Abstract
Objectives: To characterize the mechanical properties of different resin-composites for dental application. Methods: Thirteen universal dentin shade composites (n = 10) from different manufacturers were evaluated (4 Seasons, Grandio, Venus, Amelogen Plus, P90, Z350, Esthet-X, Amaris, Vita-l-escence, Natural-Look, Charisma, Z250 and Opallis). The polymerization shrinkage percentage was calculated using a video-image recording device (ACUVOL—Bisco Dental) and the hygroscopic expansion was measured after thermocycling aging in the same equipment. Equal volumes of material were used and, after 5 min of relaxation, baseline measurements were calculated with 18 J of energy delivered from the light-curing unit. Specimens were stored in a dry-dark environment for 24 h then thermocycled in distilled water (5–55 °C for 20,000 cycles) with volume measurement at each 5000 cycles. In addition, the pulse-excitatory method was applied to calculate the elastic modulus and Poisson ratio for each resin material and the degree of conversion was evaluated using Fourier transform infrared spectroscopy. Results: The ANOVA showed that all composite volumes were influenced by the number of cycles (α = 0.05). Volumes at 5 min post-polymerization (12.47 ± 0.08 cm3) were significantly lower than those at baseline (12.80 ± 0.09 cm3). With regard to the impact of aging, all resin materials showed a statistically significant increase in volume after 5000 cycles (13.04 ± 0.22 cm3). There was no statistical difference between volumes measured at the other cycle steps. The elastic modulus ranged from 22.15 to 10.06 GPa and the Poisson ratio from 0.54 to 0.22 with a significant difference between the evaluated materials (α = 0.05). The degree of conversion was higher than 60% for all evaluated resin composites.
Highlights
In recent years, there has been an increasing interest in the development of new dental adhesives and composites for direct restorations
The maintenance of the marginal sealing and good quality of restoration filling techniques are the main focus during the treatment with conservative dental restorations [7,8]
Complex interactions in adhesive interfaces such the underperformed bonding approach associated with high polymerization shrinkage strain, stress, and elastic modulus [13,14,15,16], rather than the differences in the composite formulation, can lead to interfacial gaps, affecting the restoration integrity [17]
Summary
There has been an increasing interest in the development of new dental adhesives and composites for direct restorations. Complex interactions in adhesive interfaces such the underperformed bonding approach associated with high polymerization shrinkage strain, stress, and elastic modulus [13,14,15,16], rather than the differences in the composite formulation, can lead to interfacial gaps, affecting the restoration integrity [17]. When the composites initiate the polymerization process, stress is generated as a result of shrinkage This phenomenon is a leading reason for bond failures in adhesive restorations. Some authors used [26] the mercury dilatometer method and identified that the molecular weight and the molecular structure configuration of different monomers can affect the shrinkage Another method is to measure the dimensional alterations in composites during the polymerization, using electrical strain gauges bonded to the composite specimens [27]. The aim of this study was to evaluate the polymerization shrinkage, the hygroscopic expansion during aging, elastic modulus, Poisson ratio, and degree of conversion of thirteen composites
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