Impact of Access Cavity Design and Root Canal Taper on Fracture Resistance of Endodontically Treated Teeth: An Ex Vivo Investigation


      • We assessed the effect of the root canal taper and access cavity design on the fracture resistance of endodontically treated teeth.
      • We tried to answer whether conservative access cavity can increase the tooth fracture resistance compared to traditional access cavity design.
      • Also, the effect of 0.04, 0.06, and 0.08 tapers on root fracture resistance was evaluated.



      The susceptibility of endodontically treated teeth (ETT) to fracture is mainly associated with the loss of tooth structure. This study evaluated the effect of the access cavity design and taper preparation of root canals on ETT fracture resistance of maxillary molars.


      For tapering assessment, 30 sound distobuccal roots of maxillary molars were randomly assigned to 1 of 3 groups (n = 10): a .04 taper, a .06 taper, or a .08 taper. Endodontic canal preparations were performed using the Twisted Files rotary system (Kerr Co, Glendora, CA). In addition, 48 intact maxillary first and second molars were randomly assigned to 1 of 3 groups (n = 16) for cavity preparation approaches: intact teeth, traditional access cavity (TAC), or conservative access cavity (CAC). Fracture resistance was tested using a universal testing machine. For statistical analysis, the level of significance was P ≤ .05.


      The .04 taper instrumentation had the highest fracture resistance (259.61 ± 52.06), and the .08 taper had the lowest (168.43 ± 59.63). The .04 and .06 groups did not differ significantly (P > .05); however, these groups differed significantly from the .08 group (P ≤ .05). Regarding the cavity preparation approaches, the 3 groups of intact teeth, CAC, and TAC showed fracture resistance mean values of 2118.85 ± 336.97, 1705.69 ± 591.51, and 1471.11 ± 435.34, respectively, with no significant difference between the CAC and TAC groups (P > .05).


      Increasing the taper of the root canal preparation can reduce fracture resistance. Moreover, access cavity preparation can reduce resistance; however, CAC in comparison with TAC had no significant impact.

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        • Lam P.P.
        • Palamara J.E.A.
        • Messer H.H.
        Fracture strength of tooth roots following canal preparation by hand and rotary instrumentation.
        J Endod. 2005; 31: 529-532
        • Al Amri M.D.
        • Al-Johany S.
        • Sherfudhin H.
        • et al.
        Fracture resistance of endodontically treated mandibular first molars with conservative access cavity and different restorative techniques: an in vitro study.
        Aust Endod J. 2016; 42: 124-131
        • Lang H.
        • Korkmaz Y.
        • Schneider K.
        • Raab W.-M.
        Impact of endodontic treatments on the rigidity of the root.
        J Dent Res. 2006; 85: 364-368
        • Bóveda C.
        • Kishen A.
        Contracted endodontic cavities: the foundation for less invasive alternatives in the management of apical periodontitis.
        Endod Topics. 2015; 33: 169-186
        • Moore B.
        • Verdelis K.
        • Kishen A.
        • et al.
        Impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in maxillary molars.
        J Endod. 2016; 42: 1779-1783
        • Clark D.
        • Khademi J.A.
        Case studies in modern molar endodontic access and directed dentin conservation.
        Dent Clin North Am. 2010; 54: 275-289
        • Clark D.
        • Khademi J.
        Modern molar endodontic access and directed dentin conservation.
        Dent Clin North Am. 2010; 54: 249-273
        • Gluskin A.H.
        • Peters C.I.
        • Peters O.A.
        Minimally invasive endodontics: challenging prevailing paradigms.
        Br Dent J. 2014; 216: 347-353
        • Patel S.
        • Rhodes J.
        A practical guide to endodontic access cavity preparation in molar teeth.
        Br Dent J. 2007; 203: 133-140
        • Capar I.D.
        • Altunsoy M.
        • Arslan H.
        • et al.
        Fracture strength of roots instrumented with self-adjusting file and the ProTaper rotary systems.
        J Endod. 2014; 40: 551-554
        • Harvey T.E.
        • White J.T.
        • Leeb I.J.
        Lateral condensation stress in root canals.
        J Endod. 1981; 7: 151-155
        • Schroeder K.P.
        • Walton R.E.
        • Rivera E.M.
        Straight line access and coronal flaring: effect on canal length.
        J Endod. 2002; 28: 474-476
        • Krishan R.
        • Paqué F.
        • Ossareh A.
        • et al.
        Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars.
        J Endod. 2014; 40: 1160-1166
        • Shahrbaf S.
        • Mirzakouchaki B.
        • Oskoui S.S.
        • Kahnamoui M.A.
        The effect of marginal ridge thickness on the fracture resistance of endodontically-treated, composite restored maxillary premolars.
        Oper Dent. 2007; 32: 285-290
        • Tzimpoulas N.E.
        • Alisafis M.G.
        • Tzanetakis G.N.
        • Kontakiotis E.G.
        A prospective study of the extraction and retention incidence of endodontically treated teeth with uncertain prognosis after endodontic referral.
        J Endod. 2012; 38: 1326-1329
        • Touré B.
        • Faye B.
        • Kane A.W.
        • et al.
        Analysis of reasons for extraction of endodontically treated teeth: a prospective study.
        J Endod. 2011; 37: 1512-1515
        • Assif D.
        • Nissan J.
        • Gafni Y.
        • Gordon M.
        Assessment of the resistance to fracture of endodontically treated molars restored with amalgam.
        J Prosthet Dent. 2003; 89: 462-465
        • Linn J.
        • Messer H.H.
        Effect of restorative procedures on the strength of endodontically treated molars.
        J Endod. 1994; 20: 479-485
        • Cobankara F.K.
        • Unlu N.
        • Cetin A.R.
        • Ozkan H.B.
        The effect of different restoration techniques on the fracture resistance of endodontically-treated molars.
        Oper Dent. 2008; 33: 526-533
        • Bremer B.D.
        • Geurtsen W.
        Molar fracture resistance after adhesive restoration with ceramic inlays or resin-based composites.
        Am J Dent. 2001; 14: 216-220
        • Soares C.J.
        • Pizi E.C.G.
        • Fonseca R.B.
        • Martins L.R.M.
        Influence of root embedment material and periodontal ligament simulation on fracture resistance tests.
        Braz Oral Res. 2005; 19: 11-16
        • Molinaro J.D.
        • Diefenderfer K.E.
        • Strother J.M.
        The influence of a packable resin composite, conventional resin composite and amalgam on molar cuspal stiffness.
        Oper Dent. 2002; 27: 516-524
        • Mannan G.
        • Smallwood E.R.
        • Gulabivala K.
        Effect of access cavity location and design on degree and distribution of instrumented root canal surface in maxillary anterior teeth.
        Int Endod J. 2001; 34: 176-183
        • Belli S.
        • Erdemir A.
        • Ozcopur M.
        • Eskitascioglu G.
        The effect of fibre insertion on fracture resistance of root filled molar teeth with MOD preparations restored with composite.
        Int Endod J. 2005; 38: 73-80
        • Reeh E.S.
        • Messer H.H.
        • Douglas W.H.
        Reduction in tooth stiffness as a result of endodontic and restorative procedures.
        J Endod. 1989; 15: 512-516
        • Ree M.
        • Schwartz R.S.
        The endo-restorative interface: current concepts.
        Dent Clin North Am. 2010; 54: 345-374
        • Kishen A.
        Mechanisms and risk factors for fracture predilection in endodontically treated teeth.
        Endod Topics. 2006; 13: 57-83
        • Tang W.
        • Wu Y.
        • Smales R.J.
        Identifying and reducing risks for potential fractures in endodontically treated teeth.
        J Endod. 2010; 36: 609-617
        • Rover G.
        • Belladonna F.G.
        • Bortoluzzi E.A.
        • et al.
        Influence of access cavity design on root canal detection, instrumentation efficacy, and fracture resistance assessed in maxillary molars.
        J Endod. 2017; 43: 1657-1662
        • Plotino G.
        • Grande N.M.
        • Isufi A.
        • et al.
        Fracture strength of endodontically treated teeth with different access cavity designs.
        J Endod. 2017; 43: 995-1000
        • Kalburge V.
        • Yakub S.S.
        • Kalburge J.
        • et al.
        A comparative evaluation of fracture resistance of endodontically treated teeth, with variable marginal ridge thicknesses, restored with composite resin and composite resin reinforced with Ribbond: an in vitro study.
        Indian J Dent Res. 2013; 24: 193-198
        • Zehnder M.S.
        • Connert T.
        • Weiger R.
        • et al.
        Guided endodontics: accuracy of a novel method for guided access cavity preparation and root canal location.
        Int Endod J. 2016; 49: 966-972
        • Shovelton D.S.
        The presence and distribution of microorganisms within non-vital teeth.
        Br Dent J. 1964; 117: 101-107
        • Kishen A.
        • Kumar G.V.
        • Chen N.N.
        Stress–strain response in human dentine: rethinking fracture predilection in postcore restored teeth.
        Dent Traumatol. 2004; 20: 90-100
        • Zandbiglari T.
        • Davids H.
        • Schäfer E.
        Influence of instrument taper on the resistance to fracture of endodontically treated roots.
        Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006; 101: 126-131
        • Adorno C.G.
        • Yoshioka T.
        • Jindan P.
        • et al.
        The effect of endodontic procedures on apical crack initiation and propagation ex vivo.
        Int Endod J. 2013; 46: 763-768