Evaluation of welded titanium joints used with cantilevered implant-supported prostheses

Effectiveness of laser welding in cerclage wiring fixation: a biomechanical study

Introduction

Cerclage wiring is a common orthopedic procedure for fracture fixation. However, previous studies reported wiring-related perioperative complications, such as wire loosening or breakage, with an incidence rate of up to 77%. Recently, the use of laser welding on medical implants was introduced to connect biomedical materials. This study used laser technology to weld between wires after conventional cerclage fixation. We hypothesized that the laser welding could significantly increase the biomechanical properties of cerclage wiring fixation.

Materials and methods

Twenty-five wiring models underwent biomechanical tests in five cerclage wiring configurations (five models per group), namely, (1) single loop, (2) single loop with laser welding, (3) double loop, (4) double loop with one-side laser welding, and (5) double loop with two-side laser welding. Characteristics such as load to failure, mode of failure, and wiring failure were compared between groups. The biocompatibility for a 316L stainless steel wire with laser welding was evaluated via an in vitro hemolysis test.

Results

Mean load to failure of the double loop with one-side and two-side laser welding groups were 3,596 ± 346 N and 3,667 ± 240 N, which were significantly higher than for the double-loop group (2,919 ± 717 N) (p = 0.012 and p = 0.044, respectively). Conversely, no significant difference was shown in the comparison of the mean load to failure between the single loop and the single loop with laser-welded cerclage wire (1,251 ± 72 N, 1,352 ± 122 N, and p = 0.12). Untwisted wire and wire breakage were the most common mode of failure. All welding specimens revealed non-hemolytic effects from in vitro hemolysis test.

Conclusion

Laser welding on cerclage wiring significantly increases the biomechanical property of double cerclage wire fixation. However, further biocompatibility tests and clinical studies are still recommended.

Evaluation of misfit and stress distribution in implant-retained prosthesis obtained by different methods

This study evaluated the vertical misfit, passivity, and stress distribution after tightening the screws of different prosthesis. Two implants were used to simulate the rehabilitation of partially edentulous mandible space from the second premolar to the second molar. 40 three-element screw-retained fixed dental prosthesis with distal cantilever were fabricated and divided into four groups according to the method of production of framework (n = 10): G1 = conventional casting one-piece framework, G2 = conventional casting sectioned and laser welding, G3 = conventional casting sectioned and tungsten inert gas (TIG) welding and G4 = framework obtained by CAD/CAM (computer-aided design/computer-aided manufacturing) system. The vertical misfits (both screws tightened) and the passive fit (one screw tightened) were measured under a comparator optical microscope. The data was submitted to Shapiro-Wilk test to enable comparison with ANOVA followed by Tukey with Bonferroni adjust (α = .05). The qualitative analysis of the stress distribution was performed by the photoelastic method. The vertical misfit (both screws tightened) of the G2 (24 μm) and G3 (27 μm) were significantly higher than G4 (10 μm) (p = 0,006). The passive fit (for the non-tightened) of the G1(64 μm) and G3 (61 μm) were significantly higher than the G4 (32 μm) (p=0,009). G1 showed high stress between the implants in the photoelastic analysis and G4 presented lower stress. In conclusion, CAD/CAM method results in less vertical misfit, more passivity, and consequently better stress distribution to the bone.

Using the "One Shot" Concept for Immediate Loading Implant Protocol in Edentulous Patient Rehabilitation with a Fixed Prosthesis: A 6-Year Follow-Up

Immediate-loaded implants with a fixed prosthesis are a viable option for the restoration of edentulous ridges. Several procedures now allow for the fabrication of immediate-loading provisional and definitive prostheses. However, this complex treatment is not accessible to all patients with budget restrictions. By using a unique master model with a single titanium framework prosthesis can simplify and shorten the treatment, as well as reduce costs. After surgical placement of implant fixtures, an interim prosthesis was fabricated using a laser-welded definitive titanium framework. The prosthesis was fitted intraorally following the immediate loading protocols. The master cast model used to fabricate interim prosthesis was conserved and subsequently used in modifying the final prosthesis. After the healing process and complete soft tissue stability, an impression was made to register the clearance between the gingiva and resin. The light silicone material was directly injected under the prosthesis screwed in the mouth. In the master cast model, the stone was eliminated between the implants and a new plaster was poured to modify the crest profile with the posthealing new shape. With this modified model, it is possible to rehabilitate the denture to the new gingival anatomy in 3 to 4 hours and, if necessary, the tooth rearrangement. This "one shot" concept combines the single definitive titanium welded framework and limited laboratory work with a unique master model thereby decreasing the cost and the time of treatment.

Evaluation of Marginal Misfit of Metal Frameworks Welded by Gas-Torch, Laser, and Tungsten Inert Gas Methods

Purpose

The objective of this study was to evaluate the marginal fit and the flexural resistance of nickel-chromium frameworks welded by different techniques, gas-torch, laser, and tungsten inert gas (TIG), compared with that of frameworks made via one-piece casting.

Methods

To evaluate the marginal fit, a master model was fabricated simulating four implants. Transfers and replicas were used to transfer the positions of the implants to the model, using a silicone matrix. The bars were waxed up and casted. Three assessments of misfit were performed for each implant using a stereomicroscope before and after welding in two predetermined regions, totaling six readings for each implant. To evaluate the flexural resistance, one group was made casting the specimens in one piece. Other 3 groups using gas-torch, laser, and TIG welding techniques were made after sectioned transversally. The data showed normal distribution and two-way ANOVA for marginal fit and one-way ANOVA for flexural resistance, and Tukey's posttest (α=0.05) was performed.

Results

For the marginal fit, the three welding methods presented similar results and were different from one-piece casting. For the flexural resistance, significant differences were observed among the studied groups (p < 0.001), and the one-piece group presented higher resistance compared to the three welding techniques.

Conclusions

Within the limits of this study, the three welding techniques yielded similar misfit results, and the laser and TIG techniques presented similar flexural resistance but lower than gas-torch and one-piece casting.

Fatigue limits of titanium-bar joints made with the laser and the electric resistance welding techniques: microstructural characterization and hardness properties

Fatigue behavior of the titanium bars is of utmost importance for the safe and reliable operation of dental implants and prosthetic constructions based on these implants. To date, however, only few data are available on the fatigue strength of dental prostheses made with electric resistance welding and laser welding techniques. This in-vitro study highlighted that although the joints made with the laser welding approach are credited of a superior tensile strength, joints made with electric resistance welding exhibited double the minimum fatigue strength with respect to the joints made with laser welding (120 vs 60 N).

Microstructural characterization and hardness properties of electric resistance welding titanium joints for dental applications

The electric resistance welding procedure is used to join a titanium bar with specific implant abutments in order to produce a framework directly in the oral cavity of the patient. This investigation studied the effects of the welding process on microstructure and hardness properties of commercially pure (CP2 and CP4) Ti components. Different welding powers and cooling procedures were applied to bars and abutments, normally used to produce the framework, in order to simulate the clinical intraoral welding procedure. The analyses highlighted that the joining process did not induce appreciable changes in the geometry of the abutments. However, because of unavoidable microstructural modifications in the welded zones, the hardness decreased to values lower than those of the unwelded CP2 and CP4 Ti grades, irrespective of the welding environments and parameters.

Fracture force of cantilevered zirconia frameworks: an in vitro study

STATEMENT OF PROBLEM

Little evidence is available showing the effect of connector dimension and cantilever length on the ultimate fracture force of computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia implant frameworks.

PURPOSE

The purpose of the study was to determine the impact of variations in the cross-sectional dimension of connector sites and variations in the effective cantilever length (load point) on zirconia implant frameworks. This would allow verification of the fracture force with 2 proposed mathematical models.

MATERIAL AND METHODS

Forty zirconia implant-supported frameworks with 12-mm distal cantilevers were divided into 4 equal test groups (n=10). Connector dimensions (3×5 mm, 3×4 mm) and cantilever loading distance (7 mm, 10 mm) were tested for ultimate fracture force. A 2-way analysis of variance (ANOVA) was used to examine the ultimate fracture force and examine the relationship between connector dimension and ultimate fracture force. The data obtained from all 4 groups were compared and verified with calculations from 2 theoretical mathematical models.

RESULTS

Two-way ANOVA revealed significant effects for cross-sectional area connector dimension on fracture force (P<.001) and cantilever length (P=.009). No statistically significant interaction was observed between the 2 factors (P=.229). The observed data were consistent with the data from the proposed mathematical models, with group comparisons showing no statistical significance. The largest difference between the mathematical results and mathematical models was in the 7 mm 3×5 mm group of the fixed cantilever bending model (P=.032). The predominant mode of failure was fracture of the zirconia framework, without damage or plastic deformation of the abutment screws or implant analogs. The 10 mm 3×5 mm specimens fractured at a mean load of 923.7 ±234.5 N; the 10 mm 3×4 mm specimens at a mean load of 474.8 ±122.9 N; the 7 mm 3×5 mm specimens at a mean load of 1011.7 ±185.3 N; and the 7 mm 3×4 mm specimens at a mean load of 700.9 ±152.4 N.

CONCLUSIONS

Zirconia implant frameworks loaded 7 mm from the distal abutment failed at higher fracture loads than specimens loaded 10 mm from the distal abutment. Zirconia implant frameworks with cross-sectional area connector dimensions of 3×5 mm failed at higher fracture loads than specimens with cross-sectional area connector dimensions of 3×4 mm. No statistically significant interaction was observed between the cross-sectional connector area dimension and cantilever length. Calculations from the mathematical models closely approximated the observed data, which supports the use of the mathematical models as a predictor of fracture force.

Tensile and Flexural Strength of Commercially Pure Titanium Submitted to Laser and Tungsten Inert Gas Welds

This study evaluated the tensile and flexural strength of tungsten inert gas (TIG) welds in specimens made of commercially pure titanium (CP Ti) compared with laser welds. Sixty cylindrical specimens (2 mm diameter x 55 mm thick) were randomly assigned to 3 groups for each test (n=10): no welding (control), TIG welding (10 V, 36 A, 8 s) and Nd:YAG laser welding (380 V, 8 ms). The specimens were radiographed and subjected to tensile and flexural strength tests at a crosshead speed of 1.0 mm/min using a load cell of 500 kgf applied on the welded interface or at the middle point of the non-welded specimens. Tensile strength data were analyzed by ANOVA and Tukey's test, and flexural strength data by the Kruskal-Wallis test (α=0.05). Non-welded specimens presented significantly higher tensile strength (control=605.84±19.83) (p=0.015) and flexural strength (control=1908.75) (p=0.000) than TIG- and laser-welded ones. There were no significant differences (p>0.05) between the welding types for neither the tensile strength test (TIG=514.90±37.76; laser=515.85±62.07) nor the flexural strength test (TIG=1559.66; laser=1621.64). As far as tensile and flexural strengths are concerned, TIG was similar to laser and could be suitable to replace laser welding in implant-supported rehabilitations.

Stress distribution in Co-Cr implant frameworks after laser or TIG welding

Lack of passivity has been associated with biomechanical problems in implant-supported prosthesis. The aim of this study was to evaluate the passivity of three techniques to fabricate an implant framework from a Co-Cr alloy by photoelasticity. The model was obtained from a steel die simulating an edentulous mandible with 4 external hexagon analog implants with a standard platform. On this model, five frameworks were fabricated for each group: a monoblock framework (control), laser and TIG welding frameworks. The photoelastic model was made from a flexible epoxy resin. On the photoelastic analysis, the frameworks were bolted onto the model for the verification of maximum shear stress at 34 selected points around the implants and 5 points in the middle of the model. The stresses were compared all over the photoelastic model, between the right, left, and center regions and between the cervical and apical regions. The values were subjected to two-way ANOVA, and Tukey's test (α=0.05). There was no significant difference among the groups and studied areas (p>0.05). It was concluded that the stresses generated around the implants were similar for all techniques.

Análise metalográfica do titânio puro submetido à soldagem laser Nd: YAG e TIG

INTRODUÇÃO: Os métodos de soldagem mais utilizados em Odontologia não podem ser aplicados ao titânio puro e às suas ligas em função da alta reatividade do titânio com elementos atmosféricos; dessa forma, o mesmo não deve ser soldado por processo comum. OBJETIVO: O objetivo deste trabalho foi avaliar a característica metalúrgica do titânio comercialmente puro sem solda e submetido aos processos de soldagem a laser e TIG. MATERIAL E MÉTODO: Foram confeccionados 15 corpos de prova em titânio comercialmente puro, cinco para cada condição, na forma de hastes cilíndricas, obtidas por fundição odontológica, sob atmosfera de gás argônio e vácuo, com calor produzido por um arco voltaico, com a injeção do titânio sob vácuo-pressão. Três grupos foram formados I: soldagem a laser; II: soldagem TIG, e III: sem solda. Os corpos de prova do grupo I e II foram seccionados ao meio e soldados por TIG e por laser, respectivamente; o grupo III foi mantido sem corte e sem solda, como controle. A análise metalográfica foi realizada sob aumentos de 50×, 100× e 200×, em microscópio. RESULTADO: Pelos resultados obtidos nas micrografias, o titânio comercialmente puro apresentou uma morfologia de grãos equiaxiais da fase α, o cordão de solda a laser apresentou estrutura martensítica e, na TIG, microestrutura Widmanstätten. CONCLUSÃO: A microestrutura martensítica é condizente com a alta taxa de resfriamento proveniente do processo de soldagem a laser. As estruturas martensítica e Widmansttäten são mais refinadas quando comparadas à microestrutura do metal base.

Effect of plasma welding parameters on the flexural strength of Ti-6Al-4V alloy

The aim of this study was to assess the effect of different plasma arc welding parameters on the flexural strength of titanium alloy beams (Ti-6Al-4V). Forty Ti-6Al-4V and 10 NiCr alloy beam specimens (40 mm long and 3.18 mm diameter) were prepared and divided into 5 groups (n=10). The titanium alloy beams for the control group were not sectioned or subjected to welding. Groups PL10, PL12, and PL14 contained titanium beams sectioned and welded at current 3 A for 10, 12 or 14 ms, respectively. Group NCB consisted of NiCr alloy beams welded using conventional torch brazing. After, the beams were subjected to a three-point bending test and the values obtained were analyzed to assess the flexural strength (MPa). Statistical analysis was carried out by one-way ANOVA and Tukey's HSD test at 0.05 confidence level. Significant difference was verified among the evaluated groups (p<0.001), with higher flexural strength for the control group (p<0.05). No significant differences was observed among the plasma welded groups (p>0.05). The NCB group showed the lowest flexural strength, although it was statistically similar to the PL 14 group (p>0.05). The weld depth penetration was not significantly different among the plasma welded groups (p=0.05). Three representative specimens were randomly selected to be evaluated under scanning electron microcopy. The composition of the welded regions was analyzed by energy dispersive X-ray spectroscopy. This study provides an initial set of parameters supporting the use of plasma welding during fabrication of titanium alloy dental frameworks.

Tissue distribution of tungsten in mice following oral exposure to sodium tungstate

Heavy metal tungsten alloys have replaced lead and depleted uranium in many munitions applications, due to public perception of these elements as environmentally unsafe. Tungsten materials left in the environment may become bioaccessible as tungstate, which might lead to population exposure through water and soil contamination. Although tungsten had been considered a relatively inert and toxicologically safe material, recent research findings have raised concerns about possible deleterious health effects after acute and chronic exposure to this metal. This investigation describes tissue distribution of tungsten in mice following oral exposure to sodium tungstate. Twenty-four 6-9 weeks-old C57BL/6 laboratory mice were exposed to different oral doses of sodium tungstate (0, 62.5, 125, and 200 mg/kg/d) for 28 days, and after one day, six organs were harvested for trace element analysis with inductively coupled plasma mass spectrometry (ICP-MS). Kidney, liver, colon, bone, brain, and spleen were analyzed by sector-field high-resolution ICP-MS. The results showed increasing tungsten levels in all organs with increased dose of exposure, with the highest concentration found in the bones and the lowest concentration found in brain tissue. Gender differences were noticed only in the spleen (higher concentration of tungsten in female animals), and increasing tungsten levels in this organ were correlated with increased iron levels, something that was not observed for any other organ or either of the two other metals analyzed (nickel and cobalt). These findings confirmed most of what has been published on tungsten tissue distribution; they also showed that the brain is relatively protected from oral exposure. Further studies are necessary to clarify the findings in splenic tissue, focusing on possible immunological effects of tungsten exposure.

Proposals for optimization of laser welding in prosthetic dentistry

This paper points out each key parameter involved in laser welding and discusses the parameters' effects on weld microstructure and defects detected inside the weld. Solutions are proposed to adjust the parameters to provide an optimal dental assembly. Metallurgical effects as well as defects are briefly discussed. A welding procedure adapted to different compositions of dental alloys is proposed.

Repairing an implant titanium milled framework using laser welding technology: a clinical report

The application of laser welding technology allows titanium to be welded predictably and precisely to achieve accurate fit of a milled framework. Laser energy results in localized heat production, thereby reducing thermal expansion. Unlike soldering, laser energy can be directed to a small area, making it possible to laser weld close to acrylic resin or ceramic. This article describes the use of laser welding to repair an implant titanium milled fixed denture. A quick, cost-effective, accurate repair was accomplished, and the repaired framework possessed adequate strength and the same precise fit as the original framework.