Polymer Mixtures for Experimental Self-Limited Dental Burs Development-A Preliminary Approach (Part 1).

Alternative techniques have been investigated for effectiveness in caries removal because conventional metallic dental burs can lead to an excessive loss of sound tissue. The aim of the present study is to realize a preliminary approach in obtaining effective polymer mixtures for polymeric bur development, capable of removing primary dental caries using combinations of polymers to ensure the requirements for such instruments, but also a greater compatibility with the teeth structure. This study assessed the main mechanical properties, water sorption, solubility and microscopic structure of four new polymer mixture recipes to provide essential features in obtaining experimental self-limited dental burs. Two mixtures have in their composition polymer mixtures of Bis-phenol A diglycidyl ether dimethacrylate/Triethylene glycol dimethacrylate/Urethane dimethacrylates (R1, R2), and two other mixtures have Bis-phenol A diglycidyl ether dimethacrylate/Polymethyl methacrylate/Methyl methacrylates (R3, R4). The incorporation of nanoparticles into the polymer matrix has become essential due to the need of polymer biocompatibility increasing along with teeth surface remineralization, so that the powder charge was added to four recipes, such as 5% glass with BaF2 and 0.5% graphene with silver particles. All data sets were analyzed using the One-Way ANOVA test. R3, R4 showed higher compressive strength and diametrical compression values; these values increased when glass and graphene were added. Moreover, the addition of glass particles lead to an increase in flexural strength. Regarding the sorption, sample R3 had the most significant differences between day 69 and the rest of the investigation days, while the solubility varied at different intervals. From the mechanical evaluation, we could conclude that the Bis-GMA/PMMA/MMA mixtures fit the mechanical characteristics supported by polymer burs, following future studies regarding their use on the affected dentin.

On the Apparent Redox Reactivity of "Oxygen-Enriched Water".

Molecular oxygen-enriched water (OxEW) is advocated in popular media as useful for various health issues, presumably due to involvement of a purported antioxidant activity and to such notions as "active oxygen." To our knowledge, there are no explicit reports in the scientific literature where such redox reactivity would be described and explained. Reported here are data showing that a commercial preparation of OxEW does display a measurable, albeit very small, antioxidant activity as monitored by reaction with a standard reagent, DPPH. Moreover, OxEW also displays an apparent pro-oxidant reactivity, against caffeic acid. This does not correlate with any UV-vis-detectable contents of chemical substances in the water, nor can it be explained by typical chemical impurities (e.g., hydrogen peroxide or molecular hydrogen) that would arise upon enrichment with molecular oxygen of pure water by the two most common procedures: purging with gaseous O2 or electrolysis. Instead, this apparent redox reactivity is revealed to be due to differences in pH and in chemical content - and the differences in turn are most likely due to the trace amounts of inorganic ions/elements in the OxEW; importantly, electrolysis, which is often employed as a means to generate O2 in OxEW preparation, is also found to enhance the redox effect of OxEW-like preparations. Thus, in line with expectations, the herein-reported data show that there are no long-lived reactive oxygen species, no activated oxygen, and no extra reducing agents in OxEW - but that an apparent weak redox reactivity can still be measured and assigned to simple side effects of the electrolysis procedure presumably performed in order to enrich the sample in oxygen.

Preparation and Characterization of Natural Bleaching Gels Used in Cosmetic Dentistry.

The novelty of this study consists of the formulation and characterization of three experimental bleaching gels with hydroxylapatite oxides and fluorine (G28®, G29®, G30®) based on natural fruit extracts compared to the commercial Opalescence 15% (GC, Ultradent, South Jordan, UT, USA). Studies have been conducted on the effect that the experimental bleaching gels have on the color and morphology of different restorative materials (Nanofill®-Schulzer, P.L. Superior Dental Materials GmbH, Hamburg, Germany, and experimental nanocomposites (P11®, P31®, P61®)), immersed in coffee and artificial saliva (for 10 days and 30 days). The study also includes a cytotoxicity test on the gels and nanocomposites after bleaching, with ISO 109993-5 protocols on human dental follicle stem cells. UV-VIS spectroscopy, computerized measurement, and fluorescence spectrometry were used in order to observe the color changes, while the microstructure of the surface was investigated by Scanning Electron Microscopy (SEM). All of the samples immersed in coffee showed the highest color shift in comparison to the baseline. The color difference ΔE values obtained using the two methods (UV-Vis, computerized based on digital images) both after coloring and bleaching, respectively, were different for all four types of nanocomposites stored in the coffee, while no difference was observed in those stored in artificial saliva. The studied experimental gels and nanocomposites had a low cytotoxic effect on cell cultures after bleaching.

Development of new radiopaque glass fiber posts.

The aim of this study was to analyze the radiopacity and filler content of three experimental glass fiber posts (EGFP) in comparison with other glass/carbon fibers and metal posts from the dental market. Three EGFP were obtained by pultrusion of glass fibers in a polymer matrix based on 2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)-phenyl]propane (bis-GMA) and triethyleneglycol dimethacrylate (TEGDMA) monomers. Using intraoral sensor disks 27 posts, as well as mesiodistal sections of human molar and aluminum step wedges were radiographed for evaluation of radiopacity. The percentage compositions of fillers by weight and volume were investigated by combustion analysis. Two EGFP showed radiopacity higher than enamel. The commercial endodontic posts showed radiopacity as follows: higher than enamel, between enamel and dentin, and lower than dentin. The results showed statistically significant differences (p b 0.05)when evaluatedwith one-way ANOVA statistical analysis. According to combustion analyses, the filler content of the tested posts ranges between 58.84wt.% and 86.02wt.%. The filler content of the tested EGFP ranged between 68.91 wt.% and 79.04 wt.%. EGFP could be an alternative to commercial glass fiber posts. Futureglass fiber posts are recommended to present higher radiopacity than dentin and perhaps ideally similar to or higher than that of enamel, for improved clinical detection. The posts with a lower radiopacity than dentin should be considered insufficiently radiopaque. The radiopacity of some glass fiber posts is not greatly influenced by the amount of filler.

Assessing the biocompatibility of a dental composite product.

OBJECTIVE: The purpose of the study was to assess the biocompatibility of a composite material considering the reaction caused at the implant site during 21 days by daily observing the subjects' behavior as well as by macroscopic examination and histological examination upon expiry of the testing period. MATERIALS AND METHODS: We performed the tolerance test by implant of the composite material Dualcim. The implant test was made on two species of lab animals, Guinea pigs and Wistar rats in two versions: subcutaneous implant and intramuscular÷perimuscular implant. RESULTS: After a 21 days period, when the implant was in direct contact with the tissue, no change of the shape and consistency, color or surface of the implant occurred. Around the implants, the biocompatibility was kept under physiological limits. CONCLUSIONS: The product, in the structure and shape presented, could be easily placed under good conditions, both at the level of the subcutaneous tissue and at inter-muscular level. In case of both species and in all subjects, the histological exam proved a favorable development of the relationship between the implant body and the placing site.

Influence of inorganic filler content on the radiopacity of dental resin cements.

Digital radiography was used to measure the radiopacity of 18 resin cements to determine the influence of inorganic filler content on radiopacity. Four disk specimens (n=4) of each light-curing cement were digitally radiographed alongside an aluminum step wedge using an intraoral sensor (XIOS Plus, Sirona, Germany), and their mean gray value measured. Percentage of filler by weight was determined using an analytical combustion furnace. Data were statistically analyzed using one-way ANOVA and Tukey's test (α=0.05). All materials were more radiopaque than dentin and 12 materials were more radiopaque than enamel. Filler percentage ranged between 17.36 to 53.56 vol% and radiopacity between 1.02 to 3.40 mm Al. There were no statistically significant differences in inorganic filler percentage and radiopacity among the different shades of the same material (p>0.05), but the highest radiopacity was measured for the material which contained a higher percentage of filler.