Laser surface treatment to improve mechanical properties of cast titanium

Mechanical Properties and Wear Susceptibility Determined by Nanoindentation Technique of Ti13Nb13Zr Titanium Alloy after "Direct Laser Writing"

Laser treatment has often been applied to rebuild the surface layer of titanium and its alloys destined for long-term implants. Such treatment has always been associated with forming melted and re-solidified thin surface layers. The process parameters of such laser treatment can be different, including the patterning of a surface by so-called direct writing. In this research, pulse laser treatment was performed on the Ti13Nb13Zr alloy surface, with the distance between adjacent laser paths ranging between 20 and 50 µm. The obtained periodic structures were tested to examine the effects of the scan distance on the microstructure using SEM, the roughness and chemical and phase composition using EDS and XRD, and the mechanical properties using the nanoindentation technique. After direct laser writing, the thickness of the melted layers was between 547 and 123 µm, and the surface roughness varied between 1.74 and 0.69 µm. An increase in hardness was observed after laser treatment. The highest hardness, 5.44 GPa, was obtained for the sample modified with a laser beam spacing of 50 µm. The value of the distance has been shown to be important for several properties and related to a complex microstructure of the thin surface layer close to and far from the laser path.

Microstructure and Wear Behavior of TC4 Laser Cladding Modified via SiC and MoS2

A TC4 composite coating reinforced by SiC ceramic phase and MoS2 self-lubricating phase was prepared on a muzzle brake by laser cladding to improve its wear resistance properties. In this study, we investigated the microstructure and wear behavior of the composite coating. The results show that the composite coating consisted of equiaxed grains with grain sizes ranging from 102.39 to 255.31 μm on the surface and columnar grains on the bottom. The grains with mesh basket microstructure were mainly with α-Ti and β-Ti phases. When wearing against H70 brass, the main wear mechanism of the composite coating at room temperature was adhesive wear, while the wear mechanism was dominated by adhesive wear, oxidation wear, and slight abrasive wear at high temperature. Compared with TC4 coating without SiC and MoS2, the wear rate of the composite coating was reduced by 15%–35% when the temperature was below 400 °C, and the wear rate was reduced by about 55% at 600 °C, resulting from the addition of SiC. Moreover, the friction coefficient of the composite coating was about 10%, which was 30% lower than that of the substrate and TC4 coating when the temperature was below 400 °C and at 600 °C due to the forming of the dense oxide film and the MoS2 friction transfer film on the friction contact surface of the titanium-based composite coating.

The Use of Lasers in Dental Materials: A Review

Lasers have been well integrated in clinical dentistry for the last two decades, providing clinical alternatives in the management of both soft and hard tissues with an expanding use in the field of dental materials. One of their main advantages is that they can deliver very low to very high concentrated power at an exact point on any substrate by all possible means. The aim of this review is to thoroughly analyze the use of lasers in the processing of dental materials and to enlighten the new trends in laser technology focused on dental material management. New approaches for the elaboration of dental materials that require high energy levels and delicate processing, such as metals, ceramics, and resins are provided, while time consuming laboratory procedures, such as cutting restorative materials, welding, and sintering are facilitated. In addition, surface characteristics of titanium alloys and high strength ceramics can be altered. Finally, the potential of lasers to increase the adhesion of zirconia ceramics to different substrates has been tested for all laser devices, including a new ultrafast generation of lasers.

Mechanical Properties of Selective Laser Sintering Pure Titanium and Ti-6Al-4V, and Its Anisotropy

Selective laser sintering (SLS) is being developed for dental applications. This study aimed to investigate the properties of Ti-6Al-4V and pure titanium specimens fabricated using the SLS process and compare them with casting specimens. Besides, the effect of the building direction on the properties of the SLS specimens was also investigated. Specimens were prepared by SLS using Ti-6Al-4V powder or pure titanium powder. Casting specimens were also prepared using Ti-6Al-4V alloys and pure titanium. The mechanical properties (tensile strength and elongation), physical properties (surface roughness, contact angle, and Vickers hardness); corrosion resistors (color difference and corrosion), and surface properties (chemical composition and surface observation) were examined. Both Ti-6Al-4V and pure titanium specimens produced using the SLS process had comparable or superior properties compared with casting specimens. In comparing the building directions, specimens fabricated horizontally to the printing platform showed the greatest tensile strength, and the surface roughness scanned in the horizontal direction to the platform showed the smallest. However, there was no significant effect on other properties. Thus, the SLS process with Ti-6Al-4V powder and pure titanium powder has great performance for the fabrication of dental prosthesis, and there is a possibility for it to take the place of conventional methods.

The effects of Er:YAG, Nd:YAG, and Diode (940nm) Lasers irradiation on Microtensile bond strength of two steps self-etch adhesives

Background and aims

Nowadays, studies show the effective laser irradiation role on the adhesion of bonding agents to the dentin. Therefore, the present study was set to find an appropriate protocol for the use of Nd:YAG, Er:YAG, and Diode lasers during the application of two steps self-etch adhesives in direct dental restorations in order to achieve higher microtensile strength.

Materials and Methods

A total number of 100 extracted healthy teeth were selected. After removing occlusal enamel and exposing dentin, samples randomly divided into ten groups: Group Control (C), two steps self-etch adhesives was applied in accordance with the manufacturer instructions, without using laser systems; Groups Er-YAG, laser (2940 nm, 10 Hz, 0.4w, 40 mJ) irradiated Before applying Primer (Er-BP subgroup), After applying Primer (Er-AP subgroup), After applying Bonding (Er-AB subgroup); Groups Nd-YAG, laser (1064 nm, 10 Hz, 1.2w, 40 mJ) irradiated Before applying Primer (Nd-BP subgroup), After applying Primer (Nd-AP subgroup), After applying Bonding (Nd-AB subgroup); Groups Diode, laser (940 nm, 10 Hz, 0.7w, 70 mJ) irradiated Before applying Primer (D-BP subgroup), After applying Primer (D-AP subgroup), After applying Bonding (D-AB subgroup). After intervention and composite build up, the samples were stored 24 hours in 37°C distilled water. The microtensile strength was measured using the universal testing machine. The data were analyzed by one-way ANOVA test and post hoc Tukey test. (p < 0.05).

Results

The Means and standard deviations of the groups were as follow: C = 30.09 ± 4.21, Er-BP = 18.83 ± 4.21, Er-AP = 14.43 ± 3.12, Er-AB = 19.67 ± 4.96, Nd-BP = 20.35 ± 5.55, Nd-AP = 39.85 ± 4.13, Nd-AB = 18.16 ± 3.36, D-BP = 26.74 ± 5.05, D-AP = 28.11 ± 5.12, D-AB = 37.28 ± 5.61. The mean microtensile strength achieved in groups: Nd-AP and D-AB were significantly higher than control group (p < 0.05). Groups D-BP and D-AP had no significant difference in comparison with control group while the remaining groups had significantly lower values (P < 0.05).

Conclusions

Nd:YAG laser irradiation after applying the primer, and diode laser irradiation after applying the bonding agent, both can improve the microtensile bond strength in two steps self-etch adhesive systems significantly.

Bonding Strength of Ceromer with Direct Laser Sintered, Ni-Cr-Based, and ZrO2 Metal Infrastructures After Er:YAG, Nd:YAG, and Ho:YAG Laser Surface Treatments-A Comparative In Vitro Study

OBJECTIVE

Laser modalities instead of conventional surface treatment techniques have been suggested to obtain an adequate micromechanical bonding between dental super- and infrastructures. The present study was undertaken to assess the effect of surface treatment with Ho:YAG, Er:YAG, and Nd:YAG laser modalities on the shear bond strength (SBS) of ceromer to different types of metal infrastructures in in vitro settings.

METHODS

The study specimens consisted of 40 direct laser sintered (DLS), 40 Ni-Cr-based, and 40 zirconium oxide (ZrO2) infrastructures. In each infrastructure group, the specimens were divided randomly into five treatment modalities (n = 8): no treatment (controls), sandblasting, Er:YAG, Nd:YAG, and Ho:YAG lasers. The DLS, Ni-Cr-based, and ZrO2 infrastructures were prepared in the final dimensions of 7 mm in diameter and 3 mm in thickness in line with the ISO 11405 standard. Ceromer as superstructure was applied to all the infrastructures after their surface treatments according to the selected treatment modality. SBS test was performed to test the effectiveness of surface treatments. A stereomicroscope was used to determine the changes in the surface morphology of specimens.

RESULTS

Among the laser modalities and sandblasting, Ho:YAG laser caused the most important increase in the DLS and Ni-Cr-based infrastructures but sandblasting caused the most important increase in the ZrO2 infrastructure. In all the infrastructures, Nd:YAG laser has the least effectiveness, and Er:YAG laser makes an intermediate success. The stereomicroscopy images presented that the applications of laser surface treatments altered the surface in all the infrastructures.

CONCLUSIONS

Overall, in current experimental settings, Ho:YAG, Nd:YAG, and Er:YAG lasers, in order of strength, are effective in improving the bonding of ceromer to all the infrastructures. Ho:YAG laser is more effective in the DLS and Ni-Cr-based infrastructures, but sandblasting is more effective in the ZrO2 infrastructure. The studied laser modalities need to be subjected for further studies to determine their appropriate settings and the specifications to be used in prosthodontics.

Effect of Nd:YAG laser parameters on the penetration depth of a representative Ni-Cr dental casting alloy

The effects of voltage and laser beam (spot) diameter on the penetration depth during laser beam welding in a representative nickel-chromium (Ni-Cr) dental alloy were the subject of this study. The cast alloy specimens were butted against each other and laser welded at their interface using various voltages (160-390 V) and spot diameters (0.2-1.8 mm) and a constant pulse duration of 10 ms. After welding, the laser beam penetration depths in the alloy were measured. The results were plotted and were statistically analyzed with a two-way ANOVA, employing voltage and spot diameter as the discriminating variables and using Holm-Sidak post hoc method (a = 0.05). The maximum penetration depth was 4.7 mm. The penetration depth increased as the spot diameter decreased at a fixed voltage and increased as the voltage increased at a fixed spot diameter. Varying the parameters of voltage and laser spot diameter significantly affected the depth of penetration of the dental cast Ni-Cr alloy. The penetration depth of laser-welded Ni-Cr dental alloys can be accurately adjusted based on the aforementioned results, leading to successfully joined/repaired dental restorations, saving manufacturing time, reducing final cost, and enhancing the longevity of dental prostheses.

Mechanical properties of cast commercially pure titanium simulating ceramic firing cycles

AIM

To evaluate the mechanical properties (ultimate tensile strength, elongation and hardness) of the commercially pure titanium (cp Ti) as casting and after ceramic firing cycles.

MATERIALS AND METHODS

Dumbbell-shaped specimens were prepared for the tensile strength testing. Disk-shaped cast specimens were used for microhardness testing. The ceramic firing cycles were made simulating a low fusion ceramic application. Tensile testing was conducted in a universal testing machine at a crosshead speed of 1 mm/min until failure. Ultimate tensile strength and elongation were recorded. The fracture mode was analyzed by scanning electron microscopy. Vickers hardness was measured in a hardness tester. The data from the tensile and hardness tests were subjected to a one-way analysis of variance and Tukey's test (α = 0.05).

RESULTS

The mean values of tensile strength were not changed by the ceramic firing cycles. Lower hardness was observed for cp Ti as casting compared with Ti cast after the firing cycles.

CLINICAL SIGNIFICANCE

The ceramic firing cycles did not show any considerable prejudicial effects on the mechanical properties of the cp Ti.

Microstructure and mechanical properties of surface treated cast titanium with Nd:YAG laser

OBJECTIVE

To investigate the effect of laser surface treatment of cast titanium alloy on microstructure and mechanical properties.

METHODS

Dumbbell- and plate-shaped cast titanium specimens were prepared for mechanical testing and microstructure analysis. After the cast surfaces of each specimen were laser-treated using a dental Nd:YAG laser machine at 240 V and 300 V with and without argon gas shielding, tensile testing and microstructure analysis were conducted. Hardness depth profiles were also made from the cross-section of laser-treated cast specimens. Microstructural and chemical analysis were performed by means of the SEM, XRD, AES and WDS.

RESULTS

The results of tensile testing and Vickers hardness depth profiling showed that laser treatment improved the mechanical properties. Bulk microstructure of as-cast titanium was mainly composed of α-grains with acicular and widmanstatten patterns. The laser melted zone was characterized by columnar beta grains. When the emission voltage of laser increased to 300V, a larger grain size was promoted. The XRD analysis indicated that the beta phase formation was clearly noticeable after laser surface treatment. Supplementary marked peaks of the TiO, TiO(2) and Ti(2)N were detected without argon gas shielding. When argon shielding gas was used, the presence of titanium oxide was significantly reduced and the peaks of titanium nitride disappeared.

SIGNIFICANCE

Laser treatment on cast titanium surfaces showed significant enhancement of mechanical properties and modification of microstructures, and therefore could produce reliable titanium metal frameworks for dental prostheses.

Effect of laser irradiation conditions on the laser welding strength of cobalt-chromium and gold alloys

Using tensile tests, this study investigated differences in the welding strength of casts of cobalt-chromium and gold alloys resulting from changes in the voltage and pulse duration in order to clarify the optimum conditions of laser irradiation for achieving favorable welding strength. Laser irradiation was performed at voltages of 150 V and 170 V with pulse durations of 4, 8, and 12 ms. For cobalt-chromium and gold alloys, it was found that a good welding strength could be achieved using a voltage of 170 V, a pulse duration of 8 ms, and a spot diameter of 0.5 mm. However, when the power density was set higher than this, defects tended to occur, suggesting the need for care when establishing welding conditions.

Multidisciplinary approach for esthetic, functional, and quality-of-life outcome in soft palate cleft patient

The fabrication of a Suersen obturator prosthesis with titanium framework is described in the case of a 43-year-old man with congenital absence of the soft palate. The patient revealed an open soft palate, bilateral cleft lip and palate, Angle Class III dental malocclusion, and anterior and posterior crossbite. He was treated with a multidisciplinary approach. A Dolder bar was fabricated between the maxillary canines, and telescopic crowns were prepared for maxillary premolars. Angle Class III tooth relation was readjusted to tooth-tooth relation; closure of the nasopharynx and oropharynx was performed by Suersen method, which improves speech.