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    Journal of endodontics 2011 dds 1 Journal of endodontics 2011 dds 1 Document Transcript

    • Basic Research—TechnologyPhysical Properties and Interfacial Adaptation of Three EpoxyResin–based SealersMarina A. Marciano, DDS, Bruno M. Guimar~es, DDS, Ronald Ordinola-Zapata, DDS, aClovis M. Bramante, DDS, PhD, Bruno C. Cavenago, DDS, Roberto B. Garcia, PhD,Norberti Bernardineli, PhD, Flaviana B. Andrade, PhD, Ivaldo G. Moraes, DDS, PhD,and Marco A.H. Duarte, DDS, PhDAbstractIntroduction: The aim of the study was to evaluate theradiopacity, solubility, flow, film thickness, setting time,and adaptation to the root canal walls of 3 epoxy resin– N ecrosis of the pulp tissue and subsequent microbial infection are the main etiologic factors of apical periodontitis (1). Cleaning and shaping procedures offer a decon- taminated root canal environment compatible with periapical healing. It has beenbased sealers: AH Plus, Acroseal, and Adseal. Methods: accepted that long-term success can be reached with a tridimensional filling andPhysical tests were performed following American coronal restoration, which prevent bacterial leakage (2, 3). It is desirable that fillingNational Standards Institute/American Dental Associa- materials such as gutta-percha and sealers provide a high level of interfacial adaptabilitytion’s requirements. For interfacial adaptation analysis, and low toxicity (4).30 maxillary canines were shaped by using ProTaper Epoxy resin–based sealers were introduced in endodontics by Schroeder (5), andinstruments. The specimens were divided into 3 groups current modifications of the original formula are widely used for root canal filling(n = 10): group 1, AH Plus; group 2, Acroseal; and group procedures (6, 7). One of these sealers is AH Plus (Dentsply Maillefer, Ballaigues,3, Adseal. The sealers were mixed with rhodamine Switzerland), which has been extensively evaluated for its physicochemicalB dye, and the canals were filled by using the lateral properties and biological response (8, 9). There are other epoxy resin–basedcompaction technique. The percentage of gaps and voids sealers commercially available. Acroseal (Specialits-Septodont, Saint Maur-des- earea was calculated at 2, 4, and 6 mm levels from the Fosss, France) is a sealer containing 28% calcium hydroxide in its composition. eapex. Statistical evaluation was performed by using anal- Previous studies have shown its antimicrobial activity against Enterococcus faecalis,ysis of variance for physical analysis and nonparametric low toxicity, and proper film thickness (10–12). Another epoxy resin–based sealerKruskal-Wallis and Dunn tests for interfacial adaptation is Adseal (Meta, Biomed, Cheongju, South Korea), a sealer with very few reports in(P < .05). Results: No statistical differences were found literature about physical properties except for the reported radiopacity value (13).for adaptation, percentage of voids, solubility, flow, and Physical tests are performed to analyze the properties of endodontic sealers, antic-film thickness among the sealers (P > .05). AH Plus was ipating the clinical performance, consistency, and workability (14). American Nationalsignificantly more radiopaque (P < .05). For the setting Standards Institute/American Dental Association’s (ANSI/ADA) requirements for sealerstime, there were statistical differences among all the include radiopacity of at least 3 mm Al, solubility less than 3%, flowability >20 mm, filmstudied sealers (P < .05). Conclusions: AH Plus, Acroseal, thickness no more than 50 mm, and a setting time that does not exceed 10% of the timeand Adseal presented similar root canal adaptation, solu- specified by manufacturer’s statement (15). Besides these requirements, root canalbility, flow, and film thickness. Statistical differences were sealers should provide an adherence between gutta-percha and root canal walls, avoid-found for radiopacity and setting time (P < .05). (J Endod ing the occurrence of gaps at the sealer/dentin interface (16, 17). The null hypotheses2011;-:1–5) that were tested are that there is no difference in the degree of adaptability to the root canal walls among AH Plus, Acroseal, and Adseal and that there is no difference in theKey Words physicochemical properties of these sealers.Confocal microscopy, epoxy resin sealers, physical prop-erties, root canal filling Materials and Methods Thirty maxillary canines with a curvature less than 5 degrees (18) were selected. The ethics committee approved the use of extracted teeth for research purposes (CEP 109-2009). The teeth were cleaned and stored in distilled water at 4 C. The coronal From the Department of Operative Dentistry, Dental Mate- portions were sectioned by using a 0.3-mm Isomet saw (Buehler, Lake Bluff, IL),rials and Endodontics, Bauru Dental School, University ofS~o Paulo, Bauru, S~o Paulo, Brazil. a a and the root canal length was standardized in 15 mm. The working length was estab- Supported by the State of S~o Paulo Research Foundation, a lished by measuring the penetration of a size 10 K-file until it reached the apical foramenFAPESP (2009/09470-4 and 2009/15233-5). and then subtracting 1 mm. The root canals were shaped by using ProTaper instruments Address requests for reprints to Dr Marina A. Marciano, (Dentsply Maillefer) to a size of the F5 instrument (50.05) at the working length. AfterFaculdade de Odontologia de Bauru – USP, Al. Octvio Pinheiro aBrisolla, 9-75, CEP 17012-901 Bauru, S~o Paulo, Brazil. E-mail a the use of each instrument, 2 mL of 2.5% sodium hypochlorite was used to irrigate theaddress: marinangelica@usp.br canal. Passive ultrasonic irrigation was performed at the end of the shaping as previ-0099-2399/$ - see front matter ously reported (19). A final flush of 2 mL of 17% ethylenediaminetetraacetic acid (Bio- Copyright ª 2011 American Association of Endodontists. din^mica, Ibipor~, Paran, Brazil) for 3 minutes was used to eliminate the smear layer, a a adoi:10.1016/j.joen.2011.06.023 and the canals were finally washed with 2 mL of distilled water and dried with paper points (Dentsply Maillefer).JOE — Volume -, Number -, - 2011 Analysis of 3 Epoxy Resin–based Sealers 1
    • Basic Research—Technology Specimens were randomly divided into 3 groups (n = 10) (http:// were radiographed on occlusal films (D-speed; Kodak Corporation,www.openepi.com/Menu/OpenEpiMenu.htm): group 1, AH Plus; group Rochester, NY) with an aluminum step-wedge graduated from 2–162, Acroseal; and group 3, Adseal. The composition of the evaluated mm (in 2-mm increments). A radiographic unit (Gnatus XR 6010; Gna-sealers is shown in Table 1. To facilitate fluorescence under the tus, Ribeir~o Preto, SP, Brazil) was used with exposures set at 60 kV, 10 aconfocal laser scanning microscope, the sealers were mixed with fluo- mA, 0.3 seconds, and a focus-film distance of 30 cm. The radiographsrescent rhodamine B dye (Sigma-Aldrich, St Louis, MO) to an approx- were digitized and analyzed by using Digora 1.51 software (Soredex,imate concentration of 0.1% (20, 21). A rhodamine-sealer mixture Helsinki, Finland). The radiopacity was determined according to Duarte(approximately 0.05 mL) was applied in each root canal by using et al (8).a size 30 lentulo spiral (Dentsply Maillefer), keeping the instrument2 mm from the apex. A size 50.02 gutta-percha cone (Dentsply Maille- Solubilityfer) coated with sealer was inserted into the full working length. The Three polytetrafluoroethylene rings with 1.5 mm in thickness androot canals were filled by using the lateral compaction technique, an inner diameter of 20 mm were used for each sealer. The rings werewith the aid of a size B finger spreader (Dentsply Maillefer) inserted filled with the evaluated sealers and supported by a glass plate covered2 mm short of the working length and accessory gutta-percha points with a cellophane sheet. A nylon thread was positioned inside the mate-size 20.02 (Dentsply Maillefer). Filled roots were stored in 100% rial and another glass plate covered with cellophane film (8, 24). Thehumidity at 37 C for 1 week to allow the sealers to set. Then the spec- assembly was placed in an incubator (37 C, 95% relative humidity) forimens were included in epoxy resin (Triepox; Socorro, S~o Paulo, a a period corresponding to 3 times the setting time. The sealers wereBrazil), sectioned horizontally at 2, 4, and 6 mm from the apex by using removed from the mold and weighed 3 times each with an accuracya 0.3-mm disk (Isomet; Buehler), and polished as previously reported of 0.0001 g (UMark 210; Bel Engineering, Monza, Italy). The(Politriz; Arotec, Cotia, SP, Brazil) (22). samples were suspended by nylon thread and placed 2 by 2 inside a plastic vessel containing 50 mL of deionized distilled water. TheInterfacial Adaptation and Voids Area containers were stored for 24 hours in an incubator (37 C, 95% The root canal perimeters (mm) and voids area (mm2) were relative humidity). The samples were rinsed with deionized distilledmeasured by using a stereomicroscope (Stemi 2000C; Carl Zeiss, water, blotted dry with absorbent paper, placed in desiccators for 24Jena, Germany) and the Axiovision software (Carl Zeiss). Then the hours, and then reweighed. The experiment was repeated 3 times forpercentages of voids in each section were calculated (22). Interfacial each sealer. The weight loss of each sample (initial mass minus finalintegrity was analyzed on an inverted Leica TCS-SPE confocal laser scan- mass), expressed as the percentage of the original mass, was takenning microscope (Leica Microsystems GmbH, Mannheim, Germany) set as the solubility of the sealer (8).in the fluorescent mode. The respective absorption and emission wave-lengths for rhodamine B were 540 and 590 nm. The samples wereanalyzed 10 mm below the sampled surface by using the Â10 lens. Flow TestImages obtained were recorded in a format of 1024 Â 1024 pixels A volume of 0.5 mL of sealer was placed on a glass plate accordingby using the Leica Application Suite-Advanced Fluorescence software to ANSI/ADA’s specifications (15). Three minutes after the start of mix-(LAS AF; Leica Microsystems GmbH). Sealer/dentin interface was eval- ing, another plate with a mass of 20 Æ 2 g and a load of 100 g plus wasuated by calculating the ratio between the total sealer/dentin interface applied centrally on top of the plate. Ten minutes after the start of mix-(perimeter) and the gap-containing regions as previously reported; ing, the load was removed, and the average of the major and minorthe result was expressed in terms of percentage (17, 23). diameters of the compressed sealer was measured by using a digital caliper (Mitutoyo MTI Corporation, Tokyo, Japan). Three measure-Radiopacity ments were performed for each sealer (8). Three cylindrical samples were fabricated from each sealer byplacing the manipulated sealers into metallic rings with 10 mm internal Setting Timediameter and 1 mm thickness (15). Then the filled rings were kept at Three stainless steel rings with an inner diameter of 10 mm and 237 C until cements were completely set. The thickness was checked mm in thickness were used for each sealer. The rings were filled with thewith a digital caliper (Mitutoyo Corp, Tokyo, Japan), and the samples sealers, fixed on a glass plate, and stored in an incubator at 37 C. ToTABLE 1. Composition of Evaluated Sealers Sealer Components AH Plus Paste A Paste B 25%–50% bisphenol A 2.5%–10% N, n-dibenzyl-5-oxanonandiamin-1,9 10%–25% zirconium dioxide 2.5%–10% amantadine NS calcium tungstate NS iron oxide Acroseal Base Catalyst <60% bisphenol A diglycidylether 25% hexamethylenetetramine 28% calcium hydroxide 0-25% Venice turpentine NS bismuth subcarbonate 0-5% enoxolone Adseal Base Catalyst <20% epoxy resin NS amines NS calcium phosphate NS bismuth subcarbonate NS zirconium dioxide NS calcium oxide NS ethylene glycol salicylateNS, nonspecified percentages.2 Marciano et al. JOE — Volume -, Number -, - 2011
    • Basic Research—Technology determine the setting time, a modified ANSI/ADA specification that uses 0.0 (0.0–19.7)a 0.0 (0.0–2.2)a 0.6 (0.0–2.6)a a Gilmore needle with a weight of 110 g and an active tip of 1.0 mm Voids 6 mm diameter was used at 60-second intervals (8). Three measurements Median and range of interfacial adaptation represented as percentage of gap containing regions. Median and range of percentage of voids in root canal fillings are also presented. Different letter in each column indicates statistically significant differences (P < .05). were performed for each sealer. Film Thickness 2.1 (0.0–4.6)a 0.0 (0.0–5.9)a 1.6 (0.0–5.4)a Two 5-mm-thick glass plates were used, and their thickness was Voids 4 mm confirmed by using a digital caliper (Mitutoyo MTI Corporation). A total of 0.5 mL of sealer was placed in the middle of one glass plate, and then the other plate was positioned centrally to the sealer (15). Three minutes after the start of mixing, a load of 150 N was applied vertically 0.0 (0.0–2.5)a 0.0 (0.0–2.7)a 0.0 (0.0–6.6)a on top of the glass plate. After 7 minutes, the load was removed, and the Voids 2 mm thickness of the 2 glass plates with the sealer interposed was measured by using a digital caliper (Mitutoyo MTI Corporation) (8). The film thickness was established as the difference of thickness between the 2 glass plates with and without the sealer interposed (8, 24). Three 0.0 (0.0–18.5)a 0.0 (0.0–20.0)a 3.46 (0.0–28.6)a measurements were performed for each sealer. Gap 6 mm Statistical Analysis Statistical analysis was performed by using analysis of variance for physical tests and nonparametric Kruskal-Wallis and Dunn for adapta- tion tests (P < .05) as a result of the absence of normal distribution 0.0 (0.0–43.2)a 0.0 (0.0–29.3)a 0.0 (0.0–20.2)a Gap 4 mm confirmed in preliminary analysis. Results Means and standard deviations of the physical tests are shown in Table 2. All the sealers showed solubility values inferior to 0.30%. Acro- 0.0 (0.0–26.0)a 0.0 (0.0–10.8)a 0.0 (0.0–23.8)a Gap 2 mm seal presented significantly low solubility compared with AH Plus and Adseal (P < .05). For the radiopacity test, AH Plus showed statistically higher values in comparison to the other evaluated sealers (P < .05). All the tested sealers were statistically different for setting time (P < .05). The higher setting time was found for Acroseal (P < .05), and the low 43.65a Æ 0.49 65.50a Æ 6.36 65.00a Æ 7.07 Film thickness value was observed for Adseal (P < .05). Statistical similarities for film (mm) thickness and flow tests were observed among the sealers (P > .05). Other statistical differences are present in Table 1. Medians and ranges of gap and voids observed are represented in Table 1. The analysis of interfacial adaptation and percentage of voids revealed no statistical 711.33a Æ 95.03 1230.00b Æ 42.42 differences among the sealers at all levels (P > .05). Representative 70.00c Æ 9.00 Setting time sections are shown in Figure 1. (min) Discussion Epoxy is a polymer that, when combined with hardener substances, initializes the process of polymerization (5, 25). Amines are agents used 14.50a Æ 1.69 5.86b Æ 0.73 5.84b Æ 0.66 in epoxy resin sealers to initiate the process of polymerization (26). The Radiopacity (mm Al) TABLE 2. Means and Standard Deviations of Physical Tests type and quantity of the substances used can determine solubility, adhe- sion, setting time, and thermal stability of the resin. Cured epoxy resins are considered resistant and not sensitive to moisture with solvents (5, 27); this could elucidate the low degree of solubility found in this 39.16a Æ 3.85 39.66a Æ 2,51 37.66a Æ 2.08 study, which confirms previous results (8, 28). Flow (mm) The setting time found in this study was significantly different among the evaluated sealers. In addition, the values presented were inside the 10% variation acceptable by ANSI/ADA (15) and are in agree- ment with the manufacturers’ statements. The results of physical tests 0.30a Æ 0.02 0.10b Æ 0.04 0.24a Æ 0.00 Solubility (%) found in this study suggested that all the sealers evaluated have similar solubility and flowability and showed differences in the setting time and the radiopacity value, thus accepting partially the second null hypothesis tested. Acroseal showed the longest setting time (P < .05). This sealer contains calcium hydroxide as another epoxy resin–based sealer Acroseal AH Plus (Sealer 26; Dentsply, Rio de Janeiro, Brazil). The higher setting time Group Adseal could favor a calcium ion release that generally occurs before the setting of materials (29), although a previous study showed that the calciumJOE — Volume -, Number -, - 2011 Analysis of 3 Epoxy Resin–based Sealers 3
    • Basic Research—TechnologyFigure 1. (A and B). Representative correlative stereomicroscopic/confocal pictures of canal filled with Adseal sealer and lateral compaction technique. Twoevident voids (*) and gaps are visible at sealer/dentin interface (arrows). Higher contrast between sealer and dentin is shown in confocal picture. However, stereo-microscopic picture allows discriminating clearly the area of the voids. (C and D). Apical sections of Acroseal and AH Plus sealers. A thin layer of sealer is evident intotal circumference of root canal without evidence of voids and gaps. (E and F). Representative picture at 6-mm sections of canal filled with Adseal and Acroseal. Anadequate adaptation of sealer to root canal walls can be observed in confocal images. Bar in confocal pictures represents 100 mm.release was inferior in comparison to Sealapex because of the presence value found for Adseal, this property did not interfere with the flowabil-of the insoluble epoxy base (30). AH Plus showed an intermediate ity. The different percentages of hardeners found in the evaluatedsetting time (711.33 minutes), and Adseal had the lower setting time sealers might explain the differences in the setting time.(70 minutes). A previous study has suggested that the flowability can An adequate flowability and film thickness are necessary for satis-be influenced by the setting time (31). Despite the lower setting time factory distribution of the sealer into the anatomical irregularities (32).4 Marciano et al. JOE — Volume -, Number -, - 2011
    • Basic Research—TechnologyHowever, an excessive flow rate increases the probability of extrusion 9. Leonardo MR, Flores DSH, Silva FWP, Leonardo RT, Silva LA. A comparison study ofinto periodontal tissues (32). According to ANSI/ADA’s specifications, periapical repair in dog’s teeth using RoekoSeal and AH plus root canal sealers: a histopathological evaluation. J Endod 2008;34:822–5.the sealers should present at least 25-mm-diameter disk at flow test 10. Pinheiro CR, Guinesi AS, Pizzolitto AC, Bonetti-Filho I. in vitro antimicrobial activityand a film thickness not more than 50 mm. In a previous article it of Acroseal, Polifil and Epiphany against Enterococcus faecalis. Braz Dent J 2009;has been stated that a high film thickness is an undesirable property 20:107–11.because of the possible interference with the proper seating of gutta- 11. Gambarini G, Andreasi-Bassi M, Bolognini G, et al. Cytotoxicity of a new endodonticpercha cones into root canal during filling procedure (33). There filling material. Aust Endod J 2003;29:17–9. 12. Testarelli L, Andreasi Bassi M, Gambarini G. in vitro evaluation of five root canalwere no statistical differences among the tested epoxy resin sealers sealers. Minerva Stomatol 2003;52:19–24.for flowability and film thickness (P > .05). 13. Tasdemir T, Yesilyurt C, Yildirim T, Er K. Evaluation of the radiopacity of new root ¸ Another desirable property for an endodontic sealer is the adher- canal paste/sealers by digital radiography. J Endod 2008;34:1388–90.ence to root canal walls (17). According to Tay et al (34), the critical 14. Ørstavik D. Materials used for root canal obturation: technical, biological and clin- ical testing. Endodontic Topics 2005;12:25–38.area of fillings is located at the sealer/dentin interface. Epoxy is consid- 15. ANSI/ADA. Specification no. 57 endodontic sealing material. Chicago, IL: ANSI/ADA;ered contraction-free during set reactions (5), and this might explain 2000.the appropriate interfacial adaptation of the tested sealers. These results 16. Ordinola-Zapata R, Bramante CM, Graeff MS, et al. Depth and percentage of pene-are in agreement with previous studies, mainly for AH Plus (17, 35). tration of endodontic sealers into dentinal tubules after root canal obturation usingOur results showed a similar adaptation ability of the evaluated a lateral compaction technique: a confocal laser scanning microscopy study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:450–7.sealers to the root canal walls by using the lateral compaction 17. De-Deus G, Reis C, Di Giorgi K, Brand~o MC, Audi C, Fidel RA. Interfacial adaptation atechnique, accepting the first null hypothesis. Lateral compaction of the Epiphany self-adhesive sealer to root dentin. Oral Surg Oral Med Oral Patholtechnique was used because it is widely used during graduate Oral Radiol Endod 2011;111:381–6.teaching (36). However, despite the absence of statistical difference, 18. Schneider SW. A comparison of canal preparations in straight and curved root canals. Oral Surg Oral Med Oral Pathol 1971;32:271–5.some samples showed the presence of voids and gaps as previously re- 19. van der Sluis L, Shemesh H, Wu M, Wesselink P. An evaluation of the influence of passiveported (4). This could be correlated to the limitation of the lateral ultrasonic irrigation on the seal of root canal fillings. Int Endod J 2007;40:356–61.compaction technique to allow a homogeneous layer of sealer in the 20. D’Alpino P, Pereira J, Svizero N, Rueggeberg F, Pashley D. Use of fluorescententire root canal walls as previously shown (37). compounds in assessing bonded resin-based restorations: a literature review. Radiopacity evaluation revealed that AH Plus was significantly J Dent 2006;34:623–34. 21. Ordinola-Zapata R, Bramante C, Bernardineli N, et al. A preliminary study of themore radiopaque than the other studied sealers (P < .05). The radio- percentage of sealer penetration in roots obturated with the Thermafil andpacity value (14.5 mm Al) was higher than the values found by other RealSeal-1 obturation techniques in mesial root canals of mandibular molars.authors (8, 13). According to Duarte et al (8), AH Plus radiopacity is Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2009;108:961–8.provided by zirconium oxide and calcium tungstate. Its radiopacity 22. Marciano MA, Ordinola-Zapata R, Cunha TV, et al. Analysis of four gutta-percha techniques used to fill mesial root canals of mandibular molars. Int Endod Jcan vary in different published studies because of the deposition of ra- 2011;44:321–9.diopacifying agents at the lower end of the tube, whereas the upper 23. Bonfante EA, Pegoraro LF, de Ges MF, Carvalho RM. SEM observation of the bond oportion can present a lower quantity of its substance. Radiopacity veri- integrity of fiber-reinforced composite posts cemented into root canals. Dent Materfied for Acroseal and Adseal (5.8 mm Al) was higher than the values 2008;24:483–91.found by other authors (13, 38). Despite the presence of bismuth 24. Versiani MA, Carvalho-Junior JR, Padilha MI, Lacey S, Pascon EA, Sousa-Neto MD. A comparative study of physicochemical properties of AH Plus and Epiphany rootsubcarbonate and zirconium oxide in Adseal sealer, similar canal sealants. Int Endod J 2006;39:464–71.radiopacity values were found in comparison to Acroseal, which only 25. Bowen RL. Use of epoxy resins in restorative materials. J Dent Res 1956;35:360–9.contains bismuth subcarbonate in its composition. 26. Cohen BI, Pagnillo MK, Musikant BL, Deutsch AS. An in vitro study of the cytotoxicity In conclusion, the epoxy resin sealers AH Plus, Acroseal, and Adseal of two root canal sealers. J Endod 2000;26:228–9. 27. Bourne LB, Milner FJ, Alberman KB. Health problems of epoxy resins and amine-presented similar root canal adaptation, solubility, flow, and film thick- curing agents. Br J Ind Med 1959;16:81–97.ness. Statistical differences were found for radiopacity and setting time. 28. Flores DS, Rached FJ, Versiani MA, Guedes DF, Sousa-Neto MD, Pcora JD. Evalu- e ation of physicochemical properties of four root canal sealers. Int Endod J 2011;44: 126–35. Acknowledgments 29. Duarte MA, Demarchi AC, Giaxa MH, Kuga MC, Fraga SC, de Souza LC. Evaluation of The authors deny any conflicts of interest related to this study. pH and calcium ion release of three root canal sealers. J Endod 2000;26:389–90. 30. Eldeniz AU, Erdemir A, Kurtoglu F, Esener T. Evaluation of pH and calcium ion release of Acroseal sealer in comparison with Apexit and Sealapex sealers. Oral References Surg Oral Med Oral Pathol Oral Radiol Endod 2007;103:86–91. 1. Kakehashi S, Stanley HR, Fitzgerald RJ. The effects of surgical exposures of dental 31. Ørstavik D. Physical properties of root canal sealers: measurement of flow, working pulps in germ-free and conventional laboratory rats. Oral Surg Oral Med Oral Pathol time, and compressive strenght. Int Endod J 1983;16:99–107. 1965;20:340–9. 32. Ørstavik D. Endodontic materials. Adv Dent Res 1988;2:12–24. 2. Ray HA, Trope M. Periapical status of endodontically treated teeth in relation to the 33. Ørstavik D. Seating of gutta-percha points: effect of sealers with varying film thick- technical quality of the root filling and the coronal restoration. Int Endod J 1995;28: ness. J Endod 1982;8:213–8. 12–8. 34. Tay F, Loushine R, Weller R, et al. Ultrastructural evaluation of the apical seal in roots filled 3. 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