Bond Strength of an Amorphous Calcium Phosphate–Containing Orthodontic Adhesive

Objective: To determine whether an amorphous calcium phosphate (ACP)-containing adhesive has an acceptable level of shear bond strength to be used as an orthodontic adhesive. Materials and Methods: Sixty extracted premolars were randomly divided into three groups for orthodontic bonding. Group 1 used a composite resin adhesive (Transbond XT), group 2 was bonded with an ACP-containing adhesive (Aegis Ortho), and group 3 used a resin-modified glass ionomer (Fuji Ortho LC). All bonded teeth were stored in distilled water at 37°C for 40 ± 2 hours prior to debonding. Shear bond strength and adhesive remnant index (ARI) were recorded for each specimen. Results: The mean shear bond strengths for the three test groups were: group 1 (15.2 ± 3.6 MPa), group 2 (6.6 ± 1.5 MPa), and group 3 (8.3 ± 2.8 MPa). A one-way analysis of variance showed a significant difference in bond strengths between the groups. A post hoc Tukey test showed group 1 to be significantly (P \u3c .001) greater than groups 2 and 3. A Kruskal-Wallis test and a Mann-Whitney U-test showed groups 1 and 3 exhibited lower ARI scores than group 2, but a majority of specimens in each group had greater than 50% of the cement removed along with the bracket during debonding. Conclusions: The ACP-containing adhesive demonstrated a low, but satisfactory bond strength needed to function as an orthodontic adhesive

Analysis of Flexural Strength and Contact Pressure After Simulated Chairside Adjustment of Pressed Lithium Disilicate Glass-Ceramic

Statement of problem Research evaluating load-to-failure of pressed lithium disilicate glass-ceramic (LDGC) with a clinically validated test after adjustment and repair procedures is scarce. Purpose The purpose of this in vitro study was to investigate the effect of the simulated chairside adjustment of the intaglio surface of monolithic pressed LDGC and procedures intended to repair damage. Material and methods A total of 423 IPS e.max Press (Ivoclar Vivadent AG) disks (15 mm diameter, 1 mm height) were used in the study. The material was tested by using an equibiaxial loading arrangement (n≥30/group) and a contact pressure test (n≥20/group). Specimens were assigned to 1 of 14 groups. One-half was assigned to the equibiaxial load test and the other half underwent contact pressure testing. Testing was performed in 2 parts, before glazing and after glazing. Before-glazing specimens were devested and entered in the test protocol, while after-glazing specimens were devested and glazed before entering the test protocol. Equibiaxial flexure test specimens were placed on a ring-on-ring apparatus and loaded until failure. Contact pressure specimens were cemented to epoxy resin blocks with a resin cement and loaded with a 50-mm diameter hemisphere until failure. Tests were performed on a universal testing machine with a crosshead speed of 0.5 mm/min. Weibull statistics and likelihood ratio contour plots determined intergroup differences (95% confidence bounds). Results Before glazing, the equibiaxial flexural strength test and the Weibull and likelihood ratio contour plots demonstrated a significantly higher failure strength for 1EC (188 MPa) than that of the damaged and/or repaired groups. Glazing following diamond-adjustment (1EGG) was the most beneficial post-damage procedure (176 MPa). Regarding the contact pressure test, the Weibull and likelihood ratio contour plots revealed no significant difference between the 1PC (98 MPa) and 1PGG (98 MPa) groups. Diamond-adjustment, without glazing (1EG and 1PG), resulted in the next-to-lowest equibiaxial flexure strength and the lowest contact pressure. After glazing, the strength of all the groups, when subjected to glazing following devesting, increased in comparison with corresponding groups in the before-glazing part of the study. Conclusions A glazing treatment improved the mechanical properties of diamond-adjusted IPS e.max Press disks when evaluated by equibiaxial flexure and contact pressure tests. Clinical Implications When adjustments are made on the intaglio surface of a pressed lithium disilicate glass-ceramic, a subsequent glazing treatment is recommended to improve strength

Edge Chipping Resistance and Flexural Strength of Polymer Infiltrated Ceramic Network and Resin Nanoceramic Restorative Materials

Statement of problem Two novel restorative materials, a polymer infiltrated ceramic network (PICN) and a resin nanoceramic (RNC), for computer-assisted design and computer-assisted manufacturing (CAD-CAM) applications have recently become commercially available. Little independent evidence regarding their mechanical properties exists to facilitate material selection. Purpose The purpose of this in vitro study was to measure the edge chipping resistance and flexural strength of the PICN and RNC materials and compare them with 2 commonly used feldspathic ceramic (FC) and leucite reinforced glass-ceramic (LRGC) CAD-CAM materials that share the same clinical indications. Material and methods PICN, RNC, FC, and LRGC material specimens were obtained by sectioning commercially available CAD-CAM blocks. Edge chipping test specimens (n=20/material) were adhesively attached to a resin substrate before testing. Edge chips were produced using a 120-degree, sharp, conical diamond indenter mounted on a universal testing machine and positioned 0.1 to 0.7 mm horizontally from the specimen’s edge. The chipping force was plotted against distance to the edge, and the data were fitted to linear and quadratic equations. One-way ANOVA determined intergroup differences (α=.05) in edge chipping toughness. Beam specimens (n=22/material) were tested for determining flexural strength using a 3-point bend test. Weibull statistics determined intergroup differences (α=.05). Flexural modulus and work of fracture were also calculated, and 1-way ANOVA determined intergroup differences (α=.05) Results Significant (PLRGC=FC\u3ePICN; flexural strength: RNC=LRGC\u3ePICN\u3eFC; flexural modulus: RNCLRGC=PICN\u3eFC. Conclusions The RNC material demonstrated superior performance for the mechanical properties tested compared with the other 3 materials

A survey of high level frameworks in block-structured adaptive mesh refinement packages

pre-printOver the last decade block-structured adaptive mesh refinement (SAMR) has found increasing use in large, publicly available codes and frameworks. SAMR frameworks have evolved along different paths. Some have stayed focused on specific domain areas, others have pursued a more general functionality, providing the building blocks for a larger variety of applications. In this survey paper we examine a representative set of SAMR packages and SAMR-based codes that have been in existence for half a decade or more, have a reasonably sized and active user base outside of their home institutions, and are publicly available. The set consists of a mix of SAMR packages and application codes that cover a broad range of scientific domains. We look at their high-level frameworks, their design trade-offs and their approach to dealing with the advent of radical changes in hardware architecture. The codes included in this survey are BoxLib, Cactus, Chombo, Enzo, FLASH, and Uintah

Effect of Toothbrushing On Shade and Surface Roughness of Extrinsically Stained Pressable Ceramics

Statement of problem The effect of toothbrushing on extrinsically stained pressable ceramic materials is unknown. Purpose The purpose of this in vitro study was to investigate the effects of toothbrushing on the shade and surface roughness of extrinsically stained, pressable ceramics. Material and Methods Two materials, leucite-based (IPS Empress Esthetic [EE]; Ivoclar Vivadent AG) and lithium disilicate-based ceramic (IPS e.max Press [EP]; Ivoclar Vivadent AG), were studied. For each material, 24 disk-shaped specimens, 10 mm (diameter)×3 mm (height) were fabricated. Three different methods (n=8) of applying extrinsic stains were performed on each material: glazed only (G, control group); stained then glazed (SG); and stained and glazed together (T). The specimens were brushed with a multistation brushing machine under a load of 1.96 N at a rate of 90 strokes per minute with a soft and straight toothbrush (Oral-B #35) and a 1:1 toothpaste and distilled water slurry. Shade and roughness were measured at baseline and at 72, 144, 216, and 288 hours, which is equivalent to 3, 6, 9, and 12 years of simulated toothbrushing for 2 minutes twice a day. A repeated measures ANOVA with staining technique as a fixed factor was used to evaluate shade and roughness (α=.05). Results For EE groups, no significant change was found after 12 years of simulated toothbrushing regarding shade and surface roughness, irrespective of staining techniques (P\u3e.05). However, EP groups demonstrated a significant shade change and an increase in surface roughness after 12 years of simulated toothbrushing. Shade change was found to depend on the method of applying stain. For the EP-SG technique, a significant shade change was observed only at the 9- to 12-year interval (P=.047). However, the EP-T technique demonstrated a significant difference in shade between baseline and 3 years (P=.005) and in the 6- to 9-year interval (P=.005). Surface roughness was only significantly affected at baseline and 3 years for the EP-T group (P=.005). Conclusions For the shade and surface roughness of the EE groups, no statistically significant difference was found after 12 years of toothbrushing, irrespective of the staining technique. The shade and surface roughness of the EP groups were significantly statistically affected by toothbrushing time; only shade changes were found to depend on technique

Understanding, Assessing, and Mitigating Safety Risks in Artificial Intelligence Systems

Prepared for: Naval Air Warfare Development Center (NAVAIR)Traditional software safety techniques rely on validating software against a deductively defined specification of how the software should behave in particular situations. In the case of AI systems, specifications are often implicit or inductively defined. Data-driven methods are subject to sampling error since practical datasets cannot provide exhaustive coverage of all possible events in a real physical environment. Traditional software verification and validation approaches may not apply directly to these novel systems, complicating the operation of systems safety analysis (such as implemented in MIL-STD 882). However, AI offers advanced capabilities, and it is desirable to ensure the safety of systems that rely on these capabilities. When AI tech is deployed in a weapon system, robot, or planning system, unwanted events are possible. Several techniques can support the evaluation process for understanding the nature and likelihood of unwanted events in AI systems and making risk decisions on naval employment. This research considers the state of the art, evaluating which ones are most likely to be employable, usable, and correct. Techniques include software analysis, simulation environments, and mathematical determinations.Naval Air Warfare Development CenterNaval Postgraduate School, Naval Research Program (PE 0605853N/2098)Approved for public release. Distribution is unlimite

Physical Properties of Denture Base Resins Potentially Resistant to \u3cem\u3eCandida\u3c/em\u3e Adhesion

Purpose: The addition of anionic charge on denture base resins has been shown to inhibit Candida albicans adhesion and to facilitate adsorption of salivary defense molecules. The aim of this study was to evaluate the physical properties of a modified denture base resin for denture fabrication. Materials and Methods: Specimens made from heat polymerizing resin Lucitone 199 were used as the control group. The two experimental groups, E-10 and E-20, had 10% and 20%, respectively, of the monomer substituted with an experimental phosphate-containing monomer. Flexural strength and modulus, water sorption, solubility, and color stability tests were conducted to ensure compliance with ADA specification No. 12. Water diffusion coefficient into the resins and stainability were also assessed. ANOVA and Scheffé tests were performed for statistical significance. Results: There was an overall decline in all properties with the addition of the experimental phosphate compound. The flexural strength and modulus, water sorption and solubility for E-10, as well as the control were, however, within the ADA specifications. The diffusion coefficients were significantly different (p \u3c 0.05) for the three groups. Staining and color specimens showed no significant difference (p \u3e 0.05) among the three groups. Conclusions: Within the limitations of this study, the physical properties of the phosphate denture base resin at 10% should be suitable for denture fabrication based on the properties assessed

A pilot study on occurrence of Yersinia enterocolitica and Yersinia pseudotuberculosis in Latvian pigs at slaughtering

The aim of the study was to detect the distribution of presumptive pathogenic Yersinia spec1es in pigs of Latvian origm. In total tonsils of 108 pigs were collected from 6 farms m two abattoirs situated in different parts of Latvia. Samples were investigated by using direct plating on the selective CIN media and cold enrichment technique for 2 weeks. All presumptive isolates were confirmed biochemically. During the direct plating only 58% of cultures of Y.enterocolitica and 4 Y. pseudotuberculosts were recovered. Y. enterocolitica was isolated from the pig tonsil samples orig1nated from all six farms The distribution of positive samples among different farms varied from 15 to 45%. Y. pseudotuberculosis was recovered from 3 out of 6 herds studied rangmg from 5 to 25% on each positive farm. The mean prevalence of Y.enterocolitica and Y. pseudotuberculosis in all six farms was 31% and 8% respectively Results of study indicate that none of the investigated herds was free of potentially pathogenic Yersinia. The presence of Yersinia species in pigs indicates that a possibility for contamination with bacteria occurs during the offal removal of and meat mspection of carcasses. Further investigations on pathogenic properties and slaughtenng techniques at the slaughterhouses involved in this study should be continued

Die Spacer Thickness Reproduction for Central Incisor Crown Fabrication with Combined Computer-aided Design and 3D Printing Technology: An in vitro Study

Statement of problem The inability to control die spacer thickness has been reported. However, little information is available on the congruency between the computer-aided design parameters for die spacer thickness and the actual printout. Purpose The purpose of this study was to evaluate the accuracy and precision of the die spacer thickness achieved by combining computer-aided design and 3-dimensional printing technology. Material and Methods An ivorine maxillary central incisor was prepared for a ceramic crown. The prepared tooth was duplicated by using polyvinyl siloxane duplicating silicone, and 80 die-stone models were produced from Type IV dental stone. The dies were randomly divided into 5 groups with assigned die spacer thicknesses of 25 μm, 45 μm, 65 μm, 85 μm, and 105 μm (n=16). The printed resin copings, obtained from a printer (ProJet DP 3000; 3D Systems), were cemented onto their respective die-stone models with self-adhesive resin cement and stored at room temperature until sectioning into halves in a buccolingual direction. The internal gap was measured at 5 defined locations per side of the sectioned die. Images of the printed resin coping/die-stone model internal gap dimensions were obtained with an inverted bright field metallurgical microscope at ×100 magnification. The acquired digital image was calibrated, and measurements were made using image analysis software. Mixed models (α=.05) were used to evaluate accuracy. A false discovery rate at 5% was used to adjust for multiple testing. Coefficient of variation was used to determine the precision for each group and was evaluated statistically with the Wald test (α=.05). Results The accuracy, expressed in terms of the mean differences between the prescribed die spacer thickness and the measured internal gap (standard deviation), was 50 μm (11) for the 25 μm group simulated die spacer thickness, 30 μm (10) for the 45 μm group, 15 μm (14) for the 65 μm group, 3 μm (23) for the 85 μm group, and -10 μm (32) for the 105 μm group. The precision mean of the measurements, expressed as a coefficient of variation, ranged between 14% and 33% for the 5 groups. Conclusions For the accuracy evaluation, statistically significant differences were found for all the groups, except the group of 85 μm. For the precision assessment, the coefficient of variation was above 10% for all groups, showing the printer’s inability to reproduce the uniform internal gap within the same group