettenburg, D.J. Polymerization depths of contemporary light­ REFERENCES curing units using microhardness. J. Esthet. Dent., 1. Albers, H. F. Tooth-colored restoratives. Principles 2000; 12: 340-349. and techniques. 9th ed., 2002, BC Decker, Inc, 16. Jandt, K.D., Mills, R.W., Bla,ckwell, G .B., Hamilton, London. Ashworth, S.H. Depth of cure and compressive 2. Bowen, R.L. Dental filling material comprising strength of dental composites cured with blue light vinyl silane treated fused silica and a binder emitting diodes (LEDs). Dent. Mater., 2000; 1: consisting of the reaction product of bisphenol 41-47. and glycidyl acrylate. US Patent, 1962; 3066 112. 17. Caughman, WF., Rueggeberg, F.A. Shedding new 3. Knock, F.E, Glenn, J.F. Dental materials and light on composite polymerization. Oper. Dent., methods. US Patent, 1951; 2558139. 2002; 27: 636-638. 4. Mc Cabe, J.F. and Walls, A .WG. (2008) Applied 18. Rueggeberg, F.A., Caughman, WF., Curtis, J.W., Dental Materials 9th Edition, Blackwell, U.K. Davis, H. C. Factors affecting cure at depths within 5. Philips, A. K. J. Science of Dental Materials, light-activated resin composites. Am. J. Dent., 2003; 11th ed., Elsevier Science, London. 1993; 6: 91-95. 6. Brauer, D.S., Karpukhina, N., O'Donnell, M.D., 19. Ruyter, I.E., Oysaed, H. Conversion in different Law, R. V., Hill, R. G. Fluoride- containing bioactive depths of ultraviolet and visible light activated glasses: Effect of glass design and structure on composite materials. Acta. Odontol. Scand., 1982; degradation, pH and apatite formation in simulated 40: 179-192. body fluid. Acta Biomaterialia, 2010; 6: 3275- 20. Caughman, WF., Caughman, G.B., Shiflett, R.A. 3282. Rueggeberg, F., Schuster, G. S. Correlation oi 7. Mc Lean, J.W. Cement cements. J. Am. Dent. cytotoxicity, filler loading and curing time of dental Assoc., 1990; 120: 43-47. composites.Biomaterials, 1991; 12:737-740. 8. Milosevic, A . Calcium hydroxide in restorative 21. Davidson, C.L., Feilzer, A.J. Polymerization dentistry, J. Dent., 1991; 19: 3-13. shrinkage and polymerization shrinkage stress in 9. Wilson, A.D., Austice, H.M., Pearson, G.J. Glass polymer-based restoratives. J. Dent., 1997; 25: ionomer cements: the current status, Asian J. 435-440. Aesthet. Dent., 1997; 5: 21-27. 22. Venhoven, B.A.M., de Gee, A.J., Davidson, C.L. J Vol. 12, No. 1 - Jan - June 2009 J. Baqai Med. Univ.

Polymerization contraction and conversion of light­ halogen-based light-curing units. J. Am. Dent. curing BisGMA-based methacrylate resins. Assoc., 2002; 133: 335-341. Biomaterials, 1993;14:871-875. · 30. Gomes, G.M., Calixto, A.L., Santos, F.A., Gomes, 23. Price, R.B., Felix, C.A., Andreou, P. Effects of O.M., D'Alpino, P.H., Gomes, J.C. Hardness of resin composite composition and irradiation a bleaching-shade resin composite polymerized distance on the performance of curing lights. with different light-curing sources. Braz. Oral. Biomaterials, 2004;18:4465-4477. Res., 2006; 20: 337-341. 24. Araujo, C.S, Schein, M.T., Zanchi, C.H., 31. Tolosa, M.C., Paulillo, L.A., Giannini, M., Santos, Rodrigues, S.A. Jr., Demarco, F.F. Composite A.J., Dias, C.T. Influence of composite restorative resin microhardness: the influence of light curing . materials and light-curing units on diametrical method, composite shade, and depth of ure. J. tensile strength. Braz. Oral. Res.,2005;19:123-126. Contemp. Dent. Pract., 2008; 9:43-50. 32. Cefaly, D.F., Wang, L., Mello, L.L., Santos, J.L., 25. Bouillaguet, S., Caillot, G., Forchelet, J., Cattani­ Santos, JR., Lauris, JR. Water sorption of resin­ Lorente, M., Wataha, J.C., Krejci, I. Thermal risks rhodified glass-ionomer cements photoactivated from LED- and high-intensity QTH-curing units with LED. Braz. Oral. Res., 2006; 20: 342-346. during polymerization of dental resins. J. Biomed. 33 . Okte, Z., Villalta, P., Garcia-Godoy, F., Garcia­ Mater. Res., 2005; 72: 260-267. · Godoy, F., Jr., Murray, P. Effect of curing time 26. Rueggeberg, F. Contemporary issues in and light curing systems on the surface hardness photocuring. Compend. Contin. Educ. Dent., of compomers. Oper. Dent., 2005; 30: 540-545. 1999; 25: S4-S15. 34. Ernst, C. P. Clinical aspects of photo­ 27. Bala, 0., Olmez, A., Kalayci, S. Effect of LED polymerization. Transact. Acad. Dent. Mater. and halogen light curing on polymerization of 2004;18: 105-117. resin-based composites. J. Oral. Rehabil., 2005;32 35. Wells-Gray, E.M., Kirkpatrick, S.J., Sakaguchi, :134-140. R. L. A dynamic light scattering approach for 28. Cavalcante, L.M., Peris, A.R., Ambrosano, G.M., monitoring dental composite curing kinetics. Dent Ritter, A.V., Pimenta, L.A. Effect of photo­ Mater., 2010; Article in press. activation systems and resin composites on the 36. Cefaly, D.F.G., Paes de Mello, L.L.C., Wang., L., microleakage of esthetic restorations. J. Contemp. Lauris, J. R. P., D'Alpino, P.H.P. Effect of Light Dent. Pract., 2007; 8 : 70~ 79. Curing Unit on Resin Modified Glass-Ionomer 29. Dunn, W.J., Bush, A.C. A comparison of Cements: A Microhardness Assessment. J. Appl. polymerization by light-emitting diode and Oral. Sci., 2009;17:150-154 .

•