Porcelain bond to laser-welded titanium surfaces

OBJECTIVES

The purpose of this investigation was to determine if laser-welding titanium had an effect on the bond strength of porcelain to metal. This is an important consideration since the metal copings for many multi-unit porcelain restorations are fabricated as single units and then either soldered or welded.

METHODS

The bond strength of porcelain to laser-welded titanium was measured with a four-point bending test and the interface was examined using SEM/EDX analysis.

RESULTS

The result showed no statistically significant differences (p<0.05) in bond strengths between laser-welded surfaces and mechanically machined surfaces and neither were there any alterations in composition identified after the welding. The use of a special bonding agent did not improve the bond strength significantly.

SIGNIFICANCE

Fusing porcelain to laser-welded areas in titanium fixed restorations implies no deterioration of bond strength.

Estimation of regional pulmonary deposition and exposure for fumes from SMAW and GMAW mild and stainless steel consumables

The particle size distributions and bulk fume densities for mild steel and stainless steel welding fumes generated using two welding processes (shielded metal arc welding [SMAW] and gas metal arc welding [GMAW]) were used in mathematical models to estimate regional pulmonary deposition (the fraction of each fume expected to deposit in each region of the pulmonary system) and regional pulmonary exposure (the fraction of each fume expected to penetrate to each pulmonary region and would be collected by a particle size-selective sampling device). Total lung deposition for GMAW fumes was estimated at 60% greater than that of SMAW fumes. Considering both the potential for deposition and the fume specific surface areas, it is likely that for equal exposure concentrations GMAW fumes deliver nearly three times the particle surface area to the lungs as SMAW fumes. This leads to the hypothesis that exposure to GMAW fumes constitutes a greater pulmonary hazard than equal exposure to SMAW fumes. The implications of this hypothesis regarding the design of future health studies of welders is discussed.

The particle size distribution, density, and specific surface area of welding fumes from SMAW and GMAW mild and stainless steel consumables

Particle size distributions were measured for fumes from mild steel (MS) and stainless steel (SS); shielded metal arc welding (SMAW) and gas metal arc welding (GMAW) consumables. Up to six samples of each type of fume were collected in a test chamber using a micro-orifice uniform deposit (cascade) impactor. Bulk samples were collected for bulk fume density and specific surface area analysis. Additional impactor samples were collected using polycarbonate substrates and analyzed for elemental content. The parameters of the underlying mass distributions were estimated using a nonlinear least squares analysis method that fits a smooth curve to the mass fraction distribution histograms of all samples for each type of fume. The mass distributions for all four consumables were unimodal and well described by a lognormal distribution; with the exception of the GMAW-MS and GMAW-SS comparison, they were statistically different. The estimated mass distribution geometric means for the SMAW-MS and SMAW-SS consumables were 0.59 and 0.46 micron aerodynamic equivalent diameter (AED), respectively, and 0.25 micron AED for both the GMAW-MS and GMAW-SS consumables. The bulk fume densities and specific surface areas were similar for the SMAW-MS and SMAW-SS consumables and for the GMAW-MS and GMAW-SS consumables, but differed between SMAW and GMAW. The distribution of metals was similar to the mass distributions. Particle size distributions and physical properties of the fumes were considerably different when categorized by welding method. Within each welding method there was little difference between MS and SS fumes.

Exposure to cobalt in the welding process with stellite

In some small factories producing moulds for ceramic tiles using a cobalt alloy (stellite), environmental and biological (CoU) monitoring was conducted for eight workers employed in gas-shielded arc (MAG) and oxy-acetylene welding processes. During oxy-acetylene braze-welding, the exposure to cobalt is very low as are urinary cobalt concentrations. On the other hand, during the MAG welding process, the exposure levels can exceed the TLV-TWA levels and correlated well with CoU at the end of a working shift. Two MAG welders followed for two consecutive weeks, showed different patterns of urinary cobalt excretion: under the same environmental conditions, the higher CoU was found in the worker with greater past exposure. This aspect needs further evaluation before adopting CoU as a current indicator of occupational exposure to the metal.

Mechanical properties of laser welds of titanium in dentistry by pulsed Nd:YAG laser apparatus

The use of titanium in dentistry is increasing, and an adequate method of joining titanium units of restorations is needed. This study examined the welding of titanium with a normal pulse Nd:YAG laser. Laser welding of titanium was effective when performed in an argon atmosphere. ANOVA for the three-point bending test showed a correlation between the bending strength of a weld, the atmosphere under which the irradiation is performed, and the intensity of the irradiation.

Exposure to soluble barium compounds: an interventional study in arc welders

Soluble barium (Ba) compounds are well-known toxicants. Intoxications are mainly known in an acute form from casual or suicidal oral ingestion. No scientifically based data are available on possible health effects of inhalative exposure to soluble Ba salts at the workplace. Therefore, we investigated 18 welders in an interventional study over 1 week. They performed welding of Ba-containing stick electrodes and self-shielded flux cored wires under conditions similar to real working conditions. The welding fumes contained 31%-37% Ba, more than 90% of which was soluble in acids. Without appropriate preventive measures, a high rate of measurements exceeded the TLV values for total welding fumes of 5 mg/m3 and for soluble Ba of 0.5 mg/m3. The median fume concentrations were 13.2 mg/m3 in stick electrode welding and 12.3 mg/m3 in flux cored wire welding. The median Ba concentrations were 4.4 and 2.0 mg/m3 respectively. An integrated exhaust system built into the gun proved to be efficient in flux cored wire welding. The internal exposure to Ba reached median urine levels up to 101.7 micrograms/l (normal: below 20 micrograms/l) and median plasma concentrations of up to 24.7 micrograms/l (normal: below 8 micrograms/l). No health impact on the welders could be proven, but hypokalemia may have occurred as a result of the Ba exposure.

Exposure to fumes in typical New Zealand welding operations

Sixteen welders, welding under typical New Zealand conditions, had ambient air within their welding helmets sampled and analysed for ozone, nitrogen oxides, fluoride, carbon monoxide, aluminium, chromium, iron, nickel, zinc and total dust. Postshift urinary metals were also analysed, and a respiratory questionnaire completed for each welder. Levels above the New Zealand Workplace Exposure Standard (WES) were found for nitrogen dioxide in four welders (two TIG, one MMA and one plasma cutter), and for total chromium in one plasma cutter, who also had a nickel level of 24% of the WES. Dust levels were highest in the plasma cutters, with one reaching 8.67 mg/m3 (WES = 5 mg/m3). Urinary levels however did not indicate excessive short or long term uptake. Where efficient fume extraction was in use, levels of air contaminants were lower than with natural ventilation. Respiratory symptoms were reported by 67% of welders, 38% meeting criteria for chronic bronchitis (relative risk = 2.0). Smoking welders reported more symptoms than nonsmoking welders.

Crosslinking of extracellular matrix proteins: a preliminary report on a possible mechanism of argon laser welding

In order to elucidate the biochemical mechanism of laser welding of tissues, we have compared protein profiles from argon laser-treated specimens with controls. Extracellular matrix components from untreated and laser-welded skin and blood vessels were extracted with guanidine hydrochloride and separated by SDS polyacrylamide gel electrophoresis. When compared with matched, untreated tissues, protein electrophoretic profiles from laser-treated samples showed several changes. In both tissue types, argon laser treatment decreased the concentration of a 235 kd protein that migrates between the alpha and beta chains of type I collagen. Laser-treated blood vessels showed significantly more low molecular weight protein at the dye front than in control tissue, whereas significantly more high molecular weight protein appeared in laser-treated skin samples when compared with untreated tissue. These results suggest that the argon laser may either degrade or crosslink proteins in vivo. Laser-induced protein crosslinks may be the biochemical basis of argon laser welding.

Argon laser vascular fusion: venous and arterial bursting pressures

This study was designed to determine the optimal laser power (watts) for maximal strength of argon laser vascular fusions by measuring bursting pressures of repairs. Longitudinal incisions (n = 105) measuring either 2.5 or 5 mm in length were performed in canine femoral, carotid, and jugular veins and arteries and were fused with the argon laser at 0.3, 0.5, 0.7, or 0.9 W power. Total exposure time for each repair (50 to 80 sec/0.5 cm) was adjusted to yield identical energy fluences of 1,100 J/cm2. Bursting pressure of the fusions was determined by monitored infusion of anticoagulated blood into an isolated segment of the vessel that contained the fusion. Mean bursting pressures for venous and arterial repairs were significantly higher in the 2.5 mm incisions compared with the 5 mm incisions (P less than 0.05). Venous and arterial repairs of equal length performed at each power resulted in equivalent bursting strengths, except that 5 mm venous segments fused with 0.9 W withstood lower pressures than all other venous repairs (P less than 0.05), and 5 mm arterial segments were in turn significantly weaker at 0.3 W (P less than 0.02). We conclude that argon laser fusion is equally suitable for repair of medium-sized veins and arteries and that immediate strength decreases with increasing length of repair. To maximize strength of longer repairs, venotomies should be welded at power settings between 0.3 and 0.7 W while arteriotomies should be fused at power settings between 0.5 and 0.9 W. The differences in optimal power may be explained by variable wall composition and thickness between veins and arteries.

Dye-enhanced laser tissue welding

For vascular anastomosis, use of topical photosensitizing dye enhances selective delivery of laser energy to target tissue, thus reducing the amount of collateral thermal injury and threshold power required for welding. For fluorescein isothiocyanate (FITC)--stained rabbit aorta in vitro, the threshold for tissue blanching was 15 seconds of 100 mW exposure of cw argon ion laser compared with 15 seconds at 300 mW for unstained tissue. The threshold power density needed for argon laser welding of abdominal aortotomies in rabbits in vivo was 3.8 W/cm2 with FITC and 7.6 W/cm2 without the dye. However, bursting pressures for the two groups (164 mm Hg with FITC, 147 mm Hg without FITC) were not significantly different. Histology revealed decreased collateral thermal damage in FITC-enhanced welds. Use of photosensitizing dyes for tissue welding is feasible and may allow arterial welding with lower power laser systems and cause less thermal trauma by lowering threshold power levels.