Wataru Komada

Dentin bonding durability of two-step self-etch adhesives with improved of degree of conversion of adhesive resins

PURPOSE To evaluate (1) the initial and long-term microtensile bond strengths of two-step self-etch adhesives with different degrees of conversion (DC); (2) the elastic modulus of the respective adhesive resins; (3) the water sorption of the respective adhesive resins. MATERIALS AND METHODS Two two-step self-etch adhesives, Clearfil SE Bond (CSE) and Clearfil SE Bond 2 (CSE2) were used in this study. The DC was determined using ATR/FT-IR with a time-based spectrum analysis. Midcoronal flat dentin surfaces of 24 human molars were prepared with 600-grit SiC paper for microtensile bond strength (µTBS) testing. CSE and CSE2 were applied to the dentin surfaces according to the manufacturers instructions, followed by composite buildups. The µTBS was measured after water storage for 24 h, 6 months, and 1 year. The elastic modulus (before and after 1 month of water immersion) was determined by the three-point flexural bending test and water sorption values by the water sorption test. RESULTS CSE2 showed significantly higher DC than CSE. The µTBS of CSE2 was significantly higher than that of CSE in all water storage periods. One-year water storage decreased the µTBS of CSE; however, it did not decrease that of CSE2. Regarding the polymerized adhesive resins, the elastic modulus of CSE2 was significantly higher than that of CSE before and after water immersion (p < 0.001), and the water sorption of CSE was higher than that of CSE2. CONCLUSIONS The higher DC of adhesive resins of two-step self-etch adhesives resists water aging and improves the initial bond strengths and durability of the resin-dentin bond.

Influence of water immersion on the mechanical properties of fiber posts

PURPOSE The purpose of this study was to evaluate the influence of water immersion on the mechanical properties of three kinds of glass fiber posts and the fracture resistance of structures using resin composites with glass fiber posts. METHODS Each post was divided into three groups; a control group and two water immersion groups (30 and 90 days). Flexural strength was determined by three-point bending test. Each structure was divided into two groups; a control group and a water immersion group for 30 days. The fracture strength of structures was determined by a static loading test. RESULTS In the flexural strength, two kinds of post in water immersion groups showed lower values than control groups. In the fracture strength, two kinds of structures in water immersion group showed lower values than control groups. CONCLUSION The prefabricated glass fiber posts and structures using resin composites with glass fiber posts were affected by water immersion.

The effect of glass fiber posts and ribbons on the fracture strength of teeth with flared root canals restored using composite resin post and cores

PURPOSE This study evaluated the fracture strength and mode of failure of structurally compromised teeth with flared root canals restored using composite resin with four different systems. METHODS Sixty endodontically treated bovine teeth were uniformly shaped to simulate human mandibular premolars with flared root canals. The roots were divided into four groups of 15 specimens each based on the type of restoration: composite resin core only (control), glass fiber post, cylindroid glass fiber ribbons, and glass fiber post and ribbons. All specimens were loaded until fracture occurred using a universal testing machine. Average fracture loads were compared with a one-way ANOVA and Tukey HSD test (α=.05). The modes of failure were observed and the Fisher exact test and Bonferroni correction were used for statistical analysis. RESULTS The fiber post and ribbon group (1035.70N) and the fiber ribbon group (881.77N) showed significantly higher fracture strength than the controls (567.97N) (p<.05). The fiber post and ribbon group also showed significantly higher fracture strength than the fiber post group (769.40N). Almost all specimens showed unrestorable root fractures (p<.008). The control group had a significantly higher ratio of core sectional fractures (p<.017). CONCLUSIONS Cylindroid glass fiber ribbons significantly increased the fracture strength of the composite resin post and cores in the case of the dentin within the thin root canal wall. Based on the results, this study recommends the combined use of glass fiber post and ribbons.

The effects of post and core material combination on the surface strain of the 4-unit zirconia fixed partial denture margins

The suitability of various post and core materials for the 4-unit zirconia fixed partial denture abutment teeth was investigated to lower stress concentration. Artificial mandibular teeth (44 and 47) were used as the abutment teeth. There were two types of posts and cores: resin composite with glass fiber posts (RC), and cast platinum gold alloy (MC). Two experimental groups were analyzed. For Group RM, the premolars were restored with RC and the molars were restored with MC. For Group MR, the premolars were restored with MC and the molars were restored with RC. Static loading was applied to the occlusal surfaces, and the surface strain of the frameworks and roots was measured with a strain gauge. Group RM had a greater number of statistical differences between premolars and molars compared to Group MR. This result suggests that the Group MR post and core material combination reduces stress concentration.