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Hackbarth M, Montoya M, Noblett WC, Lima BP, Dietz M, Staley C, Ordinola-Zapata R. An In Vitro Evaluation of the Antimicrobial Efficacy of a Novel Irrigant Using Next-Generation Sequencing. J Endod 2024; 50:1314-1320.e1. [PMID: 38815857 PMCID: PMC11402568 DOI: 10.1016/j.joen.2024.05.010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2023] [Revised: 05/19/2024] [Accepted: 05/20/2024] [Indexed: 06/01/2024]
Abstract
INTRODUCTION To evaluate the antimicrobial activity of Triton irrigation versus 4% sodium hypochlorite (NaOCl) utilizing a direct contact test and an extracted tooth model. METHODS In the first experiment, a direct contact test was conducted to compare bacterial DNA removal and microbial diversity changes following irrigation with 4% NaOCl or Triton. Hydroxyapatite and dentin discs were inoculated with subgingival human-derived dental plaque for 2 weeks utilizing the Center for Disease Control biofilm reactor and subsequently challenged with the root canal irrigants for 5 minutes. In the second experiment, teeth contaminated with a multispecies biofilm (n = 24) were assigned into two treatment groups, NaOCl or Triton irrigation. Samples were obtained for quantitative real-time polymerase chain reaction and next-generation sequencing analysis before and after instrumentation. The Shannon and Chao1 indices were used to measure alpha diversity. The Bray-Curtis dissimilarity and ANOSIM was used to measure beta diversity. Differences in abundances of genera were evaluated using Kruskal-Wallis test with Bonferroni corrections. RESULTS The direct contact test revealed no significant differences in the bacterial load based on 16S rRNA gene molecules/μL, reads, or differences in the Shannon index among groups. In the extracted tooth model, a bacterial load reduction of log10 3.08 ± 0.69 and 2.76 ± 0.91 were found for NaOCl and Triton, respectively (P = .348). Next-generation sequencing showed fewer reads, lower Chao1, and beta diversity values when pretreatment and post-treatment samples were assessed in both experimental groups (P < .0001). The Kruskal-Wallis analysis found that 17 genera of bacteria were over-represented in minimal values in the Triton post-treatment group, 14 of these genera represented less than 1% of the microbial community. CONCLUSIONS Both irrigants had limited antimicrobial activity in the direct contact test. When used in conjunction with mechanical instrumentation both irrigants were able to reduce the bacterial DNA load and diversity in comparison with pretreatment communities. The NaOCl irrigation, followed by ethylenediaminetetraacetic acid flush, was more effective in decreasing DNA counts from low-abundance organisms.
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Affiliation(s)
- Mallory Hackbarth
- Division of Endodontics, University of Minnesota School of Dentistry, Minneapolis, Minnesota
| | - Meghan Montoya
- Division of Endodontics, University of Minnesota School of Dentistry, Minneapolis, Minnesota
| | - W Craig Noblett
- Division of Endodontics, University of Minnesota School of Dentistry, Minneapolis, Minnesota
| | - Bruno P Lima
- Division of Basic Sciences, Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota
| | - Matthew Dietz
- Division of Basic & Translational Research, Department of Surgery, University of Minnesota, Minneapolis, Minnesota
| | - Christopher Staley
- Division of Basic & Translational Research, Department of Surgery, University of Minnesota, Minneapolis, Minnesota
| | - Ronald Ordinola-Zapata
- Division of Endodontics, University of Minnesota School of Dentistry, Minneapolis, Minnesota.
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Auerbach D, Alaugaily I, Davis S, Azim AA. A promising approach utilising photothermal energy to disinfect the root canal system: An in vitro investigation. AUST ENDOD J 2024. [PMID: 38995151 DOI: 10.1111/aej.12872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2024] [Revised: 03/30/2024] [Accepted: 06/20/2024] [Indexed: 07/13/2024]
Abstract
This study aimed to assess root canal disinfection through various irrigation protocols, including a novel photothermal system called 'LEAP'. Mandibular premolars were infected with Enterococcus faecalis and divided into five groups for different treatments: Group 1: standard needle irrigation; Group 2: passive ultrasonic irrigation; Group 3: GentleWave; Group 4: LEAP; and Group 5: Group 1 + Group 4. Microbial counts were measured before (S1) and after disinfection (S2) using colony-forming units (CFU) and confocal laser scanning microscopy (CLSM). Results revealed a significant reduction in bacterial counts for all groups (p < 0.05). While the percentage of dead bacteria near the canal wall (0-50 μm) did not differ significantly, at 50-150 μm, LEAP and SNI + LEAP exhibited significantly higher bacterial reduction than other groups (p < 0.05). The findings indicate that LEAP is comparable to existing irrigation devices in the main root canal and notably superior in tubular disinfection.
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Affiliation(s)
- Daniela Auerbach
- Department of Endodontics, Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, California, USA
| | - Ibrahim Alaugaily
- Department of Endodontics, Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, California, USA
- Department of Restorative Dental Sciences, College of Dentistry, King Saud University, Riyadh, Saudi Arabia
| | - Scott Davis
- Department of Endodontics, Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, California, USA
| | - Adham A Azim
- Department of Endodontics, Arthur A. Dugoni School of Dentistry, University of the Pacific, San Francisco, California, USA
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Kim KH, Lévesque C, Malkhassian G, Basrani B. Efficacy of the GentleWave System in the removal of biofilm from the mesial roots of mandibular molars before and after minimal instrumentation: An ex vivo study. Int Endod J 2024; 57:922-932. [PMID: 38374488 DOI: 10.1111/iej.14044] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2023] [Accepted: 01/29/2024] [Indexed: 02/21/2024]
Abstract
AIM To compare the efficacy of Enterococcus faecalis biofilm removal using the GentleWave System (GWS) (Sonendo Inc, CA) on non-instrumented versus minimally instrumented root canal systems. METHODOLOGY Thirty-four mandibular molars were autoclaved and allocated to four groups: Negative control (n = 5); positive control (n = 5); Group 1: non-instrumentation + GWS (NI + GWS) (n = 12); and Group 2: minimal instrumentation + GWS (MI + GWS) (n = 12). Of 34 samples, 24 samples with Vertucci type 2 configuration within the mesial root of each sample were allocated to Groups 1 and 2 and then matched based on the working length and root canal configuration. After inoculation of samples with E. faecalis for 3 weeks, the GWS was used on Group 1 without any instrumentation and Group 2 after instrumentation of mesial canals until size 20/06v. CFU and SEM analysis were used. RESULTS Log10 (CFU/mL) from the positive control, and Group 1 and 2 were 7.41 ± 0.53, 3.41 ± 1.54, and 3.21 ± 1.54, respectively. Both groups showed a statistically significant difference in the reduction of viable E. faecalis cells compared to the positive control (Group 1 [p = .0001] and Group 2 [p < .0001]), whilst showing no significant difference between the two tested groups (p < .05). CONCLUSION The use of GWS on the non-instrumented root canal system could be an effective disinfection protocol in removing the biofilm without dentin debris formation.
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Affiliation(s)
- Kwang Ho Kim
- Endodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada
| | - Céline Lévesque
- Microbiology, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada
| | - Gevik Malkhassian
- Endodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada
| | - Bettina Basrani
- Endodontics, Faculty of Dentistry, University of Toronto, Toronto, Ontario, Canada
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Vieira WDA, de-Jesus-Soares A, Lopes EM, Gomes BPFA, Lima BP. Effect of supplementary sodium hypochlorite agitation techniques on an ex vivo oral multispecies biofilm during passive disinfection of simulated immature roots. Int Endod J 2024; 57:966-980. [PMID: 38387884 DOI: 10.1111/iej.14053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Revised: 02/08/2024] [Accepted: 02/11/2024] [Indexed: 02/24/2024]
Abstract
AIM To compare the effect of different sodium hypochlorite (NaOCl) agitation techniques on an ex vivo oral multispecies biofilm during passive disinfection of simulated immature roots. METHODOLOGY Extracted human teeth were prepared to simulate immature roots. They were infected with a dental plaque-derived multispecies biofilm and cultured for 14 days. The roots were randomly designated into four groups: (1) negative control (PBS), (2) 1.5% NaOCl (CNI), (3) CNI + Ultrasonic activation (UA), (4) CNI + EasyClean agitation (ECA), (5) CNI + XP-endo finisher agitation (XPF), and (6) positive control (6% NaOCl). Biofilm samples were collected from the root canals and used to determine the number of viable cells (colony-forming units), scanning electron microscopy, and 16S rRNA gene sequencing. The mean colony-forming units per mL (CFU/mL) were analysed using One-way anova. 16S rRNA sequencing data were analysed for alpha (observed OTUs, Shannon index, and Chao1) and beta diversity (Bray-Curtis dissimilarities). The LEfSe analysis was used to determine the effect of treatment procedures on the abundance of root canal microbiota. The significance was set at .05. RESULTS PBS and CNI samples had significantly higher CFU/mL counts than UA, ECA, XPF, and 6% NaOCl samples (p < .05). The pre-treatment, PBS, and CNI groups had significantly greater alpha diversity than the UA, ECA, XPF, and 6% NaOCl groups (p < .05). NaOCl agitation groups and the 6% NaOCl group achieved a more pronounced reduction in bacteria from the genera Fusobacterium, Actinomyces, Porphyromonas, and Capnocytophaga. CONCLUSIONS The effectiveness of passive disinfection protocols was enhanced by NaOCl agitation techniques, suggesting that this supplementary method can improve the outcome of revitalization procedures.
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Affiliation(s)
- Walbert de Andrade Vieira
- Division of Endodontics, Department of Restorative Dentistry, Piracicaba Dental School, Universidade Estadual de Campinas - UNICAMP, Piracicaba, Brazil
| | - Adriana de-Jesus-Soares
- Division of Endodontics, Department of Restorative Dentistry, Piracicaba Dental School, Universidade Estadual de Campinas - UNICAMP, Piracicaba, Brazil
| | - Erica M Lopes
- Division of Endodontics, Department of Restorative Dentistry, Piracicaba Dental School, Universidade Estadual de Campinas - UNICAMP, Piracicaba, Brazil
| | - Brenda P F A Gomes
- Division of Endodontics, Department of Restorative Dentistry, Piracicaba Dental School, Universidade Estadual de Campinas - UNICAMP, Piracicaba, Brazil
| | - Bruno P Lima
- Division of Basic Sciences, Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
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Park KH, Ordinola-Zapata R, Noblett WC, Lima BP, Staley C. The effect of ultrasonic and multisonic irrigation on root canal microbial communities: An ex vivo study. Int Endod J 2024; 57:895-906. [PMID: 37983635 DOI: 10.1111/iej.13996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2022] [Revised: 10/19/2023] [Accepted: 10/20/2023] [Indexed: 11/22/2023]
Abstract
AIM To analyse the effect of ultrasonic irrigant activation (UIA) and the GentleWave (GW) multisonic irrigation (GW) with minimal instrumentation on the root canal microbial diversity in an ex vivo model that used extracted molars with a history of pulp necrosis. METHODOLOGY Twenty-three mandibular molars were prepared ex vivo for collection of superficial (surface control), pre-treatment and post-treatment samples 24 h after extraction. Samples were divided into two groups: UIA using 6% NaOCl (n = 11) and GW group (n = 12). All samples were processed using quantitative real-time polymerase chain reaction (qPCR) and 16S rRNA next-generation sequencing to measure microbial diversity before and after the antimicrobial treatment. For qPCR, a t-test (α = .05) was used to compare the log10 reduction. The Chao1 and Shannon indices evaluated alpha diversity. Differences in community composition (beta diversity) were evaluated by analysis of similarity (ANOSIM). Kruskal-Wallis test with Bonferroni corrections was performed to evaluate the differences in abundances genera in the samples. RESULTS Quantitative real-time polymerase chain reaction revealed an estimated 1.6 and 2.6 log10 reduction for UIA and GW groups respectively (p = .048). An average of 5 ± 4 and 3 ± 5 operational taxonomic units (OTUs) were found in surface's samples in the UIA and GW group respectively. These values were significantly lower (p < .001) compared to the number of preoperative OTUs in those groups (155 ± 79 and 187 ± 121). In assessing beta diversity, there were no significant differences found in pre-treatment samples (R = .090, p = .070 ANOSIM with Bonferroni corrections). Also, no significant differences in community composition were observed in post-treatment samples (R = -.05, p = .829). After treatment, there was a significant reduction of Eubacterium using conventional treatment with UIA and a significant reduction of Prevotella using minimal instrumentation with GW irrigation (p = .007 and p = .002 respectively). CONCLUSION Quantitative PCR analysis revealed a significant reduction in microbial load for GW group. Overall, diversity changes were similar between UIA and GW irrigation in this ex vivo model that used extracted teeth with a history of pulp necrosis. OTUs obtained from the surface sample were negligible and did not affect the statistical outcome of the study.
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Affiliation(s)
- Ki Hong Park
- Division of Endodontics, Department of Restorative Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
| | - Ronald Ordinola-Zapata
- Division of Endodontics, Department of Restorative Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
| | - W Craig Noblett
- Division of Endodontics, Department of Restorative Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
| | - Bruno P Lima
- Division of Basic Sciences, Department of Diagnostic and Biological Sciences, School of Dentistry, University of Minnesota, Minneapolis, Minnesota, USA
| | - Christopher Staley
- Division of Basic & Translational Research, Department of Surgery, University of Minnesota, Minneapolis, Minnesota, USA
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Coaguila-Llerena H, Raphael da Silva L, Faria G. Research methods assessing sodium hypochlorite cytotoxicity: A scoping review. Heliyon 2024; 10:e23060. [PMID: 38192787 PMCID: PMC10772573 DOI: 10.1016/j.heliyon.2023.e23060] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2023] [Revised: 10/26/2023] [Accepted: 11/24/2023] [Indexed: 01/10/2024] Open
Abstract
Sodium hypochlorite (NaOCl) cytotoxicity has been assessed using different methodologies, which has led to arbitrary interpretations. This scoping review aimed to discuss the different methodological protocols for assessing NaOCl cytotoxicity. A literature review performed in the PubMed and Embase databases up to July 2023 identified manuscripts reporting NaOCl cytotoxicity. The dataset identified 546 publications, further screened by 2 reviewers. Ninety studies were identified and mined methodologically to collect information on cell type, cytotoxicity assay, NaOCl dilution solutions, presence of fetal bovine serum (FBS), and NaOCl exposure time. The culture medium used in cytotoxicity assays contains buffering substances that neutralize the pH of NaOCl, thus reducing its cytotoxicity, an approach that may lead to bias when solutions with different pH are compared. For short exposure periods, as in simulations to evaluate the contact between irrigant and periapical tissue cells during chemo-mechanical preparation, NaOCl dilution should be performed with saline, which does not buffer the irrigant. For long exposure periods, as in simulations of irrigant extrusions, NaOCl should be diluted in the culture medium, to reproduce the expected buffering effect occurring in extrusions. The presence of FBS in culture medium can decrease NaOCl toxicity. There is no standardization of NaOCl cytotoxicity methodologies. This poses the risk of arriving at incorrect results and, therefore, pertinent tests must be refined.
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Affiliation(s)
- Hernán Coaguila-Llerena
- Department of Restorative Dentistry, Araraquara School of Dentistry, São Paulo State University -UNESP, Araraquara, São Paulo, Brazil
| | - Luana Raphael da Silva
- Department of Restorative Dentistry, Araraquara School of Dentistry, São Paulo State University -UNESP, Araraquara, São Paulo, Brazil
| | - Gisele Faria
- Department of Restorative Dentistry, Araraquara School of Dentistry, São Paulo State University -UNESP, Araraquara, São Paulo, Brazil
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Lazar V, Oprea E, Ditu LM. Resistance, Tolerance, Virulence and Bacterial Pathogen Fitness-Current State and Envisioned Solutions for the Near Future. Pathogens 2023; 12:pathogens12050746. [PMID: 37242416 DOI: 10.3390/pathogens12050746] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2023] [Revised: 05/16/2023] [Accepted: 05/19/2023] [Indexed: 05/28/2023] Open
Abstract
The current antibiotic crisis and the global phenomena of bacterial resistance, inherited and non-inherited, and tolerance-associated with biofilm formation-are prompting dire predictions of a post-antibiotic era in the near future. These predictions refer to increases in morbidity and mortality rates as a consequence of infections with multidrug-resistant or pandrug-resistant microbial strains. In this context, we aimed to highlight the current status of the antibiotic resistance phenomenon and the significance of bacterial virulence properties/fitness for human health and to review the main strategies alternative or complementary to antibiotic therapy, some of them being already clinically applied or in clinical trials, others only foreseen and in the research phase.
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Affiliation(s)
- Veronica Lazar
- Department of Botany and Microbiology, Faculty of Biology, University of Bucharest, 1-3 Portocalelor Street, 060101 Bucharest, Romania
| | - Eliza Oprea
- Department of Botany and Microbiology, Faculty of Biology, University of Bucharest, 1-3 Portocalelor Street, 060101 Bucharest, Romania
| | - Lia-Mara Ditu
- Department of Botany and Microbiology, Faculty of Biology, University of Bucharest, 1-3 Portocalelor Street, 060101 Bucharest, Romania
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Matoso FB, Montagner F, Jardine AP, Quintana RM, Grecca FS, Kopper PMP. Effect of different disinfection protocols in bacterial viability of an intraradicular biofilm formed in situ. Braz Dent J 2023; 34:42-49. [PMID: 37466524 PMCID: PMC10355264 DOI: 10.1590/0103-6440202305244] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2022] [Accepted: 04/18/2023] [Indexed: 07/20/2023] Open
Abstract
The present study aimed to evaluate bacterial viability after the use of different disinfection protocols in root canals infected with a multispecies biofilm (MB) formed in situ. Palatal roots with a single canal were obtained from extracted maxillary molars and sterilized before being inserted into the mouth. The roots were contaminated with a MB in an intraoral appliance worn by ten volunteers. All volunteers wore six roots simultaneously in two intraoral devices for 21 days. One root from each volunteer was assigned to each group (n=10): PUI - passive ultrasonic irrigation; EC - Easy Clean; XPF - XP-endo Finisher; aPDT - antimicrobial photodynamic therapy; CI - conventional irrigation; and NC - negative control. The samples were evaluated under confocal laser scanning microscopy. The percentage of viable cells (VC) was calculated over the total percentage of MB biovolume. Data were statistically analyzed (α=5%). The cell viability in the entire root canal or for each third was compared between groups (Kruskal-Wallis test, Dunn post-hoc test) and for the same group (Friedman test, Dunn post-hoc test). Disinfection protocols were not significantly different from each other (P>.05). Samples in EC, PUI, and aPDT had lower cell viability than in NC (P<.05). In the coronal third of samples in the EC, XPF, PUI and aPDT, the percentage of VC biovolume was lower than in the NC (P<.05). The percentage of VC in EC samples was lower in the coronal and middle thirds than in the apical third (P<.05). EC, PUI and aPDT had significant effects on cell viability in intraradicular multispecies biofilm formed in situ when compared with untreated samples.
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Affiliation(s)
- Felipe Barros Matoso
- Graduate Program in Dentistry, Federal University of Rio Grande
do Sul (UFRGS), Porto Alegre, RS, Brazil
| | - Francisco Montagner
- Graduate Program in Dentistry, Federal University of Rio Grande
do Sul (UFRGS), Porto Alegre, RS, Brazil
| | | | - Ramiro Martins Quintana
- Graduate Program in Dentistry, Federal University of Rio Grande
do Sul (UFRGS), Porto Alegre, RS, Brazil
| | - Fabiana Soares Grecca
- Graduate Program in Dentistry, Federal University of Rio Grande
do Sul (UFRGS), Porto Alegre, RS, Brazil
| | - Patricia Maria Poli Kopper
- Graduate Program in Dentistry, Federal University of Rio Grande
do Sul (UFRGS), Porto Alegre, RS, Brazil
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Dong X, Xu X. Bioceramics in Endodontics: Updates and Future Perspectives. Bioengineering (Basel) 2023; 10:bioengineering10030354. [PMID: 36978746 PMCID: PMC10045528 DOI: 10.3390/bioengineering10030354] [Citation(s) in RCA: 21] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 03/06/2023] [Accepted: 03/09/2023] [Indexed: 03/14/2023] Open
Abstract
Bioceramics, with excellent bioactivity and biocompatibility, have been widely used in dentistry, particularly in endodontics. Mineral trioxide aggregate (MTA) is the most widely used bioceramic in endodontics. Recently, many new bioceramics have been developed, showing good potential for the treatment of endodontic diseases. This paper reviews the characteristics of bioceramics and their applications in various clinical endodontic situations, including root-end filling, root canal therapy, vital pulp therapy, apexification/regenerative endodontic treatment, perforation repair, and root defect repair. Relevant literature published from 1993 to 2023 was searched by keywords in PubMed and Web of Science. Current evidence supports the predictable outcome of MTA in the treatment of endodontic diseases. Although novel bioceramics such as Biodentine, EndoSequence, and calcium-enriched mixtures have shown promising clinical outcomes, more well-controlled clinical trials are still needed to provide high-level evidence for their application in endodontics. In addition, to better tackle the clinical challenges in endodontics, efforts are needed to improve the bioactivity of bioceramics, particularly to enhance their antimicrobial activity and mechanical properties and reduce their setting time and solubility.
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Affiliation(s)
- Xu Dong
- State Key Laboratory of Oral Diseases and National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China;
- Department of Cariology and Endodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
| | - Xin Xu
- State Key Laboratory of Oral Diseases and National Clinical Research Center for Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China;
- Department of Cariology and Endodontics, West China Hospital of Stomatology, Sichuan University, Chengdu 610041, China
- Correspondence: ; Tel.: +86-028-85503494
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