Fracture Resistance of Repaired 5Y-PSZ Zirconia Crowns after Endodontic Access

This study analyzed the fracture load before and after a chewing simulation of zirconia crowns that were trepanned and repaired using composite resin. Overall, 3 groups with 15 5Y-PSZ crowns in each group were tested. For group A, the fracture load of the unmodified crowns was evaluated. For group B, the crowns were trepanned and repaired using composite resin, also followed by a fracture test. For group C, crowns were prepared like in group B but received thermomechanical cycling before the final fracture tests. Furthermore, scanning electron microscopy (SEM) and X-ray microscopy (XRM) analysis were performed for group C. The mean fracture loads and standard deviation were 2260 N ± 410 N (group A), 1720 N ± 380 N (group B), and 1540 N ± 280 N (group C). Tukey-Kramer multiple comparisons showed a significant difference between groups A and B (p < 0.01) and groups A and C (p < 0.01). After ageing, surface fissures were detected via SEM, but no cracks that reached from the occlusal to the inner side of the crown were detected via XRM. Within the limitations of this study, it can be stated that trepanned and composite-repaired 5Y-PSZ crowns show lower fracture loads than 5Y-PSZ crowns without trepanation

Antibacterial properties and abrasion-stability: Development of a novel silver-compound material for orthodontic bracket application

Purpose: Bacteria-induced white spot lesions are a common side effect of modern orthodontic treatment. Therefore, there is a need for novel orthodontic bracket materials with antibacterial properties that also resist long-term abrasion. The aim of this study was to investigate the abrasion-stable antibacterial properties of a newly developed, thoroughly silver-infiltrated material for orthodontic bracket application in an in situ experiment. Methods: To generate the novel material, silver was vacuum-infiltrated into a sintered porous tungsten matrix. A tooth brushing simulation machine was used to perform abrasion equal to 2 years of tooth brushing. The material was characterized by energy dispersive X‑ray (EDX) analysis and roughness measurement. To test for antibacterial properties in situ, individual occlusal splints equipped with specimens were worn intraorally by 12 periodontal healthy patients for 48 h. After fluorescence staining, the quantitative biofilm volume and live/dead distribution of the initial biofilm formation were analyzed by confocal laser scanning microscopy (CLSM). Results: Silver was infiltrated homogeneously throughout the tungsten matrix. Toothbrush abrasion only slightly reduced the material’s thickness similar to conventional stainless steel bracket material and did not alter surface roughness. The new silver-modified material showed significantly reduced biofilm accumulation in situ. The effect was maintained even after abrasion. Conclusion: A promising, novel silver-infiltrated abrasion-stable material for use as orthodontic brackets, which also exhibit strong antibacterial properties on in situ grown oral biofilms, was developed. The strong antibacterial properties were maintained even after surface abrasion simulated with long-term toothbrushing

Combined NC-AFM and DFT study of the adsorption geometry of trimesic acid on rutile TiO2(110)

Greuling A, Rahe P, Kaczmarski M, Kühnle A, Rohlfing M. Combined NC-AFM and DFT study of the adsorption geometry of trimesic acid on rutile TiO2(110). Journal of Physics : Condensed Matter. 2010;22(34): 345008.The adsorption behavior of trimesic acid (TMA) on rutile TiO2(110) is studied by means of non-contact atomic force microscopy (NC-AFM) and density-functional theory (DFT). Upon low-coverage adsorption at room temperature, NC-AFM imaging reveals individual molecules, centered above the surface titanium rows. Based on the NC-AFM results alone it is difficult to deduce whether the molecules are lying flat or standing upright on the surface. To elucidate the detailed adsorption geometry, we perform DFT calculations, considering a large number of different adsorption positions. Our DFT calculations suggest that single TMA molecules adsorb with the benzene ring parallel to the surface plane. In this configuration, two carboxylic groups can anchor to the surface in a bidentate fashion with the oxygen atoms binding to surface titanium atoms while the hydrogen atoms approach oxygen atoms within the bridging oxygen rows. The most favorable adsorption position is obtained in the presence of a hydroxyl defect, allowing for additional binding of the third carboxylic group

Toward Molecular Nanowires Self-Assembled on an Insulating Substrate: Heptahelicene-2-carboxylic acid on Calcite (1014)

Rahe P, Nimmrich M, Greuling A, et al. Toward Molecular Nanowires Self-Assembled on an Insulating Substrate: Heptahelicene-2-carboxylic acid on Calcite (1014). Journal of Physical Chemistry C. 2010;114(3):1547-1552.Molecular self-assembly is employed for creating unidirectional molecular nanostructures on a truly insulating substrate, namely the (10 (1) over bar4) cleavage plane of calcite. The molecule used is racemic heptahelicene-2-carboxylic acid, which forms structures, well-aligned along the [010] crystallographic direction and stable at room temperature. Precise control of both molecule-substrate and molecule-molecule interaction is required, leading to the formation of such wire-like structures of well-defined width and lengths exceeding 100 nm. This subtle balance is governed by the heptahelicene-2-carboxylic acid used in this study, allowing for both hydrogen bond formation as well pi-pi stacking

Abrasion Behaviour of Different Charcoal Toothpastes When Using Electric Toothbrushes

Objectives: The purpose of this in vitro study was to compare the abrasion behaviour of different charcoal toothpastes when brushing with electric toothbrushes on human enamel. Materials and Methods: A self-designed brushing machine was built using six commercially available electric toothbrushes in abrasion chambers. Each chamber was constantly supplied with a toothpaste–water mix. Pieces of human enamel, which were embedded in PMMA, were brushed for 4 h. Before and after brushing, profilometer measurements were performed in order to determine the substance loss due to brushing. Results: The following calculated mean removal values (mean ± SD) were found: (4.6 ± 0.6) µm (Group C: Splat Blackwood), (3.2 ± 0.9) µm (Group D: Curaprox Black is White), (2.3 ± 0.7) µm (Group B: Sensodyne Pro Schmelz), (1.7 ± 0.6) µm (Group A: Water), (1.4 ± 0.6) µm (Group E: Prokudent Black Brilliant). A post hoc Tukey HSD test (p = 0.05) showed that the results for Group A/B/E, Group B/D and Group C each lie within subsets that differ statistically significantly from the other subsets. Conclusions: Within the limitations of this in vitro study, it can be stated that some charcoal toothpastes lead to significantly higher abrasion on human enamel, when brushing with electric brushes. Clinical Relevance: As low-abrasion toothpaste is generally advisable, and some charcoal toothpastes should be viewed critically with regard to their abrasive properties

Ab-initio-Untersuchungen von Oberflächen- und Bulksystemen

In dieser Arbeit setzen wir ab-initio-Methoden zur Untersuchung einiger Oberflächensysteme und eines Bulksystems ein. Im Wesentlichen greifen wir hierbei auf die Dichtefunktionaltheorie (DFT) und die GW-Approximation (GWA) im Rahmen der Vielteilchenstörungstheorie zurück. Wir nutzen diese Methoden um die Adsorption von TMA auf der Rutil TiO2-Oberfläche zu untersuchen, optische Spektren von TiO2 zu berechnen und um die Adsorption von [7]-HCA auf der Calcit(10-14)-Oberfläche zu verstehen. Weiterhin beschäftigen wir uns intensiv mit PTCDA auf Ag(111), welches mit einer chemisch kontaktierten STM-Spitze manipuliert wird

Automated Remodelling of Connectors in Fixed Partial Dentures

In this study, an approach for automated parametric remodelling of the connector cross-sectional area in a CAD model of a given fixed partial denture (FPD) geometry was developed and then applied to a 4-unit FPD. The remodelling algorithm was implemented using Rhinoceros and the Grasshopper plugin. The generated CAD models were used to perform a finite element analysis with Ansys to analyse the stress distribution in an implant-supported 4-unit FPD for different connector designs. The results showed that the type of connector adjustment matters and that the resulting stress can be significantly different even for connectors with the same cross-sectional area. For tensile stresses, a reduction in the connector cross-sectional area from the gingival side showed the highest influence on each connector type. It can be concluded that the developed algorithm is suitable for automatic connector detection and adjustment

Abrasion Behavior of Different Charcoal Toothpastes on Human Dentin When Using Electric Toothbrushes

The aim of this study was to investigate abrasion on human dentin after brushing with activated charcoal toothpastes. A self-designed brushing machine was used to brush five groups (Group A: Water, Group B: Sensodyne Pro Schmelz, Group C: Splat Blackwood, Group D: Curaprox Black is White, and Group E: Prokudent Black Brilliant) with electrically powered toothbrushes for 4 h. The abrasive dentin wear was calculated using profilometry data. Furthermore, thermogravimetric analyses and scanning electron microscopy were used to analyze the composition of the toothpastes. Mean dentin loss by brushing were (71 ± 28) µm (Splat Blackwood), (44 ± 16) µm (Curaprox Black is White), (38 ± 13) µm (Prokudent Black Brilliant), (28 ± 14) µm (Sensodyne Pro Schmelz), and (28 ± 13) µm (Water). Groups A/B/D/E and group C each lie in one subset, which is statistically different from the other subset according to a post hoc Tukey test (p = 0.05). Within the limitations, it can be concluded that the content of activated charcoal in charcoal toothpastes had little influence on the observed abrasive behavior, although one of the charcoal toothpastes showed the highest abrasion on dentin