Fracture Strength of Tooth Roots following Canal Preparation by Hand and Rotary Instrumentation

doi:10.1097/01.don.0000150947.90682.a0

Journal of Endodontics

Volume 31, Issue 7, July 2005, Pages 529-532

https://doi.org/10.1097/01.don.0000150947.90682.a0 Get rights and content

Abstract

The study aimed to determine fracture loads in tooth roots after canal preparation using different techniques. Mesiobuccal roots of 39 extracted mandibular molars were used. Three groups each of 13 roots were prepared by stainless steel hand files (K-files), and two rotary nickel-titanium techniques (Lightspeed and Greater Taper files). After obturation, a vertical load was applied by means of a spreader inserted into the canal until fracture occurred. The mean fracture load was 10.2 ± 4.4 kg for K-files, 15.7 ± 9.1 kg for Lightspeed and 13.2 ± 6.1 kg for Greater Taper files, but differences were not statistically significant (p > 0.05). Most fracture lines were incomplete fractures on the buccal surface, followed by proximal and compound fractures. Greater apical enlargement (Lightspeed) or increased canal taper (Greater Taper files) did not increase fracture susceptibility of tooth roots.

Section snippets

Materials and Methods

Human mandibular first and second molars extracted for routine clinical reasons were stored in 10% neutral buffered formalin for at least 2 weeks and then in distilled water until they were tested. The teeth were thoroughly cleaned with an ultrasonic scaler and examined by the naked eye for immature root apices, cracks on the root surface, fused mesial canals, gross caries involving the root, and for exceptionally short, thin, or curved roots. Teeth with these characteristics were discarded.

Load at Fracture

In Table 2 and Fig. 1 the fracture loads of the roots in the three groups are shown. LS showed the highest fracture load (15.7 ± 9.1 kg), followed by GT files (13.2 ± 6.1 kg) and then K-files (10.2 ± 4.4 kg). Fracture loads ranged from as low as 4.0 kg to a high of 38.5 kg across the three instrumentation groups, with a four- to eight-fold range in each group. The differences between groups were not statistically significant at the 95% confidence level (p = 0.132). It should be noted that one

Discussion

Resistance to fracture is an important consideration in endodontics, and in subsequent restoration and function. The root may be weakened by excessive removal of dentin during canal preparation or post space preparation, increasing susceptibility to root fracture. Experimental techniques for investigating root fracture have generally involved the generation of force within the canal space by means of a spreader inserted into the obturated canal (2, 3, 16, 17, 18). Loading of the canal walls may

Acknowledgements

This study was carried out as an undergraduate summer research project supported by a research grant from the Australian Dental Research Foundation Inc.

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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
2021, Journal of Endodontics
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.
Influence of Progressive Versus Minimal Canal Preparations on the Fracture Resistance of Mandibular Molars: A 3-Dimensional Finite Element Analysis
2021, Journal of Endodontics
This study compared the residual tooth strength and stress distribution of a mandibular molar prepared with different variable tapered file systems using finite element analysis (FEA).
Two preaccessed mandibular molar TruTeeth (Endo 3DP; Acadental, Lenexa, KS) were subjected to simulated endodontic treatment in this study. One tooth was instrumented with ProTaper Gold (Dentsply Tulsa Dental Specialties, Tulsa, OK), and the other was instrumented with V-Taper 2H (SS White Dental, Lakewood, NJ). The 2 teeth were scanned using micro–computed tomographic imaging, and stereolithographic surface meshes were developed for FEA. Each model was subjected to a 200-N multipoint load-simulating mastication. The results of the FEA provided quantitative and qualitative measurements for von Mises stress distribution and total deformation.
The maximum von Mises stress was greater in the ProTaper Gold–prepared model than the V-Taper 2H prepared model. In both models, total deformation values were highest in the clinical crown on the buccal aspect of the tooth. The highest stress values were found in the pericervical dentin, and stress decreased apically through the root.
Within the limitations of this study, it can be concluded that the maximum stress values within the tooth prepared by ProTaper Gold were higher than those in the tooth prepared by V-Taper 2H. Canal preparation with the V-Taper 2H system preserves more pericervical dentin, which may increase the resistance to fracture.
Relationship between Canal Enlargement and Fracture Load of Root Dentin Sections
2019, Dental Materials
To investigate the effect of endodontic instrumentation on fracture susceptibility of root
dentin using experiments and stress analysis.
Root canals of lower premolars were enlarged with different tapers. After, teeth were cut into 2-mm sections. A metal rod of the same taper was pushed through the center of the sections using a universal test system to fracture them. The fracture load was determined from the peak load on the load-displacement curve. To determine fracture-causing stress, an axisymmetric FE model was created. An analytical solution was developed to understand the relationship between fracture load, geometrical and material parameters.
For the same taper, increased root canal diameter did not lead to reduced fracture load. Both analytical and FE solutions showed positive linear relationship between fracture load and enlarged root canal diameter. The hoop stress was maximum at inner surface of enlarged root canal and reduced with increasing radial distance from the center. Bending of sections introduced further nonuniform stresses along the depth. Predictions for the fracture load based on the maximum hoop stress were closest to experimental values; however, account must be taken of the variation in fracture stress of dentin along the root length.
Significance Our results rejected the hypothesis that fracture load of root dentin sections reduced with endodontic instrumentation size. However, the stress distributions in whole endodontically treated teeth are more complicated. Thus, caution is necessary when using thin root sections to investigate the effect of endodontic instruments on vertical root fracture.
Root Reinforcement after Obturation with Calcium Silicate–based Sealer and Modified Gutta-percha Cone
2018, Journal of Endodontics
A root canal obturated with a calcium silicate–based sealer (bioceramic sealer [BCS]) and a modified gutta-percha cone (bioceramic cone [BCC]) might improve the fracture resistance of the root. The objective of this study was to evaluate root reinforcement of a bioceramic cone/sealer (TotalFill; FKG Dentaire SA, La Chaux-de-Fonds, Switzerland) by investigating the fracture resistance, push-out bond strength, sealer penetration, and modulus of elasticity (MOE) in comparison with gutta-percha/AH Plus (Dentsply Maillefer, Tulsa, OK) (GP/AH).
Eighty-four roots from bilateral mandibular premolars were prepared. For fracture resistance, 40 teeth were randomly divided into 4 groups (n = 10 each): intact roots (negative control), prepared roots (positive control), and the roots obturated with either BCC/BCS or GP/AH. Root canals were obturated with the matched single-cone technique and vertically loaded with a spreaderlike tip until fracture. For push-out bond strength (n = 10 each), coronal, middle, and apical root slices of BCC/BCS and GP/AH were loaded with a cylindrical plunger, and failure modes were determined. Sealer penetration of BCC/BCS and GP/AH (n = 12 each) was evaluated for the maximum depth and the circumferential and total area of penetration at the coronal, middle, and apical levels using confocal laser scanning microscopy. The MOE was investigated according to ISO 4049:2000.
The fracture load of BCC/BCS, GP/AH, and the intact roots was not significantly different but significantly higher than the prepared, nonobturated roots. BCC/BCS provided a higher bond strength, maximum depth, and circumferential penetration at the apical root level as well as a greater sealer penetration area at all levels compared with GP/AH. The MOE of all materials was much lower than dentin.
BCC/BCS and GP/AH bonded and reinforced the prepared roots; their fracture resistances were similar to the intact roots.
Impact of Access Cavity Design and Root Canal Taper on Fracture Resistance of Endodontically Treated Teeth: An Ex Vivo Investigation
2018, Journal of Endodontics
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.
In Vitro Comparative Study of the Influence of Instrument Taper on the Fracture Resistance of Endodontically Treated Teeth: An Integrative Approach–based Analysis
2018, Journal of Endodontics
The objective of this study was to examine the influence of instrument taper on the fracture resistance of endodontically treated roots under in vitro experimental conditions.
In total, 58 maxillary canines complying with the inclusion criteria were sectioned at approximately 13 mm from the apex. The roots were standardized with respect to the buccolingual-mesiodistal diameter and weight before being randomly distributed into 3 experimental groups (n = 14) and 1 control group (n = 16). The roots in group 1 were instrumented with hand files up to file 40/.02 and groups 2 and 3 with Mtwo (VDW, Munich, Germany) rotary files up to files 40/.04 and 40/.06, respectively. After mechanical preparation, the roots were obturated with gutta-percha and sealer. Roots in group 4 acted as uninstrumented controls. A vertical load was applied to each specimen using a universal testing machine until the roots fractured. Data were statistically analyzed by introducing an innovative approach integrating 1-way analysis of variance, confirmatory factor analysis, and regression analysis.
The mean fracture load was 357.47 ± 110.54 N for the control group, 338.86 ± 105.23 N for group 1, 297.74 ± 77.31 N for group 2, and 280.10 ± 68.51 N for group 3. However, only the difference between group 3 and the control group was statistically significant (P < .05).
After instrumentation using hand files up to file 40/.02 and rotary files up to files 40/.04 and 40/.06, only the last appeared to change the fracture resistance of endodontically treated roots.

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Basic Research—TechnologyFracture Strength of Tooth Roots following Canal Preparation by Hand and Rotary Instrumentation

Abstract

Section snippets

Materials and Methods

Load at Fracture

Discussion

Acknowledgements

J Endod

J Endod

J Endod

J Endod

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

J Endod

J Endod

J Endod

J Endod

J Endod

Basic Research—Technology
Fracture Strength of Tooth Roots following Canal Preparation by Hand and Rotary Instrumentation