FRACTAL ANALYSIS OF SOME RESTORATIVE NANO-FILLED COMPOSITE MATERIALS
MICROSTRUCTURE
e)
f)
Figure 1 Microstructures of Filtek Supreme XT (a-c) and Filtek Ultimate (d-f) at various magnifications:
1000× (a, d), 5000× (b,e), and 10000× (c, f)
i) the particles surface on which chemical bonds are
formed with the functional groups of the matrix; ii)
the particle surface roughness which extends the
effective area for physical contact with the matrix.
It is known that the micro- and nanosized
particle surfaces have a fractal nature that can be
characterized by the fractal dimension and other
fractal parameters. The geometry of the interface
between matrix and filler particle can be used to
compute the interfacial fractal dimension, D. The
smoothness or straightness of a curve can be
expressed by the fractal dimension, D, where 1 ≤
D = 2 (7). A perfect smooth line has D=1, while a
highly irregular line has D=2. Similarly, the surface
irregularities and roughness are also characterized
by the fractal dimension, with 2 ≤ D ≤ 3, where
D=2 corresponds to a perfectly smooth surface,
while D=3 to a highly disordered one. Thus, the
interface between the filler particles and polymeric
matrix can be quantified (8).
Several specialized software were developed
to perform fractal analysis. Generally, they
express a fractal dimension called the box
counting fractal dimension or DB. The DB is
the slope of the regression line for the loglog plot of box size (or scale) and count from
a box counting scan. The ratio quantifies
the increase in detail with increasing
magnification or resolution seen in fractals
but also in microscopy. It is measured by
the ratio of increasing detail with increasing
scale (ε).
The aims of the present study were to
evaluate and compare the microstructure
of two commercial resin based restorative
nano-composites using the fractal analysis.
STOMA.EDUJ (2015) 2 (1)
Methods - Experimental technique and materials
Two commercially available composite resins:
Filtek Ultimate and Filtek Supreme XT (3M
ESPE) were selected for this study (9,10). The
compositions of the studied composite according
to the producer’s specifications are presented in
Table 1, where similar dentin shades (A3) were
used. Twenty cylindrical samples of each material
of 5 mm in diameter and 2 mm in width were
prepared by placing them in cylindrical ringedshaped anti-sticking pre-molds. The specimens
were polymerized using the high intensity
LED mdium emmitance unit with the emitted
wavelengths between 440 and 460 nm (Optilight
LD Max, Gnatus, Ribeirao Preto, Sao Paulo, Brasilia).
The photo-polymerization time was 40 seconds.
The samples were studied by scanning electron
microscopy (SEM) using Vega Tescan LMH II
equipment. The SEM images were taken in
secondary electrons (SE); the acceleration voltage
was equal to 30 kV, and the emission current was
between 0,5pA and 500nA. The energy dispersive
detector for X-rays (EDX), QUANTAX - Bruker
equipment was used for chemical composition
measurements. From element mapping, the
filler particles were identified and their volume
percentages and cluster particle size distributions
were calculated.
Using microscopic images the fractal analysis was
performed and the average fractal dimension
was calculated for both types of materials. Firstly
the microscopic images were converted in binary
format and then they were analyzed using the
routine FracLac in Image J (11). Several grids of
decreasing caliber (box size) are placed over an
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