the oral candidiasis known as denture stomatitis is related to the use of removable 
 dentures and is considered the most common oral lesion observed ( 65% ) in patients wearing removable dentures . 

local factors associated with the denture are also related to 
 this pathology , such as : presence of biofilm , local trauma caused by 
 dentures12 , xerostomia , continuous 
 use of the dentures and alteration in salivary ph .
different treatments for denture stomatitis are available and may include topical 
 antifungal and systemic therapy , care with oral hygiene , denture cleaning and 
 disinfection procedures , replacement 
 of old dentures , elimination of anatomic irregularities , re - establishment of atraumatic 
 occlusion , and nutritional restitution .
furthermore , in order to protect and preserve the integrity of the 
 mucosal epithelium , patients should sleep without the dentures .
the choice of a treatment or association of more than 
 one treatment is an aspect to be individually considered .
re - infection of the treated 
 oral mucosa may occur in up to two weeks post - treatment , and is attributed to the 
 survival of candida spp .
therefore , it is crucial to adopt methods that reduce or preferably 
 eliminate the microorganisms from denture surfaces .  
in addition , resilient materials have been routinely used with the purpose of recovering 
 tissues that are in contact with the denture base .
these materials partially absorb chewing load on the denture 
 during function , thus reducing the energy transmitted to the associated paraprosthetic 
 tissues . however , these 
 materials are easily degradable and susceptible to microbial colonization , which may cause different degrees of 
 denture stomatitis . to prolong the clinical longevity of resilient materials and reduce plaque accumulation , 
 incorporation of antimicrobial agents into these materials
this combination may be a logical 
 therapy in the treatment of denture stomatitis because of several factors : 1 .
reducing 
 the trauma caused by the internal surface of removable dentures ; 2 . eliminating contact 
 of the contaminated surface with the oral tissues and consequently , interrupting the 
 cycle of re - infection , and 3 .
action of antimicrobial agents incorporated into the 
 material on the infected tissues . in 
 this context ,
denture stomatitis may be treated before fabricating new dentures , in a 
 relatively short period .
the reason is attributed to their gradual degradation and 
 hardening , so it should not take longer than two weeks , which is a period similar to the 
 one required for the treatment with conventional topical antifungal drugs .   the incorporation of antimicrobial agents into resilient materials has shown to be 
 effective and feasible both in in vitro and in vivo 
 studies . despite these 
 therapeutic advantages , the incorporation of drugs into polymeric materials , including 
 tissue conditioners and resilient liners , may affect their properties .
for the resilient 
 liner to adequately perform its function of recovering the tissues injured by trauma , it 
 should remain bonded to the acrylic base of the removable denture5 .
peeling of the 
 resilient material from the denture base has been reported as the cause of clinical 
 failure and the bond between the resilient materials and the denture base acrylic resins 
 has been the object of previous investigations .
thus , the aim of this 
 study was to evaluate the effect of the addition of antimicrobial agents ( nystatin , 
 miconazole , ketoconazole , and chlorhexidine diacetate ) to a resilient liner on its peel 
 bond strength to a denture base acrylic resin .
the hypothesis investigated in this study 
 was that the addition of antimicrobial agents to a resilient liner would result in 
 changes in the peel bond strength to a denture base acrylic resin .
the acrylic materials , manufacturers , batch numbers , compositions , powder / liquid ratios , 
 and polymerization conditions selected for this study are listed in figure 1 . the selected antimicrobial agents were 
 nystatin , miconazole , ketoconazole ( alonatu farmcia de manipulao 
 e cosmticos / farmcia dermatus , macei , al , brazil - req . 
 119704 - 1 ) , and 98% chlorhexidine diacetate ( acros organics , morris plains , nj , usa ) .   materials selected for this study specimens ( n=9 ) measuring 75x10x3 
 mm of heat - curing acrylic resin qc 20 ( dentsply ind .
for this purpose , stainless 
 steel matrixes measuring 75x10x3 mm were molded using laboratory silicone ( zetalabor , 
 rovigo , veneto , italy ) between two glass plates .
the mold / matrix set was invested in 
 conventional metal dental flasks in type iii dental stone ( herodent , vigodent , rio de 
 janeiro , rj , brazil ) .
the dental flasks were closed and remained under pressure ( 500 
 kgf ) in a hydraulic press during stone setting time . after this period , the dental 
 flasks were opened and the stainless steel matrixes were removed .  
qc 20 was proportioned , mixed according to the manufacturer 's instructions ( figure 1 ) , and was inserted into the silicone 
 matrix mold .
the dental flask was closed and kept under pressure at room temperature 
 ( 232c ) for 30 min .
after this period , the test specimens were 
 submitted to the polymerization cycle " b " recommended by resin manufacturer ( figure 1 ) .
when the polymerization cycle ended , 
 the dental flasks were bench cooled for 30 min and then under running water for 15 
 min .
the specimens were removed from the molds and stored in distilled water at 
 37c for 48 h.   after this period , specimens were submitted to surface preparation to receive the 
 modified resilient liner .
one of the specimen surfaces was abraded automatically in a 
 polishing machine using # 600 silica carbide abrasive paper ( norton abrasivos , 
 so paulo , sp , brazil ) .
the abraded surface was cleaned with detergent for 20 
 s , washed under running water , and dried .
the specimen was then placed in a hollow 
 stainless steel mold with internal measurements of 75x10x6 mm . the specimen area ( 650 
 mm ) to not be bonded to the resilient material was covered with a 
 polyester strip .
the antimicrobial powders in each experimental group ( figure 2 ) were manually mixed with resilient lining powder with a 
 spatula , until a homogenous mixture was obtained .
the resilient 
 lining liquid was added to this mixture and the material was mixed in accordance to 
 the manufacturer 's instructions ( figure 1 ) . 

the modified material was inserted into the hollow mold containing the test specimen 
 of the heat - curing acrylic resin prepared for the relining procedure .
this set was 
 covered with glass slide and kept under finger pressure during the resilient liner 
 polymerization time recommended by the manufacturer ( figure 1 ) .
the excesses of the modified resilient liner were eliminated 
 and the specimen was removed from the mold .
the relined specimens were then stored in 
 distilled water at 37c for 24 h prior to the peel test .  
drug dosages incorporated into the resilient liner powder in all experimental 
 groups a universal testing machine ( versat 2000 , panambra ind . tech .
sa , so paulo , 
 sp , brazil ) was used to perform the peeling bond strength test of the relined test 
 specimens at an angle of 180. a portion of modified resilient material not 
 bonded to the resin base ( 65 mm ) was folded upwards and fixed onto the top hook of 
 the equipment at 20 mm from the adhesive bond area of the test specimen .
the other 
 un - relined portion of the heat - curing acrylic resin was fixed onto the bottom hook of 
 the equipment at the same distance from the adhesive bond area . 

each test specimen was submitted to tension to promote peeling of the modified 
 resilient liner from the heat - curing acrylic resin base at a speed of 10 mm / min until 
 failure occurred .  
bond failures were visually observed and classified into three categories : adhesive , 
 when peeling occurred between the modified resilient liner and the denture base 
 acrylic resin ; cohesive , when there was tearing ( rupture of the resilient liner 
 within the area bonded to the denture base ) or snapping ( resilient material had 
 stretched and then ruptured away from the bonded area ) within the modified resilient 
 liner ; and mixed , when regions with two types of failure were observed on the surface 
 of the denture base material .  
the results of rupture force were initially obtained in n and transformed into 
 peeling bond strength in mpa and then submitted to one - way anova at a significant 
 level of 5% .
specimens ( n=9 ) measuring 75x10x3 
 mm of heat - curing acrylic resin qc 20 ( dentsply ind
for this purpose , stainless 
 steel matrixes measuring 75x10x3 mm were molded using laboratory silicone ( zetalabor , 
 rovigo , veneto , italy ) between two glass plates .
the mold / matrix set was invested in 
 conventional metal dental flasks in type iii dental stone ( herodent , vigodent , rio de 
 janeiro , rj , brazil ) .
the dental flasks were closed and remained under pressure ( 500 
 kgf ) in a hydraulic press during stone setting time . after this period , the dental 
 flasks were opened and the stainless steel matrixes were removed .  
qc 20 was proportioned , mixed according to the manufacturer 's instructions ( figure 1 ) , and was inserted into the silicone 
 matrix mold .
the dental flask was closed and kept under pressure at room temperature 
 ( 232c ) for 30 min .
after this period , the test specimens were 
 submitted to the polymerization cycle " b " recommended by resin manufacturer ( figure 1 ) .
when the polymerization cycle ended , 
 the dental flasks were bench cooled for 30 min and then under running water for 15 
 min .
the specimens were removed from the molds and stored in distilled water at 
 37c for 48 h.   after this period , specimens were submitted to surface preparation to receive the 
 modified resilient liner .
one of the specimen surfaces was abraded automatically in a 
 polishing machine using # 600 silica carbide abrasive paper ( norton abrasivos , 
 so paulo , sp , brazil ) .
the abraded surface was cleaned with detergent for 20 
 s , washed under running water , and dried .
the specimen was then placed in a hollow 
 stainless steel mold with internal measurements of 75x10x6 mm . the specimen area ( 650 
 mm ) to not be bonded to the resilient material was covered with a 
 polyester strip .
the antimicrobial powders in each experimental group ( figure 2 ) were manually mixed with resilient lining powder with a 
 spatula , until a homogenous mixture was obtained .
the resilient 
 lining liquid was added to this mixture and the material was mixed in accordance to 
 the manufacturer 's instructions ( figure 1 ) . 

the modified material was inserted into the hollow mold containing the test specimen 
 of the heat - curing acrylic resin prepared for the relining procedure .
this set was 
 covered with glass slide and kept under finger pressure during the resilient liner 
 polymerization time recommended by the manufacturer ( figure 1 ) .
the excesses of the modified resilient liner were eliminated 
 and the specimen was removed from the mold .
the relined specimens were then stored in 
 distilled water at 37c for 24 h prior to the peel test .  
sa , so paulo , 
 sp , brazil ) was used to perform the peeling bond strength test of the relined test 
 specimens at an angle of 180. a portion of modified resilient material not 
 bonded to the resin base ( 65 mm ) was folded upwards and fixed onto the top hook of 
 the equipment at 20 mm from the adhesive bond area of the test specimen .
the other 
 un - relined portion of the heat - curing acrylic resin was fixed onto the bottom hook of 
 the equipment at the same distance from the adhesive bond area . 

each test specimen was submitted to tension to promote peeling of the modified 
 resilient liner from the heat - curing acrylic resin base at a speed of 10 mm / min until 
 failure occurred .  
bond failures were visually observed and classified into three categories : adhesive , 
 when peeling occurred between the modified resilient liner and the denture base 
 acrylic resin ; cohesive , when there was tearing ( rupture of the resilient liner 
 within the area bonded to the denture base ) or snapping ( resilient material had 
 stretched and then ruptured away from the bonded area ) within the modified resilient 
 liner ; and mixed , when regions with two types of failure were observed on the surface 
 of the denture base material .  
the results of rupture force were initially obtained in n and transformed into 
 peeling bond strength in mpa and then submitted to one - way anova at a significant 
 level of 5% .
therefore , the incorporation of antimicrobial agents in the concentrations 
 assessed did not affect the peeling bond strength between the resilient liner and the 
 denture base resin after 24 h of immersion in distilled water .  
peel strength ( mpa ) at 24 h there was no statistical difference ( p>0.05 ) among the experimental 
 groups the failure modes obtained after performing the tests are shown in table 1 .
the majority of bond failures were 
 cohesive ( tearing and/or snapping ) within the resilient liner .
for the experimental 
 groups g2 ( nystatin at 500,000 u ) , g5 ( miconazole at 250 mg ) , and g8 ( 5% chlorhexidine 
 diacetate ) , a mixture of tearing and snapping was observed .
peeling away from the 
 denture base was only observed for groups g6 ( ketoconazole at 100 mg ) and g9 ( 10% 
 chlorhexidine diacetate ) . for the other groups ,
the hypothesis investigated in this study that " the addition of antimicrobial agents to 
 the resilient liner would result in alterations in the peeling bond strength to denture 
 base resin " was rejected because there was no difference between the experimental groups 
 assessed in comparison with the control group without the addition of drugs .   during clinical use ,
the resilient materials are highly subjected to degradation and 
 susceptible to the colonization by microorganisms . if these materials are not regularly 
 replaced , they may act as microorganism reservoirs , causing systemic 
 complications .
an example of 
 this is the presence in the oral cavity of staphylococcus aureus , a 
 microorganism responsible for respiratory infections .
the combination between resilient materials and antimicrobial 
 agents seems to be a logical therapeutic modality for denture stomatitis .
this method 
 results in a reduction of the trauma caused by the old denture and tissue reconditioning 
 associated with antimicrobial therapy ; important etiologic factors in triggering 
 infection by candida spp . are simultaneously eliminated .
in addition , 
 this method favors a relined denture that can more easily be kept clean by the 
 patient .  
several drugs have shown reduced water solubility , so maximum dose is required to have 
 the effectiveness required for a certain medication . among the antimicrobial agents assessed ,
chlorhexidine shows 
 higher solubility in water , followed by nystatin , miconazole , and ketoconazole . although these medications are soluble 
 in water , they are insoluble in monomers and plasticizers.thus , they could not interfere with the polymerization or 
 plasticization process of these 
 materials
. however , their physical presence within the polymer matrix could interrupt 
 the structure of the polymerized materials .
resilient materials containing nystatin showed increased water 
 sorption , and for these materials , this resulted in breaking their morphological 
 structure .
according to addy 
 and handley ( 1981 ) , change in 
 material properties may be consistent with the incorporation pattern of the medication 
 into the polymer matrix .
a previous study assessed the incorporation pattern of antimicrobial agents into a 
 tissue conditioner with the same concentrations to those investigated in this study , by 
 scanning electronic microscopy ( sem ) and energy dispersive spectroscopy x - ray ( eds ) .
the 
 test specimens containing nystatin and miconazole exhibited particles with irregular 
 shapes and sizes distributed uniformly within the tissue conditioner matrix while 
 specimens with chlorhexidine exhibited more irregular particles distributed randomly 
 within the material . however , these alterations would not prevent the incorporation of 
 drugs for release in the oral cavity if they were added to materials to reline already 
 existent dentures , without 
 necessarily reducing their strength .  
although some soft materials are submitted only to compression and shear , tensile 
 strength is used to measure the quality of the material .
the ability of the material to 
 resist tearing is of practical importance . in clinical use , including the cleaning and 
 disinfection procedures , the soft materials are submitted to conditions that start the 
 tearing process .
. clinical failure of these materials is frequently attributed to the 
 rupture of this bond , and the measurements of this bond are clinically relevant .
reduced 
 bond between the soft liner and the denture base resin effectively negates any other 
 property considered adequate for this material . in the peel bond strength test
, the stress is confined to a line 
 restricted to the end of the bond , and is considered the most clinically representative 
 of the failure modes .
this is the 
 only method in which the failure proceeds at controlled speed and it is a direct measure 
 of peeling , while it also represents the elastic deformation of the material .
the peeling test simulates the lining 
 procedure more precisely , with a uniform and constant distribution of force throughout 
 the bond area .  
the results of this study demonstrated that the addition of antimicrobial agents in all 
 the assessed concentrations did not affect the peeling bond strength of the resilient 
 liner to denture base resin .
however , the bond strength values were considered low , 
 since they were approximately 10 times lower than the acceptable value for the clinical 
 use of resilient liners ( 0.44 mpa ) .   while the methodology in this study was performed , some modifications were made , such as 
 the reduction in bond area and surface roughness of the denture base , to ensure that the 
 methodology evaluated the bonding between materials rather than the cohesive strength of 
 the liner material .
if the bond failures observed in this study were predominantly 
 cohesive within the liner material , the peeling bond strength would not be 
 measured .
the failure mode of 
 the cohesive type provides information related to the material itself and not to the 
 bond between materials .
( 1995 ) suggested the term 
 " strength failure " instead of " bond failure " when cohesive failures occur .
predominant 
 cohesive failures , such as those that occurred in this study , indicate poor resistance 
 to tearing of the resilient material .
however , mixed and adhesive failures were observed 
 in some samples , indicating that the cohesive strength values of the resilient liner and 
 bond strength values to base resin were similar .  
a previous study observed that a 
 tissue conditioner ( duraconditioner , reliance manufacturing nystatin showed cohesive 
 strength values similar to those of the control group .
these values were close , if not 
 similar , to the ones obtained in this study .
therefore , the cohesive strength of the 
 resilient material tested in this study is equivalent to its bond strength to the 
 denture base material .
thus , the material will snap or tear at the bond interface at 
 forces lower than those necessary to cause bond failures .  
one of the limitations of this study was that only one brand of the resilient liner was 
 assessed .
moreover , the peeling bond strength could have been assessed after other 
 storage periods .
this assessment is also important to observe a possible reduction in 
 bond strength of the modified liner to the denture base material , since it has been 
 reported that plasticizers and alcohols are released from resilient materials after 
 periods of storage in water and this release is responsible for the decrease in the bond 
 strength values between the materials .
within the limitations of this in vitro study , it can be concluded that 
 it is possible to incorporate any of the antimicrobial agents assessed in the selected 
 concentrations into a resilient liner without changing the bond strength of this 
 material to denture base resin .
a clinical study is still needed to determine the 
 therapeutic validity of this alternative treatment modality .
 in order to prolong the clinical longevity of resilient denture relining materials 
 and reduce plaque accumulation , incorporation of antimicrobial agents into these 
 materials has been proposed . however , this addition may affect their properties.objectivethis study evaluated the effect of the addition of antimicrobial agents into one 
 soft liner ( soft confort , dencril ) on its peel bond strength to one denture base 
 ( qc 20 , dentsply ) . 
 material and methodsacrylic specimens ( n=9 ) were made ( 75x10x3 mm ) and stored in distilled water at 
 37c for 48 h. the drug powder concentrations ( nystatin 500,000u - g2 ; 
 nystatin 1,000,000u - g3 ; miconazole 125 mg - g4 ; miconazole 250 mg - g5 ; 
 ketoconazole 100 mg - g6 ; ketoconazole 200 mg - g7 ; chlorhexidine diacetate 5% - 
 g8 ; and 10% chlorhexidine diacetate - g9 ) were blended with the soft liner powder 
 before the addition of the soft liner liquid . 
 a group ( g1 ) without any drug 
 incorporation was used as control . 
 specimens ( n=9 ) ( 75x10x6 mm ) were plasticized 
 according to the manufacturers ' instructions and stored in distilled water at 
 37c for 24 h. relined specimens were then submitted to a 180-degree peel 
 test at a crosshead speed of 10 mm / min . 
 data ( mpa ) were analyzed by analysis of 
 variance ( =0.05 ) and the failure modes were visually classified . 
 resultsno significant difference was found among experimental groups ( p=0.148 ) . 
 cohesive 
 failure located within the resilient material was predominantly observed in all 
 tested groups . 
 conclusionspeel bond strength between the denture base and the modified soft liner was not 
 affected by the addition of antimicrobial agents . 
INTRODUCTION
MATERIAL AND METHODS
Specimen preparation
Peel test
RESULTS
DISCUSSION
CONCLUSIONS