In vivo effect of UV-photofunctionalization of CoCrMo in processes of guided bone regeneration and tissue engineering.

Photofunctionalization of implant materials with ultraviolet (UV) radiation have been subject of study in the last two decades, and previous research on CoCrMo discs have showed good results in terms of bioactivity and the findings of apatite-like crystals in vitro. In the current study, CoCrMo domes were photofunctionalized with UV radiation of 254 nm on their internal faces during 24 hr; they were implanted in rabbit tibia and remained for 3, 4, and 6 weeks. The potential to induce bone formation beneath the dome-shaped membranes was evaluated through morphometric, histologic, and density measurements; and the results were compared with those obtained under control untreated domes. Higher density values were observed for irradiated domes at 3 weeks, whereas higher volumes were obtained under photofunctionalized domes for longer periods (4 and 6 weeks). Histologically, woven bone was formed by endochondral ossification in all cases; differences in the architecture and size of the trabeculae and in the number of osteoblasts were noted between irradiated and non-irradiated samples. The UV radiation of 254 nm generated a larger bone volume fraction compared to that found in the absence of UVC radiation and induced an increase of density in the early stages of healing, leading to a better initial bone quality and improved osseointegration.

Direct Laser Interference Patterning of CoCr Alloy Surfaces to Control Endothelial Cell and Platelet Response for Cardiovascular Applications.

The main drawbacks of cardiovascular bare-metal stents (BMS) are in-stent restenosis and stent thrombosis as a result of an incomplete endothelialization after stent implantation. Nano- and microscale modification of implant surfaces is a strategy to recover the functionality of the artery by stimulating and guiding molecular and biological processes at the implant/tissue interface. In this study, cobalt-chromium (CoCr) alloy surfaces are modified via direct laser interference patterning (DLIP) in order to create linear patterning onto CoCr surfaces with different periodicities (≈3, 10, 20, and 32 µm) and depths (≈20 and 800 nm). Changes in surface topography, chemistry, and wettability are thoroughly characterized before and after modification. Human umbilical vein endothelial cells' adhesion and spreading are similar for all patterned and plain CoCr surfaces. Moreover, high-depth series induce cell elongation, alignment, and migration along the patterned lines. Platelet adhesion and aggregation decrease in all patterned surfaces compared to CoCr control, which is associated with changes in wettability and oxide layer characteristics. Cellular studies provide evidence of the potential of DLIP topographies to foster endothelialization without enhancement of platelet adhesion, which will be of high importance when designing new BMS in the future.

Photoelastic comparison of as-cast and laser-welded implant frameworks.

STATEMENT OF PROBLEM: A misfit between the implant and metal framework can produce biomechanical problems. PURPOSE: The purpose of this in vitro study was to evaluate the vertical misfit, passivity, and biomechanical behavior of a prosthetic protocol-shaped I-beam framework, varying the number and inclination of implants before and after laser welding. MATERIAL AND METHODS: Two metal models with 4 or 5 implants were used. The I-beam framework for 4 or 5 implants was fabricated with cobalt-chromium alloy. The vertical misfit and passivity were evaluated with a stereomicroscope at ×80 magnification, with frameworks screwed into the respective model. The biomechanical behavior was analyzed with photoelastic studies. These analyses were performed before and after welding to observe the influence of the laser welding. RESULTS: The misfit was not significantly different among the groups studied; laser welding did not influence the vertical misfit. However, when the groups were compared for passivity, the 5 implants before welding group were statistically different (P=.025). CONCLUSIONS: Laser welding generated more passivity, less vertical misfit, and favorable stress distribution to the I-beam framework supported by 4 implants. To the I-beam framework supported by 5 implants laser welding did not influence the misfit or stress distribution, but there was an improvement in passivity.

Effectiveness of silica-lasing method on the bond strength of composite resin repair to Ni-Cr alloy.

PURPOSE: The aim of this study was to evaluate the effectiveness of silica-lasing method for improving the composite resin repair of metal ceramic restorations. MATERIALS AND METHODS: Sixty Ni-Cr cylindrical specimens were fabricated. The bonding surface of all specimens was airborne-particle abraded using 50 µm aluminum oxide particles. Specimens were divided into six groups that received the following surface treatments: group 1-airborne-particle abrasion alone (AA); group 2-Nd:YAG laser irradiation (LA); group 3-silica coating (Si-CO); group 4-silica-lasing (metal surface was coated with slurry of opaque porcelain and irradiated by Nd:YAG laser) (Si-LA); group 5-silica-lasing plus etching with HF acid (Si-LA-HF); group 6-CoJet sand lased (CJ-LA). Composite resin was applied on metal surfaces. Specimens were thermocycled and tested in shear mode in a universal testing machine. The shear bond strength values were analyzed using ANOVA and Tukey's tests (α = 0.05). The mode of failure was determined, and two specimens in each group were examined by scanning electron microscopy and wavelength dispersive X-ray spectroscopy. RESULTS: Si-CO showed significantly higher shear bond strength in comparison to other groups (p < 0.001). The shear bond strength values of the LA group were significantly higher than those of the AA group (p < 0.05). No significant difference was found among lased groups (LA, Si-LA, Si-LA-HF, CJ-LA; p > 0.05). The failure mode was 100% adhesive for AA, Si-LA, Si-LA-HF, and CJ-LA. LA and Si-CO groups showed 37.5% and 87.5% cohesive failure, respectively. CONCLUSION: Silica coating of Ni-Cr alloy resulted in higher shear bond strength than those of other surface treatments.

Welding in the dental office by fiber-delivered laser: a new technique.

OBJECTIVE: The aim of this study is to demonstrate the ability of dentists to weld different metals during daily practice using a fiber-delivered laser normally used for dental surgery, and to evaluate the possibilities offered by this new technique. BACKGROUND DATA: Laser welding is a common technique that has long been used in dental technician laboratories. It has many advantages over conventional techniques: it may be applied directly to master casts, and it avoids damage to the acrylic or ceramic portions close to the welded area. In addition, it may be applied on different types of metallic alloys, and it may provide a stronger attachment than other more traditional techniques. The cost, size, and limited flexibility of laser transmission systems using fixed lenses have restricted their use to dental technician laboratories. MATERIALS AND METHODS: The authors detail their experience with welding using an Nd:YAG fiberoptic-delivered laser that is normally used for dental therapy. RESULTS: This work describes some clinical cases that demonstrate the ease of use of this technique to weld broken appliances for both prosthetic and orthodontic therapy. CONCLUSION: Dentists using this technique can carry out immediate restoration of metallic fixed, removable, and orthodontic broken prostheses in their own offices, thus reducing the time needed for such repairs.

Flexural strength of pure Ti, Ni-Cr and Co-Cr alloys submitted to Nd:YAG laser or TIG welding.

Welding of metals and alloys is important to Dentistry for fabrication of dental prostheses. Several methods of soldering metals and alloys are currently used. The purpose of this study was to assess, using the flexural strength testing, the efficacy of two processes Nd:YAG laser and TIG (tungsten inert gas) for welding of pure Ti, Co-Cr and Ni-Cr alloys. Sixty cylindrical specimens were prepared (20 of each material), bisected and welded using different techniques. Four groups were formed (n=15). I: Nd:YAG laser welding; II- Nd:YAG laser welding using a filling material; III- TIG welding and IV (control): no welding (intact specimens). The specimens were tested in flexural strength and the results were analyzed statistically by one-way ANOVA. There was significant differences (p<0.001) among the non-welded materials, the Co-Cr alloy being the most resistant to deflection. Comparing the welding processes, significant differences (p<0.001) where found between TIG and laser welding and also between laser alone and laser plus filling material. In conclusion, TIG welding yielded higher flexural strength means than Nd:YAG laser welding for the tested Ti, Co-Cr and Ni-Cr alloys.

Flexural strength of pure Ti, Ni-Cr and Co-Cr alloys submitted to Nd: YAG laser or TIG welding

O processo de soldagem de metais e ligas é importante para a Odontologia para fabricação de próteses dentárias. Existem atualmente diversos métodos utilizados na soldagem de metais e ligas. O objetivo deste trabalho foi avaliar a solda do Titânio e ligas de Ni-Cr e Co-Cr usando o sistema TIG e o laser Nd:YAG utilizando o teste de resistência à flexão. Sessenta corpos-de-prova cilíndricos foram confeccionados (20 de cada material), seccionados ao meio e soldados por TIG ou por laser de Nd:YAG, com e sem um material da preenchimento. Quaro grupos foram formados (n=15). I: soldagem a laser de Nd:YAG; II: soldagem à laser usando um material de preenchimento; III: soldagem com TIG; IV (controle): sem soldagem (corpos-de-prova intactos) As amostras foram submetidas a ensaios de flexão e os resultados analisados pela ANOVA a um critério. Houve diferença estatisticamente significante entre o metal e as ligas íntegras (p<0.001), sendo a liga do Co-Cr o mais resistente à deflexão. Ao se comparar os diferentes processos de soldagem, diferença estatisticamente significante (p<0.001) foi encontrada entre a solda TIG e o laser de Nd:YAG e entre este e o laser mais o material de preenchimento. Conclui-se que a soldagem com TIG apresentou melhores resultados que a soldagem com o laser de Nd:YAG para os três materiais testados.

Dose perturbation in the presence of metallic implants: treatment planning system versus Monte Carlo simulations.

An increasing number of patients receiving radiation therapy have metallic implants such as hip prostheses. Therefore, beams are normally set up to avoid irradiation through the implant; however, this cannot always be accomplished. In such situations, knowledge of the accuracy of the used treatment planning system (TPS) is required. Two algorithms, the pencil beam (PB) and the collapsed cone (CC), are implemented in the studied TPS. Comparisons are made with Monte Carlo simulations for 6 and 18 MV. The studied materials are steel, CoCrMo, Orthinox, TiAlV and Ti. Monte Carlo simulated depth dose curves and dose profiles are compared to CC and PB calculated data. The CC algorithm shows overall a better agreement with Monte Carlo than the PB algorithm. Thus, it is recommended to use the CC algorithm to get the most accurate dose calculation both for the planning target volume and for tissues adjacent to the implants when beams are set up to pass through implants.

Measurement of absorbed doses near metal and dental material interfaces irradiated by x- and gamma-ray therapy beams.

Soft-tissue damage adjacent to dental restorations is a deleterious side effect of radiation therapy which is associated with low-energy electron scatter from dental materials of high electron density. This study was designed to investigate the enhancement of dose to soft tissue (or water) close to high electron-density materials and to measure the detailed lateral and depth-dose profiles in soft-tissue-simulating polymer adjacent to planar interfaces of several higher atomic-number materials: 18-carat gold dental casting alloy; Ag-Hg dental amalgam alloy; Ni-Cr dental casting alloy; and natural human tooth structure. Interleaved stacks of calibrated thin radiochromic dosimeter films and tissue-simulating polymer were used for these measurements. Assemblies of these polymer-dosimeter stacks on both sides of the dental materials were irradiated in one fixed direction by collimated 60Co gamma-ray or 10 MV x-ray beams directed perpendicularly to the material interfaces. In another test, designed to simulate more closely therapeutic treatment conditions, a phantom constructed on both sides of a row of restored and unrestored whole teeth (restoration materials: gold alloy crown; Ni-Cr alloy crown; Ag-Hg mesial-occlusal-distal (MOD) amalgam filling; unrestored tooth) was irradiated in one fixed direction by the collimated photon beams. Results indicate that the dose-enhancement in 'tissue' is as great as a factor of 2 on the backscatter side adjacent to gold and a factor of 1.2 adjacent to tooth tissue, but is insignificant on the forward-scatter side because of the predominant effect of attenuation by the high-density, high atomic-number absorbing material.

Effects of radiotherapy on mandibular reconstruction plates.

The radiation dose in the vicinity of metal mandibular implants was measured using lithium fluoride (TLD-100) thermoluminescent dosimeters. Dosimeters were positioned in contact with Vitallium and stainless steel (AO) reconstruction plates. Simple transmission was measured with a solid state detector removed from the implant at a depth of 2.5 cm in a polystyrene phantom. The measurements were made for a 6 mV photon beam from a linear accelerator. At points in front of, but in contact with the metal implants, the dose was greater by 23 percent for Vitallium and 17 percent for stainless steel than that with no implant. At contact behind the implant, the dose was reduced considerably: 14 percent for Vitallium and 13 percent for stainless steel. At remote points behind the implant, the dose was reduced due to attenuation.