although the use 
 of prefabricated posts has gained popularity , for several years 
 custom cast dowel and core has been used to retain restorations with clinical evidence 
 of success .
one important advantage 
 of this post system is that the dowel will fit a flared or irregularly shaped canal more 
 closely than prefabricated post systems do .
however , although endodontic therapy has shown a high success rate , adverse situations 
 that require endodontic retreatment are not rare .
when signs , symptoms and radiographic images suggest the failure 
 of endodontic treatment , an atraumatic and efficient post removal is essential for 
 optimal non - surgical endodontic management .
drills and extractors exert high force on the root and may result in root 
 fractures .
ultrasonic energy is transmitted to the post , causing 
 cracks in the cement thus facilitating its removal .
recent evidence suggests that ultrasonic vibration is a safe and fast method for post 
 removal .
however , several in vitro studies have evaluated post removal 
 with ultrasonic devices by using roots of extract teeth included in resin 
 cylinders . this procedure is used in order to facilitate handling 
 and test application . however
clinically , 
 the root is enveloped by periodontal ligament ( pdl ) , which presents higher resiliency 
 than resins used for root inclusion .
this difference in resiliencies enables pdl to 
 dissipate the ultrasonic energy more easily than when the root is included in a resin 
 cylinder .
thus , the facility 
 found in some in vitro studies for post removal with ultrasound 
 activation may not be consistent with the clinical reality .
the simulation of the pdl in 
 these tests would be important to bring the laboratory findings to clinical 
 application .
the aim of this in vitro study was to evaluate the effect of simulated 
 periodontal ligament ( spdl ) on custom cast dowel and core removal using an ultrasonic 
 device .
the null hypothesis was that the spdl does not influence the action of the 
 ultrasonic device used to remove the cast dowel and core from the root canal .
thirty - two human maxillary canines with mature apices , un - pronounced flattening , roots 
 with no curves and single canal were selected for this study .
crowns were removed in 
 order to obtain a 15-mm - long root remainder . for the endodontic treatment , the root 
 canals
were prepared according to a crown - down technique , using stainless - steel k - files 
 and # 2 to # 4 gates - glidden drills ( dentsply maillefer ; ballaigues , switzerland ) .
all 
 enlargement procedures were followed by irrigation with a 2.5% sodium hypochlorite 
 solution .
instrumented root canals were obturated with gutta - percha cones and sealer-26 
 resin sealer ( dentsply , petrpolis , rj , brazil ) using the lateral condensation 
 technique .
the filled roots were stored in relative humidity for at least 72 h to allow 
 the resin sealer to set .
the specimens were randomly allocated according to presence of 
 spdl and application of ultrasonic vibration .
half of the roots were included directly in self - cured acrylic resin cylinders ( jet 
 clssico , so paulo , sp , brazil ) without spdl .
the external surfaces of 
 the root remainders were dipped into melted wax ( epoxiglass , diadema , sp , brazil ) , 
 resulting in a 0.2 to 0.3-mm - thick wax layer .
after resin polymerization , the roots were removed from the cylinder , the wax 
 removed from the root surface creating a space in the resin cylinder .
the polyether 
 impression material ( impregum f , 3m / espe , seefeld , germany ) was mixed and placed in the 
 space created in the resin cylinder .
the tooth was re - inserted into the cylinder and the 
 excess material removed with a scalpel blade . in order to allow tensile testing without 
 the root becoming dislodged
, the roots included in resin cylinder with spdl were fixed 
 to cylinders with two stainless steel wires about 1 mm in diameter ( figure 2 ) .
note the presence of two wires in order to prevent the root dislodgement during 
 testing post - holes were prepared by standardizing the length at 8 mm and preparation was 
 performed with a size 6 largo drill ( dentsply maillefer ) .
this drill was used with a 
 low - speed handpiece attached to a parallelometer .
the root canal impressions were made 
 with self - cured resin acrylic ( duralay , reliance dental , worth , il , usa ) .
the dowel and cores were cast in 
 a nickel - chromium alloy ( wironia , bego , bremen , germany ) .
all custom cast dowel and 
 cores were luted with dual - cured resin cement ( panavia f ; kuraray , osaka , japan ) , in 
 accordance with the manufacturer 's instructions .
after the storage period , half of specimens of each inclusion type ( with or without 
 spdl ) were submitted to ultrasonic vibration .
this was applied by the same calibrated 
 operator , using a piezoelectric ultrasonic device ( enac , osada electric co ltd . ,
tokyo , 
 japan ) , and an st 09 tip ( osada electric co. ltd . ) , at maximum power under water 
 cooling .
the vibration was applied for 1 min to the buccal , mesial , lingual , distal , and 
 incisal surfaces , successively , with total application time of 4 min for each sample 
 ( figure 3 ) .
samples were positioned in a 
 universal testing machine ( model 4411 , instron corp . , canton , ma , usa ) and the ring of 
 the core was attached to the load cell ( 500 n ) .
tensile load was applied at a crosshead 
 speed of 0.5 mm / min until the cast dowel and core was dislodged ( figure 4 ) .
the 
 factors evaluated were " presence of spdl " and " ultrasonic vibration application " . 

post - hoc tests were calculated using tukey`s multiple - comparison test 
 ( =0.05 ) .
application of ultrasonic vibration application of tensile load at samples until dislodgment of the custom cast dowel 
 and core .
a and b - without simulated periodontal ligament ; c and d - with 
 simulated periodontal ligament
there was a statistically significant effect for the factors " presence of spdl " 
 ( p<0.01 ) , " ultrasonic vibration application " ( p<0.01 ) and for interaction between 
 factors ( p<0.05 ) .
the means tensile strength values in kgf ( sd ) necessary to dislodge 
 the cast post - and - cores and the results of the tukey 's test are shown in table 1 .
when ultrasonic vibration was not applied , 
 samples with spdl presented the lowest tensile bond strength values .
no significant 
 differences were observed in the presence or absence of spdl in samples submitted to 
 ultrasonic vibration . ultrasonic vibration application led to the lowest values when the 
 pdl was not simulated , but had no effect on samples with spdl .
tensile strength means values in kgf ( sd ) necessary to dislodge the cast 
 post - and - cores
the influence of pdl is often omitted in in vitro tests that evaluate 
 post removal using ultrasonic devices , as opposed to other studies that evaluate the 
 in vitro fracture resistance of restored teeth .
the pdl is an 
 important structure for distributing the stress generated by load application on teeth . 

based on this , elastomeric materials have been used to reproduce the pdl in several 
 studies .
polyether 
 impression material is adequate for such purpose because of its ease of use , consistency 
 and deformation limit .
one 
 difficulty of using spdl in tensile tests is the possibility of it being dislodged 
 during load application . in the present study , roots were fixed in a resin cylinder with 
 two stainless steel wires to prevent dislodgment of root and allow testing .
this 
 methodology enabled tensile load application on samples included with spdl , but it had 
 an influence on the tensile bond strength values .
samples included in the cylinder with the presence of spdl presented lower bond strength 
 values than those directly included in resin , when the ultrasonic vibrations were not 
 applied .
one possible explanation for this may be related to the forces resulting during 
 tensile load application . during the test , the deformation of wires used to fix the root 
 allowed a slight dislodgement of the root .
thus , the tensile load is more concentrated at the interface 
 between resin cement and dowel for the samples included with spdl .
this results in the 
 need for lower loads to remove these cast dowel and cores . despite this influence on the load distribution ,
the simulation of pdl also intervened 
 in the effectiveness of the ultrasonic vibration to reduce the dowel retention .
the 
 tensile bond strength of the samples included in resin cylinders with spdl was not 
 altered by use of the ultrasound device , as opposed to samples included without spdl . 

the reduction in cast dowel and core retention 
 with the application of ultrasonic energy has been demonstrated by several 
 studies .
the ultrasonic device used in this study has a 
 piezoelectric transducer that transforms electricity into ultrasonic vibrations .
quartz 
 crystals within the transducer are vibrated by the electricity flowing through them . by 
 applying an alternating electrical field across the crystal ,
these ultrasonic vibrations are transmitted through the dowel and 
 core , fracturing the cement interposed between the dowel and the root canal walls and 
 facilitate their removal .
several studies has reported that the type of luting agent can influence the post 
 retention and removal procedure .
posts cemented with resin cements usually require greater force for 
 their removal when compared to those cemented with zinc phosphate or glass ionomer 
 cements . in this study
, the cast dowel and cores 
 were luted with the resin cement panavia f. this cement contains the resin monomer 
 10-mdp ( 10-methacryloyloxydecyl di - hydrogen phosphate ) in its composition , which bonds 
 to metal oxides .
considering that it is essential for 
 the vibrations to reach the resin cement in order to facilitate dowel and core removal , 
 the root inclusion method may affect the efficacy of the ultrasonic device .
the high rigidity of acrylic resin used for sample inclusion does not allow for root 
 movement during the ultrasound application .
thus , approximately all the energy dispensed 
 by the tip of the ultrasonic device is transmitted through the cast dowel and core to 
 reach the resin cement . on the other hand , the root mobility permitted by impression 
 material may to reduce the energy that reaches the resin cement .
thus , the resin cement was submitted to 
 lower strain , which was not sufficient to reduce the retention of cast dowel and core . 

the latter situation is closer to clinical reality than directly including the root in 
 resin cylinders .
therefore , within the limitations of this study , it was demonstrated 
 that the pdl simulation had a significant effect on custom cast dowel and core removal 
 with ultrasonic vibrations .
this means that several of the in vitro 
 studies that evaluated ultrasonic devices for dowel and core removal may have 
 overestimated their efficacy .
the ultrasonic vibration had no effect on cast dowel - and - core retention when the pdl was 
 simulated .
the present outcomes demonstrate the importance of this simulation during 
 in vitro evaluation to avoid overestimating the efficacy of 
 ultrasonic vibration used for cast dowel - and - core removal .
 objectivethe aim of this study was to evaluate the effect of simulated periodontal ligament 
 ( spdl ) on custom cast dowel and core removal by ultrasonic vibration.material and methodsthirty - two human maxillary canines were included in resin cylinders with or 
 without spdl made from polyether impression material . in order to allow tensile 
 testing , 
 the roots included in resin cylinders with spdl were fixed to cylinders 
 with two stainless steel wires . 
 post - holes were prepared by standardizing the 
 length at 8 mm and root canal impressions were made with self - cured resin acrylic . 
 
 cast dowel and core sets were fabricated and luted with panavia f resin cement . 
 
 half of the samples were submitted to ultrasonic vibration before the tensile 
 test . 
 data were analyzed statistically by two - way anova and tukey 's post - hoc tests 
 ( p<0.05).resultsthe ultrasonic vibration reduced the tensile strength of the samples directly 
 included in resin cylinders . 
 there was no difference between the values , whether 
 or not ultrasonic vibration was used , when the pdl was simulated . 
 however , the 
 presence of spdl affected the tensile strength values even when no ultrasonic 
 vibration was applied.conclusionsimulation of pdl has an effect on both ultrasonic vibration and tensile 
 testing . 
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
CONCLUSION