after the development of fiber - reinforced composite posts , adhesive resin cement systems 
 are a good option for restoring endodontically treated teeth . however , the development 
 of adhesive materials that form a continuous , strong and durable interface with tooth 
 root is still a challenge .
a complete filling of the root canal is expected to form a 
 monoblock , a solid mass without gaps that seals the root perfectly and remains stable in 
 the oral environment . according to 
 this concept , the monoblock is strong enough to support mastication and dissipates 
 resistance capacity throughout the remaining tooth structure .
this is theoretical , however , and currently available 
 adhesives do not provide a hermetic , leak proof seal .
conventional dual - cure resin cements are indicated for luting procedures because they 
 have low solubility , high mechanical quality and adhesive properties .
the characteristics of the dual - cure 
 cements are independent and complementary to those of light - activated chemical cements , 
 which makes them ideal for deep cavities such as the root canal .
the use of dual - cure cements requires pretreatment of the tooth 
 root with an adhesive system . until a few years ago
, most adhesive systems available 
 were applied in a 3-step procedure , which were later combined into 2 steps and more 
 recently , into a single self - etching application step .
however , acid resinous monomers 
 present in the surface layer of the 2-step and self - etching systems can weaken the 
 adhesive binding to root dentin .
the permeability of simplified 
 adhesives therefore results in water movement , even in root - treated dentin .
recently developed self - adhesive resin cements do not require pretreatment of the 
 dentin . because these cements do not use an adhesive system , they drastically reduce the 
 number of application steps , shortening clinical treatment time and decreasing technique 
 sensitivity since it minimizes procedural errors throughout the treatment 
 phases .
self - adhesive cements contain 
 multifunctional phosphoric acid methacrylates that are reputed to react with the 
 hydroxyapatite of hard tooth tissue .
however , some studies suggest that self - adhesive 
 cements have limited capacity to diffuse and decalcify the underlying dentin 
 effectively .
some reasons for this limitation are : 1 ) high 
 viscosity , which may rapidly increase after acid - base reactions , and 2 ) a neutralization 
 effect that may occur during setting , resulting in the release of water and of alkaline 
 filler that raises ph level and buffering components of the smear layer .
these materials are relatively new and detailed information on 
 their composition and adhesive properties is limited .
this is commonly caused 
 by the inefficiency of the adhesive system or of the self - adhesive resin cements and 
 occurs at distinct levels of the root canal .
the apical portion of the root is 
 particularly vulnerable to debonding because in this area it is difficult to eliminate 
 the smear layer or remaining sealer / gutta - percha , control moisture and apply the 
 adhesive .
in addition , 
 dual - cure resin cements have limited ability to diffuse light across the entire length 
 of resin cement , thereby compromising the degree of polymerization and 
 conversion .
interfacial discontinuity is commonly attributed to 
 resin shrinkage because the 
 strength of polymerization contraction often exceeds dentin adhesiveness , forming 
 interfacial gaps at sites with weakened bonds along the dentin surface .
root canal geometry is also unfavorable for resin bonding , as 
 evidenced by the ratio of bonded to unbounded surface . with respect to clinical treatment with glass fiber 
 posts , however , some authors assert that dentin bonding is more 
 related to the dislocation resistance promoted by sliding friction and surface roughness 
 than to shrinkage stress or canal geometry . discontinuity in binding interface is a 
 serious failure in endodontic procedures because pull off or debonding may shorten 
 treatment duration and cause 
 bacterial proliferation and infiltration . the interface formed by the main resin cements currently used
we 
 therefore evaluated the continuity of dentin - cement interface formed by dual - cure and 
 self - adhesive cements .
we hypothesized that , despite the complex application , dual - cure 
 cements form a more continuous interface compared to their self - adhesive counterpart . 

because geometry and environmental conditions are quite irregular along the root 
 portions , we tested a second hypothesis that the interfacial continuity formed is 
 different in the cervical , medium and apical portions of the root .
for the present study we selected 40 single - rooted human teeth that had been extracted 
 for orthodontic or periodontal reasons after approval by the research ethics committee 
 ( approval # 753/2006 )
. they were cleaned and stored in a 0.9% solution of thymol and 
 their crowns were cut to a standard root length of 14 mm .
the roots were instrumented up to a # 45 k file ( maillefer , dentsply maillefer ind .
petrpolis , rio de janeiro , brazil ) at the working length , and they were irrigated 
 with 2% chlorhexidine digluconate solution ( clorhexidina , fgm - dental products ltd .
petrpolis , rio de janeiro , brazil ) and sealer 26 root canal sealer ( sealer 
 26 , dentsply ind .
petrpolis , rio de janeiro , brazil ) using the hybrid 
 thermoplastic technique described by tagger ( 1984 ) .
the coronal access of the roots were sealed with 
 temporary restorative cement , coltosol ( coltosol , vigodent s / a ind .
e com , rio de 
 janeiro , brazil ) and stored in a bottle with moistened foam in a microprocessor 
 controlled incubator used for cell culture and bacteriology ( model q326m2 , callmex - 
 products and services laboratory , florianpolis , sc , brazil ) at 37c for 7 days .
the samples were prepared at 10 mm , using a # 3 largo drill ( maillefer , dentsply 
 maillefer ind .
petrpolis , rio de janeiro , brazil ) , compatible to the 
 glass - fiber post reforpost # 01 ( 20 mm length ,  0.7 mm ,  1.1 mm ) ( reforpost , 
 angelus ind .
the glass - fiber posts 
 were tested into the root canal prepared and then cut in 14 mm length . the teeth and 
 their posts were separated randomly into 4 groups of 10 samples according to the 
 cement used .
londrina , pr , brazil ) was applied on the post surface during 1 min .
the hydrophobic 
 adhesive adper scotchbond plus multi - purpose ( adper 
 scotchbond plus multi - purpose , 3 m espe , sumar , sp , brazil ) was 
 applied to the post , light - curing for 20 s , using radii curing light ( radii led 
 curing light , sdi , bayswater , victoria , australia ) at an intensity of 1200 
 mw / cm .
chemical compositions of the resinous cements and adhesive systems gpdm - glycerol dimethacrylate dihydrogen phosphate tegdma - triethylenglycol dimethacrylate bisema - ethoxylated bisphenol a glycol dimethacrylate group ac : allcem conventional dual - cure resin cement ( allcem , fgm - dental products 
 ltd . , joinville , sc , brazil ) , and group arc : relyxtm arc conventional dual - cure resin 
 cement ( relyxtm arc , 3 m espe , sumar , sp , brazil ) .
the root dentin was conditioned for 15 s with 37% phosphoric acid 
 gel ( cond ac 37 , fgm - dental products ltd . ,
joinville , sc , brazil ) ; it has been washed 
 with distilled water and dried with an endodontic aspirator and absorbent paper 
 points .
the adper scotchbond plus multi - purpose adhesive system ( adpertm scotchbondtm 
 plus multi - purpose , 3 m espe , sumar , sp , brazil ) was applied in the following 
 sequence : first , the activator was applied with the microbrush , and after 30 s the 
 excess was removed with absorbent paper ; the same process was then repeated with the 
 primer and catalyst .
the cement was manipulated and inserted into the canal with 
 centrix syringe and needle headed ( centrix , dfl ind . e com sa , rio de 
 janeiro , rj , brazil ) .
the posts were then inserted , the excess cement removed and the 
 remaining cement cured for 40 s on the occluded surface with a radii curing light 
 ( radii led curing light , sdi , bayswater , victoria , australia ) at an intensity of 1200 
 mw / cm .
group u100 : relyx u100 universal self - adhesive resin luting cement 
 ( relyx u100 , 3 m espe , sumar , sp , brazil ) , and group mxc : maxcem 
 elite dual self - adhesive resin luting cement ( maxcem elite , kerr corporation , orange , 
 ca , usa ) . on the cementing procedure
, the treatment of the root canal with etching 
 agent was omitted . instead ,
the root canal was washed on distilled water ; the cement 
 was inserted with centrix syringe and needle headed ( centrix , dfl ind . 
 com .
the posts were inserted , the excess cement 
 was removed and the remaining cement cured for 40 s on the occluded surface , with a 
 radii curing light . the posts and canals were sealed with opallis composite resin ( opallis , fgm , 
 joinville , sc , brazil ) , and the samples were stored for 72 hours at 100% humidity and 
 37c in a microprocessor - controlled incubator used for cell culture and bacteriology 
 ( model q326m2 , callmex - produtos e servios para laboratrio , florianpolis , sc , 
 brazil ) .
after storaging , the roots were sectioned with an isomet low speed saw 
 ( isomet , buehler ltd . ,
the samples were cleaned 
 with 10% liquid phosphoric acid for 10 s , washed and submitted to ultrasound ( ultra 
 cleaner 1400a , unique , indaiatuba , so paulo , brazil ) for 10 min . to obtain realistic results , the present study used positive epoxy resin replicas of 
 the samples after root sectioning to preserve the interface integrity between the 
 different resin cements and the canal wall dentin .
they were then dried with an air jet , negative molds were produced using addition 
 silicone ( adsil , vigodent , rio de janeiro , rj , brazil ) , and positive replicas were 
 made with epoxy resin ( epxi , redelease , so paulo , sp , brazil ) .
two marks were made 
 in the positive replicas in the region of the root dentin 3 and 6 mm from the 
 cervical end with the aid of a scalpel for guidance when taking measurements .
the 
 replicas were cleaned in an ultrasonic bath for 10 min . and metalized , and electron 
 micrographs of each third of the root were taken using a scanning electron microscope 
 ( sem ) , operating at 15 kv ( jeol jsm-5410 , jeol ltd , tokyo , japan ) ( 35x and 200x 
 magnification ) .
the image analyst program was used to combine the electron micrographs making up each 
 root to measure the length of the interfacial continuity ( figure 2 ) . the combined electron micrographs ( 35x magnification ) 

were then analyzed with autocad 2002 software , and the following measurements were 
 taken the length of each third of the root and the sum of the interfacial continuity . 
 the integrity of the interface in each third
was then expressed as the percentage of 
 continuous ( gap - free ) interface .
the percentage of the continuous interface along the 
 entire cement / radicular dentin interface was also calculated ( figure 3 ) .
figure 4 shows 
 what was considered interfacial continuity and figure 
 5 shows a misfit .  
scanning electron micrographs of the cervical ( c ) , medium ( m ) and apical ( a ) 
 thirds combined using image analyst software .
original magnification , 40x measurements taken with the autocad 2002 software : total length ( t ) of the 
 thirds and lengths of the attached sections ( c , m , a ) .
original magnification , 
 40x representative electron micrograph of the third ; interfacial adaptation 
 ( c = cement ; d = dentin ; p = post ; a = interface continuity ) .
original magnification , 
 200x electron micrograph of a representative third ; interfacial misfit ( c = cement ; 
 d = dentin ; p = post ; g = gap ) .
the samples were prepared at 10 mm , using a # 3 largo drill ( maillefer , dentsply 
 maillefer ind .
petrpolis , rio de janeiro , brazil ) , compatible to the 
 glass - fiber post reforpost # 01 ( 20 mm length ,  0.7 mm ,  1.1 mm ) ( reforpost , 
 angelus ind .
the glass - fiber posts 
 were tested into the root canal prepared and then cut in 14 mm length . the teeth and 
 their posts were separated randomly into 4 groups of 10 samples according to the 
 cement used .
afterwards , 
 the silane coupling agent ( silano angelus , angelus ind . e com .
londrina , pr , brazil ) was applied on the post surface during 1 min .
the hydrophobic 
 adhesive adper scotchbond plus multi - purpose ( adper 
 scotchbond plus multi - purpose , 3 m espe , sumar , sp , brazil ) was 
 applied to the post , light - curing for 20 s , using radii curing light ( radii led 
 curing light , sdi , bayswater , victoria , australia ) at an intensity of 1200 
 mw / cm .
chemical compositions of the resinous cements and adhesive systems gpdm - glycerol dimethacrylate dihydrogen phosphate tegdma - triethylenglycol dimethacrylate bisema - ethoxylated bisphenol a glycol dimethacrylate group ac : allcem conventional dual - cure resin cement ( allcem , fgm - dental products 
 ltd . ,
joinville , sc , brazil ) , and group arc : relyxtm arc conventional dual - cure resin 
 cement ( relyxtm arc , 3 m espe , sumar , sp , brazil ) .
the root dentin was conditioned for 15 s with 37% phosphoric acid 
 gel ( cond ac 37 , fgm - dental products ltd . ,
joinville , sc , brazil ) ; it has been washed 
 with distilled water and dried with an endodontic aspirator and absorbent paper 
 points .
the adper scotchbond plus multi - purpose adhesive system ( adpertm scotchbondtm 
 plus multi - purpose , 3 m espe , sumar , sp , brazil ) was applied in the following 
 sequence : first , the activator was applied with the microbrush , and after 30 s the 
 excess was removed with absorbent paper ; the same process was then repeated with the 
 primer and catalyst .
the cement was manipulated and inserted into the canal with 
 centrix syringe and needle headed ( centrix , dfl ind . e com sa , rio de 
 janeiro , rj , brazil ) .
the posts were then inserted , the excess cement removed and the 
 remaining cement cured for 40 s on the occluded surface with a radii curing light 
 ( radii led curing light , sdi , bayswater , victoria , australia ) at an intensity of 1200 
 mw / cm .
group u100 : relyx u100 universal self - adhesive resin luting cement 
 ( relyx u100 , 3 m espe , sumar , sp , brazil ) , and group mxc : maxcem 
 elite dual self - adhesive resin luting cement ( maxcem elite , kerr corporation , orange , 
 ca , usa ) . on the cementing procedure ,
, the root canal was washed on distilled water ; the cement 
 was inserted with centrix syringe and needle headed ( centrix , dfl ind . 
 com .
the posts were inserted , the excess cement 
 was removed and the remaining cement cured for 40 s on the occluded surface , with a 
 radii curing light .
the posts and canals were sealed with opallis composite resin ( opallis , fgm , 
 joinville , sc , brazil ) , and the samples were stored for 72 hours at 100% humidity and 
 37c in a microprocessor - controlled incubator used for cell culture and bacteriology 
 ( model q326m2 , callmex - produtos e servios para laboratrio , florianpolis , sc , 
 brazil ) .
after storaging , the roots were sectioned with an isomet low speed saw 
 ( isomet , buehler ltd .
the samples were cleaned 
 with 10% liquid phosphoric acid for 10 s , washed and submitted to ultrasound ( ultra 
 cleaner 1400a , unique , indaiatuba , so paulo , brazil ) for 10 min . to obtain realistic results , the present study used positive epoxy resin replicas of 
 the samples after root sectioning to preserve the interface integrity between the 
 different resin cements and the canal wall dentin .
they were then dried with an air jet , negative molds were produced using addition 
 silicone ( adsil , vigodent , rio de janeiro , rj , brazil ) , and positive replicas were 
 made with epoxy resin ( epxi , redelease , so paulo , sp , brazil ) .
two marks were made 
 in the positive replicas in the region of the root dentin 3 and 6 mm from the 
 cervical end with the aid of a scalpel for guidance when taking measurements .
the 
 replicas were cleaned in an ultrasonic bath for 10 min . and metalized , and electron 
 micrographs of each third of the root were taken using a scanning electron microscope 
 ( sem ) , operating at 15 kv ( jeol jsm-5410 , jeol ltd , tokyo , japan ) ( 35x and 200x 
 magnification ) .
the image analyst program was used to combine the electron micrographs making up each 
 root to measure the length of the interfacial continuity ( figure 2 ) .
the combined electron micrographs ( 35x magnification ) 
 were then analyzed with autocad 2002 software , and the following measurements were 
 taken the length of each third of the root and the sum of the interfacial continuity . 

the integrity of the interface in each third was then expressed as the percentage of 
 continuous ( gap - free ) interface .
the percentage of the continuous interface along the 
 entire cement / radicular dentin interface was also calculated ( figure 3 ) .
figure 4 shows 
 what was considered interfacial continuity and figure 
 5 shows a misfit .  
scanning electron micrographs of the cervical ( c ) , medium ( m ) and apical ( a ) 
 thirds combined using image analyst software .
original magnification , 40x measurements taken with the autocad 2002 software : total length ( t ) of the 
 thirds and lengths of the attached sections ( c , m , a ) .
original magnification , 
 40x representative electron micrograph of the third ; interfacial adaptation 
 ( c = cement ; d = dentin ; p = post ; a = interface continuity ) .
original magnification , 
 200x electron micrograph of a representative third ; interfacial misfit ( c = cement ; 
 d = dentin ; p = post ; g = gap ) .
friedman and kruskal - wallis tests with an 5% were used to determine whether there were 
 any statistically significant differences in the results for the resin cements 
 tested .
friedman test revealed no statistically significant differences among the thirds of the 
 roots for each group : group ac ( p=0.1496 ) , group arc ( p=0.1496 ) , group u100 ( p=0.6703 ) 
 and group mxc ( p=0.7985 ) .
mean percentage of the interfacial continuity resin cements ( % ) and standard 
 deviation varying the cervical , medium and apical thirds comparison between columns : same capital letters indicate no statistically 
 significant difference .
the kruskal - wallis and dunn tests revealed a statistically significant difference 
 between cements for each of the three thirds of the roots .
groups ac , arc and u100 
 showed better performance than group mxc for cervical thirds ( p=0.0001 ) , medium thirds 
 ( p=0.0001 ) and apical thirds ( p=0.0013 ) ( table 
 1 ) .
taking into 
 account the overall interfacial continuity of the cements , it was observed that 
 u100>ac > arc > mxc ( figure 6 ) .
corroborating the first hypothesis of the present study , both the dual - cure resin 
 cements tested in vitro produced a more continuous interface than the 
 self - adhesive maxcem , which formed a discontinuous interface with many gaps .
however , 
 contradicting this same hypothesis , the interfacial continuity produced by u100 
 self - adhesive cement was as satisfactory as that formed by the dual - cure cements . in 
 relation to root portion , we rejected the hypothesis concerning different cement 
 adhesion in the cervical , medium and apical root regions .  
for the experimental assays , we used a reliable technique involving epoxy resin 
 replicas , which avoided a possible influence of shrinkage under vacuum in scanning 
 electron microscopy .
a number of variables can compromise cement adhesion , such as root dentin 
 morphology , humidity , adhesive system capabilities , compatibility of adhesive system and dual - cured luting 
 cement , deep light cure 
 capabilities , light 
 transmissibility of fiber posts , polymerization shrinkage and relief of 
 shrinkage stress .
the use of an adequate resin cement system is particularly important 
 for cement adhesion because it directly affects the quality of the tooth - luting 
 interface .
dual self - adhesive resin cements generally have better adhesion than 
 self - adhesive resin cements , suggesting that composite materials significantly influence 
 the formation of the tooth - luting interface .
corroborating this 
 hypothesis t , both dual self - adhesive resin systems tested here ( allcem and relyx arc ) 
 exhibited good adaptation and low gap formation ( ac=81.3% and arc=80.4% interfacial 
 continuity ; table 1 ) .
conventional dual - cure resin cements can be used in adhesive systems that require 
 pretreatment of the root with phosphoric acid as etching solution followed by the 
 application of a 2- or 3-step adhesive system .
we used a 3-step system , and the quality 
 of this product undoubtedly contributed to the good results obtained for groups ac and 
 arc .
after the etching solution completely dissolves the smear layer 
 and creates a partially demineralized zone of dentin , the 3-step adhesive system is 
 applied using an activator followed by a primer and a catalyst ( adper scotchbond 
 multi - purpose plus ) .
the 3-step etch & rinse adhesive system increases the 
 interfacial adaptation of dual - cure luting cement because it increases adhesive 
 penetration into dentinal tubules , thereby improving the pattern of dentin 
 hybridization . the catalyst layer of the 3-step system ( ph=5.7 ) is not composed of solvents that could 
 allow a few droplets to transude the polymerized adhesive and compromise cement 
 adhesion . in addition , the 
 3-step adhesive system lacks acid monomers , which ensures total compatibility with the 
 dual - cure luting cement .
other adhesive systems , such as 2-step and one - step - self - etch , 
 have uncured acidic resin monomers in the oxygen inhibition layer that are incompatible 
 with the tertiary amines ( initiator component ) involved in the polymerization mechanism 
 of dual - cure resin cements .
decreased ph is another disadvantage of adhesive systems containing acid monomers 
 because it weakens bond strength .
conversely , the 3-step system provides effective 
 binding between the adhesive agents and the dental structure .
the catalyst used , scotchbond multi - purpose plus , 
 contains a common initiator for self - curing resins , benzoylperoxide ( bpo ) , which reacts 
 with the tertiary amines of the self - cure and dual - cure resin cements and helps dual polymerization of the 
 dual - luting cement along the root .
other advantages of the 3-step adhesive system is 
 that no light curing is required before post cementation , overcoming an obstacle in curing deep regions .
in addition to pretreatment , the composition of dual - cure resin cements unquestionably 
 contributed to cementing quality .
these resin cements contain cross - linking monomers 
 such as bis - gma , which produce polymers of high mechanical quality because of their high 
 molecular weight , low polymerization contraction and rapid hardening .
dual - cure resin cement also contains 
 the monomer diluent triethylene glycol dimethacrilate ( tegdma ) , which has high 
 flexibility and low polymerization contraction .
tegdma also provides a high degree of 
 conversion and has hydrophobic properties that prevent substantial water uptake after 
 curing .
compared to bis - gma , tegdma allows better clinical handling owing to its low 
 viscosity .
a redox reaction of 
 benzoyl peroxide of dual - cure resin cements with aromatic tertiary amines underlies the 
 setting mechanism , a process that is compatible with the 3-step adhesive system , as 
 mentioned before .
similarly to the conventional dual - cure cements tested here , the u100 self - adhesive 
 cement exhibited good performance ( table 1 ) . 

earlier studies reported satisfactory results using relyx unicem cement , which is 
 chemically identical to the relyx u100 we tested , differing only in the application 
 procedure .
relyx unicem produces good marginal continuity , but due to its high 
 viscosity , does not form an obvious dentin hybrid layer and thus achieves limited 
 infiltration .
therefore , both relyx u100 and relyx unicem are highly 
 adapted to the substrate and can optimize physical interactions such as van der waals 
 forces , hydrogen bridges and charge transfer , which enhance micromechanical retention 
 and chemical bonding . the multifunctional , phosphoric acid modified methacrylate monomers of u100 ( ph<2 ) 
 demineralize root dentin as well as infiltrate the substrate and react with the 
 hydroxyapatite of hard tissues .
thus , the micromechanical retention associated to the chemical 
 adhesion to hydroxyapatite provides self - adhesiveness to the u100 cement ( 3 m espe 
 technical information ) .
this chemical interaction produces water , which accelerates 
 neutralization of phosphoric - acid methacrylate , basic fillers and 
 hydroxyapatite .
the system 
 likely gained water resistance , and although water and buffering of the smear layer may 
 have reduced desmineralization capacity , the effectiveness of the u100 cement was not 
 compromised , as reported in earlier study .
overall , we consider that relyx u100 cement is the best of the 
 tested cements because , in addition to the good results it obtained , its application is 
 significantly easier than that of conventional dual care cements .
in contrast to u100 , maxcem self - adhesive cement performed poorly , corroborating earlier 
 studies .
maxcem 
 contains several hydrophilic adhesive monomers of low molecular weight , such as the 
 glycerol phosphate dimethacrylate ( gpdm ) , which provide the necessary wettability for 
 adhesion to dentin substrate .
the cement is purportedly anhydrous prior to mixing , but 
 the technical specifications of this product do not inform the way this monomer is 
 initially hydrolyzed , the initial ph or the proprietary redox activator system .
this may account for the discontinuous tooth - cement interface , with many premature 
 failures , that we found in the mxc group .
maxcem has limited potential for removal or 
 modification of the smear layer and low resin infiltration into the underline 
 dentin .
therefore , it 
 does not form a dentin hybrid layer that promotes the micromechanical interlocking with 
 dentin collagen fibrils .
the thick smear layer formed 
 neutralizes the initial low ph of maxcem thereby impairing its performance . therefore , despite the excellence of maxcem monomers as bonding 
 agents of good compatibility with the humid dentin substrate , they do not provide an 
 effective cementation in deep areas of high humidity .
we however have not found 
 cementation differences in the wettest and driest portions of the root , and the bad 
 results of maxcem may derive from poor - quality of the polymer formed . for practical reasons we have not investigated chemical set cements . but some concerns 
 should be made on these materials because they are widely used in endodontic treatments 
 despite the application failures reported in other studies .
these cement sets have a 
 long setting time , with a prolonged gelation that possibly reliefs shrinkage stress via 
 resin flow .
this long setting time , 
 however , allows moisture diffusion from the dentin through the hydrophilic primer , 
 creating water blisters or droplets along the interface with the slow polymerizing resin 
 cements .
moisture contamination 
 reduces bond strength and facilitates leaching of water - soluble components from the 
 resin .
this process is as serious as the incompatibility of adhesive systems and may 
 further contribute to break down the bond , as show in both in 
 vitro and in 
 vivo studies of 
 endodontically treated teeth . some studies on the adhesive resistance of cements show that binding is stronger in the 
 cervical portion and weaker in the apical portion of the root .
some authors 
 suggest that samples of low bond strength have a high number of gaps , but the relationship between bond strength and bond integrity has not 
 yet been proved . in accordance with other authors
, we in fact found that the experimental groups had a 
 same pattern of continuity interface throughout the apical , medium and cervical portions 
 of the root .
we expected to find a higher continuity in the cervical portion of the root 
 because the curing light absorbed along the canal decreases significantly light 
 incidence in the medium and apical portions .
this is minimized when light - transmitting 
 posts are used because they improve 
 polymerization in deep areas of canal roots . in our study , however , we used opaque posts and did not found that drops in light 
 incidence have affected interfacial continuity .
the cervical third of the root had higher cement thickness , but 
 variations of this parameter did not affect interfacial continuity as well .
the major 
 implication of a high cement thickness is the shrinkage risk with consequent debonding 
 and gap formation in the resin cement / dentin interface . in the present study ,
differences in 
 cement thicknesses were rather related to the uneven root anatomy than to interface 
 quality .
continuity of dentin / cement interface is necessary to promote sliding friction , which 
 according to many authors is the main factor for adhesive resistance in the fiber 
 post / resin cement system and for micromechanical interlocking . as already observed by practitioners in routine 
 treatments ,
our results show that the cements currently used provide good cementation 
 but do not form a complete bonding and a continuous interface along the length of the 
 root channel .
complete 
 fiber luting is important because it prevents post displacement by frictional 
 retention and bacterial leakage , thereby enhancing the longevity of coronal restorations 
 in endodontically treated teeth .
according to schwartz ( 2006 ) and tay , loushine , lambrechts , et 
 al .
therefore , more attention should be 
 devoted to the recently developed low - shrinking resin composites that have been used 
 only for tooth restorations .
we therefore suggest the adaptation of these resins to 
 endodontic treatments such as post luting . this is a promising resin to prevent gap 
 formation in the dentin - adhesive interface .
based on the results of this in vitro study , we conclude that : 1 - the cements allcem , relyx arc and relyx u100 provide good cementation with 80% 
 continuity .
maxcem elite does not produce a satisfactory cementation ( only 47% 
 interfacial continuity ) ; 2 - cementation quality provided by the different cement types is similar among the 
 cervical , medium and apical portions of the tooth roots ; 3 - in practical terms , relyx u100 provides the best cementation because combines good 
 cementation and easy application ; 4- because the cements tested do not provide a complete interfacial continuity , we 
 suggest the development of novel materials using low - shrinking resin composites that are 
 already used for restoration purposes .
 during post preparation , the root canal is exposed to the oral cavity , and endodontic 
 treatment may fail because of coronal leakage , bacterial infection and sealing 
 inability of the luting cement.objectivethis study quantified the interfacial continuity produced with conventional 
 dual - cure and self - adhesive resin cements in the cervical ( c ) , medium ( m ) and 
 apical ( a ) thirds of the root . 
 material and methodsforty single - rooted human teeth were restored using reforpost # 01 conical 
 glass - fiber posts and different materials ( n=10 per group ) : group 
 ac = adper scotchbond multi - purpose plus + allcem ; group arc = adper 
 scotchbond multi - purpose plus + relyx arc ; group u100=relyx u100 ; and group 
 mxc = maxcem elite . after being kept in 100% humidity at 37c for 72 hours , the 
 samples were sectioned parallel to their longitudinal axis and positive epoxy 
 resin replicas were made . 
 the scanning electron micrographs of each third section 
 of the teeth were combined using image analyst software and measured with 
 autocad-2002 . 
 we obtained percentage values of the interfacial continuity . 
 resultsinterfacial continuity was similar in the apical , medium and cervical thirds of 
 the roots within the groups ( friedman test , p>0.05 ) . 
 comparison of the 
 different cements in a same root third showed that interfacial continuity was 
 lower in mxc ( c=45.5% ; m=48.5% ; a=47.3% ) than in ac ( c=85.9% , m=81.8% and 
 a=76.0% ) , arc ( c=83.8% , m=82.4% and a=75.0% ) and u100 ( c=84.1% , m=82.4% and 
 a=77.3% ) ( kruskal - wallis test , p<0.05 ) . 
 conclusionsallcem , rely x arc and u100 provide the best cementation ; cementation was similar 
 among root portions ; in practical terms , u100 is the best resin because it 
 combines good cementation and easy application and none of the cements provides 
 complete interfacial continuity . 