Enhanced Adhesive Performance of Hydroxyapatite-Coated Gutta-Percha with Various Root Canal Sealers: A Push-Out Bond Strength and Failure Mode Analysis

Enhanced Adhesive Performance of Hydroxyapatite-Coated Gutta-Percha with Various Root Canal Sealers: A Push-Out Bond Strength and Failure Mode Analysis | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Enhanced Adhesive Performance of Hydroxyapatite-Coated Gutta-Percha with Various Root Canal Sealers: A Push-Out Bond Strength and Failure Mode Analysis Noor Hayati Azami, Nora Sakina Mohd Noor, Afaf Al-Haddad, Rana Diab, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6684617/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 06 Nov, 2025 Read the published version in Scientific Reports → Version 1 posted 13 You are reading this latest preprint version Abstract This study evaluates the the adhesive performance of a novel hydroxyapatite-coated gutta-percha (HAGP) in combination with various root canal sealers, through push-out bond strength testing and failure mode analysis. Eighty human single canal teeth were divided into four groups: three test groups obturated with HAGP using AH Plus, iRoot SP, or GuttaFlow Bioseal, and a control group using conventional gutta-percha with AH Plus sealer. Push-out bond strength was assessed after 30 days using a universal testing machine, and failure modes were analysed via stereomicroscopy. Results revealed a significantly higher bond strength ( p < 0.001) for HAGP compared to the control, regardless of the sealer used. Failure analysis indicated 62.5% mixed failure and 37.5% cohesive failure, with no adhesive failure observed. These findings suggest that HAGP significantly improves gutta-percha adhesion which was demonstrated through the higher bond strength compared to conventional gutta-percha. Health sciences/Health care/Dentistry/Dental materials/Dental biomaterials Health sciences/Health care/Dentistry/Dental materials/Gutta percha Health sciences/Health care/Dentistry Health sciences/Health care/Dentistry/Dental materials Health sciences/Health care/Dentistry/Endodontics Health sciences/Health care/Dentistry/Restorative dentistry Gutta-percha Hydroxyapatites Root canal filling materials Push-out bond strength Figures Figure 1 Introduction The primary objective of endodontic treatment is to eradicate bacteria and maintain the tooth in a disinfected state, preventing bacterial ingress 1 . Therefore, the root canal must be hermetically sealed to hinder communication between the root canal system and the periapical tissues. Gutta-percha (GP) is the standard obturation core material, which has the major advantages of plasticity, ease of manipulation, minimal toxicity, radiopacity, and ease of removal using solvents or heat. However, it cannot fully obturate the root canal space because it does not provide a hermetic seal without the use of sealer since GP does not bond to radicular dentine 2 . Root canal sealers should fill the gaps that may allow microleakage of fluids between the filling and the canal wall in a static situation 3 . Sealers are also needed to resist dislodgement of the root filling material to maintain the integrity of the sealer-dentine interface during dynamic situations such as tooth flexure, preparation of post-space, or operative procedures. Hence, adhesion is a desirable physical property of root canal sealers 4 . Therefore, it has been recommended that GP is combined with a sealer to achieve improved sealing of the root canal systems 5 . Selecting an endodontic sealer is important to ensure the long-term success of non-surgical root canal treatment 6 . In order to overcome the limitation of inadequate adhesion of GP, a novel approach was introduced by coating conventional GP cones with materials that can bond to the sealer. Coating the non-bondable GP points with materials as an additional circumferential interface renders them bondable to the root canal sealers. Multiple coated GP products have been introduced to achieve the monoblock concept. A novel apatite calcium phosphate (Hydroxyapatite) coated GP has been introduced by immersing the substrate into simulated body fluid (SBF) solution 7 , which has been proposed to have enhanced surface properties as a root canal filling material due to the similarity of the coating components to hydroxyapatite in radicular dentine 7 , which might have increased the chemical adhesion to some sealers that bond chemically to radicular dentine, such as glass ionomer-based sealer 8 . Furthermore, the roughness of the coating surface has been suggested to permit penetration and mechanical interlocking of root sealer particles into the coated GP surface 7 . The hydroxyapatite-coated GP has shown promising results in terms of bond strength when used with bioceramic sealer 9 . Multiple sealers are available, including resin sealers which provide adhesion to radicular dentine and do not contain eugenol. AH Plus is an epoxy resin sealer with a modified formulation of AH-26 in which formaldehyde is not released 10 . It has a hydrophobic nature, which enables it to react with any exposed amino groups in collagen to form covalent bonds between the resin and collagen when the epoxide ring opens. They have been shown to achieve high bond strengths to both radicular dentine and GP, suggesting that the resin can react with both substrates 11 . Due to its excellent properties, such as low solubility, small expansion, adhesion to dentine, and very good sealing ability, AH Plus has been considered a benchmark “Gold Standard” 1213 . Bioceramic-based sealers have good physicochemical and biological properties, including bioactivity and biomineralization. In addition, they have been found to increase the in vitro fracture resistance of endodontically treated roots, especially when accompanied by Activ GP cones 14 . GuttaFlow Bioseal (Coltene/Whaledent, Altstatten, Switzerland) is a novel formulation of polydimethylsiloxane GP incorporated with calcium silicate particles. It has been shown to have higher biocompatibility compared to AH Plus, whereby it favours the cementoblast differentiation of human periodontal ligament stem cells in the absence of growth factors 15 . The aim of the study is to evaluate the HAGP adhesion by assessing the push-out bond strength of HAGP to the inorganic radicular dentine in the presence of various types of sealers. The null hypothesis is that there is no significant difference in the push-out bond strength of HAGP to radicular dentine when used with 3 different types of sealers (AH Plus, iRoot SP, and GuttaFlow Bioseal), compared to uncoated GP and AH Plus. Materials and methods This research was approved by the Medical Ethics Committee, Faculty of Dentistry, University of Malaya with reference number DF RD 2001/0001. Accordingly, the use of human extracted teeth and all related methods were conducted in full accordance with our institutional guidelines and regulations. Sample size calculation was performed using G Power 3.1.9.7. Eighty extracted teeth were collected from the Unit Pakar Ortodontik, Klinik Pergigian Cahaya Suria, Kuala Lumpur, Malaysia, following informed consent. The teeth were disinfected using a 0.5% Chloramine-T trihydrate solution for one week. Inclusion criteria for the study were as follows: fully formed root canals measuring at least 16 mm, a relatively single straight canals with curvatures less than 15°, a patent foramen, and a first binding file ≤ #20. Radiographs were used to confirm the root canal curvature. The anatomical crowns were removed with a separating disc at the level of the cemento-enamel junction perpendicular to the long axis of the root canal to the standard root canal length for all specimens (16 mm). Following that, each tooth was mounted in an impression compound to facilitate handling during root canal preparation and root canal obturation. Root canal preparation was performed using rotary ProTaper Next files (PTN; Dentsply Tulsa Dental, Tulsa, OK) until size X3, along with intermittent 5.25% sodium hypochlorite (NaOCl) solution irrigation. After preparation, the root canals were irrigated with 17% ethylenediaminetetraacetic acid (EDTA) for 1 minute, followed by rinsing with 10mL of distilled water. Samples were randomly divided into 4 groups with 20 samples each. Group 1: Conventional GP + AH Plus (Dentsply, Konstanz, Germany) Group 2: HAGP + AH Plus Group 3: HAGP + iRoot SP (Innovative BioCeramix Inc, Canada) Group 4: HAGP + ROEKO GuttaFlow Bioseal (Coltene, Switzerland) Single cone obturation technique was performed using ProTaper Next GP cone size #30/0.07 (X3, ProTaper NEXT, Dentsply, Maillefer, USA) for the first group. For the other three groups, HAGP was used for obturation after coating ProTaper Next GP cone size #30/0.07 (X3, ProTaper Next, Dentsply, Maillefer, USA) with hydroxyapatite following the method described by 7 . Each root was mounted using epoxy resin (Mirapox 950 − 230 A/B; Miracon Sdn Bhd, Malaysia), and the roots were sectioned using a sintered diamond wafering blade (Struers, Ballerup, Denmark) perpendicular to the root canal at low speed with constant water cooling. A 1 mm-thick section of mid-root dentine was obtained at a level calculated to yield a main cone diameter greater than 0.5 mm (based on main cone size and taper). Since the ProTaper Next GP cone size X3 has a tip diameter of 0.3 mm and 0.07 taper, for every 1 mm from the tip, the instrument cross-section diameter increases by 7 mm. Therefore, to yield a sample with more than 0.5 mm of apical diameter, 3 mm of the apical portion was sectioned and discarded before sectioning 1 mm thick of the sample. A single sample was taken from each tooth. Both the apical and coronal aspects of each sample were photographed and examined before testing to confirm a circular canal shape and that the GP filled the entire canal space. By using 2.5x magnification dental loupes, the obturation material was loaded with a 0.5-mm-diameter cylindrical stainless-steel plunger that provides almost complete coverage over the main cone without touching the canal wall. The plunger was mounted in the upper part of a Universal Testing Machine (Shimadzu Corporation, Kyoto, Japan). Subsequently, the samples were aligned over a 1 mm-diameter circular hole at the centre of a 10 mm-thick Perspex plate and mounted in an apical to coronal direction to avoid any constriction interference due to root canal taper during push-out testing. The tests were conducted at a cross-head speed of 0.5 mm/min using a 100 N load cell set at 50 N maximum loads. The highest value recorded was taken as the force in Newtons. Photographs of both sides of the samples were taken to check for anomalies. The thickness of the specimens was measured using a digital calliper (Mitutoyo Corporation, Kawasaki, Japan) to within 0.01 mm. The push-out value in MPa was calculated from force (N) divided by area (mm 2 ) according to the following formula: Failure modes were assessed under a stereomicroscope at 56X magnification and classified as adhesive, cohesive, or mixed. Assessments were conducted twice by the same investigator at one-month intervals. Intra-observer reliability was analyzed using Cohen's kappa coefficient. T Statistical analyses were performed with SPSS v24 (SPSS Inc., USA). Normality was verified using the Shapiro-Wilk test. One-way ANOVA and Tukey’s post hoc tests were applied for bond strength comparisons. Associations between failure mode and filling materials were examined with chi-square analysis. Significance was set at p < 0.05.T Results Table 1 shows the mean push-out bond strength for different groups. The highest mean bond strength (4.90 ± 0.66 MPa) was observed in Group 3 (HAGP/iRoot SP), and the lowest was in Group 1 (GP/AH Plus) at 2.02 ± 0.63 MPa. Table 1 Mean bond strength of different groups to radicular dentine in MPa Group Mean Bond Strength (MPa) ± SD p -value GP/AH Plus a 2.02 ± 0.63 < 0.001* HAGP/AH Plus b 4.55 ± 0.56 HAGP/iRoot SP b 4.90 ± 0.66 HAGP/GuttaFlow Bioseal b 4.49 ± 0.58 * Significant difference p < 0.05. Different small letters indicate significant difference between groups. A one-way ANOVA showed a significant difference among the various groups (p < 0.001). Post hoc comparisons using Tukey’s test showed that Group 1 had significantly lower bond strength than all other groups (p 0.05). Intra-observer agreement on failure mode classification was high (Kappa = 0.95). Figure 1 illustrates the distribution of failure modes across groups. Mixed failures predominated: 60% in Group 1, 65% in Group 2, 70% in Group 3, and 55% in Group 4. The remaining specimens exhibited cohesive failure. No adhesive failures were identified. Chi-square analysis found no significant association between filling material and failure mode (p > 0.05). Discussion The current study assessed the push-out bond strength of HAGP used with three different types of sealers and compared them to the control group of uncoated conventional GP used with AH Plus sealer. The mean push-out bond strength of the control group was significantly lower when compared to the various HAGP groups. Therefore, the null hypothesis that there is no significant difference between the groups was rejected. The AH Plus sealer served as a positive control. It is an epoxy-resin-based sealer that has been proven to have high bond strength when used with conventional GP 16 – 20 . This is associated with the sealer’s ability to form a covalent bond upon opening its epoxide ring to allow the reaction between the epoxy-resin and the exposed amino groups of the collagen matrix of the radicular dentine 11 . Additionally, its flowability leads to deeper penetration of the sealer into the dentinal tubules, thus enhancing the mechanical interlocking between the sealer and dentine 21 . The low shrinkage upon setting and long-term dimensional stability also contribute to its superior bond strength. According to the current study, the HAGP/AH Plus group had a significant increase in push-out bond strength when compared to GP/AH Plus, which might indicate the bonding of the sealer to the hydroxyapatite component of HAGP. The lower push-out bond strength of the GP/AH Plus group could be explained by the fact that conventional GP can neither bond to radicular dentine nor root sealers 6 , 9 . The HAGP groups used with iRoot SP and GuttaFlow Bioseal sealers have comparable push-out bond strength when compared to HAGP/AH Plus. This is in accordance with previous studies emphasising on the comparable performance of these sealers to each other 22 , 23 . A higher push-out bond strength demonstrated among all HAGP groups when compared to the conventional GP group can be attributed to the hydroxyapatite coating of HAGP, which was confirmed via the presence of hydroxyl groups in a previous study 7 . Additionally, the surface roughness of the apatite calcium phosphate coating provides an increased surface area for bonding and hence, increased adhesion. These irregularities might allow penetration of the sealer particles into the coating layer of the GP, leading to micromechanical retention of the sealers and hence a high bond strength 9 . The push-out strength test was used in this study since it is widely used to represent the adhesion between obturation materials and root canal walls because of its simplicity and reproducibility 15 , 19 – 21 , 24 , 25 . Additionally, in the push-out test, the fracture occurs parallel to the dentine-bonding interface, which makes it a true shear test for parallel-sided samples; hence, it has been advocated as a better evaluation of bond strength in comparison to conventional shear tests 26 , 27 . The value of push-out strength indicates a combination of the friction between the materials and root canal walls, the bonding force between molecules, and the chemical adhesion between materials and radicular dentine 28 . It is also affected by friction 29 , C factor 30 , 31 and different root canal treatment protocols 32 . The thin-slice push-out test method is considered a reliable technique to measure the bond strength of root canal filling materials to radicular dentine 30 and to evaluate 1 mm-thick samples 33 . It was chosen in the current study over the tensile and shear strength tests because the thin-slice push-out test is less sensitive to specimens’ small variations and to the variations in stress distribution during load application. Additionally, it allows easy alignment of samples during testing 20 . The root sections used for the current study were taken from the mid-root, 3 mm away from the apical portion of the root, ensuring a main cone diameter greater than 0.5 mm. This is to match the same plunger size (0.5 mm) and reduce the variables that could affect the bond strength. Earlier studies reported that the different sizes of the plunger used to push out the obturation material from different levels of the roots (apical, middle, and coronal) can influence the bond strength of the root sealer 19 , 34 . Nevertheless, when the same plunger size is used for that purpose, the bond strength does not significantly vary between the root levels 35 . The prominence of mixed failure modes in the hydroxyapatite-coated GP groups is comparable to that of Al-Haddad et. al., 9 , where the HAGP group with bioceramic sealer in that study had similar results. This can be considered evidence supporting the equivalent bond strength of the sealer to radicular dentine as well as to HAGP due to the similarity of the components in both the hydroxyapatite coating and the components of the inorganic radicular dentine, which contains 70% minerals by weight and a Ca/P molar ratio of 1.53 compared to the 1.67 Ca/P molar ratio of pure hydroxyapatite 36 . The present study has limitations, including the fact that it is a laboratory study with strict inclusion criteria. Further studies are required with a wider range of tested variables such as testing the HAGP in curved canals. Besides, additional studies are required to determine the bonding mechanism of sealers to HAGP using analytical tools such as Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction analysis (XRD). Conclusions Within the current in vitro experimental conditions and limitations, it can be concluded that regardless of the type of root sealer used (AH Plus, iRoot SP, or GuttaFlow Bioseal), the HAGP showed significantly higher bond strength compared to conventional GP. The mode of failure for all the samples showed mixed and cohesive failure. Declarations Competing interests The authors declare no competing interests. Author Contribution N.A: Supervision, Methodology, Conceptualization. N.M: Supervision, Formal analysis, Conceptualization. A.A: Writing – review & editing, Conceptualization. R.D.: Writing – original draft, review & editing. F.M.: Investigation, Data curation, Writing – original draft. Z.C: Supervision, Funding acquisition, Conceptualization. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6684617","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":479561078,"identity":"8b9ad7d6-d35d-48e8-8e8b-f03f0ca73e20","order_by":0,"name":"Noor Hayati Azami","email":"","orcid":"","institution":"Universiti Malaya","correspondingAuthor":false,"prefix":"","firstName":"Noor","middleName":"Hayati","lastName":"Azami","suffix":""},{"id":479561079,"identity":"2582f8b9-ec17-48c7-9e6a-59d9db65d3eb","order_by":1,"name":"Nora Sakina Mohd Noor","email":"","orcid":"","institution":"Universiti Malaya","correspondingAuthor":false,"prefix":"","firstName":"Nora","middleName":"Sakina Mohd","lastName":"Noor","suffix":""},{"id":479561080,"identity":"d2230917-ae6e-4eda-ae79-1613149173e5","order_by":2,"name":"Afaf Al-Haddad","email":"","orcid":"","institution":"Sana’a University","correspondingAuthor":false,"prefix":"","firstName":"Afaf","middleName":"","lastName":"Al-Haddad","suffix":""},{"id":479561081,"identity":"0d741a72-f00d-4ebf-9b3c-ae19a6eb422b","order_by":3,"name":"Rana Diab","email":"","orcid":"","institution":"Universiti Malaya","correspondingAuthor":false,"prefix":"","firstName":"Rana","middleName":"","lastName":"Diab","suffix":""},{"id":479561082,"identity":"a838aa74-9339-4b31-92a3-ca309bbb5571","order_by":4,"name":"Fauzi Majid","email":"","orcid":"","institution":"Sabah Dental Surgery","correspondingAuthor":false,"prefix":"","firstName":"Fauzi","middleName":"","lastName":"Majid","suffix":""},{"id":479561083,"identity":"ec8098d4-3893-4a60-bce9-9c730143dd9b","order_by":5,"name":"Zeti Adura Che Ab Aziz","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAz0lEQVRIie3OsQqCUBTG8SOC0w0bTxD5BIEgSNDgqwgODeHqGE25CK0+hr3BvdyhRZwdBdeC2hwMuurUYtct4v6ns/w4H4BK9aNRAASzPw0poA9kcZxC+mwqS6z4zGjTbjyn3PvwiDisU3+caAkHlhDU3TLMtLTg4JZfiI4BUIJodESfnSSIYdXAWhuJkwrykiFiEnDiI9ooiCZDkAQ2X1Ih8nvGkmJH3LwaJ1bM6uetPXhmHF6qJtqu3OuXLx/RbinMp5Ahk04mKpVK9d+9ARZsQi/AqbxXAAAAAElFTkSuQmCC","orcid":"","institution":"Universiti Malaya","correspondingAuthor":true,"prefix":"","firstName":"Zeti","middleName":"Adura Che Ab","lastName":"Aziz","suffix":""}],"badges":[],"createdAt":"2025-05-17 05:23:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6684617/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6684617/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41598-025-22842-1","type":"published","date":"2025-11-06T15:57:25+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":85915294,"identity":"bd043013-9c24-49dc-86eb-cdf739953712","added_by":"auto","created_at":"2025-07-03 06:41:32","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":16437,"visible":true,"origin":"","legend":"\u003cp\u003eMode of failure of the different groups of HAGP\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6684617/v1/1838b5232cd121f8d218ffc0.png"},{"id":95564145,"identity":"582bac4e-5e24-4ec3-8d93-2fb5f4d30510","added_by":"auto","created_at":"2025-11-10 16:08:19","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":520137,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6684617/v1/20924040-6d7f-487a-b8ee-e97449d1daf4.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Enhanced Adhesive Performance of Hydroxyapatite-Coated Gutta-Percha with Various Root Canal Sealers: A Push-Out Bond Strength and Failure Mode Analysis","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe primary objective of endodontic treatment is to eradicate bacteria and maintain the tooth in a disinfected state, preventing bacterial ingress \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Therefore, the root canal must be hermetically sealed to hinder communication between the root canal system and the periapical tissues. Gutta-percha (GP) is the standard obturation core material, which has the major advantages of plasticity, ease of manipulation, minimal toxicity, radiopacity, and ease of removal using solvents or heat. However, it cannot fully obturate the root canal space because it does not provide a hermetic seal without the use of sealer since GP does not bond to radicular dentine \u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eRoot canal sealers should fill the gaps that may allow microleakage of fluids between the filling and the canal wall in a static situation \u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. Sealers are also needed to resist dislodgement of the root filling material to maintain the integrity of the sealer-dentine interface during dynamic situations such as tooth flexure, preparation of post-space, or operative procedures. Hence, adhesion is a desirable physical property of root canal sealers \u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. Therefore, it has been recommended that GP is combined with a sealer to achieve improved sealing of the root canal systems \u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eSelecting an endodontic sealer is important to ensure the long-term success of non-surgical root canal treatment \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. In order to overcome the limitation of inadequate adhesion of GP, a novel approach was introduced by coating conventional GP cones with materials that can bond to the sealer. Coating the non-bondable GP points with materials as an additional circumferential interface renders them bondable to the root canal sealers. Multiple coated GP products have been introduced to achieve the monoblock concept.\u003c/p\u003e \u003cp\u003eA novel apatite calcium phosphate (Hydroxyapatite) coated GP has been introduced by immersing the substrate into simulated body fluid (SBF) solution \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, which has been proposed to have enhanced surface properties as a root canal filling material due to the similarity of the coating components to hydroxyapatite in radicular dentine \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e, which might have increased the chemical adhesion to some sealers that bond chemically to radicular dentine, such as glass ionomer-based sealer \u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e. Furthermore, the roughness of the coating surface has been suggested to permit penetration and mechanical interlocking of root sealer particles into the coated GP surface \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. The hydroxyapatite-coated GP has shown promising results in terms of bond strength when used with bioceramic sealer \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eMultiple sealers are available, including resin sealers which provide adhesion to radicular dentine and do not contain eugenol. AH Plus is an epoxy resin sealer with a modified formulation of AH-26 in which formaldehyde is not released \u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e. It has a hydrophobic nature, which enables it to react with any exposed amino groups in collagen to form covalent bonds between the resin and collagen when the epoxide ring opens. They have been shown to achieve high bond strengths to both radicular dentine and GP, suggesting that the resin can react with both substrates \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Due to its excellent properties, such as low solubility, small expansion, adhesion to dentine, and very good sealing ability, AH Plus has been considered a benchmark \u0026ldquo;Gold Standard\u0026rdquo; \u003csup\u003e1213\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eBioceramic-based sealers have good physicochemical and biological properties, including bioactivity and biomineralization. In addition, they have been found to increase the in vitro fracture resistance of endodontically treated roots, especially when accompanied by Activ GP cones \u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eGuttaFlow Bioseal (Coltene/Whaledent, Altstatten, Switzerland) is a novel formulation of polydimethylsiloxane GP incorporated with calcium silicate particles. It has been shown to have higher biocompatibility compared to AH Plus, whereby it favours the cementoblast differentiation of human periodontal ligament stem cells in the absence of growth factors \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe aim of the study is to evaluate the HAGP adhesion by assessing the push-out bond strength of HAGP to the inorganic radicular dentine in the presence of various types of sealers. The null hypothesis is that there is no significant difference in the push-out bond strength of HAGP to radicular dentine when used with 3 different types of sealers (AH Plus, iRoot SP, and GuttaFlow Bioseal), compared to uncoated GP and AH Plus.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cp\u003eThis research was approved by the Medical Ethics Committee, Faculty of Dentistry, University of Malaya with reference number DF RD 2001/0001. Accordingly, the use of human extracted teeth and all related methods were conducted in full accordance with our institutional guidelines and regulations. Sample size calculation was performed using G Power 3.1.9.7. Eighty extracted teeth were collected from the Unit Pakar Ortodontik, Klinik Pergigian Cahaya Suria, Kuala Lumpur, Malaysia, following informed consent. The teeth were disinfected using a 0.5% Chloramine-T trihydrate solution for one week.\u003c/p\u003e \u003cp\u003eInclusion criteria for the study were as follows: fully formed root canals measuring at least 16 mm, a relatively single straight canals with curvatures less than 15\u0026deg;, a patent foramen, and a first binding file \u0026le; #20. Radiographs were used to confirm the root canal curvature.\u003c/p\u003e \u003cp\u003eThe anatomical crowns were removed with a separating disc at the level of the cemento-enamel junction perpendicular to the long axis of the root canal to the standard root canal length for all specimens (16 mm). Following that, each tooth was mounted in an impression compound to facilitate handling during root canal preparation and root canal obturation. Root canal preparation was performed using rotary ProTaper Next files (PTN; Dentsply Tulsa Dental, Tulsa, OK) until size X3, along with intermittent 5.25% sodium hypochlorite (NaOCl) solution irrigation. After preparation, the root canals were irrigated with 17% ethylenediaminetetraacetic acid (EDTA) for 1 minute, followed by rinsing with 10mL of distilled water. Samples were randomly divided into 4 groups with 20 samples each.\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eGroup 1: Conventional GP\u0026thinsp;+\u0026thinsp;AH Plus (Dentsply, Konstanz, Germany)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eGroup 2: HAGP\u0026thinsp;+\u0026thinsp;AH Plus\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eGroup 3: HAGP\u0026thinsp;+\u0026thinsp;iRoot SP (Innovative BioCeramix Inc, Canada)\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eGroup 4: HAGP\u0026thinsp;+\u0026thinsp;ROEKO GuttaFlow Bioseal (Coltene, Switzerland)\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eSingle cone obturation technique was performed using ProTaper Next GP cone size #30/0.07 (X3, ProTaper NEXT, Dentsply, Maillefer, USA) for the first group. For the other three groups, HAGP was used for obturation after coating ProTaper Next GP cone size #30/0.07 (X3, ProTaper Next, Dentsply, Maillefer, USA) with hydroxyapatite following the method described by \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eEach root was mounted using epoxy resin (Mirapox 950\u0026thinsp;\u0026minus;\u0026thinsp;230 A/B; Miracon Sdn Bhd, Malaysia), and the roots were sectioned using a sintered diamond wafering blade (Struers, Ballerup, Denmark) perpendicular to the root canal at low speed with constant water cooling. A 1 mm-thick section of mid-root dentine was obtained at a level calculated to yield a main cone diameter greater than 0.5 mm (based on main cone size and taper). Since the ProTaper Next GP cone size X3 has a tip diameter of 0.3 mm and 0.07 taper, for every 1 mm from the tip, the instrument cross-section diameter increases by 7 mm. Therefore, to yield a sample with more than 0.5 mm of apical diameter, 3 mm of the apical portion was sectioned and discarded before sectioning 1 mm thick of the sample. A single sample was taken from each tooth. Both the apical and coronal aspects of each sample were photographed and examined before testing to confirm a circular canal shape and that the GP filled the entire canal space. By using 2.5x magnification dental loupes, the obturation material was loaded with a 0.5-mm-diameter cylindrical stainless-steel plunger that provides almost complete coverage over the main cone without touching the canal wall. The plunger was mounted in the upper part of a Universal Testing Machine (Shimadzu Corporation, Kyoto, Japan). Subsequently, the samples were aligned over a 1 mm-diameter circular hole at the centre of a 10 mm-thick Perspex plate and mounted in an apical to coronal direction to avoid any constriction interference due to root canal taper during push-out testing. The tests were conducted at a cross-head speed of 0.5 mm/min using a 100 N load cell set at 50 N maximum loads. The highest value recorded was taken as the force in Newtons. Photographs of both sides of the samples were taken to check for anomalies. The thickness of the specimens was measured using a digital calliper (Mitutoyo Corporation, Kawasaki, Japan) to within 0.01 mm. The push-out value in MPa was calculated from force (N) divided by area (mm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e) according to the following formula:\u003c/p\u003e \u003cp\u003e\u003cimg 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\" width=\"610\" height=\"116\"\u003e\u003c/p\u003e \u003cp\u003eFailure modes were assessed under a stereomicroscope at 56X magnification and classified as adhesive, cohesive, or mixed. Assessments were conducted twice by the same investigator at one-month intervals. Intra-observer reliability was analyzed using Cohen's kappa coefficient.\u003c/p\u003e \u003cp\u003eT Statistical analyses were performed with SPSS v24 (SPSS Inc., USA). Normality was verified using the Shapiro-Wilk test. One-way ANOVA and Tukey\u0026rsquo;s post hoc tests were applied for bond strength comparisons. Associations between failure mode and filling materials were examined with chi-square analysis. Significance was set at p\u0026thinsp;\u0026lt;\u0026thinsp;0.05.T\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e shows the mean push-out bond strength for different groups. The highest mean bond strength (4.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66 MPa) was observed in Group 3 (HAGP/iRoot SP), and the lowest was in Group 1 (GP/AH Plus) at 2.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.63 MPa.\u003c/p\u003e\u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eMean bond strength of different groups to radicular dentine in MPa\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMean Bond Strength (MPa)\u0026thinsp;\u0026plusmn;\u0026thinsp;SD\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGP/AH Plus \u003csup\u003ea\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e2.02\u0026thinsp;\u0026plusmn;\u0026thinsp;0.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"3\" rowspan=\"4\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.001*\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHAGP/AH Plus \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.55\u0026thinsp;\u0026plusmn;\u0026thinsp;0.56\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHAGP/iRoot SP \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.90\u0026thinsp;\u0026plusmn;\u0026thinsp;0.66\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHAGP/GuttaFlow Bioseal \u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e4.49 \u0026plusmn;\u0026thinsp;0.58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003e\u003cem\u003e*\u003c/em\u003eSignificant difference p\u0026thinsp;\u0026lt;\u0026thinsp;0.05. Different small letters indicate significant difference between groups.\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eA one-way ANOVA showed a significant difference among the various groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). Post hoc comparisons using Tukey\u0026rsquo;s test showed that Group 1 had significantly lower bond strength than all other groups (p\u0026thinsp;\u0026lt;\u0026thinsp;0.001). No statistically significant differences were found between Groups 2, 3, and 4 (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003eIntra-observer agreement on failure mode classification was high (Kappa\u0026thinsp;=\u0026thinsp;0.95). Figure\u0026nbsp;1 illustrates the distribution of failure modes across groups. Mixed failures predominated: 60% in Group 1, 65% in Group 2, 70% in Group 3, and 55% in Group 4. The remaining specimens exhibited cohesive failure. No adhesive failures were identified. Chi-square analysis found no significant association between filling material and failure mode (p\u0026thinsp;\u0026gt;\u0026thinsp;0.05).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe current study assessed the push-out bond strength of HAGP used with three different types of sealers and compared them to the control group of uncoated conventional GP used with AH Plus sealer. The mean push-out bond strength of the control group was significantly lower when compared to the various HAGP groups. Therefore, the null hypothesis that there is no significant difference between the groups was rejected.\u003c/p\u003e \u003cp\u003eThe AH Plus sealer served as a positive control. It is an epoxy-resin-based sealer that has been proven to have high bond strength when used with conventional GP \u003csup\u003e\u003cspan additionalcitationids=\"CR17 CR18 CR19\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. This is associated with the sealer\u0026rsquo;s ability to form a covalent bond upon opening its epoxide ring to allow the reaction between the epoxy-resin and the exposed amino groups of the collagen matrix of the radicular dentine \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. Additionally, its flowability leads to deeper penetration of the sealer into the dentinal tubules, thus enhancing the mechanical interlocking between the sealer and dentine \u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e. The low shrinkage upon setting and long-term dimensional stability also contribute to its superior bond strength.\u003c/p\u003e \u003cp\u003eAccording to the current study, the HAGP/AH Plus group had a significant increase in push-out bond strength when compared to GP/AH Plus, which might indicate the bonding of the sealer to the hydroxyapatite component of HAGP. The lower push-out bond strength of the GP/AH Plus group could be explained by the fact that conventional GP can neither bond to radicular dentine nor root sealers \u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e,\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe HAGP groups used with iRoot SP and GuttaFlow Bioseal sealers have comparable push-out bond strength when compared to HAGP/AH Plus. This is in accordance with previous studies emphasising on the comparable performance of these sealers to each other \u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e,\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eA higher push-out bond strength demonstrated among all HAGP groups when compared to the conventional GP group can be attributed to the hydroxyapatite coating of HAGP, which was confirmed via the presence of hydroxyl groups in a previous study \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. Additionally, the surface roughness of the apatite calcium phosphate coating provides an increased surface area for bonding and hence, increased adhesion. These irregularities might allow penetration of the sealer particles into the coating layer of the GP, leading to micromechanical retention of the sealers and hence a high bond strength\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe push-out strength test was used in this study since it is widely used to represent the adhesion between obturation materials and root canal walls because of its simplicity and reproducibility \u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e,\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. Additionally, in the push-out test, the fracture occurs parallel to the dentine-bonding interface, which makes it a true shear test for parallel-sided samples; hence, it has been advocated as a better evaluation of bond strength in comparison to conventional shear tests \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e,\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. The value of push-out strength indicates a combination of the friction between the materials and root canal walls, the bonding force between molecules, and the chemical adhesion between materials and radicular dentine \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. It is also affected by friction \u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e, C factor \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e and different root canal treatment protocols \u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe thin-slice push-out test method is considered a reliable technique to measure the bond strength of root canal filling materials to radicular dentine \u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e and to evaluate 1 mm-thick samples \u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. It was chosen in the current study over the tensile and shear strength tests because the thin-slice push-out test is less sensitive to specimens\u0026rsquo; small variations and to the variations in stress distribution during load application. Additionally, it allows easy alignment of samples during testing \u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe root sections used for the current study were taken from the mid-root, 3 mm away from the apical portion of the root, ensuring a main cone diameter greater than 0.5 mm. This is to match the same plunger size (0.5 mm) and reduce the variables that could affect the bond strength. Earlier studies reported that the different sizes of the plunger used to push out the obturation material from different levels of the roots (apical, middle, and coronal) can influence the bond strength of the root sealer \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e,\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. Nevertheless, when the same plunger size is used for that purpose, the bond strength does not significantly vary between the root levels \u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe prominence of mixed failure modes in the hydroxyapatite-coated GP groups is comparable to that of Al-Haddad et. al., \u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e, where the HAGP group with bioceramic sealer in that study had similar results. This can be considered evidence supporting the equivalent bond strength of the sealer to radicular dentine as well as to HAGP due to the similarity of the components in both the hydroxyapatite coating and the components of the inorganic radicular dentine, which contains 70% minerals by weight and a Ca/P molar ratio of 1.53 compared to the 1.67 Ca/P molar ratio of pure hydroxyapatite \u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eThe present study has limitations, including the fact that it is a laboratory study with strict inclusion criteria. Further studies are required with a wider range of tested variables such as testing the HAGP in curved canals. Besides, additional studies are required to determine the bonding mechanism of sealers to HAGP using analytical tools such as Fourier Transform Infrared Spectroscopy (FTIR) and X-ray diffraction analysis (XRD).\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eWithin the current in vitro experimental conditions and limitations, it can be concluded that regardless of the type of root sealer used (AH Plus, iRoot SP, or GuttaFlow Bioseal), the HAGP showed significantly higher bond strength compared to conventional GP. The mode of failure for all the samples showed mixed and cohesive failure.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting interests\u003c/h2\u003e \u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eN.A: Supervision, Methodology, Conceptualization. N.M: Supervision, Formal analysis, Conceptualization. A.A: Writing \u0026ndash; review \u0026amp; editing, Conceptualization. R.D.: Writing \u0026ndash; original draft, review \u0026amp; editing. F.M.: Investigation, Data curation, Writing \u0026ndash; original draft. Z.C: Supervision, Funding acquisition, Conceptualization.\u003c/p\u003e\u003ch2\u003eAcknowledgments\u003c/h2\u003e \u003cp\u003eThe authors acknowledge funding by Dental Research Postgraduate Grant, Faculty of Dentistry, University of Malaya [DPRG/13/19].\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eSchilder, H. Cleaning and shaping the root canal. \u003cem\u003eDent Clin North Am\u003c/em\u003e \u003cstrong\u003e18\u003c/strong\u003e, (1974).\u003c/li\u003e\n\u003cli\u003eSkinner, R. L. \u0026amp; Himel, V. T. 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Assessment of a new root canal sealer\u0026rsquo;s apical sealing ability. \u003cem\u003eOral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontology\u003c/em\u003e \u003cstrong\u003e107\u003c/strong\u003e, (2009).\u003c/li\u003e\n\u003cli\u003eYap, W. Y., Che Ab Aziz, Z. A., Azami, N. H., Al-Haddad, A. Y. \u0026amp; Khan, A. A. An in vitro Comparison of Bond Strength of Different Sealers/Obturation Systems to Root Dentin Using the Push-Out Test at 2 Weeks and 3 Months after Obturation. \u003cem\u003eMedical Principles and Practice\u003c/em\u003e \u003cstrong\u003e26\u003c/strong\u003e, (2017).\u003c/li\u003e\n\u003cli\u003eDrs, A., Koch, K., Brave, D. \u0026amp; Nasseh, A. A. A review of bioceramic technology in endodontics. \u003cem\u003eCE Article_bioceramic technology\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, (2013).\u003c/li\u003e\n\u003cli\u003e\u0026Uuml;reyen Kaya, B., Ke\u0026ccedil;eci, A. D., Orhan, H. \u0026amp; Belli, S. Micropush-out bond strengths of gutta-percha versus thermoplastic synthetic polymer-based systems - An ex vivo study. \u003cem\u003eInt Endod J\u003c/em\u003e \u003cstrong\u003e41\u003c/strong\u003e, (2008).\u003c/li\u003e\n\u003cli\u003eDrummond, J. L., Sakaguchi, R. L., Racean, D. C., Wozny, J. \u0026amp; Steinberg, A. D. Testing mode and surface treatment effects on dentin bonding. \u003cem\u003eJ Biomed Mater Res\u003c/em\u003e \u003cstrong\u003e32\u003c/strong\u003e, (1996).\u003c/li\u003e\n\u003cli\u003eDem, K. \u003cem\u003eet al.\u003c/em\u003e The push out bond strength of polydimethylsiloxane endodontic sealers to dentin. \u003cem\u003eBMC Oral Health\u003c/em\u003e \u003cstrong\u003e19\u003c/strong\u003e, (2019).\u003c/li\u003e\n\u003cli\u003eSoares, C. J. \u003cem\u003eet al.\u003c/em\u003e Finite element analysis and bond strength of a glass post to intraradicular dentin: Comparison between microtensile and push-out tests. \u003cem\u003eDental Materials\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e, (2008).\u003c/li\u003e\n\u003cli\u003eGoracci, C. \u003cem\u003eet al.\u003c/em\u003e The adhesion between fiber posts and root canal walls: Comparison between microtensile and push-out bond strength measurements. \u003cem\u003eEur J Oral Sci\u003c/em\u003e \u003cstrong\u003e112\u003c/strong\u003e, (2004).\u003c/li\u003e\n\u003cli\u003ePane, E. S., Palamara, J. E. A. \u0026amp; Messer, H. H. Critical evaluation of the push-out test for root canal filling materials. \u003cem\u003eJ Endod\u003c/em\u003e \u003cstrong\u003e39\u003c/strong\u003e, (2013).\u003c/li\u003e\n\u003cli\u003ePatil A, S., Dodwad K, P. \u0026amp; Patil A, A. 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Effect of plunger diameter on the push-out bond values of different root filling materials. \u003cem\u003eInt Endod J\u003c/em\u003e \u003cstrong\u003e44\u003c/strong\u003e, (2011).\u003c/li\u003e\n\u003cli\u003eBouillaguet, S. \u003cem\u003eet al.\u003c/em\u003e Alternative Adhesive Strategies to Optimize Bonding to Radicular Dentin. \u003cem\u003eJ Endod\u003c/em\u003e \u003cstrong\u003e33\u003c/strong\u003e, (2007).\u003c/li\u003e\n\u003cli\u003eDe Dios Teruel, J., Alcolea, A., Hern\u0026aacute;ndez, A. \u0026amp; Ruiz, A. J. O. Comparison of chemical composition of enamel and dentine in human, bovine, porcine and ovine teeth. \u003cem\u003eArch Oral Biol\u003c/em\u003e \u003cstrong\u003e60\u003c/strong\u003e, (2015).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Gutta-percha, Hydroxyapatites, Root canal filling materials, Push-out bond strength","lastPublishedDoi":"10.21203/rs.3.rs-6684617/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6684617/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis study evaluates the the adhesive performance of a novel hydroxyapatite-coated gutta-percha (HAGP) in combination with various root canal sealers, through push-out bond strength testing and failure mode analysis. Eighty human single canal teeth were divided into four groups: three test groups obturated with HAGP using AH Plus, iRoot SP, or GuttaFlow Bioseal, and a control group using conventional gutta-percha with AH Plus sealer. Push-out bond strength was assessed after 30 days using a universal testing machine, and failure modes were analysed via stereomicroscopy. Results revealed a significantly higher bond strength (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.001) for HAGP compared to the control, regardless of the sealer used. Failure analysis indicated 62.5% mixed failure and 37.5% cohesive failure, with no adhesive failure observed. These findings suggest that HAGP significantly improves gutta-percha adhesion which was demonstrated through the higher bond strength compared to conventional gutta-percha.\u003c/p\u003e","manuscriptTitle":"Enhanced Adhesive Performance of Hydroxyapatite-Coated Gutta-Percha with Various Root Canal Sealers: A Push-Out Bond Strength and Failure Mode Analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-03 06:41:28","doi":"10.21203/rs.3.rs-6684617/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-08-11T06:55:57+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-08-10T07:42:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"101337579849242616112966721715883530462","date":"2025-08-08T12:44:46+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"8342913263413864237279237410093529227","date":"2025-08-02T12:50:32+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-08T17:33:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"51577661916772628597090288490844214600","date":"2025-07-02T04:32:42+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"281610856829691540390488930410720537168","date":"2025-07-02T03:28:34+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"243677883287249494887177720632500656240","date":"2025-07-02T02:20:39+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-07-01T23:58:07+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-07-01T23:55:25+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-06-13T02:54:21+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-12T03:05:33+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2025-05-17T05:19:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"e0713836-8c9d-45f2-b3d9-0f59b0c7ba86","owner":[],"postedDate":"July 3rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":50922279,"name":"Health sciences/Health care/Dentistry/Dental materials/Dental biomaterials"},{"id":50922280,"name":"Health sciences/Health care/Dentistry/Dental materials/Gutta percha"},{"id":50922281,"name":"Health sciences/Health care/Dentistry"},{"id":50922282,"name":"Health sciences/Health care/Dentistry/Dental materials"},{"id":50922283,"name":"Health sciences/Health care/Dentistry/Endodontics"},{"id":50922284,"name":"Health sciences/Health care/Dentistry/Restorative dentistry"}],"tags":[],"updatedAt":"2025-11-10T16:04:19+00:00","versionOfRecord":{"articleIdentity":"rs-6684617","link":"https://doi.org/10.1038/s41598-025-22842-1","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-11-06 15:57:25","publishedOnDateReadable":"November 6th, 2025"},"versionCreatedAt":"2025-07-03 06:41:28","video":"","vorDoi":"10.1038/s41598-025-22842-1","vorDoiUrl":"https://doi.org/10.1038/s41598-025-22842-1","workflowStages":[]},"version":"v1","identity":"rs-6684617","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6684617","identity":"rs-6684617","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}