759 research outputs found
Retention of quartz fiber posts using different luting cements
No full textObjectives: To determine the effect on the pull-out strength of threads cut into the surface of quartz fiber post cemented with three luting materials.
Methods: 42 human single-rooted, crownless teeth were treated endodontically and randomly assigned to six fiber posts groups: 1) to 3) were restored with Macro-Lock#3 posts (RTD); 4) to 6) with control posts made of the same material but lacking threads (RTD). The posts were cemented 12mm deep using Panavia(Kuraray), RelyX Unicem (3M ESPE), and Fuji Plus (GC) following the manufacturer instructions. The specimens were subjected to 5000 thermal cycles at 5 and 55°C and wet stored. Retentions were made on the emerging portion of the controls using a diamod bur, then a composite core was made using a mold. A pull-out stress was applied by clamping the core with an Instron machine (2mm/min speed). The pull-out strength was recorded for each group and compared (alpha=0.05). After the test, the specimens were observed under the stereomicroscope to determine failure patterns.
Results: The Macro-Lock demonstrated higher retention with all the luting materials employed, statistically significant when RelyX and Fuji were used (
Effect of fiber posts with different emerging diameters on the fracture strength of restored crownless teeth.
No full textThe relatively low elastic modulus of fiber posts reduces the risk of root fracture, but it also decreases composite core stabilization. To compensate for the lack of rigidity, larger post sizes can be necessary when restoring crownless teeth that have significant internal destruction of the root canal. This study evaluated the effectiveness of fiber posts with different emerging diameters and shapes on composite core stabilization as measured by fracture strength testing. Fracture strengths ranged from 262.6 ± 81 N to 422.8 ± 56 N. A one-way ANOVA test showed that fracture strength was affected by type of post (p<0.0001); single-tapered posts were weaker than double-tapered posts. Pearson's linear correlation test showed that the fracture strength results appear to have a direct correlation to the emerging diameter of the post (p<0.0001; r(2)=0.6191). The emerging diameter of fiber posts is important to stabilize the core. When restoring crownless teeth, it is advisable to use fiber posts with large emerging diameters; no additional preparation of the internal root dentin is necessary to enlarge the post diameter
The effect of ceramic surface treatment on the microtensile bond strength between resin cement and alumina-based ceramic.
No full textEffect of root canal preparation, type of endodontic post and mechanical cycling on root fracture strength.
No full textOBJECTIVE:
To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots.
MATERIAL AND METHODS:
eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts- FRC and cast post and core- CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom #2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45°, 37°C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45° device with 1 mm/ min cross-head speed until failure occurred.
RESULTS:
The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not.
CONCLUSION:
The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario
Effect of cyclic loading on fracture strength and microleakage of a quartz fiber dowel with different adhesive, cement and resin core material combinations.
No full textSEM evaluation of in situ early bacterial colonization on a Y-TZP ceramic: A pilot study
No full textThis study aimed to evaluate the effect of surface glazing and polishing of yttrium-stabilized tetragonal zirconia polycrystal ceramic on early dental biofilm formation, as well as the effect of brushing on the removal of adhered bacteria. Two subjects used oral appliances with polished and glazed samples fixed to the right and left sides. After 20 minutes, 1 hour, and 6 hours, the subjects manually brushed the samples on the right side. The samples were analyzed using scanning electron microscopy. Granular material was verified on the samples, especially on irregular surfaces. After 1 hour, there was no significant difference between glazed and polished surfaces in terms of bacterial presence. However, glazed surfaces tended to accumulate more biofilm, and brushing did not completely remove the biofilm. Polished surfaces seem to present a lower tendency for biofilm formation. Int J Prosthodont 2007;20:419-422
Removing Love waves from shallow seismic SH-wave data
No full textGeophysical exploration measurements are used to obtain an image of the geological structures of the subsurface, as detailed as possible. To this end, a wavefield is generated by a seismic source. This wavefield propagates through the subsurface, and will partly reflect on boundaries between layers with contrasting properties, and it will partly propagate further into the subsurface. De wavefields that have propagated back to the surface are measured with receivers. When this experiment is repeated several times on different locations, the measured data can be used to obtain the desired image. There are two kinds of seismic waves that can propagate through the subsurface. The ones that are generally used are the pressure waves, or P-waves, where the movement of the particles is parallel to the propagation direction of the wave. The other ones are the shear waves, or S-waves, where the movement of the particles is perpendicular to the propagation direction of the wave. When the particle movement is horizontally polarized (perpendicular to the plane of propagation), this wave type is often decoupled, or in other words, it propagates independently of other wave types. These waves are also called SH-waves. The surface of the Earth behaves as a perfect reflector for SH-waves. This means that all SH-waves that reach the surface will be completely reflected back into the subsurface. When the top layer of the subsurface is thin (smaller than the wavelength of the SH-wave), and when this top layer has a lower wave velocity than deeper layers, then the presence of the surface leads to a kind of surface waves, which were first described by A.E.H. Love, and are therefore called 'Love waves'. Love wave characteristics are: their group velocity is almost equal to the shear wave velocity; since they propagate solely along the surface, they attenuate slowly and are thus often stronger than reflected waves; and they are dispersive. The presence of Love waves deteriorates the quality of the final picture (or seismogram), because they obscure the desired reflections. Existing techniques to remove Love waves from seismic data often perform insufficient, or require certain knowledge about the subsurface. This knowledge is generally not available. Therefore, the ideal method should be one where the measured data alone is sufficient to separate the Love waves from the desired reflection information. The method we describe in this thesis uses the Betti-Rayleigh reciprocity theorem for elastic media. Reciprocity is a mathematical tool to relate two different states to each other. Here, one state is the actual situation, where the medium is bounded by a stress-free surface. The other state is an ideal situation, where there is no surface, and the top layer is extended to infinity. When there is no surface, there are also no surface waves. By applying the reciprocity theorem, we derive an integral equation, from which the Love wave free wavefield can be solved as a function of the data that do contain these surface waves. Other input parameters are the (shear-) wave velocity and the mass density of the top layer, and the source wavelet. When the data are discrete, the integral equation becomes a matrix equation. This can be solved using conventional numerical methods, such as matrix inversion. When the medium is horizontally layered (a so called 1-D medium), the kernel of the matrix equation becomes diagonal in the wave-number domain. Then the matrix equation reduces to a scalar expression. We tested the method on several synthetic datasets. In all cases, the Love waves were completely removed. Even other noise in the form of scattered Love waves was removed, in the cases where it was present. The method also had no problems when the input parameters were chosen wrongly. And when distortions were introduced into the data (distortions like random noise, or the effects of anelastic attenuation), the method still performed well. To test the method on field data, we performed a seismic experiment on the site of the Sofia tunnel (before it was drilled) near Hendrik Ido Ambacht in the Netherlands. The dataset that was the result seemed all right at first. Strong Love waves were indeed present in the data. However, we could not succeed in removing these Love waves with the method. Even worse, the method added noise to the data, to such an extent, that it completely obscured the original data. Although we searched extensively for possible reasons, we were not able to find the exact cause of the bad results. In the final chapter, we made a start to remove the surface waves from coupled P- and SV-wave systems, using the same method as we did for SH-waves. Because P- and SV-waves are coupled, the resulting equations are also coupled. This means that we need all possible source and receiver combinations to remove the surface waves. But it appeared that the equations could be solved independently with regard to the source direction. We validated the theory with an example where we removed the Rayleigh wave from the response of a homogeneousCivil Engineering and Geoscience
Ceramic surface treatment with a single-component primer: Resin adhesion to glass ceramics
No full textPurpose: To evaluate the microshear bond strength (μSBS) of composite cement bonded to two machined glass ceramics and its durability, comparing conventional surface conditioning (hydrofluoric acid + silane) to a one-step primer (Monobond Etch & Prime). Materials and Methods: Machined slices of lithium disilicate ceramic (LDC) (IPS e.max CAD) and feldspathic ceramic (FC) (VITA Mark II) glass ceramics were divided into two groups (n = 10) according to two factors: 1. surface treatment: HF+S (ca 5% hydrofluoric acid [IPS Ceramic Etching GEL] + silane coupling agent [SIL; Monobond Plus]) or MEP (single-component ceramic conditioner; Monobond Etch & Prime); 2. storage condition: baseline (without aging; tested 24 h after cementing) or aged (70 days of water storage + 12,000 thermal cycles). Composite cement (Multilink Automix, Ivoclar Vivadent) was applied to starch matrices on the treated ceramic surfaces and photoactivated. A μSBS test was performed (0.5 mm/min) and the failure pattern was determined. Contact angle and micromorphological analyses were also performed. Data were analyzed with Student's t-test (α = 5%). Results: For both ceramic materials, HF+S resulted in higher mean μSBS (MPa) at baseline (LDC: HF+S 21.2 ± 2.2 > MEP 10.4 ± 2.4; FC: HF+S 19.6 ± 4.3 > MEP 13.5 ± 5.4) and after aging (LDC: HF+S 14.64 ± 2.31 > MEP 9 ± 3.4; FC HF+S: 14.73 ± 3.33 > MEP 11.1 ± 3.3). HF+S resulted in a statistically significant decrease in mean μSBS after aging (p = 0.0001), while MEP yielded no significant reduction. The main failure type was adhesive between composite cement and ceramic. HF+S resuted in the lowest contact angle. Conclusions: Hydrofluoric acid + silane resulted in higher mean μSBS than Monobond Etch & Prime for both ceramics; however, Monobond Etch & Prime had stable bonding after aging
Fatigue resistance of bovine teeth restored with resin-bonded fiber posts: effect of post surface conditioning.
No full textFiber Post Removal: Comparative Study Using a New Post Concept
No full textObjectives: To evaluate the time required to remove endodontic posts made of quartz and glass fibers, and compare them to a new glass fiber post designed for easy removal on the basis of efficiency and tooth damages.
Methods: 40 human single-rooted teeth were treated endodontically and randomly assigned to four fiber posts groups: 1) was restored with Premier#90 (Innotech); 2) with DT#2 Lightpost (Dentsply); 3) with Unicore#3 (Ultradent); 4) with a special, soft-cored “S” glass fiber post ER-Prosthetic#3 (Overfibers). An impression of the canal was taken prior post cementation. The posts were luted with Panavia F and adhesive (Kuraray). All the specimens were mounted in a dental simulation unit to reproduce the difficulty of clinical conditions. The fiber posts were removed using a diamond bur /Gates and Largo reamer combination. The teeth were examined radiographycally 2 times seeking for cement, fiber composite debris and tooth damage. After post removal, another impression of the canal was taken for each tooth to evaluate the canal enlargement. Then, the specimens were fractured and observed microscopically.
Results: No significant differences were found among the conventional posts (groups 1-3) as regards removal time and dental tissue loss (Kruskal-Wallis, alpha=0.05). The new soft-core concept applied to the ER-Prosthetics allowed a mean rank removal time significantly lower (P=0.001) than the mean rank of group 1-3 posts (Dunn's test). The canal enlargement was significantly lower with ER posts. Root perforation occurred in groups 1 to 3, but none was recorded in group 4.
Conclusion: Removal of posts avoiding dental tissue loss is a difficult task when performed in simulated clinical conditions. A new post type conceived to be removed safely in a short time was very effective to reduce the removal time without tooth damages. Further studies will be necessary to validate this new concept
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