Influence of the distance of the curing light source and composite shade on hardness of two composites

Abstract

This study evaluated the influence of curing tip distance, shade and filler particle size on Vickers microhardness (VHN) of composite resins. Two composites were tested: Filtek Z250 microhybrid (3M ESPE; shades A1 and A3.5) and Filtek Supreme nanofilled (3M ESPE; shades A1B and A3.5B). For each resin, 42 specimens (5 mm in diameter and 2 mm height) were prepared being 21 for each shade. The specimens were exposed using a 20-second exposure to a quartz-tungsten-halogen light source with an irradiance of approximately 560 mW/cm2, at the following distances: 0 mm (surface contact), 6 mm and 12 mm from composite surface. Effectiveness of cure of different resins, shades and curing distances was determined by measuring the top and bottom hardness (VHN) of specimens using a digital microhardness tester (load: 50 g; dwell time: 45 seconds) 24 hours following curing. The hardness ratio was calculated by dividing VHN of the bottom surface by VHN of top surface. Three-way ANOVA and Tukey's post-hoc test (p<0.05) revealed statistically significant differences for all analyzed factors. As for top hardness, as microhardness ratio (bottom/top), the factors shade, distance and composite filler particle size exerted influence on resin curing. Lighter shade composites (A1 and A1B) showed higher hardness values. At 6 and 12 mm curing tip distances, hardness was lower when compared to 0 mm. The microhybrid composite resin presented higheer hardness, being its microhardness ratio satisfactory only at 0 mm for both shades and at 6 mm for the lighter shade. The nanofilled composite resin did not present satisfactory microhardness at the bottom while the microhybrid composite resin had higher hardness than the nanofilled. Composite's curing tip distance and shade can influence hardness.

Curing Quality of Composites as Influenced by the Filler Content, Light Source and Curing Time

“…The greater amount of photoinitiator excited by UL in FZ, presenting less light attenuation and scattering than FS on the bottom surface [2] can explain the differences between FZ and FS concerning DC values on the bottom surface. Irradiance levels of curing devices tested in this study were crucial in determining DC values of both composites tested.…”

“…Metal ZiO2 nanofiller present in FS might decrease light transmittance through the resin increment due to light scattering [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Hence, one may assume that FS requires high irradiance levels to polymerize bottom surfaces similarly to FZ.…”

“…Photo-initiators other than camphorquinone such as Lucirin, phenylpropadione-PPD, acylphosphine oxide-PDB, bisacylphosphine BAPO-oxide may be contained in these composite resins which can be excited through lights with wavelengths lower than 455 nm. Therefore, a greater amount of photoinitiator could have been photoactivated in FZ, presenting less light attenuation and scattering than FS [2]. Further studies are needed to investigate the presence of other photoinitiators in FZ and FS in an attempt to clarify the above hypothesis.…”

“…Specimens were assigned to sixteen groups based on the factorial product: composites (2) x light curing units (4) x times (2). Eighty test specimens (n=5) were made/fabricated using individual cylindrical Teflon molds 5 mm in diameter and 2 mm high.…”

“…Since the introduction of light-cured resin-based composites, the quality of polymerization has been of concern for researchers worldwide [1]; its clinical success is directly related to its degree of cure [2]. Primary clinical manifestations of uncured composite are untoward symptoms when chewing.…”