Is canal overinstrumentation able to produce apical root dentinal microcracks in extracted teeth?

Abstract

Aim To assess the impact of mechanical overinstrumentation of root canals in extracted teeth on the development of dentinal microcracks in the apical portion of the root by means of micro‐computed tomographic (micro‐CT) analysis. Root canal preparation short of the canal terminus and at the apical foramen (AF) were used as controls. Methodology Twenty 2‐rooted maxillary premolars with two canals were selected, scanned in a micro‐CT device and the root canals prepared sequentially using Reciproc M‐Wire R25 instruments to working lengths: 1 mm short of the AF (AF − 1 mm), at the AF (AF), and overinstrumentation (AF + 1 mm). A micro‐CT scan of each specimen was performed after each time point. After reconstruction and co‐registration procedures, the images were screened from the cementoenamel junction to the apex (n = 55 352) to identify the presence of dentinal microcracks in the apical third of the root. Results After the analyses of 55 352 slices, dentinal microcracks were visualized in 12.45% of the images (6892 slices), with 5.73% (3174 slices) in the cervical, 3.57% (1976 slices) in the middle and 3.15% (1740 slices) in the apical third. All dentinal microcracks observed at all time points (AF − 1 mm, AF and AF + 1 mm) were already present in the corresponding images before canal instrumentation. Therefore, no new microcracks were detected, regardless of the working length used for canal instrumentation. Conclusion Reciprocating root canal preparation either short, at or beyond the AF (overinstrumentation) did not create dentinal microcracks in the roots of extracted 2‐rooted maxillary premolars.

A critical analysis of research methods and experimental models to study dentinal microcracks

“…In this review, it was found that studies focused on the development of microcracks at the apical third of the root (Belladonna et al, 2021;Coelho et al, 2016;de Oliveira et al, 2017ade Oliveira et al, , 2017b were based on the assumption that canal shaping would have a relevant mechanical impact on the reduced volume of dentine in this region. In some of them, the impact of the apical extension of the mechanical preparation was assessed through micro-CT and found no new microcrack at the apical region (de Oliveira et al, 2017a(de Oliveira et al, , 2017b.…”

“…By using extracted/stored teeth, as in the first sectioning studies, this method was further improved through an in situ approach employing fresh cadaveric bone blocks. The best scientific evidence provided so far by these studies are summarized in the following list and shall be taken as the main conclusions of this narrative review: Micro‐CT is an accurate method to visualize dentinal microcracks previously observed in root cross sections under microscopic‐based magnification and illumination (De‐Deus et al, 2016); Using extracted teeth, no new dentinal microcrack is created after canal preparation since observed cracks are already present pre‐operatively; therefore, there is a lack of cause–effect relationship between root canal preparation procedures and dentinal defects (Aksoy et al, 2019; Arumugam & Yew, 2021; Aydin et al, 2014; Bayram et al, 2017a, 2017b; Belladonna et al, 2021; Cassimiro et al, 2017; De‐Deus et al, 2014, 2015, 2016, 2017b, 2017c; Martins et al, 2021; Miguéns‐Vila et al, 2017, 2021; de Oliveira et al, 2017a, 2017b; Rödig et al, 2019; Vieira et al, 2020; Zuolo et al, 2017); The number of dentinal microcracks has no correlation with the force required to fracture extracted teeth (Cavalcante et al, 2020); No dentinal microcrack is observed in situ neither in the baseline images nor after root canal preparation in fresh cadaveric bone blocks, suggesting that microcracks observed in extracted/stored teeth are a laboratory phenomenon, not reproduced in a clinical environment (De‐Deus et al, 2017b, 2019). …”

“…Currently, our digital search revealed 27 confirmatory studies using micro-CT imaging technology to evaluate the frequency of dentinal microcracks after root canal preparation in extracted/stored teeth published in peer-reviewed journals from research groups worldwide (Table 2). Eighteen of them found no new dentinal microcracks (Arumugam & Yew, 2021;Bayram et al, 2017aBayram et al, , 2017bBelladonna et al, 2021;Cassimiro et al, 2017;De-Deus et al, 2014, 2017cMartins et al, 2021;Miguéns-Vila et al, 2021;de Oliveira et al, 2017ade Oliveira et al, , 2017bRödig et al, 2019;Stringheta et al, 2019;Ugur Aydin et al, 2019;Vieira et al, 2020;Zuolo et al, 2017), whilst nine studies reported the development of new defects after canal preparation (Aggarwal et al, 2021;Aksoy et al, 2019;Alkahtany & Al-Madi, 2020;Çakici et al, 2019;Ceyhanli et al, 2016;Jain et al, 2018;Jamleh et al, 2021;Mandava et al, 2018;Tsenova-Ilieva et al, 2019).…”

“…In some of them, the impact of the apical extension of the mechanical preparation was assessed through micro-CT and found no new microcrack at the apical region (de Oliveira et al, 2017a(de Oliveira et al, , 2017b. In a recent study, the apical occurrence of dentinal defects was investigated at three working lengths: short canal preparation (apical foramen −1 mm), at the apical foramen and over preparation (apical foramen +1 mm), and no new microcracks were created (Belladonna et al, 2021). Notwithstanding the similar No cracks after canal preparation findings of most publications, some micro-CT studies reported the development of new microcracks after root canal preparation (Aggarwal et al, 2021;Alkahtany & Al-Madi, 2020;Çakici et al, 2019;Ceyhanli et al, 2016;Jain et al, 2018;Jamleh et al, 2015Jamleh et al, , 2021Mandava et al, 2018;Tsenova-Ilieva et al, 2019; Table 2).…”

“…Since 2014, new findings from in vitro , ex vivo and in situ studies using micro‐computed tomographic (micro‐CT) imaging technology reshaped the overall panorama and understanding on the development of dentinal defects produced by root canal preparation and filling procedures (Aggarwal et al, 2021; Aksoy et al, 2019; Alkahtany & Al‐Madi, 2020; Arashiro et al, 2020; Arumugam & Yew, 2021; Aydin et al, 2014; Bayram et al, 2017a, 2017b; Belladonna et al, 2021; Çakici et al, 2019; Cassimiro et al, 2017; Cavalcante et al, 2020; Ceyhanli et al, 2016; De‐Deus et al, 2014, 2015, 2016, 2017b, 2017c, 2020; Jain et al, 2018; Jamleh et al, 2015, 2021; Mandava et al, 2018; Martins et al, 2021; Miguéns‐Vila et al, 2017; de Oliveira et al, 2017a, 2017b; Rödig et al, 2019; Shemesh et al, 2018; Stringheta et al, 2019; Vieira et al, 2020; Zuolo et al, 2017). The achievements from these studies identified that: (i) root dentinal microcracks observed in cross‐sectional images of extracted teeth are not caused by canal shaping procedures; (ii) dehydration often causes cracking of the dentinal tissue, regardless of canal instrumentation; (iii) dentinal microcracks do not predispose the root to fracture in a laboratory setting using extracted teeth; (iv) microcracks observed in root sections of extracted teeth ( in vitro ) cannot be confirmed in a fresh cadaver model ( in situ ); (v) dentinal microcracks caused by endodontic procedures and observed in cross‐sectional images of extracted roots are a phenomenon that has never been reported in clinical practice.…”