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VOLUME 17 , ISSUE 3 ( March, 2016 ) > List of Articles


Effects of Different Temperatures and Storage Time on the Degree of Conversion and Microhardness of Resin-based Composites

Maan M AlShaafi

Citation Information : AlShaafi MM. Effects of Different Temperatures and Storage Time on the Degree of Conversion and Microhardness of Resin-based Composites. J Contemp Dent Pract 2016; 17 (3):217-223.

DOI: 10.5005/jp-journals-10024-1830

Published Online: 01-08-2016

Copyright Statement:  Copyright © 2016; The Author(s).



Dental materials are often made at room temperature, whereas clinically they are made in the mouth. This study evaluated the effects of temperature on the degree of conversion (DC) and Knoop microhardness (KHN).

Materials and methods

Two types of resin-based composites (RBCs) were light-cured using a light-emitting diode (LED) lightcuring unit. The resin specimens were centered on an Attenuated Total Reflectance Fourier transform infrared (FT-IR) plate heated to 23°C or 33°C. The DC of the resin was calculated after 120 seconds, the specimens were removed, and the KHN was tested at the bottom of the specimens both immediately, after 24 hours, and after 7 days storage in distilled water in complete darkness at 37°C. The effects of different temperatures on the DC and KHN with their storage time were compared by analysis of variance and Fisher's protected least significant difference post hoc multiple comparison tests (p < 0.05).


Increasing the temperature had a significant and positive effect on the DC and KHN for immediate values of the RBCs. Greater conversion and hardness occurred when the curing temperature was increased from 23°C to 33°C. The KHN increased significantly after 24 hours of storage. There was a linear relationship between DC and KHN (R2 = 0.86) within the range of DC and KHN studied.


The physical properties of dental materials can be expected to be better when made in the mouth than when they are made in a laboratory at room temperature.

How to cite this article

AlShaafi MM. Effects of Different Temperatures and Storage Time on the Degree of Conversion and Microhardness of Resin-based Composites. J Contemp Dent Pract 2016;17(3):217-223.

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  1. Guidance on posterior resin composites: Academy of Operative Dentistry–European Section. J Dent 2014 Apr;42(4):377-383.
  2. Effect of light intensity and exposure duration on cure of resin composite. Oper Dent 1994 Jan-Feb;19(1):26-32.
  3. In vitro comparison of mechanical properties and degree of cure of bulk fill composites. Clin Oral Investig 2013 Jan;17(1):227-235.
  4. New-generation curing units and short irradiation time: the degree of conversion of microhybrid composite resin. Quintessence Int 2011 Sep;42(8):e89-e95.
  5. Degree of conversion and microhardness of TPO-containing resin-based composites cured by polywave and monowave LED units. J Dent 2012 Jul;40(7):577-584.
  6. State-of-the-art: dental photocuring—a review. Dent Mater 2011 Jan;27(1):39-52.
  7. Modern high powered led curing lights and their effect on pulp chamber temperature of bulk and incrementally cured composite resin. Eur J Prosthodont Restor Dent 2012 Jun;20(2):50-55.
  8. Reduced polymerization stress of MAPO-containing resin composites with increased curing speed, degree of conversion and mechanical properties. Dent Mater 2014 May;30(5):507-516.
  9. Polymerization kinetics of pre-heated composite. J Dent Res 2006 Jan;85(1):38-43.
  10. The effects of light intensity, temperature, and comonomer composition on the polymerization behavior of dimethacrylate dental resins. J Dent Res 1999 Aug;78(8):1469-1476.
  11. Use of near-IR to monitor the influence of external heating on dental composite photopolymerization. Dent Mater 2004 Oct;20(8):766-777.
  12. The effects of temperature and light intensity on the polymerization shrinkage of light-cured composite filling materials. J Contemp Dent Pract 2006 Jul 1;7(3):12-21.
  13. A new kinetic model for the photopolymerization shrinkage-strain of dental composites and resinmonomers. Dent Mater 2006 Aug;22(8):785-791.
  14. Temperature-dependent polymerization shrinkage stress kinetics of resin-composites. Dent Mater 2014 Jun;30(6):654-660.
  15. The effect of specimen temperature on the polymerization of a resincomposite. Dent Mater 2011 Oct;27(10):983-989.
  16. High irradiance curing and anomalies of exposure reciprocity law in resin-based materials. J Dent 2011 Aug;39(8):549-557.
  17. Effect of time and polymerization cycle on the degree of conversion of a resin composite. Oper Dent 2006 Jul-Aug;31(4):489-495.
  18. Influence of softening test and light-activation protocols on resin composite polymer structure. Eur J Dent 2014 Jan;8(1):9-14.
  19. Monomer conversion of pre-heated composite. J Dent Res 2005 Jul;84(7):663-667.
  20. Effect of irradiation type (LED or QTH) on photo-activated composite shrinkage strain kinetics, temperature rise, and hardness. Eur J Oral Sci 2002 Dec;110(6):471-479.
  21. Comparison of time-dependent changes in the surface hardness of different composite resins. Eur J Dent 2013 Sep;7(Suppl 1):S20-S25.
  22. Depth of cure of dental resin composites: ISO 4049 depth and microhardness of types of materials and shades. Oper Dent 2008 Jul-Aug;33(4):408-412.
  23. Knoop hardness of ten resin composites irradiated with high-power LED and quartz-tungsten- halogen lights. Biomaterials 2005 May;26(15):2631-2641.
  24. Curing characteristics of a composite. part 2: the effect of curing configuration on depth and distribution of cure. Dent Mater 2014 Jun;30(6):e134-e145.
  25. Curing characteristics of a composite–part 1: cure depth relationship to conversion, hardness and radiant exposure. Dent Mater 2014 Jun;30(6):e125-e133.
  26. Depth of cure of radiation-activated materials—effect of mould material and cavity size. J Dent 1993 Oct;21(5):305-311.
  27. Influence of specimen diameter on the relationship between subsurface depth and hardness of a light-cured resin composite. Eur J Oral Sci 2003 Dec;111(6):543-546.
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