endodontically treated teeth are widely considered to be more susceptible to fracture than vital teeth , and almost always require extraction of the fractured root or entire tooth . the reasons most often reported have been the removal of tooth structure during endodontic treatment , dehydration of dentin after endodontic therapy , and excessive pressure during obturation . these factors probably interact cumulatively to influence tooth loading and distribution of stresses , ultimately increasing the possibility of catastrophic failure . in addition to these factors , intracanal irrigants , medicaments and materials may also play parts in influencing the physical and mechanical properties of dentin , leading to fracture . one of the aims of filling the root canal is to reinforce the root canal dentin to increase the fracture resistance . therefore , the use of a root canal sealer possessing an additional quality of strengthening the root against fracture would be of obvious value . growing interest in reinforcing the root canal system has led to the development of adhesive root canal sealers with the potential to increase fracture resistance . it is thought that adhesion and mechanical interlocking between the material and root canal dentin will strengthen the remaining tooth structure , and thus reduce fracture risk . gutta percha ( gp ) has been the filling material of choice for root canals for years . ah plus is an epoxy resin - based sealer that is commonly used with gp . in recent years , a new resin - based obturation material , it is a dual curable thermoplastic synthetic resin material used with a self - etching primer to create a solid monoblock . the purpose of this in vitro study was to determine the resistance to fracture of root canals obturated with three different materials . sixty freshly extracted , intact , non - carious human mandibular premolar teeth that were going for orthodontic extraction were used for the present study . all soft tissue and debris on the teeth were removed using an ultrasonic scaler and the teeth were examined under stereomicroscope at 25x magnification to rule out any pre - existing root fractures , cracks , and craze lines . standard endodontic access cavities were prepared and the patency of the apical foramen was determined with a size 10 k file . all root canals were instrumented using the rotary protaper system to size f3 , corresponding to an apical size 30 . 10 ml of 5.25% sodium hypochlorite was used as an irrigant in between successive files . the smear layer was removed by irrigation with 10 ml 17% edta solution and 10 ml sodium hypochlorite , each for 3 min . all canals were dried with paper points and divided into four experimental groups of 15 teeth each , depending on type of obturating material used , as follows : group 1 - ah plus root canal sealer ( dentsply - detrey , switzerland ) was mixed as per manufacturer 's recommendations and teeth were obturated with gp using the lateral compaction technique . group 2 - the resilon - epiphany system ( resilon - resilon research llc , madison , ct , usa ; epiphany - pentron clinical technologies , wallingford , ct , usa ) was used in accordance with manufacturer 's recommendations and teeth were obturated using the lateral compaction technique . group 3 - zinc oxide - eugenol was mixed to sealer consistency and the teeth were obturated with gp using the lateral compaction technique . excess material was seared off from the orifice and access cavity was sealed with cavit g. the quality of root canal fillings was confirmed radiographically . all the roots were stored at 37c in 100% relative humidity for 1 week to ensure complete set of sealers . ltd , new delhi , india ) blocks , exposing 8 mm of root length . fracture strength testing was done using a universal testing machine ( wdw-5tc , shinae corp . , a metal indenter of 5 mm diameter was fixed to the upper arm of the universal testing machine which was set to deliver an increasing load until fracture occurred . a cross head speed of 1 mm / min was set and the load was applied vertically down to the long axis of the tooth . data thus obtained was evaluated statistically using one - way anova and the unpaired t - test to determine the significance of the difference between different groups . all the values of four groups are expressed in terms of mean  sd [ table 1 , figure 2 ] . one - way anova showed a significant difference among all groups at 5% level of significance ( p<0.05 ) . further unpaired t - test revealed significant difference between group 1 and 2 ( p<0.05 ) and no significant difference between control group and group 3 . mean and standard deviation (  ) of the four groups mean and standard deviation among the four groups of material however , it is understood that as dentin is removedduring the instrumentation phase , a weakening effect on theroot is inevitable . , we evaluated a new thermoplastic synthetic polymerbased on polyester , which contains bioactive and radiopaquefillers . in addition , when used in conjunction with a resin - basedsealant or bonding agent , it forms a monoblock within the canalsthat bonds to the dentinal walls . as per the monoblock concept , the restoration and the tooth act as single unit under occlusal stress.because the resin core , sealant , and dentinal wall are all  attached ,  it appears logical thatthey have the potential to strengthen the walls against fracture . we used plain zinc oxide - eugenol sealer and the lateral compaction technique , as we wanted to test new adhesive materials with the most commonly used one . when extracted human teeth are used for this type of a study , the potential for large uncontrollable variations in strength exists . each group of root specimens that was usedconsisted of randomly selected human mandibular premolar teeth from patients of similar age group going for orthodontic extractions . as done in previous studies we controlledsome dimensions of the specimens , such as root length and bucco - lingualdiameter . in order to standardize the apical canal diameter of the enlarged root canal , all roots were prepared to protaper size f3 , corresponding to an apical size 30 . a standard irrigation regimen , using edta and sodium hypochlorite , was used to remove the smear layer as this combination has been shown to enhance bonding of the materials tested to the dentinal surface of the root . as in other mechanical studies , the force was applied along the long axis of the root with a rounded punch , which produced root fracture when contact was made between the punch and the wall of the canal opening . the force in the present study was applied at an angle of zero degree , resulting in primarily a splitting stress applied over the access opening . this would result in smaller stresses because of decreased bending moments and maximum stresses located much more cervically . this study design is said to be more clinically relevant as it better simulates the support given to healthy teeth by alveolar bone , and results in less catastrophic stress build - ups caused by unrealistic bending movements . in this study , the highest mean fracture value was found in the teeth obturated with gp and ah plus ( group 1 ) which was significantly greater than that seen in teeth obturated with the resilon - epiphany system ( group 2 ) . this may be a result of greater adhesion of ah plus to root dentin than epiphany . ah plus has better penetration into the microirregularities because of its creep capacity and long setting time , which increases the mechanical interlocking between the sealer and root dentin . the results of this study can be correlated to the work done by gesi et al . ( 2005 ) who concluded in their study that the epiphany sealer and resilon core combination shows lower bond strength values as compared to the ah plus and gp core combination . this might be because of weak chemical coupling of the resin - based sealer to resilon , which may be due to the fact that amount or method of dimethacrylate incorporation in resilon may not be optimized for predictable chemical coupling . this weak bonding between the epiphany sealer and resilon core was further substantiated by work done by tay et al . the fracture resistance of the zoe - gp group ( group 3 ) was not significantly different from the control group ( group 4 ) . within the limitations of the present study , it can be concluded that teeth obturated with ah plus + gp are more resistant to fracture than those obturated with resilon - epiphany , and no statistically significant difference was found between the zinc oxide - eugenol - gp group and unobturated group .
the aim of this study was to evaluate the in vitro effect of various obturating materials on fracture resistance of root canal treated teeth . 
 sixty freshly extracted human mandibular premolars were used . after standardizing the length to 13 mm , the teeth were biomechanically prepared and divided into four groups based on type of obturating materials used . 
 teeth were embedded in acrylic resin and fracture strength was measured using a universal testing machine . 
 data obtained was evaluated statistically using one - way anova and the unpaired t - test . 
 teeth obturated with ah plus and gutta percha showed higher fracture resistance than those obturated with resilon - epiphany . 
 the results suggested that the group obturated with gutta percha and zinc oxide - eugenol sealer had the lowest fracture resistance . 
 no statistically significant difference was found between the unobturated ( control ) group and the zinc oxide - eugenol group .