Evaluation of Root-End Preparation with Two Different Endodontic Microsurgery Ultrasonic Tips

biomedicines Article Evaluation of Root-End Preparation with Two Different Endodontic Microsurgery Ultrasonic Tips Paulo J. Palma 1,2,* , Joana A. Marques 1, Margarida Casau 3, AndréSantos 3, Francisco Caramelo 4, Rui I. Falacho 5and João Miguel Santos 1,2 1Institute of Endodontics, Faculty of Medicine, University of Coimbra, 3000-075 Coimbra, Portugal; [email protected] (J.A.M.); [email protected] (J.M.S.) 2Center for Innovation and Research in Oral Sciences (CIROS), Faculty of Medicine, University of Coimbra, 3000-075 Coimbra, Portugal 3Dentistry Department, Faculty of Medicine, University of Coimbra, 3000-075 Coimbra, Portugal; [email protected] (M.C.); [email protected] (A.S.) 4Coimbra Institute for Clinical and Biomedical Research (iCBR), Laboratory of Biostatistics and Medical Informatics (LBIM), Faculty of Medicine, University of Coimbra, 3000-548 Coimbra, Portugal; [email protected] 5Institute of Oral Implantology and Prosthodontics, Faculty of Medicine, University of Coimbra, 3000-075 Coimbra, Portugal; [email protected] *Correspondence: [email protected]; Tel.: +351-239-249-151 Received: 11 August 2020; Accepted: 25 September 2020; Published: 28 September 2020   Abstract: The aim of this study is to compare root-end preparation performed with two different ultrasonic tips—CVDentus and NSK—and respective time requirements. After root-end resection, 32 teeth were randomly divided in two groups, according to the ultrasonic tip used for root-end preparation. Preparation time was recorded. Photomicrographs were taken to assess the following parameters: root surface microcracking, marginal integrity and presence of debris. One ultrasonic tip from each group was analyzed through scanning electron microscopy before and after root-end preparation. The significance level was set at α =0.05. Incidence of microcracks in both groups was 12.5%. Solely intracanal microcracking was found, consistently positioned within the widest side of the remaining dentine. No statistically significant differences were verified between both experimental groups regarding marginal integrity (p=0.102) and preparation time (p=0.780), whereas statistical differences (p=0.003) were found concerning the presence of debris (the minimum registered score was mostly verified in CVDentus group). NSK tips showed major morphological changes, with extensive surface wear and noticeable loss of particles, which was not verified on CVDentus tips. Our findings suggest significant differences regarding root-end preparation walls quality, with CVDentus tips showing better results. Concerning microcracking, as well as preparation time and marginal integrity, both ultrasonic tips showed similar results. Qualitative analysis exposed NSK tips major morphological changes and wear after use, which was not verified on CVDentus tips. Keywords: apical surgery; endodontic microsurgery; root-end preparation; ultrasonic; ultrasonic tips 1. Introduction Apical periodontitis comprises the host’s response to pathogenic microorganisms colonizing the root canal system of the tooth [ 1 , 2 ]. The principal goal of conventional endodontic treatment is prevention and/or elimination of apical periodontitis [ 1 , 2 ]. Today, the success rate of endodontic treatment stands between 85% and 95%, being frequently applied to treat irreversible inflammation or necrosis of the root canal content [ 3 ]. Endodontic microsurgery is often the last option when nonsurgical retreatment fails, is unfeasible or unlikely to improve the initial endodontic treatment [ 4 ]. Biomedicines 2020,8, 383; doi:10.3390/biomedicines8100383 www.mdpi.com/journal/biomedicines Biomedicines 2020,8, 383 2 of 19 In particular, only surgical intervention may resolve cases involving a persistent lesion with etiology related to complex canal anatomy, extra-radicular infection, foreign body reaction material, and/or cystic tissue [3]. Periapical surgery facilitates complete debridement of the root canal and placement of a root-end filling to ensure adequate apical sealing. The surgical approach comprises several sequential procedures in order to fulfill the aforementioned goals: (a) periapical resection (apicoectomy), (b) preparation of the root-end cavity, and (c) sealing of the root canal system by means of a bioactive and biocompatible root-end filling material placement [4,5]. The advent of novel diagnostic tools, instruments, and materials has greatly benefited endodontic surgery [ 5 , 6 ]. Forty-five-degree root-end resection bevels, bur driven retrograde preparations and amalgam or intermediate restorative materials for root-end filling were for many years considered the state-of-the-art with inconsistent success rates ranging from 44.2% to 59% reported prior to the introduction of microsurgical techniques [7,8]. The introduction of the dental operative microscope (DOM) in the early 1990s led to a new era in modern microsurgical endodontics [ 9 ]. Besides magnification, contemporary techniques incorporate the use of ultrasonic tips, microsurgical instruments and filling materials which exhibit superior biocompatibility such as mineral trioxide aggregate (MTA), Biodentine [ 7 , 10 – 13 ], and premixed tricalcium silicate putty (TotalFill FS putty) [ 14 ]. This new microsurgical approach allowed for a significant improvement in success rates, reaching levels above 91% [7,15]. The available literature highlights the importance of an adequate root-end preparation for a favorable prognosis, with its quality being directly related to the treatment success [ 16 ]. Root-end preparation should be parallel to the long axis of the root, 3 mm deep, and centered within the root in order to preserve adequate wall thickness and retain a biocompatible filling material [4,5,17]. Ultrasonic tips present an alternative to the conventional rotary burs and show several advantages when used to perform root-end preparation. In fact, the advent of ultrasonic tips resulted in the improvement of root-end preparation mainly due to the availability of tips with different shapes and angulations, which are meticulously selected according to the root features and location [ 18 ]. Moreover, ultrasonic tips carry numerous advantages including the possibility of performing a more conservative osteotomy and of obtaining root-end resection with minimal or inexistent bevel angles [ 19 ], thus reducing the number of exposed dentinal tubules and consequently the possibility of apical leakage [ 20 ]. Additionally, these tips enable the removal of isthmus tissue present between two canals within the same root [ 5 ] and exhibit lower risk of damaging the surrounding soft tissues during the surgical procedure [ 7 ]. Ultimately, ultrasonic preparation results in root-end cavities that are smaller, cleaner, and more retentive, as well as more centrally placed and aligned with the direction of the original root canal [ 17 ]. However, the incidence of apical microcracks following root-end preparation with ultrasonic tips has been reported [21–24]. Although not formally established, microcracks may increase the chance for apical leakage and jeopardize the overall strength of the root-end [ 25 ], with negative influence in the long-term outcome of endodontic microsurgery [ 10 ]. Optical magnification with or without the use of dyes [ 9 , 26 ], histologicalsections[ 26 ], stereomicroscopy[ 27 ], scanningelectronmicroscopy(SEM)[ 28 ], and fluorescence confocal microscopy [ 26 ] are commonly used methods for detecting microcracks resulting from ultrasound-activated root preparation. A few factors have been identified that potentially contribute to the occurrence of microcracks—namely, the use of dehydrated extracted teeth, absence of periodontal ligament, improper power settings of the ultrasound unit, sputter-coating of specimens for SEM examination, time required for root-end preparation, initial root condition, and remaining dentinal thickness [ 29 ]. Additionally, the type of coating of the ultrasonic tips may play a significant role in microcrack development [30]. Recently some attempts have been made to improve ultrasonic instruments both in terms of usability, as well as performance. New zirconium-coated and diamond-coated root-end preparation tips represent a relevant issue in this field [ 31 ]. However new technologies arise, such as the chemical Biomedicines 2020,8, 383 3 of 19 vapor deposition which comprises the formation of a thick pure diamond layer that shall produce a single stone covering the entire tip’s surface [32]. The aim of the present ex vivo study is to compare root-end preparation performed with two different ultrasonic tips—chemical vapor deposition CVDentus (CVDentus, S ã o Paulo, Brazil) and diamond-coated NSK (NSK, Tochigi, Japan)—regarding root surface microcracking (throughout the seven-day evaluation period), quality of the root-end cavity margins, presence of debris, root-end preparation tips’ wear, and respective time requirements. The null hypothesis states there are no differences between both ultrasonic tips regarding the evaluated parameters. 2. Materials and Methods 2.1. Specimen Selection The present study has been approved by the Ethical Committee of the Faculty of Medicine of the University of Coimbra (notification CE001/2013, 2 February 2015) and followed the guidelines of the Declaration of Helsinki. Forty single-rooted premolars with fully developed apices, freshly extracted for orthodontic reasons, were selected. Sample size calculation was based on a previous, unpublished, pilot study using G* Power (3.1.9.3 software, Kiel, Germany), considering a significance level of 5% and a power of 80%. All teeth were immersed in 1% sodium hypochlorite (NaOCl, CanalPro, Coltene/Whaledent AG, Altstatten, Switzerland) for 15 min, immediately after extraction. Afterward, soft tissue and debris were removed from the external root surfaces with periodontal scalers. The integrity of the roots was assessed using DOM (Leica M300 Surgical microscope, Leica Microsystems, Wetzlar, Germany) under 16 × magnification. Teeth were then kept immersed in 0.5% chloramine T for a period of one to three weeks in an incubator (Gallenkamp, London, United Kingdom) with controlled temperature of 37 ◦C, to simulate the oral environment clinical conditions. 2.2. Specimen Preparation Teeth were decoronated using a high-speed conical trunk diamond bur (Infinity, CVDentus, S ã o Paulo, Brazil) under continuous water spray. The working length was determined using a size 10 K-file (a 0.5 mm distance from the apex was considered as reference for working length determination). Root canals were then cleaned and mechanically prepared up to F2 (ProTaper universal, Dentsply Maillefer, Baillaigues, Switzerland) applying a crown-down technique. The root canals were irrigated with 1 mL of 1% NaOCl between each file usage, totaling a volume of irrigant solution of 4 mL. When preparation was completed, a final rinse with 2 mL of 70% alcohol (Meda Pharma, Lisboa, Portugal) was performed, and root canal system was then dried using sterile absorbent paper points (Zipperer Absorbent Paper Points Endo Easy Efficient, VDW; Munich, Germany). The single cone technique was then used for root canal filling with calibrated gutta-percha ProTaper points F2 (ProTaper universal, Dentsply Maillefer, Baillaigues, Switzerland) and AH Plus (Dentsply, Konstanz, Germany) as sealer. Section of the gutta-percha cone was performed at the cement enamel junction (CEJ) by using a heated instrument and then vertically condensed with Buchanan System B Pluggers (SybronEndo, Orange, CA, USA). Following obturation, each tooth was numbered, and an X-ray image was taken to confirm the quality of obturation. Finally, teeth were positioned prior to the subsequent procedures by placing the root’s two coronal thirds in high—viscosity silicone material (Colt è ne Lab-Putty, Colt è ne/Whaledent AG, Switzerland). All specimens were stored in an incubator (Gallenkamp, London, UK) at 37 ◦ C and 98% humidity throughout the experimental period. Biomedicines 2020,8, 383 4 of 19 2.3. Root-End Resection The section level was set at 3 mm from the apex, and all the roots were resected according to a 90-degree angle to their longitudinal axis. Root-end resection was performed using a H23LR (Komet, Gebr. Brasseler, Lemgo, Germany) carbide tungsten operative bur and the section surface was posteriorly smoothed with a H375R (Komet, Gebr. Brasseler, Lemgo, Germany) carbide tungsten finishing bur. Hereafter, the root surfaces were checked by an examiner, with a DOM (Leica M300 Surgical microscope, Leica Microsystems, Wetzlar, Germany) under 16 × magnification, to assess the presence of microcracks. Photomicrographs of the cutting section were taken with a stereomicroscope (objective HR Plan Apo 1X WD 54—Nikon SMZ 1500, Tokyo, Japan) before and after methylene blue dye 1% (Canal blue, DentsplySirona, Konstanz, Germany), which was applied directly on the surface during 5 min, and followed by rinsing with abundant water for 1 min, in order to improve microcracks visualization. 2.4. Root-End Preparation Thirty-two teeth that did not present any microcracks or fractures were stratified by transversal root shape and surface area, and randomly divided in two groups (stratified random sampling method), according to the ultrasonic tip used in root-end preparation: • Group 1 (n =16): ultrasonic chemical vapor deposition tip TOF-L (CVDentus, S ã o Paulo, Brazil)—lot number E7009; • Group 2 (n =16): ultrasonic diamond-coated tip E32D (NSK, Tochigi, Japan)—lot number Z217211. Root-end preparation was performed using the matching ultrasound unit and following the manufacturers’ recommendations regarding intensity, namely 30% intensity of power when using CVDentus Ultrasonic System (CVDentus; S ã o Paulo, Brazil) and Endo mode level 6 of intensity with Varios 970 (NSK iPiezo engine, Tochigi, Japan), under continuous saline solution irrigation. Root-end preparation was performed applying intermittent and minimal pressure, with in-and-out motion until an apical cavity 3 mm deep from the resected surface was achieved, followed by circumferential movements to complete the entire preparation. Specimens were kept in the silicone blocks and maintained hydrated throughout the procedures. Each tip was used on a maximum of eight roots and replaced in case of tip fracture. This procedure was accomplished by a single operator, using a DOM (Leica M300 Surgical microscope, Leica Microsystems, Wetzlar, Germany) under 16 × magnification. The root-end cavity was considered finished when the operator deemed to have obtained a visibly debris-free preparation. All preparations were class I (according to Black’s classification). Preparations were recorded using a video camera and time was measured using a video playback software in order to get a more precise measurement, counting solely the actual time of tip-root-end contact. Photomicrographs were taken following preparation of each root before and immediately after (T PO ) applying methylene blue dye 1% (Canal blue, DentsplySirona, Konstanz, Germany) as previously described, as well as 24 h (T24H) and seven days (T7D) after root-end preparation. 2.5. Data Analysis The preoperative and the postoperative photomicrographs were coded and evaluated by two blinded operators. The examiners assessed the following criteria, through photomicrographs analysis under 20×and 40×magnification: • The number, type and location (in relation to dentinal walls) of root surface microcracking (Table 1a); •The quality of root-end cavity margins produced by the ultrasonic tips (Table 1b). Biomedicines 2020,8, 383 5 of 19 Table 1. Classifications adapted to evaluate ( a ) root surface microcracking, ( b ) quality of root-end cavity margins, and (c) presence of debris within the apical cavity, following root-end preparation. (a) Root-End Surface Microcracking. Adapted Classification from Rainwater et al. [24] and De Bruyne and De Moor [33]. Type Location Designation Complete Incomplete Narrower Wider Intracanal Extra-canal Intra-dentinal Description From the root canal to the root surface Originating from the root canal and radiating into the dentine Originating from the root surface radiating into the dentine Confined to the dentine Located at the narrower side of the remaining dentine surface Located at the wider side of the remaining dentine surface (b) Marginal Integrity Adapted Classification from Taschieri et al. [31]. Score 0 1 2 3 Description Ideal preparation, with no defects A single visible defect produced by the contact between the angle of the tip and the cavity margin Chipped, ragged cavity margin Chipped, ragged cavity margin plus some defects due to the tips bouncing offthe root during root-end preparation (c) Presence of Debris Adapted Classification from Khabbaz et al. [34]. Score 0 1 2 3 4 Description Clean walls Debris on 1 wall Debris on 2 walls Debris on 3 walls Debris on 4 walls Additionally, direct stereomicroscope visualization under 40 × magnification allowed for the evaluation of the presence of debris (dentinal and/or gutta-percha remnants)—Table 1c. The scores and number of cracks were assessed independently by two examiners, and in case of disagreement both examiners discussed until a consensus was reached. In addition, one ultrasonic tip from each experimental group was randomly selected and analyzed through scanning electron microscopy (SEM) before and after root-end preparation, with the purpose of evaluating tip wear due to use. 2.6. Statistical Analysis Statistical analysis was carried out using the commercially available IBM SPSS v.24 software (Chicago, IL, USA) to assess the differences between the experimental groups. In order to evaluate the incidence of microcracks before and after (T PO , T 24H , T 7D ) root-end preparation, as well as cracking type and location, results obtained for each group were analyzed through descriptive statistics. The Mann—Whitney test was performed to evaluate the differences regarding microcracks, marginal integrity (quality of apical cavity margins) and presence of debris between groups. Concerning the time required for root-end preparation, the normality of data distribution testing was carried out using the Shapiro–Wilk test. The Mann—Whitney test was used to detect significant differences between the groups as data did not follow the normal distribution. The significance level was set at α=0.05. 3. Results 3.1. Root-End Surface Microcracking—Number, Type, and Location Table 2shows the results of the two study groups regarding the number, type and location of cracks. No visible cracks were detected after root-end resection, independently of the tip type. Regardless of the timepoint (T PO , T 24H , T 7D ) following root-end preparation, intracanal root microcracking was observed Biomedicines 2020,8, 383 6 of 19 in two samples of each experimental group. Therefore, an incidence of 12.5% was recorded concerning the occurrence of fractures in both groups. No propagation of fractures, nor the appearance of new ones, was verified throughout the complete seven-day period of evaluation. Moreover, the maximum number of microcracks recorded for the same sample was one. No extra-canal, intra-dentine, or complete microcracks were found. Regarding location, root surface microcracking was consistently positioned within the widest side of the remaining dentine surface, thus registering a frequency of 100% for the “wider” part of the root location. Figure 1(CVDentus group) and Figure 2(NSK group) display representative images of root surface microcracking of both experimental groups. Table 2. Results of the two experimental groups regarding the number, type, and location of microcracks. Immediately after Root-End Resection TPO T24H T7D CVDentus NSK CVDentus NSK CVDentus NSK CVDentus NSK Number 0 0 2 2 2 2 2 2 Type Intracanal 0 0 2 2 2 2 2 2 Extra-canal 0 0 0 0 0 0 0 0 Intra-dentinal 0 0 0 0 0 0 0 0 Complete 0 0 0 0 0 0 0 0 Location Narrower 0 0 0 0 0 0 0 0 Wider 0 0 2 2 2 2 2 2 Biomedicines 2020, 8, x FOR PEER REVIEW 6 of 18 of evaluation. Moreover, the maximum number of microcracks recorded for the same sample was one. No extra-canal, intra-dentine, or complete microcracks were found. Regarding location, root surface microcracking was consistently positioned within the widest side of the remaining dentine surface, thus registering a frequency of 100% for the “wider” part of the root location. Figure 1 (CVDentus group) and Figure 2 (NSK group) display representative images of root surface microcracking of both experimental groups. Table 2. Results of the two experimental groups regarding the number, type, and location of microcracks. Immediately after Root-End Resection T PO T 24H T 7D CVDentus NSK CVDentus NSK CVDentus NSK CVDentus NSK Number 0 0 2 2 2 2 2 2 Type Intracanal 0 0 2 2 2 2 2 2 Extracanal 0 0 0 0 0 0 0 0 Intradentinal 0 0 0 0 0 0 0 0 Complete 0 0 0 0 0 0 0 0 Location Narrower 0 0 0 0 0 0 0 0 Wider 0 0 2 2 2 2 2 2 Figure 1. Photomicrographs of one sample from CVDentus group with no visible microcrack, under 20× magnification: (a) immediately after root-end resection; (b) immediately after root-end preparation—T PO ; (c) 24 h after root-end preparation—T 24H ; (d) seven days after root end preparation—T 7D . Figure 1. Photomicrographs of one sample from CVDentus group with no visible microcrack, under 20 × magnification: ( a ) immediately after root-end resection; ( b ) immediately after root-end preparation—T PO ; ( c ) 24 h after root-end preparation—T 24H ; ( d ) seven days after root end preparation—T7D. Biomedicines 2020,8, 383 7 of 19 Biomedicines 2020, 8, x FOR PEER REVIEW 7 of 18 Figure 2. Photomicrographs of one sample from NSK group presenting one intracanal microcrack (arrow) located within the “wider” part of the remaining dentine walls, under 20× magnification: (a) immediately after root-end resection; (b) immediately after root-end preparation—TPO; (c) 24 h after root-end preparation—T24H; (d) seven days after root-end preparation—T7D. 3.2. Marginal Integrity (Root-End Cavity Margins) Regarding marginal integrity (Table 3a), the maximum value of “3” was found in one root from NSK group, totaling 6.2% of the samples from the referred experimental group. The minimum registered score was “0” mostly verified in specimens from CVDentus group (25% of the samples from the group). The score “1” was the one with highest incidence in CVDentus group with a percentage of 62.5%, whereas in NSK group the value with the highest incidence was “2” (43.8%). No statistically significant differences (U = 84.00; Z = −1.783; P = 0.102) were verified between both CVDentus and NSK groups regarding marginal integrity (Figure 3a). Table 3. Frequencies and percentages obtained in the two experimental groups regarding (a) marginal integrity and (b) presence of debris. CVDentus NSK CVDentus NSK (a) Marginal integrity * 0 4 3 25.0 18.8 1 10 5 62.5 31.2 2 2 7 12.5 43.8 3 0 1 − 6.2 (b) Presence of debris ** 0 9 2 56.2 12.5 1 6 6 37.5 37.5 2 1 7 6.2 43.8 3 0 1 − 6.2 4 0 0 − − * N = 32; Mann—Whitney test; P = 0.102, ** N = 32; Mann—Whitney test; P = 0.003. Figure 2. Photomicrographs of one sample from NSK group presenting one intracanal microcrack (arrow) located within the “wider” part of the remaining dentine walls, under 20 × magnification: ( a ) immediately after root-end resection; ( b ) immediately after root-end preparation—T PO ; ( c ) 24 h after root-end preparation—T24H; (d) seven days after root-end preparation—T7D. 3.2. Marginal Integrity (Root-End Cavity Margins) Regarding marginal integrity (Table 3a), the maximum value of “3” was found in one root from NSK group, totaling 6.2% of the samples from the referred experimental group. The minimum registered score was “0” mostly verified in specimens from CVDentus group (25% of the samples from the group). The score “1” was the one with highest incidence in CVDentus group with a percentage of 62.5%, whereas in NSK group the value with the highest incidence was “2” (43.8%). No statistically significant differences (U =84.00; Z = − 1.783; p=0.102) were verified between both CVDentus and NSK groups regarding marginal integrity (Figure 3a). Biomedicines 2020,8, 383 8 of 19 Table 3. Frequencies and percentages obtained in the two experimental groups regarding ( a ) marginal integrity and (b) presence of debris. Frequency Percentages (%) CVDentus NSK CVDentus NSK (a) Marginal integrity * 0 4 3 25.0 18.8 1 10 5 62.5 31.2 2 2 7 12.5 43.8 3 0 1 −6.2 (b) Presence of debris ** 0 9 2 56.2 12.5 1 6 6 37.5 37.5 2 1 7 6.2 43.8 3 0 1 −6.2 4 0 0 − − * N =32; Mann—Whitney test; p=0.102, ** N =32; Mann—Whitney test; p=0.003. Biomedicines 2020, 8, x FOR PEER REVIEW 8 of 18 Figure 3. Score distribution within the tested groups regarding (a) marginal integrity (Mann— Whitney test; P = 0.102) and (b) presence of debris. (Mann—Whitney test; P = 0.003). 3.3. Presence of Debris (Walls Quality) Concerning the presence of debris following root-end preparation (Table 3b), the maximum value of “3” was found in one sample from NSK group (6.2% of the samples from the referred experimental group). The minimum registered score was “0” mostly verified in specimens from CVDentus group (56.2% of the samples from the group). In NSK group the score exhibiting the highest incidence was “2” with a percentage of 43.8%. Contrariwise to marginal integrity, statistically significant differences (U = 50.50; Z = −3.093; P = 0.003) were found between the tested groups regarding the presence of debris (Figure 3b and Figure 4). Figure 4. Scanning electron microscopy (SEM) images following root-end preparation: (a) CVDentus specimen exhibiting an intracanal microcrack (arrow); (b) NSK specimen exhibiting an intracanal microcrack (arrow) and irregular root-end cavity margins, as well as showing visible accumulation of debris (asterisk) resulting from the root-end preparation. 3.4. Time Requirements Considering the time requirements to perform apical preparation (Table 4), no statistically significant differences could be detected between the tested groups (U = 120.00; Z = −0.302; P = 0.780). Figure 3. Score distribution within the tested groups regarding ( a ) marginal integrity (Mann—Whitney test; p=0.102) and (b) presence of debris. (Mann—Whitney test; p=0.003). 3.3. Presence of Debris (Walls Quality) Concerning the presence of debris following root-end preparation (Table 3b), the maximum value of “3” was found in one sample from NSK group (6.2% of the samples from the referred experimental group). The minimum registered score was “0” mostly verified in specimens from CVDentus group (56.2% of the samples from the group). In NSK group the score exhibiting the highest incidence was “2” with a percentage of 43.8%. Contrariwise to marginal integrity, statistically significant differences (U =50.50; Z = − 3.093; p=0.003) were found between the tested groups regarding the presence of debris (Figures 3b and 4). Biomedicines 2020,8, 383 9 of 19 Biomedicines 2020, 8, x FOR PEER REVIEW 8 of 18 Figure 3. Score distribution within the tested groups regarding (a) marginal integrity (Mann— Whitney test; P = 0.102) and (b) presence of debris. (Mann—Whitney test; P = 0.003). 3.3. Presence of Debris (Walls Quality) Concerning the presence of debris following root-end preparation (Table 3b), the maximum value of “3” was found in one sample from NSK group (6.2% of the samples from the referred experimental group). The minimum registered score was “0” mostly verified in specimens from CVDentus group (56.2% of the samples from the group). In NSK group the score exhibiting the highest incidence was “2” with a percentage of 43.8%. Contrariwise to marginal integrity, statistically significant differences (U = 50.50; Z = −3.093; P = 0.003) were found between the tested groups regarding the presence of debris (Figure 3b and Figure 4). Figure 4. Scanning electron microscopy (SEM) images following root-end preparation: (a) CVDentus specimen exhibiting an intracanal microcrack (arrow); (b) NSK specimen exhibiting an intracanal microcrack (arrow) and irregular root-end cavity margins, as well as showing visible accumulation of debris (asterisk) resulting from the root-end preparation. 3.4. Time Requirements Considering the time requirements to perform apical preparation (Table 4), no statistically significant differences could be detected between the tested groups (U = 120.00; Z = −0.302; P = 0.780). Figure 4. Scanning electron microscopy (SEM) images following root-end preparation: ( a ) CVDentus specimen exhibiting an intracanal microcrack (arrow); ( b ) NSK specimen exhibiting an intracanal microcrack (arrow) and irregular root-end cavity margins, as well as showing visible accumulation of debris (asterisk) resulting from the root-end preparation. 3.4. Time Requirements Considering the time requirements to perform apical preparation (Table 4), no statistically significant differences could be detected between the tested groups (U =120.00; Z = − 0.302; p=0.780). Table 4. Mean, standard deviation (SD), and minimum and maximum values of each experimental group regarding the time of apical preparation. Time of Apical Preparation Mean SD Minimum Maximum CVDentus 60.56 33.18 30.0 160.0 NSK 55.56 20.41 34.0 96.0 N=32; Mann—Whitney test; p=0.780. 3.5. Root-End Preparation Tip Wear—Qualitative Analysis Figures 5and 6depict images of the ultrasonic tips obtained by scanning electron microscopy. (SEM) examination, showing tip wear after root-end preparation. No ultrasonic tip fractures were registered in any of the groups. Biomedicines 2020,8, 383 16 of 19 10. Pinto, D.; Marques, A.; Pereira, J.F.; Palma, P.J.; Santos, J.M. Long-Term Prognosis of Endodontic Microsurgery—A Systematic Review and Meta-Analysis. Medicina 2020,56, 447. 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