advantages of using prefabricated adhesive posts include improved aesthetics and retrievability , as well as the need for only one treatment / visit . due to the lower elastic modulus of fiber posts which are closer to that of dentin , better stress distribution is expected . clinical studies ; however , show that failure can occur with all restorative systems , including post - and - core systems . debonding and retention loss are common failure modes with fiber posts . the retention properties of posts depend on their design , length , surface treatment , fitting accuracy and the resistance of luting agents to dislodging forces generated during function . of the prefabricated posts , the retentive value of parallel posts is higher than that of tapered posts . however , since the root canal anatomy may be neither circular in cross section nor cylindrical in length , shaping the canal using the drill supplied with the post kit frequently sacrifices the remaining dentin , especially in the apical third . therefore , tapered posts are preferred to avoid weakening the teeth that already have lost a part of their hard tissues due to caries or root canal therapy . however , passive tapered posts are less retentive than other prefabricated post types . to improve the retentive ability of passive tapered posts , it is important to maintain both close adaptation of the post to the post space and a homogeneous thin cement layer . however , due to the individual curvature and cross - sectional shape of root canals , differences between post space preparation and the root canal wall have been reported even when the corresponding preparation burs of a post system was used .with sub - optimally adapted posts , cement can fill the excess space between the post and root dentin , allowing excessive and hazardous stress to concentrate within the cement layer during functional loading . the mechanical properties of the luting agent must therefore be considered when determining the localized stress . voids and imperfections along the bonded interface can result in gap formation and enhance microleakage , leading to coronal and/or apical failure . these have revealed that shrinkage stress in the resin cement layer and external loading can cause irregularities , crack formation and post debonding [ 1820 ] , which are related to increased microleakage . however , few studies have directly addressed the microleakage . less microleakage was found in overflared canals restored by individually shaped posts using a polyethylene woven fiber ribbon ( ribbond ) compared to those restored by a preshaped glass fiber or quartz fiber post . however , another study revealed similar microleakage values when a custom ribbond post or glass fiber post was used . to our knowledge , it remains unknown how the close adaptation of a fiber post may affect the microleakage of such systems under fatigue loading . therefore , the aim of the present study was to compare the microleakage of teeth restored with a custom adapted fiber post and those restored with an indirect resin composite , both with and without cyclic loading . the null hypothesis was that there was no difference between the microleakages of a prefabricated fiber post , a custom adapted fiber post with a highly - filled resin composite and a custom casting post . sixty - five extracted single - rooted human teeth were used , none of which displayed cervical lesions , cracks , craze lines or resorption of the immature apices . the teeth were almost straight in the 10-mm coronal portion of the root length . to ensure similarity in teeth dimensions , the buccolingual and mesiodistal dimensions and the root length were measured using a digital caliper ( series 500 caliper , mitutoyo , tokyo , japan ) with an accuracy of 0.01 mm . teeth within 0.5 mm of an average 7-mm buccolingual dimension and 5-mm mesiodistal dimension and within 1 mm of a 15-mm rolength were selected . experimental group teeth were decoronated from the most coronal portion of the cementoenamel junction ( cej ) using a diamond bur in a high - speed hand piece under water spray . each tooth was endodontically treated with a working length 1-mm shorter than the length at which a # 10 k file tip ( mani inc . , kiohara industrial park , tochigi , japan ) passed the apical foramen , using the flat surface of a coronal section as a reference point . canals were prepared to a master file size of 40 using the step - back technique and were flared up at the middle third and coronal third using gate glidden # 2 and # 3 ( maillefer , dentsply , ballaigues , switzerland ) , respectively . the access cavity was filled with a non - eugenole provisional material ( cavit - g , 3 m espe , st paul , mn ) . the apical fourth was sealed externally with a glass ionomer cement ( ionofill , lot 002033 , voco , 3 m espe ) and stored in normal saline for 72 h before post space preparation . gutta - percha was removed with # 2 specified reamers of a dt light post ( rtd , st . specimens were randomly allocated into three experimental groups ; namely , cast post ( cp ) , custom adapted fiber post ( cf ) and prefabricated post ( pf ) groups . a groove ( 1 mm deep , 2 mm long ) was prepared as an antirotation using a diamond bur ( # 856 - 010 , d - z co. , bern , switzerland ) to prevent post rotation during cementation . passively fitting polycarbonate posts ( pin - jet , angelus dental solution , lonrina , brazil ) were adapted to the post space with auto - polymerizing acrylic resin ( pattern resin , lot 0505061 , gc america inc . , the occlusal surface was formed with two cusps of 15. a silicone index ( putty , speedex , coltene / whaledent inc . patterns were cast in a base metal alloy ( verabond , fairfield , ca ) . canals were cleaned with water and dried . a self - etching primer ( ed primer , lot 51169 , kuraray co. ltd . , osaka , japan ) was applied to each canal with a microbrush tip ( microbrush international , waterford , ireland ) and was air - thinned after 60 s. margins were light - polymerized ( coltolux 75 , coltene / whaledent ) for 60 s at 500 mw / cm and a distance of 1.0 mm . a # 2 glass fiber post ( reforpost , angelus dental solution ) was placed in the canals and cut 3 mm above the tooth surface with a diamond disk ( edenta ag dentalprodukte , hauptstrausse , switzerland ) . post spaces were coated with a thin layer of a separating agent ( gc gradia separator , gc corp . , airborne abrasion was used on the post surface with 50-m aluminum oxide particles ( shenzen co , shanghai , china ) under 3 kg / cm of pressure for 10 s at a distance of 5 cm . post surfaces were conditioned with two layers of a saline solution ( monobond s , vivadent , schaan , liechtenstein ) . one layer of a self - etching light - polymerizing bonding agent ( g bond , lot 1002051 , gc corp . ) was applied to the post surfaces , gently air dried and exposed to 500 mw / cm light ( coltolux 75 ) for 20 s at a distance of 1.0 mm . a microhybrid microfilled resin ( mfr ) composite ( shade da2 , lot 0909102 gradia indirect , gc corp . ) was applied to the post surfaces and in the canals using a microbrush ( microbrush international ) . any voids or defects on the post surfaces were corrected by adding composite and light polymerizing for 60 s. the core was fabricated by indirect composite ( da2 gc gradia , gc corp . ) to a height of 5 mm . each layer was initially light polymerized in the gradia step light unit for 10 s. a quartz fiber post ( dt light post , rtd ) was inserted in the prepared post space cut 12 mm from the apical end using a diamond disk ( edenta ag dentalprodukte ) . the negative control group included 10 untreated teeth that were sectioned 4 mm above the most coronal portion of the cej . the teeth were sealed on both ends with cyanoacrylate ( super glue , razi chemicals , terhan , iran ) . in the positive control group ( n= 10 ) , the canals were obturated with gutta percha , but no sealer was used and the access cavity was not temporized . for the experimental groups , a double layer of nail varnish ( my , kahl & co , ghazvin , iran ) was painted on the root surfaces at 1-mm apical to the core interface . for the control groups , all surfaces except ( positive control ) or including ( negative control ) the access cavity were coated . all specimens were immersed for 24 h in 50 cc of a thallium 201 chloride solution ( mds nordion , fleurus , belgium ) with the specific activity of 1 mci . the specimens were washed with a liquid detergent material ( prill , henkel , saveh , iran ) on a swab tip for 60 s. specimens were inserted in a specific tube , with care being taken to position them identically and were placed in a gamma counter device ( kontron gammamatic , neufahrn , germany ) . the radiation was counted with a thallium 201 photon pick of 77 kev and an energy window of 15% for 60 s. to eliminate the radioactive physical contamination , the specimens were then kept in a lead shield container for 12 day . to simulate the oral condition , all specimens were subjected to thermal cycling ( tc ) between 5 and 55 for 60 s each and a dwelling time of 12 s. the periodontal ligament was simulated on the roots of teeth in the cyclic loading ( cl ) test groups using a silicone index . specimens were subjected to 100,000 cycles of 50 n load at a frequency of 1.5 hz to simulate 6 months of service . the microleakage was measured after immersing the specimens in thallium 201 solution , as described above . the net microleakage in experimental groups was calculated by subtracting the mean microleakage value of negative controls  known as surface contamination  from the measured value of each specimen . one - way anova , tukey hsd post - hoc and dunnett t3 tests were used to reveal any difference between the mean microleakage values of the tested groups , either before or after tc / cl . to compare the microleakage values of each group before and after tc / cl , the significance level was set to  = 0.05 and the statistical software spss ver . each tooth was endodontically treated with a working length 1-mm shorter than the length at which a # 10 k file tip ( mani inc . , kiohara industrial park , tochigi , japan ) passed the apical foramen , using the flat surface of a coronal section as a reference point . canals were prepared to a master file size of 40 using the step - back technique and were flared up at the middle third and coronal third using gate glidden # 2 and # 3 ( maillefer , dentsply , ballaigues , switzerland ) , respectively . files were replaced after use in four canals . the access cavity was filled with a non - eugenole provisional material ( cavit - g , 3 m espe , st paul , mn ) . the apical fourth was sealed externally with a glass ionomer cement ( ionofill , lot 002033 , voco , 3 m espe ) and stored in normal saline for 72 h before post space preparation . gutta - percha was removed with # 2 specified reamers of a dt light post ( rtd , st . specimens were randomly allocated into three experimental groups ; namely , cast post ( cp ) , custom adapted fiber post ( cf ) and prefabricated post ( pf ) groups . a groove ( 1 mm deep , 2 mm long ) was prepared as an antirotation using a diamond bur ( # 856 - 010 , d - z co. , bern , switzerland ) to prevent post rotation during cementation . passively fitting polycarbonate posts ( pin - jet , angelus dental solution , lonrina , brazil ) were adapted to the post space with auto - polymerizing acrylic resin ( pattern resin , lot 0505061 , gc america inc . , the occlusal surface was formed with two cusps of 15. a silicone index ( putty , speedex , coltene / whaledent inc . patterns were cast in a base metal alloy ( verabond , fairfield , ca ) . canals were cleaned with water and dried . a self - etching primer ( ed primer , lot 51169 , kuraray co. ltd . , osaka , japan ) was applied to each canal with a microbrush tip ( microbrush international , waterford , ireland ) and was air - thinned after 60 s. margins were light - polymerized ( coltolux 75 , coltene / whaledent ) for 60 s at 500 mw / cm and a distance of 1.0 mm . a # 2 glass fiber post ( reforpost , angelus dental solution ) was placed in the canals and cut 3 mm above the tooth surface with a diamond disk ( edenta ag dentalprodukte , hauptstrausse , switzerland ) . post spaces were coated with a thin layer of a separating agent ( gc gradia separator , gc corp . , airborne abrasion was used on the post surface with 50-m aluminum oxide particles ( shenzen co , shanghai , china ) under 3 kg / cm of pressure for 10 s at a distance of 5 cm . post surfaces were conditioned with two layers of a saline solution ( monobond s , vivadent , schaan , liechtenstein ) . one layer of a self - etching light - polymerizing bonding agent ( g bond , lot 1002051 , gc corp . ) was applied to the post surfaces , gently air dried and exposed to 500 mw / cm light ( coltolux 75 ) for 20 s at a distance of 1.0 mm . a microhybrid microfilled resin ( mfr ) composite ( shade da2 , lot 0909102 gradia indirect , gc corp . ) was applied to the post surfaces and in the canals using a microbrush ( microbrush international ) . any voids or defects on the post surfaces were corrected by adding composite and light polymerizing for 60 s. the core was fabricated by indirect composite ( da2 gc gradia , gc corp . ) to a height of 5 mm . a quartz fiber post ( dt light post , rtd ) was inserted in the prepared post space cut 12 mm from the apical end using a diamond disk ( edenta ag dentalprodukte ) . the negative control group included 10 untreated teeth that were sectioned 4 mm above the most coronal portion of the cej . the teeth were sealed on both ends with cyanoacrylate ( super glue , razi chemicals , terhan , iran ) . in the positive control group ( n= 10 ) , the canals were obturated with gutta percha , but no sealer was used and the access cavity was not temporized . for the experimental groups , a double layer of nail varnish ( my , kahl & co , ghazvin , iran ) was painted on the root surfaces at 1-mm apical to the core interface . for the control groups , all surfaces except ( positive control ) or including ( negative control ) the access cavity were coated . all specimens were immersed for 24 h in 50 cc of a thallium 201 chloride solution ( mds nordion , fleurus , belgium ) with the specific activity of 1 mci . the specimens were washed with a liquid detergent material ( prill , henkel , saveh , iran ) on a swab tip for 60 s. specimens were inserted in a specific tube , with care being taken to position them identically and were placed in a gamma counter device ( kontron gammamatic , neufahrn , germany ) . the radiation was counted with a thallium 201 photon pick of 77 kev and an energy window of 15% for 60 s. to eliminate the radioactive physical contamination , the specimens were then kept in a lead shield container for 12 day . to simulate the oral condition , all specimens were subjected to thermal cycling ( tc ) between 5 and 55 for 60 s each and a dwelling time of 12 s. the periodontal ligament was simulated on the roots of teeth in the cyclic loading ( cl ) test groups using a silicone index . specimens were subjected to 100,000 cycles of 50 n load at a frequency of 1.5 hz to simulate 6 months of service . the microleakage was measured after immersing the specimens in thallium 201 solution , as described above . the net microleakage in experimental groups was calculated by subtracting the mean microleakage value of negative controls  known as surface contamination  from the measured value of each specimen . one - way anova , tukey hsd post - hoc and dunnett t3 tests were used to reveal any difference between the mean microleakage values of the tested groups , either before or after tc / cl . to compare the microleakage values of each group before and after tc / cl the significance level was set to  = 0.05 and the statistical software spss ver . dislodgements that caused loss of contact with the loading head or fracture were considered failures . greatest microleakage occurred in the positive control and pf groups before and after tc / cl . except for the negative control , the lowest microleakage was found in the cp and cf groups before and after tc / cl ( table 1 ) . before tc / cl , anova revealed significant differences in the mean microleakage values among post systems . multiple comparison tests indicated that cp and cf had significantly lower microleakage values than pf and the positive control , but pf and the positive control were not significantly different ( table 2 ) . no difference was found between the microleakage values of each test group before and after tc / cl . the null hypothesis of the present study was rejected , because the custom adapted fiber post and the cast post had significantly lower microleakage values than the prefabricated fiber post . however , tc / cl did not affect the microleakage values in the tested groups . due to the use of different combinations of post systems , luting materials and methodologies , it is not possible to directly compare the results of previous studies to the present results . however , previous studies have generally shown that a lower microleakage value corresponds to improved fiber post fitness . using systems without cores , usumez et al . found significantly less microleakage using a direct custom fiber post with a polyethylene woven fiber post ribbon ( ribbond ) compared to systems using a prefabricated stainless steel ( para post ) or zirconia post . no difference was seen compared to a prefabricated fiber post in contrast to the results of the present study . our custom adaptation procedure improved post accuracy through a process of removing the post from the canal and directly repairing any voids with composite resin . a third generation indirect composite ( gradia ) was used to closely adapt the custom frc post . the mfr composite incorporates ceramic fillers with a mean particle size of less than 1 m , which is twice the content of organic matrix (  66% inorganic fillers and 33% resin matrix ) . the increased filler content improves fracture toughness ( resistance to crack propagation ) and decreases polymerization shrinkage . surfaces bonded to gradia are more compliant ( i.e. , can relieve shrinkage strain )   than those directly bonded to the post surface ( such as in the pf group ) . furthermore , the elastic modulus of gradia ( 50 mpa )   is 400 times lower than that of the dt light post ( 20 gpa ) , permitting the composite resin layer to undergo more plastic deformation and to compensate for the negative effect of stress production under loading and during polymerization . the poor correlation among different microleakage evaluation methods is related to differences in the mechanisms of action . the fluid filtration method assesses the liquid forced through the voids and gaps between dentin , cement , post and/or sealer and the filtration law is applied to any liquid movement . the results of the present study were consistent with those of a study conducted by erkut et al . , in which individually formed fiber posts performed better than pre - shaped glass or quartz fiber posts in term of microleakage measured by dye penetration . a dual polymerizing adhesive cement ( rely x arc ) was used to compensate for the remaining space in the coronal portion of the overflared canals , which appear to be weaker . this finding may have contributed to the higher microleakage values of the two prefabricated post types in their study . thermal cycling and mechanical loading did not influence the microleakage values of posts in the present study . repeatedly applying a low magnitude force to restorative materials in the oral environment can introduce failure over time , by propagating flaws and microcracks along the interface between the post - and - core and tooth structure . it is recommended to simulate the masticatory cyclic loading when investigating the clinical application of a restorative material . application of an insufficient number of loading cycles may help explain our obtained results , because sufficient time is required for the cracks to become macroscopically detectable . mechanical loading protocols that simulate years of clinical service may be considered as  accelerated aging  protocols . in reality , it takes years for a cement to disintegrate due to microleakage subsequent to a gap . in addition , simultaneous tc / cl was not possible because of the design limitations of the machine used . more cycles and simultaneous tc are recommended for future investigations .several attempts were made to standardize the specimens in the present study . the dimensions of included teeth were measured to be similar and standardized rotary instruments were used to finish the root canals and prepare post spaces . however , no crown or ferrule ( a minimum residual 1.52 mm vertical length of coronal dentin ) was considered . the reinforcement effect of these factors could obscure the effect of the post and cement types . in vitro microleakage investigations are increasingly criticized for their limited clinical application . nevertheless , quantified methods ( e.g. , fluid filtration ) are preferred over non - quantified methods ( e.g. , dye penetration ) . the method adopted in the present study , namely gamma counting , may be considered a quantified method . radioisotopes are routinely used in visualizing physiologic body images , and thallium 201 is a cyclotron - generated radionuclide that degrades to mercury ( emitting x - rays ) and thallium ( emitting gamma rays ) . a specific gamma counter or high resolution camera can produce the gamma profile absorbed by a specimen immersed in the appropriate solution for several hours . the solution concentration used in the present study was determined by trial and error , since similar studies were unavailable from the literature . similar to fluid filtration , the gamma counting method is repeatable and non - destructive to the specimens , allowing other tests to be performed simultaneously . the size of the hydrated thallium 201 ion is similar to that of the hydrated potassium ion , which can enter any gap along in a water molecule . thallium tracing may reveal the amount of water contaminating a test specimen and is therefore relevant to the physiological oral condition . in the future , a specified camera could be used to obtain more information on the pattern of microleakage . within the limitations of the present study , we conclude that the microleakages of the custom - adapted fiber post - and - core and cast post - and - core systems were significantly less than that of the prefabricated fiber post system . the microleakage values of the test groups showed no significant difference after short - term tc / cl .