Biaxial flexural strength of hydrothermally aged resin-based materials.

PURPOSE: The strength of temporary restorations plays a vital role in full-mouth reconstruction, and it can be impacted by the aging process. The aim of this in vitro study was to evaluate the biaxial flexural strength and fractographic features of different resin-based materials submitted to thermal aging. MATERIAL AND METHODS: One hundred and ninety-two resin disc-shaped specimens (6.5 mm in diameter and 0.5 mm in thickness) were fabricated and divided into six experimental groups according to the resin-based materials (Filtek Bulk-Fill flowable resin; J-Temp temporary resin; and Fuji Lining glass ionomer cement) and aging process (before and after thermal cycling). Biaxial flexural strength test was performed using a universal testing machine at a crosshead speed of 0.5 mm/min before and after thermal cycling (5 °C and 55 °C, 5760 cycles, 30 s). The mechanical properties were assessed using Weibull parameters (characteristic strength and Weibull modulus) (n = 30). Fractured specimens were examined under a polarized light stereomicroscope to identify crack origin and propagation direction. The surface microstructure of the resin-based materials was assessed by scanning electron microscopy (n = 2). The Weibull modulus (m), characteristic strength, and reliability properties were calculated, and a contour plot was used to detect differences among groups (95% confidence interval). RESULTS: The Weibull modulus (m), characteristic strength, and reliability of the resin-based compounds were influenced by material type and thermal aging (p < 0.05). Weibull modulus (m) revealed no differences when comparing the materials and aging process (p > 0.05), except for the preceding aging period where Filtek Bulk-Fill exhibited higher values compared to J-Temp (p < 0.05). Filtek Bulk-Fill demonstrated superior characteristic strength and reliability compared to J-Temp and Fuji Lining before and after thermal cycling (p < 0.05). Fractography of the resin-based materials showed fractures originating from surface defects exposed to tensile side and their propagation toward the compressive side. Generally, no differences in surface microstructure were observed on micrographs before and after thermal aging for Filtek Bulk-Fill and Fuji Lining. However, the aging process developed flaws in J-Temp. CONCLUSION: Resin-based material composition resulted in different flexural strength performance, impacting the Weibull modulus (m), characteristic strength, and reliability of the resin-based restorations.

The impact of methylene blue photosensitizer, aPDT and a calcium hydroxide-based paste on the physicochemical and mechanical characteristics of root canal dentin and the bonding interface of fiberglass posts.

PURPOSE: To investigate the influence of methylene blue (MB)-mediated antimicrobial photodynamic therapy (aPDT) and calcium hydroxide (CH) medication on the mechanical characteristics, degree of conversion (DC), quantification, and volume of gaps at the adhesive interface of glass fiber posts (GFPs) luted to distinct thirds of root canal dentin. Additionally, the microhardness (MH), elastic modulus (Eit), morphology, and chemical structure of the intraradicular dentin were assessed. MATERIALS AND METHODS: 6 experimental groups were formed by sorting 102 bovine incisors. Canals receiving deionized water irrigation as a negative control; canals receiving deionized water irrigation and filled with CH as a positive control; groups treated with CH + MB at 50 and 100 mg/L without irradiation; and groups treated with CH + MB at 50 and 100 mg/L irradiated by red laser for 60 s (660 nm; 100 mW; 6.5 J; 72 J/cm2). MH, Eit, and DC properties were evaluated for both the resin cement layer and root dentin substrate (n = 8). Volume and quantification of gaps at the bonding interface (n = 6), and dentin morphology and chemical content were investigated (n = 3). Data were analyzed using a repeated-measures 2-way ANOVA followed by Tukey post hoc analysis (α = 0.05). RESULTS: The distinct intraradicular thirds and treatment with MB-mediated aPDT, whether activated or not, in combination with CH, had a significant impact on the mechanical characteristics of the root dentin. This effect was also observed in the MH, Eit, DC, quantification, and volume of gaps at the luting interface (P < .05). In general, a higher concentration of MB, whether activated by a red laser or not, led to lower values in the mechanical properties of the root dentin, as well as in MH, Eit, and DC at the adhesive interface (P < .05). Additionally, these groups exhibited higher values for quantification and volume of gaps at the luting substrate (P < .05). Scanning electron micrographs and energy dispersive X-ray spectra showed qualitative similarity among all groups, except for the negative experimental control group. CONCLUSIONS: MB-mediated aPDT at 50 mg/L, in combination with CH, demonstrated favorable physico-chemical and mechanical characteristics in intraradicular dentin, along with satisfactory mechanical features and the adhesive interface integrity for GFPs at all intraradicular depths. CLINICAL SIGNIFICANCE: MB-mediated aPDT at a concentration of 50 mg/L combined to CH medication represents a suitable choice for photosensitization in the context of intracanal disinfection following the biomechanical procedure and prior to luting of intraradicular restorations.