The purpose of this study was to evaluate the influence of a disinfection technique based on photolysis of H₂O₂ on the mechanical properties and color change of acrylic denture base resin. Resin specimens were immersed in 1 M H₂O₂ irradiated with light-emitting diode (LED) light at 400 nm for 1 week. The immersion duration of 1 week (168 h) corresponded to performing approximately 500 times of 20-min cleaning. Hydroxyl radicals are potent oxidants and they were generated via the photolysis of H₂O₂. Oxidative damage caused by these radicals included reduced flexural strength and altered color for the acrylic resin. Nonetheless, the degraded flexural strength and altered color of acrylic resin after 500 times of cleaning in the disinfection system would be within clinically acceptable levels.

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To evaluate failure loads of teeth restored by use of alumina-coping, and to assess the effects of different amounts of residual tooth structure and different cements, standardized artificial alumina copings were fabricated on seventy-two molars. 24 of the copings were cemented by use of an adhesive resin cement (P-group), n=24 by use of glass-ionomer cement (K-group), and n=24 by use of a self-adhesive modified composite resin-cement (R-group). After artificial ageing (10,000 thermal-cycles between 6.5 and 60°C; 1,200,000 chewing cycles with F_max=64 N), the specimens were loaded until failure (cross-head-speed: 0.5 mm/min). In the K-group 83% of the specimens failed during chewing simulation. Statistical analysis included chi-squared-test, unpaired-to-sample-t-test, and ANOVA. For severely damaged teeth, loads to failure in the P-group (384 N) were significantly (p=0.03) higher than in the R-group (295 N). For severely damaged teeth, use of composite resin cement resulted in higher loads to failure than use of other cements.

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Chemically synthesized collagen with a triple helix structure similar to that of natural collagen is attractive as a safe biomaterial. Hybrids of chemically synthesized collagen and apatite are proposed for novel bone substitutes. However their apatite-forming ability in simulated body fluid is still quite low. We examined acceleration of apatite formation on collagen by immobilized poly-γ-glutamic acid (PGA), which has excellent apatite-forming ability. Apatite was formed within 3 days when collagen was treated with PGA solutions containing an appropriate amount of CaCl₂. A mixture of apatite and calcite was formed at high CaCl₂ concentration. The present results indicate the possibility of preparing hybrid materials, with tailored mechanical and biological properties, based on chemically synthesized collagen.

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To reduce the polymerization shrinkage of the dental resin composites, a new liquid-crystalline resin monomer was developed. The acrylate liquid crystalline resin monomer (ALCRM), (4-3-(acryloyloxy)-2-hydroxypropoxy) phenyl 4-(3-(acryloyloxy)-2-hydroxypropoxy) benzoate, was synthesized by a three-step method. Using the ALCRM as the main monomer, the degree of conversion (DC) and the volume shrinkage of the resin matrix were compared with the traditional composite resin monomer (Bis-GMA), 2,2-bis[4-(2-hydroxy-3-methacryloyloxy-propoxy)-phenyl] propane. The new monomer showed liquid crystalline characteristics with a mesomorphic phasetransition temperature between 18ºC and 42ºC. When copolymerized with triethylene glycol dimethacrylate (TEGDMA) at a weight ratio of 7:3, the DC of ALCRM was higher and the volume shrinkage was 3.62±0.26%, which was less than that of the Bis-GMA. The ALCRM exhibits promising potential for the development of superior dental resins with low volume shrinkage.

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The purpose of this study was to evaluate the effects of different surface conditioning procedures on microleakage and unfilled area proportions of three fissure sealants(Aegis, Helioseal and Helioseal F) in primary molar teeth. One hundred and fifty teeth were randomly divided into five main groups according to surface conditioning procedures. Main groups were; acid-etching(Group A); laser 3.75 W(Group B) and 5 W(Group D); acid-etching combined with laser 3.75 W(Group C) and 5 W(Group E). Samples were aged by thermocycling and water bath. Afterwards, they were immersed in basic fuchsin solution for 24 h and bucco-lingual sections were obtained from each tooth. Digital images were taken using a stereo-microscope and the microleakage and unfilled area proportions were assessed by using a software system. Consequently, Aegis FS containing amorphous calcium phosphate was found to exhibit the lowest microleakage in all surface conditioning procedures. Unfilled areas were not detected in Groups C and E of all FSs.

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This study aimed to improve Ti-porcelain bonding strength through SiO₂ modifications. Wax patterns were coated with SiO₂ mixed with tetraethoxy silane (group C), patterns without coating were used as controls and subdivided into sandblasting group (group S) and polishing group (group P). Castingsurfaces were analyzed with XRD, while Ti-ceramic interfaces were characterized using SEM/EDS. Metal-ceramic specimens were tested in three point bending, and characterizations were also analyzed with SEM/EDS of porcelain debonding surfaces. In group C, SiO₂ and Ti₅Si₃ phases were observed; SEM micrograph showed that Ti-porcelain had a compacted interface, and EDS maps of the interface illustrated the diffusion of Si, Al, and Sn to Ti, and cohesive fracture within the bonding agent. The bond strength of group C was 39.04±5.0 MPa, which was 15% higher than that of group S and 32% higher than that of group P. SiO₂ coating could improve Ti-porcelain bond strength.

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The purpose of the present study is to examine the relationship between the supportive designs of proximal region of zirconia framework on the fracture load. The zirconia frameworks with four different supportive designs on the proximal region were fabricated and classified with their radiuses of curvature (R): R=0.5 mm, R=1.0 mm, R=1.5 mm, and R=2.0 mm. The zirconia frameworks were conditioned with sandblast and veneering porcelain was fired. Subsequently, fracture tests were performed at 3 different load points: right above the lowest point of the boundary between veneering porcelain and zirconia framework; 0.5 mm inside from right above point; and 0.5 mm outside from right above point. The fracture load increased with an increase in the radius of curvature of supportive design when loading was applied from above and inside. This suggested that supportive design influenced the fracture load.

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This study aimed to investigate the effect of fluoride concentration in adhesives on morphology of acid-base resistant zone (ABRZ). Seven experimental adhesives with different concentrations of NaF (0 wt%; F0 to 100 wt%: F100) were prepared based on the formulation of a commercially available adhesive (Clearfil Protect Bond, F100). The resin-dentin interface of the bonded specimen was subjected to demineralizing solution and NaOCl, sectioned, polished and argon-ion etched for SEM observation. Fluoride release from each adhesive was measured using an ion-selective electrode. Fluoride ion release from the adhesive linearly increased with higher NaF concentration. The ABRZ area increased significantly with higher NaF concentration except for F0, F10, and F20 (p<0.05). F100 showed the largest ABRZ, where a slope of acid-resistant dentin was clearly observed at the bottom of the ABRZ. The concentration of NaF in the two-step self-etching adhesive resin influenced the amount of dentin structure remaining after acid-challenge.

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Oral bacteria adhered to dental material surfaces are known to cause various oral diseases. This study aimed to develop a highsensitive and non-radioisotopic fluorescence dye method for quantification of oral bacteria (Streptococcus, Actinomyces and Veillonella) adhered to denture material surfaces. The amount of adhered bacteria was estimated from the fluorescence intensity derived from resazurin, which is reduced by bacterial metabolic reactions. The addition of bacterial metabolic substrates (glucose for Streptococcus and Actinomyces and sodium lactate for Veillonella) to the reaction mixture increased the fluorescence intensity by 2.3–110 times, subsequently improved the sensitivity. Furthermore, an experimental device having silicon wells containing test material was carefully designed for accurate quantification of bacteria adhered to test materials. The improved resazurin method using a new experimental device successfully enabled the quantification of bacterial adhesion to polymethyl methacrylate and other three conventional denture materials.

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This study investigated the effects of aging and irradiation time on the macro- and micro-mechanical properties of a highly translucent nanohybrid composite (IPS Empress Direct, Trans Opal shade, Ivoclar Vivadent). Flexural strength, flexural modulus, indentation modulus, Vickers hardness, and creep were measured after being irradiated with different durations (5, 10, 20, and 40 s) and aged under different conditions (24 h at 37°C in water; 5,000 times of thermocycling between 5°C and 55°C followed by 4-week storage in artificial saliva or alcohol). Rate of cure was also measured for these four irradiation times at composite specimen surface and at 2 mm depth. Effects of aging and irradiation time were statistically analyzed using one-way ANOVA with Tukey’s HSD post hoc test (α=0.05), partial eta-squared statistic, and Weibull analysis. Alcohol aging significantly reduced the mechanical properties. Aging in saliva produced a positive effect on micro-mechanical properties. Irradiation time should be at least 20 s to yield favorable mechanical properties.

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The aim of this study was to determine the performance of an experimental all-in-one adhesive. The adhesive, named MTB-200 (Kuraray Medical), contained components to enhance both bond strength and hydrophobicity. The performance of the adhesive was compared with that of CLEARFIL TRI-S BOND (Kuraray Medical) and BeautiBond (SHOFU) using micro-tensile bond strength test and ultramicroscopic observations. The study revealed that the new adhesive had the highest tensile strength value among the three adhesives over time, although transmission electron microscopic images showed the phenomenon of filler de-bonding in the adhesive resin layer. In spite of modification in the experimental adhesive, the adhesive was suspected to degrade bond performance. However, revision of the composition of adhesives would be one of the solutions to enhance durability of interface.

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Reinforcement with bioresorbable polymer such as PLGA is one of the useful ways to improve the mechanical property of brittle carbonate apatite (CO₃Ap) foam. In the present study, CO₃Ap foam was reinforced with various concentrations of PLGA solution (5, 10, 15 and 20 wt%) using vacuum infiltration method and its influence on structure, porosity and mechanical property was investigated. It was found that the amount of PLGA inside the hollow space of the CO₃Ap foam strut increased with the concentration of PLGA. Porosity likewise was significantly (p<0.05) reduced from 94% (CO₃Ap foam without PLGA) down to 82% (CO₃Ap foam reinforced with 20 wt% PLGA). Compressive strength of CO₃Ap foam significantly (p<0.05) increased from 0.02 MPa (CO₃Ap foam without PLGA) up to 1.5 MPa (CO₃Ap foam reinforced with 20 wt% PLGA).

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This study aimed to evaluate the ability of a newly developed calcium-phosphate desensitizer in dentin permeability reduction and its integration with dentin surface before and after immersion in artificial saliva (AS) under two different dentin surface characteristics; with or without the collagen exposure.Humandentin discs treated by EDTA to expose collagen fibrils or EDTA/NaOCl to expose plain dentin surface were subjected to a calcium-phosphate desensitizer (Teethmate Desensitizer; TMD), while non-desensitizer treatment served as control. TMD application showed the occlusion in dentinal tubules and reduction in dentin permeability up to 92%, regardless of dentin surface characteristics. After AS immersion, permeability reduction percent (PR%) significantly increased in EDTA/NaOCl pretreatment (p<0.05). Newly-formed crystallites were observed on desensitizer treated dentin and EDTA/NaOCl pretreatment control group, whereas the crystallites did not exist on EDTA pretreatment control group. Ultrasonication revealed the integration of the calcium-phosphate rich layer of desensitizer on dentin surface after AS immersion.

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The influence of different adherend and substrate materials on shear bond strength (SBS) test was estimated. Ceramic plates (IPS e.max press) were cut, polished, abraded, and applied with two resin cements (Panavia F/Biscem). The SBS values of 30 groups were measured. The groups consisted of five combinations of adherend and substrate materials for each adhesive system and three different bonded areas (2, 4, and 6 mm diameter) for each combination. The failure modes were examined using a stereomicroscope. Groups with ceramic adherends showed higher SBS values in both adhesive systems and all three bonded areas. Small bonded areas are associated with significantly high SBS values. Groups with similar bonded areas and high SBS values showed more mixed or cohesive failures. Groups with small bonded areas and high SBS values had more interfacial failures. Adherend and substrate material significantly influenced the in vitro SBS value.

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The purpose of this study was to evaluate how the temperature affects the stability of polymerized additional photoinitiator-containing composite resins. Five resin products were light-cured using a quartz-tungsten-halogen, and single and dual emission peaks lightemitting diodes. The degree of conversion (DC) and water sorption, solubility, and color change of the specimens were evaluated after immersion in the solutions of different temperatures (4, 37, and 60ºC) for 14 days. On the top surface, the light-curing units had no significant influence on DC of the tested specimens. On the bottom surface, the influence was inconsistent. As the solution temperature increased, water sorption also consistently increased in all specimens, whereas solubility changed inconsistently. Water sorption and solubility had a high linear correlation only at low temperature solution. Color change of the specimens was similar, mostly slight, and statistically inconsistent regardless of solution temperature. The restored composite resins are needed to avoid contact with hot solutions for durable dental restoration.

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The aim of this study was to elucidate the association between the bone structure at implant insertion sites and stress distribution around the mandibular canal by means of three-dimensional finite element (3D FE) analysis. Four FE models were created with slice data using micro-computed tomography (micro-CT), and 3D FE analysis was performed. Mechanical analysis showed that the load reached the mandibular canal via the trabecular structure in all FE models. High levels of stress were generated around the mandibular canal when the distance between the mandibular canal and the implant decreased. High stress levels were also observed when cortical bone thickness and bone volume/total volume (BV/TV) were low. Our findings suggest that load is transmitted to the mandibular canal regardless of differences in the thickness of cortical bone or cancellous bone structure, but excessive load may be generated in bone with thin cortical and coarse cancellous structures.

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We previously discovered that when a cone-shaped indenter coated with paint was pressed into an object, the paint disappeared in accordance with the depth of the indentation. Based on this fact, we developed the Cariotester, a portable system for measuring the Knoop hardness (KHN) of carious dentin. The Cariotester is composed of a handpiece with an indenter, a microscope, and a computer. In this system, the painted indenter is forced into the material with a 150-gf load, and the indentation depth (CT depth) is obtained from the paint disappearance. The CT depth by the Cariotester and the KHN by a microhardness tester were determined at 14 dentin regions. From the data, a program was created to convert the CT depth of the carious dentin into the KHN. As a result, if the CT depth is measured with this system, the KHN of carious dentin can be displayed in real time.

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This study aimed to compare the ability of casein-phosphopeptide amorphous-calcium-phosphate (CPP-ACP) and glass-ionomer (GI) in remineralizing proximal artificial caries lesions (ACLs). Molar enamel-slabs were divided into: original-lesion control, intra-oral controls, and experimental (CPP-ACP or GI) groups. Specimens received ACLs and were bonded on subject maxillary first molars. After 4-weeks, mineral density (MD) was analyzed by μCT. Compared to control, CPP-ACP increased MD at 0–38/68–84 microns and the GI group had an increase at 0–68 microns, with a greater increase in MD compared to the CPP-ACP group from 0–53 microns. The mean percent remineralization (%R) showed differences between the GI, CPP-ACP groups and their paired controls. GI tended to increase remineralization more than CPP-ACP. In conclusion, CPP-ACP and GI demonstrated distinct remineralizing ability. GI induced greater remineralization in the superficial lesion, while CPP-ACP remineralized the lesion body. Their effects on percent remineralization and reducing lesion depth of proximal ACLs were similar.

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This study investigated hydrogen peroxide (H₂O₂) concentration of two home bleaching gels, in their dispensing syringes and their degradation in vivo in intraoral bleaching trays. Two bleaching gels were studied, 7.5% hydrogen peroxide (HP) and 20% carbamide peroxide (CP). The concentration of H₂O₂ was determined in dispensing syringes. Twenty individuals were involved in this study. The gels were placed in trays of both arches and their degradation determined at 5, 10, 15, 20, 30, 40, 60 and 75 min. The concentrations of H₂O₂ in syringes were (HP) 8.12% and (CP) 7.95%. For the HP gel in custom-trays the concentration of H₂O₂ was 73% at 5 min and 42% after 75 min. In the 20% CP gel it was 75% at 5 min and 39% after 75 min. Activity decreased linearly up to 75 min, where the mean concentration of H₂O₂ exceeded 35% for the CP and HP gels.

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The purpose of this study was to compare the retention of fiber-reinforced composite (FRC) posts luted with either conventional or self-adhesive resin cement. The FRC posts and core resin were built up in bovine teeth. The posts were luted with standard etch-andrinse cement, self-etch cement, or one of two self-adhesive cements. The samples were stored in water for 1 or 14 days or subjected to thermal cycling (TC). Retention value was measured with the pull-out test using a universal testing machine. Conventional adhesive resin cement yielded significantly greater retention than self-adhesive resin cement at 1 day. No significant difference was observed in retention among the adhesive systems tested at 14 days or after TC. During the early luting stage, self-adhesive resin cement yielded lower retention value than conventional resin cement. After 14 days storage or TC, retention was comparable to that with conventional resin cement.

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This study aimed to evaluate the validity of a portable microhardness testing system (Cariotester) for diagnosis of progression in active caries lesions by comparing data from this device and a laser fluorescence device (DIAGNOdent). Carious dentin in 12 specimens (stained clearly with a caries detector dye) was incrementally removed with a round bur at 150 μm depth intervals from the dentin surface in the direction of the pulp chamber. After each increment (total 138 sites), the Knoop hardness (HK) (evaluated with Cariotester) and DIAGNOdent (D) values were measured. HK values increased as D values decreased (regression formula: HK=0.419+238.342/D (p<0.001); coefficient of determination (R²): 0.602). Although DIAGNOdent quantitatively evaluates the degree of caries progression and bacterial infection status in caries lesions, our results demonstrate the validity and convenience of alternatively using microhardness measurements during caries removal to evaluate disease progression.

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