Mechanical properties of metal connectors soldered by gas torch versus an infrared technique

Soldering in Dentistry: An Updated Technical Review

INTRODUCTION

The need to permanently join two or more pieces of metal using heat is a frequent condition in various fields of medicine such as dentistry. Welding, brazing and soldering are permanent joining techniques between different metals that require in-depth background knowledge in order to obtain predictable results.

AIM

This review examines the different methods of joining metals using heat and their fields of application.

DISCUSSION

It is possible to create permanent metal joints in various phases of the creation of final products that will be used on the patient. In several cases, welds are also made directly by the manufacturer during industrial processing. In dentistry, dental laboratories perform complex welds mainly on dental prostheses and orthodontic appliances during the production process. It is also possible to obtain intraoral welding carried out by the clinician inside the patient's oral cavity. Welding can be carried out using combustible gases, electric current, infrared light and laser light through different technical procedures which must be chosen according to the specific needs and the metals to be joined.

CONCLUSIONS

It is useful for the dentist and dental technician to know the different welding methods, including those carried out in the factory by the manufacturer, to better understand the physical properties and mechanical resistance of the components marketed for the construction of prostheses and orthodontic appliances. The enormous variety of conditions in which those who practice welding can find themselves therefore presupposes in-depth knowledge in this field in order to apply the most suitable technique.

Decreasing Shear Stresses of the Solder Joints for Mechanical and Thermal Loads by Topological Optimization

A methodology for obtaining the optimal structure and distribution for the gradient properties of a material in order to reduce the stress level in a soldered joint was constructed. The developed methodology was based on a combination of topological optimization methods (the moving asymptotes method) and the finite elements method; it was first implemented to solve problems of optimizing soldered joints. Using the proposed methodology, a number of problems were solved, allowing one to obtain optimal structural characteristics, in which a decrease in stress is revealed. Designing compounds using this technique will provide more robust designs. The proposed technique can be applied to a wide class of practical problems.

Successful Management of Early Peri-Implant Infection and Bone Loss Using a Multidisciplinary Treatment Approach

INTRODUCTION

Peri-implant infections can occur any time postloading. Although management of peri-implant infections has been described extensively in the literature, no consensus exists on the best approach to its treatment. Infections and bone loss can also occur around implants prior to loading, leading to early implant loss. Little has been reported on the management of peri-implant infections occurring prior to loading. This report describes the identification as well as the surgical and restorative management of infection and bone loss around a preloaded dental implant.

CASE PRESENTATION

A 52-year-old systemically healthy, non-smoking white female had severe inflammation with bleeding on probing and bone loss around implant #28 (Universal Numbering System) 7 weeks after placement and augmentation with autogenous and deproteinized bovine bone and a resorbable collagen membrane (RCM). Surgical exposure revealed a deep bony crater around the entire implant. The implant was cleaned for 4 to 5 minutes with a tetracycline and saline slurry. Guided bone regeneration was performed with demineralized freeze-dried bone allograft and an RCM. Azithromycin, ibuprofen 800 mg three times daily, and 0.12% chlorhexidine gluconate rinse were given post-surgery. Postoperative healing was uneventful. Nearly complete bone fill was noted at 1 year of observation when implants were permanently restored. A combination of screw- and cement-retained restorations were placed. Tissues remained healthy 5.5 years postloading with maximum 3-mm probing depth and no changes in bone levels.

CONCLUSIONS

This case shows that it is possible to arrest early peri-implant infection, regenerate bone, and maintain health over 5.5 years postloading. Early detection and multidisciplinary care resulted in long-term success.

Mechanical properties, fracture surface characterization, and microstructural analysis of six noble dental casting alloys

STATEMENT OF PROBLEM

Because noble dental casting alloys for metal ceramic restorations have a wide range of mechanical properties, knowledge of these properties is needed for rational alloy selection in different clinical situations where cast metal restorations are indicated.

PURPOSE

The purpose of this study was to compare the mechanical properties and examine both the fracture and polished surfaces of 6 noble casting alloys that span many currently marketed systems. Five alloys were designed for metal ceramic restorations, and a sixth Type GPT has Type IV alloy for fixed prosthodontics (Maxigold KF) was included for comparison.

MATERIAL AND METHODS

Specimens (n=6) meeting dimensional requirements for ISO Standards 9693 and 8891 were loaded to failure in tension using a universal testing machine at a crosshead speed of 2 mm/min. Values of 0.1% and 0.2% yield strength, ultimate tensile strength, elastic modulus, and percentage elongation were obtained. Statistical comparisons of the alloy mechanical properties were made using 1-way ANOVA and the REGW multiple-range test (α=.05). Following fracture surface characterization using scanning electron microscopy (SEM), specimens were embedded in epoxy resin, polished, and again, examined with the SEM.

RESULTS

When the multiple comparisons were considered, there were generally no significant differences in the elastic modulus, 0.1% and 0.2% offset yield strength, and ultimate tensile strength for the d.SIGN 91 (Au-Pd), d.SIGN 59 (Pd-Ag), Capricorn 15 (Pd-Ag-Au) and Maxigold KF (Au-Ag-Pd) alloys, except that the ultimate tensile strength was significantly lower (P<.05) for Maxigold KF than these other 3 alloys. These 4 mechanical properties were generally significantly lower (P<.05) for Aquarius XH (Au-Pt-Pd) and Brite Gold XH (Au-Pt). The d.SIGN 59 (14.6%) and Capricorn 15 (13.8%) alloys had the highest values of mean percentage elongation, which were not significantly different. Aquarius XH (6.0%) and Maxigold KF (4.2%) had the lower mean values of percentage elongation, which were also not significantly different. The polished and etched surfaces for all alloys revealed equiaxed, fine-grain microstructures, and all fracture surfaces contained casting porosity. Incomplete solidification suggestive of dendritic structures was observed for some alloys. Fracture surfaces were complex, with characteristic features of both brittle and ductile fracture. Precipitate particles on the fracture surfaces indicated the multi-phase character of the alloys.

CONCLUSIONS

For the important mechanical property of yield strength, there were generally no significant differences among the Au-Pd, Pd-Ag, Pd-Ag-Au and Au-Ag-Pd alloys. Wide variation was found in percentage elongation, with the Pd-Ag and Pd-Ag-Au alloys having the highest values and the Au-Pd-Pt and Au-Ag-Pd alloys having the lowest values.

Effect of soldering techniques and gap distance on tensile strength of soldered Ni-Cr alloy joint

PURPOSE

The present study was intended to evaluate the effect of soldering techniques with infrared ray and gas torch under different gap distances (0.3 mm and 0.5 mm) on the tensile strength and surface porosity formation in Ni-Cr base metal alloy.

MATERIALS AND METHODS

Thirty five dumbbell shaped Ni-Cr alloy specimens were prepared and assigned to 5 groups according to the soldering method and the gap distance. For the soldering methods, gas torch (G group) and infrared ray (IR group) were compared and each group was subdivided by corresponding gap distance (0.3 mm: G3 and IR3, 0.5 mm: G5, IR5). Specimens of the experimental groups were sectioned in the middle with a diamond disk and embedded in solder blocks according to the predetermined distance. As a control group, 7 specimens were prepared without sectioning or soldering. After the soldering procedure, a tensile strength test was performed using universal testing machine at a crosshead speed 1 mm/min. The proportions of porosity on the fractured surface were calculated on the images acquired through the scanning electronic microscope.

RESULTS

Every specimen of G3, G5, IR3 and IR5 was fractured on the solder joint area. However, there was no significant difference between the test groups (P > .05). There was a negative correlation between porosity formation and tensile strength in all the specimens in the test groups (P < .05).

CONCLUSION

There was no significant difference in ultimate tensile strength of joints and porosity formations between the gas-oxygen torch soldering and infrared ray soldering technique or between the gap distance of 0.3 mm and 0.5 mm.

Infrared gold alloy brazing on titanium and Ti-6Al-4V alloy surfaces and its application to removable prosthodontics

PURPOSE

This study investigated the area size of the flow of a gold braze alloy on commercially pure titanium and Ti-6Al-4V alloy plates, and elemental composition at the interface was determined. In the second part of this study, the tensile strengths of titanium plates brazed using a gold alloy were investigated.

MATERIALS AND METHODS

Chips of Type IV gold alloy and silver braze alloys were melted onto commercially pure titanium and Ti-6Al-4V surfaces in a dental infrared radiation unit. Flow area of each braze alloy was measured using a digital image analyzer. Tensile specimens (n = 5) were also prepared by infrared brazing using the braze alloys. Five specimens for each combination of the two titanium plates and the two braze alloys were subjected to tensile loading using a Universal testing machine. Electronprobe microanalysis of x-rays at cross-section of the brazed joints to determine elemental composition across the interface, as well as scanning electron microscopic observation at the fracture surfaces, were also conducted.

RESULTS

The braze alloys flowed well and spread over the Ti and Ti-6Al-4V plates. Braze alloy type significantly influenced flow, and the gold alloy flowed less on the titanium materials. The mean tensile strengths of Ti and Ti-6Al-4V plates brazed using the gold braze alloy were 219 MPa and 417 MPa, respectively. The fracture surfaces of Ti-6Al-4V specimens with the gold braze alloy exhibited typical ductile behavior. Ti with the same braze alloy showed brittle surfaces. A greater concentration of Cu was found at the Ti with gold braze interface.

CONCLUSION

The flow and the tensile strength of the gold alloy coating on titanium surface by means of an infrared brazing is adequate for dental use.

Mechanical and elemental characterization of solder joints and welds using a gold-palladium alloy

PURPOSE

This study was conducted to determine whether newer infrared or laser welding technologies created joints superior to traditional furnace or torch soldering methods of joining metals. It was designed to assess the mechanical resistance, the characteristics of the fractured surfaces, and the elemental diffusion of joints obtained by four different techniques: (1) preceramic soldering with a propane-oxygen torch, (2) postceramic soldering with a porcelain furnace, (3) preceramic and (4) postceramic soldering with an infrared heat source, and (5) laser welding.

MATERIAL AND METHODS

Mechanical resistance was determined by measuring the ultimate tensile strength of the joint and by determining their resistance to fatigue loading. Elemental diffusion to and from the joint was assessed with microprobe tracings. Scanning electron microscopy micrographs of the fractured surface were also obtained and evaluated.

RESULTS

Under monotonic tensile stress, three groups emerged: The laser welds were the strongest, the preceramic joints ranged second, and the postceramic joints were the weakest. Under fatigue stress, the order was as follows: first, the preceramic joints, and second, a group that comprised both postceramic joints and the laser welds. Inspection of the fractographs revealed several fracture modes but no consistent pattern emerged. Microprobe analyses demonstrated minor diffusion processes in the preceramic joints, whereas significant diffusion was observed in the postceramic joints.

CLINICAL IMPLICATIONS

The mechanical resistance data conflicted as to the strength that could be expected of laser welded joints. On the basis of fatigue resistance of the joints, neither infrared solder joints nor laser welds were stronger than torch or furnace soldered joints.

Effect of corrosion on the strength of soldered titanium and Ti-6Al-4V alloy

OBJECTIVE

Finding an optimal soldering system for a titanium prosthesis has become increasingly important with the successful introduction of titanium and titanium alloys to dentistry. This study examined the effect of corrosion on the strength of the soldered joints of pure titanium and Ti-6Al-4V alloys joined using various solders.

METHODS

Commercially pure titanium and Ti-6Al-4V alloy rods (2 mm in diameter; 25 mm long) were soldered in an argon atmosphere using four solders: two kinds of titanium-based solder, a gold-based solder, and a silver-based solder. Tensile strengths were examined before or after immersion treatments. Specimens were immersed in either a 0.9% NaCl or 1.0% lactic acid solution held at 35 degrees C for 3 and 8 wk. The amounts of various metal elements released were determined by atomic absorption photospectroscopy. The natural potentials and potentiodynamic polarization behavior of the soldered specimens in 0.9% NaCl or 1.0% lactic acid were determined by a computer-assisted corrosion measurement system. The results were analyzed by ANOVA and Student's t-test.

RESULTS

The cp-titanium and Ti-6Al-4V samples soldered with titanium-based solders exhibited tensile strengths of 300-400 MPa and were not significantly affected by immersion in either solution (no significant difference at p < 0.05). The strengths of both the cp-titanium and titanium alloy specimens soldered with gold-based solder were significantly lower than for any of the other specimens and were affected by immersion in the 0.9% NaCl solution (p < 0.01). The cp-titanium and Ti-6Al-4V specimens that were soldered with titanium-based solders did not show any transpassive regions or breakdown in the natural electrode potential range. On the contrary, the specimens soldered with gold-based and silver-based solders showed transpassive regions or breakdown potentials at less than 0 mV in 0.9% NaCl solution.

SIGNIFICANCE

It is recommended that titanium-based solder be employed for titanium and titanium alloys.

A comparison of infrared- and torch-soldering of Au-Pd and Co-Cr metal-ceramic alloys using a high-fusing solder

PURPOSE

The purpose of this study was to compare the bond strengths and fracture modes of soldered joints formed by infrared and gas-oxygen torch heating of a high-fusing, gold-based solder in two metal-ceramic alloys.

MATERIALS AND METHODS

Pairs of half-dumbbell-shaped specimens of either an Au-Pd or a Co-Cr alloy were positioned with a 0.25-mm gap and were joined using a high-fusing, gold-based solder by either gas-oxygen torch heating or infrared heating. The resulting specimens were subjected to a heat treatment that simulated ceramic firing. Each specimen was fractured in tension at a loading rate of 0.5 cm/min, and its bond strength was measured. The halves of the specimen were rejoined using the other heating method and were heat treated, and the specimen's bond strength was again measured. Fractured cross-sections were examined at a magnification of 40x to determine the following: the fracture mode (adhesive, cohesive, or mixed); the percentage of adhesive fracture; the presence or absence of voids, porosities, or flux inclusions; and the percentage of the cross-section that was discolored.

RESULTS

Three-factor analyses of variance showed that neither the heating method, the particular specimen tested, nor the order of testing significantly affected the bond strength (P < .05). For each alloy, significantly fewer infrared-heated joints than torch-heated joints contained voids, porosities, or flux inclusions visible at 40x (chi 2 test, P < .05). All fractures were either entirely cohesive in the solder or mixed cohesive and adhesive. When infrared heating was used, entirely cohesive fractures occurred more frequently in the Au-Pd alloy specimens than in the Co-Cr alloy specimens (chi 2 test, P < .05). The coefficients of variation of the bond strengths for the infrared-heated joints were smaller than those for the torch-heated joints.

CONCLUSIONS

Although the two heating methods produced solder joints that had strengths that were not significantly different, infrared-heated joints showed less scatter in bond strengths. It was suggested that, in the hands of most technicians, fewer infrared-heated joints would contain defects visible at a magnification of 40x. The presence of such defects may increase the probability of in vivo failure caused by cyclic stresses.

Investigation of stiffness and microstructure of joints soldered with gas-oxygen torch and infrared methods

The stiffness of soldered connectors fabricated with the gas-oxygen torch technique was compared with those fabricated with the infrared technique. Untreated solder materials were used as controls. Untreated solder materials of gold-palladium, palladium-silver, and chromium-cobalt alloys exhibited significantly higher stiffness than the soldered specimens fabricated with either method. There was no significant difference between the gas-oxygen torch and the infrared groups of the gold-palladium and palladium-silver alloys. Photomicrographs revealed that the soldered specimens displayed porosities. For the chromium-cobalt alloy, the infrared group demonstrated significantly higher stiffness than the gas-oxygen torch group. Photomicrographs also disclosed that the chromium-cobalt alloy soldered with the gas-oxygen torch technique had a significant heat-affected zone.