Effect of root canal treatment procedures with a novel rotary nickel titanium instrument (TRUShape) on stress in mandibular molars: a comparative finite element analysis

Effect of several nickel-titanium rotary systems on stress distribution in mandibular molars under occlusal forces: a finite element analysis

This study assessed the stress distribution under occlusal forces in mandibular molars after utilizing several nickel-titanium rotary systems and identified potential root fracture patterns through finite element analysis (FEA). Five three-dimensionally printed mandibular molars were used, with one tooth left unshaped and the remaining four shaped using ProTaper Gold (Dentsply, Tulsa Dental Specialties, Tulsa, OK), Reciproc Blue (VDW, Munich, Germany), XP-endo Shaper (FKG Dentaire, La Chaux-de-Fonds, Switzerland), and Hyflex EDM (Coltene/Whaledent, Altst€atten, Switzerland) rotary systems. Subsequently, micro-CT scans were performed on the teeth, and representative FEA models were generated. Two distinct loadings, vertical and oblique, were applied, and stress parameters including von Mises stress, maximum principal stress, and minimum principal stress were recorded and compared across groups. Although stress values in both loading conditions correlated with volume increases post-shaping, the stress distribution patterns indicative of potential fractures were comparable across groups. Stresses under oblique loads were observed to be higher than those under vertical loads. Several rotary systems, based on the volumetric changes they induce in dental hard tissues, may elevate stress values throughout the tooth, leading to root fractures in regions where stress concentration occurs. Conservative root canal shaping leads to a lower overall stress concentration. In mandibular molars, oblique forces have a more destructive effect compared to vertical forces.

Cryotherapy Treatment Effect on Heat-Treated Nickel-Titanium (NiTi) Rotary Single-File System: An In Vitro Comparative Study by Finite Element Analysis

Background The use of endodontic files multiple times can cause fatigue in them and can lead to their separation in the root canal. The purpose of this study was to achieve a reduction in cyclic fatigue stress in a newly introduced nickel-titanium (NiTi) rotary single-file system. The study aimed to determine whether cryotherapy could help reduce cyclic fatigue and stress on rotary files after multiple uses during root canal treatment. By utilizing finite element analysis (FEA), the study provided a comprehensive evaluation of how cryotherapy might enhance the performance and longevity of these instruments, ultimately benefiting patients undergoing root canal therapy. Methodology This in vitro comparative study used scanned plastic teeth with genuine root canal anatomy and FEA to investigate the mechanical response to cyclic fatigue and stress of NiTi rotary file system. The endodontic file (Procodile, Komet) was created through the complex root canal geometries, for which mandibular tooth models were scanned and created by a computer software (IDEAS11 NX; UGSiPlano, TX). The total sample size was 34, divided into two groups, with each group comprising 17 participants (n = 17). The results were analyzed by analysis of variance (ANOVA) test. Results The results revealed that the p-values were more than 0.525, indicating no significant reduction in cyclic fatigue when the NiTi rotary single-file system (Procodile, Komet) was treated with cryotherapy (eight cycles). However, stress reduction was observed in the NiTi rotary single-file system when it was treated with cryotherapy. Conclusion This in vitro comparative study concluded that cryotherapy helps to reduce the stress of NiTi rotary single-file system. Nonetheless, more research is needed to understand the clinical significance of the findings of the current in vitro study.

Evaluation of stress distributions of calcium silicate-based root canal sealer in bulk or with main core material: A finite element analysis study

This research aimed to assess the stress distribution in lower premolars that were obturated with BioRoot RCS or AH Plus, with or without gutta percha (GP), and subjected to vertical and oblique forces. One 3D geometric model of a mandibular second premolar was created using SolidWorks software. Eight different scenarios representing different root canal filling techniques, single cone technique with GP and bulk technique with sealer only with occlusal load directions were simulated as follows: Model 1 (BioRoot RCS sealer and GP under vertical load [VL]), Model 2 (BioRoot RCS sealer and GP under oblique load [OL]), Model 3 (AH Plus sealer with GP under VL), Model 4 (AH Plus sealer with GP under OL), Model 5 (BioRoot RCS sealer in bulk under VL), Model 6 (BioRoot RCS in bulk under OL), Model 7 (AH Plus sealer in bulk under VL), and Model 8 (AH Plus sealer in bulk under OL). A static load of 200 N was applied at three occlusal contact points, with a 45° angle from lingual to buccal. The von Mises stresses in root dentin were higher in cases where AH Plus was used compared to BioRoot RCS. Furthermore, shifting the load to an oblique direction resulted in increased stress levels. Replacing GP with sealer material had no effect on the dentin maximum von Mises stress in BioRoot RCS cases. Presence of a core material resulted in lower stress in dentin for AH Plus cases, however, it did not affect the stress levels in dentin for cases filled with BioRoot RCS. Stress distribution in the dentin under oblique direction was higher regardless of sealer or technique used.

Improvement and analysis of mechanistic modeling of root canal preparation by a computer-based method

BACKGROUND AND OBJECTIVE

Root canal preparation is a cutting process between nickel-titanium (Ni-Ti) file and root canal, which aims to remove the bacteria and to keep teeth from infection. A mechanistic model in root canal preparation is proposed to investigate the mechanical mechanism of Ni-Ti file, which is essential to prevent physical and thermal damage on root canal.

METHODS

First, the mathematic modeling is introduced based on oblique cutting theory, which the loading condition of Ni-Ti file is derived from each cutting element by expressing a function of geometric parameters. For the modeling improvement, a cutting simulation algorithm (CSA) based on Boolean operation is proposed to achieve the complicated cutting situation between root canal and Ni-Ti file instantaneously. After establishment of model, the predictive precision is verified by conducting in vitro experiments. Eighteen artificial root canals were prepared in 6 mm straight and 2 mm C-shaped curved specification with 0.3 mm diameter, which was a single canal for each position, all the canals do not have connections with each other. During experiments, root canals were prepared using Wave One Gold (GWO) instruments with reciprocating rotational motion. Different influential factors (curvatures of root canal and movements of Ni-Ti file) and cutting parameters (feed rate and spindle speed) were analyzed by conducting a series of simulations under the mechanistic model.

RESULTS

Experiment results show that the predictive error of thrust force based on the proposal model is around 15%. The thrust force will increase dramatically after Ni-Ti file gets into craved canal. It can be indicated that the curvatures of root canal, movements of Ni-Ti file have a strong influence on root canal preparation. 20° increasement of curved degrees can lead to the 0.73 N increase of thrust force, while pecking movement can decrease 19.88% of thrust force compared with continues one. Furthermore, investigation on pecking distance represent that 2-1 mm movement can effectively reduce the thrust force of 15.82% compared to 4-2 mm movement.

CONCLUSION

Based on simulation results, 2-1 mm pecking movement is recommended for dentists compared with 4-2 mm pecking movement or continues movement. In addition, this paper provides a novel insight of interactive mechanism between Ni-Ti file and root canal, so as to contribute to both the theoretical and practical research by elucidating mechanisms and providing quantitative predictions that can be validated. Compared with conventional analytical model, both calculated precision and efficiency are improved in the proposed model.

Present Status and Future Directions - Canal Shaping

This narrative review will focus on the evolution, present and future of engine‐driven root canal preparation. Root canal preparation changed drastically when Walia in 1988 introduced the use of nickel‐titanium (NiTi) alloys in Endodontics. In 2013, five generations of NiTi endodontic instruments had been established based on their metallurgical, mechanical properties and design features. Since then, manufacturers have been introducing further major changes in instrument design and characteristics that have not been translated in new recognized generations of instruments. In general, those changes have demonstrated enhanced instrument properties, but it is not clear yet if all those improvements are directly translated to an improvement in clinical success. This narrative review attempts to address the present status of engine‐driven instruments in terms of both evidence from laboratory‐based studies and clinical data, to identify potential further generations of instruments, and last to anticipate future directions for research and development.

Finite Element Analysis of Restored Principal Abutment in Free-End Saddle Partial Denture

PURPOSE

This study analyzed the stress distribution of restored principal abutments in free-end saddle partial dentures.

MATERIALS AND METHODS

The mandibular second premolar was modeled with class II cavity restored with composite resins (Tetric N Ceram and Charisma Smile). Finite element analysis (FEA) was used to examine the stresses under 200-N static load vertically and horizontally and the results were graphically illustrated in the form of von Mises stresses.

RESULTS

The von Mises stress distribution patterns of two different composite resins (Tetric N Ceram and Charisma Smile) were very similar in all modes of loading.

CONCLUSION

Composite resins with a similar modulus of elasticity in class II cavities with occlusal rest seat preparation had similar stress distributions.

CLINICAL SIGNIFICANCE

Nanohybrid composite resin restorations may be a possible method for preparing abutments for receiving elements of the removable partial denture (RPD).

3D Finite Element Analysis of Rotary Instruments in Root Canal Dentine with Different Elastic Moduli

The aim of the present investigation was to calculate the stress distribution generated in the root dentine canal during mechanical rotation of five different NiTi endodontic instruments by means of a finite element analysis (FEA). Two conventional alloy NiTi instruments F360 25/04 and F6 Skytaper 25/06, in comparison to three heat treated alloys NiTI Hyflex CM 25/04, Protaper Next 25/06 and One Curve 25/06 were considered and analyzed. The instruments’ flexibility (reaction force) and geometrical features (cross section, conicity) were previously investigated. For each instrument, dentine root canals with two different elastic moduli(18 and 42 GPa) were simulated with defined apical ratios. Ten different CAD instrument models were created and their mechanical behaviors were analyzed by a 3D-FEA. Static structural analyses were performed with a non-failure condition, since a linear elastic behavior was assumed for all components. All the instruments generated a stress area concentration in correspondence to the root canal curvature at approx. 7 mm from the apex. The maximum values were found when instruments were analyzed in the highest elastic modulus dentine canal. Strain and von Mises stress patterns showed a higher concentration in the first part of curved radius of all the instruments. Conventional Ni-Ti endodontic instruments demonstrated higher stress magnitudes, regardless of the conicity of 4% and 6%, and they showed the highest von Mises stress values in sound, as well as in mineralized dentine canals. Heat-treated endodontic instruments with higher flexibility values showed a reduced stress concentration map. Hyflex CM 25/04 displayed the lowest von Mises stress values of, respectively, 35.73 and 44.30 GPa for sound and mineralized dentine. The mechanical behavior of all rotary endodontic instruments was influenced by the different elastic moduli and by the dentine canal rigidity.

The Effect of Access Cavity Designs and Sizes of Root Canal Preparations on the Biomechanical Behavior of an Endodontically Treated Mandibular First Molar: A Finite Element Analysis

INTRODUCTION

This study aimed to compare the biomechanical properties of a mandibular first molar with different endodontic cavity designs and increasing sizes of root canal preparations using finite element analysis (FEA).

METHODS

The experimental finite element models were designed with 3 different endodontic access cavities and 2 sizes of canal preparations: traditional access cavity, conservative access cavity, and truss access cavity and #30/.04 and #40/.04 of root canal preparations. Vertical and oblique loads were applied with a 250-N static force to simulate masticatory forces. Mathematical analysis was performed to evaluate the stress distribution patterns. Maximum von Mises (VM) stresses were assessed at the occlusal surface; cervical line; and 1 , 3, 5, and 7 mm from the root apices.

RESULTS

Decreasing the size of the access cavity was associated with a higher magnitude of cervical stresses. The magnitude of VM stresses was maximum at the 7-mm level and was minimum at the 1-mm level from the root apex. Increasing the size of the access cavity was associated with the transmission of stresses to a further apical direction regardless of the extent of root canal enlargement. The root canal enlargement from #30 to #40 increased radicular VM stresses within all models.

CONCLUSIONS

Within the limitations of this study, conservative and truss access designs preserved a significant volume of tooth structure. The extent of root canal enlargement should be as small as practical without jeopardizing the biologic objectives of root canal treatment.

Stress distribution in a mandibular premolar after separated nickel-titanium instrument removal and root canal preparation: a three-dimensional finite element analysis

Objective

This study used finite element analysis (FEA) to assess the von Mises stresses of a mandibular first premolar after removing a separated instrument with an ultrasonic technique.

Methods

FEA models of the original and treated mandibular first premolar were reconstructed, and three models (the original canal, size 30/taper 0.04 canal, and separated instrument removal canal) were created. Two-direction (vertical and lateral) loading patterns were simulated with a 175-N force. The maximum von Mises stresses of the models within the roots from the apex to the cervical region were collected and summarized.

Results

Under vertical and lateral loads, all maximal values in the three models were localized in the straight-line access region. Compared with the original model (model 1), the treated models (models 2 and 3) had greater maximum stress values from the apex to the cervical region. Greater differences in the maximum von Mises stresses between models 2 and 3 were present in the straight-line access region.

Conclusions

Separated instrument removal caused changes in stress distribution and increases in stress concentration in the straight-line access region of roots.

Impact of contracted endodontic cavities on fracture resistance of endodontically treated teeth: a systematic review of in vitro studies

OBJECTIVE

This systematic review was performed to answer the following question: do contracted endodontic cavities (CECs) increase resistance to fracture in extracted human teeth compared to traditional endodontic cavities (TECs)?

METHODS

A literature search without restrictions was carried out in PubMed, Science Direct, Scopus, Web of Science, and Open Grey databases. Articles were selected by two independent reviewers. In addition, a reference and hand search was also fulfilled. All included in vitro studies evaluated the influence of CECs on strength to fracture in extracted human teeth and compared to TECs. The quality of the selected studies was evaluated and they were classified as having a low, moderate or high risk of bias.

RESULTS

A total of 810 articles were obtained in the electronic search. After the application of the eligibility criteria, reference and hand search, and duplicate removal, six studies were included in this systematic review. All included studies evaluated the influence of CECs on strength to fracture in extracted human teeth and compared to TECs. Characteristics investigated in the selected articles included the sample size and tooth type, access cavity design, filling and restoration procedures, load at fracture test characteristics, and results. The studies demonstrated large variability among the fracture resistance values and standard deviations and low power. Three of the reviewed studies presented low risk of bias and the other three showed medium risk of bias.

CONCLUSION

Overall, this systematic review of in vitro studies showed that there is no evidence that supports the use of CECs over TECs for the increase of fracture resistance in human teeth.

CLINICAL RELEVANCE

Recently, CECs have gained attention in endodontics due to maximum tooth structure preservation including the pericervical dentin, which could improve the strength to fracture of endodontically treated teeth. However, the influence of access cavity design on fracture resistance remains limited and controversial.

Influence of nickel-titanium rotary systems with varying tapers on the biomechanical behaviour of maxillary first premolars under occlusal forces: a finite element analysis study

AIM

To evaluate the effect of three nickel-titanium (Ni-Ti) rotary systems with varying tapers on stress distribution and to analyse potential fracture patterns as well as the volume of fracture-susceptible regions in two-rooted maxillary premolars.

METHODOLOGY

The root canals of three single-rooted premolars were prepared with either HeroShaper (Micro-Mega, Besançon, France) to (size 30, .04 taper), Revo-S (Micro-Mega) to AS30 (size 30, .06 taper) or ProTaper Universal (Dentsply Maillefer, Ballaigues, Switzerland) to F3 (size 30, .09 taper) Ni-Ti files. The three root canals were scanned using micro-computed tomography (μCT) (Skyscan 1174, Skyscan, Kontich, Belgium) and modelled according to the μCT data. An intact tooth model with a root length of 16 mm was also constructed based on μCT images of an extracted maxillary premolar with two roots. New models were constructed by replacing both of the original canals of the intact two-rooted premolar model with the modelled canals prepared with the HeroShaper, Revo-S or ProTaper Universal system. Occlusal forces of 200 N were applied in oblique and vertical directions. Finite element analysis was performed using Abaqus FEA software (Abaqus 6.14, ABAQUS Inc., Providence, RI, USA).

RESULTS

Upon the application of oblique occlusal forces, the palatal external cervical root surface and the bifurcation (palatal side of the buccal root) in tooth models experienced the highest maximum principal (Pmax) stresses. The application of vertical forces resulted in minor Pmax stress values. Models prepared using the ProTaper system exhibited the highest Pmax stress values. The intact models exhibited the lowest Pmax stress values followed by the models prepared with the HeroShaper system.

CONCLUSION

The differences in Pmax stress values amongst the different groups of models were mathematically minimal under normal occlusal forces. Rotary systems with varying tapers might predispose the root fracture on the palatal side of the buccal root and cervical palatal root surface in two-rooted premolars.