Influence of Modeling Liquids and Universal Adhesives Used as Lubricants on Color Stability and Translucency of Resin-Based Composites

The use of lubricants during restorative procedures is a clinically common practice to alleviate the stickiness of resin-based composite (RBCs) materials and to improve its handling. This study evaluated the effects of three modeling liquids (ML) and one universal adhesive (UA) used as lubricants during composite layering on the color stability and translucency of RBCs. Methods. The following materials were applied between every 1 mm RBC layer (total restoration height of 4 mm): GC modeling liquid (GCML, GC Corporation, Tokyo, Japan), composite wetting resin (UPWR, Ultradent Products, South Jordan, UT, USA), Bisco modeling resin (BSMR, Bisco Inc., Schaumburg, IL, USA) as an ML and Clearfil Universal Bond Quick (KUBQ, Kuraray Noritake Dental, Tokyo, Japan) as a UA. Lubricant-free specimens were used as the control. Color coordinates (L*, a* and b*) were recorded at baseline and after a simulation of 1 month of coffee consumption. Data were analyzed using ANOVA and a post hoc Tukey test (p < 0.05). Results. All lubricants induced a color change higher than the perceptibility threshold (ΔE00 > 0.81). GCML showed the highest color stability. The use of KUBQ resulted in significantly higher a* values (p = 0.001) at baseline and after staining. KUBQ and UPWR significantly influenced the color stability (ΔE00, p = 0.0001) after staining, overcoming the clinical acceptability threshold (ΔE00 > 1.77). Conclusions. The use of lubricants may affect color stability at baseline and after simulation of staining. Translucency was not affected at baseline nor after staining. Clinical Significance. Clinicians should be aware that some lubricants may affect color stability, even at baseline

CRITICAL SPEED OF FLAWED ROTORS: GLOBAL VS. LOCAL APPROACH

The burst of a disc in rotating machinery can cause catas- trophic damage of the equipment and, more importantly, it can represent a mortal threat to anyone in the sphere of influence of the event. In order to minimize the danger associated to a rotating component failure, burst testing is required by the au- thorities in order to set safety margins to the normal operating speeds. Moreover more accurate predicting tools are required for designing the components. This paper presents the results of a numerical and analytical study on the assessment of the crack driving force for discs containing surface flaws. The aim is to provide a simple, though reliable, tool in order to be able to calculate the possible dangerous in-service speed for a rotating component and, therefore, to set burst margins above the nor- mal operating conditions of the equipment. An R6-like flaw as- sessment procedure is adopted considering different assumptions in the definition of the critical speed and the analytical predic- tions are compared with the results of elastic-plastic finite ele- ment analysis of disc. In particular, the validity and potentiality of the method is proved for surface flaws in different positions in the disc

Sodium arsenite induces radiation-like damage in mammalian cells

92nd Annual Meeting of the American Association for Cancer Researc

Distribution of adhesive layer in class II composite resin restorations before/after interproximal matrix application

Objectives: This study aimed to morphologically investigate the distribution of the adhesive layer when placed prior, or subsequent, to matrix positioning in direct-bonded Class II RBC restorations. Additional aim was to evaluate possible differences when using two-steps (CSE, Clearfil SE Bond2) or one-step adhesive system (CU, Clearfil Universal Bond Quick). Methods: Standardized mesio-occlusal and disto-occlusal cavities were prepared on 20 human molars. Teeth were randomly allocated to two protocols according to the positioning of contoured sectional metal matrices before (M->A, n = 10), or after adhesive application (A->M, n = 10). Both adhesive systems were additioned with crystal violet dye (CV, 10 vol%). Specimen sections were evaluated using optical and scanning electron microscopy (SEM). Dynamic viscosity, pH, microshear bond strength test (\u3bc-SBS) on enamel and dentin, and three-point bend test (3PB) of polymerized adhesive rods, were performed on both pristine and CV-additioned adhesives. Results: M->A produced a layer of adhesive both on tooth-restoration interface and on external restoration surfaces in contact with the matrix. A->M produced a thin layer of adhesive on external tooth surfaces, well beyond cavity and RBC restoration margins. In all restorations, excess RBC material with uneven margins was observed protruding over the cervical margin. CV addition slightly increased pH and decreased viscosity. \u3bc-SBS: CU + CV showed a 10-fold reduction in adhesion forces on dentine. 3PB: CSE yielded higher flexural strength values than CU. CV addition reduced flexural strength of CSE. Conclusions: Both M > A and A > M generated adhesive placement disadvantages with adhesive materials being expressed in difficult to reach locations that may jeopardize complete adhesive polymerization. Clinical Significance: All cervical margins of RBC restorations should be carefully finished to improve longevity, no matter the clinical protocol adopted. CV addition labelled the tested adhesives without compromising their performances considerably

Induction of DNA double strand breaks by arsenite: comparative studies with DNA breaks induced by X-rays.

Chinese hamster ovary (CHO-K1) cell line and two of its DNA double strand break (DSB) repair deficient mutant cell lines, xrs-5 (Ku80 mutant) and irs-20 (DNA-PKcs mutant), were treated with various concentrations of sodium arsenite for 2.5 hrs, and the colony forming abilities were studied. The wild type cells showed the highest cell survival, while xrs-5 cells showed the lowest survival, and irs-20 cells had an intermediate survival. These results are very similar to the cell survival curves induced by x-rays in these three cell lines. Our data also shows the dose dependent induction of DNA DSBs in these cell lines exposed to arsenite. However, in order to obtain a similar cell survival in wild type cells, twice as many DNA DSBs are necessary with arsenite exposure when compared with x-rays, suggesting that the types of DNA lesions leading to DSB induced by arsenite are different from those by x-rays. Based on these data, further mechanistic investigations including the involvement of DNA DSB repair proteins are warranted in the recovery process from arsenic exposure

DCPD-containing composites prevent secondary caries: An in-vitro biofilm model

Purpose/aim: The aim of this study was to evaluate the ability of dicalcium phosphate dihydrate (DCPD) filler-containing resin-based composites (RBC) to prevent secondary caries formation using two in vitro models of cariogenic biofilm challenge. Materials and methods: Eight sound human molars had their root removed 3 mm apical to cement-enamel junction, and the pulp chamber filled (Majesty ES-2, Kuraray, Japan). Four Class II cavities were made in each tooth having cervical margin in dentin. Cavities were filled with: a conventional resin-modified glass ionomer cement (RMGIC, Ionolux, VOCO GmbH, Germany) or experimental RBCs having a BisGMA-TEGDMA resin blend and: 60 vol% Ba glass (RBC-0); 40 vol% Ba glass, 20 vol% DCPD (RBC-20); 20 vol% Ba glass, 40 vol% DCPD (RBC-40). Restorations were finished (diamond burs, silicon carbide papers), then specimens were sterilized, stored in artificial saliva for one week and randomly divided into 2 groups (n = 4/group) according to the biofilm model. Group 1: specimens were inserted in 6-well plates, and Streptococcus mutans biofilm formation on the specimens\u2019 surfaces was obtained in an orbital shaker (37 \ub0C, 100 rpm) incubating in 1:25 diluted BHI + 5 wt% sucrose for two weeks. Culture broth was changed daily. Group 2: specimens were inserted into the flow-cell of a continuous flow bioreactor (37 \ub0C, 20 ml/h), and S. mutans biofilm formation on the specimens\u2019 surfaces was obtained incubating in 1:25 diluted BHI + 5 wt% sucrose for two weeks. pH values of the culture broth and absence of contamination were checked daily in both groups. Before and after microbiological procedures, specimens were scanned using microCT (Skyscan 1176, 9 \u3bcm resolution, 80 kV, 300 mA). Image reconstruction was performed, and demineralization depths (\u3bcm) were evaluated at the margins and at 1.0 mm from the margins. Results: pH values stayed constant throughout the incubation time (Group 1: 4.2 \ub1 0.1; Group 2: 4.3 \ub1 0.1), and no contamination was observed. Dentin demineralization (no enamel demineralization) could be observed in all specimens. Significantly higher overall demineralization depth was found in specimens from Group 2 compared to Group 1. RBC-0 and RBC-20 showed secondary caries development, while RBC-40 and RMGIC showed a secondary caries prevention effect (Table 1). Table 1. Mean demineralization depth (\u3bcm \ub1 1 SD) of the tested specimens according to the microbiological models. Different superscript letters indicate significant differences between materials (Tukey test, p < 0.05). Material Group 1 Group 2 Margin Margin + 1.0 mm Margin Margin + 1.0 mm RBC-0 146.8(28.7)a,b 132.8(12.5)a,b 217.4(32.5)a 156.4(21.0)a RBC-20 156.5(42.8)a 108.8(11.6)b 214.5(44.9)a 163.4(29.8)a RBC-40 80.8(33.6)b 144.8(4.6)a 84.4(47.6)b 157.9(58.1)a RMGIC 87.8(20.8)b 125.5(25.4)a,b 100.0(51.0)b 176.8(60.9)a Conclusions: Experimental RBC-40 is a promising bioactive material, able to prevent secondary caries in vitro, similarly to the control RMGIC material. The bioreactor model displayed secondary caries formation in a similar way as in vivo