The Antibacterial and Antifungal Activity of Chlorhexidine Diacetate Incorporated into Acrylic Resins Used in Provisional Restorations.

Objective: The surface of provisional restorations applied before conventional or implant- supported fixed restorations may cause bacterial or fungal biofilm formation. The aim of this study was to evaluate the antimicrobial activity of acrylic resins used in provisional restorations modified with chlorhexidine diacetate. Methods: 120 cylindrical, auto-polymerized resin samples modified with chlorhexidine diacetate were prepared at concentrations of 0 (control), 1, 3, 5 wt %. The antimicrobial activity was examined against Streptococcus mutans, Enterococcus faecalis, and Candida albicans using Crystal Violet quantification, MTT assay, and Scanning Electron Microscopy. Data were analyzed by ANOVA and paired sample t-tests (α=0.05). Results: The addition of chlorhexidine diacetate influenced the growth rate and metabolic activity of microorganisms. The antimicrobial effect against C. albicans and S. mutans statistically increased with the percentage of chlorhexidine diacetate. E. faecalis bacteria were less affected by chlorhexidine diacetate compared to other pathogens. Conclusion: It has been shown that the effectiveness of CHDA in inhibiting the proliferation of microorganisms correlated positively with increasing concentration levels. More research is needed to confirm the impact of different chlorhexidine concentrations on the mechanical properties, clinical efficacy, and antimicrobial properties of CDHA.

Push-out Bond Strength of Fiber Posts in Long-Term Hypobaric Pressure Changes.

BACKGROUND: The purpose of this study was to evaluate the bond strength of fiber posts with different mixing methods and insertion into root canal techniques in long-term hypobaric pressure changes.METHODS: We chose and decoronated 42 teeth with straight and single root canals. After post-space preparation, the posts were cemented with hand-mixed and auto-mixed resin cements that were inserted into the canals with an endodontic file (lentilo), dual-barrel syringe, and root canal tip (14 for each group). After cementation, each group was divided into two subgroups (N = 7): the control (ambient pressure) group and the hypobaric pressure group. The samples were exposed to hypobaric pressure 90 times. They were cut into 2-mm-thick segments and the push-out bond strength test was performed using a Universal Testing Machine. One-way ANOVA tests, Bonferroni tests, and Student-t-tests were used for statistical analysis.RESULTS: The environmental pressure changes and insertion techniques affected the bond strength values. The auto-mixed with root-canal tip group showed the highest push-out bond strength values in both hypobaric (dual-barrel syringe group: 10.01 MPa; root-canal tip group: 11.61 MPa) and control (dual-barrel syringe group: 12.29 MPa; root-canal tip group: 14.58 MPa) group. In all root segments, the bond strength values of hypobaric groups were lower than atmospheric pressure groups. The most frequent failure type was adhesive between dentin and cement in all groups.DISCUSSION: Dentists should use auto-mixed self-adhesive resin with a root canal tip for post cementations in patients likely to be exposed to hypobaric pressure changes.Ozkan Ata S, Ata N, Yazgan E, Akkor T. Ugurlutan R. Push-out bond strength of fiber posts in long-term hypobaric pressure changes. Aerosp Med Hum Perform. 2023; 94(7):508-513.

Influence of atmospheric pressure changes on dentin bond strength of conventional, bulk-fill and single-shade resin composites.

INTRODUCTION: The purpose of this study was to investigate the dentin bond strength of composite resins in response to environmental pressure changes. METHODS: Ninety extracted human molar teeth were used. A mould (3 mm x 4 mm) was adapted on dentin, resin composites (conventional [n = 30] and single-shade composites [Ohmnicroma] [n = 30]) were filled in two increments of 2 mm. The bulk-fill composites (n = 30) were filled with one 4 mm increment. The specimens were stored for 30 days in artificial saliva. The specimens were exposed to hyperbaric pressure (283.6 kPa; 2.8 atmospheres absolute [atm abs]) or hypobaric pressure (34.4 kPa; 0.34 atm abs) once daily for 30 days and the control group was stored at atmospheric pressure for 30 days. The bond strength was tested with a universal testing machine and the failures were examined with a stereomicroscope and scanning electron microscope. Statistical analyses were performed using analysis of variance with post hoc tests, and the Weibull analysis. RESULTS: Regardless of environmental pressure changes, the bulk-fill composites showed the highest bond strength. There was no significant difference in bond strength between the hypobaric and atmospheric pressure (control) groups after 30 days in all resins. The hyperbaric group showed lower bond strength for bulk-fill composites than the control group. CONCLUSIONS: Dentists experienced in diving and aviation medicine should definitely take part in the initial and periodic medical examinations of divers and aircrew to give appropriate treatment. Bulk-fill composite resins can be preferred in divers and aircrew due to high bond strength values.

In vitro comparison of the cytotoxicity of acetal resin, heat-polymerized resin, and auto-polymerized resin as denture base materials.

This in vitro study aims to evaluate three different base materials (acetal, heat-polymerized, and auto-polymerized resins) on L-929 mouse fibroblast cells over 1 h-, 1-, 3-, 5-, 7-day periods. The hypothesis was that acetal resin would show higher cytotoxic effect than heat-polymerized and auto-polymerized acrylic resins, as it seems possible that residual formaldehyde might be leaching from the material into the cell culture medium. The samples were produced according to the manufacturer's protocol. Then they were placed in Dulbecco's Modified Eagle Medium/Ham's F12 (DMEM/F12) for 1 h, 1, 3, 5, 7 days. After the incubation periods, cytotoxicity of the extracts to cultured fibroblasts (L-929) was measured by MTT assay. The degree of cytotoxicity of each sample was determined according to the reference value represented by the cells with a control. Statistical significance was determined by one-way ANOVA. Tukey and Tamhane tests were used as a post-hoc method to determine differences among the groups. Statistically significant difference was found among test groups at all time incubation periods (p = 0.000). The auto-polymerized resin performed higher cytotoxic effect than heat-polymerized resin and it was statistically significant at 1-day period (p < 0.05). The highest cytotoxic effect of acetal resin was observed at 5-day incubation period. In conclusion, the hypothesis was verified, since acetal resin showed more cytotoxic effect on the 3rd, 5th, and 7th days than heat- and auto-polymerized resins. Cell survival rates (% of control) of acetal resin were 58, 54, and 60%, respectively.