Abstract
Objectives
This study assessed the influence of preparation size on the efficacy of shock wave–enhanced emission photoacoustic streaming (SWEEPS) and conventional irrigation (CI) on removal of accumulated hard tissue debris (AHTD) from isthmus-containing mandibular molars using micro-computed tomographic analysis.
Materials and methods
Sixty extracted mandibular molars with two mesial canals connected by an isthmus were selected. Canals were shaped with Mtwo instruments (VDW, Munich, Germany) up to sizes 25/.06, 40/.04 or 40/.06 (n = 20), and specimens were distributed into 2 final irrigation groups (n = 10): SWEEPS and CI. Roots were scanned at a resolution of 10.5 µm before and after preparation and final irrigation. Data sets were co-registered, and the percentage reduction of AHTD calculated for each specimen was statistically compared using analysis of variance with a of 5% significance level.
Results
The preparation size did not significantly influence the percentage reduction of AHTD (p < 0.05), whereas the final irrigation technique had a significant effect on debris removal (p < 0.05). A significant reduction of AHTD was achieved after final irrigation in all groups (p < 0.05); however, SWEEPS was associated with a significantly greater percentage reduction of debris than CI (p < 0.05). None of the specimens presented a completely clean isthmus.
Conclusions
Removal of AHTD was not significantly affected by the preparation size. SWEEPS was associated with significantly less debris than CI.
Clinical relevance
SWEEPS performed significantly better than CI regarding the removal of AHTD from isthmus-containing mandibular molars irrespective of the preparation size.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
Introduction
Mechanical root canal preparation results in accumulated hard-tissue debris (AHTD) in anatomic complexities of the root canal system [1,2,3]. In infected root canals, AHTD may harbour microorganisms and serve as a reservoir for root canal reinfection. Additionally, debris packed in irregularities of the root canal space may impede thorough disinfection in cases with apical periodontitis [2, 4, 5]. It can also negatively interfere with the sealing ability of root canal filling materials as the remaining dentine debris hinders the gutta-percha to penetrate into recesses of the root canal space even when thermoplasticized obturation techniques are used [6] and prevent their adaptation into hard-to-reach areas [6, 7].
Conventional irrigation (CI) using a syringe and needle is often inefficient on the removal of AHTD from anatomic complexities because fluid penetration and exchange beyond the needle tip is limited [8]. Moreover, irrigant velocity and wall shear stress which are important parameters for the mechanical cleaning effect of irrigation [9, 10] are restricted during syringe irrigation thereby decreasing the penetration depth of the irrigation solution into anatomic irregularities such as fins or isthmuses [3, 7, 11, 12]. Thus, several activation techniques such as sonic or ultrasonic devices have been proposed to enhance the mechanical flushing action of the irrigant to increase its effectiveness [13, 14]. Recent studies have investigated the efficacy of these machine-assisted agitation systems in removing AHTD from isthmus-containing mesial root canals of mandibular molars [15,16,17,18]. Although sonically or ultrasonically activated irrigations are the predominant techniques in clinical application [19], laser-activated irrigation (LAI) has been introduced as a promising tool to improve root canal debridement [20,21,22,23,24]. The effect of LAI is based on the absorption of laser energy from erbium lasers (erbium-doped yttrium aluminium garnet, Er:YAG) in an aqueous irrigant [25] which creates vapour bubbles at the fibre tip. These vapour bubbles expand and collapse, resulting in cavitation-induced shock waves and microjets in the fluid [25]. However, these observations have been mainly noted in large liquid reservoirs and cannot be directly applicable to phenomena inside the confined volume of a root canal system [26, 27]. It was recently shown that single laser pulses did not result in the emission of shock waves in narrow reservoirs such as liquid-filled root canals [26]. The main reasons for this decelerated cavitation bubble dynamics are the friction on the root canal walls and the limited space available for a quick displacement of the irrigant during the expansion and contraction of the bubble [27, 28].
Photon-induced photoacoustic streaming (PIPS) uses Er:YAG laser energy (2940 nm) at subablative power levels (0.3 W, 20 mJ at 15 Hz) and a single short pulse duration (50 µs) [24, 29] and has been reported to be more effective than syringe irrigation in removing debris from root canal irregularities [30,31,32,33].
Recently, a novel shock wave–enhanced emission photoacoustic streaming (SWEEPS) modality for Er:YAG laser has been proposed, which is based on the delivery of pairs of laser pulses, properly timed to generate enhanced irrigant streaming and shock wave emission [27, 34]. During the SWEEPS mode, a fibre tip is placed inside the pulp chamber, which emits a subsequent laser pulse into the irrigant when the initial bubble is in the final phase of its collapse [27]. The secondary bubble exerts pressure on the collapsing initial bubble, thus accelerating its collapse and resulting in the formation of shock waves and an improved photoacoustic current, thereby increasing the cleaning and antimicrobial efficacy of the standard PIPS procedure [27]. This phenomenon has been observed even in spatially confined root canals, as enhanced shock waves were created using the SWEEPS modality [27].
Until now, limited data is available for the SWEEPS technique with regard to the removal of dentine debris. A recent study using micro-computed tomography (micro-CT) to assess the removal of AHTD from the root canal system of mandibular molars reported significantly less debris after SWEEPS activation compared to PIPS and ultrasonically activated irrigation [35].
As opposed to the conventional LAI procedure, in which root canal enlargement to a size #30 is mandatory to allow the laser fibre to be inserted in the apical third of the root canal [36, 37], PIPS and SWEEPS techniques require the fibre tip to be placed into the irrigant reservoir in the pulp chamber. Thus, some authors suggested that a minimally invasive root canal preparation to apical sizes 20/0.06, 25/0.06 or 20/0.07 is considered sufficient for effective debridement [24, 29]. Although this concept aims to preserve a maximum amount of healthy dental hard tissues in order to maintain the structural integrity of the tooth [38, 39], irrigant flow and penetration is compromised in the apical root canal third during syringe irrigation due to the limited insertion depth of the irrigation needle and the low wall shear stress [9, 40, 41].
Previous studies investigating the debridement and cleaning efficacy of SWEEPS selected different apical preparation sizes ranging from 25/0.04 to 40/0.06 [35, 42,43,44,45]. However, these studies can only be compared to a limited extent since apical preparation size and taper affect flushing action, wall shear stress and irrigant replacement during syringe and ultrasonically activated irrigation [9, 40, 46,47,48,49]. Moreover, it was shown that sequential apical enlargement from sizes 25 to 40 significantly reduced the amount of accumulated debris using a conventional irrigation protocol [50]. Thus, it can be assumed that root canal dimensions also influence the performance of the novel SWEEPS technique.
So far, there is no information on the effect of preparation size in the removal of debris using SWEEPS. Thus, the aim of this in vitro study was to evaluate the influence of preparation size and taper on the efficacy of the SWEEPS technique and conventional syringe irrigation in removing AHTD from the isthmus of the mesial canals of mandibular molars using micro-CT imaging. The null hypotheses tested were that neither the apical preparation size nor the final irrigation protocol has an influence on the reduction of AHTD.
Material and methods
Sample size estimation
Sample size calculation was based on a previous study on the removal of hard-tissue debris with four final irrigation protocols [11]. In that study, the percentage volume of AHTD after passive ultrasonic irrigation was 0.6% ± 0.7% compared with apical positive pressure (3.7% ± 1.5). An alpha-type error of 0.05, power beta of 0.95% and allocation ratio N2/N1 of 1 was also specified. A total of 7 samples per group were calculated as the minimum size for observing significant differences (https://www.stat.ubc.ca/~rollin/stats/ssize/n2.html).
Specimen selection
After approval of the local Ethics committee (protocol no. 27/8/13), a total of 241 mesial roots of mandibular molars with fully developed apices and without previous endodontic treatment were selected and stored in 0.1% thymol solution until use. Mesial canals were accessed, and a size 10 reamer (Dentsply Sirona, Ballaigues, Switzerland) was inserted into the root canal until the tip of the instrument was just visible at the apical foramen. Digital radiographs were taken in a bucco-lingual direction, and root canal curvatures and radii were measured [51, 52]. Only specimens with curved root canals ranging from 20 to 40° and a radius between 5.5 and 16.5 mm were included. The roots were pre-scanned in a micro-CT device (SkyScan 1272; Bruker-microCT, Kontich, Belgium) with an isotropic resolution of 21.7 µm to obtain a preoperative outline of root canal anatomy. Overall, 60 specimens presenting a type II Vertucci’s canal configuration system [53] with two mesial root canals containing an isthmus with a length of at least 2 mm in the corono-apical dimension [54] were obtained.
The apices of the roots were sealed with fast-set epoxy resin to create a closed-end system, and the reconstruction of the distal wall of the pulp chamber was performed using a dentine adhesive and a resin composite to provide a reservoir for the irrigant. The cusps of the specimens were flattened to a standardized root length of 19 mm with a working length (WL) of 18 mm. Subsequently, the roots were scanned with a high isotropic resolution of 10.5 µm at 80 kV, 125 µA, 180° rotation around the vertical axis, a rotation step of 0.4°, a camera exposure time of 3230 ms and frame averaging of 3. X-rays were filtered using a 1-mm-thick aluminium filter. The acquired projection images were reconstructed (NRecon v.1.7.0.3 software, Bruker-microCT) using 45% beam hardening correction and ring artefact correction of 20–22. Volumetric analyses of the 3-dimensional models were performed by using CTAn v.1.17.7.2 software (Bruker-microCT). Subsequently, the specimens were allocated to three groups (n = 20) based on the morphological parameters of the root canal system (root canal volume and surface, isthmus length in corono-apical direction and isthmus width in bucco-lingual direction). The homogeneity of the values among the groups was verified using Kruskal–Wallis test, thus confirming anatomical matching between experimental groups (p > 0.05; Table 1).
Root canal preparation
A glide path was established with a size 10 reamer (VDW, Munich, Germany) up to WL. Both mesial root canals were instrumented using the basic sequence of Mtwo instruments (VDW) 10/0.04, 15/0.05, 20/0.06 and 25/0.06 taper driven with an electric motor (VDW Silver, VDW). According to the manufacturer, all instruments were used with a brushing motion until WL was reached. Each time the instrument was removed, 2 mL NaOCl (1%) was applied using a 30-gauge open-end tip needle (Endo-EZE, Ultradent, South Jordan, UT, USA). According to the experimental groups, no further root canal preparation was performed in group 1 (25/0.06). The root canals of the remaining specimens were further enlarged using the instrument sequence recommended by the manufacturer, followed by an additional rinse with 2 mL NaOCl (1%) after each NiTi instrument, resulting in either a final apical size 40/0.04 (group 2) or 40/0.06 (group 3). Instruments were discarded after four uses or if an unwinding occurred. After completion of preparation, an additional rinse with 2 mL NaOCl (1%) was performed, root canals were dried with paper points and a second micro-CT scan was performed and reconstructed using the same parameters as the first scan.
Postoperative scans were co-registered with their respective preoperative data sets in DataViewer 1.5.2.4 software (Bruker-microCT) using a pseudo 3D registration tool. Quantification of AHTD was performed by the difference between the root canal spaces before and after preparation using CTAn software (CTAn, 1.17.7.2, Bruker-microCT). The volume of interest (VOI) was defined as the region previously occupied by air in the non-prepared root canal. The additional material that was pushed into the isthmus during preparation (before final irrigation procedure [VBFI]), with density similar to dentine, was considered as debris, and its volume was estimated as the volume of dentine-like material inside the VOI [2, 55]. In addition, unprepared areas were quantified by calculating the number of static surface voxels, which was expressed as a percentage of the total number of surface voxels.
Final irrigation protocols
Specimens from each experimental group were further assigned into two subgroups (n = 10) according to the final irrigation technique used: CI and SWEEPS. The equality of the values regarding the root canal volumes and surfaces after preparation and the percentages of unprepared areas as well as the volume of AHTD before final irrigation among the subgroups was evaluated using Mann–Whitney U-test. p-values were adjusted using Bonferroni-Holm method (p > 0.05) (Table 1).
Specimens of each group were submitted to a final rinse using 15 mL of 1% NaOCl, 10 mL distilled water and 5 mL of 17% EDTA during a total time of 4.5 min according to one of the following irrigation protocols:
CI
Five millilitres of NaOCl was applied for 30 s with a syringe and a 30-gauge Endo-EZE needle (Ultradent) positioned at 2 mm from WL, followed by a 30 s resting phase. After this procedure has been repeated three times, root canals were irrigated for 30 s with 5 mL distilled water, for 30 s with 5 mL EDTA and for 30 s with 5 mL distilled water.
SWEEPS
Five millilitres of NaOCl was continuously delivered using a syringe and a 30-gauge Endo-EZE needle (Ultradent) to maintain hydration during activation. A special Auto SWEEPS Er:YAG laser modality and a special conical fibre tip with a flat end (SWEEPS 600, Fotona) were used at a wavelength of 2940 nm Er:YAG laser at 0.6 W, 15 Hz and 20 mJ per pulse without water and air. The SWEEPS tip was inserted 3 mm deep into the access cavity and activated for 30 s, followed by a 30 s resting phase between activation when using NaOCl. This procedure was repeated three times. Then, 5 mL distilled water was continuously irrigated and activated for 30 s, followed by a continuous flush of 5 mL EDTA within an activation time of 30 s. Finally, 5 mL distilled water was flushed and activated for 30 s as previously described.
Final irrigation procedures were performed by one operator. Root canals were dried with sterile paper points, and a final micro-CT scan was performed. Data sets of the samples after final irrigation were co-registered with their respective counterparts after preparation, and the volume of AHTD (mm3) in each root canal system was calculated (VAFI). The percentage reduction was obtained according to the following formula [(VBFI – VAFI)/VBFI]*100, where VBFI and VAFI are the volume of AHTD (mm3) before and after final irrigation procedures, respectively.
Statistical analysis
As normality assumptions were verified in the data set, means were compared using a two-way ANOVA to calculate the percentage reduction of debris after final irrigation. Paired sample t-tests were carried out to analyse differences between debris volumes before and after final irrigation. p-values were adjusted using Bonferroni-Holm correction method. The level of statistical significance was set at α = 0.05. All analyses were performed with Statistica software v. 13.0 (StatSoft, Tulsa, OK, USA).
Results
Root canal volumes, surface areas, percentages of unprepared areas and volumes of AHTD after preparation did not differ significantly between the two tested groups within the same preparation size (p > 0.05; Table 1).
The preparation size did not significantly influence the percentage reduction of AHTD (p > 0.05); thus, the first null hypothesis was accepted.
Conversely, the final irrigation technique significantly affected the percentage reduction of AHTD (p < 0.05; Table 1). Final irrigation using SWEEPS was associated with a significantly greater percentage reduction of debris than CI (p < 0.05; Table 1). Therefore, the second null hypothesis was rejected. No interaction of factors (preparation size, final irrigation technique) was observed (p > 0.05).
Nevertheless, the percentage volume of AHTD after preparation was significantly reduced irrespective of the final irrigation technique (p < 0.05).
None of the specimens presented a completely clean isthmus. Three-dimensional models of representative mesial root canal systems in each group demonstrate the distribution of AHTD after preparation and the remaining debris after final irrigation (Fig. 1).
Discussion
This in vitro study assessed the effectiveness of laser-activated and conventional final irrigation on the removal of AHTD from mesial root canal systems of mandibular molars prepared to different apical sizes using micro-CT imaging. In laboratory-based research, the removal of accumulated dentine debris from root canals is usually used as a surrogate end-point to evaluate the efficacy of irrigation [56]. Although recent research demonstrated the visualization of pulp tissue to assess root canal debridement by using contrast-enhanced micro-CT imaging [57], the vast majority of investigations has applied conventional micro-CT technology as a precise tool for quantitative and qualitative evaluation of hard-tissue debris within the root canal system [2, 16, 18, 35, 55, 58, 59]. The main advantage of this three-dimensional, non-destructive technology is considered to be the longitudinal evaluation of the same specimen at different time-points during several experimental procedures [18, 35]. Nevertheless, micro-CT imaging enables only in vitro measurements due to the high radiation and long scanning times [55].
Isthmus-containing mesial roots of mandibular molars were selected for the present study as these teeth exhibit a complex internal anatomy [60] where hard-tissue debris tends to accumulate during instrumentation [2]. These isthmuses represent a major challenge for adequate cleaning and disinfection [61] since effective delivery and exchange of irrigants into these hard-to-reach areas of the root canal system is often impeded [15, 62].
In order to increase the internal validity of the study by substantially reducing the anatomical bias among the specimens, groups were balanced with regard to morphometric parameters of the root canal systems (volume, surface area, length and width of isthmus) [12, 63, 64]. Additionally, root canal volumes and surface areas after preparation as well as the percentages of non-instrumented surface areas did not differ significantly between CI and SWEEPS within the same preparation size. Although the root canals were prepared to different apical sizes, equal amounts of AHTD were obtained during instrumentation in all groups prior to final irrigation. As a result, statistical analysis demonstrated no significant differences between experimental groups and confirmed a consistent baseline with respect to relevant parameters prior to final irrigation.
After separation of the mesial roots, the distal wall of the pulp chamber was reconstructed with a resin composite to provide a reservoir for the irrigant [17, 62] as suggested for laser-activated irrigation protocols [24]. Subsequently, the length of the specimens was standardized to 19 mm by flattening of the cusps, resulting in slightly different volumes of the irrigant reservoirs. In previous studies evaluating the efficacy of laser-activated irrigation using PIPS and SWEEPS, the specimens were also reduced to a standardized length of 12 mm [44] or 14 mm, and an artificial irrigant reservoir was created with Gates-Glidden drills [24]. Although the volume of the irrigant reservoir was not standardized in the present study, the irrigant in the access cavity was continuously replenished to maintain a constant irrigant level which is crucial for the success of laser-activated irrigation techniques [21]. Conversely, even if the crowns of the specimens remained intact in previously published studies on LAI [35, 59], this does not necessarily indicate standardized volumes of the access cavities nor the irrigant reservoirs.
Previous studies on AHTD removal used none or minimal irrigation solution during instrumentation to obtain a maximum amount of accumulated debris in the isthmus area [2, 11, 15, 35]. In contrast, NaOCl was used during root canal preparation in the present study as it is not advisable to modify the chemomechanical preparation protocols to favour debris accumulation since this creates an unrealistic challenge for the irrigants [56]. In the present study, the mean debris volume related to the total root canal system before preparation was 39.9% ± 11.4%. In a previous investigation, a mean debris volume of 29.2% ± 14.5% was created during instrumentation with ProTaper instruments to size F3 although no irrigation was performed [2]. These discrepancies between preoperative amounts of debris are notable and can be explained with differences in sample selection with regard to Vertucci’s configuration presenting small or large isthmus areas. Moreover, quantitative data extracted from micro-CT scans are strongly affected by the voxel size [56, 65]. In the present study, a voxel size of 10.5 µm was applied during micro-CT imaging which is within the range between 8.6 µm and 30 µm reported previously [3, 11, 16, 18, 35, 59]. Another confounding factor which contributes to variances regarding the preoperative amount of AHTD among previous studies is related to different calculations as the volume of AHTD can be expressed as the percentage of the total root canal system volume before [2, 3, 17] or after preparation [11, 15, 18, 35, 59]. For example, in previous micro-CT studies, substantially smaller amounts of debris between 7 and 15% with ProTaper Universal F3 and WaveOne Gold Primary instruments were produced, respectively, despite minimal or none irrigation [15, 35]. Nevertheless, these debris volumes were related to the total root canal system after preparation which impedes a direct comparison of these findings. These methodological differences highlight the relevance of standardizing experimental protocols to allow a more precise analysis of the various irrigation techniques applied [66].
In the present study, the novel SWEEPS technique was compared to conventional syringe irrigation as this procedure remains the most popular technique for delivering root canal irrigants amongst endodontists and general dentists [19, 67, 68] to set a common point of reference [56]. This approach facilitates a realistic comparison between any irrigant activation technique and the traditional irrigation protocol [66].
Irrespective of the apical preparation size, SWEEPS resulted in a significantly higher percentage reduction of AHTD than conventional manual irrigation. This increased efficiency of SWEEPS has been explained by the photoacoustic shock waves and cavitation generated by the dual pulsed laser [27, 34, 69], which improved the removal of a greater amount of dentine debris compared with syringe irrigation. Previous studies evaluating the efficacy of PIPS on the removal of debris from the mesial root canal system of mandibular molars [32] or from artificial root canal irregularities in canine roots [31] also reported advantages over the conventional syringe irrigation, supporting the findings of the present study.
Instrumentation size did not significantly influence the removal of AHTD in the present study. This result is in contrast to a previous micro-CT investigation in which root canal enlargement from size 25 to size 40 significantly reduced the overall amount of hard tissue debris by 34% [50]. However, this study focused on the amount of AHTD produced after chemomechanical preparation to different apical sizes with single-file reciprocating systems and a conventional multifile rotary system and not on the final irrigation procedure [50]. These different findings may be explained by anatomical variations such as isthmus width and length which may affect irrigant penetration and the amount of debris removal. A recent study on biofilm removal using confocal microscopic imaging demonstrated the challenges of debriding the isthmus region and the influence of the cross-sectional shape of the isthmus, with the most restricted isthmus area being the most difficult to clean [69]. Further reasons for the divergent results with regard to the reduction of hard-tissue debris by apical enlargement may be differences in irrigant volume and concentration, flow rate and irrigation time.
Final irrigation using conventional irrigation significantly reduced the amount of AHTD created by chemomechanical preparation which is consistent with a previous micro-CT study with a similar experimental set-up [17]. Syringe irrigation was performed according to an optimum clinically relevant protocol as several factors such as needle type, insertion depth and flow rate were shown to influence efficacy of manual irrigation [8, 9]. An open-ended needle was used for irrigant delivery because the high-velocity jets created by this needle are more effective in terms of irrigant penetration and exchange [9, 70]. The applied flow rate of 0.166 mL−1 represents an intermediate value in the range employed by clinicians and can be achieved clinically [71]. A recent study using a computational fluid dynamics model reported a higher irrigant velocity and wall shear stress in a simulated isthmus when the flow rate was increased from 0.033 to 0.166 mL−1 [72]. Another factor that promoted removal of AHTD by syringe irrigation was the needle depth placement at 2 mm short of WL. Positioning the irrigation needle at WL minus 1 mm resulted in percentage levels of AHTD removal from the isthmus of mandibular molars almost three times higher than an insertion depth of 5 mm from the WL [73].
Previous studies on AHTD removal from isthmus-containing mandibular molars using micro-CT imaging reported a higher reduction of AHTD after syringe irrigation between 43.7 and 57.1% [11, 16, 74]. This difference may be attributed to anatomical variations such as C-shaped root canals [74] or a Vertucci type I configuration [11] which may allow better penetration of the irrigants into the isthmus area [62]. In addition, flow rates and needle insertion depth for syringe irrigation, overall irrigant volume and volume of AHTD after preparation varied significantly between these studies and therefore might have influenced these results.
To date, only one study has investigated SWEEPS for removing AHTD from the mesial root canal system of mandibular molars using micro-CT imaging, which reported an overall debris reduction of 84.3% [35]. Although these findings for SWEEPS were better than in the present study, a reliable comparison of these data is hardly feasible due to several differences in the experimental set-up. Firstly, anatomical variations such as the dimensions of root canals and isthmuses have an impact on AHTD removal as penetration of the irrigant is reduced in narrow isthmuses [62]. To overcome anatomical variations, 3D-printed root canal models were recently introduced to allow a reproducible and standardized assessment of different irrigation techniques [72, 75]. However, substitution of dentine by artificial root canals may also affect irrigant penetration since the surface properties of dentine are different from those of hydrophobic resins [56, 76]. Secondly, different final irrigation protocols were applied for SWEEPS with regard to the additional use of EDTA or the resting time of the irrigant between activation. Thirdly, Yang et al. (2020) did not include conventional syringe irrigation as a control group which impedes a comparison of the SWEEPS technique to a current clinical standard [56, 66].
None of the irrigation protocols was able to render the mesial root canal system free from dentine debris which is in accordance to several previous studies [3, 11, 12, 16,17,18, 50, 77].
Histological analysis of mesial root canal systems of mandibular molars revealed that biofilms embedded in hard-tissue debris remain in inaccessible recesses and isthmuses after root canal preparation [4]. Moreover, a percentage of non-instrumented root canal surfaces ranging from 37.84 to 58.94% emphasizes the suboptimal mechanical action of Mtwo instruments on canal walls. Nevertheless, previous micro-CT studies also reported a range of 2.66 to 79.04% untouched root canal walls after biomechanical preparation irrespective of the instrumentation technique [78,79,80,81]. In infected root canals, these unprepared surfaces contain pulp remnants and bacteria [5] which are suggested to be the primary cause for endodontic treatment failure [82]. Thus, the need to optimize chemomechanical preparation to reduce the accumulation of hard-tissue debris is highlighted [15, 50].
A limitation of the present study is that AHTD was used as a surrogate end-point to evaluate the efficacy of the irrigation techniques under investigation since this parameter has not been directly correlated to the healing of apical periodontitis [56]. Thus, future studies on root canal irrigation should focus on the validation of this surrogate end-point whether it is suited to be correlated with the reduction of the microbial load.
Conclusions
The preparation size did not significantly affect the removal of AHTD from isthmus-containing mandibular molars. Although both final irrigation techniques resulted in a significant reduction of AHTD, SWEEPS performed significantly better than conventional irrigation.
References
Metzger Z, Solomonov M, Kfir A (2013) The role of mechanical instrumentation in the cleaning of root canals. Endod Topics 29:87–109. https://doi.org/10.1111/etp.12048
Paqué F, Laib A, Gautschi H, Zehnder M (2009) Hard-tissue debris accumulation analysis by high-resolution computed tomography scans. J Endod 35:1044–1047. https://doi.org/10.1016/j.joen.2009.04.026
Paqué F, Boessler C, Zehnder M (2011) Accumulated hard tissue debris levels in mesial roots of mandibular molars after sequential irrigation steps. Int Endod J 44:148–153. https://doi.org/10.1111/j.1365-2591.2010.01823.x
Nair PNR, Henry S, Cano V, Vera J (2005) Microbial status of apical root canal system of human mandibular first molars with primary apical periodontitis after “one-visit” endodontic treatment. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 99:231–252. https://doi.org/10.1016/j.tripleo.2004.10.005
Siqueira JF, Pérez AR, Marceliano-Alves MF et al (2018) What happens to unprepared root canal walls: a correlative analysis using micro-computed tomography and histology/scanning electron microscopy. Int Endod J 51:501–508. https://doi.org/10.1111/iej.12753
De-Deus G, Reis C, Beznos D et al (2008) Limited ability of three commonly used thermoplasticized gutta-percha techniques in filling oval-shaped canals. J Endod 34:1401–1405. https://doi.org/10.1016/j.joen.2008.08.015
Gutarts R, Nusstein J, Reader A, Beck M (2005) In vivo debridement efficacy of ultrasonic irrigation following hand-rotary instrumentation in human mandibular molars. J Endod 31:166–170. https://doi.org/10.1097/01.don.0000137651.01496.48
Boutsioukis C, Lambrianidis T, Verhaagen B et al (2010) The effect of needle-insertion depth on the irrigant flow in the root canal: evaluation using an unsteady computational fluid dynamics model. J Endod 36:1664–1668. https://doi.org/10.1016/j.joen.2010.06.023
Boutsioukis C, Gutierrez Nova P (2021) Syringe irrigation in minimally shaped root canals using 3 endodontic needles: a computational fluid dynamics study. J Endod 47:1487–1495. https://doi.org/10.1016/j.joen.2021.06.001
Chen JE, Nurbakhsh B, Layton G et al (2014) Irrigation dynamics associated with positive pressure, apical negative pressure and passive ultrasonic irrigations: a computational fluid dynamics analysis. Aust Endod J 40:54–60. https://doi.org/10.1111/aej.12027
Leoni GB, Versiani MA, Silva-Sousa YT et al (2017) Ex vivo evaluation of four final irrigation protocols on the removal of hard-tissue debris from the mesial root canal system of mandibular first molars. Int Endod J 50:398–406. https://doi.org/10.1111/iej.12630
Versiani MA, Alves FRF, Andrade-Junior CV et al (2016) Micro-CT evaluation of the efficacy of hard-tissue removal from the root canal and isthmus area by positive and negative pressure irrigation systems. Int Endod J 49:1079–1087. https://doi.org/10.1111/iej.12559
Gu L, Kim JR, Ling J et al (2009) Review of contemporary irrigant agitation techniques and devices. J Endod 35:791–804. https://doi.org/10.1016/j.joen.2009.03.010
Nusstein JM (2015) Sonic and ultrasonic irrigation. Endodontic irrigation: Chemical dininfection of the root canal system. Springer, Switzerland, pp 173–198
Chan R, Versiani MA, Friedman S et al (2019) Efficacy of 3 supplementary irrigation protocols in the removal of hard tissue debris from the mesial root canal system of mandibular molars. J Endod 45:923–929. https://doi.org/10.1016/j.joen.2019.03.013
Linden D, Boone M, De Bruyne M et al (2020) Adjunctive steps for the removal of hard tissue debris from the anatomic complexities of the mesial root canal system of mandibular molars: a micro-computed tomographic study. J Endod 46:1508–1514. https://doi.org/10.1016/j.joen.2020.05.009
Rödig T, Koberg C, Baxter S et al (2019) Micro-CT evaluation of sonically and ultrasonically activated irrigation on the removal of hard-tissue debris from isthmus-containing mesial root canal systems of mandibular molars. Int Endod J 52:1173–1181. https://doi.org/10.1111/iej.13100
Silva EJNL, Carvalho CR, Belladonna FG et al (2019) Micro-CT evaluation of different final irrigation protocols on the removal of hard-tissue debris from isthmus-containing mesial root of mandibular molars. Clin Oral Investig 23:681–687. https://doi.org/10.1007/s00784-018-2483-1
Dutner J, Mines P, Anderson A (2012) Irrigation trends among American Association of Endodontists members: a web-based survey. J Endod 38:37–40. https://doi.org/10.1016/j.joen.2011.08.013
Blanken J, Verdaasdonk R (2007) Cavitation as a working mechanism of the Er, Cr:YSGG laser in endodontics: a visualization study. J Oral Laser Appl 7:97–106
de Groot SD, Verhaagen B, Versluis M et al (2009) Laser-activated irrigation within root canals: cleaning efficacy and flow visualization. Int Endod J 42:1077–1083. https://doi.org/10.1111/j.1365-2591.2009.01634.x
De Moor RJG, Meire M, Goharkhay K et al (2010) Efficacy of ultrasonic versus laser-activated irrigation to remove artificially placed dentin debris plugs. J Endod 36:1580–1583. https://doi.org/10.1016/j.joen.2010.06.007
George R, Meyers IA, Walsh LJ (2008) Laser activation of endodontic irrigants with improved conical laser fiber tips for removing smear layer in the apical third of the root canal. J Endod 34:1524–1527. https://doi.org/10.1016/j.joen.2008.08.029
Peters OA, Bardsley S, Fong J et al (2011) Disinfection of root canals with photon-initiated photoacoustic streaming. J Endod 37:1008–1012. https://doi.org/10.1016/j.joen.2011.03.016
Meire MA, Poelman D, De Moor RJ (2014) Optical properties of root canal irrigants in the 300–3,000-nm wavelength region. Lasers Med Sci 29:1557–1562. https://doi.org/10.1007/s10103-013-1307-4
Lukač N, Gregorčič P, Jezeršek M (2016) Optodynamic phenomena during laser-activated irrigation within root canals. Int J Thermophys 37. https://doi.org/10.1007/s10765-016-2071-z
Lukač N, Muc BT, Jezersek M, Lukac M (2017) Photoacoustic endodontics using the novel SWEEPS Er:YAG laser modality. J LA&HA 2017:1–7
Gregorcic P, Lukac N, Možina J, Jezeršek M (2016) In vitro study of the erbium:yttrium aluminum garnet laser cleaning of root canal by the use of shadow photography. J Biomed Opt 21:15008. https://doi.org/10.1117/1.JBO.21.1.015008
DiVito E, Peters OA, Olivi G (2012) Effectiveness of the erbium:YAG laser and new design radial and stripped tips in removing the smear layer after root canal instrumentation. Lasers Med Sci 27:273–280. https://doi.org/10.1007/s10103-010-0858-x
Arslan H, Capar ID, Saygili G et al (2014) Effect of photon-initiated photoacoustic streaming on removal of apically placed dentinal debris. Int Endod J 47:1072–1077. https://doi.org/10.1111/iej.12251
Deleu E, Meire MA, De Moor RJG (2015) Efficacy of laser-based irrigant activation methods in removing debris from simulated root canal irregularities. Lasers Med Sci 30:831–835. https://doi.org/10.1007/s10103-013-1442-y
Lloyd A, Uhles JP, Clement DJ, Garcia-Godoy F (2014) Elimination of intracanal tissue and debris through a novel laser-activated system assessed using high-resolution micro-computed tomography: a pilot study. J Endod 40:584–587. https://doi.org/10.1016/j.joen.2013.10.040
Passalidou S, Calberson F, Bruyne MD et al (2018) Debris removal from the mesial root canal system of mandibular molars with laser-activated irrigation. J Endod 44:1697–1701. https://doi.org/10.1016/j.joen.2018.06.007
Jezeršek M, Lukač N, Lukač M (2021) Measurement of simulated debris removal rates in an artificial root canal to optimize laser-activated irrigation parameters. Lasers Surg Med 53:411–417. https://doi.org/10.1002/lsm.23297
Yang Q, Liu MW, Zhu LX, Peng B (2020) Micro-CT study on the removal of accumulated hard-tissue debris from the root canal system of mandibular molars when using a novel laser-activated irrigation approach. Int Endod J 53:529–538. https://doi.org/10.1111/iej.13250
Gordon W, Atabakhsh VA, Meza F et al (2007) The antimicrobial efficacy of the erbium, chromium:yttrium-scandium-gallium-garnet laser with radial emitting tips on root canal dentin walls infected with Enterococcus faecalis. J Am Dent Assoc 138:992–1002. https://doi.org/10.14219/jada.archive.2007.0297
Schoop U, Goharkhay K, Klimscha J et al (2007) The use of the erbium, chromium:yttrium-scandium-gallium-garnet laser in endodontic treatment: the results of an in vitro study. J Am Dent Assoc 138:949–955. https://doi.org/10.14219/jada.archive.2007.0291
Gluskin AH, Peters CI, Peters OA (2014) Minimally invasive endodontics: challenging prevailing paradigms. Br Dent J 216:347–353. https://doi.org/10.1038/sj.bdj.2014.201
Gutmann JL (2013) Minimally invasive dentistry (Endodontics). J Conserv Dent 16:282–283. https://doi.org/10.4103/0972-0707.114342
Boutsioukis C, Gogos C, Verhaagen B et al (2010) The effect of apical preparation size on irrigant flow in root canals evaluated using an unsteady Computational Fluid Dynamics model. Int Endod J 43:874–881. https://doi.org/10.1111/j.1365-2591.2010.01761.x
Hsieh YD, Gau CH, Kung Wu SF et al (2007) Dynamic recording of irrigating fluid distribution in root canals using thermal image analysis. Int Endod J 40:11–17. https://doi.org/10.1111/j.1365-2591.2006.01168.x
Bago I, Batelja-Vuletić L, Tarle A et al (2022) Novel laser activated photoacoustic streaming for removing pulp remnants from round root canals after single file reciprocating instrumentation. Photodiagnosis Photodyn Ther 37:102631. https://doi.org/10.1016/j.pdpdt.2021.102631
Golob BS, Olivi G, Vrabec M et al (2017) Efficacy of photon-induced photoacoustic streaming in the reduction of Enterococcus faecalis within the root canal: different settings and different sodium hypochlorite concentrations. J Endod 43:1730–1735. https://doi.org/10.1016/j.joen.2017.05.019
Kosarieh E, Bolhari B, SanjariPirayvatlou S et al (2021) Effect of Er:YAG laser irradiation using SWEEPS and PIPS technique on dye penetration depth after root canal preparation. Photodiagnosis Photodyn Ther 33:102136. https://doi.org/10.1016/j.pdpdt.2020.102136
Vatanpour M, Toursavadkouhi S, Sajjad S (2022) Comparison of three irrigation methods: SWEEPS, ultrasonic, and traditional irrigation, in smear layer and debris removal abilities in the root canal, beyond the fractured instrument. Photodiagnosis Photodyn Ther 37:102707. https://doi.org/10.1016/j.pdpdt.2021.102707
Falk KW, Sedgley CM (2005) The influence of preparation size on the mechanical efficacy of root canal irrigation in vitro. J Endod 31:742–745. https://doi.org/10.1097/01.don.0000158007.56170.0c
Huang T-Y, Gulabivala K, Ng Y-L (2008) A bio-molecular film ex-vivo model to evaluate the influence of canal dimensions and irrigation variables on the efficacy of irrigation. Int Endod J 41:60–71. https://doi.org/10.1111/j.1365-2591.2007.01317.x
Khademi AA, Mohammadi Z, Havaee A (2006) Evaluation of the antibacterial substantivity of several intra-canal agents. Aust Endod J 32:112–115. https://doi.org/10.1111/j.1747-4477.2006.00033.x
Rödig T, Sedghi M, Konietschke F et al (2010) Efficacy of syringe irrigation, RinsEndo and passive ultrasonic irrigation in removing debris from irregularities in root canals with different apical sizes. Int Endod J 43:581–589. https://doi.org/10.1111/j.1365-2591.2010.01721.x
De-Deus G, Marins J, Silva EJNL et al (2015) Accumulated hard tissue debris produced during reciprocating and rotary nickel-titanium canal preparation. J Endod 41:676–681. https://doi.org/10.1016/j.joen.2014.11.028
Schäfer E, Diez C, Hoppe W, Tepel J (2002) Roentgenographic investigation of frequency and degree of canal curvatures in human permanent teeth. J Endod 28:211–216. https://doi.org/10.1097/00004770-200203000-00017
Schneider SW (1971) A comparison of canal preparations in straight and curved root canals. Oral Surg Oral Med Oral Pathol 32:271–275. https://doi.org/10.1016/0030-4220(71)90230-1
Vertucci FJ (2005) Root canal morphology and its relationship to endodontic procedures. Endod Top 10:3–29. https://doi.org/10.1111/j.1601-1546.2005.00129.x
Paqué F, Al-Jadaa A, Kfir A (2012) Hard-tissue debris accumulation created by conventional rotary versus self-adjusting file instrumentation in mesial root canal systems of mandibular molars. Int Endod J 45:413–418. https://doi.org/10.1111/j.1365-2591.2011.01991.x
De-Deus G, Marins J, Neves A de A et al (2014) Assessing accumulated hard-tissue debris using micro-computed tomography and free software for image processing and analysis. J Endod 40:271–276. https://doi.org/10.1016/j.joen.2013.07.025
Boutsioukis C, Arias-Moliz MT, Chávez de Paz LE (2022) A critical analysis of research methods and experimental models to study irrigants and irrigation systems. Int Endod J. https://doi.org/10.1111/iej.13710
De-Deus G, Belladonna FG, Cavalcante DM et al (2021) Contrast-enhanced micro-CT to assess dental pulp tissue debridement in root canals of extracted teeth: a series of cascading experiments towards method validation. Int Endod J 54:279–293. https://doi.org/10.1111/iej.13408
Keleş A, Alçin H, Sousa-Neto MD, Versiani MA (2016) Supplementary steps for removing hard tissue debris from isthmus-containing canal systems. J Endod 42:1677–1682. https://doi.org/10.1016/j.joen.2016.07.025
Verstraeten J, Jacquet W, De Moor RJG, Meire MA (2017) Hard tissue debris removal from the mesial root canal system of mandibular molars with ultrasonically and laser-activated irrigation: a micro-computed tomography study. Lasers Med Sci 32:1965–1970. https://doi.org/10.1007/s10103-017-2297-4
de Pablo OV, Estevez R, Péix Sánchez M et al (2010) Root anatomy and canal configuration of the permanent mandibular first molar: a systematic review. J Endod 36:1919–1931. https://doi.org/10.1016/j.joen.2010.08.055
Alves FRF, Andrade-Junior CV, Marceliano-Alves MF et al (2016) Adjunctive steps for disinfection of the mandibular molar root canal system: a correlative bacteriologic, micro-computed tomography, and cryopulverization approach. J Endod 42:1667–1672. https://doi.org/10.1016/j.joen.2016.08.003
Susin L, Yoon JC, Liu Y et al (2010) Canal and isthmus debridement efficacies of two irrigant agitation techniques in a closed system. Int Endod J 43:1077–1090. https://doi.org/10.1111/j.1365-2591.2010.01778.x
Guerreiro MYR, Belladonna FG, Monteiro LPB et al (2020) The influence of the addition of surfactants to sodium hypochlorite on the removal of hard tissue debris. Int Endod J 53:1131–1139. https://doi.org/10.1111/iej.13307
Versiani MA, Pécora JD, Sousa-Neto MD (2013) Microcomputed tomography analysis of the root canal morphology of single-rooted mandibular canines. Int Endod J 46:800–807. https://doi.org/10.1111/iej.12061
Paqué F, Peters OA (2011) Micro-computed tomography evaluation of the preparation of long oval root canals in mandibular molars with the self-adjusting file. J Endod 37:517–521
Barbosa AFA, de Lima CO, Sassone LM et al (2021) Effect of passive ultrasonic irrigation on hard tissue debris removal: a systematic review and meta-analysis. Braz Oral Res 35:e123. https://doi.org/10.1590/1807-3107bor-2021.vol35.0123
Willershausen I, Wolf TG, Schmidtmann I et al (2015) Survey of root canal irrigating solutions used in dental practices within Germany. Int Endod J 48:654–660. https://doi.org/10.1111/iej.12360
de Gregorio C, Arias A, Navarrete N et al (2015) Differences in disinfection protocols for root canal treatments between general dentists and endodontists: a web-based survey. J Am Dent Assoc 146:536–543. https://doi.org/10.1016/j.adaj.2015.01.027
Kumar K, Teoh Y-Y, Walsh LJ (2022) Root canal cleaning in roots with complex canals using agitated irrigation fluids. Aust Endod J. https://doi.org/10.1111/aej.12646
Boutsioukis C, Verhaagen B, Versluis M et al (2010) Evaluation of irrigant flow in the root canal using different needle types by an unsteady computational fluid dynamics model. J Endod 36:875–879. https://doi.org/10.1016/j.joen.2009.12.026
Boutsioukis C, Lambrianidis T, Kastrinakis E, Bekiaroglou P (2007) Measurement of pressure and flow rates during irrigation of a root canal ex vivo with three endodontic needles. Int Endod J 40:504–513. https://doi.org/10.1111/j.1365-2591.2007.01244.x
Pereira TC, Boutsioukis C, Dijkstra RJB et al (2021) Biofilm removal from a simulated isthmus and lateral canal during syringe irrigation at various flow rates: a combined experimental and computational fluid dynamics approach. Int Endod J 54:427–438. https://doi.org/10.1111/iej.13420
Perez R, Neves AA, Belladonna FG et al (2017) Impact of needle insertion depth on the removal of hard-tissue debris. Int Endod J 50:560–568. https://doi.org/10.1111/iej.12648
Zhao Y, Fan W, Xu T et al (2019) Evaluation of several instrumentation techniques and irrigation methods on the percentage of untouched canal wall and accumulated dentine debris in C-shaped canals. Int Endod J 52:1354–1365. https://doi.org/10.1111/iej.13119
Widbiller M, Keim L, Schlichting R et al (2021) Debris removal by activation of endodontic irrigants in complex root canal systems: a standardized in-vitro-study. Appl Sci 11:7331. https://doi.org/10.3390/app11167331
Boutsioukis C, Kastrinakis E, Lambrianidis T et al (2014) Formation and removal of apical vapor lock during syringe irrigation: a combined experimental and Computational Fluid Dynamics approach. Int Endod J 47:191–201. https://doi.org/10.1111/iej.12133
Freire LG, Iglecias EF, Cunha RS et al (2015) Micro-computed tomographic evaluation of hard tissue debris removal after different irrigation methods and its influence on the filling of curved canals. J Endod 41:1660–1666. https://doi.org/10.1016/j.joen.2015.05.001
Gagliardi J, Versiani MA, de Sousa-Neto MD et al (2015) Evaluation of the shaping characteristics of ProTaper Gold, ProTaper NEXT, and ProTaper Universal in curved canals. J Endod 41:1718–1724. https://doi.org/10.1016/j.joen.2015.07.009
Lopes RMV, Marins FC, Belladonna FG et al (2018) Untouched canal areas and debris accumulation after root canal preparation with rotary and adaptive systems. Aust Endod J 44:260–266. https://doi.org/10.1111/aej.12237
De-Deus G, Belladonna FG, Silva EJNL et al (2015) Micro-CT evaluation of non-instrumented canal areas with different enlargements performed by NiTi systems. Braz Dent J 26:624–629. https://doi.org/10.1590/0103-6440201300116
Pérez AR, Alves FRF, Marceliano-Alves MF et al (2018) Effects of increased apical enlargement on the amount of unprepared areas and coronal dentine removal: a micro-computed tomography study. Int Endod J 51:684–690. https://doi.org/10.1111/iej.12873
Ricucci D, Siqueira JF, Bate AL, Pitt Ford TR (2009) Histologic investigation of root canal-treated teeth with apical periodontitis: a retrospective study from twenty-four patients. J Endod 35:493–502. https://doi.org/10.1016/j.joen.2008.12.014
Funding
Open Access funding enabled and organized by Projekt DEAL. The research was supported by the German Research Foundation (DFG/MWK INST 1525/39–1 FUGG).
Author information
Authors and Affiliations
Contributions
Tina Rödig: methodology, writing–original draft. Valerie Westbomke: investigation, visualization. Franziska Haupt: formal analysis, writing–review and editing. Marc Münster: resources. Steffi Baxter: methodology, writing–review and editing. All authors read and approved the final manuscript.
Corresponding author
Ethics declarations
Competing interests
The authors declare no competing interests.
Ethical approval
This article does not contain any studies with human participants or animals performed by any of the authors. All procedures performed involving human tissues were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. The study was approved by the Ethics Committee of the University Medical Center of Göttingen, Germany (no. 27/8/13).
Informed consent
For this type of study, formal consent is not required.
Conflict of interest
The authors declare no competing interests.
Additional information
Publisher's note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Rödig, T., Westbomke, V., Haupt, F. et al. Effect of preparation size on the removal of accumulated hard-tissue debris from the mesial root canal system of mandibular molars using SWEEPS technology. Clin Oral Invest 27, 2787–2796 (2023). https://doi.org/10.1007/s00784-023-04862-1
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00784-023-04862-1