restoration of endodontically treated teeth is still one of the most important problems in dentistry .
the posts are necessary for adequate retention of core , when significant coronal tissues are lost . nowadays ,
fiber posts are increasingly used for this purpose.[14 ] long - term success of a post / core restoration depends on different factors including : the material selected for core buildup , type of post , and quality of the core adhesion to the post . in order to enhance the retention between different structures , surface treatments of posts are recommended .
many studies have been performed on chemical and mechanical treatment procedures for better bonding of fiber posts to core and dental tissues.[79 ] previous studies demonstrated that mechanical treatment techniques such as sandblasting or air abrasion with silica increase bond strength between the fiber post and composite resin substrate .
these treatments may modify the post shape and consequently decrease its fitness within the root canals.[1016 ] chemical treatments are performed to roughen the post surface , leading to greater mechanical retention .
hydrofluoric acid , potassium permanganate , silane and hydrogen peroxide are the chemical solutions used for surface treatments.[1820 ] it has been reported that hydrogen peroxide has the ability to dissolve the resin matrix , breaking epoxy resin bonds and exposing the fibers .
therefore , it can provide stronger adhesion between post surface and resin composite . a few experimental studies
have shown the long - term effect of these treatments on bond strength of post to composite core .
on the other hand , there are several factors in the oral cavity such as functional loading , thermo cycling , oral fluids ( commonly water ) that penetrate within the interfaces and can affect the retention between composite and fiber post . providing the similar conditions of the oral environment in the laboratory may help in achieving actual results .
water as the main element in the oral cavity can interfere with long - term durability of the bond . for this reason , water storage is considered as an in vitro accelerated aging test . due to the lack of definitive information concerning the role of different post treatments in long - term storage ,
the present study was carried out to evaluate the effect of two different surface treatments on the microtensile bond strength of quartz fiber posts to composite core in long - term storage time .
the null hypotheses were that storage duration and post surface treatment had no effect on bond strength of fiber posts to resin core .
forty - eight white quartz fiber posts ( dt light - post radiopaque , rtd , grenoble , france ) with maximum 1.8 mm diameter were selected .
twenty - four posts were immersed in 24% hydrogen peroxide solution for 10 min at room temperature and then rinsed under running water for 2 min and gently air dried .
the remaining posts were sandblasted with 110 m aluminum oxide particles ( rocatector delta , 3 m , espe , seefeld , germany ) for 5 s at 0.28 mpa from a 1 cm distance .
a light cured fifth generation adhesive ( single bond , 3 m espe , ltd , usa ) was used on all the posts according to the manufacturer 's instructions .
core build up was , then , performed using a light cured flowable composite ( lite flow , bisco , inc , shaumburg , il , usa ) .
each post was positioned upright on a glass slab and fixed with a drop of sticky wax .
a cylindrical matrix was made with 10 mm in diameter and the length was equal to the nontapered portion of the post ( 6 mm ) .
it was placed around the post and adjusted so that the post was positioned exactly at the center .
flowable composite was applied on the post in 1 mm thickness increments and each layer was cured separately using a halogen light curing unit ( degulux , degussa dental , hanau , germany ) . to ensure optimal polymerization of the core material
an additional 40 s curing was performed from the bottom of the cylinder before removing the matrix .
hydrogen peroxide treated samples were divided into four groups ( six in each group ) .
group 1 was not stored and groups 2 , 3 , and 4 were stored in deionized water at 37c for 3 , 6 , and 9 months , respectively .
groups 5 , 6 , 7 , and 8 included the sandblasted samples in the same manner .
then , by means of a water - cooled blade of a sectioning machine ( isomet , buehler ltd . , lake bluff , il , usa ) , first two sections parallel to the long axis of the post and then sections perpendicular to the long axis of the post were done , resulting in sections containing the post in the center and composite cores on both ends .
the final sections had 10.1 mm diameter measured by a digital caliper ( mitutoyo cd15 , mitutoyo co. , kawasaki , japan ) .
after the specific storage time , each stick was glued to the two free sliding components of a jig mounted on the microtensile tester ( ez test , shimadzu co. , kyoto , japan ) .
this set - up was designed to apply pure tensile forces to the post - core interface .
the specimens were loaded at a crosshead speed of 0.5 mm / min until failure .
bond strength was expressed in mpa , by dividing the load at failure point ( n ) to the bonding surface area ( mm ) .
failure modes of the samples were assessed using a stereomicroscope ( nikon eclips e600 , tokyo , japan ) at 20 magnification and recorded as cohesive failure ( failure in post or core material ) , adhesive failure ( failure at the interface of post and core material ) , and mixed failure ( adhesive - cohesive failure ) .
two randomly selected fractured sticks of each group were sputter coated with gold - palladium and assessed with scanning electron microscope ( jsm-5310 , jeol , tokyo , japan ) at 500 and 1000 magnifications .
mean and standard deviations of microtensile bond strength of the groups tested are given in table 1 .
two - way anova indicated that the main effect of surface treatment and storage duration were significant ( p=0.0001 ) .
variance analysis demonstrated that significant differences existed among all groups treated with hydrogen peroxide ( group 14 ) . also , all sandblasted groups had significant differences except group 6 with group 7 and group 7 with group 8 .
in addition , paired comparisons of sandblasted groups and hydrogen - peroxide - treated groups showed that there were no significant differences between group 4 with groups 7 and 8 .
means and standard deviations of microtensile bond strength of tested groups the mean microtensile bond strength of groups tested had significant differences with each other except group 4 with 7 and 8 , group 6 with group 7 and group 7 with 8 .
assessment of sem images in the sandblasted groups showed that fibrils were destroyed and some of the fibrils were completely broken . but in groups treated with h2o2 , fibrils were relatively intact and just the epoxy resin between fibrils was eliminated .
voids and disintegrates were observed in stored groups [ figures 14 ] . sandblasted post without storage sandblasted post after 9 months water storage h2o2 treated post without storage h2o2 treated post after 9 months water storage
this study evaluated the effect of different post surface treatment methods and storage duration on microtensile bond strength between quartz fiber post and resin composite core .
since frc posts contain epoxy resins or methyl methacrylate , it seems that water uptake by diffusion can cause some changes in post - core adhesion ; while metallic posts do not undergo such changes .
dt light quartz fiber posts contain 60% quartz fibers embedding in the epoxy resin matrix .
some studies reported that adhesion of these posts was improved after treatment with h2o2 and silane .
use of flowable composites as core materials is recommended in some studies because of ease of manipulation , structural homogeneity , and good adaptation due to its low viscosity .
in addition , its lower filler content has an advantage to perform as a stress absorber that results in higher bond strength.[2427 ] this study demonstrated that water storage decreased bond strength values regardless of the surface treatment method .
this result can be attributed to water sorption potential of composite core and consequently , production of hydrated swollen layers and dimensional changes in composite bulk .
therefore , water sorption can generate stresses in the interface of post and core . on the other hand ,
the presence of hydrophilic monomers in the adhesive layer is one of the possible reasons for results obtained .
vichi revealed that exposure to water forms microcracks in hema containing polymer networks depending on the concentration of hema .
additionally , epoxy resin existing between fibrils can undergo degradation and dislodgement because of its resinous nature , and this may be the reason for decreased bond strength in the stored groups .
the previous studies have reported that effective factors on microtensile strength are the type of composite , water storage , surface treatment on fiber post , aging , and application of adhesive bonding . in this study ,
storage duration and condition , type of composite and type of the adhesive system were similar in all the groups .
the other finding of this study was that bond strength values of hydrogen - peroxide - treated posts were higher than the sandblasted posts .
recent studies , also confirmed that treatment with hydrogen peroxide increases bond strength of glass and quartz fiber posts to resin composite.[1720 ] yenisey found that the surface treatment of fiber posts with hydrogen peroxide had greater shear bond strength in comparison with application of methylene chloride and silane .
reported similar results for improving bond strength of hydrogen - peroxide - treated fiber posts .
equilibrium in absorption of water after 6 months is reason for lack of difference between group 6 with group 7 and group 7 with group 8 in the sandblasted groups .
it means that material saturation and hydrolytic equilibrium in sandblasted groups occurred rapidly in comparison with the hydrogen - peroxide - treated groups .
this might be due to the presence of greater amount of epoxy resin in the posts treated with hydrogen peroxide .
since hydrogen peroxide method is more conservative than sandblasting , so the greater content of resin remains after treatment .
paired comparison of the sandblasted groups indicated that bond strength values was not different between groups 7 and 8 , but in the hydrogen peroxide groups decreasing of bond strength continued from groups 1 to 4 .
one possible explanation is that the amount of water absorption increases until material saturation and hydrolytically stability achieved . finally , there were significant differences between the bond strength values of hydrogen peroxide and sandblasted groups .
after 6 and 9 months , the presence of higher number of voids and discontinuities between fiber and the resin material could be a reason for this result .
sem observations confirmed all the results and revealed that voids can have negative effects on adhesion .
considering the fact that post - core complex is not directly exposed to oral fluids in vivo , and water exposure usually occurs after leakage ; the times assessed could be attributed to longer times in vivo . in this study ,
water storage was assessed without thermal and load cycling . for more similarities to the oral conditions
in addition , in this study , one type of fiber post and adhesive were evaluated , future studies on other types of fiber post and adhesive systems are recommended .
within the limitations of this study , it was concluded that 
 water aging significantly decreased microtensile bond strength regardless of the type of the post surface treatment;duration of water storage was effective in reducing microtensile bond strength in both treatment groups , although bond strength after 9 months storage was not significantly different between sandblasted and h2o2-treated groups . 
 
water aging significantly decreased microtensile bond strength regardless of the type of the post surface treatment ; duration of water storage was effective in reducing microtensile bond strength in both treatment groups , although bond strength after 9 months storage was not significantly different between sandblasted and h2o2-treated groups .
 aim : the aim was to evaluate the influence of water storage on fiber post - resin composite adhesion after different postsurface treatments.materials and methods : forty - two fiber posts were used . 
 half of them were treated by hydrogen - peroxide and the other half were sandblasted . 
 the adhesive ( single bond , 3 m , usa ) was applied on the post . 
 core was built - up using flowable composite ( lite flow , bisco , usa ) . 
 the specimens were divided into eight groups . 
 group 1 was treated with h2o2 . 
 groups 24 were treated with h2o2 but stored for 3 , 6 , and 9 months , respectively . 
 groups 58 were sandblasted and stored for 0 , 3 , 6 , and 9 months . 
 tbs was measured and data analyzed using one - way anova and tukey hsd . 
 the fractured surfaces were evaluated by a stereomicroscope . 
 the morphology of interfaces was assessed under sem . 
 h2o2-treated groups showed higher bond-strength.results:the effect of  surface - treatment method  and  storage - time  was significant ( p<0.0001 ) , but there was no significant difference for their interaction effect ( p=0.05 ) . 
 water aging significantly decreased tbs.conclusions:water aging significantly decreased microtensile bond strength regardless of the type of post surface treatment . 
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
CONCLUSIONS