The aim of this study was to investigate the influence of light curing method, composite shade, and depth of cure on composite microhardness.
Methods and Materials
Forty-eight specimens with 4 mm of depth were prepared with a hybrid composite (Filtek Z-100, 3M ESPE); 24 with shade A1 and the remaining with shade C2. For each shade, two light curing units (LCUs) were used: a quartz-tungsten-halogen (QTH) LCU (Optilight Plus - Gnatus) and a light emitting diode (LED) LCU (LEC 470 II - MM Optics). The LED LCU was tested using two exposure times (LED 40 seconds and LED 60 seconds). After 24-hour storage, three indentations were made at mm depth intervals using a Knoop indenter. Data were submitted to three-way analysis of variance (ANOVA) and Tukey's test (p<0.05).
Results
The three factors tested (light curing method, shade, and depth) had a significant influence on the composite microhardness (p<0.05). All groups presented similar hardness values in the first mm, except for composite shade C2 cured with LED for 40 seconds. The hardness decreased with depth, especially for shade C2 for 40 seconds. Increasing light-curing time with LED produced hardness values similar to the QTH.
Conclusions
The light curing method including variations of time, the depth of cure, and the composite shade influence the composite microhardness.
Clinical Significance
Clinicians should avoid thicker increments when working with composite restorations. Extended light-curing time might be indicated depending on the composite shade and on the light-curing device.
Citation
de Araújo CS, Schein MT, Zanchi CH, Rodrigues SA Jr, Demarco FF. Composite Resin Microhardness: The Influence of Light Curing Method, Composite Shade, and Depth of Cure. J Contemp Dent Pract 2008 May; (9)4:043-050.
Buonocore Memorial Lecture. Review of the clinical survival of direct and indirect restorations in posterior teeth of the permanent dentition. Oper Dent 2004;29:481-508. Review.
Correlation of parameters used to estimate monomer conversion in a light-cured composite. J Dent Res 1988; 67:932-937.
Raman scattering determination of the depth of cure of light-activated composites: influence of different clinically relevant parameters. J Oral Rehabil 2002; 29:510-515.
How light irradiance and curing time affect monomer conversion in lightcured resin composites. Eur J Oral Sci 2003; 11:536-542.
Light-emitting diode (LED) polymerization of dental composites: flexural properties and polymerization potential. Biomaterials 2000; 21:1379-1385.
Comparison of linear polymerization shrinkage and microhardness between QTH-cured & LED-cured composites. Oper Dent 2005; 30:461-467.
Polymerization depths of contemporary light-curing units using microhardness. J Esthet Dent 2000; 12:340-349.
Microhardness of resin-based materials polymerized with LED and halogen curing units. Braz Dent J 2005; 16:98-102.
Effect of light curing tip distance and resin shade on microhardness of a hybrid resin composite. Pesqui Odontol Bras 2005;19:302-306. Epub 2006 Feb 14.
Pesqui Odontol Bras 2002; 16:246-250.
Class II composite resin restorations with two polymerization techniques: relationship between microtensile bond strength and marginal leakage. J Dent 2005; 33:603-610.
In situ evaluation of the polymerization kinetics and corresponding evolution of the mechanical properties of dental composites. Polymer Testing 2003; 22:77-81.
Depth of cure and surface microhardness of composite resin cured with blue LED curing lights. Dent Mater 2004; 20:364-369.
Degree of polymerization of resin composites by different light sources. J Oral Rehabil 2002; 29:1165-1173.
Depths of cure and effect of shade using pulse-delay and continuous exposure photo-curing techniques. Oper Dent 2002; 27:593-599.
Factors affecting cure at depths within light-activated resin composites. Am J Dent 1993; 6:91-95.
Influence of curing lights and modes on cross-link density of dental composites. Oper Dent 2004; 29:410-415.
Effect of irradiation type (LED or QTH) on photo-activated composite shrinkage strain kinetics, temperature rise, and hardness. Eur J Oral Sci 2002; 110:471-479.
The effect of composite type on microhardness when using quartz-tungsten-halogen (QTH) or LED lights. Oper Dent 2005; 30:649-654.
The effect of curing light variations on bulk curing and wall-to-wall quality of two types and various shades of resin composites. Dent Mater 1997; 13:344-352.
Clinical evaluation of a highly wear resistant composite. Am J Dent 1993; 6:85-87.
Influence of water exposure on three-body wear of composite restoratives. J Biomed Mater Res 2000;53:547-553.
