Cytotoxic outcomes of orthodontic bands with and without silver solder in different cell lineages.

INTRODUCTION: The safety of orthodontic materials is a matter of high interest. In this study, we aimed to assess the in-vitro cytotoxicity of orthodontic band extracts, with and without silver solder, by comparing the viability outcomes of the HaCat keratinocytes, the fibroblastic cell lineages HGF and MRC-5, and the kidney epithelial Vero cells. METHODS: Sterilized orthodontic bands with and without silver solder joints were added to culture media (6 cm2/mL) and incubated for 24 hours at 37°C under continuous agitation. Subsequently, the cell cultures were exposed to the obtained extracts for 24 hours, and an assay was performed to evaluate the cell viability. Copper strip extracts were used as positive control devices. RESULTS: The extracts from orthodontic bands with silver solder joints significantly reduced the viability of the HaCat, MRC-5, and Vero cell lines, whereas the viability of HGF was not altered by this material. Conversely, the extracts of orthodontic bands without silver solder did not significantly modify the viability index of all evaluated cell lines. CONCLUSIONS: Except for HGF fibroblasts, all tested cell lines showed decreased viability percentages after exposure to extracts of orthodontic bands containing silver solder joints. These data show the relevance of testing the toxicity of orthodontic devices in different cell lines.

Efeito da soldagem híbrida (plasma + maçarico) na suavização da assinatura torque-ângulo em supraestruturas de COCR sobre minipilares de zircônia ­ parte 1 / Effect of hybrid soldering (plasma + gas torch) technique on suavization of torque-angle signatures at Co-Cr frameworks over zirconia mini-abutmets ­ part I

Objetivo: avaliar as desadaptações em supraestruturas de implantes e a curva de assinatura torque-ângulo dos parafusos protéticos nas condições monobloco e pós-soldagem. Material e métodos: uma base retangular de aço inox recebeu três implantes de hexágono externo (4,1 mm x 10 mm), onde foram parafusados minipilares de zircônia. Após o enceramento e inclusão, as supraestruturas foram fundidas em monobloco com uma liga de cobalto-cromo, e os cilindros foram numerados sequencialmente (1, 2 e 3). A leitura na interface supraestrutura/pilar foi realizada com um microscópio comparador (precisão de 1 µm), três vezes em cada cilindro. A tensão de torque nos parafusos foi medida com um torquímetro eletrônico odontológico (OsseoCare, Nobel Biocare). Depois, as supraestruturas foram seccionadas e soldadas a plasma (pontos de estabilização) e maçarico (preenchimento da área restante). Novamente, as desadaptações e assinaturas dos parafusos foram avaliadas pela mesma metodologia. Resultados: as médias de desadaptações foram maiores nas supraestruturas em monobloco (C1=3,5 µm; C2=0 µm; C3=31,2 µm) do que nas supraestruturas pós-soldagem (C1=3,0 µm; C2=2,9 µm; C3=18,1 µm). Dentro de cada condição, o teste de Kruskal-Wallis mostrou diferença estatisticamente significativa apenas para o cilindro 3 (monobloco: p < 0,00003 / pós-soldagem: p=0,008) em relação aos cilindros 1 e 2. Uma diferença estatisticamente significante foi encontrada apenas no C3, comparando as condições monobloco e pós-soldagem (teste t pareado, p=0,03). A assinatura dos parafusos se mostrou melhor na condição pós-soldagem. Conclusão: a fundição monobloco gera instabilidade na assinatura dos parafusos. A desadaptação nos parafusos protéticos de supraestruturas sobre minipilares de zircônia melhora após secção e soldagem híbrida.

Objective: to evaluate the misfi t at implant frameworks and the torque-angle signature curves at the prosthetic screws at one-piece and after soldering conditions. Material and methods: a stainless steel rectangular base received 3 external hex implants (4.1 x 10 mm) where zirconia mini-abutments were fastened. After wax-up and investing, the frameworks were one-piece cast with a Co-Cr alloy, and the prosthetic cylinders sequentially identified (1, 2, and 3). The misfit at the framework/abutment interface was measured with a microscope (reading error 1 µm) 3 times for each cylinder. The screw tension was investigated with an electronic torqued device (Osseocare, Nobel Biocare). After, the frameworks were sectioned and soldered with plasma (stabilization points) and gas torch (filling of the remaining areas). Again, the misfit and torque-angle signatures were measured as described. Results: mean misfit values were greater for one-piece castings (C1=3.5 µm; C2=0 µm; C3=31.2 µm) than after soldering (C1=3.0 µm; C2=2.9 µm; C3=18.1 µm). Within each condition, the Kruskal-Wallis test demonstrated a statistically significant difference only for C3 (one-piece casting: p < 0.00003 / after soldering: p=0.008) compared to C1 and C2. Between each condition, a significant difference was seen only for C3 in the one-piece and after soldering conditions (paired t test, p=0.03). The torque-angle signatures demonstrated a better behavior after soldering. Conclusion: one-piece castings provide instability at torque-angle signatures. Thus, the seating of the prosthetic abutments over the zirconia mini-abutments improves after sectioning and hybrid soldering.

Release of toxic ions from silver solder used in orthodontics: an in-situ evaluation.

INTRODUCTION: The objective of this study was to test the hypothesis that toxic metallic ions in silver solder used in orthodontics are released into saliva. METHODS: The sample included 60 children, 8 to 14 years of age, divided into 2 groups (n = 30 in each group): the control group and the study group (needing maxillary expansion with the hyrax appliance). For analysis of the release of metallic ions, saliva samples from each patient were collected at 6 times in both groups: before placement of the appliance and 10 minutes, 24 hours, and 7, 30, and 60 days after placement. The analysis of saliva was performed by atomic absorption spectrophotometry in a graphite oven to determine the concentrations of cadmium, copper, zinc, and silver ions. Statistical analyses were performed by the mixed model for repeated-measures covariance structure of the symmetrical component type, at P <0.05. RESULTS: The ion concentrations in the control group had low values for cadmium, copper, and zinc (P >0.05); for silver ions, the values did not reach the detection limit. In the study group, all ions showed expressive concentrations at 10 minutes after placement of the appliance (P <0.001), with the highest mean for copper (70.60 µg/L) and the lowest mean for zinc (0.07 µg/L). Comparison between groups revealed significant differences for copper (all periods), zinc (10 minutes, 24 hours, 7 and 30 days), and for cadmium only at 10 minutes. CONCLUSIONS: Great amounts of these ions were released, with the highest concentrations immediately after placement of the appliance.

Cytotoxicity of silver solder employed in orthodontics.

OBJECTIVE: To test the null hypothesis that the silver soldering employed in orthodontics is not cytotoxic for fibroblasts. MATERIALS AND METHODS: This in vitro study was performed using a culture of mice fibroblasts (lineage NIH/3T3), divided into four groups (n = 10 each): control, negative control (stainless steel archwire), positive control (amalgam disks), and test group (silver soldering). After cell culture in complete Dulbecco modified eagle medium and achievement of confluence in 80%, the suspension was added to the plates of 24 wells containing the specimens and incubated in an oven at 37 degrees C for 24 hours. The plates were analyzed on an inverted light microscope, photomicrographs were obtained, and the results were recorded as response rates based on modifications of the parameters of Stanford according to the size of the diffusion halo of the toxic substance and quantity of cell lysis. RESULTS: The results revealed a maximum response rate for the silver soldering group, as well as severe inhibition of cell proliferation and growth, more round cells with mostly darkened and granular aspects, suggesting lysis with cell death. A similar response was seen in the positive control group. CONCLUSION: The hypothesis is rejected. The silver soldering used in orthodontics represents a highly cytotoxic material for the cells analyzed.

Dimensional change of laser-welded gold alloy induced by heat treatment.

PURPOSE: This study examined the effects of laser welding and heat treatment on the dimensional change of cast gold alloy frameworks. MATERIALS AND METHODS: Pairs of cast gold alloy plates were matched, fixed in a jig, and welded in a laser-welding machine at constant welding parameters. The specimens were welded unilaterally (on one surface) or bilaterally (on two surfaces) with five spots as follows: two ends fixed/unilaterally welded (A); two ends fixed/bilaterally welded (AA); one end fixed/unilaterally welded (B); two ends fixed/welded on one surface and then one end fixed/welded on the opposite surface (AB); or one end fixed/bilaterally welded (BB). The dimensional change was determined by measuring the gap between the jig base and one end of the specimen after each welding application. Dimensional change was also measured after two different heat treatments (softening and hardening). The results were analyzed using a two-way ANOVA and Duncan's test (p < 0.05). RESULTS: The dimensional change of the specimens fixed at only one end on either surface (AB, B, and BB) was higher compared with the two ends-fixed specimens (A and AA) after laser welding. The heat treatments also increased the dimensional change in all groups except for the B group. The dimensional change was similar for each fixing method between the two types of heat treatment. CONCLUSIONS: The method of fixing the specimens in the jig significantly affected the amount of dimensional change of the gold alloys. The heat treatments of the laser-welded specimens increased the dimensional change by releasing the residual stress.

The use of three-dimensional oral mucosa cell cultures to assess the toxicity of soldered and welded wires.

The aim of the present study was to determine whether there is a difference in toxicity and loss of viability of three-dimensional (3D) reconstructed human oral epithelium (RHOE) cell cultures induced by point-welded (PW), laser-welded (LW), and silver-soldered (SiS) orthodontic wires. Three types of soldered stainless steel (SS) wires: PW, LW, and SiS were prepared (n = 3) and subjected to multiple end-point analysis (MEA). Six pieces were cut from each wire. Each piece was placed on the triplicate cell cultures (RHOE model based on TR 146 cells). After 24 hours of topical exposure, the cell cultures were cut and stained with haematoxylin/eosin. Toxicity was assessed by evaluating the morphological changes and classifying these as mild, moderate, or severe. The in vitro cell cultures were subjected to a 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) assay in order to quantify viability. Copper wires served as the control to determine severe toxicity and native cell cultures were used as a baseline. Untreated SS wire (0.9 mm) was included for comparison with the welded wires. Histological evaluation with respect to toxicity and measurement of viability in the 3D cell cultures showed no severe toxicity or loss of viability for any of the wires. The morphological ranking of the tested wires from mild to severe toxicity was: SS = PW = LW < SiS. MTT tests revealed the following mean viability values: native cell line (negative control) 98.1 per cent, SS 96.8 per cent, PW 95.5 per cent, LW 95.5 per cent, SiS 85.7 per cent, and copper wires (positive control) 51.2 per cent. Relative comparison between the different welding techniques tested on RHOE revealed, however, that LW and PW wires induced less toxicity/loss of viability compared with SiS wires.

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

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.

Evaluation of biocompatibility of metallic dental materials in cell culture model.

Biocompatibility of metals for dental use was tested using a three-dimensional model consisting of oral keratinocytes cultured on de-epidermised sub-mucosa. The toxicity of orthodontic metallic wire and soldering material was assessed through parameters such as the morphology and growth rate of the keratinocytes, as well as by classical histology, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The sharp composition of metallic wires and soldering materials was assessed by Auger Electron Spectroscopy (AES). The results of our experiment showed that the new model revealed inhibition of keratinocyte growth and stratification near soldering material, whereas mucosal cells were able to grow and layer out on dental wire. It is concluded that this experimental model, which simulates the oral environment, is useful for studying the effects of materials for dental use for its sensibility and reproducibility. Moreover it can provide morpho-functional information which cannot be achieved by traditional methods.

Interactions of fibroblasts with soldered and laser-welded joints.

Relatively little is known about the biocompatibility of the soldered or laser-welded joints of dental appliances. We investigated the reaction of human gingival fibroblasts cultured in vitro in direct contact with samples of soldered and laser-welded joints from orthodontic lingual arches. Contrast phase light microscopy was used to evaluate cell adhesion, morphology and proliferation after 6 and 24h and after 7 and 16 days. Scanning electron microscopy (SEM) was performed at 16 days. Our in vitro findings provide evidence that laser-welded orthodontic appliances have superior fibroblast biocompatibility.

[Dental alloys and allergy. Case report]. / Dentallegierung und Allergie. Ein Fallbericht.

The case of a 67-year-old woman, who had been wearing an upper partial removable denture with a cast metal framework made of CoCrMo alloy for years without any problems, is described. After the extraction of a molar tooth a nickel alloy retention was soldered to the framework. Following reinsertion allergic reactions appeared. The soldered joint showed considerable corrosion. After removing the retention and the soldered joint, the allergic reactions disappeared, although an epicutanceous test had revealed a positive reaction to cobalt. This case supports the high corrosion resistance and biocompatibility reported for CoCrMo alloys in the literature and the loss of these properties due to inadequate processing. Furthermore, the case illustrates a true allergic reaction. In contrast to the rather indiscriminate use of the term allergy to describe various vague disorders, this diagnosis should be restricted to clearly identified clinical situations.

Estudo comparativo das propriedades de resistência à traçäo e ao dobramento e análise metalográfica de uniöes soldadas, pré e pós-cerâmica, de liga de metal nobre / Comparative study of the properties of tensile strenght and bending and metallographic analysis of soldered joints, pre and post-ceramic, of precious metal alloy

Utilizou-se 66 hemi-corpos de prova, de metal nobre (Degudent Universal), para trabalhos metalo-cerâmicos, que proporcionaram 33 juntas soldadas (corpos de prova) unidos com solda de alta temperatura de fusäo (solda pré-cerâmica) e solda de baixa temperatura de fusäo (solda pós-cerâmica). Estes corpos de prova foram submetidos a testes que permitiram avaliar, comparativamente, suas propriedades de resistência à traçäo e resistência ao dobramento, assim como o comportamento estrutural, destas uniöes soldadas, através do microscópio metalográfico. A "máquina de ensaios universal" foi empregada para verificar a força de traçäo necessária para romper 18 dessas juntas soldadas; 12 dessas juntas foram unidas com solda de alta temperatura de fusäo sendo a metade submetida a recozimentos sucessivos, simulando a aplicaçäo das diversas camadas de porcelana...