Effect of ionizing radiation on polymer brackets.

OBJECTIVE: The purpose of this study was to investigate whether the mechanical properties of polymer brackets can be improved without discoloration by electron beam (EB) irradiation applied with a Rhodotron electron accelerator using standard high-energy parameters including a 10 MV acceleration voltage and 100 kGy of energy. We analyzed polymer samples and several commercially available brackets. MATERIALS AND METHODS: The first group included three polymeric base materials (polyoxymethylene, polycarbonate, polyurethane) currently used in various bracket systems. The second group included five bracket types, three of which are on the market (Aesthetik-Line and Brillant by Forestadent; Envision by Ortho Organizers) while the other two were experimental brackets containing urethane dimethacrylate as a monomer matrix and functional silane-treated SiO2 fillers with a filler content of 10 or 40 vol%. Each category included 40 specimens previously irradiated by a commercial provider (Beta-Gamma-Service, Bruchsal, Germany) and another 40 nonirradiated controls. The polymer specimens were analyzed for fracture toughness, Vickers hardness, and wear resistance, and the bracket specimens for Vickers hardness and color stability. The Wilcoxon-Mann-Whitney U test was used for pairwise comparison to identify significant differences (p ≤ 0.05). RESULTS: Significant increases in fracture toughness and Vickers hardness were observed in polycarbonate and polyurethane after EB irradiation, while EB irradiation of polyoxymethylene resulted in a significant decrease in these parameters. The polyurethane samples demonstrated significantly less postirradiation wear. All the commercially available brackets except for Brillant revealed significant increases in Vickers hardness. Significant discoloration was observed in all brackets after irradiation. CONCLUSION: Although our evaluation of polymer brackets revealed considerable improvements in mechanical properties after EB irradiation, this benefit was marred by very obvious discoloration. We cannot therefore recommend industrial scale EB irradiation for any polymer bracket currently on the market.

Effects of mechanical and bacterial stressors on cytokine and growth-factor expression in periodontal ligament cells.

OBJECTIVES: The goal of the study was to examine the effects of a mechanical (orthodontic force simulation by static compressive loading) and a bacterial (endotoxins from a heat-inactivated gram-negative periodontal pathogen) stressor on the expression patterns of factors that are key to regulating osteoclastogenesis and bone remodeling. MATERIALS AND METHODS: Three experimental groups were formed with fifth-passage periodontal ligament (PDL) fibroblasts treated by the static application of compressive force (2 g/cm(2)), heat-inactivated aggregatibacter actinomycetemcomitans (1 × 10(7) cells), or both of these stressors combined. Real-time polymerase chain reaction (RT-PCR) was used to study gene expression of IL-6, IL-8, COX-2, IGF-1, VEGF, and MMP-13 in the 3 groups. Protein levels of COX-2, prostaglandin E2 (PGE(2)), and IL-8 production were quantified using immunoblotting and enzyme-linked immunosorbent assay (ELISA). RESULTS: The mechanical stressor upregulated the genes of COX-2, IL-8, IGF-1, and MMP-13 in PDL fibroblasts and the bacterial stressor upregulated IL-6, IL-8, COX-2 and MMP-13. Both stressors in combination upregulated VEGF and caused COX-2 gene expression to increase further; the latter effect was also detected at the protein level and indirectly via the enhanced production of PGE(2). We noted that the posttranscriptional regulation of IL-8 was induced by the mechanical stressor and influenced by PGE(2). CONCLUSION: While mechanical-stressor application increased the gene expression of COX-2, IL-8, and VEGF in the presence of the bacterial stressor, IL-8 production was posttranscriptionally regulated by the mechanical stressor, whereas COX-2 expression correlated with enhanced production of the inflammatory tissue hormone PGE(2), which exerted a suppressive effect on endotoxin-induced IL-8 production.

Flexural strength of experimentally filled resins made of electron beam irradiated silica fillers.

This study investigated the influence of different silica fillers on the flexural strength of experimentally filled resins. Hydrophilic (non-silanated) silica, hydrophobic silica modified by organofunctional silane, and silica modified by organofunctional silane that additionally contains polymerizable carbon double bonds were assigned into further subgroups: the first subgroup was electron beam irradiated with 10 kGy (dose rate) and the second with 30 kGy, whereas the third constituted the non-irradiated control group. In total, nine experimentally filled resin blends were mixed. Rectangular specimens were constructed, and a flexural strength test was performed. Regardless of the type of silica, specimens constructed of blends containing non-irradiated fillers showed the lowest flexural strength in comparison to their corresponding irradiated groups. With increasing dose rates from 10 to 30 kGy, filler irradiation prior to blend mixing resulted in slightly increased flexural strength values for hydrophilic as well as for organofunctional silanated silica. Specimens constructed of blends with fillers that were not only modified by silane containing polymerizable carbon double bonds but were additionally irradiated showed the highest flexural strength. The results of this study indicate that the flexural strength of filled resins could be enhanced by advance preparation of silica fillers with silane coupling agents followed by electron beam irradiation.

Investigations about N-aminopropyl transferases probably involved in biomineralization.

Polyamines are widespread distributed all over in living organisms. In Thalassiosira pseudonana 10 N-aminopropyl transferase like nucleotide sequences exists. It is assumed that these sequences are involved in the biomineralization of the diatom shell. The cDNA of the sequences were cloned, recombinant overexpressed and assayed with decarboxylated S-adenosylmethionine and several radioactive labelled polyamines. However, only a spermidine synthase and a thermospermine synthase were found to be enzymatically active in an in vitro assay. Both enzyme activities could be recognized in the crude extracts of Thalassiosira pseudonana and Cyclotella meneghiana. In further investigations the kinetics of the thermospermine synthase was determined and a site-specific mutagenesis of the bindig cavity of decarboxylated S-adenosylmethionine was carried out.

Conventionally ligated versus self-ligating metal brackets--a comparative study.

The purpose of this study was to compare the frictional properties of four self-ligating metal brackets, Speed, Damon 2, In-Ovation, and Time, with those of three conventionally ligated metal brackets, Time, Victory Twin, and Discovery. The self-ligating Time bracket can also be used as a conventionally ligated bracket. Friction was tested 20 times for each bracket/wire combination using a Zwick testing machine with stainless steel wires in three different wire dimensions (0.017 x 0.025, 0.018 x 0.025, and 0.019 x 0.025 inches). All brackets had a 0.022 inch slot and the prescription of an upper first premolar. The data were statistically analysed with unsigned comparisons of all bracket/wire combinations using the Mann-Whitney U-test and the Games-Howell post hoc test. The results showed almost all brackets to have the lowest frictional force with a wire dimension of 0.018 x 0.025 inch. Friction of the self-ligating brackets using wire with a dimension of 0.018 x 0.025 inches was 45-48 per cent lower than with 0.017 x 0.025 and 0.019 x 0.025 inch wires. Friction of the conventionally ligated brackets showed a 14 per cent or less reduced friction with 0.018 x 0.025 inch wire compared with 0.017 x 0.025 and 0.019 x 0.025 inch wires. The self-ligating metal brackets showed lower frictional forces with a 0.018 x 0.025 inch wire than conventionally ligated brackets, whereas conventionally ligated brackets showed lower friction with 0.017 x 0.025 and 0.019 x 0.025 inch wire. Friction values vary with different bracket/archwire combinations and, therefore, the choice of a bracket system for treatment should consider the correct wire dimension to produce the lowest possible frictional forces.

Experimental composites made of electron beam irradiated reinforced fillers.

This study investigated the influence of electron beam irradiated reinforced fillers on the three body wear and flexural strength of experimental composite blends. Three formulations of reinforced fillers were investigated: (A) high loaded inorganic filler composite with 60 wt.% SiO2, (B) low loaded inorganic filler composite with 40 wt.% SiO2, (C) organic filler composite (precipitated Bis-phenol-A-di-methacrylate). The fillers were assigned to two subgroups of unswollen (A, B, C) and monomer swollen (As, Bs, Cs) fillers. The experimental blends (matrix: Urethane-dimethacrylate) were mixed using un-treated, annealed (90 degrees C), or electron beam irradiated fillers with 30 and 90 kGy, respectively. All specimens were heat-cured for 20 min at 140 degrees C. Three-body abrasion and flexural strength tests were performed. The highest flexural strength was evaluated for composites made of the 30 kGy irradiated type Bs filler. The comparison with annealed fillers showed that the effect was independent of increasing temperatures during the radiation process. Blends with a SiO2 content of 60 wt.% (type A, As) had significantly less wear than blends with 40 wt.% (type B, Bs) or blends with organic fillers (type C, Cs). The flexural strength of the composite could be improved by using pre-irradiated reinforced fillers. However, wear was not affected using this procedure.

Frictional properties of aesthetic brackets.

The purpose of this study was to compare the frictional properties of two self-ligating aesthetic brackets, Opal (Ultradent Products) and Oyster (Gestenco Int.), with those of four conventionally ligated aesthetic brackets, Transcend (3M Unitek), Inspire (Ormco), Allure (GAC Int.), and Image (Gestenco Int.). Friction was tested with different wire dimensions and qualities [stainless steel (SS) wire 0.017 x 0.025 inches; SS 0.019 x 0.025 inches; TMA 0.019 x 0.025 inches] using a Zwick testing machine. All brackets had a 0.022-inch slot and the prescription of an upper first premolar of the Roth system (tip: 0 degrees, torque: -7 degree). Each bracket/archwire combination was tested 10 times and each test was performed with a new bracket/wire sample that was pulled through twice. Additionally, two sets of 30 Opal brackets each were aged with an ageing machine under standardized conditions for 9-10 and 18-20 months, respectively. Friction of the aged brackets was tested with identical wire dimensions and qualities using the same testing procedure. All data were statistically analysed with unsigned comparisons of all bracket/wire combinations using GLM and the Games-Howell post hoc test. The results showed Opal brackets to have the lowest frictional forces for all wire dimensions and qualities. Furthermore, friction was lower at a significant level (P

Electron beam irradiation of denture base materials.

UNLABELLED: Electron beam irradiation can be used to influence the properties of polymers. It was the aim of this study to investigate whether PMMA denture base materials can benefit from irradiation in order to have increased fracture toughness, work of fracture or hardness. Rectangular specimens of heat-and auto-curing denture base materials were electron beam irradiated (post-cured) with 25, 100 and 200 kGy using an electron acceleration of 10 MeV or 4.5 MeV respectively. Fracture toughness, work of fracture, Vickers hardness and colour changes were measured and compared with not-irradiated specimens. The toughness, work of fracture and hardness increased using 10 MeV with a dose of 25 kGy and with 100 kGy using 4.5 MeV. However, the clinical use may not benefit from the observed small changes. Higher dosage (200 kGy) decreased the values significantly. The colour changes reached a level which was found to be not clinically acceptable. CONCLUSION: PMMA denture base materials do not benefit from post-curing with electron beam irradiation.