The participation of bacterial biofilms in the over-filled gutta-percha points associated with refractory periapical periodontitis has recently been reported. This study investigated the initial biofilm-forming ability of root canal isolates (Enterococcus faecalis, Streptococcus sanguis, Strep. intermedius, Strep. pyogenes, Staphylococcus aureus, Fusobacterium nucleatum, Propionibacterium acnes, Porphyromonas gingivalis and Prevotella intermedia) on gutta-percha points in vitro. Each bacterial strain was suspended in 100% cell culture medium or in culture medium containing 4.5, 45 or 90% (vol/vol) serum. The bacterial suspensions were then co-incubated anaerobically with gutta-percha points for 7 d. The gutta-percha points were processed for scanning electron microscopic observation and examined for biofilm presence and thickness. E. faecalis, Strep. sanguis, Strep. intermedius, Strep. pyogenes and Staph. aureus biofilms were generated on the surfaces of the specimens incubated in culture medium supplemented with 45 or 90% (vol/vol) serum. The E. faecalis and Strep. sanguis biofilms were significantly thicker than those of Strep. intermedius, Strep. pyogenes and Staph. aureus. No biofilms were detected on the specimens incubated with F. nucleatum, Prop. acnes, Porph. gingivalis and Prev. intermedia. These findings suggest that Gram-positive facultative anaerobes have the ability to colonize and form extracellular matrices on gutta-percha points, while serum plays a crucial role in biofilm formation.

Hydroxyapatite/soluble calcium phosphate composites (HAp/SCaP) are novel HAp-based materials with enhanced solubility that have been developed by annealing HAp in a vacuum. This study compared the effects of HAp and HAp/SCaP on osteoblast proliferation, differentiation, and mineralization using an MC3T3-E1 cell culture system. MC3T3-E1 cells were cultured on HAp or HAp/SCaP, and the number of attached cells and their morphology were examined. The influence of the extract from HAp/SCaP on osteoblast differentiation was determined by the measurement of alkaline phosphatase activity and reverse transcriptase-polymerase chain reaction analysis of the expression of osteoblastic markers. In addition, mineralization was evaluated by the staining of calcium deposits with Alizarin red. Attachment of a greater number of cells exhibiting no degeneration in their morphology was observed on HAp/SCaP compared with HAp after incubation for 7 days or more. Culturing cells with the extract from HAp/SCaP resulted in promotion of alkaline phosphatase activity, the expression of type I collagen, and bone-like tissue formation. The results of the present study indicate that HAp/SCaP shows greater ability in osteogenesis than HAp by increasing collagen synthesis and calcification of the extracellular matrix.

Cyclosporin A (CsA) might induce immune response alterations in periapical lesions and modify bone remodeling. This study determined the changes that occur in the periapical lesions of rats during CsA administration and after CsA withdrawal. After the induction of periapical lesions, the animals were treated with CsA (0–20 mg/kg/day) for 4 wks. Lesion volumes were measured by computed tomography. Histological observations and immunohistochemical evaluations were performed with anti-CD3 and anti-CD25 antibodies. CsA administration reduced lesion volumes, and the lesions significantly expanded after CsA withdrawal. CsA inhibited the proliferation and activation of T-cells at lesion sites. The effects of CsA on T-cells were dose-dependent up to 10 mg/kg/day, after which no significant difference was evident. These results suggest that CsA inhibits periapical destruction by interfering with T-cell function in periapical lesions.

Calcium phosphates with high solubility in water such as α-tricalcium phosphate (α-TCP) and tetracalcium phosphate (TetCP) have received considerable attention as components of bone-substitution materials. However, the osteoblast response to these materials has not yet been clearly understood. This study examined the effects of α-TCP and TetCP on osteoblast proliferation, differentiation and mineralization in the culture system of MC3T3-E1 cells. Cells were cultured in a differentiation medium with or without α-TCP or TetCP at 1 or 10μm, and the number of cells attached to the culture plates was determined. To examine osteoblast differentiation, the alkaline phosphatase (ALP) activity was measured and the expression of osteoblastic markers analyzed by RT-PCR. In addition, mineralization was evaluated by staining the calcium deposit with Alizalin red. Culture in the presence of α-TCP or TetCP showed no significant influence on cell proliferation. ALP activities of the cells were enhanced by both calcium phosphates for 3d and the expression of type I collagen was promoted at 12h and 1d after incubation. Enhancement of bone-like tissue formation by the addition of α-TCP or TetCP at 10μm was observed after 7d incubation and thereafter. The results of the present study indicate that α-TCP and TetCP promote osteogenesis by increasing collagen synthesis and calcification of the extra-cellular matrix.

HAp and the related calcium phosphates have been of great interest as biological materials for regenerating hard tissues, but their solubility should be improved to fit the remodeling cycle of hard tissues in vivo before their practical use for bone grafts. Control of the grain size of hydroxyapatite (HAp) matrix and change in constituent phase of the surface layer were examined to improve the dissolution rate in HAp ceramics. Surface and boundary layers composed of calcium phosphate phases with high solubility were formed by annealing at 1350 C in a vacuum, and the apparent mass transfer coefficient in the initial stage of the solubility experiment remarkably increased in an acetate buffer solution at pH of 4.0. The soluble surface and boundary layers are composed of tetracalcium diphosphate monoxide (TTCP), alpha-tricalcium phosphates (alpha-TCP) and amorphous calcium oxide (CaO) with high solubility, and their formation mechanism was discussed. Refinement of the grain size of HAp matrix also contributed to a slight increase in the apparent solubility.

The aim of this study was to examine morphologically the participation of extraradicular biofilm in refractory periapical periodontitis. Six teeth and five extruded root filling gutta-percha points associated with refractory periapical periodontitis were investigated by scanning electron microscope.In nine of 11 samples examined, bacterial biofilms were seen at the extraradicular area. The gutta-percha surface was covered with glycocalyx-like structures, and filaments, long rods, and spirochete-shaped bacteria were predominant in the extraradicular sites. Planktonic cells, which were filaments and spirochete-shaped bacteria, emigrated from the glycocalyx structures in some spots. In the extracted teeth, biofilm consisting of both bacteria and glycocalyx-like structures were observed on the periapical root surfaces. Next to the residual periodontal ligament, a few filaments, rods, and fusiforms were attached on the healthy cementum surface.The present findings suggested that bacterial biofilms formed in the extraradicular areas were related to refractory periapical periodontitis.

Crystallinity of hydroxyapatite reflecting crystal size and crystal elastic strain was controlled by the mechanical grinding (MG) technique using a set of container and balls made of SUS304 stainless steel or agate. Variation in the crystallinity through MG was monitored by the XRD method and represented by the broadening of the diffraction peak. Effect of changes in crystallite size and strain on the crystallinity was also examined using the Hall-plot method.

Objective. Differential thermal analysis (DTA) using a split fiber optic light source has been reported to be a convenient method of measuring the degree of conversion (DC) of light-activated composites. The purpose of this study was to compare the results by DTA and Fourier transformation infrared spectroscopy FIR), and evaluate the usefulness of the DTA method.Methods. Experimental 2,2-bis[4-(3-methacryloyloxy-2-hydroxypropoxy)phenyl]propane-based composites containing SiO2 filler and various amounts of triethyleneglycol dimethacrylate (TEGDMA) were prepared, and the DC of each composite was determined by DTA or FTIR with 60 s irradiation. The DC of three proprietary composites containing hybrid filler or prepolymerized resin filler were also measured by both methods with 20 or 60 s irradiation. The results were analyzed by ANOVA and Fisher's protected least significant difference test.Results. By both DTA and FTIR, the DC of experimental composites increased as the proportion of TEGDMA increased, although DTA showed 3-10%,greater values (p < 0.05) than FTIR. For proprietary composites that contain hybrid filler, the values by DTA were not significantly different from those by FTIR at 20 s exposure. Longer irradiation time resulted in greater DC (p < 0.05) for both methods, and DTA showed 5-7% greater values than FTIR. However, the DC of the composite containing prepolymerized resin filler was 30% less by FTIR than by DTA, possibly due to the influence of unpolymerized species in the filler.Significance. The DC values determined by DTA and FTIR showed good agreement for most materials including model composites. In addition, DTA may be more useful than FTIR to measure the DC of composites containing prepolymerized resin filler. (C) 2001 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.

We attempted to develop a resin with a recoverable antibacterial activity based on the desorption/adsorption of a cationic bactericide by the ion-exchange mechanism. The aims of this study were to investigate the release kinetics of the agent and the antibacterial activity of this newly designed resin system. An experimental resin was prepared by the addition of methacrylic acid as a cation-exchanger and a cationic antibacterial agent, cetylpyridinium chloride (CPC), to triethyleneglycol dimethacrylate. The amount of CPC desorbed from the experimental resin into buffer solutions at pH 4-8 was measured. The adsorption of CPC to control resin and re-adsorption of CPC to the experimental resin, which had once desorbed the agent, were also determined. The antibacterial activity of experimental resin against Streptococcus mutans was evaluated, and the relationship between bacterial acid production and antibacterial effect was assessed. The experimental resin desorbed CPC at pH << 6, and the amount of agent desorbed increased with increasing acidity. The control resin adsorbed CPC when immersed in CPC aqueous solution at a rate determined by the concentration of the agent and immersion time. The experimental resin, once desorbed CPC, could re-adsorb the bactericide by being exposed to a solution of the agent. Less plaque formed on the experimental resin, and the growth and survival of S. mutans was inhibited in the condition in which acid was produced. These results demonstrate that the resin system proposed was able to desorb and re-adsorb the cationic bactericide by an ion-exchange mechanism and could show an inhibitory effect on S. mutans growth and plaque formation.

Objective: This study was conducted to evaluate the effect of the amount of TEGDMA on post-irradiation polymerization of bis-GMA based composites.Methods: Four experimental composites containing bis-GMA and TEGDMA at the ratios (w/w) of 75/25, 70/30, 67/33, and 50/50 were prepared. The degree of conversion of each composite was measured by Fourier transformation infrared spectroscopy immediately after being cured and after 24 h of storage, and the post-irradiation polymerization was determined. In addition, the change in respective amounts of residual bis-GMA and TEGDMA in cured specimens over 24 h was determined by high performance liquid chromatography. Data were analyzed by means of ANOVA, followed by a Fisher's PLSD test at a significance level of 0.05.Results: At both stages of as-cured and after 24h-storage, the composites containing greater amounts of TEGDMA showed a greater degree of conversion. The amount of post-irradiation polymerization decreased as die content of the incorporated TEGDMA increased. The reduction in the amount of TEGDMA remaining unreacted during post-irradiation polymerization also decreased as the content of TEGDMA increased, while the amount of unreacted bis-GMA showed almost constant values.Significance: An increase in the amount of TEGDMA-incorporation in bis-GMA based composites resulted in less pest-irradiation polymerization. As the change in the amount of residual unreacted TEGDMA in cured specimens showed the same trend as the results of the post-irradiation polymerization, TEGDMA is considered to be the main contributor to post-irradiation polymerization of bis-GMA based composites. (C) 1999 Academy of Dental Materials. Published by Elsevier Science Ltd. All rights reserved.

Objectives: A monomer methacryloyloxydodecylpyridinium bromide (MDPB) has antibacterial activity before polymerization. Furthermore, the antibacterial agent is immobilized by the polymerization of MDPB and the resin-based material incorporating MDPB is able to show an antibacterial effect even after being cured. The purpose of this study was to investigate the antibacterial effect of a dentine primer containing MDPB after curing. Methods: The inhibitory effect of a cured MDPB-containing primer on the growth of Streptococcus mutans, Actinomyces viscosus and Lactobacillus casei was determined by the agar-disc method. The bactericidal activity of cured primer during a 1-h contact period was assessed using S. mutans, and the elution of unpolymerized MDPB was measured with high performance liquid chromatography. Results: Cured MDPB-containing primer showed an inhibitory effect on the growth of all species which were in contact with the specimen surface, and displayed a little bactericidal effect on S. mutans without releasing any unpolymerized antibacterial components. Conclusion: Incorporation of antibacterial monomer MDPB into dentine primer is beneficial for providing antibacterial activity after curing.