Katsura Ohashi

Relevance of surface characteristics in the adhesiveness of polymicrobial biofilms to crown restoration materials

We used a polymicrobial (PM) biofilm model to examine associations of bacterial adhesiveness with surface characteristics of various dental materials. Four types of dental materials (apatite pellet, zirconia, ceramic, and composite resin) with rough and mirror surfaces were used. Surface roughness, surface free energy, zeta potential, and colony-forming units (CFUs) of the biofilm formations were measured. Biofilms were cultured for 24 h under anaerobic conditions, plated onto blood agar medium, and anaerobically cultured for 4 days. After culturing, CFU per mm2 was calculated, and samples were observed under a scanning electron microscope. Means and standard deviations of the experimental data were estimated, and one-way ANOVA and Tukey multiple comparison assays were performed. Pearson correlation coefficients were obtained for the CFU and surface characteristics. Surface roughness and surface free energy appeared to affect generation of PM biofilms on oral materials, and zeta potential was involved in generation of PM biofilms on mirror-ground oral materials.

Effects of resin-based temporary filling materials against dentin demineralization.

This study investigated the in vitro anti-demineralization effects of resin-based temporary filling materials containing surface prereacted glass-ionomer (S-PRG) filler on dentin. Bovine root dentin specimens with a 3×3 mm experimental surface were divided into four treatment groups: DuraSeal (DU) as a control, S-PRG filler-free temporary material (S0), material containing 10% (S10) and 20% (S20) S-PRG filler. Each material was applied to 3×2 mm of the experimental surface, and the specimens were immersed in 8% methylcellulose gel demineralization system for one week at 37˚C. Mineral profiles and integrated mineral loss (IML) of lesions induced on the surface (3×1 mm) adjacent to the materials were computed by transversal microradiography. S10 and S20 yielded thick surface layers and shallow lesion bodies, with significantly lower IML than DU and S0 (p<0.05, Tukeys test). These findings indicate that temporary filling resin-based materials containing over 10% of S-PRG filler content have anti-demineralization effects on adjacent dentin.

Synthesis of bone formation deriving biosilanes.

Six silane coupling agents having amide group (biosilanes) were synthesized with the aim to construct the material surface that allows cells to be compatible with it without their destruction. These agents were expected to make a soft landing to cytoplasm through the hydrogen bonding between their amide groups and cells. Evaluations of cell affinity using glass substrates modified with the synthesized biosilanes revealed that many cells remain on the modified glass plate. In addition, the implantation into the body of immunodeficient mouse of a composite material composed of porous hydroxyapatite and osteoblast showed the formation of a bone-like structure.

Bond Strength and Water Resistance of a Resin Composite Bonded to Glass Plates Treated with Commercial Ceramic Primers

Background: Silane coupling agents are used as a bonding agent between ceramics and resins in dentistry. The effectiveness of these agents is often enhanced by the addition of acid or by heat treatment. Objective: This study aimed to evaluate, the clinical characteristics, TBS (tensile bond strength) and water resistance of eight commercial ceramic primers (seven silane coupling agents and one alumina zirconia primer). Method: Glass plates were used as the adherent. The TBS of the resin composite and the wettability of the resin monomer to glass surfaces treated with ceramic primers was investigated, with 3-MPS (methacryloxypropyltrimethoxysilane) used as a control. The values obtained from the experiments were analyzed using one-way ANOVA followed by Tukey’s multiple comparison tests (p < 0.05). Results: No significant differences in TBS were observed between the commercial products and MPS, except for the alumina zirconia primer. However, four products (three of the seven agents and the alumina zirconia primer) exhibited significantly lower TBS values after application of thermal stress when compared with those stored in water (p < 0.05). All but one of the eight primers displayed significantly higher contact angles between the treated glass and the resin monomer when compared with MPS (p < 0.05). These results suggest that some commercial ceramic primers may contribute to increased strength and durability.

Antimicrobial Activity of a Novel Silane Coupling Agent Consisting of a Quaternary Ammonium Salt Using a Polymicrobial Biofilm Model

Because the Japanese population is rapidly aging, the involvement of oral indigenous bacteria in systemic diseases has been receiving particular attention in Japan. Although tooth loss rate has decreased because of increased awareness of oral care, more than 50 % of elderly individuals are still using dentures,1,2 indicating that oral care is not sufficient.3 The elderly and individuals requiring nursing care show significantly higher morbidity from chronic diseases, and they are more likely to develop multiple complications. The age-associated decline in immune function increases the susceptibility of the elderly to opportunistic infections caused even by generally nonpathogenic low-virulent microbes, leading to refractory infectious diseases, such as respiratory infection, caused by bacteria indigenous to the oral cavity.4,5 Moreover, dentures used by several elderly individuals facilitate the accumulation of plaque, called denture plaque, causing bacterial infections that can result in diseases, such as aspiration pneumonia and cerebrovascular disorders.6–9 Therefore, maintaining good oral hygiene not only contributes to oral comfort and the prevention of oral diseases but may also play a role in reducing the incidence of respiratory infections, such as aspiration pneumonia, which are the major causes of mortality among the elderly. We have developed various surface modifiers capable of reducing the surface free energy of tooth substances and dental restoration and prostheses materials, rendering them acid resistant. We have also studied their application for caries prevention and periodontal disease through the suppression of adhesion and plaque formation and decalcification of dentine.10–13 Because the Japanese population is aging, development of an advanced surface modifier that not only prevents the adhesion and accumulation of plaque but also has antimicrobial activity is of urgent importance to actively kill the adhered microorganisms for the prevention of systemic complications. Quaternary ammonium salts, a class of commercially available antimicrobial agents sometimes referred to as invert soaps, display potent bactericidal and disinfecting effects with minimal irritation and low toxicity, and they are promising antimicrobial compounds because of their improved safety.14 Immobilization of an antimicrobial agent is the most common approach to prolong the duration of its antimicrobial effect; we chose an antimicrobial compound containing a silane coupling agent-derived molecular structure as the most promising and reliable method to achieve this purpose. We synthesized a new quaternary ammoniumbased antibacterial silane coupling agent, N-allyl-N-decyl-N-methylN-trimethoxysilylpropylammonium iodide (10-I; Tokyo University of Science), to immobilize the antimicrobial activity on substrate surfaces.15 10-I did not inhibit colony formation of the cells.16 Glass plate surfaces modified with 200 and 400 ppm of 10-I inhibited the growth of the following oral bacteria: Actinomyces viscosus, Candida albicans, Fusobacterium nucleatum, Lactobacillus casei, Porphyromonas gingivalis, Prevotella intermedia, Staphylococcus aureus, and Streptococcus mutans. C. albicans cultured in the presence of a glass plate treated with the 400-ppm 10-I showed strong growth inhibition.17 However, bacteria in the oral cavity include both