Recently, the use of adhesive resin cements and resin core materials has been increasing due to the need for core build-up after root canal treatment. The possibility of polymerization inhibition by a zinc oxide eugenol cement (ZOE) has been reported for methacrylate-containing resin materials. The purpose of the present study was to investigate the effects of ZOE on the surface hardness of resin materials in contact with ZOE and on the pull-out strength of the core build-up resin composite. Canals, Canal Sealer Normal and Canal Sealer Quick were used as ZOE sealers. Canals N was used as a Non-ZOE as a control. Clearfil DC Core and UniFil Core EM were used for the resin composites for core build-up. Super-Bond C&B and ResiCem were used as adhesive resin cements. Brinell hardness was measured to evaluate the degree of polymerization inhibition of resin surfaces in contact with ZOE after 24 hours and at the start of hardening. The conditions with and without light curing were also tested. The pull-out test was performed to evaluate the dentin bond strength of the resin fiber posts in human root canals. The following results were obtained: 1. After complete setting of ZOE cement sealers (after 24 hours), light activation of resin materials for core build-up showed no changes in hardness of resin surfaces. 2. By using a ZOE sealer with rapid setting time, the influence of light activation of resin materials on hardness at the initial setting time (10 or 60 minutes) of a ZOE cement sealer was slightly decreased. 3. No changes in hardness were detected with Super-Bond C&B and ResiCem because polymerization conceivably proceeded by the ionic mechanism and not by the radical mechanism. 4. No decrease in pull-out bond strengths was observed for all the sealers tested. It was suggested that ZOE root canal sealers can be applied in combination with resins for core build-up.

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Tooth wear is a worldwide multifactorial experience and is usually caused by a combination of erosion, attrition and abrasion. The mechanism of the tooth wear of enamel is complex and many studies have been conducted to clarify this combined phenomenon. However, it is difficult to determine the clinical causes of tooth wear. The purpose of this in vitro study was to measure the interaction of attrition and erosion of bovine enamel under several different acidic conditions. Seventy-two bovine enamel specimens were randomly divided into nine groups that served as specimens for the impacting-sliding wear test. After completion of the wear cycle, the tooth wear loss and surface texture were measured using scanning 3D laser microscopy. The wear loss and surface roughness of enamel after the impacting-sliding wear test differed among the materials used, depending on their chemical components and pH concentration. The correlation between the wear loss and surface roughness was significant. The frequency of acidic drinks and foods and how they are consumed may be important in clinical management.

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Passive ultrasonic irrigation (PUI) is used to reduce bacteria within the root canal. Although biophysical forces such as microstreaming and cavitation may play an important role in PUI, the details of these mechanisms have not been elucidated. The aim of this study was to clarify the involvement of biophysical forces for PUI using a high-speed camera. Files of different sizes (#15, #20, #25, #30, and #35) were immersed in free water, and the displacement amplitude of the oscillating files was measured under different ultrasonic intensities. In addition, the cavitation bubbles around the files were observed, and the fluid flow in the apical region was evaluated using glass-bead tracers. Thinner ultrasonic file and higher ultrasonic power resulted in a higher amplitude of the oscillating file in free water. Cavitation bubbles were observed only around the tip and anti-node of a vibrating file in a simulated canal. Active fluid flow was found within a region of approx. 1 mm under the file tip. When the file was placed 5 mm short of the bottom, the fluid flow was relatively slow in the apical region even at a high power. In conclusion, ultrasonic activation of the irrigant using a thin file that is set at a near-apical position at low ultrasonic intensity might be recommended for effective PUI.

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Experimental approaches for measuring adhesive bond strengths in dentistry have consisted primarily of tensile or shear bond-strength determinations performed within a defined area. Although the testing procedures used appear to be similar, the results have differed widely among studies. The purpose of this study was to investigate the influence of the bonded surface area and the crosshead speed on the tensile bond strengths of self-etch adhesives to bovine dentin. The dentin bonding systems employed in this study were Clearfil Mega Bond (Kuraray Medical) and Clearfil tri-S Bond (Kuraray Medical). Bovine mandibular incisors were mounted in self-curing resin and wet-ground with #600-grit silicon carbide paper to expose labial dentin. Adhesives were applied and resin composites were condensed into a mold (2.4 or 4.0 mm in internal diameter) on the dentin and light irradiated. The finished specimens were transferred to distilled water, and stored at 37℃ for 24 h. Ten specimens per group were tested in tensile mode in a universal testing machine (Type 5500R, Instron) at crosshead speeds of 0.1, 0.5, 1.0, 5.0, and 10.0 mm/min. Two-way ANOVA and Tukey's HSD test (α=0.05) were performed for each adhesive system. The results showed that dentin bond strength increased with increase in crosshead speed. On the other hand, bond strength increased with decrease in bonded area. Thus, a higher crosshead speed was associated with a higher dentin bond strength. This relationship was for specimens with smaller dentin bonded surface area.

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The purpose of this study was to investigate the toxicity of hypochlorous-acid electrolyzed water (HEW) against host cell and alkaline phosphatase (ALP) activity. HEW is a neutral (pH 7.2) solution that contains 650 ppm effective chloride. HEW is produced by electro-disintegration of carbonic acid and NaCl solutions. The bactericidal activity of HEW has been attributed to the superoxide anion and HClO. The cytotoxic activity of HEW and NaOCl solution against human pulp cells (HPC), human periodontal ligament cells (HPDL), polymorphonuclear cells (PMNs) and a three-dimensional (3D) human epithelial tissue model was evaluated by MTT assay. HPC, HPDL and PMNs were placed on culture plates and were treated with various concentrations of HEW or NaOCl solution. The cytotoxicity of both the HEW and NaOCl solutions emerged in both a time-dependent and dose-dependent manner. HEW showed much lower cytotoxicity than the NaOCl solution. We investigated the effect of these agents on the ALP activity of HPC, using an ALP assay kit. Although both HEW and NaOCl inhibited ALP activity, the inhibitory effect of HEW was much less than that of NaOCl. In a 3D human epithelial tissue model, only the NaOCl solution showed significant cytotoxicity. These results suggest that HEW, which shows much less cytotoxicity than NaOCl, could be useful as a root canal irrigant.

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The purpose of this study was to evaluate the adaptability of matched-taper single points to curved root canals prepared in different apical sizes using Endowave™ NiTi instruments. Nine simulated curved canals in clear resin blocks were prepared using Endowave™ rotary instruments (0.06 taper) to sizes of #30, #35 or #40. Each specimen was then filled using a matched-taper gutta-percha cone and sealer. All specimens were sectioned horizontally at 1 to 5 mm intervals from the apex. The percentage of the gutta-percha-filled area (PGP) and the thickness of sealer (TS) were measured. Data were analyzed and compared using ANOVA-tests (p<0.05). The lowest PGP was present at the 1 mm level from the apex in the #40 group. The PGP of the #40 group was lower than other groups at the 1, 2, 3, and 4 mm levels, and increased towards the coronal levels. A high PGP was showed at the 5 mm level in all groups. In the #40 group, significant differences in PGP were found between 1 mm level and other levels, and between 2 mm level and 3, 4 and 5 mm levels. In the #35 group, PGP exhibited a significant difference between 1 mm level and 3, 4 and 5 mm levels (p<0.05). Significant PGP differences were also found between the #30 and #40 groups in all levels, between the #30 and #35 groups at the 1, 4, and 5 mm levels and between the #35 and #40 groups at the 1 mm level. Significant TS differences were found between the #30 and #40 groups and between the #35 and #40 groups at the 1 mm level; between the #30 and #40 groups at the 2 mm level; between the #30 and #35 groups and between the #30 and #40 groups at the 4 and 5 mm levels (p<0.05). The TS in size #40 decreased towards the coronal levels. The results suggest that the adaptability of a single gutta-percha point to curved root canals prepared using Endowave™ was adversely affected by large root canal enlargement and in the vicinity of the root apex.

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The purpose of this study was to examine the effect of dynamic load on adhesion of hybrid ceramic onlay restoration. Standardized MODB cavities were prepared for 32 extracted human lower molars. The cavities were coated with dentin using an all-in-one adhesive system, and impressions of cavities were taken with a silicon rubber impression material. A die stone was poured and hybrid ceramics onlays were made on the working stone model. The cavities were restored by onlays using adhesive luting cement. Specimens were divided into two groups and following tests (n=16) were performed, dynamic load stress condition (+; 300,000 repeated load stress of 16.0 kgf), control condition (-; non stress). The micro-tensile bond strength (μ-TBS) to the pulpal wall (P) and axial wall (A) was measured. The data were examined using two-way ANOVA. Student's t-test and Weibull analysis. The μ-TBS of P(+)/P(-)/A(+)/A(-) conditions was 7.94 (2.20)/10.53 (1.60)/9.56 (2.16)/10.12 (2.44) MPa. The μ-TBS of P(+) was significantly smaller than P(-) (p<0.01), and the μ-TBS of A(+) was similar to those of A(-). The μ-TBS of P(-) was similar to those of A(-), but the μ-TBS of P(+) was significantly lower than that of A (+) (p<0.05). The Weibull modulus of P(+)/P(-)/A(+) /A(-) conditions was 4.03/7.39/4.73/4.37, and the modulus decreased in response to a dynamic load stress at P (p<0.01). The Weibull modulus of P(-) was significantly smaller than A(-) (p<0.01), and the Weibull modulus of P(+) was similar to those of A(+). The effect of dynamic load varied in response to the cavity wall. Both the μ-TBS and adhesive reliability had decreased statistically at P, but not recognized at A. Under the (-) condition, the μ-TBS of P was similar to those of A, and the reliability of P was superior to those of A, but dynamic load stress reversed the inclination.

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