Post Surfaces Research Articles

Capillary driven flow in micro scale surface structures

A variety of micro scale surface wicking structures that form open/covered post surfaces and open channels are investigated to probe the effect of the geometry, inter-connectivity, and surface porosity on the wicking efficiency of such surfaces. The surfaces are examined using a capillary rise flow experiment and the study is focused on the Lucas–Washburn flow regime in which capillary forces balance viscous forces.

Effect of Ferrule and Bonding on the Compressive Fracture Resistance of Post and Core Restorations

The purpose of this study was to compare the fracture resistance of endodontically treated teeth restored with different post and core systems in combination with complete metal crowns in teeth with no coronal structure. Fifty extracted mandibular premolars were divided into five groups. The coronal portion of each tooth was removed at the cementoenamel junction (CEJ) in all groups except Group 1. In this group the teeth were sectioned 1 mm above the CEJ to create a ferrule. After root canal preparations, cast posts were placed in the first four groups. Prefabricated glass fiber posts and composite cores were placed in the fifth group. An opaque porcelain layer was applied to the metal post surfaces in the third group and an alloy primer was applied to the posts in the fourth group before using Panavia F2 resin cement. No bonding agent or surface treatments were used for the first and second groups. A Ni-Cr full cast crown for each sample was prepared and cemented. A compressive load was applied at an angle of 45 degrees to the crown with a universal testing machine. After 500,000 mechanical cycles at 1.5Hz, the maximum load at fracture (N) was recorded. Significantly higher fracture resistance values (216.87 N) and survival rates (75%) were demonstrated for non-ferrule teeth restored with opaque layered posts than for other non-ferrule groups. The prefabricated post group showed the most favorable fracture pattern in all test groups (P=0.04). Either a ferrule preparation or bonding with the use of an opaque porcelain layer can increase the fracture resistance of teeth with little remaining tooth structure that are restored with cast crowns following endodontic therapy. Bonding cast posts to the tooth structure has a significant effect on compensating for the lack of a ferrule on endodontically treated teeth.

Influence of different surface treatments on the short-term bond strength and durability between a zirconia post and a composite resin core material

Reliable bonding between zirconia posts and composite resin core materials is difficult to achieve because of the smooth surface texture and lack of silica content of zirconia posts. The purpose of this study was to evaluate the effect of different surface treatments on the short-term bond strength and durability between a zirconia post and a composite resin core material. Eighty zirconia posts were divided into 4 groups (n=20). Specimens received 1 of 4 different surface treatments: group AIRB, airborne-particle abrasion; group TSC-SIL, tribochemical silica coating (CoJet system) and silanization (ESPE Sil); group AIRB-BSIL, airborne-particle abrasion and MDP-containing primer (Clearfil SE Bond Primer)/silane coupling agent (Clearfil Porcelain Bond Activator) mixture application; and group TSC-BSIL, tribochemical silica coating and MDP-containing primer/silane coupling agent mixture application. Average surface roughness (Ra) of zirconia posts produced by airborne-particle abrasion or silica coating was measured using an optical profilometer. Composite resin core foundations (Build-it FR) were formed using transparent acrylic resin tubes (12mm in length and 7mm in diameter). Each group was further divided into 2 subgroups of 10 specimens and stored in distilled water at 37 degrees C, either for 24 hours or for 150 days with 37,500 thermal cycles between 5 degrees C and 55 degrees C, with a dwell time of 30 seconds. Following water storage, the specimens were sectioned perpendicular to the bonded interface into 2-mm-thick post-and-core specimens under water cooling. Push-out tests were performed with a universal testing machine at a crosshead speed of 0.5mm/min. Debonded post surfaces were examined with SEM. Data were analyzed with 1- and 2-way ANOVA and Tukey multiple comparison tests (alpha=0.05). No significant differences were detected between the Ra values of airborne-particle-abraded and silica-coated specimens (P=.781). The short-term mean bond strengths for group TSC-BSIL (27.1 +/- 3.2 MPa) and TSC-SIL (25.2 +/- 2.4 MPa) were statistically higher (P<.001) than AIRB-BSIL (23.3 +/- 2.2 MPa). The relatively high bond strengths for groups TSC-BSIL and TSC-SIL decreased significantly after 150 days of water storage to 13.5 +/- 1.6 and 11.8 +/- 1.2 MPa, respectively (P<.001). Durable bonding was obtained only in group AIRB-BSIL (21.8 +/- 2.7 MPa), which was also the only group demonstrating predominantly cohesive failures in the core material after long-term water storage. Data suggest that the short-term high bond strength obtained with a silane coupling agent or MPD-containing primer/silane coupling agent mixture to silica-coated zirconia posts was decreased with water storage and thermal cycling, whereas a durable bond could be obtained when an MPD-containing primer/silane coupling agent mixture was applied to the airborne-particle-abraded post surface.

Surface Roughness Analysis of Fiber Post Conditioning Processes

The chemo-mechanical surface treatment of fiber posts increases their bonding properties. The combined use of atomic force and confocal microscopy allows for the assessment and quantification of the changes on surface roughness that justify this behavior. Quartz fiber posts were conditioned with different chemicals, as well as by sandblasting, and by an industrial silicate/silane coating. We analyzed post surfaces by atomic force microscopy, recording average roughness (R(a)) measurements of fibers and resin matrix. A confocal image profiler allowed for the quantitative assessment of the average superficial roughness (R(a)). Hydrofluoric acid, potassium permanganate, sodium ethoxide, and sandblasting increased post surface roughness. Modifications of the epoxy resin matrix occurred after the surface pre-treatments. Hydrofluoric acid affected the superficial texture of quartz fibers. Surface-conditioning procedures that selectively react with the epoxy-resin matrix of the fiber post enhance roughness and improve the surface area available for adhesion by creating micro-retentive spaces without affecting the post's inner structure.

Drops on Microstructured Surfaces Coated with Hydrophilic Polymers: Wenzel's Model and Beyond

In the experiments described in this paper, micromachined silicon post surfaces were coated with thin films of a polymer for which the contact angle on the smooth material was around 70 degrees . Drops wetted these surfaces in the Wenzel or "penetration" mode. We have determined the advancing and receding angles as a function of the roughness geometry and quantitatively compared our results to the contact angles predicted by Wenzel's model. We discuss reasons for discrepancies and propose a model for the motion of the meniscus where we take into account the precise shape of the liquid front during its movement through the post structure.

Influence of surface remodelling using burs on the macro and micro surface morphology of anatomically formed fibre posts

To evaluate the effect of modifying preformed fibre-reinforced composite (FRC) endodontic posts on their surface morphology and to determine how this procedure affects the integrity of the posts. Surfaces of 10 preformed glass-fibre posts (group 1) and carbon-fibre posts (group 2) were compared with those of individually formed glass-fibre posts (group 3). Ten FRC posts were modelled in order to give them a shape as close as possible to the anatomy of oval root canals. Starting from a preformed cylindrical fibre post 2.5 mm in diameter, it was modelled in such a way as to passively occupy the entire post-space length, using a cast previously created as a guide. Microscopic analyses (optical stereomicroscope and scanning electron microscope) of the post surfaces revealed similar features in all three groups. All posts had regular surfaces after cutting with a diamond bur. Smear layer mainly attributable to the cutting procedures covered the cut surface of some specimens. In conclusion, modulation of a fibre post using a diamond-coated bur did not show a loss of integrity of the post. *Because of the importance of micromechanical retention, the surface integrity of fibre posts may be important for adhesion between post and composite resin. *Modification of a fibre post using a diamond-coated bur did not damage the surface integrity of the posts. *Fibre posts can be ground to a different shape without losing their surface integrity, resulting in posts with a surface that is not visibly different from unmodified commercially available fibre posts.

Effects of chemical surface treatments of quartz and glass fiber posts on the retention of a composite resin

Failure of a fiber post and composite resin core often occurs at the junction between the 2 materials. This failure process requires better characterization. The purpose of this study was to evaluate the effect of 2 chemical solvents, hydrogen peroxide and methylene chloride, on the shear bond strength of quartz and glass fiber posts to a composite resin. Twenty-four posts (3 +/-0.1 mm in length) were prepared for each quartz (LIGHT-POST (LP)) and glass fiber (Cytec blanco (CB)) post. Posts were horizontally embedded in acrylic resin with half of the post diameter exposed. The exposed surfaces were successively ground with 400-, 800-, and 1200-grit silicon carbide papers, to ensure uniform smoothness. The specimens were divided into 3 subgroups (n=8) representing different surface treatment techniques, including application of silane for 60 seconds (S), etching with hydrogen peroxide for 20 minutes (H), and etching with methylene chloride for 5 seconds (M). Silane-treated specimens served as controls. A dual-polymerized composite resin (Tetric EvoCeram) was placed in a polytetrafluoroethylene mold (30 x 2 mm) positioned upon the post specimens and polymerized for 20 seconds with a light-emitting diode (LED) polymerization unit. The specimens were stored in water at 37 degrees C for 24 hours. Shear bond strength values (MPa) of posts and composite resin cores were measured using a universal testing machine with a crosshead speed of 0.5 mm/min. Data were analyzed by 2-way analysis of variance (ANOVA). Post hoc Tukey intervals for comparison among the 2 post materials and 3 surface treatment techniques were calculated (alpha =.05). The effect of the chemical surface treatments on glass and quartz fiber post surfaces were examined with a scanning electron microscope (SEM). There were significant differences between the shear bond strength for LP and CB (P<.001). For all groups, the application of H showed the highest bond strength values. There was no significant difference between the S and M groups (P>.05). The SEM observations demonstrated that the fiber post surfaces were modified after chemical surface treatment techniques. The surface treatment of quartz and glass fiber posts with hydrogen peroxide significantly enhanced the shear bond strength of the composite resin tested due to its ability to dissolve the epoxy resin matrix used in each post. The lowest bond strength was obtained with M and S groups. Application of methylene chloride to the fiber post surfaces for 5 seconds was not effective in increasing the shear bond strength of the fiber post to composite resin.

Decoupling of the Liquid Response of a Superhydrophobic Quartz Crystal Microbalance

Recent reports using particle image velocimetry and cone-and-plate rheometers have suggested that a simple Newtonian liquid flowing across a superhydrophobic surface demonstrates a finite slip length. Slippage on a superhydrophobic surface indicates that the combination of topography and hydrophobicity may have consequences for the coupling at the solid--liquid interface observed using the high-frequency shear-mode oscillation of a quartz crystal microbalance (QCM). In this work, we report on the response of a 5 MHz QCM possessing a superhydrophobic surface to immersion in water--glycerol mixtures. QCM surfaces were prepared with a layer of SU-8 photoresist and lithographically patterned to produce square arrays of 5 mum diameter circular cross-section posts spaced 10 microm center-to-center and with heights of 5, 10, 15, and 18 microm. Non-patterned layers were also created for comparison, and both non-hydrophobized and chemically hydrophobized surfaces were investigated. Contact angle measurements confirmed that the hydrophobized post surfaces were superhydrophobic. QCM measurements in water before and after applying pressure to force a Cassie-Baxter (non-penetrating) to Wenzel (penetrating) conversion of state showed a larger frequency decrease and higher dissipation in the Wenzel state. QCM resonance spectra were fitted to a Butterworth-van Dyke model for the full range of water-glycerol mixtures from pure water to (nominally) pure glycerol, thus providing data on both energy storage and dissipation. The data obtained for the post surfaces show a variety of types of behavior, indicating the importance of the surface chemistry in determining the response of the quartz crystal resonance, particularly on topographically structured surfaces; data for hydrophobized post surfaces imply a decoupling of the surface oscillation from the mixtures. In the case of the 15 microm tall hydrophobized post surfaces, crystal resonance spectra become narrower as the viscosity-density product increases, which is contrary to the usual behavior. In the most extreme case of the 18 microm tall hydrophobized post surfaces, both the frequency decrease and bandwidth increase of the resonance spectra are significantly lower than that predicted by the Kanazawa and Gordon model, thus implying a decoupling of the oscillating surface from the liquid, which can be interpreted as interfacial slip.

Effect of Adhesive Resin Cements and Post Surface Silanization on the Bond Strengths of Adhesively Inserted Fiber Posts

This study evaluated the tensile bond strengths and the effect of silanization of fiber posts inserted with different adhesive systems. Sixty DT Light Posts (size 1) were used. Thirty posts were pretreated with silane. The posts were cemented into form-congruent artificial root canals (12 mm) of bovine dentine. Six groups were formed: G1, Prime&Bond NT/Calibra; G2, Monobond-S+Prime&Bond NT/Calibra; G3, ED Primer/Panavia 21ex; G4, Monobond-S+ED Primer/Panavia 21ex; G5, RelyX Unicem; and G6, Monobond-S+RelyX Unicem. The mean (standard deviation) tensile bond strengths (megapascals) were 7.69 (0.85) for G1, 7.15 (1.01) for G2, 6.73 (0.85) for G3, 6.78 (0.97) for G4, 4.79 (0.58) for G5, and 4.74 (0.88) for G6. G1 achieved significantly higher bond strengths than G3 and G5; G3 had significantly higher values than G5 (P < .05; Scheffé procedure). Silanization had no significant effect (P > .05, one-way analysis of variance). Tensile bond strengths were significantly influenced by the type of resin cement. Silanization of fiber post surfaces seems to have no clinical relevance.

Bond strength between fibre posts and composite resin cores: effect of post surface silanization

To evaluate the tensile bond strength between two different composite resin cores and (Clearfil Core, MultiCore Flow) and fibre posts (DT Light Post), with and without silanization of the post surface. Forty fibre posts were shortened to a length of 15 mm. Specimens were then produced by covering the upper 3 mm of the posts with standardized composite core build-ups. The bonding surfaces of twenty posts were treated with silane coupling agent (Monobond-S). Four experimental groups were formed: G1: Clearfil Core; G2: Monobond-S + Clearfil Core; G3: MultiCore Flow; G4: Monobond-S + MultiCore Flow. Each post was positioned upright in a post centric device with moulds to ensure standardized shapes of the abutments. After tensile bond strength testing, the type of failure at the interface was determined. The results obtained were compared using an unpaired sample t-test. The mean tensile bond strengths and standard deviations were [MPa] 10.08 +/- 0.92 for Clearfil Core, 10.47 +/- 1.05 for Clearfil Core + silane; 6.65 +/- 0.79 for MultiCore Flow and 6.91 +/- 0.83 for MultiCore Flow + silane. Statistical analysis revealed that Clearfil Core achieved significantly higher bond strengths than MultiCore Flow (P < 0.0001). Post silanization had no significant effect. All tested specimens had an adhesive failure mode. Type of composite had a significant effect on tensile bond strength. Silanization of fibre post surfaces had no effect on core retention.

Influence of Surface Treatments on the Flexural Properties of Fiber Posts

The aim of this study was to evaluate the effect of three post-surface treatments on flexural properties of fiber posts. Three types of posts were selected (n = 88 per post type). Four groups of specimens were prepared for each different post (n = 22). For the control group, posts were used as supplied by the manufacturers. Silanization, hydrofluoric etching, and sandblasting with 50 microm Al(2)O(3) were performed on post surfaces for each of the other groups. Two posts of each group were submitted to a qualitative scanning electron microscopy (SEM) analysis. Remaining specimens were positioned in a universal testing machine and a three-point bending test was conducted (n = 20) until fracturing of the posts. Flexural strengths and flexural modules were calculated and recorded. None of the surface pretreatments had a significant influence on the tested properties of the posts (p > 0.05). Visual analysis of SEM micrographs showed significant changes of post surfaces determined by each conditioning treatment, which could increase post-retentive properties.

Condensation and Wetting Transitions on Microstructured Ultrahydrophobic Surfaces

On rough surfaces, two distinct wetting modes can appear. These two states are usually described by the theories of Cassie (drops suspended on top of roughness features) and Wenzel (drops impaled on roughness features). Whereas the wetting transition from the Cassie to the Wenzel state has been relatively well studied both experimentally and theoretically, the question of whether metastable Wenzel drops exist and how they transition to the Cassie state has remained open. In this work, we study the wetting behavior of microstructured post surfaces coated with a hydrophobic fluoropolymer. Through condensation, the formation of metastable Wenzel droplets is induced. We show that under certain conditions drops can transition from the Wenzel to the Cassie state.

Contact Line Shape on Ultrahydrophobic Post Surfaces

In this work, we investigate the configuration of the contact line of a water drop lying on an ultrahydrophobic post surface using the numerical algorithm Surface Evolver. For the special situation of Cassie wetting, we propose a modified definition of the contact line as the line in space where the meniscus starts to curve upward out of the plane of the composite surface. In our simulations, it is found that the contact line is very strongly distorted, indicating a strong tendency of the drop to "ball up" in those areas where it is not in contact with the solid surface. The distortion of the contact line corresponds to a pronounced deformation of the liquid-air interface around the base of the drop. We discuss the consequences of this distortion for the definition and practical measurement of the contact angle on ultrahydrophobic surfaces.

Effect of Surface Treatments on Tensile Bond Strength and on Morphology of Quartz-fiber Posts

This study evaluated the effect of three post surface treatments on quartz-fiber post (a) retention and (b) morphology. A control group was not treated. Different treatments were performed for the other posts: silanization; etching by hydrofluoric acid 9.5%; sandblasting with 50 μm Al 2O 3. Two specimens of each group were submitted to a qualitative scanning electron microscopy (SEM) analysis. Remaining specimens were luted in prepared root canals ( n = 10) and retentions were determined using a universal testing machine. Retentive post bond strengths were significantly enhanced with any tested post surface pretreatment. The increase in retentive strength was more remarkable in sandblasted and etched posts. Significant changes of post surfaces were SEM observed after different conditioning treatments.

Advancing and Receding Motion of Droplets on Ultrahydrophobic Post Surfaces

We have fabricated a range of silicon post surfaces where post width and spacing have been systematically varied. As one subset, we have generated surfaces where the post spacings in x and y assume different values. On these surfaces, the dynamic contact angles become anisotropic. A fluoropolymer monolayer is photochemically attached to the microstructured silicon, leading to the appearance of ultrahydrophobic properties. On one side, the advancing contact angles on these surfaces are not affected by variations in the geometric parameters. This furthers the conclusion that, during the advancing motion, a true contact angle of 180 degrees is reached. On the other side, the receding angles are strongly influenced by the post size and spacing. We quantitatively analyze this dependence and relate variations in the receding angle to the shape and movement of the three-phase contact line. It is suggested that during the receding motion the meniscus successively dewets from one post at a time, with a step function running along the contact line until it has receded from a row of posts over its entire length.

The fit of tapered posts in root canals luted with zinc phosphate cement: A histological study

Stress transmission to the root through passive fitting dental posts is partly influenced by the thickness of the cement layer between the post and the prepared root canal surface as well as the fit of the post in the root canal. The objective of this study was to compare the cement gap between the post surfaces and the root canals using five prefabricated, tapered, unthreaded titanium posts of different manufacturers, without and with cement. Following the endodontic treatment with hand instruments of 100 intact anterior teeth, post spaces were prepared using opening drills of the corresponding size of post. Fifty posts were cemented with zinc phosphate cement into the roots for each system while another 50 posts were inserted into the canal without using the cement. After histological sectioning, the cement gap was measured at six sites for three times at the coronal, middle and apical regions between the root canal wall and the post surface under a light microscope before and after cementation. Before cementation, the highest overall cement gap was observed with the Dr Mooser post system (46 microm) and the lowest with the Velva post system and Cylindro-Conical system (30 microm). Significantly less (P<0.05) mean cement gap was observed with respect to the Erlangen post system (41 microm), the Dr Mooser post system (48 microm), the MP Pirec post system (34 microm) and Velva post system (33 microm) when compared with the Cylindro-Conical system (62 microm). The Cylindro-Conical system (79, 61 microm) and MP Pirec post system (25, 24 microm) demonstrated no significant difference (P>0.001) compared with Velva-Post (38, 20 microm) at the coronal and middle part, respectively (Mann-Whitney U-test, Boneferroni correction). Significant differences (P<0.001) were observed between the cement gap at the coronal and apical part for the Cylindro-Conical system (79, 46 microm), Dr Mooser post system (45, 56 microm) and MP Pirec post system (25, 52 microm). After cementation, the highest cement gap at the coronal part was obtained with the Cylindro-Conical system (79+/-21 microm) and the lowest with the MP Pirec post system (25+/-9 microm). However, at the apical end, the MP Pirec post system (52+/-89 microm) and Dr Mooser post system (56+/-16 microm) revealed the highest gap. Form-congruence between the preparation drill and the post systems exhibited differences. The most consistent cement gap either at the coronal, middle or apical parts of the root canals was obtained with the Erlangen post system.

Effects of Wet Chemistry Pre-gate Clean Strategies on the Organic Contamination of Gate Oxides for Metal-Oxide-Semiconductor Field Effect Transistor

It is known that organic contamination can seriously degrade the electrical performance of gate oxides for metal-oxide-semiconductor field effect transistor (MOSFET) applications. In this paper, organic contamination of wafer surfaces cleaned by different pre-gate clean conditions and subsequently exposed to cleanroom ambience was investigated using time-of-flight secondary ion mass spectroscopy (TOF-SIMS), and the carbon level from thermally decomposed organic species directly trapped in the gate oxides after thermal oxidation and polysilicon deposition was probed using secondary ion mass spectroscopy (SIMS) depth profiling. The C concentration in the oxide-polysilicon gate stack obtained from SIMS depth profiling closely correlates with the total TOF-SIMS peak intensity of organic contaminants detected on post clean wafer surfaces. A quantified carbon concentration on the order of 1012 atoms/cm2 was obtained at the interfaces using SIMS depth profiling calibrated with an implanted C standard. It was found that the susceptibility of wafer surfaces to organic contamination that eventually affects the level of oxide-polysilicon interfacial carbon appears to be highly dependent on the surface termination.

Negative plastic flow and its prevention in elasto-plastic finite element computation

The phenomenon of negative plastic flow and its prevention in elasto-plastic numerical analyses, such as finite element computations, are investigated in detail. Discussions are confined to materials with smooth but otherwise arbitrary initial and post yield surfaces which obey associated or non-associated flow rules, with specializations for materials obeying the von Mises yield condition and its associated flow rule, and to materials with cornered yield surfaces obeying the associated flow rule. Current ad hoc treatments of this phenomenon and their effects on the accuracy and reliability of computer codes are discussed. Explicit results for some commonly used stress integration algorithms are presented as to when and why negative plastic flow will occur, and how it can be avoided with proper modification to the existing stress calculation procedures. Meanwhile, it is pointed out that in the case negative flow happens to tangent stiffness based algorithms, numerical errors are also involved in other algorithms. Finally, a general and numerically efficient approach for stress calculation at corner yield points is proposed, which is consistent with the Koiter's flow rule. The subject of uniqueness of the Koiter's flow rule representation is addressed in detail.

Preparation of TEM Sections using Natural Lithography

ABSTRACTWe have developed and used a simple lithographic technique that allows preparation of TEM sections from a variety of materials in 10–45 minutes. To obtain TEM sections, 50–5,000 Å diameter cylindrical post structures are microfabricated on the surface of the sample using colloidal particles as an etch mask. The technique simultaneously prepares 104 – 108 posts. This not only allows a statistical characterization of sample structure but also provides enough material for studies of the electronic, spectroscopic and chemical properties of edge sites exposed on the post surfaces. These lithographically prepared posts have been used to study the structure of materials as diverse as a layered transition metal chalcogenide catalysts, semi-insulating polysilicon, amorphous semiconductor superlattices, crystalline metallic and semiconductor superlattices, and molecular-scale microporous superlattices.