***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Dental laboratory technicians may be exposed to metal alloys that are used in the production of crowns , bridges and removable partial dentures . These alloys consist of 35 - 65 % cobalt , 20 - 30 % chromium , 0 - 30 % nickel , and small amounts of molybdenum , silica , beryllium , boron and carbon . The aim of this study was to assess whether dental technicians are occupationally exposed to chromium , cobalt and nickel , by analyzing urinary excretion levels of these metals and to investigate the genotoxic effects of occupational exposure associated with dental prostheses production operations by analyzing cytokinesis-blocked micronucleus ( CB-MN ) frequencies in peripheral lymphocytes and micronucleus ( MN ) frequencies in exfoliated nasal cells from 27 dental laboratory technicians and 15 control subjects . The differences in the urinary excretion of metals between technicians and controls were statistically significant . The mean ( + /-S.D. ) CB-MN frequencies ( per thous and ) in peripheral lymphocytes were 4.00 ( + /-2.98 ) among the dental technicians and 1.40 ( + /-1.30 ) among the controls , a statistically significant difference ( P<0.005 ) . The mean ( + /-S.D. ) MN frequencies ( per thous and ) in nasal cells were 3.50 ( + /-1.80 ) among the dental technicians and 1.19 ( + /-0.53 ) among the controls , which was also a statistically significant difference ( P<0.005 ) . There was a significant correlation between duration of exposure and MN frequencies in lymphocytes ( r=0.642 , P<0.01 ) , but not in nasal cells of technicians . Our data reveal that in vivo exposure to chromium , nickel and cobalt metals is evident and that this occupational exposure may contribute to the observed genotoxic damage in two types of cells , e.g. lymphocytes and exfoliated nasal cells . However , it can not be determined which compound(s ) are responsible for the genotoxic damage observed in this study The extent of oxidative DNA damage is considered a biomarker of carcinogenic process and could be investigated in population studies using easily obtained cells . The oxidized DNA base adduct 8-hydroxy-2-deoxyguanosine ( 8-OHdG ) released by enzymatic hydrolysis of DNA is commonly assayed by high performance liquid chromatography with electrochemical detection . It is expressed as a ratio of 8-OHdG to unoxidized deoxyguanosine . We modified and improved this method , determined the optimal time for harvesting buccal mucosa cells ( BMC ) , assessed whether they mirror peripheral circulating blood cell DNA damage , and compared the anticoagulants , heparin , and EDTA for consistency in measurement of leukocyte 8-OHdG. Thirty-one healthy participants , r and omized into two groups , donated BMC and blood sample s. Sample s were collected at baseline and either 3 or 7 days after baseline . Results showed no correlation between 8-OHdG/deoxyguanosine ratios in BMC and peripheral blood leukocytes at any time point regardless of harvest time . BMC had much higher oxidative DNA damage , but displayed a 25.6 % reduction in the oxidized DNA adduct level ( P < 0.04 ) at 3 days after baseline . Leukocytes collected in heparin and EDTA had similar 8OHdG/deoxyguanosine ratios ; however , EDTA was preferred , as it produced a clean nuclear pellet without hemoglobin contamination , and the results were less variable . This improved assay shows within subject stability over time in both leukocyte and BMC DNA damage , increasing the probability that small intervention differences can be detected in healthy subjects . Buccal cells provide an accessible pool of epithelial cells that represents higher levels of DNA damage than circulating leukocytes . ( Cancer Epidemiol Biomarkers Prev 2008;17(1):212–9 INTRODUCTION The release of metal ions from fixed orthodontic appliances is a source of concern . The aim of this study was to evaluate genotoxic damage in the oral mucosal cells of patients wearing fixed appliance , and the nickel and chromium ion contents in these cells . METHODS Twenty patients undergoing orthodontic treatment formed the experimental group , and 20 untreated subjects comprised the control group . Oral mucosal smears were collected at 2 times : at debonding and 30 days after debonding . The smears were stained with Papanicolaou stain and studied under a light microscope to evaluate the presence of micronuclei .  Inductively coupled plasma-mass spectrometry was used to quantify the presence of metal ions . The data were subjected to the Mann-Whitney U test and the Spearman rank correlation test . RESULTS The mean micronuclei frequency was significantly higher in the treated group than in the control group at debonding ; the difference was smaller and not statistically significant 30 days after debonding . The nickel and chromium ion contents in the experimental group were not significantly higher than in the control group . No correlation could be established between micronuclei frequency and metal ion content . CONCLUSIONS Nickel and chromium alloys of orthodontic appliances emit metal ions in sufficient quantities to induce localized genotoxic effects , but these changes revert on removal of the appliances This study is aim ed at determining whether a commercially available varnish , containing 40 % chlorhexidine , is able to reduce the numbers of mutans streptococci and lactobacilli in saliva , in a moderately caries-active population in Surinam . 238 children , ages 13–14 years , were selected from different schools in Paramaribo , Surinam . From these children , total dental status was recorded and saliva sample s were taken . At baseline and every 6 months , a 40 % chlorhexidine varnish ( EC40 ® ) was applied . The control group received a neutral gel that did not contain chlorhexidine .  The numbers of salivary mutans streptococci and lactobacilli were calculated by st and ard methods , and the caries status was recorded every 12 months . The study lasted 30 months . The results indicate that chlorhexidine varnish did not decrease the numbers of cariogenic bacteria , nor did it decrease caries progression . Moreover , in this population with a low dental health care , children with lactobacilli present in the saliva above our detection level , the chlorhexidine varnish even tended to increase caries progression , possibly due to selection of aciduric and acidogenic oral bacterial species . We therefore conclude that 40 % chlorhexidine varnish is not likely to decrease caries in children in a high-treatment-need population without treatment of the sources of infection 
    Output:
    
Acute DNA/cellular damage in oral mucosa cells is induced by orthodontic appliances .
Nevertheless , even though these effects were no longer detected after removing the appliances , more rigorous RCTs are needed to explore the extent to which acquired damage can be observed in the oral mucosa