In vitro toxicity evaluation of silver soldering, electrical resistance, and laser welding of orthodontic wires

Abstract

The long-term effects of orthodontic appliances in the oral environment and the subsequent leaching of metals are relatively unknown. A method for determining the effects of various types of soldering and welding, both of which in turn could lead to leaching of metal ions, on the growth of osteoblasts, fibroblasts, and oral keratinocytes in vitro, is proposed. The effects of cell behaviour of metal wires on osteoblast differentiation, expressed by alkaline phosphatase (ALP) activity; on fibroblast proliferation, assayed by the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulphophenil)-2H-tetrazolium-phenazine ethosulphate method; and on keratinocyte viability and migration on the wires, observed by scanning electron microscopy (SEM), were tested. Two types of commercially available wires normally used for orthodontic appliances, with a similar chemical composition (iron, carbon, silicon, chromium, molybdenum, phosphorus, sulphur, vanadium, and nitrogen) but differing in nickel and manganese content, were examined, as well as the joints obtained by electrical resistance welding, traditional soldering, and laser welding. Nickel and chromium, known as possible toxic metals, were also examined using pure nickel- and chromium-plated titanium wires. Segments of each wire, cut into different lengths, were added to each well in which the cells were grown to confluence. The high nickel and chromium content of orthodontic wires damaged both osteoblasts and fibroblasts, but did not affect keratinocytes. Chromium strongly affected fibroblast growth. The joint produced by electrical resistance welding was well tolerated by both osteoblasts and fibroblasts, whereas traditional soldering caused a significant (P < 0.05) decrease in both osteoblast ALP activity and fibroblast viability, and prevented the growth of keratinocytes in vitro. Laser welding was the only joining process well tolerated by all tested cells.

Metal ion release from silver soldering and laser welding caused by different types of mouthwash

“…These results are similar to those from previous studies. 10,14,18 Sestini et al 18 reported that laser welding was the only bonding method that was well tolerated by cells, whereas silver soldering was evaluated as highly toxic for all cell types.…”

“…The results of the few existing toxicity studies that compared laser welding and silver soldering methods support this result. [10][11][12][13][14][15][16][17][18] Sestini et al 18 noted that laser welding was the only well-tolerated bonding method, whereas silver soldering was highly toxic to all types of cells. Bagatin et al 19 used scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy in an in vivo study in which they investigated the corrosion of silver soldered Haas expanders in patients using antimicrobial agents.…”

Cytotoxicity of Silver Solder Employed in Orthodontics

“…[5][6][7] The metal parts that remain in the oral cavity are subject to corrosion because this environment's physical properties, ie, the chemical and microbiological properties, stimulate the dissolution of metals. [8][9] Among the cations present in the alloys, gold and palladium (noble elements) may not be detected, whereas silver, copper, zinc, and gallium are always found. 3,8 According to the International Register of Potentially Toxic Chemicals of the United Nations Environment Program, metallic ions such as cadmium, copper, silver, and zinc are present in silver soldering Use an amalgam carrier with a 2-mm-diameter opening to determine the disk width.…”

Fracture Strength of Soldered and Laser Welded Orthodontic Bands and Wires With and Without Filling Material: A Preliminary Report

“…5 In conventional dental brazing -defined as soldering over a temperature of 450°C -the parent metals are joined with different types of metals, which may reduce corrosion resistance because of galvanic corrosion between metals. [6][7][8] The high corrosion rates can influence the biocompatibility [9][10][11] and mechanical strength. 9 Laser welding using a pulsed Nd:YAG (neodymium-doped yttrium aluminium garnet; Nd:Y3Al5O12) laser is a current technology and has been developed for joining purposes in the dental laboratory and offers clear-cut advantages compared to the various soldering methods.…”