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Impact of access cavities on root canal preparation, restorative protocol quality, and fracture resistance of teeth

Abstract

The survival of endodontically treated teeth depends on the remaining tooth structure. The aim of this study was to evaluate the impact of different access cavities on root canal preparation, restorative protocol, and fracture resistance of endodontically treated teeth. Fifty-six mandibular molars were divided into control (n=8) and experimental (n=16) groups according to access cavity: Traditional, Conservative, and Truss; and redistributed (n=8) according to instrumentation protocols: Reciproc Blue and R-motion. After, teeth were scanned in micro-CT and then filled and redistributed according to composite resin restoration (n=8): Filtek One BulkFill and Filtek Z350. A new micro-CT scan was performed to analyze the restorative material. Then, samples were submitted to fracture resistance testing and the failure pattern was determined. Data were analyzed using paired T-test, ANOVA, Tukey, and chi-square tests (α=0.05). In Truss, R-Motion promoted less transportation in different thirds of root canals. Higher percentages of voids (5.05%) and filling material (11.7%) were observed in Truss. Fracture resistance values were higher for the control group, followed by Truss, Conservative, and Traditional. The predominant failure pattern was type-II. In Truss, reciprocating instruments with smaller taper showed less canal transportation. Also, Truss provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material. Thus, in Truss, reciprocating files with smaller taper showed less canal transportation, and these cavities provided higher values of fracture resistance, although it presented a higher percentage of voids and remaining filling material.

Endodontics; Root Canal Preparation; Dental Restoration

Introduction

The literature shows controversial results regarding the impact of endodontic access cavities on fracture resistance of endodontically treated teeth.11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...
, 22.Silva EJ, Pinto KP, Ferreira CM, Belladonna FG, De-Deus G, Dummer PM, et al. Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature. Int Endod J. 2020 Dec;53(12):1618-35. https://doi.org/10.1111/iej.13391
https://doi.org/10.1111/iej.13391...
Some studies demonstrate that traditional endodontic access results in lower fracture resistance compared to conservative access, which preserves the pericervical dentin and part of the pulp chamber ceiling,33.Krishan R, Paqué F, Ossareh A, Kishen A, Dao T, Friedman S. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod. 2014 Aug;40(8):1160-6. https://doi.org/10.1016/j.joen.2013.12.012
https://doi.org/10.1016/j.joen.2013.12.0...

4.Plotino G, Grande NM, Isufi A, Ioppolo P, Pedullà E, Bedini R, et al. Fracture strength of endodontically treated teeth with different access cavity designs. J Endod. 2017 Jun;43(6):995-1000. https://doi.org/10.1016/j.joen.2017.01.022
https://doi.org/10.1016/j.joen.2017.01.0...
- 55.Makati D, Shah NC, Brave D, Singh Rathore VP, Bhadra D, Dedania MS. Evaluation of remaining dentin thickness and fracture resistance of conventional and conservative access and biomechanical preparation in molars using cone-beam computed tomography: an in vitro study. J Conserv Dent. 2018;21(3):324-7. https://doi.org/10.4103/JCD.JCD_311_17
https://doi.org/10.4103/JCD.JCD_311_17...
and the Truss access,66.Santosh SS, Ballal S, Natanasabapathy V. Influence of minimally invasive access cavity designs on the fracture resistance of endodontically treated mandibular molars subjected to thermocycling and dynamic loading. J Endod. 2021 Sep;47(9):1496-500. https://doi.org/10.1016/j.joen.2021.06.020
https://doi.org/10.1016/j.joen.2021.06.0...
, 77.Abou-Elnaga MY, Alkhawas MA, Kim HC, Refai AS. Effect of truss access and artificial truss restoration on the fracture resistance of endodontically treated mandibular first molars. J Endod. 2019 Jun;45(6):813-7. https://doi.org/10.1016/j.joen.2019.02.007
https://doi.org/10.1016/j.joen.2019.02.0...
which leaves the central fossa and the lingual and mesio-buccal groove intact, separated by an enamel/dentin bridge in the buccal-lingual direction. On the other hand, other studies found no differences in fracture resistance of teeth endodontically treated through different endodontic accesses cavities.22.Silva EJ, Pinto KP, Ferreira CM, Belladonna FG, De-Deus G, Dummer PM, et al. Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature. Int Endod J. 2020 Dec;53(12):1618-35. https://doi.org/10.1111/iej.13391
https://doi.org/10.1111/iej.13391...
, 88.Moore B, Verdelis K, Kishen A, Dao T, Friedman S. Impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in maxillary molars. J Endod. 2016 Dec;42(12):1779-83. https://doi.org/10.1016/j.joen.2016.08.028
https://doi.org/10.1016/j.joen.2016.08.0...

9.Özyürek T, Ülker Ö, Demiryürek EÖ, Yılmaz F. the effects of endodontic access cavity preparation design on the fracture strength of endodontically treated teeth: traditional versus conservative preparation. J Endod. 2018 May;44(5):800-5. https://doi.org/10.1016/j.joen.2018.01.020
https://doi.org/10.1016/j.joen.2018.01.0...

10.Lima CO, Barbosa AF, Ferreira CM, Ferretti MA, Aguiar FH, Lopes RT, et al. Influence of ultraconservative access cavities on instrumentation efficacy with XP-endo Shaper and Reciproc, filling ability and load capacity of mandibular molars subjected to thermomechanical cycling. Int Endod J. 2021 Aug;54(8):1383-93. https://doi.org/10.1111/iej.13525
https://doi.org/10.1111/iej.13525...
- 1111.Chlup Z, Zizka R, Kania J, Pribyl M. Fracture behaviour of teeth with conventional and mini-invasive access cavity designs. J Eur Ceram Soc. 2017;37(14):4423-9. https://doi.org/10.1016/j.jeurceramsoc.2017.03.025
https://doi.org/10.1016/j.jeurceramsoc.2...
These differences can be attributed to non-standardization of the methods used to evaluate fracture resistance, different sets of teeth, and different restorative protocol.11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...
Therefore, it is necessary to discuss the technique beyond the evaluation of the restorative material used, since the restorative protocol has a direct impact on treatment prognosis.1212.Pedro FM, Marques A, Pereira TM, et al. Status of endodontic treatment and the correlations to the quality of root canal filling and coronal restoration. J Contemp Dent Pract. 2016;17(10):830-836. Published 2016 Oct 1. https://doi.org/10.5005/jp-journals-10024-1939
https://doi.org/10.5005/jp-journals-1002...

The first choice of restorative protocols for the restoration of endodontically treated teeth is the use of composite resins, which have similar mechanical properties to dentin and can restore up to 72% of the fracture resistance.88.Moore B, Verdelis K, Kishen A, Dao T, Friedman S. Impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in maxillary molars. J Endod. 2016 Dec;42(12):1779-83. https://doi.org/10.1016/j.joen.2016.08.028
https://doi.org/10.1016/j.joen.2016.08.0...
However, it is important to note that composite resins have high polymerization shrinkage, which can result in the formation of gaps between the tooth interface and the restorative material.1313.Pai S, Naik N, Patil V, Kaur J, Awasti S, Nayak N. Evaluation and comparison of stress distribution in restored cervical lesions of mandibular premolars: three-dimensional finite element analysis. J Int Soc Prev Community Dent. 2019;9(6):605-611. Published 2019 Nov 4. doi:10.4103/jispcd.JISPCD_301_19
https://doi.org/10.4103/jispcd.JISPCD_30...
To mitigate this situation, bulk fill composite resin have been developed in regular and flowable forms that exhibit less polymerization contraction and have better performance than incremental composites regarding adaptability and less gap formation in the pulp wall.1414.Rosatto CM, Bicalho AA, Veríssimo C, Bragança GF, Rodrigues MP, Tantbirojn D, et al. Mechanical properties, shrinkage stress, cuspal strain and fracture resistance of molars restored with bulk-fill composites and incremental filling technique. J Dent. 2015 Dec;43(12):1519-28. https://doi.org/10.1016/j.jdent.2015.09.007
https://doi.org/10.1016/j.jdent.2015.09....
, 1515.Veloso SR, Lemos CA, Moraes SL, Vasconcelos BCE, Pellizzer EP, Monteiro GQM. Clinical performance of bulk-fill and conventional resin composite restorations in posterior teeth: a systematic review and meta-analysis. Clin Oral Investig. 2019 Jan;23(1):221-33. https://doi.org/10.1007/s00784-018-2429-7
https://doi.org/10.1007/s00784-018-2429-...

Regarding root canal preparation, the technological improvement and development of NiTi-treated alloy systems in different designs and kinematics produced a new generation of instruments with greater flexibility and resistance to cyclic fatigue. This allows creating accesses with less coronal wear. On the other hand, the use of mechanized instruments in conservative, ultraconservative, and Truss access cavities, especially those with greater taper in reciprocal kinematics, has been associated with greater apical transport and higher percentage of unprepared walls compared to their use in traditional cavities.33.Krishan R, Paqué F, Ossareh A, Kishen A, Dao T, Friedman S. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod. 2014 Aug;40(8):1160-6. https://doi.org/10.1016/j.joen.2013.12.012
https://doi.org/10.1016/j.joen.2013.12.0...
, 44.Plotino G, Grande NM, Isufi A, Ioppolo P, Pedullà E, Bedini R, et al. Fracture strength of endodontically treated teeth with different access cavity designs. J Endod. 2017 Jun;43(6):995-1000. https://doi.org/10.1016/j.joen.2017.01.022
https://doi.org/10.1016/j.joen.2017.01.0...
Recently, the R-Motion instrumentation system (FKG, Switzerland) was developed, consisting of instruments made of heat-treated NiTi alloy with a higher percentage of martensitic phase. These instruments are available in two different tapers, 0.4 and 0.6, which are smaller compared to other single instrument systems in reciprocal kinematics with larger tapers. In addition, they have a rounded triangular cross-section with cutting edges and active tip, which favors cutting and penetration efficiency with less stress on the dentin.1616.Carvalho KK, Petean IB, Silva-Sousa AC, Camargo RV, Mazzi-Chaves JF, Silva-Sousa YT, et al. Impact of several NiTi-thermally treated instrumentation systems on biomechanical preparation of curved root canals in extracted mandibular molars. Int Endod J. 2022 Jan;55(1):124-36. https://doi.org/10.1111/iej.13649
https://doi.org/10.1111/iej.13649...

Thus, the aim of the present study was to evaluate the impact of different access cavities on root canal preparation using reciprocating instruments with low taper on the restorative protocol and fracture resistance of endodontically treated teeth restored with different low-viscosity resins. The null hypothesis was that the different access cavities do not impact on root canal preparation, restorative protocol, and fracture resistance of endodontically treated teeth.

Methodology

Sample selection

The G*Power version 3.1.9.7 software (Düsseldorf, Germany) was used to determine the sample size by means of F-tests and Anova for fixed, special, main, and interaction effects. Type I error of α = 0.05, statistical power β=0.8, numerator dF = 3, number of groups = 6 or 7 were used as fixed parameters. From previous studies, the effect size was determined to be 0.5 and 0.52 for percentage of change in volume and surface area,1717.Gagliardi J, Versiani MA, Sousa-Neto MD, Plazas-Garzon A, Basrani B. Evaluation of the shaping characteristics of protaper gold, protaper NEXT, and ProTaper universal in curved canals. J Endod. 2015 Oct;41(10):1718-24. https://doi.org/10.1016/j.joen.2015.07.009
https://doi.org/10.1016/j.joen.2015.07.0...
0.50 for percentage of unprepared root canal walls,33.Krishan R, Paqué F, Ossareh A, Kishen A, Dao T, Friedman S. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod. 2014 Aug;40(8):1160-6. https://doi.org/10.1016/j.joen.2013.12.012
https://doi.org/10.1016/j.joen.2013.12.0...
, 88.Moore B, Verdelis K, Kishen A, Dao T, Friedman S. Impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in maxillary molars. J Endod. 2016 Dec;42(12):1779-83. https://doi.org/10.1016/j.joen.2016.08.028
https://doi.org/10.1016/j.joen.2016.08.0...
0.55 for voids in the coronal restoration11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...
and 0.60 for fracture resistance.33.Krishan R, Paqué F, Ossareh A, Kishen A, Dao T, Friedman S. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod. 2014 Aug;40(8):1160-6. https://doi.org/10.1016/j.joen.2013.12.012
https://doi.org/10.1016/j.joen.2013.12.0...
, 44.Plotino G, Grande NM, Isufi A, Ioppolo P, Pedullà E, Bedini R, et al. Fracture strength of endodontically treated teeth with different access cavity designs. J Endod. 2017 Jun;43(6):995-1000. https://doi.org/10.1016/j.joen.2017.01.022
https://doi.org/10.1016/j.joen.2017.01.0...
, 88.Moore B, Verdelis K, Kishen A, Dao T, Friedman S. Impacts of contracted endodontic cavities on instrumentation efficacy and biomechanical responses in maxillary molars. J Endod. 2016 Dec;42(12):1779-83. https://doi.org/10.1016/j.joen.2016.08.028
https://doi.org/10.1016/j.joen.2016.08.0...
, 1818.Silva EJ, Vieira VT, Hecksher F, Oliveira MRS, Antunes HS, Moreira EJ. Cyclic fatigue using severely curved canals and torsional resistance of thermally treated reciprocating instruments. Clin Oral Investig. 2018 Sep;22(7):2633-8. https://doi.org/10.1007/s00784-018-2362-9
https://doi.org/10.1007/s00784-018-2362-...
From these parameters, the estimated minimum sample size was 8 specimens per group for percentage of volume and surface area change, 7.5 for percentage of unprepared root canal walls, 6.83 for voids, and 5 for fracture resistance. Thus, the sample size was set at 8 specimens for each group, and a total of 56 samples.

After approval of this study by the local ethics committee (No 42341321.0.0000.5419), healthy human mandibular molars recently extracted due to periodontal diseases, without caries, with complete root formation, and without macroscopically visible fracture were preselected. The teeth were scanned using a 1174 v.2 SkyScan microcomputed tomograph, operated at 50 kV, 276 mA, isotropic resolution of 23.5 μm, 360° rotation around the vertical axis, 1.8° rotation step, total of 2 frames, and a 0.5-mm thick aluminum filter. In order to ensure proper alignment of the images taken at different stages of the study, the teeth were positioned with their buccal surfaces perpendicular to the radiation source. The two-dimensional images were reconstructed in NRecon v.1.6.6.0 software (Bruker microCT, Kontich, Belgium) and analyzed in CTAn v.1.14.4.1+ software (Bruker microCT, Kontich, Belgium) to calculate crown and root length and volume, and determine root canal volume and surface area. From these data, 56 mandibular molars with 2 mesial canals (type IV) and one distal canal (type I)1919.Vertucci FJ. Root canal anatomy of the human permanent teeth. Oral Surg Oral Med Oral Pathol. 1984 Nov;58(5):589-99. https://doi.org/10.1016/0030-4220 (84)90085-9
https://doi.org/10.1016/0030-4220 (84)90...
were selected and grouped according to anatomical aspects, randomized and divided into 1 control (n = 8) and 2 experimental (n = 16) groups according to the type of access cavity: Traditional (TAC), Conservative (CAC), and Truss. Then, samples were randomized again and divided according to root canal preparation protocol (n = 8): Reciproc Blue (RB) and R-motion (RM). The homogeneity of the morphological aspects between groups was checked using one-way ANOVA test (p > 0.05) and two-way ANOVA test (p > 0.05), respectively. The randomizations were performed using SPSS software (SPSS, Inc., Chicago, USA).

All experimental procedures were performed by a single expert using a DM Plus IB surgical microscope (Opto Eletrônica, São Carlos, Brazil) with 2× to 12× magnification. In the control group, the teeth remained intact and were used only for fracture resistance and failure pattern evaluation.

Endodontic access cavity

The endodontic access cavities were prepared following the classification proposed previously.2020.Shabbir J, Zehra T, Najmi N, Hasan A, Naz M, Piasecki L, et al. Access cavity preparations: classification and literature review of traditional and minimally invasive endodontic access cavity designs. J Endod. 2021 Aug;47(8):1229-44. https://doi.org/10.1016/j.joen.2021.05.007
https://doi.org/10.1016/j.joen.2021.05.0...
For the preparation of the traditional access (TAC), a 1014HL spherical diamond bur (KG Sorensen, São Paulo, Brazil) was used at high rotation, positioned in the center of the main groove parallel to the long axis of the tooth with a slight inclination towards the distal canal until reaching the pulp chamber, followed by “in-out” movements until the entire pulp chamber roof was removed. Next, an Endo Z bur (Dentsply Sirona, Ballaigues, Switzerland) was used for smoothing the cavity walls and slightly diverge them toward the occlusal surface, resulting in a trapezoidal shape ( Figure 1A and 1D ). For the conservative endodontic access cavities (CAC), the same steps as for traditional cavities were followed until the pulp chamber was reached, but “in to out” movements in the pulp chamber were performed until interference-free access to the root canal openings was achieved. Then, an E7D ultrasonic insert with diamond tip (Helse Ultrasonic, Santa Rosa do Viterbo, SP, Brazil) was used to smooth the cavity walls, which converged towards the occlusal surface to preserve the cusps ( Figure 1B and 1E ). For the Truss access cavity, a 1013HL spherical diamond bur (KG Sorensen) was used for the access, and an ultrasonic insert with E7D and E4D diamond tips (Helse) was used for the refinement of the cavity. After analyzing the volume of the pulp chambers on micro-CT, a standard design of the access was performed2020.Shabbir J, Zehra T, Najmi N, Hasan A, Naz M, Piasecki L, et al. Access cavity preparations: classification and literature review of traditional and minimally invasive endodontic access cavity designs. J Endod. 2021 Aug;47(8):1229-44. https://doi.org/10.1016/j.joen.2021.05.007
https://doi.org/10.1016/j.joen.2021.05.0...
( Figure 1C and 1F ).

Figure 1
Schematic representation of access cavities in micro-CT images. Sagittal reconstruction in first line and axial reconstruction in second line. (A) and (D) show Traditional access cavity; (B) and (E) show Conservative access cavity; (C) and (F) show Truss access cavity.

Root canal preparation

The working length (WL) was established at 1 mm below the apical foramen. The root canal preparation was performed with the Reciproc Blue (RB) or R-motion (RM) reciprocating systems, following the manufacturer’s recommendations, powered with a Sirona 6:1 counter angle reducer (SN 25185; VDW GmbH, Munich, Germany) coupled to the SMR 114058 motor (VDW GmbH), which was connected to the VDW Silver electric motor (VDW GmbH) with reciprocating motion selection. To standardize the irrigation volume during preparation, root canals were irrigated with 10 mL of 2.5% NaOCl. For the RB group, the mesial canals were prepared with the R25 file (25.08) and the distal canals with the R50 file (50.05). For the RM group, the glide path was initially performed with 15.03 RM file and then the mesial canals were prepared with the 30.04 RM and the distal canals with the 50.04 RM files. The final irrigation was performed with 2 mL of 17% etylenediaminetetraacetic acid (EDTA) for 5 minutes, followed by 10 mL of distilled water. The specimens were re-scanned in micro-CT for reconstruction and data analysis after root canal preparation following the same parameters as before.

3D evaluation of root canal preparation

Post-instrumentation images were aligned with the images obtained in the initial microtomographic examination (pre-instrumentation) in the DataViewer v.1.5.0 software. Using the 3D Analysis tool of the CTAn software, data on crown and root volume were obtained, as well as the three-dimensional morphometric parameters of the root canal volume, surface area, calculation of transportation in the cervical, middle and apical thirds, and the percentage of prepared and unprepared walls (15,17). In addition, the percentage of coronal structure removal (% removal) after performing the endodontic accesses was determined by the formula %removal = (Initial Volume - Remaining Volume)*100/(Initial Volume), where “Remaining Volume” corresponds to the remaining coronal volume and “Initial Volume” corresponds to the initial coronal volume.

Root canal filling and restorative procedures

The root canal filling was performed using the single cone technique with AH Plus sealer and gutta-percha cones Reciproc Blue R25 and R50 (VDW GmbH) in the mesial and distal root canals, respectively, for the Reciproc Blue group, and cones 30.04 and 50.04 (FKG Dentaire, La Chaux-de-Fonds, Switzerland) for the RM group. The cleaning of the pulp chamber was performed with 70 percent isopropyl alcohol and Soffitsonic ultrasonic insert (Helse Ultrasonic, Santa Rosa do Viterbo, Brazil). The coronal volumes obtained after root canal preparation were used for further randomization (two-way ANOVA, p>0.05) and distribution into two experimental subgroups (n = 8), according to restorative protocol, for each access cavity group.

For the restorative procedures, selective acid etching was performed on enamel with 37% phosphoric acid (Ultradent Products, Inc., South Jordan, USA) for 30 seconds. The cavities were washed for 30 seconds with water jets and lightly dried with air jets and absorbent paper. The SingleBond Universal adhesive system (3M ESPE, St Paul, USA) was then applied to enamel and dentin for 20 seconds, followed by solvent evaporation with light air jets for 10 seconds, and photoactivation with a LED unit in standard mode at 1000 mW/cm22.Silva EJ, Pinto KP, Ferreira CM, Belladonna FG, De-Deus G, Dummer PM, et al. Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature. Int Endod J. 2020 Dec;53(12):1618-35. https://doi.org/10.1111/iej.13391
https://doi.org/10.1111/iej.13391...
(VALO, Ultradent Products) for 20 seconds.

For the restorative protocol with Filtek Z350 resins (FZ350) (3M), two layers of 2 mm each of Filtek Z350 flow resin (FZ350-F) were applied and the rest of the cavity was filled with 2 mm oblique increments with regular Filtek Z350 (FZ350), each increment being light-cured for 10 seconds. For the restorative protocol with Filtek One Bulk Fill resins (FOBF) (3M), a 4 mm layer of Filtek One Bulk Fill flow resin (FOBF-F) was applied, followed by the addition of a single increment of regular Filtek One Bulk Fill (FOBF), and each layer was light-cured for 20 seconds.

A standard mode LED-curing unit (VALO, Ultradent Products Inc) with a power of 1000mW/cm22.Silva EJ, Pinto KP, Ferreira CM, Belladonna FG, De-Deus G, Dummer PM, et al. Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature. Int Endod J. 2020 Dec;53(12):1618-35. https://doi.org/10.1111/iej.13391
https://doi.org/10.1111/iej.13391...
was used, with the tip of the light placed on the tooth cusps. Analysis and measurement of the irradiance values (1,000 mW/cm22.Silva EJ, Pinto KP, Ferreira CM, Belladonna FG, De-Deus G, Dummer PM, et al. Current status on minimal access cavity preparations: a critical analysis and a proposal for a universal nomenclature. Int Endod J. 2020 Dec;53(12):1618-35. https://doi.org/10.1111/iej.13391
https://doi.org/10.1111/iej.13391...
), emission spectrum, and total energy delivered were performed with a radiometer (PM10-19C; Coherent, Ely, UK) for each sample. After 24 hours of storage at 37ºC in 100% relative humidity, the restorations were finished and polished with diamond tips (KG Sorensen, Barueri, Brazil) and abrasive rubber tips (KG Sorensen, Barueri, Brazil).

Determining the remaining filling material and voids in the restoration

Due to the different densities of the restorative and filling materials, after the root canal filling and restoration protocols, the specimens were re-scanned in Sky Scan microCT (1176 model, Bruker mi-croCT) operated with 90 kV, 276 mA, with a resolution of 23.5 µm and 360º on the vertical axis with rotation steps of 0.7º using a 0.5 mm aluminum filter. The images were reconstructed (NRecon software) and analyzed using CTAn software to determine the volume of restorative material (mm33.Krishan R, Paqué F, Ossareh A, Kishen A, Dao T, Friedman S. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod. 2014 Aug;40(8):1160-6. https://doi.org/10.1016/j.joen.2013.12.012
https://doi.org/10.1016/j.joen.2013.12.0...
) (Volrestorativematerial), volume of empty spaces in the restoration (mm33.Krishan R, Paqué F, Ossareh A, Kishen A, Dao T, Friedman S. Impacts of conservative endodontic cavity on root canal instrumentation efficacy and resistance to fracture assessed in incisors, premolars, and molars. J Endod. 2014 Aug;40(8):1160-6. https://doi.org/10.1016/j.joen.2013.12.012
https://doi.org/10.1016/j.joen.2013.12.0...
) (Volspaces), and volume of remaining filling material (RFM) across the entire length of the pulp chamber, with the floor of the cavity as the end reference.

Fracture resistance test

The teeth were embedded in polystyrene resin with the periodontal ligament simulated with polyether-based molding material (Impregum F, 3M ESPE, St. Paul, USA)11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...
and subjected to compressive loading at a speed of 0.5 mm/min in a universal testing machine EMIC 23-5S (Instron Corporation, Canton, MA, USA) with a 5000 N load cell. The load was applied to the central fossa using a stainless-steel rod with a tip diameter of 8 mm at an angle of 30° to the long axis of the tooth. The fracture type was analyzed under a stereomicroscope (Leica M165C, Leica Microsystems GmbH, Wetzlar, Germany) at 2X magnification. The types of fracture were classified into: Type I (crown fractures involving the occlusal or middle thirds of the crown), Type II (crown fracture involving the cervical third of the crown), Type III (root fracture involving the cervical third of the root), and Type IV (root fracture involving the middle or apical third of the root).11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...

Statistical analyses

The tests were performed in SPSS software, version 25 (IBM, SPSS, Armonk, USA), with a significance level of 95% (p < 0.05). Data were subjected to normality (Shapiro-Wilk) and homogeneity of variance (Levene) tests. The impact of the endodontic cavity on the root canal preparation regarding volume, surface area, and percentage of prepared walls was evaluated using a three-way analysis of variance and Tukey post-test. Root canal transportation was evaluated using split-plot ANOVA for the influence of endodontic access cavities, instrumentation protocols, and root canal thirds. Data related to the restorative protocol and fracture resistance test were subjected to three-way ANOVA and Tukey post-test for multiple comparisons between groups. The failure pattern was analyzed by the chi-square test. All tests were performed in SPSS software, version 25 (IBM, SPSS, Armonk, USA), with 95% significance level (p <0 .05).

Results

3D analysis of changes in root canal

Regarding surface area and volume, the results showed no statistically significant difference between types of cavity and instrumentation systems, in any of the evaluated canals (p > 0.05) ( Table 1 ). Regarding the percentage of prepared and unprepared walls, the type of endodontic access cavity did not result in differences between the different instrumentation systems, in any of the evaluated canals (p > 0.05) ( Table 1 ).

Table 1
Mean and Standard Deviation of Morphometric Tridimensional Data of surface area (mm2), volume (mm3), and percentage of prepared walls of root canals of mandibular molars according to the root canal preparation protocols.

For root canal transportation, no statistically significant differences were observed in TAC and CAC between the instrumentation protocols (p > 0.05) ( Table 2 ). In Truss, the RM promoted the lowest transport values for the mesio-buccal canal in the middle and apical thirds (p < 0.05), for the mesio-lingual canal in the cervical, middle, and apical thirds (p < 0.05), and for the distal canal in the middle and apical thirds (p < 0.05), compared to the RB ( Table 2 ).

Table 2
Mean and standard deviation of root canal transportation by thirds for endodontic access cavities and instrumentation protocols.

The Truss access resulted in the lowest mean percentages of tooth structure removal (5.51 ± 0.74%), showing a statistically significant difference compared to the conservative access cavities (CAC) (14.66 ± 0.70%) and traditional access cavities (TAC) (19.95 ± 0.84%) (p < 0.05).

Analysis of root canal filling and restorative procedures

The Truss access resulted in a higher percentage of remaining filling material ( Table 3 ), followed by the CAC and the TAC (p < 0.05).

Table 3
Mean (± standard deviation) percentage of voids in restorative material and remaining filling material for endodontic access cavities and restorative materials on tooth/restorative material set.

The qualitative analysis of the three-dimensional models showed the presence of voids in the junction areas between the composite resin increments of the FZ350 and FOBF groups, and at the tooth/restoration interface for the TAC and CAC. For the Truss, voids were observed mainly under the pulp chamber roof, on the buccal and lingual walls, and between the layers of restorative material ( Figure 2 ).

Figure 2
Micro-CT images of restorative material (gray), empty spaces (blue), and residual filling material (red) in Traditional (A and D), Conservative (B and E), and Truss (C and F) access cavities restored with Filtek One Bulk Fill (first line) and Filtek Z350 (second line).

The Truss showed a higher percentage of voids compared to the TAC and CAC (p < 0.05). Regarding the restorative material, there were no statistically significant differences between cavities restored with FOBF and FZ350 resin (p > 0.05) ( Table 3 ).

The highest values of fracture resistance were observed for the control group (intact teeth), which was statistically different from the experimental groups (p < 0.05) ( Table 4 ). Among the experimental groups, the Truss access resulted in the highest values of fracture resistance, being statistically different from the CAC and TAC (p<0.05), regardless of the instrumentation and restorative protocols used. The type II failure pattern was more prevalent in all evaluated groups (p < 0.05), regardless of the restorative protocol used ( Table 4 ).

Table 4
Mean (±standard deviation) fracture resistance in Newtons (N) and failure pattern for endodontic access cavities and restorative material.

Discussion

With the introduction of mechanized instruments in the 80’s, modifications to the shape of the endodontic access cavity were proposed to preserve coronal tissue. Initially, the guidelines recommended large cavities that allowed straight access to the root canals.2121.Patel S, Rhodes J. A practical guide to endodontic access cavity preparation in molar teeth. Br Dent J. 2007 Aug;203(3):133-40. https://doi.org/10.1038/bdj.2007.682
https://doi.org/10.1038/bdj.2007.682...
Technological improvement of instruments2222.Sousa-Neto MD, Silva-Sousa YC, Mazzi-Chaves JF, Carvalho KKT, Barbosa AFS, Versiani MA, et al. Root canal preparation using micro-computed tomography analysis: a literature review. Braz Oral Res. 2018;32(suppl 1):e66. https://doi.org/10.1590/1807-3107bor-2018.vol32.0066
https://doi.org/10.1590/1807-3107bor-201...
, 2323.Peters OA, Arias A, Choi A. Mechanical properties of a novel nickel-titanium root canal instrument: stationary and dynamic tests. J Endod. 2020 Jul;46(7):994-1001. https://doi.org/10.1016/j.joen.2020.03.016
https://doi.org/10.1016/j.joen.2020.03.0...
and emergence of magnifying tools2424.Estrela C, Pécora JD, Estrela CR, Guedes OA, Silva BS, Soares CJ, et al. Common operative procedural errors and clinical factors associated with root canal treatment. Braz Dent J. 2017;28(2):179-90. https://doi.org/10.1590/0103-6440201702451
https://doi.org/10.1590/0103-64402017024...
, 2525.Mendes EB, Soares AJ, Martins JN, Silva EJ, Frozoni MR. Influence of access cavity design and use of operating microscope and ultrasonic troughing to detect middle mesial canals in extracted mandibular first molars. Int Endod J. 2020 Oct;53(10):1430-7. https://doi.org/10.1111/iej.13352
https://doi.org/10.1111/iej.13352...
allowed preparation of smaller cavities with less wear of the coronal tissue, aiming to decrease the risk of tooth fracture.2020.Shabbir J, Zehra T, Najmi N, Hasan A, Naz M, Piasecki L, et al. Access cavity preparations: classification and literature review of traditional and minimally invasive endodontic access cavity designs. J Endod. 2021 Aug;47(8):1229-44. https://doi.org/10.1016/j.joen.2021.05.007
https://doi.org/10.1016/j.joen.2021.05.0...
, 2626.Clark D, Khademi J. Modern molar endodontic access and directed dentin conservation. Dent Clin North Am. 2010 Apr;54(2):249-73. https://doi.org/10.1016/j.cden.2010.01.001
https://doi.org/10.1016/j.cden.2010.01.0...

27.Auswin MK, Ramesh S. Truss access new conservative approach on access opening of a lower molar: a case report. J Adv Pharm Ed Res. 2017;7(3)344-7.
- 2828.Neelakantan P, Khan K, Hei Ng GP, Yip CY, Zhang C, Pan Cheung GS. Does the orifice-directed dentin conservation access design debride pulp chamber and mesial root canal systems of mandibular molars similar to a traditional access design? J Endod. 2018 Feb;44(2):274-9. https://doi.org/10.1016/j.joen.2017.10.010
https://doi.org/10.1016/j.joen.2017.10.0...
However, these changes can affect root canal preparation and restorative protocol,11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...
, 44.Plotino G, Grande NM, Isufi A, Ioppolo P, Pedullà E, Bedini R, et al. Fracture strength of endodontically treated teeth with different access cavity designs. J Endod. 2017 Jun;43(6):995-1000. https://doi.org/10.1016/j.joen.2017.01.022
https://doi.org/10.1016/j.joen.2017.01.0...
, 66.Santosh SS, Ballal S, Natanasabapathy V. Influence of minimally invasive access cavity designs on the fracture resistance of endodontically treated mandibular molars subjected to thermocycling and dynamic loading. J Endod. 2021 Sep;47(9):1496-500. https://doi.org/10.1016/j.joen.2021.06.020
https://doi.org/10.1016/j.joen.2021.06.0...
, 99.Özyürek T, Ülker Ö, Demiryürek EÖ, Yılmaz F. the effects of endodontic access cavity preparation design on the fracture strength of endodontically treated teeth: traditional versus conservative preparation. J Endod. 2018 May;44(5):800-5. https://doi.org/10.1016/j.joen.2018.01.020
https://doi.org/10.1016/j.joen.2018.01.0...
, 1010.Lima CO, Barbosa AF, Ferreira CM, Ferretti MA, Aguiar FH, Lopes RT, et al. Influence of ultraconservative access cavities on instrumentation efficacy with XP-endo Shaper and Reciproc, filling ability and load capacity of mandibular molars subjected to thermomechanical cycling. Int Endod J. 2021 Aug;54(8):1383-93. https://doi.org/10.1111/iej.13525
https://doi.org/10.1111/iej.13525...
, 2727.Auswin MK, Ramesh S. Truss access new conservative approach on access opening of a lower molar: a case report. J Adv Pharm Ed Res. 2017;7(3)344-7. besides favoring the longevity of the endodontically treated teeth. Thus, the present study analyzed the impact of different access cavities on root canal preparation, tooth/restorative material set, and fracture resistance in the same specimen to have an integrated analysis of the observed results, since the prognosis of endodontic treatment is related not only to the endodontic technique, but also to the restorative protocol.11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...
, 1111.Chlup Z, Zizka R, Kania J, Pribyl M. Fracture behaviour of teeth with conventional and mini-invasive access cavity designs. J Eur Ceram Soc. 2017;37(14):4423-9. https://doi.org/10.1016/j.jeurceramsoc.2017.03.025
https://doi.org/10.1016/j.jeurceramsoc.2...
The different access cavities led to different results regarding impact on root canal preparation, restorative protocol, and fracture resistance, which reject the null hypothesis of this study.

The Truss access provided greater transportation in the mesiobuccal canal compared to the CAC (p < 0.05), which, in turn, provided greater transportation compared to the TAC (p < 0.05), regardless of the instrument used (p > 0.05). However, with the use of instruments with smaller taper (RM) in the Truss access, lower transport values were observed in the middle and apical thirds for the mesiobuccal canal (p < 0.05), in the cervical, middle and apical thirds for the mesio-lingual canal (p < 0.05), and in the middle and apical thirds for the distal canal (p<0.05), compared to instruments with larger taper (RB). This can be attributed to the volume of the metal mass of the file, which is directly affected by the taper, the cross-section design, and the tip diameter.2929.Vivan RR, Alcalde MP, Candeiro G, Gavini G, Caldeira CL, Duarte MA. Torsional fatigue strength of reciprocating and rotary pathfinding instruments manufactured from different NiTi alloys. Braz Oral Res. 2019;33:e097. https://doi.org/10.1590/1807-3107bor-2019.vol33.0097
https://doi.org/10.1590/1807-3107bor-201...

The R-motion and Reciproc Blue instrumentation systems presented similar values of volume, surface area, and percentage of prepared root canal walls regardless of cavity shape (p > 0.05). These results can be attributed to the design of the instruments, since the R-Motion files have an active part with fixed taper that is the same in D0 and D16.1616.Carvalho KK, Petean IB, Silva-Sousa AC, Camargo RV, Mazzi-Chaves JF, Silva-Sousa YT, et al. Impact of several NiTi-thermally treated instrumentation systems on biomechanical preparation of curved root canals in extracted mandibular molars. Int Endod J. 2022 Jan;55(1):124-36. https://doi.org/10.1111/iej.13649
https://doi.org/10.1111/iej.13649...
Therefore, the R- Motion 30.04 file presents a final diameter (D16) of 0.94 mm, close to the Reciproc Blue 25.08 file, which has a fixed taper of 0.08 in the first 3 mm (D0 to D3) and final diameter (D16) of 1.05 mm,3030.Duque JA, Bramante CM, Duarte MA, Alcalde MP, Silva EJ, Vivan RR. Cyclic fatigue resistance of nickel-titanium reciprocating instruments after simulated clinical use. J Endod. 2020 Nov;46(11):1771-5. https://doi.org/10.1016/j.joen.2020.08.010
https://doi.org/10.1016/j.joen.2020.08.0...
justifying the similar values for volume, surface area, and prepared roof canal walls (p > 0.05), as also observed in a previous study.1616.Carvalho KK, Petean IB, Silva-Sousa AC, Camargo RV, Mazzi-Chaves JF, Silva-Sousa YT, et al. Impact of several NiTi-thermally treated instrumentation systems on biomechanical preparation of curved root canals in extracted mandibular molars. Int Endod J. 2022 Jan;55(1):124-36. https://doi.org/10.1111/iej.13649
https://doi.org/10.1111/iej.13649...
The lower taper of the R-Motion file allows the instrument to work freely along the root canal up to the working length, without interference in the cervical region, even with Conservative and Truss access cavities, with similar results to the files with higher tapers. In addition, instruments with greater taper tend to present higher metal mass, as the Reciproc Blue file, which impacts the resistance to torsion and shape memory effect, since the instrument tends to regain its original shape as a function of temperature.3131.De-Deus G, Belladonna FG, Simões-Carvalho M, Cavalcante DM, Ramalho CN, Souza EM, et al. Shaping efficiency as a function of time of a new heat-treated instrument. Int Endod J. 2019 Mar;52(3):337-42. https://doi.org/10.1111/iej.13000
https://doi.org/10.1111/iej.13000...
This factor can lead to unnecessary dentin removal,3131.De-Deus G, Belladonna FG, Simões-Carvalho M, Cavalcante DM, Ramalho CN, Souza EM, et al. Shaping efficiency as a function of time of a new heat-treated instrument. Int Endod J. 2019 Mar;52(3):337-42. https://doi.org/10.1111/iej.13000
https://doi.org/10.1111/iej.13000...
and these characteristics are not as pronounced in files with lower metal mass, such as the R-Motion.1616.Carvalho KK, Petean IB, Silva-Sousa AC, Camargo RV, Mazzi-Chaves JF, Silva-Sousa YT, et al. Impact of several NiTi-thermally treated instrumentation systems on biomechanical preparation of curved root canals in extracted mandibular molars. Int Endod J. 2022 Jan;55(1):124-36. https://doi.org/10.1111/iej.13649
https://doi.org/10.1111/iej.13649...

In the analysis of the tooth/restorative material set, the Truss cavity showed a higher percentage of remaining filling material in the cavity (p < 0.05) and a higher percentage of empty spaces, regardless of the restorative protocol (p < 0.05). This can be attributed to the small size of the Truss cavity and the difficulty of accessing the pulp chamber region under the roof with instruments and materials. Similarly, these factors influenced the execution of the restorative technique3232.Han SH, Park SH. Comparison of internal adaptation in class II bulk-fill composite restorations using micro-CT. Oper Dent. 2017;42(2):203-14. https://doi.org/10.2341/16-023-L
https://doi.org/10.2341/16-023-L...
during the resin insertion procedure in the ultraconservative access cavity,11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...
, 3333.Uzunoglu-Özyürek E, Küçükkaya Eren S, Karahan S. Contribution of XP-Endo files to the root canal filling removal: a systematic review and meta-analysis of in vitro studies. Aust Endod J. 2021 Dec;47(3):703-14. https://doi.org/10.1111/aej.12503
https://doi.org/10.1111/aej.12503...
regardless of the resin used, even with the use of operating microscopy, as recommended for cases of conservative and ultraconservative cavities.2525.Mendes EB, Soares AJ, Martins JN, Silva EJ, Frozoni MR. Influence of access cavity design and use of operating microscope and ultrasonic troughing to detect middle mesial canals in extracted mandibular first molars. Int Endod J. 2020 Oct;53(10):1430-7. https://doi.org/10.1111/iej.13352
https://doi.org/10.1111/iej.13352...

The evaluation of the remaining filling material, percentage of empty space, and fracture resistance were performed considering the entire tooth/restorative material set. For this restorative procedure, layers of flow composite resin and regular composite resin were used since flow composite resins have low surface hardness and low elasticity modulus. Because of these characteristics, flow resins cannot be used as a single restorative material, but must be coated with a surface layer of regular resin over this material in order to provide greater abrasion resistance during masticatory stresses.1414.Rosatto CM, Bicalho AA, Veríssimo C, Bragança GF, Rodrigues MP, Tantbirojn D, et al. Mechanical properties, shrinkage stress, cuspal strain and fracture resistance of molars restored with bulk-fill composites and incremental filling technique. J Dent. 2015 Dec;43(12):1519-28. https://doi.org/10.1016/j.jdent.2015.09.007
https://doi.org/10.1016/j.jdent.2015.09....

Regarding fracture resistance of endodontically treated teeth, the highest values were observed for the Truss cavity group compared to CAC and TAC (p < 0.05). This may be related to the lower percentage of dentin removal (5.51%), since the volume of lost coronal dentin plays a significant role in the prognosis of endodontically treated teeth,2626.Clark D, Khademi J. Modern molar endodontic access and directed dentin conservation. Dent Clin North Am. 2010 Apr;54(2):249-73. https://doi.org/10.1016/j.cden.2010.01.001
https://doi.org/10.1016/j.cden.2010.01.0...
, 3434.Nagasiri R, Chitmongkolsuk S. Long-term survival of endodontically treated molars without crown coverage: a retrospective cohort study. J Prosthet Dent. 2005 Feb;93(2):164-70. https://doi.org/10.1016/j.prosdent.2004.11.001
https://doi.org/10.1016/j.prosdent.2004....
regardless of remaining filling material and voids observed with this access type. Similar data were found in the analysis of the failure pattern, in which all groups showed a higher prevalence of favorable and restorable fractures (Type I, II and III),3535.Burke FJ. Tooth fracture in vivo and in vitro. J Dent. 1992 Jun;20(3):131-9. https://doi.org/10.1016/0300-5712(92)90124-U
https://doi.org/10.1016/0300-5712(92)901...
similar to the control group (p > 0.05). This may be attributed to the preservation of the marginal ridges, which have a direct influence on the fracture pattern of the tooth structure, and correlate the type of fracture to the stress distribution pattern along the tooth structure 11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...
. It is worth noting that in all groups the access cavities were restored with composite resins associated with the adhesive system, which according to some authors promotes the internal reinforcement of the dental structure of the endodontically treated teeth by reducing cusp deflection.11.Pereira RD, Leoni GB, Silva-Sousa YT, Gomes EA, Dias TR, Brito-Júnior M, et al. Impact of conservative endodontic cavities on root canal preparation and biomechanical behavior of upper premolars restored with different materials. J Endod. 2021 Jun;47(6):989-99. https://doi.org/10.1016/j.joen.2021.03.009
https://doi.org/10.1016/j.joen.2021.03.0...

Therefore, according to the obtained results, the influence of the access cavity on root canal preparation and fracture resistance of mandibular molars is evident. Instruments with lower tapers effectively shape the root canal even in teeth with the Truss cavity. In addition, this access cavity, due to the maintenance of the enamel/dentin bridge in the labial-lingual direction, showed greater resistance to fracture compared to CAC and TAC. Thus, given the changes in the approach of endodontic access, it is necessary to evaluate the remaining tooth as well as the planning of root canal preparation and the choice of the restorative protocol individually, since they have a direct influence on the prognosis.

Conclusions

In endodontic treatment with Truss access cavities, reciprocating instruments with lower taper promoted less root canal transportation. Also, Truss access cavities resulted in higher fracture resistance values, but a higher percentage of voids and remaining filling material was observed.

Acknowledgments

We gratefully acknowledge the financial support by the Coordination for the Improvement of Higher Education Personnel (CAPES, Brazil, nº33002029032P4) and São Paulo Research Foundation (FAPESP, Brazil, nº2018/14450-1). The authors declare no conflicts of interest related to this study.

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Publication Dates

  • Publication in this collection
    27 Oct 2023
  • Date of issue
    2023

History

  • Received
    3 May 2023
  • Accepted
    15 June 2023
  • Received
    11 July 2023
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