Journal of Conservative Dentistry

: 2022  |  Volume : 25  |  Issue : 5  |  Page : 547--554

Effect of guided conservative endodontic access and different file kinematics on debris extrusion in mesial root of the mandibular molars: An in vitro study

Sathish Sundar1, Aswathi Varghese1, Krithika J Datta2, Velmurugan Natanasabapathy1,  
1 Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Meenakshi Academy of Higher Education and Research University, Chennai, Tamil Nadu, India
2 Department of Conservative Dentistry and Endodontics, Saveetha Dental College, Saveetha Institute of Medical and Technical Sciences, Saveetha University, Chennai, Tamil Nadu, India

Correspondence Address:
Dr. Sathish Sundar
Department of Conservative Dentistry and Endodontics, Faculty of Dentistry, Meenakshi Academy of Higher Education and Research University, No. 1, Alapakkam Main Road, Maduravoyal, Chennai - 600 095, Tamil Nadu


Background: Guided conservative endodontic access is a novel technique and the influence of such access cavities on apical debris extrusion (ADE) can have a significant effect on postoperative pain. Objective: This study compared ADE and preparation time (PT) in the mesial canals of the mandibular first permanent molars in different access cavity designs and the amount of sodium hypochlorite in the extruded debris using attenuated total reflection-Fourier transform infrared spectrometer (ATR-FTIR). Materials and Methods: Human mandibular first permanent molars (N = 72) were selected and randomly divided into six groups (n = 12) based on type of cavity design and files used: Group 1, Conservative Access Cavity [ConsAC])-WaveOne Gold; Group 2, ConsAC-Mtwo; Group 3, ConsAC-XP-endo shaper; Group 4, Traditional Access Cavity [TradAC])-WaveOne; Group 5, TradAC-Mtwo; and Group 6, TradAC-XP-endo shaper. All the ConsAC were prepared with a customized template fabricated using cone beam computed tomography. ADE evaluation was done using the Myers and Montgomery set up. All the instruments were used according to the manufacturers' instructions, followed by a final irrigation using Endoactivator. The time taken for preparation was calculated using a digital watch. Five samples in each group was taken and subjected to ATR-FTIR analysis. Results: There was no significant difference between the groups with respect to ADE (P > 0.05). Whereas, a statistically significant difference was seen in PT between the TradAC and ConsAC (P < 0.05). Using ATR-FTIR, it was found that all the samples of extruded debris had the presence of sodium hypochlorite. Conclusions: All instrumentation systems produced ADE irrespective of access cavity design. The time taken for preparation of canals in ConsAC was significantly longer compared to TradAC. Clinical Relevance: ADE can translate clinically as postoperative pain. Assessing the ADE in ConsAC could shed light on the type of file systems that can be used in such cavities in order to minimize postoperative pain clinically.

How to cite this article:
Sundar S, Varghese A, Datta KJ, Natanasabapathy V. Effect of guided conservative endodontic access and different file kinematics on debris extrusion in mesial root of the mandibular molars: An in vitro study.J Conserv Dent 2022;25:547-554

How to cite this URL:
Sundar S, Varghese A, Datta KJ, Natanasabapathy V. Effect of guided conservative endodontic access and different file kinematics on debris extrusion in mesial root of the mandibular molars: An in vitro study. J Conserv Dent [serial online] 2022 [cited 2023 Dec 9 ];25:547-554
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Full Text


Biomechanical preparation of the root canals plays a pivotal role for the success of endodontic treatment. Apical debris extrusion (ADE) occurs inadvertently during cleaning and shaping.[1],[2] This may result in a flare up leading to pain and swelling after root canal instrumentation resulting in delayed healing.[3] Tooth type, canal curvature, apical patency and apical diameter, file type and kinematics, irrigant agitation, and dynamics are some of the factors that can affect ADE.[4],[5] Among these factors, file design and kinematics play a major role in influencing ADE.[6]

Recently, conservative access cavities (ConsAC) were introduced as a part of the concept of minimal invasive dentistry (MID),[7] which relies on the concept of partial deroofing preserving the pericervical dentin. Although ConsAC is reported to have superior fracture resistance,[8],[9],[10],[11] many disadvantages include increased difficulties in canal detection,[12],[13] biomechanical preparation, incomplete pulp chamber disinfection,[14],[15],[16] and increased risk of iatrogenic errors.[17],[18]

At present, the influence of ConsAC on various endodontic parameters is scarce and ambiguous. Tüfenkçi et al. assessed the influence of ADE in ConsAC instrumented with Reciproc Blue and One Curve files and concluded that Reciproc Blue resulted in more ADE.[19] Further investigation on the effect of different file kinematics on ADE in ConsAC could shed valuable information that can be translated clinically.

The preparation of ConsAC in most of the earlier studies have been done based on anatomical landmarks hence it is hugely dependent on the skill of the operator.[7] Using an access cavity template similar to the ones used in guided endodontics for negotiation of pulp canal obliteration, could possibly allow for a precise and accurate access preparation.[20] In our study, a customized 3D printed template was fabricated for this purpose.

Silva et al. had assessed the preparation time (PT) for minimal invasive access in premolar teeth and concluded, that the time taken for preparation of minimal invasive access was significantly longer in comparison to traditional access cavities (TradAC).[9] Free hand preparation of conservative access is time consuming. However, till now, there are no studies evaluating the PT in molars using customized printed template in molar teeth.

Vast majority of the earlier studies on extrusion have avoided using NaOCl as an irrigant, since it could get crystallized and affect the amount of debris extruded.[5] However, in a clinical scenario, the debris extruded can contain NaOCl and it is well established fact that NaOCl is toxic to periapical tissues.[5] Hence, the aim of this study was to assess the effect of guided conservative access and different file kinematics on the amount of ADE and PT in comparison with traditional access preparation. The secondary aim was to quantify the amount of NaOCl in ADE using attenuated total reflection-Fourier transform infrared spectrometer (ATR-FTIR).

 Materials and Methods

This manuscript of this laboratory study has been written based using the Preferred Reporting items for Laboratory studies in Endodontology 2021 guidelines.[21] The study was approved by the Institutional Review Board (MAHER University, Chennai, Tamil Nadu) IRB number: (MADC/IRB-XXXIII/2020/532).

Sample size calculation and selection

The sample size was calculated with power of 80% (0.08) and an alpha of 0.05. A total of 72 freshly extracted human mandibular first permanent molars with similar length (20 ± 1 mm) and width (apical diameter up to size 25) and having a mesial root canal anatomy of Vertucci classification type IV were selected for the study. A preoperative CBCT scan was taken for all the teeth (90 kVp, 4 mA and 0.11-mm voxel size Planmeca, Finland, Prexion 3D unit Teracom, San Mateo). Immature teeth, root canals (curvature >20°), teeth with apical diameter greater than ISO #25, fractures, cracks, and aberrant canal morphology were excluded.

Teeth were disinfected according to the OSHA guidelines[22] and stored in 0.1% thymol solution at 4°C before experimental studies. The teeth were divided randomly into six groups (n = 12) based on type of access cavity preparation and different file kinematics:

Group 1, Conservative access cavity-WaveOne Gold (ConsAC-WOG)Group 2, Conservative access cavity-Mtwo (ConsAC-M2)Group 3, Conservative access cavity-XP-endo shaper (ConsAC-XP)Group 4, Traditional access cavity-WaveOne Gold (TradAC-WOG)Group 5, Traditional access cavity-Mtwo (TradAC-M2)Group 6, Traditional access cavity-XP-endo shaper (TradAC-XP).

Debris collection

ADE was estimated using a modified version of Myers and Montgomery (1991) as suggested in previous studies.[23],[24],[25] The empty Eppendorf tubes were preweighed using an electronic microbalance (Satelec, Kolkata, India) with a precision of 10−3 g. The measurements were performed thrice for each Eppendorf tube, and the mean value was taken as preweight. The Eppendorf tubes were inserted into glass vials through a stopper that sealed the vials. Teeth were inserted into Eppendorf tubes up to cementoenamel junction and stabilized with elastomeric impression material to prevent the leakage of irrigation solution through the insertion interfaces. A 27-gauge needle was inserted alongside the stopper to balance the internal and external air pressures. The glass vials were covered with aluminum foil and sheet of rubber dam to blind the operator from observing the root apex during root canal instrumentation. Following instrumentation, the teeth were removed from the tube and the debris adhering to the root apices was collected by washing off the apical area of the tooth with 1 ml of distilled water into the tube. The Eppendorf tubes were stored in an incubator at 70°C for 5 days, to desiccate the debris, before weighing the dry debris using an electronic balance. Post-weight of the Eppendorf tubes was calculated similar to the preweight calculation. The ADE was obtained by subtracting the weight of the empty Eppendorf tube from the post-weight measurements.

Conservative access cavity

The occlusal details of the teeth in conservative access groups (1, 2 and 3) were scanned using a surface scanner (Shining 3D, Zhejiang, China). Using the CBCT and surface scans, a virtual image of the 3D preparation template was designed (Geomagic Freeform plus, 3D systems South Carolina software, USA). A custom-made 3D printed template (Form 2 SLA 3D printer) Formlabs, Massachusetts, USA) was fabricated for each tooth such that the outline of the access cavity was enough to locate the root canal orifices. In ConsAC groups, the access cavity with help of the fabricated template using an endo access bur 1 (size 1 Dentsply Maillefer, Ballaigues, Switzerland) [Figure 1].{Figure 1}

Traditional access cavity

TradAC was prepared using endo-access bur (size 3) (Dentsply Maillefer, Ballaigues, Switzerland) following complete deroofing with exposure of the pulp horns and straight-line access to the root canals.[26],[27]

Root canal preparation

After establishing apical patency, working length (WL) was determined and prior to instrumentation, a glide path was created using a K file in the mesial canals with ISO #15 for all the teeth.

Cleaning and shaping

ConsAC-WOG and TradAC-WOG

The WOG Primary file (25/0.07) was used in 'Wave OneAll' mode in a dedicated endodontic motor (X smart plus, Dentsply Maillefer, Ballaigues, Switzerland). The file was used in a slow in-and-out pecking motion with a 3-mm amplitude limit, and gentle apical pressure at 350 rpm speed and 1.2 N torque. Irrigation was performed periodically at 3 pecks usage of file such that a total of 10 ml of 5.25% NaOCl was used.

ConsAC-M2 and TradAC-M2

Mtwo NiTi rotary instruments (VDW, Munich, Germany) were used in an Endodontic motor (X-martplus, Dentsply Maillefer, Ballaigues, Switzerland) at 280–300 rpm at 1.2–2.3 Ncm torque according to the manufacturers' instruction and the mesial root canals were enlarged upto size 25/06. The mesial root canals were irrigated with a total of 10 ml of 5.25% NaOCl equally distributed after the use of every file.

ConsAC-XP and TradAC-XP

The XP-endo shaper was used in a torque-limited electric motor at 900–1000 rpm and 1 Ncm. The instrument size (10/0.01–30/0.04) was used with gentle 4–8-mm-long strokes upto WL in the mesial root canals. During instrumentation intermittently a total of 10 ml of 5.25% NaOCl was used as irrigation.

Dental operating microscope (Labomed Dental Microscope Prima DNT, USA) at 3.5X magnification was used for all the procedures. All the root canal preparations were performed by a final year postgraduate student who was trained to use the various root canal instrumentation procedures.

Final irrigation protocol

In all the groups, EndoActivator system (size 15, 0.02 taper) (Dentsply Tulsa Dental Specialities, Tulsa, OK, USA) was used for the final irrigation protocol. The sequence of irrigation included, 5 ml of 5.25% NaOCl (Parcan; Septodont, Delhi, India), 3 ml of 17% Ethylenediaminetetraacetic acid (Dent Wash; Prime Dental Products Pvt. Ltd., Thane, India) and 5 ml of 5.25% NaOCl was used for a total time of 1 min (20 s each irrigant).

After biomechanical preparation, the teeth were removed from the Eppendorf tubes and debris at the apex was collected with 1 ml of distilled water. After drying the tubes in an incubator (5 days, 70°C), the average postinstrumentation weight was calculated with help of an electronic weighing balance. The amount of ADE was calculated by subtracting the preoperative weight from the postoperative weight. A digital stop clock was used to calculate the total PT which included time taken from the beginning of instrumentation till final irrigation.

Estimation of amount of NaOCl in the extruded debris

Five representative samples from each group which showed the highest ADE was selected. The compositional analysis of the selected samples was performed using diamond ATR-FTIR spectrophotometer (Brukers alpha E spectophometer, Germany). The samples were placed on a field of 4 cm × 4 cm polished surface in contact with the diamond crystal of the ATR to obtain spectra ranging from 400 and 4000 cm−1. The resulting spectra was analyzed was performed using Opus software (11.0010 version). Absorbance peaks of the obtained samples were compared with known values in literature for Na linked and O-Cl linked bonds to confirm if NaOCl was present in the representative samples.

Statistical analysis

Statistical analysis was done using STATA 16.1 software (STATA Corporation, College Station, Texas, USA). Homogeneity of variance among the groups was tested using Levene's test. As the equality of variance hypothesis was rejected, intergroup comparison was performed using Welch analysis of variance (ANOVA) test followed by post hoc Dunnett C test (after Welch ANOVA) test [Table 1]. Intergroup comparison between access preparation types was performed using Welch t-test for preweight and conventional unpaired t-test for variables (postweight, ADE difference, and time). Intergroup comparison between rotary and other instrumentation groups (ConsAC) was performed using Welch t-test for variables (preweight, post weight, ADE difference, and time). Intergroup comparison between rotary and other instrumentation groups (TradAC) using Welch t-test for variables (preweight, postweight, ADE difference, and time).{Table 1}


Apical debris extrusion

The mean and standard deviations of the ADE in the groups tested are given [Table 2]. There was no significant difference in the ADE between all the tested groups (P > 0.05). The amount of ADE was in the following order: ConsAC-WOG > ConsAC-M2 = Trad AC-M2 > TradAC-WOG > ConsAC-XP > TradAC-XP. Furthermore, there was no significant difference in ADE between the groups with respect to file kinematics (reciprocation, rotary multiple file and rotary single file) [Table 3].{Table 2}{Table 3}

Preparation time

The mean and standard deviations of the PT is shown in the [Table 2]. PT was in the following order, ConsAC-WOG > ConsAC-M2 > Cons AC-XP > TradAC-M2 > TradAC- WOG > TradAC-XP. Overall, TradAC PT was significantly lesser in comparison to ConsAC (P < 0.05). Within the ConsAC, ConsAC-XP took significantly lesser time in comparison to ConsAC-WOG and ConsAC-M2 (P < 0.05). Within TradAC and TradAC-WOG took significantly lesser time in comparison to TradAC-M2. Also, there was a significant difference in PT between the groups with respect to file kinematics (reciprocation, rotary-multiple file and rotary-single file) [Table 3].

Amount of NaOCl in apically extruded debris

The absorbance spectra showed peaks from 900 to 500 cm-1 in all specimens confirming the presence of hypochlorite. The area under the spectra in this range was calculated to obtain the average percentage of hypochlorite bonds. It was highest in the ConsAC-WOG group and lowest in TradAC-XP group [Table 3] and [Figure 2].{Figure 2}


Apically extruded debris during chemo-mechanical preparation leads to increased postoperative pain.[3] Hence it is imperative for the clinicians to minimize AED to have minimum postoperative pain. This study was done in the mesial roots of the mandibular first molars using three file systems, Mtwo (conventional NiTi, rotary motion, nonheat treated), XP-endo shaper (MaxWire, rotary, heat-treated single file) and WaveOne Gold (gold wire, reciprocation, heat treated) representing different file kinematics.

The quantification of ADE was done based on modified Myers and Montgomery (1991)[22] method as done in previous studies.[11],[28],[29] In the current study, all the endodontic procedures in ConsAC groups were performed with the 3D printed template under magnification enabling standardization, precision and thereby eliminating operator variability. Although templates have been used for locating calcified canals in molars, this is the first laboratory study to use a customized single-tooth template for the purpose of preparation of minimally invasive access cavity in molar teeth. This customized guide could be used even by inexperienced operator to open access cavity in molar teeth.

Various authors have claimed that MIA preparation designs may compromise the cleaning and shaping performances of NiTi instruments due to constricted access.[14],[16] The use of irrigation agitation systems such as EndoActivator has been suggested to overcome this short coming[30],[31] and hence it was used as an activation technique in this study.

Minimal amount of debris extrusion occurs inadvertently during cleaning and shaping which is taken care by the body's immune response system. However, if the debris extrusion is more, it may result in postoperative pain or delayed healing which could in turn effect the quality of life after endodontic treatment.[3] The result of the ADE and PT obtained in this study was due to the cumulative effect of the file specification including kinematics and type of the access preparation. In the present study all instrumentation systems (rotary and reciprocation) caused varying degrees of ADE in both the TradAC and ConsAC. ADE in all the groups of ConsAC was more when compared to TradAC. The lesser dimension of ConsAC would have negative effect leading to more ADE.[32],[33] However, there was no statistical difference among the groups with respect to ADE. Although there was no significant difference, the greatest amount of ADE in the ConsAC-WOG must be viewed with caution. The ADE in ConsAC-WOG group was 4.2 times more than ConsAC-M2 and almost 4.9 more than ConsAC-XP. Although WOG results in well centered and conservative root canal preparations in TradAC, Alovisi et al. showed that there was more canal transportation when used in ConsAC.[13] Coronal interferences in ConsAC alter the angle of the entry of the WOG files during instrumentation creating more friction on the outer aspect of the root canal wall leading to greater generation of debris at each level of the canal. It can be contemplated that this altered shaping of the WOG along with reciprocating kinematics might be the reason for the greatest ADE in ConsAC-WOG. However, the existing evidence is not able to provide adequate proof whether reciprocating motion by itself can cause ADE.

Continuous rotational motion acts like a screw conveyor and usually enables coronal augmentation of debris thereby minimizing ADE.[24] The results of the current study supports this hypothesis wherein ADE in group ConsAC-M2, ConsAC-XP, TradAC-M2, ConsAC-XP was less when compared to ConsAC-WOG. Mtwo (NiTi) are nonheat-treated files and have less flexibility when compared with the heat treated NiTi. Although progressive pitch design in Mtwo enables coronal augmentation, lesser flexibility of the final instrumentation files (ISO #20 6% taper and ISO # 25 6%) can act a piston creating more pressure on the walls of the access preparation and root canals, thereby forcing more debris apically. Besides this, XP-endo shaper is an adaptive single-file system and hence the greater ADE in ConsAC-M2 and TradAC-M2 compared to ConsAC-XP and TradAC-XP although not statistically significant.

Least amount of ADE and time in ConsAC-XP can be justified by innovative design features of the file. Based on the “adaptive” core instrument design concept XP-endo shaper works in an “serpentine motion,” transforming based on the original root canal anatomy and removing very minimal dentin structure resulting in lesser debris accumulation at different levels of the canal. The booster tip and the ability of the instrument to expand and contract mesiodistally and buccolingually enables it to conform to the restricted dimensions of the ConsACs enabling unhindered progression of the file apically.[34]

Significant difference in PT between ConsAC and TradAC can be explained by the smaller circumference of the ConsAC and absence of straight-line access which prolongs the time taken for instruments and irrigation agitation devices to reach the WL. Although our study evaluated only the time taken for chemomechanical preparation, total operative time from access cavity preparation till obturation should be evaluated to translate the results clinically. It is interesting to note that though a customized guide was used, which could have helped to identify the canals more easily in ConsAC cavity preparation, the time taken for instrumentation was still longer. The highest PT of ConsAC-WOG was in accordance with Alovisi et al. showed that WOG in ConsAC requires more pecking motions to reach the WL. Greater taper at the tip of the WOG instrument (ISO #25 7%) when compared with the other instruments (6% in M2, 1–4% in XP-endo shaper) makes this instrument to bind more frequently hence increasing the time taken to reach the WL.[13] Similarly, there was a longer PT for ConsAC-M2 and TradAC-M2 in comparison to ConsAC-XP and TradAC-XP which can be attributed due to the multiple sequence of Mtwo. However, the duration of time taken to perform the procedure in a laboratory setting could be completely different from the clinical scenario; hence, this result should be viewed with caution. Future studies are required to further evaluate this aspect.

As NaOCl is indispensable during ConsAC instrumentation in a clinical scenario, its presence in ADE was confirmed using ATR-FTIR. The presence of O-Cl bonds which was confirmed by ATR-FTIR in all the tested samples must be viewed with caution and every effort should be taken in a clinical scenario to minimize the extrusion of NaOCl. ATR-FTIR has been used in literature to estimate the detect the changes in root dentin after chelation using various irrigants.[35],[36],[37] To the best of our knowledge, this is the first study of its kind the quantification of NaOCl using ATR-FTIR. The obtained absorbance spectra (900–500 cm−1) were correlated with the already existing absorbance spectra for a hypochlorite bond. By using peak area of vibrational banding of bonds in FTIR, we can get information about relatively concentration of ions in a given sample.[38] The area under the spectra in this range was calculated to obtain the average percentage of hypochlorite bonds in our study, which is a representative of the amount of hypochlorite in the ADE and is not a direct comparison of NaOCl between ConsAC and TradAC.

The limitations of the study were that periapical tissues were not simulated. There was also a variation in the final apical diameter after instrumentation among the groups and difference in the kinematics of the tested files, which could have influenced the outcome of the study. Furthermore, only teeth with moderate curvature and full formed apices were selected for this study. Clinical trials evaluating postoperative pain and long-term healing are required.


Within the limitations of this study, it can be concluded that ADE in ConsAC was comparable to TradAC. There was no significant differences between the debris extruded and PT taken with respect to type of files and kinematic of files. PT taken for access opening and cleaning shaping was significantly higher in all groups of the ConsAC in comparison to TradAC groups. The ATR-FTIR data showed the presence of NaOCl in all the tested extruded debris samples. This being the first study evaluating ADE in conservative access cavity, future laboratory studies to assess the influence of other paramenters on ADE are needed.

Financial support and sponsorship

This was a self-funded study.

Conflicts of interest

There are no conflicts of interest.


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