Basic Research| Volume 47, ISSUE 9, P1467-1471, September 2021

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The Effect of Root Canal Preparation Size and Taper of Middle Mesial Canals on Fracture Resistance of the Mandibular Molar Teeth: An In Vitro Study



      The aim of the present study was to investigate the influence of root canal preparation size and taper of middle mesial (MM) canals on fracture resistance of mandibular molars.


      Fifty-five mandibular molar teeth having an MM canal were selected based on the cone-beam computed tomographic analysis. After the decoronation and distal root separation procedure, the lengths of the mesial roots were standardized to 13 mm. The specimens were randomly distributed into 5 groups (n = 11). Mesiobuccal and mesiolingual canals were prepared up to size 30.06 using VDW.ROTATE rotary files (VDW, Munich, Germany). The MM canal was prepared up to size 25.04, 25.06, 30.04, and 30.06, respectively. No preparation was done in the MM canal in the control group. After the irrigation protocol, the canals were obturated with the single-cone technique. A thin layer of silicone-coated specimens was embedded in acrylic resin and subjected to a fracture strength test by a universal testing machine. A vertical force was applied to the roots until they fracture. Statistical analysis was performed with 1-way analysis of variance and post hoc Duncan tests (P = .05).


      There was no significant difference between group 25.04 and the control group, but the fracture strengths of these groups were found to be significantly higher than that of groups 25.06, 30.04, and 30.06 (P < .05).


      Within the limitations of this study, we concluded that increasing the apical diameter and taper in the MM canal reduces the fracture strength of mandibular molar teeth. Among the tested instrumentation sizes, fracture strength decreased significantly when greater than 25.04 instrumentation sizes were chosen.

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        • Card S.J.
        • Sigurdsson A.
        • Ørstavik D.
        • Trope M.
        The effectiveness of increased apical enlargement in reducing intracanal bacteria.
        J Endod. 2002; 28: 779-783
        • Dalton B.C.
        • Ørstavik D.
        • Phillips C.
        • et al.
        Bacterial reduction with nickel-titanium rotary instrumentation.
        J Endod. 1998; 24: 763-767
        • Harvey T.E.
        • White J.T.
        • Leeb I.J.
        Lateral condensation stress in root canals.
        J Endod. 1981; 7: 151-155
        • 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
        • Plotino G.
        • Özyürek T.
        • Grande N.M.
        • Gündoğar M.
        Influence of size and taper of basic root canal preparation on root canal cleanliness: a scanning electron microscopy study.
        J Endod. 2019; 52: 343-351
        • Haueisen H.
        • Gärtner K.
        • Kaiser L.
        • et al.
        Vertical root fracture: prevalence, etiology, and diagnosis.
        Quintessence Int. 2013; 44: 467-474
        • 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 Dent J. 2016; 42: 124-131
        • Lang H.
        • Korkmaz Y.
        • Schneider K.
        • W-H Raab M.
        Impact of endodontic treatments on the rigidity of the root.
        J Dent Res. 2006; 85: 364-368
        • Sabeti M.
        • Kazem M.
        • Dianat O.
        • et al.
        Impact of access cavity design and root canal taper on fracture resistance of endodontically treated teeth: an ex vivo investigation.
        J Endod. 2018; 44: 1402-1406
        • Adorno C.
        • 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
        • Zandbiglari T.
        • Davids H.
        • Schäfer E.
        Influence of instrument taper on the resistance to fracture of endodontically treated roots.
        J Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006; 101: 126-131
        • Lam P.P.
        • Palamara J.E.
        • Messer H.H.
        Fracture strength of tooth roots following canal preparation by hand and rotary instrumentation.
        J Endod. 2005; 31: 529-532
        • Buchanan L.
        The standardized-taper root canal preparation–part 1. Concepts for variably tapered shaping instruments.
        Int Endod J. 2000; 33: 516-529
        • Testori T.
        • Badino M.
        • Castagnola M.
        Vertical root fractures in endodontically treated teeth: a clinical survey of 36 cases.
        J Endod. 1993; 19: 87-90
        • Fuss Z.
        • Lustig J.
        • Tamse A.
        Prevalence of vertical root fractures in extracted endodontically treated teeth.
        Int Endod J. 1999; 32: 283-286
        • Gluskin A.H.
        • Peters C.I.
        • Peters O.A.
        Minimally invasive endodontics: challenging prevailing paradigms.
        Br Dent J. 2014; 216: 347-353
        • Zelic K.
        • Vukicevic A.
        • Jovicic G.
        • et al.
        Mechanical weakening of devitalized teeth: three-dimensional finite element analysis and prediction of tooth fracture.
        Int Endod J. 2015; 48: 850-863
        • Fabra-CampoS H.
        Three canals in the mesial root of mandibular first permanent molars: a clinical study.
        Int Endod J. 1989; 22: 39-43
        • Martínez-Berná A.
        • Badanelli P.
        Mandibular first molars with six root canals.
        J Endod. 1985; 11: 348-352
        • Holtzmann L.
        Root canal treatment of a mandibular first molar with three mesial root canals.
        Int Endod J. 1997; 30: 422-423
        • Jacobsen E.L.
        • Dick K.
        • Bodell R.
        Mandibular first molars with multiple mesial canals.
        J Endod. 1994; 20: 610-613
        • Weine F.S.
        • Kelly R.F.
        • Lio P.J.
        The effect of preparation procedures on original canal shape and on apical foramen shape.
        J Endod. 1975; 1: 255-262
        • Karapinar-Kazandag M.
        • Basrani B.R.
        • Friedman S.
        The operating microscope enhances detection and negotiation of accessory mesial canals in mandibular molars.
        J Endod. 2010; 36: 1289-1294
        • Keleş A.
        • Keskin C.
        • Karataşlıoğlu E.
        • et al.
        Middle mesial canal preparation enhances the risk of fracture in mesial root of mandibular molars.
        J Endod. 2020; 46: 1323-1329
        • Jiang Q.
        • Huang Y.
        • Tu X.
        • et al.
        Biomechanical properties of first maxillary molars with different endodontic cavities: a finite element analysis.
        J Endod. 2018; 44: 1283-1288
        • Teixeira F.
        • Sano C.
        • Gomes B.
        • et al.
        A preliminary in vitro study of the incidence and position of the root canal isthmus in maxillary and mandibular first molars.
        Int Endod J. 2003; 36: 276-280
        • Krikeli E.
        • Mikrogeorgis G.
        • Lyroudia K.
        In vitro comparative study of the influence of instrument taper on the fracture resistance of endodontically treated teeth: an integrative approach–based analysis.
        J Endod. 2018; 44: 1407-1411
        • Uzunoglu E.
        • Aktemur S.
        • Uyanik M.O.
        • et al.
        Effect of ethylenediaminetetraacetic acid on root fracture with respect to concentration at different time exposures.
        J Endod. 2012; 38: 1110-1113
        • Singla M.
        • Aggarwal V.
        • Logani A.
        • Shah N.
        Comparative evaluation of rotary ProTaper, Profile, and conventional stepback technique on reduction in Enterococcus faecalis colony-forming units and vertical root fracture resistance of root canals.
        J Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2010; 109: 105-110
        • Prado M.
        • De Lima N.
        • De Lima C.
        • et al.
        Resistance to vertical root fracture of root filled teeth using different conceptual approaches to canal preparation.
        Int Endod J. 2016; 49: 898-904
        • Souza E.M.
        • Calixto A.M.
        • Lima C.N.
        • et al.
        Similar influence of stabilized alkaline and neutral sodium hypochlorite solutions on the fracture resistance of root canal–treated bovine teeth.
        J Endod. 2014; 40: 1600-1603
        • Adorno C.G.
        • Yoshioka T.
        • Suda H.
        The effect of root preparation technique and instrumentation length on the development of apical root cracks.
        J Endod. 2009; 35: 389-392
        • Yared G.M.
        • Dagher F.E.B.
        Influence of apical enlargement on bacterial infection during treatment of apical periodontitis.
        J Endod. 1994; 20: 535-537
        • Torabinejad M.
        • Khademi A.A.
        • et al.
        A new solution for the removal of the smear layer.
        J Endod. 2003; 29: 170-175
        • Keles A.
        • Keskin C.
        • Alqawasmi R.
        • et al.
        Evaluation of dentine thickness of middle mesial canals of mandibular molars prepared with rotary instruments: a micro-CT study.
        Int Endod J. 2020; 53: 519-528