Kee Yeon Kum

Microbial Analysis in Primary and Persistent Endodontic Infections by Using Pyrosequencing

INTRODUCTIONnThe aim of this study was to investigate the bacterial community profile of intracanal microbiota in primary and persistent endodontic infections associated with asymptomatic chronic apical periodontitis by using GS-FLX Titanium pyrosequencing. The null hypothesis was that there is no difference in diversity of overall bacterial community profiles between primary and persistent infections.nnnMETHODSnPyrosequencing analysis from 10 untreated and 8 root-filled samples was conducted.nnnRESULTSnAnalysis from 18 samples yielded total of 124,767 16S rRNA gene sequences (with a mean of 6932 reads per sample) that were taxonomically assigned into 803 operational taxonomic units (3% distinction), 148 genera, and 10 phyla including unclassified. Bacteroidetes was the most abundant phylum in both primary and persistent infections. There were no significant differences in bacterial diversity between the 2 infection groups (P > .05). The bacterial community profile that was based on dendrogram showed that bacterial population in both infections was not significantly different in their structure and composition (P > .05).nnnCONCLUSIONSnThe present pyrosequencing study demonstrates that persistent infections have as diverse bacterial community as primary infections.

Analysis of heavy metal contents in gray and white MTA and 2 kinds of Portland cement: a preliminary study

OBJECTIVEnThe levels of 10 heavy metals (arsenic, bismuth, cadmium, chromium, copper, iron, lead, manganese, nickel, and zinc) in gray Portland cement (GPC), white Portland cement (WPC), gray MTA (GMTA), and white MTA (WMTA) were analyzed by inductively coupled plasma-atomic emission spectrometry (ICP-AES).nnnSTUDY DESIGNnOne gram of each material was digested with 80 degrees C aqua-regia (7 mL of 60% HNO3 and 21 mL of 35% HCl), filtered, and analyzed by ICP-AES. The analysis was performed 6 times and the data were analyzed statistically.nnnRESULTSnArsenic and lead concentrations were the highest in GPC (P < .05). GPC had much more of 7 heavy metals than the other 3 cements (P < .05). GMTA and WMTA had higher purity than GPC and WPC (P < .05), particularly when arsenic content was considered.nnnCONCLUSIONnIf a clinician is considering using Portland cement versus MTA, the differences in purity may be considered.

Correlation study between distal caries in the mandibular second molar and the eruption status of the mandibular third molar in the Korean population

OBJECTIVESnThe purpose of this study was to analyze the correlation parameters between the distal caries of the mandibular second molars (M2Ms) and the eruption status of the mandibular third molars (M3Ms).nnnSTUDY DESIGNnThe records of 786 patients who had their M3Ms extracted from 2002 to 2007 at Samsung Medical Center were reviewed. The distal caries of M2Ms, age, gender, angulations, impaction degree, and distance between M2M and M3M were assessed.nnnRESULTSnAmong 883 M2Ms, 152 had distal caries (17.2%, caries group). In the caries group, 79.6% of M3Ms exhibited mesial angulation between 40 degrees and 80 degrees and 82.2% of M3Ms exhibited an impaction level in which the most coronal aspect of the M3M was located superior to the occlusal surface of the M2M. The distance between M2M and M3M (between cemontoenamel junctions) was 7-9 mm for 57.2% of the caries group.nnnCONCLUSIONSnThe M3Ms under eruption status as described here could be considered for preventive extraction.

Comparison of the rheological properties of four root canal sealers.

The flowability of a root canal sealer is clinically important because it improves the penetration of the sealer into the complex root canal system. The purpose of this study was to compare the flowabilities of four root canal sealers, measured using the simple press method (ISO 6876), and their viscosities, measured using a strain-controlled rheometer. A newly developed, calcium phosphate-based root canal sealer (Capseal) and three commercial root canal sealers (AH Plus, Sealapex and Pulp Canal Sealer EWT) were used in this study. The flowabilities of the four root canal sealers were measured using the simple press method (n=5) and their viscosities were measured using a strain-controlled rheometer (n=5). The correlation between these two values was statistically analysed using Spearmans correlation test. The flow diameters and the viscosities of the root canal sealers were strongly negatively correlated (ρ=−0.8618). The viscosity of Pulp Canal Sealer EWT was the lowest and increased in the following order: AH Plus<Sealapex<Capseal (P<0.05). All of the tested root canal sealers showed characteristic time- and temperature-dependent changes in their rheological properties. The viscosities measured using the strain-controlled rheometer were more precise than the flowabilities measured using the simple press method, suggesting that the rheometer can accurately measure the rheological properties of root canal sealers.

Evaluation of three obturation techniques in the apical third of mandibular first molar mesial root canals using micro-computed tomography

Background/purpose Recent studies have demonstrated a high incidence of isthmuses in mandibular first molar mesial roots, and intratubular mineralization following mineral trioxide aggregate obturation. This study assessed the filling quality of three obturation techniques in the apical 5 mm of mandibular first molar mesial root canals. Materials and methods Sixty extracted human mandibular first molar mesial roots with two separate canals that had interconnecting isthmuses, were prepared to an apical size of 40/0.06. They were allocated to three groups of 20 roots for obturation by either cold lateral compaction (CLC) or the continuous wave of condensation (CW) that used gutta-percha and AH Plus sealer, or by an orthograde canal obturation using OrthoMTA. The obturated roots were scanned by micro-computed tomography and assessed for the volumetric ratio (%) of gutta-percha, sealer, and OrthoMTA within the main canals or isthmuses in the apical 5 mm area. Measurements were analyzed statistically for differences among three obturation techniques. Results In the main canals, filled volume ratios were not significantly different among groups. Within isthmuses, the filled volume ratio for CLC was lower than in CW (P = 0.025) or OrthoMTA (P = 0.002). In isthmuses, the gutta-percha volume ratio in CLC was lower than in CW (P = 0.005), although the sealer volume ratio was higher than in CW (P = 0.049). Conclusion CLC demonstrated lower filling densities in isthmuses in the apical region than either CW or OrthoMTA. Orthograde MTA obturation showed comparable filling quality to gutta-percha with sealer.

Effect of preheating on the viscoelastic properties of dental composite under different deformation conditions

Preheating of dental composites improves their flowability, facilitating successful restorations. However, the flowability of dental composites is affected not only by temperature but also by the deformation conditions. In the present work, the effects of various deformation conditions upon the viscoelastic properties of a preheated dental composite were studied. The rheological properties of Z350 dental composites at 25, 45, and 60°C were measured by a strain-controlled rheometer. When a low strain (0.03%) was applied, the preheated composite exhibited greater shear storage modulus (G) and complex viscosity (η*) than a room-temperature composite. Oppositely, when a high strain (50%) was applied, G and η* of a preheated composite were lower than those of a room-temperature composite. Preheating of dental composites might be helpful in clinical practice both to increase the slumping resistance when minimal manipulation is used (e.g., during the build-up of a missing cusp tip) and to increase flowability when manipulation entailing high shear strain is applied (e.g., when uncured composite resin is spread on a dentin surface).

In vitro Antibacterial Effect of Orthodontic Adhesives Mixed with Silver Nanoparticles

Purpose: To examine the antibacterial effectiveness of silver nanoparticles (SNP) mixed with commercial orthodontic adhesives. Materials and Methods: SNP was prepared by dissolving silver perchlorate in an organic solvent and reducing it with ultraviolet radiation. SNP was then mixed with four commercial orthodontic adhesives (Light Bond, Blugloo, Transbond XT, and Fuji Ortho LC) (0.05 wt %), which were then formed into disc-shape specimens (8.0 ㎜×3.0 ㎜). Commercial orthodontic adhesives containing no SNP were used as the control groups. Specimens of the four experimental and four control groups were incubated with streptococcus mutans and the medium turbidity was assessed at 3, 6, 9, 12, and 24 hours after incubation. The agar diffusion test was also performed to examine the growth inhibition zone of these groups. The data were statistically analyzed using a Wilcoxon rank sum test and t-test with a Bonferroni’s correction (P＜0.05). Result: The SNP containing groups had a superior antibacterial effect compared to the control groups. In the agar diffusion test, the control groups without SNP did not produce an inhibition zone, whereas the SNP containing groups showed inhibition zone of 10~13 ㎜. Conclusion: The incorporation of SNP into orthodontic adhesives can inhibit cariogenic bacterial growth.

Dentinal tubule sealing effects of 532-nm diode-pumped solid-state laser, gallic acid/Fe3+ complex, and three commercial dentin desensitizers

The purpose of this study was to compare dentinal tubule sealing effects of a 532-nm diode-pumped solid-state (DPSS) laser, gallic acid/Fe3+ complex, and three commercially available dentin desensitizers. Human premolars (nu2009=u200944) extracted for orthodontics had standardized cervical cavities prepared, etched (37% phosphoric acid) and randomly assigned to either a control (nu2009=u20094), or one of five treatment groups (nu2009=u20098/group). Desensitizing treatments were either a 532-nm DPSS laser, gallic acid/Fe3+ complex, oxalate-based Super Seal™ (SS), DIO™ Enamel Coating Pen Pro Tooth (Dio), or adhesive-type Hybrid Coat™ (HC). Dentinal fluid flow (DFF) was monitored continuously in real time during the application of each desensitizing agent, by using a nanoliter-scaled fluid flow-measuring device. Following treatment, morphological changes on dentinal surfaces and within tubules were observed by scanning electron microscopy (SEM). DFF rates were significantly reduced after treatment in all experimental groups (Pu2009<u20090.05), except SS (Pu2009>u20090.05). The gallic acid/Fe3+ complex reduced DFF rates the most, and significantly (Pu2009<u20090.05) more than the three commercial dentin desensitizers. There were no significant differences in DFF reduction rates between the gallic acid/Fe3+ complex and the DPSS laser groups (Pu2009>u20090.05). There were no significant differences in DFF reduction rates among the three commercial dentin desensitizers (Pu2009>u20090.05). SEM examination of treated dentin showed that the degree of occlusion of dentinal tubules correlated closely with the corresponding reduction in DFF rates. The gallic acid/Fe3+ complex and 532-nm DPSS laser were superior to other desensitizing methods in occluding dentinal tubules and reducing DFF rates.

Antifungal Effects of Synthetic Human Beta-defensin-3-C15 Peptide on Candida albicans –infected Root Dentin

Introduction The aim of this study was to assess the antifungal efficacy of a synthetic human beta‐defensin‐3‐C15 peptide (HBD3‐C15) in Candida albicans–infected human root dentin. Methods Standardized root dentin blocks were prepared (6‐mm thick, 0.7‐mm‐wide canal) from single‐rooted human permanent premolars and infected with C. albicans for 3 weeks. They were randomly divided into 4 groups (n = 8/group), and their canals were filled with calcium hydroxide (CH), HBD3‐C15 peptide, or chlorhexidine digluconate (CHX, 2%) as disinfectants or saline as control. After 1 week of disinfection, dentinal debris were harvested at depths of 200 and 400 &mgr;m from the canal lumen, and incubated in Yeast broth for 72 hours at 37°C. Then, colony‐forming units (CFU) were measured to assess the antifungal efficacy of each medicament and analyzed statistically. Results All medicaments showed significantly lower CFU than saline (P < .05), and their antifungal efficacies were similar at both 200‐ and 400‐&mgr;m tubular depths (P > .05). HBD3‐C15 had similar antifungal efficacy to that of CHX at both depths (P > .05), and both medicaments had significantly lower CFU than CH at both depths (P < .05). Conclusions In this ex vivo model of C. albicans–infected human root dentin, the antifungal efficacy of synthetic HBD3‐C15 was comparable with CHX. HighlightsCandida albicans biofilm is closely related to initiation and persistence of refractory apical periodontitis.Antifungal efficacy of various intracanal medicaments were assessed in C. albicans‐infected human root dentin.In C. albicans‐infected human dentin blocks, root canals were covered by mature biofilms with tubular penetration of 400 &mgr;m.In this standardized ex vivo model, chlorhexidine and synthetic human &bgr;‐defensin‐3‐C15 peptide were similar and highly effective at reducing C. albicans CFU, whereas calcium hydroxide had limited efficacy.

Study on Biocompatibility and Mineralization Potential of Capseal

Purpose: Capseal I and Capseal II are calcium silicate and calcium phosphate based experimental root canal sealers. This study sought to evaluate the biocompatibility and mineralization potential of Capseal I and Capseal II. Materials and Methods: The biocompatibility and mineralization related gene expression (alkaline phosphatase [ALP], bone sialoprotein [BSP], and osteocalcin) of Capseal I and Capseal II were compared using methylthiazol tetrazolium assay and reverse transcription-polymerization chain reaction analysis, respectively. The results were analyzed by Kruskal-Wallis test. A P-value of Result: Both Capseal I and Capseal II were favorable in terms of biocompatibility, infl uencing the messenger RNA expression of ALP and BSP. Conclusion: Within the limitation of this study, Capseal is biocompatible, with mineralization promoting potential; thus, it could be a promising root canal sealer.