The effect of ultrasonic and multisonic irrigation on root canal microbial communities: An ex vivo study

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.

Antimicrobial activity, surface properties, and cytotoxicity of microencapsulated phytochemicals incorporated into three-dimensionally printable dental polymers

OBJECTIVES

This study aimed to investigate the antimicrobial properties of three dimensionally-printed dental polymers (3DPs) incorporated with microencapsulated phytochemicals (MPs) and to assess their surface characteristics and cytotoxicity.

METHODS

MPs derived from phytoncide oil and their specific chemical components were introduced into suspensions of three microbial species: Streptococcus gordonii, Streptococcus oralis, and Candida albicans. Optical density was measured to determine the microbial growth in the presence of MPs for testing their antimicrobial activity. MPs at 5% (w/w) were mixed with dental polymers and dispersants to 3DP discs. These microbial species were then seeded onto the discs and incubated for 24 h. The antibacterial and antifungal activities of MP-containing 3DPs were evaluated by counting the colony-forming units (n = 3). The biofilm formation on the 3DP was assessed by crystal violet staining assay (n = 3). Microbial viability was determined using a live-dead staining and CLSM observation (n = 3). Surface roughness and water contact angle were assessed (n = 10). Cytotoxicity of MP-containing 3DPs for human gingival fibroblast was evaluated by MTT assay.

RESULTS

MPs, particularly (-)-α-pinene, suppressed the growth of all tested microbial species. MP-containing 3DPs significantly reduced the colony count (P ≤ 0.001) and biofilm formation (P ≤ 0.009), of all tested microbial species. Both surface roughness (P < 0.001) and water contact angle (P < 0.001) increased. The cytotoxicity remained unchanged after incorporating MPs to the 3DPs (P = 0.310).

CONCLUSIONS

MPs effectively controlled the microbial growth on 3DPs as evidenced by the colony count, biofilm formation, and cell viability. Although MPs modified the surface characteristics, they did not influence the cytotoxicity of 3DPs.

CLINICAL SIGNIFICANCE

Integration of MPs into 3DPs could produce dental prostheses or appliances with antimicrobial properties. This approach not only provides a proactive solution to reduce the risk of oral biofilm-related infection but also ensures the safety and biocompatibility of the material, thereby improving dental care.

Optimizing the use of low-frequency ultrasound for bacterial detachment of in vivo biofilms in dental research-a methodological study

OBJECTIVES

Low-frequency, low-intensity ultrasound is commonly utilized in various dental research fields to remove biofilms from surfaces, but no clear recommendation exists in dental studies so far. Therefore, this study aims to optimize the sonication procedure for the dental field to efficiently detach bacteria while preserving viability.

MATERIALS AND METHODS

Initial biofilm was formed in vivo on bovine enamel slabs (n = 6) which were worn by four healthy participants for 4 h and 24 h. The enamel slabs covered with biofilm were then ultrasonicated ex vivo for various time periods (0, 1, 2, 4, 6 min). Colony-forming units were determined for quantification, and bacteria were identified using MALDI-TOF. Scanning electron microscopic images were taken to also examine the efficiency of ultrasonications for different time periods.

RESULTS

Ultrasonication for 1 min resulted in the highest bacterial counts, with at least 4.5-fold number compared to the non-sonicated control (p < 0.05). Most bacteria were detached within the first 2 min of sonication, but there were still bacteria detached afterwards, although significantly fewer (p < 0.0001). The highest bacterial diversity was observed after 1 and 2 min of sonication (p < 0.03). Longer sonication periods negatively affected bacterial counts of anaerobes, Gram-negative bacteria, and bacilli. Scanning electron microscopic images demonstrated the ability of ultrasound to desorb microorganisms, as well as revealing cell damage and remaining bacteria.

CONCLUSIONS

With the use of low-frequency, low-intensity ultrasound, significantly higher bacterial counts and diversity can be reached. A shorter sonication time of 1 min shows the best results overall.

CLINICAL RELEVANCE

This standardization is recommended to study initial oral biofilms aged up to 24 h to maximize the outcome of experiments and lead to better comparability of studies.

Influence of Contemporary Photoactivated Disinfection on the Mechanical Properties and Antimicrobial Activity of PMMA Denture Base: A Systematic Review and Meta Analysis

PURPOSE

The present study aimed to perform a systematic review and meta-analysis to investigate the effectiveness of the contemporary photoactivated disinfection methods on the mechanical features and/or antimicrobial activity of polymethyl methacrylate (PMMA) dentures bases.

METHODS

THE FOCUSED RESEARCH QUESTION WAS: : "What is the effect of contemporary photoactivated disinfection methods as compared to conventional disinfection protocols on the mechanical features and/or antimicrobial activity of PMMA dentures bases?". An electronic literature search was carried out by the author and a senior librarian specialized in health sciences on Web of Science, PubMed, and Scopus. In vitro investigations evaluating the antimicrobial and/or mechanical effects of photoactivated disinfectants as compared to conventional chemical disinfectants on the microbes formed on PMMA denture bases were included. Meta-analysis was performed for calculating the standard mean difference (SMD) with a 95% confidence interval.

RESULTS

Four out of eight studies concluded that photoactivated disinfectants, including riboflavin-mediated photodynamic therapy (PDT), hematoporphyrin-mediated PDT, poly-L-glycolic acid loaded with methylene blue, Erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) laser, erbium-doped yttrium-aluminum-garnet (Er:YAG) laser, and chitosan-mediated PDT, demonstrated a significant reduction in colony-forming unit per milliliter (CFU/mL) of exposed viable colonies of Escherichia coli (E. coli), Streptococcus mutans (S. mutans), Staphylococcus aureus (S. aureus), and Candida albicans (C. albicans) comparable to the conventionally used chemical disinfectants of PMMA denture bases. Contrarily, two studies concluded that the PMMA denture base colonized with C. albicans and disinfected with conventional chemical disinfectants showed the greatest anti-fungal efficaciousness. All the included studies concluded that the application of photoactivated disinfectants does not negatively impact the mechanical features of the PMMA denture bases colonized with microbes including E. coli, S. mutans, S. aureus, and C. albicans. The meta-analysis revealed statistically significant reduction in C. albicans counts (CFU/mL [Log10]) (p < 0.00001) and improvement in the flexural strength (p = 0.0002) of PMMA-based denture base after the application of conventional disinfectants, while a statistically significant improvement in the fracture strength of PMMA-based denture base was observed after the application of photoactivated disinfectants (p = 0.03).

CONCLUSION

According to the systematic review (qualitative synthesis), photoactivated disinfectants demonstrated comparable mechanical features and antimicrobial activity of PMMA dentures bases to conventional chemical disinfectants suggesting their potential to be utilized as an alternative to conventional chemical disinfectants. However, the meta-analysis (quantitative synthesis) revealed that the application of conventional disinfectants demonstrated better outcomes related to antimicrobial activity and flexural strength of PMMA-based denture based.

A critical analysis of research methods and experimental models to study irrigants and irrigation systems

Irrigation plays an essential role in root canal treatment. The purpose of this narrative review was to critically appraise the experimental methods and models used to study irrigants and irrigation systems and to provide directions for future research. Studies on the antimicrobial effect of irrigants should use mature multispecies biofilms grown on dentine or inside root canals and should combine at least two complementary evaluation methods. Dissolution of pulp tissue remnants should be examined in the presence of dentine and, preferably, inside human root canals. Micro-computed tomography is currently the method of choice for the assessment of accumulated dentine debris and their removal. A combination of experiments in transparent root canals and numerical modeling is needed to address irrigant penetration. Finally, models to evaluate irrigant extrusion through the apical foramen should simulate the periapical tissues and provide quantitative data on the amount of extruded irrigant. Mimicking the in vivo conditions as close as possible and standardization of the specimens and experimental protocols are universal requirements irrespective of the surrogate endpoint studied. Obsolete and unrealistic models must be abandoned in favour of more appropriate and valid ones that have more direct application and translation to clinical Endodontics.

Present status and future directions - irrigants and irrigation methods

Irrigation is considered the primary means of cleaning and disinfection of the root canal system. The purpose of this review was to set the framework for the obstacles that irrigation needs to overcome, to critically appraise currently used irrigants and irrigation methods, to highlight knowledge gaps and methodological limitations in the available studies and to provide directions for future developments. Organization of bacteria in biofilms located in anatomic intricacies of the root canal system and the difficulty to eliminate them is the main challenge for irrigants. Sodium hypochlorite remains the primary irrigant of choice, but it needs to be supplemented by a chelator. Delivery of the irrigants using a syringe and needle and activation by an ultrasonic file are the most popular irrigation methods. There is no evidence that any adjunct irrigation method, including ultrasonic activation, can improve the long‐term outcome of root canal treatment beyond what can be achieved by instrumentation and syringe irrigation. It is necessary to redefine the research priorities in this field and investigate in greater depth the penetration of the irrigants, their effect on the biofilm and the long‐term treatment outcome. New studies must also focus on clinically relevant comparisons, avoid methodological flaws and have sufficiently large sample sizes to reach reliable conclusions. Future multidisciplinary efforts combining the knowledge from basic sciences such as Chemistry, Microbiology and Fluid Dynamics may lead to more effective antimicrobials and improved activation methods to bring them closer to the residual biofilm in the root canal system.

Mechanical and antimicrobial effects of riboflavin-mediated photosensitization of in vitro C. albicans formed on polymethyl methacrylate resin

PURPOSE

This study assessed the potential of riboflavin-mediated photodynamic therapy (RF-PDT) against Candida albicans (C. albicans) and compared the effects of RF-PDT with other therapeutic modalities in terms of mechanical and surface characteristics of acrylic denture base material.

MATERIALS AND METHODS

Molds (10 × 10 × 2 mm) of acrylic resin specimens were prepared and underwent artificial ageing. C. albicans were grown aerobically over the specimens and divided into four groups (n = 10/group); Group-I: no decontamination; Group-II: nystatin suspension; Group-III: riboflavin 0.1% in darkness, Group-IV: blue LED light only, and Group-V: riboflavin 0.1% for 10 minutes (pre-irradiation time) and photoactivated by the blue LED light (light dose). Fungal viability was assessed using MTT assay and characterized using scanning electron microscopy and confocal laser microscopy (CLSM). Treated specimens were subjected to surface roughness (R_a), flexural strength (FS), and flexural modulus (FM).

RESULTS

Group-I showed the highest C. albicans viability followed by Group-III. Nystatin group (Group-II) showed ∼50% of the viability while RF-PDT showed the least C. albicans viability among the four groups (p<0.05). On SEM, specimens treated with Group-IV and V showed almost clear and free from C. albicans that was evidenced on CLSM. Post-treated specimens and storage after 72 h revealed that FS was significantly higher for RF-PDT group as compared to any other group (>105.82 MPa) (p<0.05). The FM and Ra showed statistically no significant difference between the groups (p>0.05).

CONCLUSION

RF-PDT showed the highest anti-fungal capacity against C. albicans over acrylic denture surface without any surface deterioration.

Incorporation of antimicrobial agents in denture base resin: A systematic review

STATEMENT OF PROBLEM

Denture base resins (DBRs), such as polymethyl methacrylate, are commonly used in the fabrication of removable dentures because of their physical, mechanical, and esthetic properties. However, the denture base acts as a substrate for microorganism adherence and biofilm formation, which may lead to denture stomatitis and be further complicated by fungal infections, of especial importance with geriatric and immunosuppressed patients. Therefore, methods to enhance the antimicrobial property of DBRs will be beneficial.

PURPOSE

The purpose of this systematic review was to evaluate the literature on the antimicrobial activity of DBRs incorporating antimicrobial agents or materials.

MATERIAL AND METHODS

A search of English peer-reviewed literature up to February 2019 reporting on antimicrobial activity of DBRs with respect to antimicrobial agents or materials, antimicrobial test effects and methods, and conclusion or knowledge gaps was conducted by using Embase, Google Scholar, PubMed, and Web of Science databases. Search terms included denture base resin and antibacterial, denture base resin and antifungal, and denture base resin and antimicrobial. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were applied for subsequent data analysis.

RESULTS

Of 2536 identified articles, 28 met the inclusion criteria for the systematic review. Antimicrobial materials were divided into 3 groups: antimicrobial monomer or copolymer, phytochemical or phytomedical components, and other compounds. Strategies on how to incorporate these substances into DBRs and their impact on the reduction and prevention of the growth of microorganisms were identified.

CONCLUSIONS

Although many efforts have been made to improve the antimicrobial ability of DBRs, this systematic review found that the effectiveness of incorporating of antimicrobial agents into DBRs has not been demonstrated conclusively.

Ultrasonic Irrigant Activation during Root Canal Treatment: A Systematic Review

INTRODUCTION

The aim of this study was to systematically review the evidence on the cleaning and disinfection of root canals and the healing of apical periodontitis when ultrasonic irrigant activation is applied during primary root canal treatment of mature permanent teeth compared with syringe irrigation.

METHODS

An electronic search was conducted of the Cochrane Library, Embase, LILACS, PubMed, SciELO, and Scopus databases using both free-text key words and controlled vocabulary. Additional studies were sought through hand searching of endodontic journals and textbooks. The retrieved studies were screened by 2 reviewers according to predefined criteria. The included studies were critically appraised, and the extracted data were arranged in tables.

RESULTS

The electronic and hand search retrieved 1966 titles. Three clinical studies and 45 in vitro studies were included in this review. Ultrasonic activation did not improve the healing rate of apical periodontitis compared with syringe irrigation after primary root canal treatment of teeth with a single root canal. Conflicting results were reported by the in vitro microbiological studies. Ultrasonic activation was more effective than syringe irrigation in the removal of pulp tissue remnants and hard tissue debris based on both clinical and in vitro studies. Ultrasonic activation groups were possibly favored in 13 studies, whereas syringe irrigation groups may have been favored in 3 studies.

CONCLUSIONS

The level of the available evidence was low, so no strong clinical recommendations could be formulated. Future studies should focus on the antimicrobial effect and healing of apical periodontitis in teeth with multiple root canals.

Historical and Contemporary Perspectives on the Microbiological Aspects of Endodontics

The microbiota of the oral cavity plays a significant role in pulpal and periapical diseases. Historically, 100 years ago little was known on microbiota, but after a century of investigations, only now can many of the intimate secrets of microbial growth, expansion, persistence, communal activities, and virulence be revealed. However, with the capabilities of the microbiota for mutation, quorum sensing, and information transference, researchers are hard-pressed to keep up with both the changes and challenges that an amazingly wide range of bacterial species pose for both the scientist and clinician. Fortunately, the development and expansion of a vast array of molecular biological investigative techniques have enabled dentistry and its associated medical fields to attempt to keep pace with the wide and fascinating world of oral microbiology.

Apical negative pressure irrigation versus syringe irrigation: a systematic review of cleaning and disinfection of the root canal system

The aim of this study was to systematically review and critically analyse the published data on the treatment outcome (primary outcome) and on the cleaning and disinfection of root canals (secondary outcomes) achieved by negative pressure irrigation as compared to syringe irrigation. An electronic search was conducted in EMBASE, LILACS, PubMed, SciELO, Scopus and Web of Knowledge using both free-text keywords and controlled vocabulary. Additional studies were sought through hand searching of endodontic journals and of the relevant chapters of endodontic textbooks. No language restriction was imposed. The retrieved studies were screened by two reviewers according to predefined criteria. Included studies were critically appraised and the extracted data were arranged in tables. The electronic search and hand search retrieved 489 titles. One clinical study and 14 in vitro studies were finally included in the review; none of these studies assessed treatment outcome, four studies assessed the antimicrobial effect, seven studies evaluated the removal of pulp tissue remnants, and four studies investigated the removal of hard tissue debris or both hard tissue debris and pulp tissue remnants. Poor standardization and description of the protocols was evident. Inconclusive results were reported about the cleaning and disinfection accomplished by the two irrigation methods. Negative pressure irrigation was more effective under certain conditions when compared to suboptimal syringe irrigation; however, the variability of the protocols hindered quantitative synthesis. There is insufficient evidence to claim general superiority of any one of these methods. The level of the available evidence is low, and the conclusions should be interpreted with caution.