***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: The split-mouth design is a popular design in oral health research . In the most common split-mouth study , each of two treatments are r and omly assigned to either the right or left halves of the dentition . The attractiveness of the design is that it removes a lot of inter-individual variability from the estimates of the treatment effect . However , already about 20 years ago the pitfalls of the design have been reported in the oral health literature . Yet , many clinicians are not aware of the potential problems with the split-mouth design . Further , it is our experience that most statisticians are not even aware of the existence of this design . Since most of the critical remarks appeared in the oral health literature , we argue that it is necessary to introduce the split-mouth design to a statistical audience , so that both clinicians and statisticians clearly underst and the advantages , limitations , statistical considerations , and implication s of its use in clinical trials and advise them on its use in practice Two formulations of posterior composite resin ( P-30 and Bisfil-P ) were evaluated and compared to a high-copper , dispersed-phase amalgam ( Dispersalloy ) .  One hundred twenty-eight restorations were placed in 27 patients so that each patient received at least one of each material . After 3 years of clinical service , all three restorative material s produced clinical ly acceptable restorations , according to US Public Health Service and Leinfelder criteria . The amalgam restorations , however , underwent less wear ( 44 microns ) than did the posterior composite resin restorations ( 60 to 74 microns ) . Stratification of data by type of tooth , class of restoration , and size of restoration produced the same ranking of wear from lowest to highest : Dispersalloy , Bisfil-P , and P-30 . Resin restorations showed 45 % more wear in molars than in premolars , and more wear was associated with moderately sized restorations than with conservative restorations . The surface texture of restorations of composite resin with porous strontium glass filler was nearly as smooth as that of enamel and was significantly smoother than that of the restorations of composite resin with zinc glass filler or of unpolished amalgam Previous studies noted specific changes in urinary porphyrin excretion patterns associated with exposure to mercury ( Hg ) in animals and humans . In our study , urinary porphyrin concentrations were examined in normal children 8–18 years-old from a re analysis of data provided from a r and omized , prospect i ve clinical trial that was design ed to evaluate the potential health consequences of prolonged exposure to Hg from dental amalgam fillings  ( the parent study ) . Our analysis examined dose-dependent correlations between increasing Hg exposure from dental amalgams and urinary porphyrins utilizing statistical models with adjustments for the baseline level ( i.e. study year 1 ) of the following variables : urinary Hg , each urinary porphyrin measure , gender , race , and the level of lead ( Pb ) in each subject ’s blood . Significant dose-dependent correlations between cumulative exposure to Hg from dental amalgams and urinary porphyrins associated with Hg body-burden ( pentacarboxyporphyrin , precoproporphyrin , and coproporphyrin ) were observed . Overall , 5–10 % increases in Hg-associated porphyrins for subjects receiving an average number of dental amalgam fillings in comparison to subjects receiving only composite fillings were observed over the 8-year course of the study . In contrast , no significant correlations were observed between cumulative exposure to Hg from dental amalgams and urinary porphyrins not associated with Hg body-burden ( uroporphyrin , heptacarboxyporphyrin , and hexacarboxyporphyrin ) . In conclusion , our study , in contrast to the no-effect results published from the parent study , further establishes the sensitivity and specificity of specific urinary porphyrins as a biomarker for low-level Hg body-burden , and also reveals that dental amalgams are a significant chronic contributor to Hg body-burden In 41 patients class 11 cavities each of the lower jaw were filled with the material s Adaptic , Concise cap , Epoxydent or amalgam . The models made from impressions were systemically measured by a coordinate measuring machine according to a procedure determined by us ( measuring error of this method about 15 micron ) . After one year the following abrasions were found : amalgam 18 micron + /- 58 micron , Adaptic 92 micron + /- 97 micron , Concise Cap 146 micron + /- 75 micron , Epoxydent 38 micron + /- 50 micron . Evaluation of the clinical examination showed that the material s Concise and Epoxydent were significantly inferior as regards border closure than amalgam and Adaptic . We determined further that a large percentage of composite filling showed visible discoloration of the borders ( Adaptic 42 % , Concise 55 % , Epoxydent 80 % ) . Many of the fillings were discolored after a year .  Adaptic was highly significantly different with 31.6 % discolored fillings to both other material s ( Concise 79 % , Epoxydent 78.4 % ) Dental amalgams are a commonly used dental restorative material , and amalgams are about 50 % mercury ( Hg ) . In our study , urinary Hg levels was examined in children of age 8–18 years , with and without dental amalgam fillings , from a completed clinical trial ( parent study ) that was design ed to evaluate the potential health consequences of prolonged exposure to Hg from dental amalgam fillings . Our study was design ed to determine whether there was a significant dose-dependent correlation between increasing Hg exposure from dental amalgams and urinary Hg levels . Hg exposure depends on the size and number of teeth with dental amalgams . Overall , consistent with the results observed in the parent study , there was a statistically significant dose-dependent correlation between cumulative exposure to Hg from dental amalgams and urinary Hg levels , after covariate adjustment . Further , it was observed that urinary Hg levels increased by 18 % to 52 % among 8 to 18 year old individuals , respectively , with an average exposure to amalgams , in comparison to study subjects with no exposure to amalgams . The results of our study suggest that dental amalgams contribute to ongoing Hg exposure in a dose-dependent fashion Resin-based composite dental restoration material s may release bisphenol-A , an endocrine-disrupting chemical . Using secondary analysis of a r and omized clinical safety trial of amalgam vs. composites , we tested the hypothesis that dental restoration material s affect children ’s growth . Children ( N = 218 boys , N = 256 girls ) aged 6 to 10 yrs at baseline with ≥ 2 decayed posterior teeth were r and omized to amalgam or composites ( bisphenol-A-diglycidyl-dimethacrylate composite for permanent teeth , urethane-dimethacrylate compomer for primary teeth ) for treatment of posterior caries throughout follow-up . Primary outcomes for this analysis were 5-year changes in BMI -for-age z-scores , body fat percentage ( BF% ) , and height velocity ; exploratory analyses ( n = 113 ) examined age at menarche . Results showed no significant differences between treatment assignment and changes in physical development in boys [ ( composites vs. amalgam ) BF% , 4.9 vs. 5.7 , p = 0.49 ; ( BMI -z-score ) 0.13 vs. 0.25 , p = 0.36 ] or girls ( 8.8 vs. 7.7 , p = 0.95 ; 0.36 vs. 0.21 , p = 0.49 ) . Children with more treatment on primary teeth had greater increases in BF% regardless of material type . Girls assigned to composites had lower risk of menarche during follow-up ( hazard ratio = 0.57 , 95 % CI 0.35 - 0.95 ) . Overall , there were no significant differences in physical development over 5 years in children treated with composites or amalgam . Additional studies examining these restoration material s in relation to age at menarche are warranted ( clinical trials.gov number NCT00065988 ) CONTEXT Dental ( silver ) amalgam is a widely used restorative material containing 50 % elemental mercury that emits small amounts of mercury vapor . No r and omized clinical trials have determined whether there are significant health risks associated with this low-level mercury exposure . OBJECTIVE To assess the safety of  dental amalgam restorations in children . DESIGN A r and omized clinical trial in which children requiring dental restorative treatment were r and omized to either amalgam for posterior restorations or resin composite instead of amalgam . Enrollment commenced February 1997 , with annual follow-up for 7 years concluding in July 2005 . SETTING AND PARTICIPANTS A total of 507 children in Lisbon , Portugal , aged 8 to 10 years with at least 1 carious lesion on a permanent tooth , no previous exposure to amalgam , urinary mercury level < 10 microg/L , blood lead level < 15 microg/dL , Comprehensive Test of Nonverbal Intelligence IQ > or = 67 , and with no interfering health conditions . INTERVENTION Routine , st and ard-of-care dental treatment , with one group receiving amalgam restorations for posterior lesions ( n = 253 ) and the other group receiving resin composite restorations instead of amalgam ( n = 254 ) . MAIN OUTCOME MEASURES Neurobehavioral assessment s of memory , attention/concentration , and motor/visuomotor domains , as well as nerve conduction velocities . RESULTS During the 7-year trial period , children had a mean of 18.7 tooth surfaces ( median , 16 ) restored in the amalgam group and 21.3 ( median , 18 ) restored in the composite group . Baseline mean creatinine-adjusted urinary mercury levels were 1.8 microg/g in the amalgam group and 1.9 microg/g in the composite group , but during follow-up were 1.0 to 1.5 microg/g higher in the amalgam group than in the composite group ( P<.001 ) . There were no statistically significant differences in measures of memory , attention , visuomotor function , or nerve conduction velocities ( average z scores were very similar , near zero ) for the amalgam and composite groups over all 7 years of follow-up , with no statistically significant differences observed at any time point ( P values from .29 to .91 ) . Starting at 5 years after initial treatment , the need for additional restorative treatment was approximately 50 % higher in the composite group . CONCLUSIONS In this study , children who received dental restorative treatment with amalgam  did not , on average , have statistically significant differences in neurobehavioral assessment s or in nerve conduction velocity when compared with children who received resin composite material s without amalgam . These findings , combined with the trend of higher treatment need later among those receiving composite , suggest that amalgam should remain a viable dental restorative option for children . TRIAL REGISTRATION clinical trials.gov Identifier : NCT00066118 A three-year clinical study was completed at the College of Dentistry comparing the overall performance of Class I amalgam restorations with preventive resin restorations ( PRRs ) . Seventy-four PRRs and fifty-two amalgam restorations were placed in the posterior teeth of thirty-eight patients . The PRR was composed of two material s : P-50 ( 3 M Corp. ) , a heavily filled composite resin , and White Sealant ( 3 M Corp. ) , a light-cured sealant . Fast-set Dispersalloy ( Johnson and Johnson Corp. ) was used for the amalgam restorations . The restorations were evaluated at six months , one year , two years and three years . The USPHS/Ryge system was used to evaluate anatomic form , marginal adaptation , marginal discoloration and recurrent caries of both type restorations . A restoration was considered a failure if any part of the restoration was replaced due to secondary caries . There were two failures of PRRs at six months , and four failures at one year . Failures were due to non retention of the sealant of the PRR and possibly related to operator error . The failures were easily repaired and removed from the study . No PRR failed at the two or three year evaluations . No amalgam restoration failed within the three year period The aim of this study was to obtain information on the restorative dental care of adults in Finl and . A r and om sample of private dentists was drawn from the register , and in spring 2000 they were sent a question naire requesting them to record information for each restoration placed during one ordinary working day . A total of 800 dentists were contacted and 548 responded . The dentists reported placement of 3,455 restorations .  Of these , 5 % were Class I , 36 % were Class II , 13 % were Class III , 9 % were Class IV , 21 % were Class V , and 16 % were extensive restorations including 4 or more surfaces . Overall , composite resin was the most common restorative material , and it was used in 79 % of the restorations , whereas amalgam was used in 5 % , compomers in 4 % , and glass ionomers ( either conventional or resin‐modified ) in 7 % of cases . In 5 % of the cases , the tooth was restored with indirect restorative methods , using either gold or ceramic material s. Of the treatments , 65 % were replacements of previous restorations . Secondary caries was the most common reason for replacement ( 36 % , 52 % , and 41 % for composite , glass ionomer , and amalgam , respectively ) . Other common reasons were fractures of the tooth or 
    Output:
    
The investigators found no difference in adverse effects between composite and amalgam restorations .
There is low- quality evidence to suggest that resin composites lead to higher failure rates and risk of secondary caries than amalgam restorations .
This review reinforces the benefit of  amalgam restorations  and the results are particularly useful in parts of the world where  amalgam  is still the material of choice to restore posterior teeth with proximal caries .