LED lights with nine wavelengths: Influence on composite properties

Objective: The purpose of this study was to examine the properties of a light curing composite while using LED curing lights with nine emission maximum from 400 to 517 nm.

Methods: LED curing lights with emission maximum of 400, 430, 445, 470, 480, 490, 500, 512 and 517 nm were used. Each light intensity was 800 mW/cm²; every curing time was 20 s. The composite was Tetric EvoCeram A4 (IvoclarVivadent), which has two initiators (Camphorquinone and 2,4,6-Trimethylbenzoyldiphenylphosphine oxide). Measurements concerned: depth of cure (n=4, in accordance with ISO 4049); Vickers hardness (n=6, 24 h storage) on top and on the bottom of a 2-mm sample; and shrinkage stress (n=4, Ø=10 mm, h=0.8 mm) for 30 min.

Results:

Curing light Emission maximum (±SE) [nm]	Vickers hardness, top (±SE) [MPa]	Vickers hardness, bottom (2 mm) (±SE) [MPa]	Depth of cure (±SE) [mm]	Shrinkage stress (after 30 min) (±SE)  [MPa]
400	634±1.7	531±4.9	3.02±0.015	6.82±0.092
430	638±1.6	542±3.9	3.54±0.021	6.18±0.044
445	602±2.7	562±4.9	4.55±0.019	5.72±0.110
470	600±3.2	570±4.0	5.12±0.017	5.66±0.063
480	595±2.8	577±1.5	4.84±0.027	5.96±0.062
490	579±1.5	551±2.6	4.65±0.017	5.64±0.036
500	566±4.1	523±3.8	4.44±0.018	5.32±0.086
512	554±3.2	464±3.0	3.73±0.016	4.25±0.066
517	557±2.6	451±1.9	3.32±0.023	4.18±0.017

Conclusions: A multivariate ANOVA confirms the existence of significant differences for all dependent variables; the reliability of specific differences between means can be inferred in the table from the reported standard errors of the means. The Vickers hardness on the top decreases with increasing wavelength. The Vickers hardness at 2 mm and the depth of cure show peaks at 480 and 470 nm, respectively, with decreasing values in both wavelength directions. The shrinkage stress shows irregular behavior, with peaks at 400 and 480 nm.