controversy exists as to whether endodontic procedures 
 are the primary cause for loss of strength . panitvisai and messer ( 1995 ) reported that cuspal deflection 
 increased with increasing the extension of cavity preparations and was greatest when 
 endodontic access was incorporated into a preparation . it has been reported that 
 endodontically treated teeth and their contralateral vital pairs exhibited similar 
 biomechanical properties , such as punch shear strength , toughness , and load required for 
 fracture . although the insertion of a post does not strengthen or reinforce endodontically treated 
 teeth , it is basically used to provide sufficient retention of 
 the core material which in turn is used to retain a fixed restoration . for the inserted post to perform its 
 function , several variables must be put into consideration such as post length , 
 diameter , geometric design , and surface configuration . additionally , special attention should be given to the 
 material the post is made of in order to ensure adequate distribution of the absorbed 
 stresses and to prevent root fracture during . regarding with consideration to the well - known success of 
 metallic posts there are now many concerns regarding the associated inhomogeneous stress 
 distribution , biological side effects due to microleakage and corrosion , and the 
 influence of their dark color under an all - ceramic restorations . the introduction of non - metallic fiber reinforced composite ( frc ) posts helped improving 
 stress distribution because their elastic modulus is similar to that of dentin as 
 indicated by several clinical and laboratory studies . frc post systems showed more frequent favorable failure 
 modes than did metal post systems . although fiber posts proved effective 
 in withstanding compressive loads in posterior teeth , they behave differently in anterior teeth where non - axial biting 
 forces prevail and where their flexural behavior becomes more effective . recent studies suggested that glass - fiber posts contributed to the reinforcement 
 and strengthening of endodontically treated teeth under full coverage crowns . a ferrule or encircling band of cast metal around the remaining coronal surface can 
 provide protective reinforcement to endodontically treated teeth by encapsulation of the 
 remaining coronal structure and by resisting functional lever forces during mastication . a minimum 1 to 2 mm of ferrule height is necessary to achieve such protective 
 effect . recent clinical 
 studies reported that the ferrule structure have a direct influence on the clinical 
 success rate of endodontically treated premolars restored with fiber posts and the 
 failure events were due mainly to post debonding . an in 
 vitro study reported that incomplete crown ferrule was associated with 
 greater variation in load capacity after chewing simulation , while other studies found no effect of different 
 ferrule heights in teeth restored with fiber posts and resin cores . the aim of this study was to evaluate the fracture resistance and failure pattern of 
 endodontically treated mandibular premolars restored with different ferrule heights in 
 combination with fiber posts and all - ceramic crowns . the null hypothesis was that 
 different ferrule heights do not improve the fracture resistance or the failure pattern 
 of the tested restorations . all 
 external debris were removed with an ultrasonic scaler , and examined stereoscopically 
 at 10x magnification to verify the absence of cracks , defects and dental caries . teeth were stored in a 0.5% chloramine t ( prolabo , paris , france ) in saline solution . buccolingual and mesiodistal coronal dimensions plus root length of all selected 
 teeth were measured using a digital caliper ( digimatic calipers , mitsutoyo , tokyo , 
 japan ) and only teeth with the following mean dimensions were selected : 14.1 mm root 
 length , 7.3 mm buccolingual width , and 4.9 mm mesiodistal width . standardized root canal preparations were made using the following procedure : initial 
 probing using no . 10 k - files ( flexo files , maillefer , ballaigues , switzerland ) ; the 
 root canal length was established through direct observation of the file extruding 
 from the apical foramen . the specimens were then prepared endodontically with a 
 stepback procedure with size 45 ( flex r file ; union broach , york pa ) . after 
 intermittent rinsing with 2.5% sodium hypochlorite solution , the endodontic treatment 
 was completed using manual lateral condensation method ( ah plus , dentsply , de tray , 
 konstanz , germany ) . after endodontic treatment , each root was thinly covered with a silicone impression 
 material ( aquasil , dentsply ) to simulate thickness of periodontal ligament . all specimens were embedded in 
 self - polymerized acrylic resin ( orthoresin , dentsply , degudent gmbh , postfach 1364 , 
 d-63403 hanau , germany ) poured into a mold while maintaining 2 mm below the cervical 
 line exposed . the teeth were embedded along their long axis using a surveyor ( ney 
 surveyor ; dentsply ) . a new diamond 
 point ( lot - nr 1599 , dfs dental and technical products , gmbh , germany ) was attached to 
 the milling machine ( k9 milling apparatus-990 , kavo , germany ) for every group . the 
 mrd gauged diamond had a self - limiting tip , which produced a 1-mm - deep chamfer and 
 the margins and the angle of convergence were standardized . after preparation of the finish line , the coronal dentinal extension was modified 
 accordingly ( figure 1 ) : group 1 ( control ) : 1 mm 
 circumferential ferrule from the gingival margin without a fiber post ; group 2 : 1 mm 
 circumferential ferrule with fiber post and resin core ; group 3 : non - uniform ferrule 
 height ( 2 mm buccally and 1 mm lingually ) with fiber post and resin core ; group 4 : a 
 non - uniform ferrule height ( 3 mm buccally and 2 mm lingually ) with fiber and resin 
 core post ; group 5 : received no ferrule preparation with fiber post and resin 
 core . schematic representation of the different tested groups in the control group , excess gutta - percha was removed to a depth of 2 mm from the 
 coronal surface of the preparation , using a carbide bur ( 171l-012 , brasseler , usa ) . the coronal walls were etched with 36% phosphoric acid ( total etch , ivoclar - vivadent , 
 schaan , liechtenstein ) for 15 s , washed with water spray and then gently air - dried . one coat of adhesive resin ( excite , ivoclar - vivadent ) was applied using a microbrush 
 and light polymerized for 20 s ( astralis 10 , ivoclar - vivadent ) . a hybrid composite 
 resin ( tetric ceram , ivoclar - vivadent ) was applied and light polymerized for 40 
 s. for the remaining groups , post space was created using no . 1 peeso reamer ( union 
 broach co. , long island , ny , usa ) and corresponding calibrating drill ( frc postec 
 plus , # 1 , ivoclar - vivadent ) leaving 4 mm of apical gutta - percha intact . a translucent 
 glass fiber reinforced composite post ( frc postec plus # 1 ivoclar - vivadent , schaan , 
 liechtenstein ) was used . each post was cut to a suitable length with a diamond bur so 
 that it was covered with at least 2 mm of resin composite occlusally . post cementation was carried out with self - polymerized resin cement ( multilink , 
 ivoclar vivadent ) following manufacturer s instructions . silane coupling agent 
 ( monobond - s , ivoclar - vivadent ) was applied on the post surface for 60 s and then 
 air - dried . after post cementation , the surrounding dentin surface was etched with 36% 
 phosphoric acid ( total etch , ivoclar - vivadent ) for 15 s , washed with water spray and 
 gently air - dried . one coat of adhesive resin ( excite , ivoclar - vivadent ) was applied 
 using a microbrush and light polymerized for 20 s ( astralis 10 , ivoclar - vivadent ) . then core build - up was performed using hybrid composite resin ( tetric ceram , 
 ivoclar - vivadent ) in 1-mm - thick increments and light polymerized ( astralis 10 ; 
 ivocar - vivadent ) for 40 s until the core was restored to predetermined dimensions . the final layer was placed using a transparent matrix to allow for shape consistency 
 between specimens . the dimensions of the prepared cores were confirmed with a 
 measuring microscope with 30x magnification lens with precision of 5 um . a single - phase impression was made using polyvinylsiloxane impression material 
 ( virtual , ivoclar - vivadent ) and master dies were fabricated with type 4 die stone 
 ( jad stone , whip mix , louisville , kentucky , usa ) . a press ceramic ( e max , a3 , 
 ivoclar - vivadent ) was selected to fabricate all - ceramic crowns of the restored 
 specimens . crown dimensions were standardized by using a mold for the external shape 
 of each specimen . the fitting surface of the crowns was pretreated with hydrofluoric 
 acid ( ips ceramic etching gel , ivoclar - vivadent ) for 20 s , rinsed off , air dried , 
 silanized for 60 s and air dried . dentine primer liquids were mixed and applied on 
 the whole prepared tooth surface for 15 s. resin cement was dispensed from the 
 automix syringe directly into the inner surface of the crowns which were seated and 
 held in position under fixed load of 20 n ; excess resin was removed immediately with 
 a micro brush . exposed margins were covered with glycerin gel and rinsed off after 
 complete polymerization of the resin cement . the specimens were stored in distilled 
 water at 37c for 7 days prior to testing . all specimens were subjected to cyclic loading according to the following regime : 
 sinusoidal load between 50 and 200 n at a rate of 2 hertz . all specimens received 
 15,000 cycles and surface damage was prevented by insertion of a 0.5 mm silicon sheet 
 between the occlusal surface of the ceramic crown and the loading indenter ( 3 mm 
 diameter ) of the pneumatically activated loading machine . after completion of cyclic 
 loading , a universal testing machine ( instron 8500 plus , instron , 100 royal st . canton , ma , usa ) was used to deliver a compressive load to the specimens at a 
 crosshead speed of 1 mm / min at 45 degree angle to the long axis of the teeth ( root 
 apex tilted lingually ) until failure . load - time curves were recorded using a 
 universal testing machine s computer software . the 
 failure load of the specimen was determined when the forceversus - time graph showed an 
 abrupt change in load , indicating a sudden decrease in the specimen s resistance to 
 compressive loading . after loading , the failure mode recorded for each specimen and classified as either 
 favorable facture above the cement - enamel junction ( repairable ) or catastrophic 
 fracture of the root below cement - enamel junction ( non repairable ) . these inspections 
 were made using a stereomicroscope ( stereoscopic zoom microscope , smz-1000 , nikon , 
 japan ) and during inspection , the teeth were trans - illuminated with a fiber optic 
 cable . complete or partial debonding of the crown or of the post and core were also 
 considered as favorable failure modes . data were analyzed statistically by one - way 
 anova and tukey s post - hoc test was used for pair - wise comparisons 
 ( =0.05 ) . all 
 external debris were removed with an ultrasonic scaler , and examined stereoscopically 
 at 10x magnification to verify the absence of cracks , defects and dental caries . teeth were stored in a 0.5% chloramine t ( prolabo , paris , france ) in saline solution . buccolingual and mesiodistal coronal dimensions plus root length of all selected 
 teeth were measured using a digital caliper ( digimatic calipers , mitsutoyo , tokyo , 
 japan ) and only teeth with the following mean dimensions were selected : 14.1 mm root 
 length , 7.3 mm buccolingual width , and 4.9 mm mesiodistal width . standardized root canal preparations were made using the following procedure : initial 
 probing using no . 10 k - files ( flexo files , maillefer , ballaigues , switzerland ) ; the 
 root canal length was established through direct observation of the file extruding 
 from the apical foramen . the specimens were then prepared endodontically with a 
 stepback procedure with size 45 ( flex r file ; union broach , york pa ) . after 
 intermittent rinsing with 2.5% sodium hypochlorite solution , the endodontic treatment 
 was completed using manual lateral condensation method ( ah plus , dentsply , de tray , 
 konstanz , germany ) . after endodontic treatment , each root was thinly covered with a silicone impression 
 material ( aquasil , dentsply ) to simulate thickness of periodontal ligament . all specimens were embedded in 
 self - polymerized acrylic resin ( orthoresin , dentsply , degudent gmbh , postfach 1364 , 
 d-63403 hanau , germany ) poured into a mold while maintaining 2 mm below the cervical 
 line exposed . the teeth were embedded along their long axis using a surveyor ( ney 
 surveyor ; dentsply ) . a new diamond 
 point ( lot - nr 1599 , dfs dental and technical products , gmbh , germany ) was attached to 
 the milling machine ( k9 milling apparatus-990 , kavo , germany ) for every group . the 
 mrd gauged diamond had a self - limiting tip , which produced a 1-mm - deep chamfer and 
 the margins and the angle of convergence were standardized . after preparation of the finish line , the coronal dentinal extension was modified 
 accordingly ( figure 1 ) : group 1 ( control ) : 1 mm 
 circumferential ferrule from the gingival margin without a fiber post ; group 2 : 1 mm 
 circumferential ferrule with fiber post and resin core ; group 3 : non - uniform ferrule 
 height ( 2 mm buccally and 1 mm lingually ) with fiber post and resin core ; group 4 : a 
 non - uniform ferrule height ( 3 mm buccally and 2 mm lingually ) with fiber and resin 
 core post ; group 5 : received no ferrule preparation with fiber post and resin 
 core . in the control group , excess gutta - percha was removed to a depth of 2 mm from the 
 coronal surface of the preparation , using a carbide bur ( 171l-012 , brasseler , usa ) . the coronal walls were etched with 36% phosphoric acid ( total etch , ivoclar - vivadent , 
 schaan , liechtenstein ) for 15 s , washed with water spray and then gently air - dried . one coat of adhesive resin ( excite , ivoclar - vivadent ) was applied using a microbrush 
 and light polymerized for 20 s ( astralis 10 , ivoclar - vivadent ) . a hybrid composite 
 resin ( tetric ceram , ivoclar - vivadent ) was applied and light polymerized for 40 
 s. for the remaining groups , post space was created using no . 1 peeso reamer ( union 
 broach co. , long island , ny , usa ) and corresponding calibrating drill ( frc postec 
 plus , # 1 , ivoclar - vivadent ) leaving 4 mm of apical gutta - percha intact . a translucent 
 glass fiber reinforced composite post ( frc postec plus # 1 ivoclar - vivadent , schaan , 
 liechtenstein ) was used . each post was cut to a suitable length with a diamond bur so 
 that it was covered with at least 2 mm of resin composite occlusally . post cementation was carried out with self - polymerized resin cement ( multilink , 
 ivoclar vivadent ) following manufacturer s instructions . silane coupling agent 
 ( monobond - s , ivoclar - vivadent ) was applied on the post surface for 60 s and then 
 air - dried . after post cementation , the surrounding dentin surface was etched with 36% 
 phosphoric acid ( total etch , ivoclar - vivadent ) for 15 s , washed with water spray and 
 gently air - dried . one coat of adhesive resin ( excite , ivoclar - vivadent ) was applied 
 using a microbrush and light polymerized for 20 s ( astralis 10 , ivoclar - vivadent ) . then core build - up was performed using hybrid composite resin ( tetric ceram , 
 ivoclar - vivadent ) in 1-mm - thick increments and light polymerized ( astralis 10 ; 
 ivocar - vivadent ) for 40 s until the core was restored to predetermined dimensions . the final layer was placed using a transparent matrix to allow for shape consistency 
 between specimens . the dimensions of the prepared cores were confirmed with a 
 measuring microscope with 30x magnification lens with precision of 5 um . a single - phase impression was made using polyvinylsiloxane impression material 
 ( virtual , ivoclar - vivadent ) and master dies were fabricated with type 4 die stone 
 ( jad stone , whip mix , louisville , kentucky , usa ) . a press ceramic ( e max , a3 , 
 ivoclar - vivadent ) was selected to fabricate all - ceramic crowns of the restored 
 specimens . crown dimensions were standardized by using a mold for the external shape 
 of each specimen . the fitting surface of the crowns was pretreated with hydrofluoric 
 acid ( ips ceramic etching gel , ivoclar - vivadent ) for 20 s , rinsed off , air dried , 
 silanized for 60 s and air dried . dentine primer liquids were mixed and applied on 
 the whole prepared tooth surface for 15 s. resin cement was dispensed from the 
 automix syringe directly into the inner surface of the crowns which were seated and 
 held in position under fixed load of 20 n ; excess resin was removed immediately with 
 a micro brush . exposed margins were covered with glycerin gel and rinsed off after 
 complete polymerization of the resin cement . the specimens were stored in distilled 
 water at 37c for 7 days prior to testing . all specimens were subjected to cyclic loading according to the following regime : 
 sinusoidal load between 50 and 200 n at a rate of 2 hertz . all specimens received 
 15,000 cycles and surface damage was prevented by insertion of a 0.5 mm silicon sheet 
 between the occlusal surface of the ceramic crown and the loading indenter ( 3 mm 
 diameter ) of the pneumatically activated loading machine . after completion of cyclic 
 loading , a universal testing machine ( instron 8500 plus , instron , 100 royal st . canton , ma , usa ) was used to deliver a compressive load to the specimens at a 
 crosshead speed of 1 mm / min at 45 degree angle to the long axis of the teeth ( root 
 apex tilted lingually ) until failure . load - time curves were recorded using a 
 universal testing machine s computer software . the 
 failure load of the specimen was determined when the forceversus - time graph showed an 
 abrupt change in load , indicating a sudden decrease in the specimen s resistance to 
 compressive loading . after loading , the failure mode recorded for each specimen and classified as either 
 favorable facture above the cement - enamel junction ( repairable ) or catastrophic 
 fracture of the root below cement - enamel junction ( non repairable ) . these inspections 
 were made using a stereomicroscope ( stereoscopic zoom microscope , smz-1000 , nikon , 
 japan ) and during inspection , the teeth were trans - illuminated with a fiber optic 
 cable . complete or partial debonding of the crown or of the post and core were also 
 considered as favorable failure modes . data were analyzed statistically by one - way 
 anova and tukey s post - hoc test was used for pair - wise comparisons 
 ( =0.05 ) . statistical analysis revealed no significant differences between the failure load of the 
 tested groups and the control group restored without fiber post 
 ( p<0.780 ) . although fracture resistance of the control group was 
 comparable to that of the other groups that received fiber post , there was a higher 
 catastrophic failure rate ( 70% ) in the control specimens in the form of vertical root 
 fracture . the groups restored with fiber post , on the other hand , had almost complete 
 favorable fracture in the form of cervical fracture above the cervical line , previous 
 data are summarized in table 1 . failure load ( standard deviation ) and failure type of tested groups similar superscript letter indicates no significant difference between 
 different test groups in all specimens , the cemented ceramic crown was fractured without evidence of debonding 
 of either the crown or the cemented post . the internal surface of the fractured ceramic 
 fragments demonstrated evidence of resin cement and part of the core material indicating 
 cohesive fracture of the resin core . considering the results obtained in this study , different ferrule heights did not 
 improve the fracture resistance or the failure pattern of the tested specimens . on the 
 other hand , the use of fiber posts with a modulus of elasticity close to that of dentin 
 changed the catastrophic failure type of the control group to almost complete favorable 
 fracture for the other four groups . the 
 dynamic cyclic loading program was intended to quickly screen any possible weakness in 
 the cemented restorations . providing occlusal protection prevented generation of cone 
 cracks in the brittle ceramic crowns which was the reason why all specimens survived 
 without failure . longer periods of cyclic loading are required to shed light on the 
 long - term performance of these restorations , but investigating this issue was not within 
 the scope of this study . the results of the fracture resistance test showed that the amount of residual coronal 
 structure ( ferrule height ) did not increase significantly the fracture resistance of 
 endodontically treated teeth . these results are in agreement with those of previous 
 studies ; while contrary 
 results were reported by other authors . this could be 
 explained by the fact that fiber posts transmitted the forces and distributed the 
 loading stresses over a bigger surface area of the tooth structure similarly for all 
 tested groups . these results may also be interpreted as the resin 
 bonded fiber posts with resin composite core exerted a reinforcing effect by supporting 
 the remaining tooth structure regardless of the ferrule design . these 
 non - metallic post systems have gained widespread popularity in recent years because of 
 other advantages such as their superior esthetics , ease of retrievability , and simple 
 application technique , which allow the clinician to complete the procedure in a single 
 short appointment . according to the results of the present study , specimens in the control group ( no fiber 
 post ) revealed higher catastrophic failure rate compared to the other groups , which 
 indicates that insertion of a fiber post may enhance the clinical performance of 
 endodontically treated teeth even if the failure load remains relatively not 
 effected . the presence of a uniform 1-mm - thick coronal structure 
 ( group 2 ) resulted in the highest fracture resistance value , especially when compared to 
 the control group , which is in agreement with the results of previous studies . a point of clinical relevance is that the fracture resistance of specimens with 
 non - uniform coronal structure ( group 3 and 4 ) was lower than the specimens without a 
 ferrule ( group 5 ) , with consideration to maintaining as much as possible of sound tooth 
 structure . it could be advised to adjust the coronal structure evenly to provide a flat 
 seat for the core build up material , which could improve the fracture resistance of 
 endodontically , treated teeth . lithia disilicate - based all - ceramic crowns were used in this study because of its high 
 flexural strength ( 400 mpa ) , easily etched using hydrofluoric acid , readily silanized 
 and bonded with any suitable resin cement . it has also been reported that the mean 
 chewing force of adults ranges between 7 to 15 kg , and the maximum biting force could 
 reach up to 90 kg . as the fracture 
 loads in all groups in the present study were found to be greater than the ordinary 
 chewing force , and even greater than the maximum biting force , their mechanical strength 
 could be considered satisfactory from a clinical point of view . in terms of the failure modes , the obtained results are in accordance with those of 
 previous studies , showing that the application of fiber posts resulted in 
 more favorable fracture patternswhile 
 the specimens restored without posts showed a higher incidence of catastrophic failure . it could be postulated that specimens restored with fiber - reinforced post systems 
 offered more homogenous stress distribution due to their modulus of elasticity close to 
 that of dentin resulting in a better stress distribution that occurs at the post - dentin 
 interface . this could explain why all favorable fractures were 
 limited to the cervical portion of the root including the core - dentin interface , since 
 the stresses were concentrated in the cervical area and the outer root surface . 
 supporting this opinion is the cohesive fracture of the resin core material , which 
 remained attached to the fractured segments of ceramic crowns , thus indicating good bond 
 strength between the core build up material and the cemented ceramic crown . the limited 
 number of specimens and the difficulty related to reproducing the complexity of 
 functional loads in the oral environment may be some of the shortcomings of the present 
 study . further investigations including finite element analysis and long - term cyclic 
 loading studies are recommended to complement the present study . within the limitations of this study , it may be concluded that increasing the ferrule 
 length did not improve the fracture resistance of endodontically treated teeth restored 
 with glass ceramic crowns . insertion of a fiber post could reduce the percentage of 
 catastrophic failure of these restorations under functional loads .
objectivethis study investigated the effect of different ferrule heights on endodontically 
 treated premolars.materials and methodsfifty sound mandibular first premolars were endodontically treated and then 
 restored with 7-mm fiber post ( frc postec plus # 1 ivoclar - vivadent ) luted with 
 self - polymerized resin cement ( multilink , ivoclar vivadent ) while the coronal 
 section was restored with hybrid composite core build - up material ( tetric ceram , 
 ivoclar - vivadent ) , which received all - ceramic crown . 
 different ferrule heights 
 were investigated : 1-mm circumferential ferrule without post and core ( group 1 
 used as control ) , a circumferential 1-mm ferrule ( group 2 ) , non - uniform ferrule 
 2-mm buccally and 1-mm lingually ( group 3 ) , non - uniform ferrule 3-mm buccally and 
 2-mm lingually ( group 4 ) , and finally no ferrule preparation ( group 5 ) . 
 the 
 fracture load and failure pattern of the tested groups were investigated by 
 applying axial load to the ceramic crowns ( n=10 ) . 
 data were analyzed statistically 
 by one - way anova and tukey s post - hoc test was used for pair - wise 
 comparisons ( =0.05).resultsthere were no significant differences among the failure load of all tested groups 
 ( p<0.780 ) . 
 the control group had the lowest fracture resistance 
 ( 891.43202.22 n ) and the highest catastrophic failure rate 
 ( p<0.05 ) . compared to the control group , the use of fiber post reduced the 
 percentage of catastrophic failure while increasing the ferrule height did not 
 influence the fracture resistance of the restored specimens.conclusionswithin the limitations of this study , increasing the ferrule length did not 
 influence the fracture resistance of endodontically treated teeth restored with 
 glass ceramic crowns . 
 insertion of a fiber post could reduce the percentage of 
 catastrophic failure of these restorations under function .