Impact of Fast High-Intensity versus Conventional Light-Curing Protocol on Selected Properties of Dental Composites

Abstract

To study the influence of fast high-intensity (3-s) and conventional (20-s) light curing protocols on certain physical properties including light-transmission and surface wear of two nano-hybrid composite resins (Tetric PowerFill and Essentia U) specifically designed for both curing protocols. According to ISO standards, the following properties were investigated: flexural properties, fracture toughness and water sorption/solubility. FTIR-spectrometry was used to calculate the double bond conversion (DC%). A wear test using a chewing simulator was performed with 15,000 chewing cycles. A tensilometer was used to measure the shrinkage stress. Light transmission through various thicknesses (1, 2, 3 and 4 mm) of composite resins was quantified. The Vickers indenter was utilized for evaluating surface microhardness (VH) at the top and the bottom sides. Scanning electron microscopy was utilized to investigate the microstructure of each composite resin. The light curing protocol did not show a significant (p > 0.05) effect on the mechanical properties of tested composite resins and differences were material-dependent. Shrinkage stress, DC% and VH of both composite resins significantly increased with the conventional 20 s light curing protocol (p < 0.05). Light curing conventional composite resin with the fast high-intensity (3-s) curing protocol resulted in inferior results for some important material properties.

Keywords: 3s PowerCure; Tetric PowerFill; composite resin; curing protocol; physical properties.

Figure 1

Spectral emission of both light curing units at 0 mm from the sensor.

Figure 2

Bar graph showing means of flexural strength (MPa) and flexural modulus (GPa) with standard deviations (SD) of tested composite resins (WS refers to one month water storage at 37 °C). Non-statistically relevant variations (p > 0.05) between the materials are represented by the same letters within the bars. Differences between curing protocols presented as %.

Figure 3

Bar graph showing mean fracture toughness (KIC) with standard deviations (SDs) of investigated composite resins. Non-statistically relevant variations (p > 0.05) between the materials are represented by the same letters within the bars. Differences between curing protocols presented as %.

Figure 4

Bar graph illustrating means of the degree of conversion percentage (DC%) calculated at the bottom surface of the tested composite resins. Non-statistically relevant variations (p > 0.05) between the materials are represented by the same letters within the bars. Differences between curing protocols presented as %.

Figure 5

Bar graph showing means of the shrinkage stress (MPa) and standard deviations (SDs) of the investigated composite resins. Non-statistically relevant variations (p > 0.05) between the materials are represented by the same letters within the bars. Differences between curing protocols presented as %.

Figure 6

Bar graph showing means of surface microhardness (VH) at the top (T) and bottom (B) of 2- and 4-mm-thick specimens. Arrows above the columns indicate that the VH of these groups dropped below 80% of the top surface values. Non-statistically relevant variations (p > 0.05) between the materials are represented by the same letters within the bars. Differences between curing protocols at various thicknesses presented as %.

Figure 7

Bar graph showing means of wear depth (µm) and surface roughness (µm) with standard deviations (SDs) of investigated composite resins. Non-statistically relevant variations (p > 0.05) between the materials are represented by the same letters within the bars. Differences between curing protocols presented as %.

Figure 7

Bar graph showing means of wear depth (µm) and surface roughness (µm) with standard deviations (SDs) of investigated composite resins. Non-statistically relevant variations (p > 0.05) between the materials are represented by the same letters within the bars. Differences between curing protocols presented as %.

Figure 8

The irradiance (mW/cm²) of the light curing units at various thicknesses relative to the sensor through composite resins.

Figure 9

Bar graph showing means of water sorption and solubility with standard deviations (SDs) of tested composite resins during 30 days of storage in water at 37 °C. Non-statistically relevant variations (p > 0.05) between the materials are represented by the same letters within the bars. Differences between curing protocols presented as %.

Figure 10

SEM photomicrographs (magnifications: 1000× and 2500×) of polished surface of investigated composite resins showing the filler sizes and distributions. (A) Tetric PowerFill and (B) Essentia U.