Effects of aging and irradiation time on the properties of a highly translucent resin-based composite

Interlaminar Shear Strength Change and Storage Life Prediction of Carbon Fiber/Epoxy Composites with Hygrothermal Accelerated Aging

In order to investigate the durability of fiber-reinforced polymer composites in hygrothermal environments, hygrothermal accelerate aging tests, for 360 days at 70 °C, RH70%; 70 °C, RH85%; 85 °C, RH70%; and 85 °C, RH85% and natural storage for 2 years in Guangzhou, China, were carried out for composite laminates. Then, the moisture absorption and interlaminar shear strength were measured. The hygrothermal damage mechanism of the composite was studied by Fourier transform infrared (FTIR), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FSEM). A dual stress storage life prediction model and the equivalent relationship between natural storage and hygrothermal acceleration were established. The results show that the order of moisture absorption rates, moisture absorption contents, and the severity effect order on the interlaminar shear strength is RH85%; 85 °C > 70 °C; RH85% > 85 °C; RH70% > 70 °C; and RH70%. The time to achieve an effective moisture absorption balance is opposite to this. The moisture absorption rate meets Fick's law before the effective moisture absorption balance, and then shows a linear trend. The interlayer shear strength still decreases exponentially with aging, which is mainly caused by the resin plasticization and interface weakening. Hygrothermal accelerated aging for 13.4831 days at 85 °C; RH85% is equivalent to that for one-year actual storage in Guangzhou. According to the failure criterion of shear strength decreasing to 77%, the storage life of T700/epoxy in Guangzhou is 14.4661 years.

How the Duration and Mode of Photopolymerization Affect the Mechanical Properties of a Dental Composite Resin

Composite materials are the most common materials in use in modern dentistry. Over the years, the methods of photopolymerization of composite materials have been improved with the use of various devices, such as quartz tungsten halogen lamps (QTHs), light-emitting diode units (LEDs), plasma-arc lamps and argon-ion lasers. This study aimed to compare the mechanical properties of a composite material, depending on the time and mode of photopolymerization. One hundred and forty rectangular specimens (25 × 2 × 2 mm) and forty-two disc-shaped samples (5 mm diameter and 2 mm thickness) were prepared from shade A2 Boston composite resin. Samples were cured using the following seven photopolymerization protocols: four fast-cure modes (full power for 3, 5, 10, and 20 s), two pulse-cure modes (5 and 10 shots of 1 s exposures at full power), and one step-cure mode (soft start with a progressive cycle lasting 9 s). Specimens were subjected to a flexural strength test, Vickers microhardness test, and FTIR spectroscopy test. A 2-factor ANOVA and post-hoc tests were carried out to assess the differences in the flexural strength parameter between the tested groups of samples before and after aging. A mixed-model ANOVA was carried out to assess the differences in the Vickers microhardness parameter between the tested groups of samples before and after aging. The lowest values of flexural strength (p < 0.001) and Vickers microhardness (p < 0.001) were obtained for the 3 s mode for the pre- and post-aging groups. The FTIR mapping tests showed a much more homogeneous chemical structure of the composite after 20 s of continuous irradiation, compared to the sample irradiated for 5 s in the continuous mode. The mode and cure time affects the mechanical properties of the composite resin. Appropriate selection of the cure mode and time ensures better mechanical properties of composite resin. This suggests that the survival of dental restorations within the oral cavity could be extended by using longer photopolymerization durations.

Ageing of Dental Composites Based on Methacrylate Resins-A Critical Review of the Causes and Method of Assessment

The paper reviews the environmental factors affecting ageing processes, and the degradation of resins, filler, and the filler-matrix interface. It discusses the current methods of testing materials in vitro. A review of literature was conducted with the main sources being PubMed. ScienceDirect, Mendeley, and Google Scholar were used as other resources. Studies were selected based on relevance, with a preference given to recent research. The ageing process is an inherent element of the use of resin composites in the oral environment, which is very complex and changes dynamically. The hydrolysis of dental resins is accelerated by some substances (enzymes, acids). Bonds formed between coupling agent and inorganic filler are prone to hydrolysis. Methods for prediction of long-term behaviour are not included in composite standards. Given the very complex chemical composition of the oral environment, ageing tests based on water can only provide a limited view of the clinical performance of biomaterial. Systems that can reproduce dynamic changes in stress (thermal cycling, fatigue tests) are better able to mimic clinical conditions and could be extremely valuable in predicting dental composite clinical performance. It is essential to identify procedure to determine the ageing process of dental materials.

The Influence of Aging in Solvents on Dental Cements Hardness and Diametral Tensile Strength

Prosthetic materials must exhibit adequate resistance to the oral environment. The aim of this paper was to study the resistance of selected cements used for cementing restorations (Breeze-composite, Adhesor Carbofine-zinc-polycarboxylate and IHDENT-Giz type II-glass-ionomer) against ethanol, soda and green tea solutions. The highest values of hardness and DTS (diametral tensile strength) were obtained by composite cement (HV = 15-31, DTS = 34-45 MPa). Ethanol solution had the greatest impact on the hardness value of composite cement, and soda solution on zinc-polycarboxylate cement. No significant differences were noted in the DTS values of composite cements after immersion in solvents; however, the DTS value of zinc-polycarboxylate cement increased after prolonged immersion time in ethanol and the DTS of glass-ionomer cement (IHDENT Giz type II) clearly decreased after submersion in soda solutions. Variation in pH across the range of 6 (tea) to 9 (soda solution) had a low impact on the properties of dental cements. Extended exposure to solvents appears to worsen the properties of cements.

Creep, Hardness, and Elastic Modulus of Lingual Fixed Retainers Adhesives

The aims of this study were twofold: a) to characterize a wide array of time-independent and -dependent properties and b) to find possible correlations among the properties tested. Seven commercially available orthodontic adhesives were included in this study and ten cylindrical specimens were prepared from each material. Five specimens from each material were used for the characterization of Martens Hardness (HM), indentation modulus (E_IT), and elastic index (η_IT), and the remaining five for the determination of indentation creep (C_IT). Al the aforementioned properties were identified by employing an Instrumented Indentations Testing (IIT) device with a Vickers indenter. The results of HM, E_IT, η_IT, and C_IT were statistically analyzed by one way ANOVA and Tukey post hoc test, while the possible correlations among the aforementioned properties were determined by Spearman correlation test. Statistical significant differences were identified for all properties among the materials tested. Spearman correlation reveals that HM has a positive correlation with E_IT. Both properties demonstrated a negative correlation with η_IT and C_IT, while no correlation was identified between η_IT and C_IT. Significant differences in the mechanical properties tested may also imply differences in their clinical behavior and efficacy.

Flexural strength and microhardness of anterior composites after accelerated aging

BACKGROUND

This study aimed to evaluate the flexural strength and microhardness of three different anterior composites after 10 000 thermocycles.

MATERIAL AND METHODS

The mechanical properties of a nano-fill composite (Filtek Ultimate Universal Restorative (FUR) (Enamel)), a nano-hybrid composite (Clearfil Majesty ES2 (ES2) (Enamel)), and a micro-hybrid composite (G Aenial Anterior (GAA)) were investigated in this study. For the microhardness test, 8-mm diameter and 2-mm thickness composite discs were used (n = 10), and for the flexural strength test, 25x2x2 mm bar-shaped specimens were prepared (n = 13). The specimens were tested at 24 h and after 10 000 thermocycles. Data were analyzed using two-way analysis of variance and the post-hoc Tukey test (p < .05). Correlations between hardness and flexural strength were calculated using Pearson's correlation analysis.

RESULTS

There was a significant difference in the microhardness values of the materials (p < .05). FUR exhibited significantly higher microhardness than ES2 and GAA. However, the flexural strength of three composites was statistically similar at 24 h (p > .05). Pearson correlation analysis revealed that there was a negative relationship between the mean hardness and flexural strength values (correlation coefficient = -0.367, p = .043). After 10 000 thermocycles, microhardness values of each material and flexural strength of ES2 and GAA decreased significantly according to 24 h.

CONCLUSIONS

The nano-fill composite FUR displayed significantly higher microhardness values. However, each resin composite was statistically similar for flexural strength values. Ten thousand thermocycles significantly affected microhardness and flexural strength. Key words:Flexural strength, microhardness, anterior composites.

Mechanical properties of contemporary orthodontic adhesives used for lingual fixed retention

Objective:

The aim of the present study was to test the mechanical properties of different adhesives used in orthodontics for fixed retainers and to investigate their possible interrelations.

Materials and methods:

Specimens of six different adhesive resins were prepared: Transbond XT, Transbond LR and an experimental BPA-free orthodontic adhesive, as well as IPS Empress Direct (IPS-ED), ZNano and Accolade. The mechanical properties tested were Martens hardness (HM), indentation modulus (E

Results:

Significant differences were identified among all the materials tested for HM, with Transbond LR presenting the highest value. This resin presented the highest E

Conclusions:

The materials tested demonstrated significant differences in their mechanical properties, and thus differences in their clinical performance are anticipated.

Comparison of time-dependent changes in the surface hardness of different composite resins

OBJECTIVE

The aim of this study was to evaluate the change in surface hardness of silorane-based composite resin (Filtek Silorane) in time and compare the results with the surface hardness of two methacrylate-based resins (Filtek Supreme and Majesty Posterior).

MATERIALS AND METHODS

From each composite material, 18 wheel-shaped samples (5-mm diameter and 2-mm depth) were prepared. Top and bottom surface hardness of these samples was measured using a Vicker's hardness tester. The samples were then stored at 37°C and 100% humidity. After 24 h and 7, 30 and 90 days, the top and bottom surface hardness of the samples was measured. In each measurement, the rate between the hardness of the top and bottom surfaces were recorded as the hardness rate. Statistical analysis was performed by one-way analysis of variance, multiple comparisons by Tukey's test and binary comparisons by t-test with a significance level of P = 0.05.

RESULTS

The highest hardness values were obtained from each two surfaces of Majesty Posterior and the lowest from Filtek Silorane. Both the top and bottom surface hardness of the methacrylate based composite resins was high and there was a statistically significant difference between the top and bottom hardness values of only the silorane-based composite, Filtek Silorane (P < 0.05). The lowest was obtained with Filtek Silorane. The hardness values of all test groups increased after 24 h (P < 0.05).

CONCLUSION

Although silorane-based composite resin Filtek Silorane showed adequate hardness ratio, the use of incremental technic during application is more important than methacrylate based composites.