In 2005, 116 million resin restorations were placed in the United States.1 Although evidence suggests that the longevity of these restorations can equal amalgam,2 some studies have shown that resin restorations are not lasting as long as they could.3-7 For example, a recent study from Sweden reported that resin restorations lasted an average of only 6 years.4 In another recent study, replacement rates were significantly higher for resin restorations than for amalgam.7 Why, then, the reduced longevity?
The success of resin restorations depends upon many factors, including technique, moisture control, polymerization shrinkage, the resin used, porosity within the resin and adequate curing of the resin. Dental resins that receive inadequate amounts of energy from a curing light, or energy at the wrong wavelengths, are inadequately polymerized.8,9 This adversely affects their physical properties,10-16 reduces bond strengths,12,13,17 increases wear and breakdown at the margins,14,15 and increases bacterial colonization. 18 All of these outcomes may lead to secondary caries, the major cause of failure of resin restorations. In addition, inadequately polymerized resins are less biocompatible.19-23
A recent study using new curing lights tested the ability of 20 dental professionals to deliver energy to simulated restorations.24 There was a large variation between operators, with 27% delivering less than 10 J/cm2 to a Class I restoration and 82% delivering less than 10 J/cm2 to a posterior Class V restoration. Thus, even with new curing lights capable of delivering sufficient energy, operator technique often prevented sufficient useful light from reaching the resin.
Four variables determine how long a curing light should be used to adequately cure a resin.
- Curing light design and condition. Dentists rely on hand-held dental radiometers to test the output of curing lights, but these radiometers are inaccurate and unreliable.25,26 Consequently dentists have no way of knowing how much energy they are delivering to their restorations. Instead, dentists must rely on manufacturer recommended curing times, but many of these include "fine print" details (e.g., shade, increment thickness, distance from light source to the resin, light output), the implications of which may not always be fully understood. In addition, reports indicate that curing lights in many dental offices deliver insufficient light output. This can result in inadequate polymerization even if the light is used for the recommended curing times.27-31
- Technique used by the operator. Some dentists deliver as little as 20% of the energy achieved by others using the same curing light in the same location.24 This happens because they do not use protective glasses, do not stabilize the curing light at 90° to the restoration and do not pay attention when light curing. Due to potential temperature increases during light curing,32-36 dentists cannot arbitrarily increase curing times to ensure that sufficient energy is delivered. Dentists can get a sense of this temperature increase by using the light on the back of their hand for the same time they use the light in the mouth.
- Type and location of the restoration. When curing lights are used for the same amount of time, significantly less energy is delivered to hard-to-reach restorations compared to more accessible restorations.24 Furthermore, if the curing light is used for the same amount of time for all increments, the resin at the bottom of a 6-mm deep proximal box will receive much less energy than the final increment.
- Energy requirement of resins varies greatly. Depending on the brand and shade, as little as 6 J/cm2 or as much as 36 J/cm2 is required to adequately cure a 2-mm thick increment of resin.37
To manage these 4 variables, dental professionals need more specific, consistent and accurate information on the energy required to adequately cure a resin restoration and how much energy they are actually delivering to the restoration. Delivering the energy required to achieve the properties intended by the resin manufacturers should allow these restorations to last longer.
- American Dental Association. 2005-06 survey of dental services rendered. Chicago (Ill.): ADA; 2007.
- Opdam NJ, Bronkhorst EM, Roeters JM, Loomans BA. A retrospective clinical study on longevity of posterior composite and amalgam restorations. Dent Mater. 2007; 23(1):2-8. Epub 2006 Jan 18.
- Kovarik RE. Restoration of posterior teeth in clinical practice: evidence base for choosing amalgam versus composite. Dent Clin North Am. 2009;53(1):71-6, ix.
- Sunnegårdh-Grönberg K, van Dijken JW, Funegård U, Lindberg A, Nilsson M. Selection of dental materials and longevity of replaced restorations in Public Dental Health clinics in northern Sweden. J Dent 2009;37(9):673-8. Epub 2009 May 4.
- Bernardo M, Luis H, Martin MD, Leroux BG, Rue T, Leitão J, et al. Survival and reasons for failure of amalgam versus composite posterior restorations placed in a randomized clinical trial. J Am Dent Assoc. 2007;138(6):775-83.
- DeRouen TA, Martin MD, Leroux BG, Townes BD, Woods JS, Leitao J, et al. Neurobehavioral effects of dental amalgam in children: a randomized clinical trial. JAMA. 2006;295(15):1784-92.
- Simecek JW, Diefenderfer KE, Cohen ME. An evaluation of replacement rates for posterior resin-based composite and amalgam restorations in U.S. Navy and marine corps recruits. J Am Dent Assoc. 2009;140(2):200-9; quiz 249.
- Halvorson RH, Erickson RL, Davidson CL. Energy dependent polymerization of resin-based composite. Dent Mater. 2002;18(6):463-9.
- Nomoto R, Asada M, McCabe JF, Hirano S. Light exposure required for optimum conversion of light activated resin systems. Dent Mater. 2006;22(12):1135-42. Epub 2006 Jan 4.
- Correr AB, Sinhoreti MA, Correr-Sobrinho L, Tango RN, Schneider LF, Consani S. Effect of the increase of energy density on knoop hardness of dental composites light-cured by conventional QTH, LED and xenon plasma arc. Braz Dent J. 2005;16(3):218-24. Epub 2006 Jan 12.
- Lohbauer U, Rahiotis C, Krämer N, Petschelt A, Eliades G. The effect of different light-curing units on fatigue behavior and degree of conversion of a resin composite. Dent Mater. 2005;21(7):608-15.
- Xu X, Sandras DA, Burgess JO. Shear bond strength with increasing light-guide distance from dentin. J Esthet Restor Dent. 2006; 8(1):19-27; discussion 28.
- Staudt CB, Krejci I, Mavropoulos A. Bracket bond strength dependence on light power density. J Dent. 2006;34(7):498-502. Epub 2006 Jan 18.
- Ferracane JL, Mitchem JC, Condon JR, Todd R. Wear and marginal breakdown of composites with various degrees of cure. J Dent Res. 1997;76(8):1508-16.
- Vandewalle KS, Ferracane JL, Hilton TJ, Erickson RL, Sakaguchi RL. Effect of energy density on properties and marginal integrity of posterior resin composite restorations. Dent Mater. 2004;20(1):96-106.
- Caldas DB, de Almeida JB, Correr-Sobrinho L, Sinhoreti MA, Consani S. Influence of curing tip distance on resin composite Knoop hardness number, using three different light curing units. Oper Dent. 2003;28(3):315-20.
- Kim SY, Lee IB, Cho BH, Son HH, Um CM. Curing effectiveness of a light emitting diode on dentin bonding agents. J Biomed Mater Res B Appl Biomater. 2006;77(1):164-70.
- Brambilla E, Gagliani M, Ionescu A, Fadini L, Garcia-Godoy F. The influence of light-curing time on the bacterial colonization of resin composite surfaces. Dent Mater. 2009;25(9):1067-72. Epub 2009 Apr 17.
- de Souza Costa CA, Hebling J, Hanks CT. Effects of light-curing time on the cytotoxicity of a restorative resin composite applied to an immortalized odontoblast-cell line. Oper Dent. 2003;28(4):365-70.
- Franz A, König F, Anglmayer M, Rausch-Fan X, Gille G, Rausch WD, et al. Cytotoxic effects of packable and nonpackable dental composites. Dent Mater. 2003;19(5):382-92.
- Knezevic A, Zeljezic D, Kopjar N, Tarle Z. Cytotoxicity of composite materials polymerized with LED curing units. Oper Dent. 2008;33(1):23-30.
- Uhl A, Völpel A, Sigusch BW. Influence of heat from light curing units and dental composite polymerization on cells in vitro. J Dent. 2006;34(4):298-306. Epub 2005 Sep 19.
- Sigusch BW, Völpel A, Braun I, Uhl A, Jandt KD. Influence of different light curing units on the cytotoxicity of various dental composites. Dent Mater. 2007;23(11):1342-8. Epub 2007 Jan 16.
- Price RB, Felix CM, Whalen JM. Factors affecting the energy delivered to simulated Class I and Class V preparations. J Can Dent Assoc. 2010;76:a94.
- Leonard DL, Charlton DG, Hilton TJ. Effect of curing-tip diameter on the accuracy of dental radiometers. Oper Dent. 1999;24(1):31-7.
- Roberts HW, Vandewalle KS, Berzins DW, Charlton DG. Accuracy of LED and halogen radiometers using different light sources. J Esthet Restor. Dent 2006;18(4):214-22; discussion 223-4.
- Barghi N, Fischer DE, Pham T. Revisiting the intensity output of curing lights in private dental offices. Compend Contin Educ Dent. 2007;28(7):380-4; quiz 385-6.
- Santos GC Jr, Santos MJ, El-Mowafy O, El-Badrawy W. Intensity of quartz-tungsten-halogen light polymerization units used in dental offices in Brazil. Int J Prosthodont. 2005;18(5):434-5.
- El-Mowafy O, El-Badrawy W, Lewis DW, Shokati B, Soliman O, Kermalli J, et al. Efficacy of halogen photopolymerization units in private dental offices in Toronto. J Can Dent Assoc. 2005;71(8):587. Available from: www.cda-adc.ca/jcda/vol-71/issue-8/587.html.
- El-Mowafy O, El-Badrawy W, Lewis DW, Shokati B, Kermalli J, Soliman O, et al. Intensity of quartz-tungsten-halogen light-curing units used in private practice in Toronto. J Am Dent Assoc 2005; 136(6):766-73; quiz 806-7.
- Ernst CP, Busemann I, Kern T, Willershausen B. Feldtest zur Lichtemissionsleistung von Polymerisationsgeräten in zahnärztlichen Praxen. Deutsche Zahnärztliche Zeitschrift. 2006;61(9):466-71.
- Baroudi K, Silikas N, Watts DC. In vitro pulp chamber temperature rise from irradiation and exotherm of flowable composites. Int J Paediatr Dent. 2009;19(1):48-54. Epub 2008 Feb 19.
- Santini A, Watterson C, Miletic V. Temperature rise within the pulp chamber during composite resin polymerisation using three different light sources. Open Dent J. 2008;2:137-41.
- Guiraldo RD, Consani S, Lympius T, Schneider LF, Sinhoreti MA, Correr-Sobrinho L. Influence of the light curing unit and thickness of residual dentin on generation of heat during composite photoactivation. J Oral Sci. 2008;50(2):137-42.
- Durey K, Santini A, Miletic V. Pulp chamber temperature rise during curing of resin-based composites with different light-curing units. Prim Dent Care. 2008;15(1):33-8.
- Bagis B, Bagis Y, Ertas E, Ustaomer S. Comparison of the heat generation of light curing units. J Contemp Dent Pract. 2008;9(2):65-72.
- Calheiros FC, Kawano Y, Stansbury JW, Braga RR. Influence of radiant exposure on contraction stress, degree of conversion and mechanical properties of resin composites. Dent Mater. 2006;22(9):799-803. Epub 2006 Jan 19.