direct relining of removable dentures with hard or resilient autopolymerizing reline 
 materials can be used as an alternative to the laboratory relining system to improve the 
 retention and stability of the prostheses and the distribution of the masticatory forces 
 transmitted to the underlying tissues .
several studies have demonstrated the adherence of candida spp to both 
 denture base acrylic resins and lining materials .
candida 
 spp has been well - established as a primary microbial factor in the etiology 
 of denture stomatitis .
therefore , 
 the denture fitting - surface can act as a reservoir of candida 
 spp and the use of 
 removable dentures is a predisposing factor for denture related stomatitis .
another concern has been the continuous 
 swallowing or aspiration of microorganisms from denture plaque , which may have significant implications for the general 
 health of the patients and in cases of immunocompromised host or medicated elderly 
 individuals .
therefore , proper routine cleaning of the denture is essential for the 
 prevention and treatment of denture stomatitis .
studies have shown that immersion in 
 peroxide solutions and microwave irradiation are effective methods to inactivate plaque 
 microorganisms from removable dentures .
ideally , a disinfection method should be effective without detrimental effects on the 
 properties of the materials used for the fabrication and the relining of denture bases . 
 among these properties , roughness is important , as rough 
 surfaces of resilient liners and acrylic resins are significantly more prone to 
 microorganisms accumulation and plaque formation than smooth surfaces .
surface roughness 
 provides niches in which microorganisms are protected from the shear forces and oral 
 hygiene measures , thus allowing the entrapped microbial cells time to attach 
 irreversibly to a surface .
studies have evaluated the effect of immersion solutions of the properties of denture 
 base acrylic resins and resilient and hard relining materials , such as color , hardness , water sorption and solubility and porosity . with regard to microwave irradiation ,
the studies have been 
 focused on the effects on hardness , 
 bond strength to denture base resins , flexural strength , 
 and residual monomer . on the other 
 hand , few studies have investigated the influence of disinfection by immersion on the 
 surface roughness of denture base 
 and reline materials .
the information 
 on the effects of microwave disinfection on this property is even more limited .
however , considering that repeated use 
 of a disinfection method may cause alterations on the material 's surface , thus 
 facilitating the adhesion of microorganisms , the effect of disinfection methods on the 
 roughness of reline materials should be further investigated .
( 2008 ) demonstrated that 
 temporary and permanent soft lining materials showed rapid and extensive microbial 
 colonization on the palatal surfaces of dentures carried by volunteers in 
 vivo .
this is particularly important for the temporary soft liners that have been 
 used as essential adjuncts in prosthodontic treatment and management of traumatized oral 
 mucosa .
the aim of this study was to evaluate the surface roughness of one denture base acrylic 
 resin , three hard chairside reline resins and three resilient lining materials .
the 
 effect of disinfection by immersion in sodium perborate solution and microwave 
 irradiation on this property was also evaluated .
the null hypotheses were that the 
 surface roughness of the denture base and the reline materials is similar and that both 
 disinfection methods could be used without adverse effects on this property .
the product names , codes , batch numbers , manufacturers , compositions , powder / liquid 
 proportions , and polymerization / gelation conditions of the materials studied are listed 
 in figure 1 .
thirty specimens of each material 
 were made using a stainless steel mould with a breakaway compartment ( 12 mm12 mm2 mm ) . 

when the specimens were made using the heat - polymerizing acrylic resin lucitone 550 , 
 initially silicone impression material ( zetaplus putty , zhermack , badia polesine , 
 rovigo , italy ) was adapted into the stainless steel mold .
the silicone patterns were 
 then invested by sandwiching them between two glass slides in type iv stone ( troquel 
 quatro , polidental indstria e comrcio ltda , so paulo , sp , brazil ) , using a 
 conventional denture processing flask .
the lucitone 550 acrylic resin was proportioned , 
 packed under pressure , and processed according to the manufacturer 's instructions ( figure 1 ) .
after polymerization , the flasks were 
 bench cooled at room temperature for 30 min and 15 min under running water before the 
 specimens were removed from the flasks .
materials used in this study pema , poly ( ethyl methacrylate ) ; aaem - 2-acetoacetoxy ( ethyl ) methacrylate ; 
 pmma , poly ( methyl methacrylate ) ; ibma , isobutyl methacrylate ; dbp , di - n - butyl 
 phthalate ; 1,6-hdma , 1,6-hexanediol dimethacrylate ; mma , ( methyl methacrylate ) ; 
 edgma , ( ethylene glycol dimethacrylate ) to obtain the specimens of the relining resins tr , nt and uh , the materials were mixed 
 according to the manufacturers ' instructions and inserted into the mold placed on an 
 acetate sheet and a glass slab .
a second acetate sheet and glass slab was placed over 
 the material and light pressure was applied to expel excess material from the mould . 
 when the specimens were made using the resilient liners t ,
s and d specimens of the 
 denture base resin l were made as described .
these specimens were then placed into a 
 stainless steel mould with a breakaway compartment with 12 mm12 mm4 mm placed on the 
 center of a glass plate .
the surfaces were treated with the bonding agents supplied by 
 the manufacturers of each resilient liner and the remaining 2.0 mm was filled with the 
 resilient liners .
( 2008 ) which reported 
 that , to be effective , a thickness of 1.5 to 2 mm of the soft liner is recommended . 

material t was mixed according to the manufacturer 's instructions ( figure 1 ) . for the resilient liner s and d ,
the 
 specimens were made by expressing the cartridge - mixed material directly into the mold . 

an acetate sheet and a second glass slab were placed over the material and light 
 pressure was applied to expel excess material from the mould .
all autopolymerizing 
 specimens were allowed to polymerize undisturbed until their 
 polymerization / gelation .
the edges of the specimens of the denture base l and the hard chairside reline resins 
 tr , nt and uh were carefully finished with 400-grit silicon carbide paper to remove 
 irregularities .
for the resilient liners t , s and d , the flash was trimmed with a razor 
 blade , and the edges were smoothed with 600-grit silicon carbide paper .
the surface roughness ( ra - m ) was analyzed with a surface roughness profilometer 
 ( mitutoyo surftest sj-401 , mitutoyo corporation , tokyo , japan ) with a diamond stylus 
 ( tip radius 5 m ) .
a reading was obtained by the needle passing across 0.8 mm length at 
 1 mm / s to the nearest of 0.01 m .
this procedure was repeated two more times at the same 
 position for a total of three readings . as surface roughness
was measured at four 
 positions , radially across each specimen , a final ra average was calculated and the 
 means of individual specimens were averaged ( baseline reading ) . an orientation jig was 
 fabricated to position the stylus of the profilometer instrument to the same location on 
 the specimen for repeated measurements . for the autopolymerizing reline materials , the roughness measurements were performed 
 within the first hour in dry condition at room temperature ( 232c ) .
these values were 
 used as controls due to the fact that the patients will be wearing the relined denture 
 bases soon after polymerization , without any effect of water sorption and disinfection . 
 for the resin l ,
the specimens were stored in distilled water at 372c for 48 hours 
 before roughness measurements .
this time was used as representative of the time elapsed 
 between relining procedure and denture insertion , when laboratory - processed reline 
 system is performed . during this 
 waiting time
thereafter , the specimens of each material ( n=30 ) were divided into three groups , 
 according to the following experimental conditions : c = specimens were not submitted to the disinfection procedures , but kept in water at 
 372c for 4 weeks ( control ) .
p = specimens were submitted to daily disinfection by immersing into 3.8% sodium 
 perborate solution at 50c for 8 hours at room temperature , and immersed into distilled 
 water for the remainder of the 24 h period at 37c , thus simulating an overnight daily 
 soaking . for each immersion , 

this cycle was repeated up to 4 weeks , so that the period of chemical disinfection would 
 be comparable with that of microwave disinfection and control .
mw = specimens were submitted to microwave disinfection ( 6 min/650 w ) , with the 
 specimens immersed in 200 ml of water during irradiation .
the irradiations were 
 performed three times a week for a total of four weeks .
for all groups , the specimens were 
 individually placed in 500-ml beakers and the volume of liquid ( distilled water or 
 perborate solution ) used was 200 ml .
this minimum volume was calculated by measuring the 
 volume of liquid that would completely cover a maxillary complete denture in a standard 
 denture pot .
the surface roughness of each specimen was measured again at 1 , 3 and 28 days , using the 
 same procedures described above . for each material ,
the differences between the 
 roughness values obtained in each period and the baseline reading was then calculated 
 and used to evaluate the changes in roughness due to the disinfection procedures or 
 immersion in water .
baseline roughness values were analyzed by kruskal - wallis test to 
 determine differences among materials . for each material ,
the changes in roughness 
 ( differences between the roughness values obtained in each period and the baseline 
 reading ) at the different time intervals within each group were analyzed statistically 
 using student 's t - test .
table 1 shows the mean surface roughness values 
 recorded at baseline and standard deviations , and the results from the kruskal - wallis 
 test . at baseline ,
material s exhibited significantly higher surface roughness than the hard 
 chairside reline resins nt and uh ( p<0.001 ) , which were not 
 significantly different from each other ( p=1.00 ) .
no significant 
 differences were found among uh , tr , d and l , and among tr , l , d and s 
 ( p>0.05 ) .
mean baseline roughness ( ra - m ) and standard deviations ( sd ) for all materials 
 evaluated means with identical letter were not significantly different ( kruskal - wallis ; 
 p>.05 ) .
table 2 shows the results from the t - student 
 test for the analysis of the differences between the roughness measurements obtained at 
 three evaluation periods ( 1 , 3 and 28 days ) and the baseline readings , for the three 
 groups analyzed in this study .
no significant changes in roughness were found for the 
 materials tr , l , s and d during the 28 days , regardless of experimental condition 
 evaluated ( p>0.05 ) .
the resilient liner t presented significant 
 decrease in roughness after the first day of immersing in water 
 ( p=0.019 ) .
the decrease in roughness was greater in the 3 
 ( p=0.004 ) and 28 days periods ( p=0.001 ) .
when 
 immersed in sodium perborate solution , material t also showed a decrease in roughness ; 
 however , this decrease was significant in comparison to the baseline reading only after 
 28 days of immersion ( p=0.013 ) .
the hard reline resin nt also showed 
 significant changes in roughness . in the control group , significant increase in 
 roughness was observed at the 3 ( p=0.018 ) and 28 days periods 
 ( p=0.019 ) .
for the disinfected specimens , significant changes in 
 roughness were found after the first day of disinfection by immersing into sodium 
 perborate solution ( p=0.001 ) or microwave irradiation 
 ( p<0.001 ) . a significant increase in roughness of material
nt was 
 also observed at the 3 and 28 days periods ( p<0.001 ) .
the reline 
 resin uh also exhibited significantly increased roughness when immersed in water for 1 , 
 3 and 28 days ( p=0.030 ; p=0.041 ; 
 p=.014 ; respectively ) , and in sodium perborate solution for 3 
 ( p=0.039 ) and 28 days ( p=0.019 ) . when subjected to 
 disinfection by microwave irradiation , the changes in roughness of uh specimens observed 
 at the 1 ( p<0.001 ) and 3-days ( p=0.002 ) were higher 
 than that of the 28-days period ( p=0.015 ) .
figure 2 shows trusoft material after microwave disinfection , and 
 figures 3 and 4 illustrate the scanning electron microscopy ( sem ) of the materials trusoft 
 and sofreliner after microwave disinfection , respectively .
it can be seen from figures 2 and 3 , that microwaving produced severe alterations on the surface of the material 
 t , which impeded roughness measurements after this procedure .
means ( sd ) roughness differences relative to the baseline readings statistical difference between the roughness measurements obtained at three 
 evaluation periods ( 1 , 3 and 28 days ) and the baseline readings ( t - student 
 test ; p < .05 ) .
trusoft material after microwave disinfection scanning electron microscopy ( sem ) micrograph of material trusoft after microwave 
 disinfection scanning electron microscopy ( sem ) micrograph of material sofreliner after 
 microwave disinfection
the adherence 
 of microorganisms on the surface of polymeric materials , such as denture base acrylic 
 resins and hard and resilient liners , is the first step for the colonization and 
 development of an oral infection in denture wearers .
therefore , these materials should present the smoothest surfaces 
 possible in order to prevent biofilm formation and oral mucosa inflammation and 
 facilitate denture cleansing . the results of the present study demonstrated that the hard reline materials presented 
 similar ( tr and uh ) or lower ( nt ) mean initial surface roughness values compared to 
 those of the denture base acrylic resin l. these findings may be related to the fact 
 that the denture base and hard reline materials were processed against glass following 
 the recommendation of radford , et al .
( 1998 ) who stated that control surfaces must be as smooth as 
 possible . with regard the resilient lining materials
, there were no significant 
 differences between the mean values obtained for s and d and those obtained for l. 
 however , t presented the highest initial roughness mean value ( table 1 ) .
the manner 
 how the resilient relining materials evaluated in this study are supplied could help 
 explain the differences observed in their surface roughness . while material t is 
 supplied as separate powder and liquid components that should be mixed , s and d soft 
 liners are automatically mixed and extruded using the dual paste cartridge and dispenser 
 system .
it is possible that air bubbles incorporated to the material during mixing were 
 clustered close to the surface , contributing to the higher roughness of t compared to 
 the other resilient relining materials .
conversely , the use of cartridge and dispenser 
 system probably prevented bubble formation within the s and d specimens and on their 
 surface . the second null hypothesis that both disinfection methods could be used without adverse 
 effects on the surface roughness of the materials
the results showed 
 that the relining resilient materials had different behaviors when subjected to 
 disinfection methods evaluated , which is in agreement with the findings of previous 
 investigations . in the present 
 study ,
the surface roughness of s and d materials remained unaltered regardless of the 
 experimental conditions ( figure 4 ) . on the other 
 hand ,
the soft liner t showed a significant decrease in surface roughness when immersed 
 in water and the differences compared to the initial roughness mean value ( baseline 
 reading ) were more pronounced after longer immersion periods ( table 2 ) . a decrease in surface roughness
was also observed after 
 disinfection with 3.8% sodium perborate , though it was less pronounced and occurred only 
 after 28 days of immersion .
microwaving of t produced severe alterations on the 
 material 's surface , which impeded roughness measurements after this procedure ( figures 2 and 3 ) .
the different behaviors of the resilient relining materials may be partially 
 explained by the differences in their compositions .
t is a plasticized acrylic resin , 
 which , according to its manufacturer , presents a poly(ethylmethacrylate)-based powder 
 component and a liquid component with high concentration of a plasticizing agent ( alkyl 
 phthalate ) and ethanol .
therefore , it is likely that the presence of the plasticizing 
 agent in its composition and the viscoelastic behavior of plasticized resins allowed the material to flow over time 
 when immersed in water .
it may be considered that this flow permitted the filling of 
 porosities , irregularities and possible depressions formed on acrylic surface , resulting 
 in lower roughness mean values . in 
 addition
, two phenomena take place when plasticized resins are immersed in water : loss 
 of plasticizing agent and water sorption . if the sorption of 
 water by the relining material t was greater than the loss of plasticizing agent , a 
 volume increase might have occurred , making the surface smoother . when material t was immersed in the 
 sodium perborate solution , surface roughness also decreased , but more slowly ( 28 days ; 
 table 2 ) .
it is likely that the higher ionic 
 concentration in the sodium perborate solution compared to water resulted in greater 
 release of soluble components . 

however , the water sorption and solubility of this material when subjected to the same 
 conditions evaluated in the present study should be further investigated to confirm 
 these hypotheses .
the severe alterations observed on the surface of t specimens when 
 disinfected by microwave irradiation may be related to the temperature . during 
 microwaving ,
the water in which the materials are immersed reached the boiling 
 temperature after approximately 1 minute and 30 seconds and remained at this temperature 
 up to the end of the microwaving cycle .
it is possible that the heating of t during 
 microwave disinfection has favored the diffusion and release of soluble components and 
 accelerated the aging process . 

conversely , in silicone - based relining materials , such as s and d ( polyorganosiloxanes ) , 
 the polymer is an elastomer and does not need external plasticizing agents .
furthermore , the polymer chains in s 
 and d are formed by addition reaction and thus no byproduct is formed .
it has been demonstrated that 
 silicone - based resilient materials polymerized by addition reaction remain stable during 
 water storage for long periods . 

therefore , the lack of significant effects of the disinfection methods on the surface 
 roughness of s and d may be partially attributed to the favorable characteristics of 
 water sorption and solubility of these resilient relining materials .
( 2003 ) have also found 
 that , in general , silicone - based resilient materials were more stable regarding surface 
 roughness and color change than the plasticized resins . concerning the hard reline materials ,
the most significant alterations were observed for 
 nt . among the hard relining materials evaluated in this study ,
nt has the highest 
 liquid / powder mixing ratio , and this might have resulted in the presence of a larger 
 number of residual monomer molecules in the polymerized resin .
in addition , nt also presents a plasticizing agent 
 ( di - n - butyl phthalate ) in its composition .
the release of these residual monomer molecules and the 
 plasticizing agent might have contributed to alter the surface characteristics of the 
 material , increasing its surface roughness .
this release might have been facilitated by 
 the ionic concentration of the sodium perborate solution and by the temperature of the water during microwave 
 disinfection , which could 
 partially explain the more significant alterations observed after use of both 
 disinfection methods compared to the control ( immersion water ) .
the results also showed that the surface roughness of the denture base acrylic resin l 
 and the hard reline material tr was not affected by their immersion in water and neither 
 by the disinfection methods evaluated in this study .
( 2004 ) , 
 and may be related to the type of polymerization of the materials .
heat - polymerized 
 materials , such as l , present a higher monomer - to - polymer conversion rate and lower 
 residual monomer content . although the hard reline tr material is 
 an autopolymerized resin , it contains the monomer 2-acetoacetoxyethyl methacrylate , 
 which has been used in experimental materials to increase the polymerization rate due to 
 its molecular structure and higher reactivity .
this monomer presents a longer lateral chain and several 
 reactive centers , which provide a more complete polymerization .
in addition , l and tr 
 contain crosslinking agents in their compositions ( ethylene glycol dimethacrylate and 
 1,9-nonanediol dimethacrylate , respectively ) , which may have contributed to the 
 formation of more dense and stable polymer structures .
this may have 
 contributed to the absence of significant effect on the surface roughness of these 
 materials after immersion in water or disinfection .
the alterations observed in the surface roughness of the reline resin uh were not 
 expected because this material also has a high concentration of the crosslinking agent 
 1,6-hexanediol dimethacrylate . due to the greater distance between the methacrylate 
 groups , this crosslinking agent also presents a more reactive second group , thus favoring the monomer - to - polymer conversion .
nevertheless , it 
 has been demonstrated that uh material showed significantly higher residual monomer 
 content and release than a reline resin with similar composition ( tokuso rebase 
 fast ) .
the goal of subjecting dentures to disinfection by immersion in a sodium perborate 
 solution or microwave irradiation is controlling the biofilm formed on the acrylic 
 surface .
nevertheless , if the repeated use of a disinfection method causes significant 
 alterations on the material 's surface , this goal is not achieved because the increase in 
 the surface roughness may favor the adhesion of microorganisms .
it is important to 
 emphasize , however , that the influence of the changes in surface roughness observed in 
 the present study on the adherence of microorganisms to the reline materials was not 
 investigated .
in addition , surface roughness is not the only factor involved in the 
 adhesion of microorganisms to polymer - based materials .
the presence of salivary pellicle and the surface free 
 energy have been also reported to influence the adhesion of microorganisms .
others factors such as wettability , 
 hydrophobicity and electrostatic interactions of materials used in prosthodontics may 
 also influence the microbial retention .
these are limitations of the present study and should be considered 
 in further investigations . despite these limitations , the findings presented here 
 demonstrated that immersion in sodium perborate and microwave irradiation may not be 
 seen as a general recommendation for denture disinfection , since it may increase the 
 surface roughness of some materials used for relining dentures , as observed 
 previously .
this may help 
 dental practitioners instructing their patients regarding the most effective methods for 
 biofilm control , according to the type of relining material used in their dentures .
within the limitations of this study the following conclusions were drawn : in all conditions evaluated , the resilient relining material t presented the highest 
 surface roughness mean values .
there were no significant differences in the surface roughness of the denture base resin 
 l and the relining materials tr , s and d under the conditions evaluated .
t presented a significant decrease in surface roughness after immersion in water or in a 
 3.8% sodium perborate solution ; microwave disinfection caused severe alterations on the 
 surface of this material .
nt and uh reline resins showed significant increase of surface roughness after immersion 
 in water or disinfection , and more pronounced effects were observed for new truliner 
 after microwave disinfection .
 objectivethe effect of disinfection by immersion in sodium perborate solution and microwave 
 irradiation on surface roughness of one denture base resin ( lucitone 550 -l ) , 3 
 hard chairside reline resins ( tokuyama rebase ii - tr , new truliner - nt , ufi gel 
 hard - uh ) and 3 resilient reline materials ( trusoft - t ; sofreliner - s , dentusil - d ) 
 was evaluated . 
 material and methodsthirty specimens of each material were made and divided into 3 groups : control - 
 not disinfected ; p - daily disinfection by immersing in sodium perborate solution 
 ( 3.8% ) ; mw - microwave disinfection ( 6 min/650 w ) . 
 roughness measurements were 
 made after polymerization ( baseline ) and after 1 , 3 and 28 days . 
 roughness 
 differences relative to the baseline readings were analyzed by student 's t - test 
 ( p=0.05 ) . 
 resultsat baseline , trusoft showed the highest ( p<0.001 ) mean surface roughness ( 3.54 
 m ) , and its surface roughness was significantly reduced after 28 days of 
 disinfection by immersion in sodium perborate ( p=0.013 ) . 
 roughness measurements of 
 material trusoft were not performed after microwave disinfection due to the severe 
 alterations on the surface . in the 3 groups evaluated , changes in roughness were 
 significant for materials ufi gel hard ( from 0.11 to 0.26 m ; p0.041 ) and new 
 truliner ( 0.19 to 0.76 m ; p0.019 ) . 
 the roughness of materials lucitone 550 ( 0.37 
 m ) , tokuyama rebase ii ( 0.37 m ) , sofreliner ( 0.49 m ) and dentusil ( 0.38 m ) 
 remained unaffected ( p>0.05 ) . 
 conclusionsthe roughness of the hard reline materials ufi gel hard and new truliner was 
 adversely affected by microwave disinfection , immersion in water or in sodium 
 perborate . 
 microwave disinfection caused severe alterations on the surface of the 
 resilient liner trusoft . 
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
CONCLUSION