Tatiana Siqueira Gonçalves

Residual Monomer of Autopolymerized Acrylic Resin According to Different Manipulation and Polishing Methods

OBJECTIVE To test the hypothesis that no difference exists in the in situ levels of residual monomer of an autopolymerized acrylic resin, irrespective of the method of manipulation and polishing. MATERIALS AND METHODS Forty volunteers received the test specimens. The residual monomer was evaluated by means of gas chromatography using methylethylketone as extraction solvent. The samples of autopolymerized acrylic resin were submitted to two methods of manipulation--mass and addition--as well as to two types of polishing-mechanical and chemical. Four test groups were determined according to manipulation and polishing techniques: mass-mechanical; mass-chemical; addition-mechanical; addition-chemical. The data obtained were analyzed by the Students t-test for paired samples as well as by analysis of variance. RESULTS Residual methylmethacrylate was verified in high concentrations in the beginning of the testing as well as 24 hours after the test specimens had been worn. Mechanical polishing was associated with lower levels of residual monomer. The mass-mechanical group showed the lowest values. Mechanical polishing was associated with the lowest levels of residual monomer, and the lowest level of all occurred in mass-mechanical group. CONCLUSIONS The hypothesis is rejected. Variations of residual polymer were associated with variations in the manipulation and polishing, but high concentrations of residual monomer were present in all groups. These concentrations were reduced after 24 hours.

Cytotoxicity of Two Autopolymerized Acrylic Resins Used in Orthodontics

OBJECTIVE To test in vitro the null hypothesis that the toxic effect of different acrylic resins used in orthodontics cannot be reduced when a prior elution is performed. MATERIALS AND METHODS Three established cell lines were used (HeLa, NIH3T3, and Hep2) and cultured under standard conditions. Resin segments were immersed in a culture medium and left to elute for 24 and 48 hours. Cells were exposed to medium containing eluates for 24 or 48 hours. The 3-(4,5 dimethyl-2-thiazolyl)-2.5-diphenyl-2H-tetrazolium bromide (MTT) assay was used as the cytotoxicity test. Control cells contained standard medium with no eluate. Analysis of variance and Tukey test were used for statistical analysis. RESULTS Fibroblastic viability was not affected when the elution time was 24 hours, but treatments showed higher cell viability than controls when the elution time was 48 hours. When left to elute for 24 hours, both resins had a cytotoxic effect on epithelial cells, but this effect was not observed when the elution time was 48 hours. CONCLUSIONS The hypothesis was rejected as both tested materials showed lower cytotoxic effect when treated with 48-hour elutes compared with 24-hour elutes, which indicates that a longer elution time reduces resin toxicity.

Cytotoxicity and genotoxicity of orthodontic bands with or without silver soldered joints.

Stainless steel bands, with or without silver soldered joints, are routinely used in orthodontics. However, little is known about the toxic biological effects of these appliances. The aims of this study were to evaluate the cytotoxic, cytostatic, genotoxic and DNA damage-inducing effects of non-soldered bands (NSB) and silver soldered bands (SSB) on the HepG2 and HOK cell lines and to quantify the amount of ions released by the bands. The 24-h metallic eluates of NSBs and SSBs were quantified by atomic absorption spectrophotometry. An MTT reduction assay was performed to evaluate the cytotoxicity, alkaline and modified comet assays were employed to measure genotoxicity and oxidative DNA damage effects, and cytokinesis-block micronucleus cytome (CBMN-Cyt) assays were used to verify DNA damage, cytostasis and cytotoxicity. Ag, Cd, Cr, Cu and Zn were detected in SSB medium samples, and Fe and Ni were detected in both the SSB and NSB medium samples. The SSB group induced stronger cytotoxic effects than the NSB group in both evaluated cell lines. NSB and SSB induced genotoxicity as evaluated by comet assays; stronger effects were observed in the SSB group. Both groups induced similar increases in the number of oxidative DNA lesions, as detected by the FPG and Endo III enzymes. Nucleoplasmic bridges, biomarkers of DNA misrepair and/or telomere end fusions, were significantly elevated in the SSB group. The SSB eluates showed higher amounts of Ni and Fe than NSB, and all the quantified ions were detected in SSB eluates, including Cd. The SSB eluates were more cytotoxic and genotoxic than the NSB samples. Based on these results, we propose that other brands, materials and techniques should be further investigated for the future manufacture of orthodontic appliances.

Biocompatibilidade dos materiais em Ortodontia: mito ou realidade?

O objetivo deste trabalho e apresentar uma revisao sobre os conceitos relacionados a biocompatibilidade dos materiais empregados em Ortodontia. Fatos relacionados as reacoes de hipersensibilidade aos diversos materiais ortodonticos sao discutidos, sendo apresentadas as condutas recomendaveis nestas situacoes.

Influência de variáveis metodológicas na resistência de união ao cisalhamento

Objectives: Evaluate the influence of several methodological variables on the shear bond strength of in vitro studies. Methods: 105 bovine incisors were sectioned at the cervical level. The coronary portion was included in PVC rings, fulfilled with auto polymerized acrylic resin, with its labial surfaces positioned upward. All the samples were prepared for bonding, cleaned and acid etched on the central area of the crowns. In this area, central incisors’ Morelli™ brackets were bonded with Concise™ (3M/Unitek). Three testing groups were established, according to the studied variable: Group 1—storage previous to bonding (a- thymol 0.1%; b- distilled water; c- freezing); Group 2—crosshead speed of the universal testing machine (a- 0.5 mm/min; b- 1.0 mm/min; c- 2.00 mm/min) and Group 3—commercial brand of 37% phosphoric acid (a- 3M/Unitek; b- Acid Gel; c- Attack Tek). The shear bond strength test was performed at the Emic DL2000™ universal testing machine. Data was analyzed through the Student’s t test for independent samples. Results: In Group 1, the freezing group showed the higher values of shear bond strength when compared to the others, although no statistical difference was observed (p > 0.05). For Group 2, the higher the crosshead speed, the lower the shear bond strength, with no statistical difference. In Group 3, the 3M/Unitek brand showed the highest average of shear bond strength in MPa, but also no statistical difference was shown. Conclusions: The variable analyzed in this research had not presented enough influence to determine significant differences between the results.

Differences of Cytotoxicity of Orthodontic Bands Assessed by Survival Tests in Saccharomyces cerevisiae

The aim of this study was to evaluate the cytotoxicity induced by orthodontic bands through survival tests on Saccharomyces cerevisiae, a microorganism that presents several genetic and biochemical characteristics similar to human cells. Three groups of bands were evaluated: silver soldered (SSB), laser soldered (LSB), and bands without any solder (WSB). Yeast cells were directly exposed to the bands and indirectly, when a previous elution of the metals in artificial saliva was performed. The negative control was composed of yeast cells or artificial saliva not exposed to any kind of metal. In the direct exposure experiments, all tested groups of bands induced a slight reduction in yeast viability compared to the control. This effect was more intense for the SSB, although not statistically significant. For the indirect exposure experiments, the SSB induced a statistically significant decrease in cell viability compared to the LSB. There were no significant differences between the survival rates of the negative control and the LSB group in both direct and saliva tests. SSBs were cytotoxic, whilst LSBs were not, confirming that laser soldering may be a more biocompatible alternative for use in connecting wires to orthodontic appliances.

In vivo evaluation of the genotoxic effects of Hyrax auxiliary orthodontic appliances containing silver-soldered joints.

Auxiliary appliances consisting of silver-soldered joints may be present in the patients oral cavity for a long time. The aim of this study was to investigate, in vivo, the potential genotoxic effects of Hyrax-type maxillary expanders containing silver-soldered joints on the cells of the buccal mucosa. Buccal cells were collected from 20 patients and processed to perform the buccal comet assay (BCA) and the buccal micronucleus cytome (BMCyt) assay, to investigate DNA and chromosomal damage, respectively. For the BCA, patients were evaluated before and 14 days after the appliances were installed. For the BMCyt assay, the patients were evaluated longitudinally; before the insertion of the appliance and after one, six, and twelve months. The BCA showed significant increases in damage frequency and damage index in exfoliated buccal cells, following insertion of the appliance. For the BMCyt assay, the endpoints related to cell proliferation, cell death, and chromosomal damage (micronuclei and nuclear buds) resulted in no significant differences over the 12-month study period. In conclusion, the use of orthodontic appliances containing silver-soldered joints can significantly increase DNA damage as measured by the BCA.