Mechanical Stress Analysis of Different Configurations of the All-on-4 Concept in Atrophic Mandible: A 3D Finite Element Study.

PURPOSE: This study evaluated the mechanical behavior of different configurations of the All-on-4 treatment concept designed with straight short (6-mm-length), straight standard (11-mm-length), or tilted standard (30-degree angled; 11-mm-length) posterior implants. MATERIALS AND METHODS: The All-on-4 configurations were performed in atrophic mandible models and consisted of anterior straight standard and posterior tilted standard implants (H1 model), anterior straight standard and posterior straight short implants (H2 model), and anterior and posterior straight standard implants (H3 model). Three oblique forces of 100 N were simulated in the posterior region of the prosthetic bar. The values of stress were obtained for the ductile materials using the von Mises equivalent stress (σvm) criteria. The stress peaks in the peri-implant bone crest were measured by the maximum (σmax) and minimum (σmin) principal stresses. The two-way analysis of variance (two-way ANOVA) and Tukey post hoc tests determined significant differences (P < .01) of stress values among the ductile materials (implant and prosthetic components). RESULTS: The use of tilted standard posterior implants (H1 model) showed the lowest values of σmax and σmin in the posterior region of the peri-implant bone area. On the other hand, the use of straight short (H2 model) or straight standard (H3 model) posterior implants significantly reduced the von Mises mean stresses in the bar screws, abutments, and abutment screws (P < .01). CONCLUSION: The higher odds of technical failures (screw fracture/loosening) may be expected when the All-on-4 configuration is performed with tilted standard posterior implants. Also, peri-implant bone overload may occur when the All-on-4 design is performed with straight short or straight standard posterior implants in atrophic mandibles.

Effect of surface roughness on the hydrophobicity of a denture-base acrylic resin and Candida albicans colonization.

AIM: The aim of the present study was to evaluate the effect of surface roughness (roughness average [Ra] µm) on the hydrophobicity of a denture-base acrylic resin and the initial adherence and biofilm formation of Candida albicans (C. albicans). METHODS: Disk-shaped specimens were divided into six groups: Ra 0.05, Ra 0.2, Ra 0.4, Ra 0.8, Ra 1.5, and Ra 3.0. Water contact angles (WCA) were measured, and the specimens incubated with C. albicans for 90 min (initial adherence, n = 108) or 48 h (biofilm formation, n = 108). Adhered and biofilm cells were evaluated by c.f.u./mL and 2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT), and the correlation between the two methods was evaluated. The surface of the specimens and cells (adhered and biofilm) were also analyzed by scanning electron microscopy (SEM). RESULTS: Groups Ra 0.05 and 3.0 exhibited the lowest (~75°) and the highest (~100°) WCA mean values, respectively. For both initial adherence and biofilm formation, no statistically-significant differences were observed among all groups, as determined by c.f.u./mL and XTT. A positive correlation between these two methods was found. SEM analysis showed the presence of scratches and valleys on the acrylic specimens and densely-packed yeast cells covering the entire surface. CONCLUSIONS: Roughness significantly increased hydrophobicity (WCA), but had no effect on the number and metabolic activity of adherent and biofilm cells of C. albicans.

Potentiated electron transference in α-Ag2WO4 microcrystals with Ag nanofilaments as microbial agent.

This study is a framework proposal for understanding the antimicrobacterial effect of both α-Ag2WO4 microcrystals (AWO) synthesized using a microwave hydrothermal (MH) method and α-Ag2WO4 microcrystals with Ag metallic nanofilaments (AWO:Ag) obtained by irradiation employing an electron beam to combat against planktonic cells of methicillin-resistant Staphylococcus aureus (MRSA). These samples were characterized by X-ray diffraction (XRD), FT-Raman spectroscopy, ultraviolet visible (UV-vis) measurements, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). The results reveal that both AWO and AWO:Ag solutions have bacteriostatic and bactericidal effects, but the irradiated sample is more efficient; i.e., a 4-fold of the MRSA planktonic cells as compared to the nonirradiated sample was observed. In addition, first principles calculations were performed to obtain structural and electronic properties of AWO and metallic Ag, which provides strong quantitative support for an antimicrobacterial mechanism based on the enhancement of electron transfer processes between α-Ag2WO4 and Ag nanoparticles.