Abstract
ObjectivesResidual 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 MethodsA 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. ConclusionDue 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.
Highlights
Heat-polymerization is the most widely used method of polymerization for acrylic resin denture base fabrication and usually is accomplished in a heated water-bath[10,12,26].The nature and duration of the conditions to which the molded acrylic resin subjected is described as the polymerization cycle[14,26]
Heat-polymerizing, PMMA based denture base acrylic resin (Meliodent Heat-cure Denture %DVH 0DWHULDO +HUDXV .XO]HU *P%+ &R +DQDX Germany) without cadmium was tested in the present study
As far as the existing scientific data on in vitro cytotoxicity of denture base materials are FRQFHUQHG WKHUH LV QR DYDLODEOH VWXG\ WKDW LGHQWL¿HV RU TXDQWL¿HV WKH OHDFKLQJ FRPSRQHQW LQ HOXDWHV RI WHVW VSHFLPHQV 7KLV VWXG\ VKRZHG DQG TXDQWL¿HG that residual Methyl methacrylate (MMA) leached into eluates
Summary
Heat-polymerization is the most widely used method of polymerization for acrylic resin denture base fabrication and usually is accomplished in a heated water-bath[10,12,26]. The nature and duration of the conditions to which the molded acrylic resin subjected is described as the polymerization cycle[14,26]. The conventional method of polymerization cycle is a long, slow-temperature water-bath polymerization where the heat-polymerization of acrylic resin is processed for 9 h at 74oC26. It has been reported that total polymerization time shorter than 2 h is widely preferred than the long polymerization cycles[3]. There has been several reported variations of polymerization temperature and time, the conversion of monomer is not complete and this might result in unreacted, residual monomer in the denture base acrylic resin[2-5,10,12,14,25]. It has been stated that the residual MMA content might change due to polymerization method[4,5,31] and cycle[10,12,14,25,32]
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