Chitosan-containing gum chewing accelerates antibacterial effect with an increase in salivary secretion.

OBJECTIVES: This study was designed to confirm the mechanical efficacy of chewing chitosan-containing gum to suppress the growth of oral bacteria compared to a mouth rinse, and to demonstrate the increased salivary secretion due to chewing chitosan-containing gum. METHOD: Twelve healthy subjects were recruited from among the staff and students of Nagasaki University School of Dentistry. For the slab of gum study, the subjects chewed chitosan-containing gum for 5 min and then rested for 5 min. For the testing of the chitosan mouth rinse solution, the subjects gargled 10 mL of solution for 30s followed by resting for 9 min 30s. These protocols were continuously repeated five times for 50 min on the same day. For the salivary secretion experiment, the gum chewing was repeated three times per day for 2 days. RESULTS: The amount of oral bacteria in the subjects who chewed chitosan-containing gum significantly decreased during all three sampling times except at 60 min for total bacteria in comparison to those in the rinse group. Chitosan-containing gum chewing also significantly increased the secretion of saliva. CONCLUSIONS: Chitosan-containing gum chewing has a greater antibacterial effect and it also increases salivary secretion. The present findings strongly indicate that the application of natural materials such as chitosan is useful for both oral health and the quality of life.

Expression of alkaline phosphatase induces rapid and artificial mineralization in specific transformed Escherichia coli.

Matrix vesicles (MV) having high alkaline phosphatase (ALP) activity act as initiators of biological mineralization. Although bacteria have similar membranous structures to MV, ALP mediated mineralization has not been studied in bacterial cells. Escherichia coli was transformed with a bacterial ALP gene in this study. Recombinant E. coli overproducing ALP induced mineralization through hydrolysis of calcium-glycerophosphate (Ca-GP). Fourier transform infrared spectroscopy and electron microscopy combined with electron diffraction revealed newly formed hydroxyapatite mineral deposits. These findings suggest that hydrolysis of Ca-GP through ALP induced high Ca and Pi concentrations within bacterial cells followed by complete bacterial mineralization.

Structure and chemical composition of an experimentally formed apical barrier after the application of calcium-glycerophosphate.

Transformation in the structure and composition of calcium-glycerophosphate (Ca-GP) was investigated using a scanning electron microscope fitted with an energy dispersive X-ray microanalysis (EDX) system. Ca-GP was packed inside roots that were subsequently implanted into the mandibles of rats to stimulate the formation of an apical barrier. Scanning electron microscopic observations of packed Ca-GP revealed three types of structures: globular aggregates, plate or flake-like aggregates, and granular aggregates. The average Ca/P molar ratios of EDX by area mode--postoperatively obtained at days 1, 3, 5, and 7--were 1.300, 1.533, 1.472, and 1.495 (analytic area: 0.01 to 0.03 mm2) and those of EDX by point mode were 1.220, 1.451, 1.487, and 1.467 (analytic point: 0.05 micron 2). The magnesium (Mg) weight percentage was found to be approximately 1.9 at days 3, 5, and 7, similar to Mg-substituted whitlockite. These findings suggest that Ca-GP are transformed, over a period of 3 days into Mg-substituted whitlockite as a result of being hydrolyzed by tissue fluid.

Hydroxyapatite applied as direct pulp capping medicine substitutes for osteodentin.

Tissue changes in rat incisors after direct pulp capping with hydroxyapatite (OH-AP) have been investigated using light and electron microscopy. Immediately after direct pulp capping, necrotic cells and cell debris were scattered only in the superficial zone of an exposed site. At day 1, both neutrophils having many vacuoles and macrophages phagocytizing numerous OH-AP granules appeared in the lower part of the OH-AP layer. At day 3, the cells surrounding the basal part of the OH-AP layer had large nuclei and well-developed rough-surfaced endoplasmic reticulum. At day 5, the newly formed mineralized tissue consisting of needle-like crystals was observed directly adjacent to the deepest zone of the OH-AP layer. However, fibroblast-like cells phagocytosing applied OH-AP granules were seen even at this period. These findings suggest that the applied OH-AP could directly substitute for osteodentin.

High-resolution electron microscopy of crystal contact in the demineralized dentine.

The mechanism of the dimensional increase in demineralized dentine crystals was investigated using a high-resolution transmission electron microscope. Lattice fringes were observed even in the demineralized crystals. The characteristics of demineralized dentine crystals mainly consisted of a partial disappearance of their lattice fringes along their lateral surface. High-resolution transmission electron microscopy also revealed that an intricate association between partially demineralized crystals occurred at the interface where incoherent or coherent tilt boundary, the dislocation of lattice fringes appeared. The present findings suggest that the dimensional increase in carious dentine could be brought by a crystal fusion.

Pathogenicity of bacteria using a simulated root canal system.

The purpose of this study was to investigate the reliability of an implantation test using Teflon-simulated root canals for evaluating the pathogenicity of root canal bacteria. Models including suspensions of lyophilized strains (Actinomyces israelii, Streptococcus faecalis, and Porphyromonas asaccharolyticus) were implanted in rat subcutaneous tissue for 1 wk, and histological changes were observed. Severe inflammation occurred around the models. Among them, P. asaccharolyticus induced the severest inflammatory response. Further study using P. asaccharolyticus was conducted to compare the implantation test's ability to evaluate pathogenicity with that of an injection test at 1, 2, or 4 wk. Tissue injected with a bacterial suspension showed no clear response through the experimental periods, whereas tissue around implantation sites showed a severe response at 1 wk. However, the inflammatory response subsided at later stages. Consequently, further improvement is needed to investigate pathogenicity for long periods.