Masahiro Kaketani

Usefulness of orthodontic adhesive-containing fluorescent dye

Orthodontic adhesive is often left on the tooth surface when a multibracket appliance is debonded, and it is difficult to remove because its colour is similar to that of the tooth. If the adhesive changed colour during debonding, residual adhesive could be more easily removed. This in vitro study evaluated the usefulness of adhesive mixed with a small amount of fluorescent dye for clinical orthodontics. Sixty-four metal brackets were bonded to flattened bovine enamel surfaces using adhesives with three concentrations (0.001, 0.002, and 0.003 per cent) of fluorescent dye, and the shear bond strength (SBS) and adhesive remnant index (ARI) scores for each adhesive were determined. Colour penetrating through the transparent bracket was measured using a colour analyser. SBS and fluorescence intensity were examined to determine the stability of the adhesives after they were subjected to a thermal cycle test (1000 cycles). For data that were normally distributed, one-way analysis of variance followed by the Student-Newman-Keuls test was used to identify significant differences among the groups. If the data were not normally distributed, the Kruskal-Wallis H-test followed by the Mann-Whitney U-test with Bonferroni correction was used. Differences in ARI were determined with the chi-square test. The SBS of the adhesive with 0.003 per cent fluorescent dye was significantly lower than that of the control (Transbond). In ARI tests, significantly more of the adhesive with 0.003 per cent dye was left on the tooth surface after 24 hours compared with the other adhesives. With regard to colour penetration, the adhesive with 0.003 per cent dye was five times more visible than to others. SBS and fluorescence intensity of the adhesives were not affected by thermal cycling. Therefore, an adhesive containing less than 0.002 per cent fluorescent dye provides both sufficient bond strength for orthodontic brackets and sufficient fluorescent colour for easy visualization without aesthetic impairment.

Castability and mechanical properties of Ti-15Mo-5Zr-3Al alloy in dental casting

The castability, mechanical properties, and fracture characteristics of Ti-15Mo-5Zr-3Al alloy were compared with those of Ti-6Al-7Nb alloy and pure titanium (CP Ti) for application of this β-type titanium alloy in cast dental prostheses. Cast specimens were prepared with a centrifugal casting machine. A tensile test was performed according to ISO standard 22674. The castability index for Ti-15Mo-5Zr-3Al was lower than those for Ti-6Al-7Nb and CP Ti. The tensile strength of Ti-15Mo-5Zr-3Al was 852 MPa, which was lower than that of Ti-6Al-7Nb and higher than that of CP Ti. The proof strength of Ti-15Mo-5Zr-3Al was 799 MPa, which was comparable to that of Ti-6Al-7Nb and higher than that of CP Ti. The elastic modulus of Ti-15Mo-5Zr-3Al was 81.0 GPa, which was lower than the values for Ti-6Al-7Nb and CP Ti. Elongation of Ti-15Mo-5Zr-3Al was 5.1%, which was comparable to that of Ti-6Al-7Nb and less than that of CP Ti. The shape of the fractured segment was narrower for Ti-15Mo-5Zr-3Al than for Ti-6Al-7Nb and CP Ti. The deformation characteristics of Ti-15Mo-5Zr-3Al may result in decreased stress relative to increased strain during plastic deformation in the stress-strain diagram. In conclusion, Ti-15Mo-5Zr-3Al alloy has a low elastic modulus and exhibits limited ductile plastic deformation in cast dental prostheses.

Surface porosity of stone casts resulting from immersion of addition silicone rubber impressions in disinfectant solutions.

This study investigated the effects of immersion of addition silicone rubber impressions in disinfectant solutions on the surface porosity of the resulting stone casts. Five brands of type 2 and 3 addition silicone rubber impression materials and one brand of type 4 dental stone were used. Impressions of a master die designed to simulate an abutment tooth were immersed in disinfectant for 30 minutes. The disinfectants used were 2% glutaraldehyde solution and 0.55% ortho-phthalaldehyde solution. The surface porosities of stone casts obtained from two brands of impression materials immersed in disinfectant for 30 minutes were determined. Results suggest that impression materials immersed in disinfectant solutions need sufficient time before pouring into dental stone.

[Adaptability of post core constructed by die-investing technique. Comparison in adaptability with post core constructed by die-pattern technique].

A comparative study was made on the adaptability of the post core made by the dieinvesting technique and that of the post core made by the die-pattern technique. As a results, the following conclusions were obtained.1. Vertical adaptability: As for the rising of the post at the apical portion, the die-pattern technique was found to cause a bigger rise. In other words, the length of the post tended to shorten when die-pattern technique was used. On the other hand, as for the rising of the post at the root-surface portion, no significant difference was noted between the two techniques.2. Horizontal adaptability: As for the gap between the post and the wall at the apical portions, the die-pattern technique tended to enlarge the gap. On the other hand, as for the gap between the post and the wall at the root-surface portion, no significant difference was noted between techniques.