The study aimed at estimating the effect of insertion length of posts with composite restorations on stress and strain distributions in central incisors and surrounding bone.
The typical, average geometries were generated in a FEA environment. Dentin was considered as an elastic orthotropic material, and periodontal ligament was coupled with nonlinear viscoelastic mechanical properties. The model was then validated with experimental data on displacement of incisors from published literature. Three post lengths were investigated in this study: root insertion of 5, 7, and 9 mm. For control, a sound incisor model was generated. Then, a tearing load of 50 N was applied to both sound tooth and simulation models.
Post restorations did not seem to affect the strain distribution in bone when compared to the control. All simulated post restorations affected incisor biomechanics and reduced the root's deforming capability, while the composite crowns underwent a higher degree of deformation than the sound crown. No differences could be noticed in incisor stress and strain. As for the influence of post length, it was not shown to affect the biomechanics of restored teeth.

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The present study was conducted to determine the effect on the distribution of stress with the use of short-post cores and over restorations composed of different materials. The restorative materials used were namely two different composite resin materials (Valux Plus and Tetric Flow), a polyacid-modified resin material (Dyract AP), and a woven polyethylene fiber combination (Ribbond Fiber + Bonding agent + Tetric Flow). Finite element analysis (FEA) was used to develop a model for the maxillary primary anterior teeth. A masticatory force of 100 N was applied at 148° to the incisal edge of the palatal surface of the crown model. Stress distributions and stress values were compared using von Mises criteria. The tooth model was assumed to be isotropic, homogeneous, elastic, and asymmetrical. It was observed that the highest stress usually occurred in the cervical area of the tooth when Tetric Flow was used as the short-post core and over restoration material. The same maximum stress value was also obtained when Ribbond fiber + Tetric Flow material was used for the short-post core. The results of FEA showed that the mechanical properties and elastic modulus of the restorative material influenced the stresses generated in enamel, dentin, and restoration when short-post core restorations were loaded incisally. Resin-based restorative materials with higher elastic moduli were found to be unsuitable as short-post core materials in endodontically treated maxillary primary anterior teeth.

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The aims of this study were to evaluate the effects of CPP method on the crystallinity of apatite powder and on the acid resistance of bovine enamel. Crystallinity degrees of apatite powder before and after CPP treatment were measured by powder X-ray diffraction analysis. Polished bovine enamel specimens treated with CPP method or NaF were immersed in a lactic acid solution for up to five days. The demineralized depth of enamel was measured with a surface roughness analyzer. XRD peaks became sharper after the CPP treatment, indicating an increased crystallinity of the apatite powder. The demineralized depth of bovine enamel treated with CPP method was shallower than that of enamel treated with NaF. Results of this study revealed that the CPP method increased the crystallinity of apatite powder and the acid resistance of enamel. Therefore, the CPP method would be useful not only for treating dentin hypersensitivity, but also for the prevention of dental caries.

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This study evaluated the effect of 1% hydrofluoric acid (HF) treatment on the bonding of an adhesive cement (Panavia F 2.0) to an indirect resin composite (Estenia C&B). Pairs of composite disks (10 and 8 mm in diameter by 3 mm thickness) were prepared. Adhesive surfaces were pretreated with either airborne particle abrasion or HF etching before being soaked for 30 seconds, five minutes or 10 minutes, with or without application of silane coupling agent. Adhesive specimens were fabricated by cementing a pair of treated disks. Shear bond strength was determined before and after 50,000 times of thermocycling (4 and 60°C). All data were statistically analyzed using two-way ANOVA and Bonferroni's test (α=0.05). Bond strength achieved with five minutes of HF etching (18.3±1.1 MPa) was significantly higher (P=0.0025) than that obtained with airborne particle abrasion followed by application of silane coupling agent (14.3±1.8 MPa) after thermocycling.

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The aim of this study was to investigate the effects of light intensity and light-curing time on the polymerization of composite resins. Four composite resins were light-cured with different light-curing conditions. In the non-thermocycled case, specimens showed almost the same or similar microhardness values if energy density was identical or similar. As the energy density decreased, maximum polymerization shrinkage decreased. At higher energy densities, specimens had a lower coefficient of thermal expansion than at lower energy densities. At the same or similar energy density, most resin products showed coefficient values which were not statistically different. After 10,000 thermocycles, specimens showed decreases of 2.4–16.5% and 4.6–25.2% in microhardness and coefficient of thermal expansion respectively. Within the limitations of the present study, it was found that light-curing composite resins with higher energy density was beneficial to acquiring higher microhardness values and lower coefficients of thermal expansion.

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A novel matrix resin for photo-activated resin composites was developed using α-fluoroacrylic acid derivatives. To render resin composites with improved mechanical properties, silica fillers were also used. It was found that the newly developed fluorine-substituted monomer was polymerized quite easily not only by free radical chemical initiators, but also by photo-irradiation using free radical photoinitiator system. In particular, the photopolymerization rate of the novel monomer was more than two times faster than that of corresponding methacrylate-based monomer. Composite based on the newly developed matrix resin had higher micro-Vickers hardness and compressive strength values than the methacrylate-based composite, and that it contained only trace residual monomers compared with the methacrylate-based material. The high polymerization conversion of the fluorine-substituted monomer could be attributed to the polar effect or the small steric hindrance of fluorine at the α-position.

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This study investigated the effect of the diameter of glass fibers on the flexural properties of fiber-reinforced composites. Bar-shaped test specimens of highly filled fiber-reinforced composites (FRCs) and FRC of 30 vol% fiber content were made from a light-cured dimethacrylate monomer liquid (mixture of urethane dimethacrylate and triethylene glycol dimethacrylate) with silanized E-glass fibers (7, 10, 13, 16, 20, 25, 30, and 45 μm in diameter). Flexural strength and elastic modulus were measured. The flexural strength of the highly filled FRCs increased with increasing fiber diameter. In particular, the strengths of highly filled FRCs with 20-, 25-, 30-, and 45-μm-diameter fibers was significantly higher than the others (p<0.05). The flexural strength of FRC of 30 vol% fiber content increased with increasing fiber diameter, except for the FRC with 45-μm-diameter fibers; FRCs with 20-, 25-, and 30-μm-diameter fibers were significantly stronger than the others (p<0.05). Therefore, it was revealed that the diameter of glass fibers significantly affected the flexural properties of fiber-reinforced composites.

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In the diagnosis of dental occlusion, it is necessary to quantitatively measure interocclusal contacts and transfer them to a computer model. In this aspect, three-dimensional computer models of upper and lower dental casts play a significant role. In this study, we proposed a new method to measure occlusal interaction by using a microfocus X-ray CT technique. Measurement accuracy was determined as ±0.03 mm in comparison with a coordinate measuring machine. A superimposition procedure for two sets of three-dimensional dental cast models was also established. Using the same dental cast, the standard deviation between the two sets of models was ±0.015 mm—which was defined as measurement precision. Between an optical laser scanner and the microfocus X-ray CT system, the standard deviation measured between the two models was ±0.05 mm. Data were acquired when upper and lower dental casts mounted on the bite impression were scanned, and then occlusal interaction, contacts, and distance distribution between the casts were visualized by a colored map on the cast models. Within the limitations of the current study, it was successfully demonstrated that microfocus X-ray CT was well poised for quantitative measurement of occlusal interaction.

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This study sought to investigate the effects of acetic NaF solutions on titanium and Ti alloy brackets. To this end, two different brackets were immersed in various NaF-containing solutions for three days. The Equilibrium Ti (EQ) bracket was composed of Ti only, whereas the Ortho 2 (OR) bracket was composed of Ti (base) and Ti-6Al-4V (wings). Brackets that were immersed in the acetic NaF solution of pH 3.5 yielded no reliable surface microhardness values due to corrosion. In other test solutions, however, there was minimal reduction (at best 3%) in microhardness. Further on microhardness, the values of the OR bracket at the base and wings were different. On the release of elements, it was significant only in the acetic NaF solution of pH 3.5. However, the release of Al (6.11±0.93 ppm) and V (1.16±0.40 ppm) in this solution was low. In conclusion, an acetic NaF solution of low pH could damage Ti-based orthodontic brackets.

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The mechanical properties of polycarboxylate cements containing 20 mass% of four kinds of aluminoborate whiskers with different fiber lengths and diameters were evaluated. Bending strength of the cements increased with increase in fiber length, whereby the strength of the cement with the longest fiber was about two times greater than that of whisker-free cement. The diametral tensile strengths of the four fiber-reinforced cements were also about two times greater than that of whisker-free cement, but which was not dependent on fiber length. Compressive strength was the same or slightly higher than that of whisker-free cement. SEM observation of fractured specimen after diametral compression test showed high affinity between the cement matrix and the whisker.

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The purpose of this study was to evaluate the inhibition of biofilm formation on newly developed coating materials with self-cleaning properties. A series of experimental coating materials containing fluoroalkylated acrylic acid oligomer (FAAO) were applied to resin composite substrates. The surfaces of the coating materials were analyzed by X-ray photoelectron spectroscopy (XPS) and contact angle measurement. Biofilm formation on the surface was assessed using Streptococcus mutans biofilms inside an oral simulator in vitro. The results indicated that an increase in the concentration of FAAO in the coating materials enhanced surface hydrophilicity and oil-repellency. Biofilm assays demonstrated that the amount of biofilm retained on the coating materials gradually decreased when the concentration of FAAO increased in the materials. It was concluded that the coating materials incorporated with FAAO possessed self-cleaning properties and displayed signs of inhibiting biofilm formation on their surfaces.

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The adsorption behaviors of lysozyme on dentally related Au, SiO₂, and TiO₂ surfaces were investigated by a quartz crystal microbalance with dissipation monitoring (QCM-D) method. Frequency shifts indicated that while lysozyme (pI 11) was fairly adsorbed on the SiO₂ (pI 1.9) surface at both pH 3 and 7, it was adsorbed on TiO₂ (pI 6.3) surface only at pH 7. However, adsorption was disturbed by 50 mM NaCl. These results strongly suggested an electrostatic nature of the adsorption behavior. Though a large-scale adsorption of the lysozyme on Au sensor was pH-insensitive, softness of the adlayer as seen from the dissipation profile was pH-dependent, indicating an interaction of another type. With all the surfaces, the small dissipation change indicated a stiff lysozyme adlayer. Results of this study revealed that the controlled electrostatic interaction between the material surface and lysozyme might be a useful method for imparting antibacterial property to the dental materials.

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The influence of three curing modes of a high-powered LED curing unit on temperature rise under 2-mm-thick dentin was investigated during the polymerization of resin composite samples of Admira, Filtek P60, Premise, Tetric Flow, Tetric Ceram, and Filtek Z250. Ninety standard specimens were prepared. The bonding agents and resin composites were cured with standard, pulse, or soft-start mode (n=5 for each curing mode). Temperature rise was measured using a type L thermocouple. Data were analyzed by two-way ANOVA and Tukey's test. Soft-start curing led to statistically higher temperature rises compared than the other two modes. The highest temperature rise was observed for Admira and Tetric Flow cured with soft-start mode. The lowest temperature rise was observed for Premise cured with pulse mode. However, temperature rise did not reach the critical value that can cause pulpal damage by virtue of a prominent safety feature of the high-powered LED LCU, which ensures that no excessive heat is produced by all the three curing modes.

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The effect of fluoride-containing orthodontic resin bonding systems on acid resistance of adjacent enamel was evaluated using transversal microradiography.
Four fluoride-containing orthodontic resin bonding systems : BeautyOrtho Bond (BO), BeautyOrtho Bond+Salivatect (BOS), Kurasper F (KP), Transbond XT (TB) and a resin-modified glass-ionomer (Fuji Ortho LC (FO)) were used. Superbond Orthomite (SB) was used as a non-fluoride material. Rectangular bovine enamel specimens (10×6 mm) were prepared. After curing the materials, nail varnish was applied to the enamel surfaces, leaving a gap of 1 mm from the cured material's periphery. The specimens were demineralized with 8% Methocel MC gel and 0.1 M lactic acid. BO, BOS, and FO revealed shallow lesions and distinct surface layers. The mineral losses of BO, BOS, and FO were significantly lower than those of TB, KP, and SB (p<0.05). In conclusion, the new system induced superior acid resistance in enamel surrounding orthodontic brackets.

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This study evaluated the immediate effects of halogen, LED (light-emitting diode), and plasma arc curing units on microleakage of bleached enamel. The buccal and lingual enamel surfaces of experimental groups (n=30) were bleached with 16% carbamide peroxide for a period of 10 days, with a daily contact time of 90 minutes. Box-shaped Class V cavities were also prepared on 60 extracted molar teeth (n=30, control group). For all groups, a composite resin (Grandio) was bonded with one of the two employed adhesive systems, Single Bond 2 or Prime & Bond NT. After restoration, all specimens were thermocycled for 200 cycles between 5°C and 55°C with a dwell time of 60 seconds in each bath, and then exposed to a dye. In the control groups, microleakage was statistically lower than the bleached groups (p<0.01). Groups cured with QTH and PAC showed no statistical differences (p>0.05). However, groups cured with LED system showed statistically significant differences (p<0.01) in microleakage

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Although composite resin core is used with various types of prefabricated posts, it remains unclear which kind of material is most suitable for the post. The aim of this study was to evaluate the influence of prefabricated posts on the stress distribution within the root by finite element analysis. Posts and cores were built up with composite resin and four types of prefabricated posts: two types of glass fiber posts (GFP1, GFP2) with low and high Young's moduli, a titanium post (TIP), and a stainless steel post (SSP). In all models, stress distribution during function was calculated. There were differences in stress concentration at the root around the end of posts. The magnitudes of stress for GFP1, GFP2, TIP, and STP were 8.7, 9.3, 11.7, and 13.9 MPa respectively. Given the results obtained, GFP1 was the most suitable material for post fabrication since this model showed a lower stress value. It would therefore mean a lower possibility of root fracture.

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The cytotoxicity of silver is a known property of this metal. Interestingly, in the cases of argyria and tattoos, Ag remains in the tissue for a long time without causing harm to the host except pigmentation. To understand these contradictions, pure silver implantation by an original subcutaneous injection method was performed. Two sizes of silver powder particles were implanted subcutaneously: 100 nm (P-silver) and the maximum 45 μm (G-silver). The sulfuration of silver and histopathologic changes were observed for a year. Results were as follows: silver affected the host in the case of P-silver to a greater extent than in G-silver, especially on the 7^th day and after 2–4 weeks. Nonetheless, the effect of silver weakened at 12 months after implantation. The presence of P-silver caused various histological reactions, while the decline of silver effect on the host was correlated with an increase in the sulfuration of silver.

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The effects of dentin and cement thicknesses on stress level and distribution of crack propagation in ceramic-cement-dentin multilayer complex were analyzed. Custom-designed finite element analysis program based on JL Analyzer was used to analyze the stress distribution and present the maximum principal stress locations.
In Zirconia, all the maximum stress values were above 100 MPa. In Empress II, they ranged between 50 and 105 MPa, which were approximately one-third of those of Zirconia. In Feldspathic, the maximum stress values were generally lower than 50 MPa. In all groups with 30 μm cement thickness, the highest values were observed at the bottom surface. For cement thicknesses at 50, 70, and 100 μm, maximum stress was found to occur at the top surface. However, changes in dentin thickness did not bring about significant changes in maximum stress values.
Results of this study revealed the roles played by the following variables in the failure of a multilayer structure: cement thickness had a minor influence, dentin thickness exerted no influence, but the thickness and type of ceramic system played a significant role.

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With use of dental implants on the rise, there is also a tandem increase in the number of implant fracture reports. To the end of investigating the stress occurring in implants, elasticity and plasticity analyses were performed using the finite element method. The following results were obtained:
(1) With one-piece type of implants of 3.3 mm diameter, elasticity analysis showed that after applying 500 N in a 45-degree direction, stress exceeding 500 MPa—which is the proof stress of grade 4 pure titanium—occurred. This suggested the possibility of fatigue destruction due to abnormal occlusal force, such as during bruxism.
(2) With two-piece type of implants that can tolerate vertical loading of 5,000 N, plasticity analysis suggested the possibility of screw area fracture after applying 500 N in a 45-degree direction.
(3) On the combined use of an abutment and a fixture from different manufacturers, fracture destruction of even Ti-6Al-4V, which has a high degree of strength, was predicted.

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The aim of this study was to determine the effect of autoclave polymerization on the transverse strength of denture base polymers. To this end, 30 rectangular test specimens were fabricated of two heat-polymerized denture base polymers. The test groups were: (I) control, i.e., conventional water bath to polymerize resins by heat at 100°C for 30 minutes; (II) autoclave polymerization at 60°C for 30 minutes followed by 130°C for 10 minutes; and (III) autoclave polymerization at 60°C for 30 minutes followed by 130°C for 20 minutes. The specimens were tested with three-point bending test at a crosshead speed of 5 mm/min. It was revealed that the transverse strength of specimens increased with statistical significance when the autoclave was used for polymerization.

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