This study aimed to evaluate the effects of root canal enlargement on the danger zone (DZ) of mandibular molars.
Thirty mesial roots of mandibular first molars were scanned in micro-computed tomography (S1). Canals were sequentially enlarged with rotary instruments up to sizes 30/0.04 (S2) and 30/0.06 (S3). The dentin thickness was measured at 0.1-mm intervals after each preparation step (n = 2964 slices). Root level and position of the DZ were also recorded. Data were compared using analysis of variance with Bonferroni pairwise comparison, Cochran's Q method, and Pearson's test (α = 5%).
Comparing the specimens before (S1) and after (S2 and S3) preparations showed a significant reduction in the thickness of the DZ (P < .05), as well as between S2 and S3 steps (P < .05). At S1, the DZ was mostly located in the middle third of the root, but after preparation, it shifted toward the coronal direction (P < .05). Both S2 (P = .004, r = 0.508) and S3 (P = .004, r = 0.506) preparation steps showed a positive correlation between canal length and the root level of the DZ. At S1, the DZ was positioned toward the distal and mesial in 73.4% (n = 22) and 26.6% (n = 8) of the specimens, respectively. After S3, the number of specimens with DZ positioned toward the mesial aspect of the root significantly reduced to 3.3% (n = 1), whereas none of the specimens with DZ positioned toward the distal changed its position after root canal enlargements (P > .05).
Overall, the enlargement of mesial canals of mandibular first molars with final instruments sizes 30/0.04 and 30/0.06 affected the thickness, root level, and position of the DZ.
To read this article in full you will need to make a payment
Purchase one-time access:Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
One-time access price info
- For academic or personal research use, select 'Academic and Personal'
- For corporate R&D use, select 'Corporate R&D Professionals'
Subscribe:Subscribe to Journal of Endodontics
Already a print subscriber? Claim online access
Already an online subscriber? Sign in
Register: Create an account
Institutional Access: Sign in to ScienceDirect
- Mechanical preparation of root canals: shaping goals, techniques and means.Endod Topics. 2005; 10: 30-76
- Current challenges and concepts in the preparation of root canal systems: a review.J Endod. 2004; 30: 559-567
- The effect of root canal taper on the irrigant flow: evaluation using an unsteady Computational Fluid Dynamics model.Int Endod J. 2010; 43: 909-916
- Accumulated hard tissue debris produced during reciprocating and rotary nickel-titanium canal preparation.J Endod. 2015; 41: 676-681
- Cleaning and shaping the root canal.Dent Clin North Am. 1974; 18: 269-296
- Mastering Endodontic Instrumentation. Ramsey.Arbor Books, Inc, 2007
- Histological evaluation of the effectiveness of increased apical enlargement for cleaning the apical third of curved canals.Int Endod J. 2010; 43: 988-994
- Effect of different apical preparation sizes on outcome of primary endodontic treatment: a randomized controlled trial.J Endod. 2012; 38: 1309-1315
- The quality of apical canal preparation using hand and rotary instruments with specific criteria for enlargement based on initial apical file size.J Endod. 2002; 28: 658-664
- Present status and future directions–Minimal endodontic access cavities.Int Endod J. 2022; 55: 531-587
- The anticurvature filing method to prepare the curved root canal.J Am Dent Assoc. 1980; 101: 792-794
- Root groove depth and inter-orifice canal distance as anatomical predictive factors for danger zone in the mesial root of mandibular first molars.Clin Oral Investig. 2021; 25: 3641-3649
- Thickness of dentine in mesial roots of mandibular molars with different lengths.Int Endod J. 2010; 43: 555-559
- Danger zone analysis using cone beam computed tomography after apical enlargement with K3 and K3XF in a manikin model.J Clin Exp Dent. 2016; 8: e361-e367
- Danger zone in mandibular molars before instrumentation: an in vitro study.J Appl Oral Sci. 2003; 11: 324-326
- Comparison of the relative risk of molar root perforations using various endodontic instrumentation techniques.J Endod. 1983; 9: 439-447
- Evaluation of radicular dentin thickness of danger zone in mandibular first molars.J Dent (Tehran). 2010; 7: 196-199
- The minimum residual root thickness after using ProTaper, RaCe and Gates-Glidden drills: a cone beam computerized tomography study.Eur J Dent. 2015; 9: 228-233
- Thickness of cementum/dentin in mesial roots of mandibular first molars.J Endod. 1992; 18: 545-548
- Prevalence and associated periodontal status of teeth with root perforation: a retrospective study of 2,002 patients' medical records.J Endod. 2010; 36: 797-800
- 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
- The risk of perforation in the curved canal: anticurvature filing compared with the stepback technique.Int Endod J. 1987; 20: 33-39
- Root canal wall thickness of mandibular molars after biomechanical preparation.J Endod. 1985; 11: 257-263
- An anatomic investigation of the mandibular first molar using micro-computed tomography.J Endod. 2013; 39: 1374-1378
- Anatomical danger zone reconsidered: a micro-CT study on dentine thickness in mandibular molars.Int Endod J. 2019; 52: 1501-1507
- Three-dimensional modelling and concurrent measurements of root anatomy in mandibular first molar mesial roots using micro-computed tomography.Int Endod J. 2015; 48: 380-389
- Correlation of root dentin thickness and length of roots in mesial roots of mandibular molars.J Endod. 2014; 40: 1435-1438
- Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature.Int Endod J. 2020; 53: 1618-1635
- Influence of size and taper of basic root canal preparation on root canal cleanliness: a scanning electron microscopy study.Int Endod J. 2019; 52: 343-351
- The efficacy of ultrasonic irrigation to remove artificially placed dentine debris from human root canals prepared using instruments of varying taper.Int Endod J. 2005; 38: 764-768
- Influence of taper of root canal shape on the intracanal bacterial reduction.Open Dent J. 2016; 10: 568-574
- Critical appraisal of published smear layer-removal studies: methodological issues.Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2011; 112: 531-543
- The impact of minimally invasive root canal preparation strategies on the shaping ability of mandibular molars.Int Endod J. 2020; 53: 1680-1688
- The impact of TruNatomy and ProTaper gold instruments on the preservation of the periradicular dentin and on the enlargement of the apical canal of mandibular molars.J Endod. 2022; 48: 650-658
- A laboratory study of the impact of ultraconservative access cavities and minimal root canal tapers on the ability to shape canals in extracted mandibular molars and their fracture resistance.Int Endod J. 2020; 53: 1516-1529
Published online: February 23, 2023
Publication stageIn Press Corrected Proof
© 2023 American Association of Endodontists.