Browsing by Subject "Flexural Strength"

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    The effect of polymerization methods and fiber types on the mechanical behavior of fiber-reinforced composite resin
    (2015) Huang, Nan-Chieh; Chu, Tien-Min Gabriel; Hara, Anderson T.; Brown, David T.; Bottino, Marco C.; Levon, John A.
    Background: Interim restoration for a lost anterior tooth is often needed for temporary esthetic and functional purposes. Materials for interim restorations usually have less strength than ceramic or gold and can suffer from fracture. Several approaches have been proposed to reinforce interim restorations, among which fiber reinforcement has been regarded as one of the most effective methods. However, some studies have found that the limitation of this method is the poor polymerization between the fibers and the composite resin, which can cause debonding and failure. 64 Purpose: The purpose of this study was to investigate the effects of different polymerization methods as well as fiber types on the mechanical behavior of fiberreinforced composite resin. Material and Methods: A 0.2-mm thick fiber layer from strip fibers or mesh fibers embedded in uncured monomers w as fabricated with polymerization (two-step method) or without polymerization (one-step method), on top of which a 1.8-mm composite layer was added to make a bar-shape sample, followed by a final polymerization. Seventy-five specimens were fabricated and divided into one control group and four experimental groups (n=15), according to the type of glass fiber (strip or mesh) and polymerization methods (one-step or two-step). Specimens were tested for flexural strength, flexural modulus, and microhardness. The failure modes of specimens were observed by scanning electron microscopy (SEM). Results: The fiber types showed significant effect on the flexural strength of test specimens (F = 469.48; p < 0.05), but the polymerization methods had no significant effect (F = 0.05; p = 0.82). The interaction between these two variables was not significant (F = 1.73; p = 0.19). In addition, both fiber types and polymerization steps affected the flexural modulus of test specimens (F = 9.71; p < 0.05 for fiber type, and F = 12.17; p < 0.05 for polymerization method). However, the interaction between these two variables was not significant (F = 0.40; p = 0.53). Both fiber types and polymerization steps affected the Knoop hardness number of test specimens (F = 5.73; p < 0.05 for polymerization method. and F = 349.99; p < 0.05 for fiber type) and the interaction between these two variables was also significant (F = 5.73; p < 0.05). SEM images revealed the failure mode tended to become repairable while fiber reinforcement was 65 existed. However, different polymerization methods did not change the failure mode. Conclusion: The strip fibers showed better mechanical behavior than mesh fibers and were suggested for use in composite resin reinforcement. However, different polymerization methods did not have significant effect on the strength and the failure mode of fiber-reinforced composite
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    Effect of Toothbrushing on a Monolithic Dental Zirconia Submitted to an Accelerated Hydrothermal Aging
    (2022) Almajed, Norah; Sochacki, Sabrina Feitosa; Cook, Norman Blaine; Capin, Oriana Reis
    Objectives: The objectives of this study were (1) to evaluate the biaxial flexural strength of monolithic 3Y-TZP ceramic specimens and (2) to assess their surface roughness after being submitted to accelerated hydrothermal aging (simulation 1-10 years of aging); and simulated toothbrushing (simulation 1-10 years of toothbrushing). Materials/Methods: 84 discs of monolithic zirconia (Lava Plus High Translucency Zirconia, 3M ESPE) were prepared, sintered (1450°C, 2h), and randomly allocated into four experimental groups as follows: Control group (CT): no HA and no toothbrushing; 1-year group (1YR): 20 minutes of HA and 10,000 cycles of toothbrushing; 5 years group (5 YR): 100 minutes of HA and 50,000 cycles of toothbrushing; and 10 years group (10 YR): 200 minutes of HA and 100,000 cycles of toothbrushing. Specimens were submitted to autoclave hydrothermal aging at 134°C and 2.0 bar, followed by toothbrush simulation. After aging, specimens in each group were submitted to the biaxial flexural strength test (ISO 6872) using a universal testing machine, and the number of fragments was evaluated. Surface roughness was performed before and after aging using a noncontact profilometer (Ra, Rq, and Rz parameters). For the statistics, one-way analysis of variance (ANOVA) and pairwise comparison were used (α=0.05). Hypothesis: The accelerated hydrothermal aging and simulated toothbrushing will affect the results of the biaxial flexural strength and surface roughness of the zirconia specimens. Results: No significant aging effects were detected for the biaxial flexural strength (p=0.239) for groups CT (874.25±124.61 MPa), 1YR (869.56±132.60 MPa), 5YR (854.40±122.34 MPa), and 10YR (948.55±144.85 MPa). In addition, no significant aging effects were detected comparing the number of fragments, with a minimum of two and a maximum of five fragments (p=0.325). The collected data on the changes in surface roughness after hydrothermal aging and toothbrush simulation showed that for the parameters Ra and Rq, group 1YR presented significantly higher surface roughness than groups 5YR and 10YR. For the parameter Rz, group 1YR presented significantly higher surface roughness than groups 5YR and 10YR. In addition, group 5YR showed higher surface roughness than group 10YR. Conclusion: Hydrothermal aging associated with simulated toothbrushing did not significantly impact the biaxial flexural strength of monolithic 3Y-TZP zirconia. However, there was a significant initial increase in the zirconia surface roughness, which decreased after simulating five and ten years of aging.
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    Flexural strength and shear bond strength of self-etching/self-adhesive resin luting agents
    (2009) Adcook, Richard S.; Cochran, Michael A.; Platt, Jeffrey A.; Gonzalez-Cabezas, Carlos, 1966-; Matis, Bruce A.; Lund, Melvin R.
    Traditional resin luting agents generally have mechanical properties that are superior to the newer so-called “universal” self-etching/self-adhesive resin luting agents. However, recent reports indicate that some properties of these new luting agents have been improved, approaching those of the traditional etch and rinse resin luting agents. The objective of this study was to test some mechanical properties of four of these self-etching/self-adhesive resin luting agents [Maxcem Elite (ME), Multilink Automix (MA), RelyX Unicem (RU), SmartCem 2 (SC)] and compare them to a traditional etch and rinse resin luting agent [RelyX ARC (RA)] and a resin-modified glass ionomer luting cement [Fuji Plus (FP)], both of which have much longer histories of clinical success. By comparing the properties of the newer cements to the standards, it may be possible to determine how clinically successful the newer cements may be. The mechanical properties tested were flexural strength (FS) and shear bond strength (SBS). The FS test included making beams of each material, storing them in water for periods of time (24 hours and 90 days) and then performing a three-point bending test on a universal testing machine. The 90 day groups were thermocycled. The SBS test involved preparing human molar specimens, making flat dentin surfaces. Composite cylinders were fabricated, luted to the dentin surfaces with each of the materials tested, stored in water for periods of time (24 hours or 90 days), and then a knife edge shear test was performed on a universal testing machine. The 90 day groups were thermocycled. A Weibull-distribution survival analysis was performed. The results revealed significant differences in the FS of all materials tested at 24 hours. After 90 days and thermocycling, only SC and RA were not significantly different. At both time periods, FP had the lowest and MA the highest FS. The SBS results showed MA, RA, and RU to have the highest bond strengths; SC and ME the lowest at 24 hours. After 90 days and thermocycling, RA had significantly higher bond strength than all other groups; ME, FP and SC had the lowest. The self-etching/self-adhesive resin luting agents all performed at least as well as FP, with the exception of SC (SBS 24 hour). They did not all perform as well as RA, with the exception of SC (FS 90 day), MA (SBS 24 hour, FS 24 hour and 90 day), and RU (SBS 24 hour). The newer luting agents should expect to have clinical success, regarding flexural strength and shear bond strength, at least as good as resin-modified glass ionomer luting cements and approach the level of traditional etch and rinse resin luting agents.