Assessment of methyl methacrylate genotoxicity by the micronucleus test

The aim of this study was to evaluate the genotoxic potential of methyl methacrylate (MMA) vapor by simulating standard occupational exposure of 8 hours per day and using the micronucleus test. We used 32 adult male Wistar rats divided into three groups: A - 16 rats exposed to MMA for 8 hours a day, B - Eight rats receiving single subcutaneous doses of cyclophosphamide on the first day of the experiment (positive control), C - Eight rats receiving only water and food ad libitum (negative control). Eight rats from group A and all of the rats from groups B and C were sacrificed 24 hours after beginning the experiment (acute exposure in group A). The remaining animals in group A were sacrificed 5 days after the experiment began (repeated exposure assessment in group A, simulating occupational exposure 40 hours/week). Femoral bone marrow was collected from each rat at the time of sacrifice for use in the micronucleus test. Two slides were completed per animal and were stained with Giemsa staining. Two thousand polychromatic erythrocytes were counted per animal. The Kruskal-Wallis test followed by a multiple comparisons test (Dunn test) was used for statistical analysis. The median number of micronuclei was 7.00 in the group exposed to MMA for 1 day, 2.00 in the group exposed to MMA for 5 days, 9.00 in the group exposed to cyclophosphamide (positive control) and 0.756 in the negative control group (p < 0.0001). MMA was genotoxic when measured after 1 day of exposure but was not evidently genotoxic after 5 days.

Effect of leaching residual methyl methacrylate concentrations on in vitro cytotoxicity of heat polymerized denture base acrylic resin processed with different polymerization cycles

OBJECTIVES: Residual methyl methacrylate (MMA) may leach from the acrylic resin denture bases and have adverse effects on the oral mucosa. This in vitro study evaluated and correlated the effect of the leaching residual MMA concentrations ([MMA]r) on in vitro cytotoxicity of L-929 fibroblasts. MATERIAL AND METHODS: A total of 144 heat-polymerized acrylic resin specimens were fabricated using 4 different polymerization cycles: (1) at 74ºC for 9 h, (2) at 74ºC for 9 h and terminal boiling (at 100ºC) for 30 min, (3) at 74ºC for 9 h and terminal boiling for 3 h, (4) at 74ºC for 30 min and terminal boiling for 30 min. Specimens were eluted in a complete cell culture medium at 37ºC for 1, 2, 5 and 7 days. [MMA]r in eluates was measured using high-performance liquid chromatography. In vitro cytotoxicity of eluates on L-929 fibroblasts was evaluated by means of cell proliferation using a tetrazolium salt XTT (sodium 3´-[1-phenyl-aminocarbonyl)-3,4-tetrazolium]bis(4-methoxy-6-nitro)benzenesulphonic acid) assay. Differences in [MMA]r of eluates and cell proliferation values between polymerization cycles were statistically analyzed by Kruskal-Wallis, Friedman and Dunn's multiple comparison tests. The correlation between [MMA]r of eluates and cell proliferation was analyzed by Pearson's correlation test (p<0.05). RESULTS: [MMA]r was significantly (p<0.001) higher in eluates of specimens polymerized with cycle without terminal boiling after elution of 1 and 2 days. Cell proliferation values for all cycles were significantly (p<0.01) lower in eluates of 1 day than those of 2 days. The correlation between [MMA]r and cell proliferation values was negative after all elution periods, showing significance (p<0.05) for elution of 1 and 2 days. MMA continued to leach from acrylic resin throughout 7 days and leaching concentrations markedly reduced after elution of 1 and 2 days. CONCLUSION: Due to reduction of leaching residual MMA concentrations, use of terminal boiling in the polymerization process for at least 30 min and water storage of the heat-polymerized denture bases for at least 1 to 2 days before denture delivery is clinically recommended for minimizing the residual MMA and possible cytotoxic effects.

Toxicidade pulmonar e hepática aos vapores do metil metacrilato: um estudo experimental em ratos / Pulmonary and liver toxicity of methyl methacrylate vapors: an experimental study in rats

Methyl methacrylate (MMA) is widely used in medicine and in dentistry in dental braces and prostheses. The most important occupational exposure route of MMA is inhalation. These study aims at evaluating the MMA toxicity to the rat lung and liver related to the time of exposure. Male and female albino Wistar rats were exposed to MMA by inhalation. One group (n=36) was exposed continuously, and the other (n=36) was exposed during 8-hours/day, without water and food intake during the exposure period as to prevent the risk of water and food contamination by MMA. A control group (n=8) received water and food without MMA exposure. Rats were sacrificed 5, 8 and 10 days after exposure. Significant morphological alterations observed were pulmonary emphysema and hepatic esteatosis early detected after 5 days of MMA exposure in 26.4 percent (n=19) and 25 percent (n=18) of the animals, respectively. Pulmonary emphysema was observed in 77.7 percent (n=28) of the rats under continuous exposure, in 66.6 percent (n=24) of the 8-hours/day-exposure group, and in only one animal from the control group. Hepatic esteatosis was observed in 94.5 percent (n=34) of the continuous exposure group, and in 72.2 percent (n=26) of the rats exposured per 8-hours/day, and statistically significant differences were observed among the groups. The literature describes many pulmonary changes related to the exposure to MMA, emphysema being the main one, what is in accordance with our data. Hepatic damage has only been seen when the MMA is administered by intravenous injection. The results of this investigation show that toxicity of MMA appeared very early at the first days of inhalation of this agent. It indicates thata proper exhaustion system should be implemented prior to using MMA in order to prevent occupational related MMA injuries.

O metil metacrilato (MMA) é amplamente usado na medicina e odontologia. A principal via de exposição ocupacional é inalatória. Este trabalho visa avaliar a ação tóxica do MMA em pulmão e fígado de ratos em diferentes períodos de exposição. Ratos Wistar albinos, machos e fêmeas, foram expostos ao MMA por inalação. Um grupo (n= 36) foi exposto continuamente e outro (n=36) exposto durante oito horas diárias, sem água e ração durante a exposição, para excluir a possibilidade de contaminação da água e ração pelo MMA. Um grupo controle (n=8) recebeu água e ração e não foi exposto ao MMA. Os animais foram sacrificados com 5, 8 e 10 dias de exposição. As alterações morfológicas significativas foram enfisema pulmonar e esteatose hepática, detectados precocemente com 5 dias de exposição ao MMA, em 26,4 por cento (n=19) e 25 por cento (n=18) dos animais, respectivamente. Enfisema pulmonar foi observado em 77,7 por cento (n=28) dos animais com exposição contínua, em 66,6 por cento (n=24) dos expostos 8 horas/ dia e em 1 animal do grupo controle. Esteatose hepática foi observada em 94,5 por cento (n=34) dos animais com exposição contínua e em 72,2 por cento (n=26) dos expostos 8 horas/dia, sendo a diferença entre os grupos estaticamente significante. A principal alteração pulmonar na literatura é o enfisema, concordando com nossos achados. Alterações hepáticas somente foram observadas na administração endovenosa do MMA. Os dados do presente trabalho mostram que o efeito tóxico do MMA se manifesta precocemente nos primeiros dias de inalação deste agente, indicando que um sistema adequado de exaustão deve ser instalado antes do uso do MMA para prevenir danos ocupacionais a ele relacionados.

Assessment of methyl methacrylate vapor toxicity on the rat tracheal epithelium / Análise da toxicidade dos vapores de metil metacrilato sobre o epitélio traqueal de ratos

O metil metacrilato (MMA) é um monômero que se polimeriza em resina pela ação da luz e do calor, transformando-se em plástico claro, resistente e durável, relativamente inerte. Por apresentar tais características, o MMA tem sido muito usado na Medicina, como cimento ósseo, e na Odontologia, em aparelhos e próteses dentais, o que tem suscitado interesse na avaliação de sua toxicidade. Estudos experimentais e clínicos têm mostrado que os monômeros podem causar uma gama de efeitos adversos. A principal via de exposição ocupacional ao MMA é a inalatória. Este trabalho visa a avaliar a ação tóxica do MMA sobre o epitélio traqueal em relação ao tempo de exposição. Para isso, dois grupos experimentais de ratos foram expostos ao MMA por inalação, com restrição de ventilação: um grupo (n = 36) foi exposto continuamente, e outro (n = 36) foi exposto durante oito horas diárias, sem água e comida durante o período de exposição. Um grupo controle (n = 8) recebeu ar normal. Doze animais de cada grupo de estudo foram sacrificados com 5, 8 e 10 dias de exposição, junto com dois ou quatro animais do grupo controle. Vinte e nove (80,5%) dos ratos expostos continuamente ao MMA apresentaram inflamação do epitélio traqueal, assim como 58,33% (n = 21) daqueles expostos 8 horas/dia e 87,5% (n = 7) dos controles. Não se observou associação entre o processo inflamatório e a exposição ao MMA, nem alterações significativas na medida da espessura do epitélio traqueal. Novos estudos, com tempo mais prolongado de exposição e análise de outros parâmetros, devem ser realizados para que seja excluída, totalmente, a possibilidade de dano traqueal por vapores de MMA.