Clinical Investigation of the Inhibitory Effects of Tooth-Coating Materials on Initial Active Root Caries: A Pilot Randomized Controlled Trial.

Background and Objectives: Caredyne ZIF-C is a novel, capsule-mixed zinc-containing prototype glass ionomer cement (GIC). Zinc ions are reported to inhibit root dentin demineralization, dentin collagen degradation, bacterial growth, acid production, and in vitro bacterial biofilm formation. However, the effectiveness of GICs against initial root caries lesions is unclear. Therefore, this study aimed to evaluate the efficacy of GICs, especially the new zinc-containing Caredyne ZIF-C GIC, as tooth-coating materials in patients with initial active root caries. Materials and Methods: A total of 58 lesions in 47 older adults (age > 65 years) were randomly allocated to one of the following three groups: Caredyne ZIF-C, Fuji VII (a conventional GIC), and sodium fluoride (NaF). All the lesions were treated with the assigned materials without removing the infected dentin, and the rates of dental plaque attachment and coating material fall-out were evaluated after 3, 6, and 12 months. The failure rate was defined as the number of teeth that needed restoration due to caries progression. Results: The plaque attachment rates tended to be lower in the material-coated root surfaces than in the healthy exposed root surfaces after 3, 6, and 12 months, although the differences among the three groups were not significant. Moreover, the coating material fall-out rate tended to be lower in the Caredyne ZIF-C group than in the Fuji VII group. There was no significant difference in the failure rate among the three groups at the 12 months mark. Conclusions: Though this pilot study offers a new direction for suppressing the progression of initial active root caries by controlling plaque attachment using GICs including Caredyne ZIF-C, clinical studies with a larger sample size are needed.

Mechanical behavior of endodontically treated teeth: A three-dimensional finite element analysis using displacement vector.

PURPOSE: This study aimed to analyze the effects of core materials, remaining tooth structures, and interfacial bonding on stress distribution in endodontically treated teeth using finite element analysis (FEA). MATERIALS AND METHODS: Three-dimensional FEA was conducted using a reverse engineering technique based on maxillary premolars scanned by micro-computed tomography. Six models were generated with or without ferrules and with one of the following three abutment systems: metal core, resin core, or resin core with fiber posts. In each model, bonding and debonding were assumed in the dentin and surrounding structures: bonded and debonded models. The maximum principal stress values were recorded, and stress distribution of the entire restored teeth and dentin was generated. Furthermore, the distribution of the displacement vector of the debonded models was generated. RESULTS: In comparing the bonded and debonded models, the debonded models showed larger values for tensile stresses than those in bonded models for all abutment models. The models without ferrules rotated around the center of the abutment, whereas those with ferrules did not show remarkable displacement in the analysis. CONCLUSION: FEA assuming fracture of adhesive interface proved to be an effective method to clarify the significance of ferrules. It prevents stress concentration in dentin by reducing the rotation of the abutment, even when the adhesive fails.

Streptococcus gordonii programs epithelial cells to resist ZEB2 induction by Porphyromonas gingivalis.

The polymicrobial microbiome of the oral cavity is a direct precursor of periodontal diseases, and changes in microhabitat or shifts in microbial composition may also be linked to oral squamous cell carcinoma. Dysbiotic oral epithelial responses provoked by individual organisms, and which underlie these diseases, are widely studied. However, organisms may influence community partner species through manipulation of epithelial cell responses, an aspect of the host microbiome interaction that is poorly understood. We report here that Porphyromonas gingivalis, a keystone periodontal pathogen, can up-regulate expression of ZEB2, a transcription factor which controls epithelial-mesenchymal transition and inflammatory responses. ZEB2 regulation by P. gingivalis was mediated through pathways involving ß-catenin and FOXO1. Among the community partners of P. gingivalis, Streptococcus gordonii was capable of antagonizing ZEB2 expression. Mechanistically, S. gordonii suppressed FOXO1 by activating the TAK1-NLK negative regulatory pathway, even in the presence of P. gingivalis Collectively, these results establish S. gordonii as homeostatic commensal, capable of mitigating the activity of a more pathogenic organism through modulation of host signaling.

Intracellular density is a novel indicator of differentiation stages of murine osteoblast lineage cells.

Osteoblasts are primary bone-making cells originating from mesenchymal stem cells (MSCs) in the bone marrow. The differentiation of MSCs to mature osteoblasts involves an intermediate stage called preosteoblasts, but the details of this process remain unclear. This study focused on the intracellular density of immature osteoblast lineage cells and hypothesized that the density might vary during differentiation and might be associated with the differentiation stages of osteoblast lineage cells. This study aimed to clarify the relationship between intracellular density and differentiation stages using density gradient centrifugation. Primary murine bone marrow stromal cell cultures were prepared in an osteogenic induction medium, and cells were separated into three fractions (low, intermediate, and high-density). The high-density fraction showed elevated expression of osteoblast differentiation markers (Sp7, Col1a1, Spp1, and Bglap) and low expression of MSC surface markers (Sca-1, CD73, CD105, and CD106). In contrast, the low-density fraction showed a high expression of MSC surface markers. These results indicated that intracellular density increased during differentiation from preosteoblasts to committed osteoblasts. Intracellular density may be a novel indicator for osteoblast differentiation stages. Density gradient centrifugation is a novel technique to study the process by which preosteoblasts transform into bone-forming cells.

Application of a direct pulp capping cement containing S-PRG filler.

OBJECTIVES: To evaluate new pulp capping cements containing surface pre-reacted glass ionomer (S-PRG) filler and to investigate ion release kinetics and pH shift of eluates from the cement. MATERIALS AND METHODS: Molars of Wistar rats were directly pulp capped using three kinds of cement containing S-PRG filler and mineral tri-oxide aggregate (MTA) was used as a control. After 1, 2, or 4 weeks, histological evaluation was performed and differences of tertiary dentin formation were analyzed. Release of Sr2+, BO33-, SiO32-, Na+, and Al3+ ions was determined by inductively coupled plasma-atomic emission spectrometry, and F- ion release was measured using a fluoride ion selective electrode. The pH of the eluate from each cement after mixing was measured with a pH electrode. RESULTS: One of S-PRG cements promoted tertiary dentin formation to the same extent as the control (p > 0.05) and it showed a tendency of less inflammatory response. This cement released more BO33- and SiO32-, but less Sr2+, Na+, and F- than other S-PRG specimens. Each cement recovered nearly neutral compared with glass ionomer cement. CONCLUSIONS: S-PRG cement induced tertiary dentin formation based on multiple ion releases, suggesting that it is suitable as a pulp capping material. CLINICAL RELEVANCE: This new material can be an alternative pulp capping agent to MTA.

HipOP mesenchymal population has high potential for repairing injured peripheral nerves.

Bone marrow stromal cells (BMSCs) are reportedly a heterogeneous population of mesenchymal stem cells (MSCs). Recently, we developed a simple strategy for the enrichment of MSCs with the capacity to differentiate into osteoblasts, chondrocytes, and adipocytes. On transplantation, the progenitor-enriched fractions can regenerate the bone with multiple lineages of donor origin and are thus called "highly purified osteoprogenitors" (HipOPs). Although our previous studies have demonstrated that HipOPs are enriched with MSCs and exhibit a higher potential to differentiate into osteoblasts, adipocytes, and chondrocytes than BMSCs, their potential to differentiate into neural cells has not been clarified. In this study, we evaluated the efficacy of HipOPs as a resource of neural stem cells. The neurosphere assay showed that neurospheres formed by HipOPs exhibited self-renewal ability and their size was generally larger than that of neurospheres formed by BMSCs. A limiting dilution assay was used to evaluate the frequency of neural progenitors in BMSCs and HipOPs. The results demonstrated that the frequency of neural progenitors in HipOPs was 120-fold higher than that in BMSCs. Furthermore, to investigate the in vivo regenerative potential of the peripheral nerve, we modified a murine peripheral nerve injury experimental model and demonstrated that HipOPs exhibit a higher efficacy in repairing injured peripheral nerves. These findings suggest that HipOPs are a useful cell resource for regenerative therapies such as that in case of peripheral nerve injury.

RabGDIα is a negative regulator of interferon-γ-inducible GTPase-dependent cell-autonomous immunity to Toxoplasma gondii.

IFN-γ orchestrates cell-autonomous host defense against various intracellular vacuolar pathogens. IFN-γ-inducible GTPases, such as p47 immunity-related GTPases (IRGs) and p65 guanylate-binding proteins (GBPs), are recruited to pathogen-containing vacuoles, which is important for disruption of the vacuoles, culminating in the cell-autonomous clearance. Although the positive regulation for the proper recruitment of IRGs and GBPs to the vacuoles has been elucidated, the suppressive mechanism is unclear. Here, we show that Rab GDP dissociation inhibitor α (RabGDIα), originally identified as a Rab small GTPase inhibitor, is a negative regulator of IFN-γ-inducible GTPases in cell-autonomous immunity to the intracellular pathogen Toxoplasma gondii. Overexpression of RabGDIα, but not of RabGDIß, impaired IFN-γ-dependent reduction of T. gondii numbers. Conversely, RabGDIα deletion in macrophages and fibroblasts enhanced the IFN-γ-induced clearance of T. gondii. Furthermore, upon a high dose of infection by T. gondii, RabGDIα-deficient mice exhibited a decreased parasite burden in the brain and increased resistance in the chronic phase than did control mice. Among members of IRGs and GBPs important for the parasite clearance, Irga6 and Gbp2 alone were more frequently recruited to T. gondii-forming parasitophorous vacuoles in RabGDIα-deficient cells. Notably, Gbp2 positively controlled Irga6 recruitment that was inhibited by direct and specific interactions of RabGDIα with Gbp2 through the lipid-binding pocket. Taken together, our results suggest that RabGDIα inhibits host defense against T. gondii by negatively regulating the Gbp2-Irga6 axis of IFN-γ-dependent cell-autonomous immunity.

Novel evaluation method of dentin repair by direct pulp capping using high-resolution micro-computed tomography.

OBJECTIVES: We evaluated a novel micro-computed tomography (micro-CT) assessment for quality and quantity of dentin repair, which is difficult to visualize by histological analysis, after direct pulp capping under standardized cavity preparation. MATERIALS AND METHODS: Standardized cavities were prepared on Wistar rats and direct pulp capping was performed using two commercial bioceramics, ProRoot MTA, and iRoot BP Plus. After 2 or 4 weeks, quality and quantity of tertiary dentin formation were evaluated using high-resolution micro-CT analyses including dentin mineral density, dentin mineral contents, compactness and integrity of tertiary dentin, and dentin volume with/without void space. Reproducibility of micro-CT analyses was confirmed by histological evaluation of the same specimen. RESULTS: The exposed pulp area sizes were similar between iRoot BP Plus and ProRoot MTA. Micro-CT analysis of 2-week samples showing compactness of tertiary dentin was significantly higher in iRoot BP Plus than ProRoot MTA (p < 0.05). Tertiary dentin volume without void space, dentin mineral contents, and density were not significantly different between the groups. In 4-week samples, a significant increase was observed in dentin mineral density, compactness, and dentin volume with/without void space induced by iRoot BP Plus (p < 0.05). Micro-CT analysis of tertiary dentin integrity demonstrated that some ProRoot MTA specimens had small defects and lacked continuity (6/512 images). No defects were observed with iRoot BP Plus. CONCLUSIONS: Micro-CT analysis was confirmed as an accurate, objective, and inclusive approach for evaluating quality and quantity of dentin repair. CLINICAL RELEVANCE: These multifaceted approaches to evaluate pulp capping materials may accelerate review processes, ultimately improving vital pulp therapy.

Factors that cause endodontic failures in general practices in Japan.

BACKGROUND: Bacterial biofilms that develop on root surfaces outside apical foramens have been found to be associated with refractory periapical periodontitis. However, several other factors cause endodontic failures apart from extraradicular biofilms. The aim of this study was to identify the factors causing endodontic failures in general practices in Japan. METHODS: Patients diagnosed as having refractory periapical periodontitis by general practitioners and who requested endodontic treatment at Osaka University Dental Hospital were selected by checking medical records from April 2009 to March 2013. Factors causing endodontic failures were identified. RESULTS: A total of 103 teeth were selected, and 76 teeth completed root-canal treatment. Tooth extractions were required for 18 teeth after or without endodontic treatment. Six teeth required apicoectomy after endodontic treatment. One tooth needed hemisection. One tooth needed intentional replantation. One tooth needed adhesion and replantation. The main causes of treatment failure were open apices (24 teeth), perforation (18 teeth), and root fracture (13 teeth). In six teeth with open apices that required apicoectomy or extraction, extraradicular biofilms may have been related to endodontic failure. CONCLUSIONS: Most endodontic cases diagnosed with refractory periapical periodontitis by general practitioners were compromised by any other factors rather than extraradicular biofilms.

Role of mouse and human autophagy proteins in IFN-γ-induced cell-autonomous responses against Toxoplasma gondii.

IFN-γ mediates cellular innate immunity against an intracellular parasite, Toxoplasma gondii, by inducing immunity-related GTPases such as p47 IFN-γ-regulated GTPases (IRGs) and p65 guanylate-binding proteins (GBPs), which also participate in antibacterial responses via autophagy. An essential autophagy protein, Atg5, was previously shown to play a critical role in anti-T. gondii cell-autonomous immunity. However, the involvement of other autophagy proteins remains unknown. In this study, we show that essential autophagy proteins differentially participate in anti-T. gondii cellular immunity by recruiting IFN-γ-inducible GTPases. IFN-γ-induced suppression of T. gondii proliferation and recruitment of an IRG Irgb6 and GBPs are profoundly impaired in Atg7- or Atg16L1-deficient cells. In contrast, cells lacking other essential autophagy proteins, Atg9a and Atg14, are capable of mediating the anti-T. gondii response and recruiting Irgb6 and GBPs to the parasites. Although IFN-γ also stimulates anti-T. gondii cellular immunity in humans, whether this response requires GBPs and human autophagy proteins remains to be seen. To analyze the role of human ATG16L1 and GBPs in IFN-γ-mediated anti-T. gondii responses, human cells lacking ATG16L1 or GBPs were generated by the Cas9/CRISPR genome-editing technique. Although both ATG16L1 and GBPs are dispensable for IFN-γ-induced inhibition of T. gondii proliferation in the human cells, human ATG16L1 is also required for the recruitment of GBPs. Taken together, human ATG16L1 and mouse autophagy components Atg7 and Atg16L1, but not Atg9a and Atg14, participate in the IFN-γ-induced recruitment of the immunity-related GTPases to the intracellular pathogen.

Density Gradient Centrifugation for the Isolation of Cells of Multiple Lineages.

We recently developed a simple strategy for the enrichment of mesenchymal stem cells (MSCs) with the capacity for osteoblast, chondrocyte, and adipocyte differentiation. On transplantation, the progenitor-enriched fraction can regenerate bone with multiple lineages of donor origin. Although comprising multiple precursor cell types, the population is enriched >100-fold in osteoprogenitors, hence the name "highly purified osteoprogenitors" (HipOPs). To establish a new modified method of purifying pure MSCs, it is useful to know the expression patterns of surface markers on heterogeneous MSCs and committed cells such as osteoblasts, adipocytes, and chondrocytes. However, calcium deposition by osteoblasts is a critical obstacle in visualizing the expression patterns of surface markers. We now report a new method of separating differentiated osteoblastic HipOPs (OB-HipOPs) from calcium deposits using the Percoll density gradient centrifugation technique. After centrifuge separation, calcium deposits were observed at the bottom of the centrifuge tube, and living OB-HipOPs were harvested from the 10-70% fractions. However, there were no living cells in the 70-80% fraction. We concluded that living OB-HipOPs are separated by one 10-70% Percoll gradient. Furthermore, we analyzed the expression patterns of putative MSC markers on differentiated HipOPs. FACS analysis revealed that Sca-1, CD44, CD73, CD105, and CD106 were decreased in OB-HipOPs. In adipogenic- and chondrogenic-HipOPs, Sca-1, CD73, CD105, and CD106 were decreased. This new technique is a helpful tool to identify MSC surface markers and to clarify in more detail the differentiation stages of osteoblasts.

Inhibition of polysaccharide synthesis by the sinR orthologue PGN_0088 is indirectly associated with the penetration of Porphyromonas gingivalis biofilms by macrolide antibiotics.

Microbes commonly adhere to surfaces, aggregate in self-produced extracellular polymeric substances (EPS) and live in biofilms. Periodontitis is a serious oral infection that is initiated by the formation of biofilms by Porphyromonas gingivalis. EPS act as a barrier that protects biofilm-forming cells against sources of stress, including those induced by host immune cells and antimicrobial agents. Therefore, drugs intended to kill such micro-organisms cannot be used for the treatment of biofilm infections. Our previous studies revealed that subminimal inhibitory concentrations (subMIC) of two macrolide antibiotics (azithromycin, AZM and erythromycin, ERY) reduced P. gingivalis biofilms. Furthermore, we demonstrated that the Bacillus subtilis sinR orthologue (PGN_0088) inhibits the synthesis of carbohydrates that are components of EPS in P. gingivalis biofilms. Here, we constructed a novel sinR mutant from P. gingivalis ATCC 33277 and reveal that the increased abundance of carbohydrate in EPS of the mutant led to a reduced infiltration rate of AZM and ERY through EPS, and consequently elevated biofilm resistance to these macrolides. Detailed elucidation of the interaction between the product of the sinR gene and EPS will assist in the development of novel approaches that target EPS to prevent and inhibit the formation of biofilms.

LIF/STAT3/SOCS3 signaling pathway in murine bone marrow stromal cells suppresses osteoblast differentiation.

Leukemia inhibitory factor (LIF) is a pleiotropic cytokine that belongs to the interleukin-6 family and is expressed by multiple tissue types. This study analyzed the effect of LIF on osteoblast differentiation using primary murine bone marrow stromal cells (BMSCs). Colony-forming unit-osteoblast formation by BMSCs was significantly suppressed by LIF treatment. To clarify the mechanism underlying the LIF suppressive effect on osteoblast differentiation, we analyzed the downstream signaling pathway of LIF. LIF/signal transducer and activator of transcription 3 (STAT3) signaling induces the expression of suppressor of cytokine signaling 3 (SOCS3). SOCS3 knockdown experiments have previously demonstrated that short-hairpin SOCS3-BMSCs reversed the LIF suppressive effect. Our results demonstrated that LIF suppresses osteoblast differentiation through the LIF/STAT3/SOCS3 signaling pathway.

Promotion of endodontic lesions in rats by a novel extraradicular biofilm model using obturation materials.

Although extraradicular biofilm formation is related to refractory periapical periodontitis, the mechanism of extraradicular biofilm development, as well as its effect on periapical lesions, is unknown. Therefore, we aimed to develop an in vivo extraradicular biofilm model in rats and to identify and quantify extraradicular biofilm-forming bacteria while investigating the effect of extraradicular biofilms on periapical lesions. Periapical lesions were induced by exposing the pulpal tissue of the mandibular first molars of male Wistar rats to their oral environment. Four weeks later, gutta-percha points were excessively inserted into the mesial root canals of the right first molars (experimental sites) but not the left first molars (control sites). After 6 and 8 weeks of pulp exposure, the presence of extraradicular biofilms was confirmed histomorphologically, and biofilm-forming bacteria were identified by using classical culture methods. The biofilms were observed in the extraradicular area of the experimental sites. Similar species were detected both inside and outside the root canals. The bacterial count, quantified by real-time PCR assays, in the extraradicular area gradually increased in the experimental sites until 20 weeks after pulp exposure. After 8 weeks of pulp exposure, the periapical lesion volume that was measured by micro-computed tomography was significantly larger in the experimental sites than in the control sites (P < 0.05 by Welch's t test). These results suggest that we developed an extraradicular biofilm model in rats and that extraradicular biofilms affect developing periapical lesions.

Dentistry in the 21st century: challenges of a globalising world.

Oral health is - literally - vital to good general health, not least because the mouth is the sentinel of the body. Dentistry, the Cinderella of health care, faces immense challenges of globalisation. Governments, having spent freely on everything from defence to social security, face mountains of debts which make budget cutbacks essential. Simultaneously, most developed countries have to pay increasing costs of caring for rapidly ageing populations. Dentistry is being pulled two ways: wealthy members of society demand high-end expensive treatment, much of it cosmetic rather than necessary to deal with disease, whereas many millions of poor people in developing countries cannot afford basic dental treatment and may never see a dentist. Too many governments and dentists persist with the expensive and destructive regime of 'drill and fill (and bill)'. International advances in care may not reach the clinician's chair because treatment guidelines and payments are set locally. An international symposium to celebrate Mikako Hayashi becoming Professor of Restorative Dentistry and Endodontology at Osaka University concluded that dentistry should move from an increasingly un-affordable curative model to a cost-effective evidence-based preventive model. The goal is to help people retain healthy natural teeth throughout their lives, as an essential part of enhancing their general health.

Effect of age-related extended high frequency hearing loss on the subjective impressions of dental drill noise.

Fear and anxiety among patients are sometimes evoked in dental clinics due to the sound of dental drills. This study aimed to explore the impact of age-related hearing loss in the extended high frequency (EHF) range above 8 kHz on individuals' subjective discomfort towards dental drill noise. After measuring pure-tone audiometric thresholds at both conventional and extended high frequencies, we used a psychoacoustic approach to evaluate subjective impressions of four dental drill sound stimuli, which featured varying frequency components, in 62 participants (aged 12-67 years). We found a significant decrease in hearing sensitivity within the EHF range as age increased, with notable differences in hearing thresholds at 14 kHz between teenage and older adults exceeding 65 dB. Furthermore, significant differences were observed between younger and older (above 40 years) participants in the subjective impressions of dental drill noise, emphasizing age as a critical factor in the perception of high frequency components. Consequently, age may influence the unpleasantness of dental drilling noise. Compared to older individuals, young participants may exhibit increased fear of dental procedures owing to physiological factors. These results underscore the need for age-appropriate noise control strategies in dental clinics to mitigate anxiety and improve patient comfort.

Effect of Push-Pull HEPA Filters on Air Age in a Dental Treatment Room.

Air quality was evaluated by visualizing with CFD (Computational Fluid Dynamics) where air tends to stagnate in the dental practice space when natural ventilation and HEPA filters are used together. The results showed that natural ventilation by opening and closing windows and doors alone was not sufficient.

Time-course study of genetic changes in periodontal ligament regeneration after tooth replantation in a mouse model.

This research focused on analyzing gene expression changes in the periodontal ligament (PDL) after tooth re-plantation to identify key genes and pathways involved in healing and regeneration. Utilizing a mouse model, mRNA was extracted from the PDL at various intervals post-replantation for RNA sequencing analysis, spanning from 3 to 56 days. The results revealed significant shifts in gene expression, particularly notable on day 28, supported by hierarchical clustering and principal component analysis. Gene ontology (GO) enrichment analysis highlighted an upregulation in olfactory receptor and G protein-coupled receptor signaling pathways at this time point. These findings were validated through reverse transcription-quantitative PCR (RT-qPCR), with immunochemical staining localizing olfactory receptor gene expression to the PDL and surrounding tissues. Moreover, a scratch assay indicated that olfactory receptor genes might facilitate wound healing in human PDL fibroblasts. These results underscore the importance of the 28-day post-transplant phase as a potential "tipping point" in PDL healing and regeneration. In conclusion, this research sheds light on the potential role of olfactory receptor genes in PDL regeneration, providing a foundation for developing new therapeutic approaches in tooth replantation and transplantation, with broader implications for regenerative medicine in oral health.

Synergistic effects of arginine and fluoride on human dental biofilm control.

OBJECTIVES: The aim of this study was to quantitatively and comprehensively investigate the combined effects of arginine and fluoride on the suppression of pathogenicity using an in situ biofilm model and next-generation sequencing (NGS). METHODS: Using the in situ model, dental biofilms were formed and the viable bacterial counts and arginine activity in the arginine- and fluoride-containing dentifrice and control groups were measured. We also compared their effects on the bacterial microbiota and predictive functional factors in the control, arginine (arg), and arginine + fluoride (argF) groups using NGS analysis. RESULTS: Compared to the control treatment, the use of 8 % arginine and 1450 ppm fluoride toothpaste resulted in significantly high oral NH4+ concentrations without affecting the number of viable bacteria (P < 0.05). NGS analysis revealed that the oral microbiota of the control, arg, and argF groups were significantly different. Heat map analysis of the predicted functional factors revealed that the arg group had different properties from the other groups and activated specific substrate metabolic pathways; contrastingly, argF treatment inhibited the activity of these pathways and prevented an increase in the abundance of bacterial genera that utilize substrates such as sucrose, suggesting the synergistic effect of arginine and fluoride. CONCLUSIONS: This study indicates that the combination of arginine and fluoride has a synergistic effect on the bacterial microbiota and pathogenicity of dental biofilms compared with arginine alone. CLINICAL SIGNIFICANCE: Our findings suggest that the combination of arginine and fluoride could be used as an effective prebiotic and may inhibit the growth of bacteria associated with dental diseases.

Microstructural Evaluation of the Mineralized Apical Barrier Induced by a Calcium Hydroxide Paste Containing Iodoform: A Case Report.

INTRODUCTION: A 65-year-old man had nonsurgical retreatment using an iodoform and calcium hydroxide paste in a maxillary left canine with persistent apical periodontitis. An apical mineralized barrier (AMB) was observed 3-months postoperatively. Unfortunately, the tooth was extracted due to a cementum tear. This provided an opportunity to analyze the AMB histologically, as there is a lack of previous reports on its microstructure. METHODS: After extraction and removal of the granulation tissue from the root surface, the canine was processed, and observed using micro-computed tomography (µCT) and light microscopy. Thereafter, the specimen was resin-embedded specimen was evaluated by scanning electron microscopy, micro-X-ray fluorescence spectroscopy and Raman spectroscopy to understand the mechanism and nature of the AMB formation during apical healing. RESULTS: Nonsurgical retreatment was clinically successful based on the absence of clinical symptoms of apical periodontitis and the radiographic presence of an AMB. The AMB was opaque and could be readily differentiated from dentin under a light microscope. Micro-computed tomography analysis revealed that the AMB had the same mineral density as dentin. Scanning electron microscopy revealed that the AMB had two distinct layers based on the size of the calcified particles. Elemental mapping using micro-X-ray fluorescence spectroscopy showed that the localization of calcium and phosphorus differed between AMB and other areas of biomineralization. Raman spectral mapping revealed that the surface layer of the AMB consisted of collagen, calcium carbonate, and hydroxyapatite. CONCLUSIONS: This study explored new analytical methods for elucidating the apical wound-healing process and the nature of the mineralized repair. The findings provided detailed information on the AMB highlighting a bilaminar structure with high calcium components higher on the inside and a brightness similar to cementum not dentin and the presence of hydroxyapatite.