| Acrylic esin bases of removable partial or complete dentures and ooth-supported or implant-retained overdentures are used to replace the lost tissues and to transfer masticatory forces from the denture to the residual ridges . Most microorganisms that are present intraorally , especially those responsible for caries,periodontal disease , and denture- related stomatitis , can only survive in the mouth if they adhere to nonshedding oral surfaces and start forming colonies . Bacterial adhesion on hard dental surfaces is followed by the accumulation of dental plaque . Several studies have demonstrated that rough acrylic resin surfaces are significantly more prone to bacterial accumulation and plaque formation than smooth surfaces.Some in vivo studies have suggested a threshold level of surface roughness (Ra= 0.2 mm) below which no further reduction in plaque accumulation could be expected . An increase in roughness of surface beyond this borderline level , however , resulted in a simultaneous increase inplaque accumulation . Lower levels of surface roughness are attainable by prepolishing with water and fine pumice , or silicone polishers , and ended by fine polishing using polishing paste that contains fine aluminum oxide particles . This traditional way also has its limitations , it is really time- consuming and some parts of the denture are not easilly achieved .Some glazes have been used for sealing dentures . They would make the acrylic resin surface smoother , decreasing accumulation of residual food and plaque adhesion , and providing improved oral hygiene conditions . We developped a newly denture glazing material , it can not only seal the denture surface , but also be hydrophobic and bacterial- inhibitory . So it can reduce plaque adhesion,and improve oral hygiene conditions .The MTT test has been used extensively to assess cytotoxicity of dental materials . The MTT assay indicates the effects on cell viability by alterations of mitochondrial dehydrogenase activities . In this test methylthiazol tetrazolium is metabolically reduced to coloured formazan . Factors that inhibit dehydrogenase activity will affect the associated colour reaction . It has been shown that activated cells produce more formazan than resting cells , therefore it is possible to measure cell activity or enzyme activities .The aim of the study is to evaluate the cytotoxicity of the glazing material on L929 mouse fibroblasts.Methods : the experiment is consisted of two parts . First , the cytotoxicity of the extracts.Two denture resin specimens measuring 40mm×40mm×2mm were made by the water bath curing process . One of two the specimens is coated by the glazing materials on both sides . Both the specimens were immersed into the RPMI-1640 cell culture medium for three periods of 24-hours . The extracts of each period were obtained . The cytotoxicity on L929 cells of these extracts were tested using the MTT assay.Second , the cytotoxicity of the monomers . HEMA , PDDA , TMPTA (three major monomers of the glazing materials) and MMA (major monomer of the denture bases) were prepared in dimethyl sulfoxide with the solution of 1 mol/l , then they were serially diluted from 4096μmol/L to 2μmol/L by cell culture medium . There was totally 12 groups of dilutions . The cytotoxicity on L929 cells of each dilution was tested using the MTT assay.Dose response curves of cell survival rates and serial dilutions of monomers were fitted to the data.Concentrations corresponding to TC50 values were evaluated from the fitted dose-response curves .We can see that there is no statistically significant difference between the extractions of denture base materials and the new glazing materials (P﹥0.05), and to the glazing materials , the D490 value of the first period extraction was much lower than the third period(P﹤0.05). TC 50 values have been used frequently in in vitro cytotoxicity investigations of dental materials . However , these values varied between investigations , these differences have been suggested to be related to the experimental conditions . Cell types may respond differently when exposed to dental resin monomers . This suggests , that the value of these kinds of investigations is to compare and rank the relative toxicity of tested agents . According to TC50 values and the fitted dose-response curves , within the concentration of 2μmol/L-4096μmol/L , the cytotoxicity of the monomer decreases as it follows : TMPTA﹥PDDA﹥HEMA≈MMA . Exposure time may significantly influence biocompatibility of dental resins . It has been demonstrated that , in laboratory situations , leaching is essentially complete in 24 h and so this suggests that most toxic effects from resin composites occur during the first 24 h . In the present study , the cytotoxicity of the glazed denture base was decreased a lot after extracted by two periods of 24h . This suggests that the amount of the uncured monomers leaching from the glazing materials is becoming more and more small as time passes by . Compared to the cell medium , the extract of the glazed denture base speciment at the first peiod shows cytotoxicity , but at the second period , it shows no toxity.This said that after 24h'extraction , leaching was such little that it could not induce cytotoxic effects . Nevertheless , leached monomer concentrations seem to be much lower than those required to induce cytotoxic effects as shown in the current study . For example , the total accumulated release of HEMA at 30 days from several resin-based materials specimens (6 mm diameter and 1 mm depth) in 4 ml water ranged between 0.0012 and 0.128 mg/l (9.33–983 nM) . By comparison , the minimal toxic value of HEMA from the previously study (1.77 mM)would be over 1000 times greater . In our study , the concentration of HEMA reached to 4096μMol/l (4000 times) , still no cytotoxicity appeared.This may be the reason why PDDA and TMPTA are more toxic than MMA , while the glazed denture resin and the non-glazed have no significantly difference on cytotoxicity(P﹥0.05).From the present study , we can conclude the following three :①there is no significantly difference between the newly developped denture glazing materials and the denture base resin .②After extract 24h,the cytotoxicity of the glazing materials significantly decreased .③The cytotoxicity of the monomer on L929 decreases as it follows: TMPTA﹥PDDA﹥HEMA≈MMA .
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