impression materials are largely used to record the geometry of hard and soft dental 
 tissue during dental treatment or to record the relations of teeth with the surrounding 
 tissues .
these materials can be 
 classified into elastic and non - elastic , and the two groups of the elastic ones are the 
 hydrocolloids ( e.g. , alginates ) and the elastomers ( polysulfides , condensation 
 silicones , addition silicones and polyethers ) .
elastic recovery , accuracy , strain in 
 compression , tear energy and tensile strength are some of the commonly investigated 
 properties which enables the development of better materials , but 
 radiodensity measurement studies are uncommon for new materials .
irrespective of the impression 
 technique , all dental impression materials are introduced into the oral cavity right 
 after having been mixed and come in direct contact with the oral tissues . under this 
 condition
some studies have reported allergic 
 responses to impression materials and their potential cytotoxicity , even if the period 
 of contact with oral tissues is short .
therefore , if materials with low tear strength are left around or 
 under gingival margins without any perception by the dentist , an inflammatory response 
 may possibly rise with time .
in addition to the potential cytotoxicity , by means of a 
 radicular impression for indirect fabrication of post - and - cores , fragments can be left inside root 
 canals making it difficult to adapt cast metal posts ; otherwise , these materials can act 
 as foreign bodies whose aspiration by patient can result is serious problems .
it is generally accepted that materials should be sufficiently radiopaque to be detected 
 against a background of enamel and dentin . the radiopacity degree required for ideal clinical 
 performance can vary within the same class of material .
common methods for evaluation of density of 
 radiographic images employ conventional x - ray films and densitometers or spectrophotometers .
since 1987 , alternatives to silver - halide receptors for intraoral 
 radiographic imaging have included ccd - based systems and storage phosphor 
 technology .
digital intraoral 
 radiography reduces patients ' exposure to x - rays , permits the improvement of image quality by image manipulation , 
 it is faster and less expensive than conventional techniques and easy to use and also enables the accurate evaluation 
 of radiodensity .
in the past 20 years , after constant development of impression materials , very few 
 studies have investigated their radiodensity .
it is hypothesized 
 that an acceptable degree of radiodensity would enable the detection of small fragments 
 left inside gingival sulcus or root canals .
thus , the aim of this study was to evaluate 
 the radiodensity of different impression dental materials and to compare the results to 
 the radiodensity of human and bovine enamel and dentin .
material 
 types , commercial names , manufacturers and composition are listed in figure 1 .
five samples of each material were 
 produced according to the manufacturers ' instructions and inserted in a 1.0-mm - thick 
 stainless steel mold with 4.0 mm in diameter to obtain standardized samples .
materials 
 were mixed and allowed to set during the period recommended by each manufacturer .
after 
 removal of the samples from the mold , the thickness was checked with a digital caliper 
 ( mytutoyo , tokyo , japan ) in order to fit 1.0 mm ( 0.1 mm ) .
a 99%-pure aluminum 
 stepwedge ( 12 steps ) ranging from 1.0 mm to 12.0 mm in thickness served as a 
 control .
impression materials used in the study italicized components mean that composition was not provided by manufacturer 
 and a general composition was obtained on anusavice2 ( 2003 ) ten human third molars ( h ) from 20 to 30-year - old donators , and 10 bovine central 
 incisors from 48-month animals , 
 recently extracted , were selected and stored in 0.2% thymol ( biopharma , 
 uberlndia , mg , brazil ) .
all human teeth were collected in accordance with the 
 ethics committee of dental school of the state university of campinas ( # 049/2006 ) .
the 
 teeth were sectioned transversally with a diamond saw ( kg sorensen , barueri , sp , brazil ) 
 and ground with a 600-grit silicon carbide paper under running water in order to produce 
 superficial dentin ( d ) or enamel ( e ) samples with 1.00.1 mm in thickness , 
 checked with the digital caliper .
the samples were positioned over a phosphor plate and the radiographic exposition was 
 performed using an x - ray machine ( ge 1000 , general electric , milwaukee , usa ) , exposing 
 it for 0.2 s at 70 kv and 10 ma , with a source - to - sample distance of 40 cm .
the radiographs were transferred from the 
 phosphor plate to the computer via a digora scanner ( digora optime ; soredex , helsinki , 
 finland ) .
the radiodensity ( in pixels ) of the samples were determined with the resident software 
 provided by the manufacturer .
the digora system has a windows - based software ( digora for 
 windows 2.5 rev , soredex , helsinki , finland ) that is capable to measure density curves 
 of digital radiographies obtained by x - ray impregnation on the image phosphor plate .
the 
 radiodensity of each radiographed material was obtained by clicking with the software 
 cursor right above the digital image .
each digital image had its radiodensity measured 
 immediately after scanning , without any modification in contrast or brightness .
this 
 software shows data concerning the highest and the lowest radiodensity of the sample , 
 and an average value , which was considered to be the sample 's initial radiodensity . 

since each sample was submitted to three exposures , the sample 's final radiodensity was 
 considered to be the mean of those values . for observations of materials filler characteristics ,
materials were examined using 
 scanning electron microscopy ( sem ) after dissolution of the organic matrix .
unmixed 
 elastomer samples were soaked in 100% acetone ( 3 baths with centrifugation ) and followed 
 by 100% chloroform ( 3 baths with centrifugation ) . for alginates ,
thereafter , the specimens were sputter - coated with gold ( med 010 ; balzers union , 
 balzers , liechtenstein ) and observed with a scanning electron microscope ( dsm 940a ; 
 zeiss , oberkoshen , germany ) .
statistical analysis of data was performed using spss 12.0 for windows ( spss inc . , 
 chicago , il , usa ) and biostat 3.0 ( sociedade civil mamirau / mct - cnpq , brazil ) . 

data were subjected to shapiro - wilk test of normality , kruskal - wallis and dunn 's test 
 ( =0.05 ) .
comparisons were made among all impression materials , impression 
 materials versus teeth structures , and materials allocated into groups 
 of type of impression materials ( addition silicon , condensation silicon , alginates and 
 polyether plus polysulfides ) .
the aluminum stepwedge was also compared to each group by 
 kruskal - wallis and dunn 's test .
table 1 and 2 , and figures 2 - 6 show the results of radiodensity measurements together with the 
 statistical analysis .
radiodensity means and standard deviations are presented only to 
 facilitate the understanding . however , since data were not normally distributed , the sum 
 of the ranks as obtained by the nonparametric analysis is also provided . the 
 kruskal - wallis test showed a highly significant difference among the experimental groups 
 ( p<0.001 ) .
the dunn 's test showed that permlastic light ( ps ) and 
 permlastic regular ( ps ) , adsil heavy body ( as ) , speedex ( cs ) , adsil regular body ( as ) , 
 silon 2aps putty ( cs ) , perfil putty ( as ) and oranwash l ( cs ) were the most radiopaque 
 groups .
express light body ( as ) , ezact krom ( alg ) , aquasil light ( as ) , silon 2aps light 
 ( cs ) , perfil light ( as ) , jeltrate chromatic ortho ( alg ) , jeltrate ( alg ) , aquasil 
 extra - light ( as ) , reprosil a putty ( as ) , optosil p comfort ( cs ) , impregum soft medium 
 body ( p ) and reprosil a regular ( as ) were the most radiolucent groups ( table 1 ) . in general ,
heavy - body materials from the 
 same brand presented higher radiodensity values than regular or light - body materials . 

comparisons between tooth structures and impression materials showed that only 
 permlastic light ( ps ) and permlastic regular ( ps ) were similar to human enamel , but 
 there was no similarity with bovine enamel .
human dentin was similar to adsil heavy body 
 ( as ) , and bovine dentin was similar to almost all materials , with except for permlastic 
 light ( ps ) and permlastic regular ( ps ) ( table 
 2 ) .
means and standard deviations ( pixels ) and results of statistical analysis of 
 impression materials radiodensity ( kruskal - wallis and dunn 's method ; 
 p<0.05 ) mean ranks not connected by the same line are statistically different 
 ( p<0.05 ) . comparison of radiodensity ( pixels ) between tooth structures and impression 
 materials by kruskal wallis and dunn 's method ( p<0.05 ) groups marked with an asterisk are statistically similar to the respective 
 tooth structure ( p>0.05 ) comparison of radiodensity of addition silicon materials boxes not 
 connected by the same line are statistically different by kruskal wallis and 
 dunn 's method ( p<0.05 ) comparison between materials and aluminum stepwedge bars not connected by the same line are statistically different by kruskal wallis 
 and dunn 's method ( p<0.05 ) comparisons within each group of impression material did not show heavy - body addition 
 silicon materials presenting significantly higher radiodensity ( figure 2 ) than lower viscosity ones . on the other hand , condensation 
 silicon showed that heavy - body materials of the same brand presented higher degree of 
 radiodensity than other materials ' viscosities ( figure 
 3 ) , except for the comparison between optosil p comfort and xantopren vl plus . 
 because of the smaller number of studied polysulfides and polyether , these materials 
 were compared to each other , showing higher radiodensity for the former ( figure 4 ) . regarding the alginate products , hydrogum 
 showed statistically significant higher radiodensity than the other alginates , but 
 similar to jeltrate plus ( figure 5 ) .
figure 6 presents the comparison between the aluminum 
 stepwedge and experimental groups , showing that permlastic light ( ps ) and permlastic 
 regular ( ps ) presented degree of radiodensity comparable to thicker aluminum stepwedges , 
 and reprosil a putty ( as ) , optosil p comfort ( cs ) , impregum soft medium body ( p ) and 
 reprosil a regular ( as ) comparable to the thinnest aluminum stepwedge .
sem evaluation showed different filler types for each material ( figure 8) , with some types of addition silicon 
 showing remnants of polymer matrix not completely removed from fillers .
diatomaceous 
 earth was found in impregum soft ( figure 8a ) , 
 reprosil a regular ( figure 8e ) and jeltrate ( figure 8f ) .
perfil putty ( figure 8c ) showed bigger fillers than perfil light ( figure 8d ) , and permelastic showed irregular filler 
 particles ( figure 8b ) .
comparison of radiodensity of condensation silicon materials boxes not connected by the same line are statistically different by kruskal wallis 
 and dunn 's method ( p<0.05 ) comparison of radiodensity of polysulfide and polyether materials boxes not connected by the same line are statistically different by kruskal wallis 
 and dunn 's method ( p<0.05 ) comparison of radiodensity of alginate materials boxes not connected by the same line are statistically different by kruskal wallis 
 and dunn 's method ( p<0.05 ) sem images of impression materials fillers .
a , diatomaceous earth fillers of 
 impregum soft ( p ) showing a rounded structure ( white arrow ) ; b , irregular fillers 
 of permlastic regular ( ps ) ; c and d , fillers of perfil putty ( cs ) and perfil light 
 ( cs ) , respectively , showing the increased size of fillers of the heavy - body 
 material ; e , fillers of reprosil a regular ( as ) showing the presence of 
 diatomaceous earth ( white arrow ) and inorganic fillers ( black arrow ) ; f , 
 diatomaceous earth in jeltrate ( alg )
the accuracy and stability of dental impression materials is closely related to the 
 filler volume fraction and type of matrix .
heavy - body materials tend to present higher tear properties and 
 tensile strength than light - body materials .
similarly , it was expected that different compositions would render 
 different degree of radiodensity , for the several studied dental impression materials . 
 generally , impression materials with high filler content show lower strain in 
 compression and lower elastic recovery , due to the relatively lower presence of 
 polymeric matrix .
interestingly , 
 some materials exhibit high elastic recovery and low strain in compression irrespective 
 of the consistence type ( light or heavy body materials ) , which seems to be related to the type of polymer which 
 composes materials matrix .
( 2006 ) , the polymeric fraction of dental 
 materials is not responsible for increasing radiodensity values .
the addition of 
 chemical elements with high atomic numbers , such as lead , zinc , strontium , zirconium , 
 barium and lanthanum , result in more radiopaque materials .
if the filler composition does not 
 provide a radiopaque material , materials with good mechanical properties by high filler 
 content or improved polymers will show themselves with low radiodensity , as observed in 
 the present study .
of all the classes of impression materials , polysulfides were the most radiopaque ones 
 ( figure 7 ) .
apparently , the reason for such a 
 degree of radiodensity is the presence of lead dioxide in the composition , which acts as 
 a catalyst of the setting reaction .
visually , it seems that it would be easy to detect 
 these materials against a background of enamel or dentin .
the same finding might not be 
 true for radiolucent materials , such as polyethers , but further studies are necessary to 
 prove this assumption .
careful attention must be paid for the analysis of table 2 because the large number of studied 
 materials can make different materials became statistically similar to each 
 other .
thus , the comparison 
 within groups of materials seemed more interesting , and table 2 can only illustrate that different materials with different 
 composition show different radiodensity .
impression 
 materials : 1 , impregum soft ( medium body ) ; 2 , permlastic regular ; 3 , permlastic 
 light ; 4 , speedex ; 5 , oranwash l ; 6 , silon 2 aps putty ; 7 , silon 2 aps light ; 8 , 
 xantopren vl plus ; 9 , optosil p comfort ; 10 , perfil putty ; 11 , perfil light ; 12 , 
 adsil heavy body ; 13 , adsil regular body ; 14 , adsil light body ; 15 , aquasil 
 extra - light ; 16 , aquasil ligth ; 17 , virtual extra light body ; 18 , reprosil a 
 regular ; 19 , reprosil a putty ; 20 , express light body ( regular set ) ; 21 , jeltrate 
 plus ; 22 , jeltrate chromatic ortho ; 23 , jeltrate ; 24 , ezact krom ; 25 , hydrogum . 
 aluminum stepwedge : a1 , 1.0 mm ; a2 , 2.0 mm ; a3 , 3.0 mm ; a4 , 4.0 mm ; a5 , 5.0 mm ; 
 a6 , 6.0 mm ; a7 , 7.0 mm ; a8 , 8.0 mm ; a9 , 9.0 mm ; a10 , 10.0 mm ; a11 , 11.0 mm ; a12 , 
 12.0 mm .
tooth structures , h , human ; b , bovine when considering the materials in separate groups , for the polysulfides , it was expected 
 that the regular - body one would have higher radiodensity , but it did not occur , which 
 proves that composition rather than filler content is more important for polysulfides 
 ( figure 4 ) .
the studied polyether was already 
 expected to present a low degree of radiodensity due to the absence of radiopaque 
 fillers in its composition and also due to the reduced amount of filler content 
 ( manufacturer 's information ) .
the effect of filler content was more pronounced in the 
 addition and condensation silicones , although within the same material brand , 
 statistically significant differences where found just for condensation silicones ( figures 2 and 3 ) .
this occurrence means that for addition silicones , besides filler type and 
 volume fraction , other factors are responsible for the observed results .
platinum and 
 palladium seem to offer an important contribution to the observed radiodensity of these 
 materials .
platinum salts are generally used as a catalyst for the setting reaction , and 
 palladium is used for eliminating hydrogen release from the polymeric reaction . on the 
 other hand
, condensation silicon materials showed that heavy - body materials from the 
 same commercial brand presented the highest degree of radiodensity ( figure 3 ) , except for optosil p comfort and xantopren vl plus .
thus , 
 for this group of materials , filler type and volume fraction seem to be the most 
 important factor for radiodensity .
although xantopren vl plus is the light - body material 
 for optosil p comfort , they probably present similar filler content , which could explain 
 these findings .
condensation silicones have tin oxides in their composition , which 
 participates of the setting reaction , and could also be the reason for the observed 
 radiodensity .
alginate impression materials generally have a volumetric filler fraction composed by 
 diatomaceous earth of around 80 - 90% , 
 but this did not result in high radiodensity .
jeltrate , for example , was significantly 
 more radiolucent than hydrogum ( figure 5 ) .
zinc 
 oxide is usually found in these materials , which seem to be related to their 
 radiodensity
. however , the composition informed by manufacturers ( figure 1 ) barely explains these results . as stated before , the 
 presence of chemical elements with high atomic number enables higher radiodensity .
a 
 pilot - study using dispersive x - ray analysis showed the presence of antimony in their 
 composition , which is a metalloid with high atomic number present in higher proportion 
 in hydrogum and jeltrate plus , the most radiopaque alginates in this study .
thus , 
 composition seems to be the most important factor for the radiodensity of alginates .
although this is not an usual recommendation for impression materials , restorative 
 materials need a slightly higher degree of radiopacity than that of enamel in order to enable ideal clinical performance .
enamel and dentin 
 from human and bovine teeth are reported to be similar to each other in 
 radiodensity , but on this 
 study it was rare to find impression materials that were at the same time similar to 
 human and bovine enamel , or dentin ( table 2 ) .
it 
 is likely that alterations in mineral deposition and microstructure may be the reason for these findings . 

some studies have established the standard 
 enamel radiodensity , based on a comparison with aluminum stepwedges , to be equivalent to 2- or 3-mm - thick 
 aluminum . among all
studied materials , only jeltrate ( alg ) , aquasil extra - light ( as ) , 
 reprosil a putty ( as ) , optosil p comfort ( cs ) , impregum soft medium body ( p ) and 
 reprosil a regular ( as ) presented a degree of radiodensity lower than 2 mm aluminum , 
 which would virtually eliminate the possibility of detection against a background of 
 enamel or dentin in a conventional periapical x - ray examination .
however , if we consider 
 results from table 2 , only both permelastic 
 viscosities were similar to human enamel and adsil heavy body to human dentin , which 
 would virtually eliminate all other materials from an easier radiographic detection 
 against hard tooth structures .
interestingly , both reprosil viscosities and impregum 
 soft ( materials with the lowest radiodensity ) have diatomaceous earth in composition 
 ( not stated by reprosil manufacturer ) , which appears not to contribute to high 
 radiodensity levels , similarly to what happened in alginates .
as the use of radiopaque 
 impression materials aims instant and clear material radiographic detection , the higher 
 the radiodensity , the easier the visualization . in this situation
, polysulfides 
 presented the best behavior , being comparable to 10- , 11- and 12-mm - thick aluminum .
table 2 showed that human and bovine tooth 
 structures did not have the same behavior when compared to impression materials .
in 
 spite of the fact that on a previous study human and bovine enamel and dentin were 
 considered similar in radiodensity , 
 it was not possible to establish similarity between human and bovine tooth structures 
 with the same materials ; thus , the use of bovine teeth showed limited results .
the use of radiopaque impression materials seems important for the detection of 
 materials in the oral environment .
( 2002 ) , even a 10-min exposure of human gingival 
 fibroblast cells to various impression materials had a cytotoxic effect .
manufacturers 
 should be stimulated to produce materials with an adequate level of radiodensity , as 
 demonstrated in the present study .
it was found that different impression materials showed different degrees of 
 radiodensity and the reasons were related to their composition .
filler type and volume 
 fraction , and the presence of radiopaque chemical elements are suggested as the main 
 characteristics that render different radiodensity .
limitations of the present study , 
 such as the need for specific research on materials ' composition , must be overcome in 
 order to confirm these assumptions .
only permlastic viscosities had similar radiodensity 
 to that of human enamel and adsil heavy body to human dentin , enabling easier 
 radiographic detection against hard tooth structures .
 in the most recent decades , several developments have been made on impression 
 materials ' composition , but there are very few radiodensity studies in the 
 literature . 
 it is expected that an acceptable degree of radiodensity would enable the 
 detection of small fragments left inside gingival sulcus or root canals.objectivethe aim of this study was to determine the radiodensity of different impression 
 materials , and to compare them to human and bovine enamel and dentinmaterial and methodstwenty - five impression materials , from 5 classes , were studied : addition and 
 condensation silicones , polyether , polysulfides and alginates . 
 five 1-mm - thick 
 samples of each material and tooth structure were produced . 
 each sample was 
 evaluated 3 times ( n=15 ) , being exposed to x - ray over a phosphor plate of digora 
 digital system , and radiodensity was obtained by the software digora for windows 
 2.5 rev 0 . 
 an aluminum stepwedge served as a control . 
 data were subjected to 
 kruskal- wallis and dunn 's method ( =0.05).resultsdifferent materials and respective classes had a different behavior with respect 
 to radiodensity . 
 polysulfides showed high values of radiodensity , comparable to 
 human enamel ( p>0.05 ) , but not to bovine enamel ( p<0.05 ) . 
 human dentin was 
 similar only to a heavybody addition silicon material , but bovine dentin was 
 similar to several materials . 
 generally , heavybody materials showed higher 
 radiodensity than light - body ones ( p<0.05).conclusionimpression materials ' radiodensity are influenced by composition , and almost all 
 of them would present a difficult detection against enamel or dentin background in 
 radiographic examinations . 
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS