The influence of dynamic fatigue loading on the separate components of the bracket-cement-enamel system.

PURPOSE: To evaluate the influence of cyclic loading and type of adhesive on the shear bond strength of the bracket-cement-enamel bond. METHODS: The materials studied were: Transbond XT (a Bis-GMA resin composite cement), Fuji Ortho LC (a resin-modified glass-ionomer cement), and Fuji IX Fast (a conventional glass-ionomer cement). The shear bond strength (SBS) and the shear bond fatigue limits (SBFL) were determined after 72-hour storage in 37 degrees C water for the cement itself, the button-cement interface, the cement-enamel interface, and the bracket-cement-enamel system. The SBFL was determined with the aid of the "staircase method" at 10,000 cycles. The results were analyzed using ANOVA and Tukey HSD post hoc test (P < 0.05). RESULTS: ANOVA showed significant differences between the SBS of the materials. Fatigue was observed in all substrate combinations, with the exception for the Fuji IX Fast cement-enamel and the Fuji Ortho LC bracket-cement-enamel combinations.

The influence of different bracket base surfaces on tensile and shear bond strength.

Fracture of the bracket-cement-enamel system usually takes place between the bracket and the cement. Especially for glass ionomer-based materials, it is helpful if this part of the system can be improved. The aim of this in vitro study was to investigate the influence of different bracket base pre-treatments in relation to three different cements, Transbond XT, a resin composite, Fuji Ortho LC, a resin-modified glass ionomer cement (GIC), and Fuji IX Fast, a conventional glass ionomer cement, on shear as well as on the tensile bond strength. Upper incisor brackets with three types of base treatment, sandblasted, silicoated, and tin-plated, were bonded to bovine enamel. Untreated brackets were used as the controls. Ten specimens were tested for each group. The brackets were stored for 24 hours after bonding and tested in shear as well as in tensile mode. After fracture the remaining adhesive was scored using the adhesive remnant index (ARI). Analysis of variance was used to detect statistical differences between the bond strengths at a level of P < 0.05. Although some of the bracket pre-treatments had a statistically significant effect on bond strength, no clear improvement was measured. The ARI scores of the test groups did not show a change when compared with the control groups. The investigated base pre-treatments did not have such a beneficial influence on bond strength that improved clinical results can be expected. Improvement of the bond between bracket and cement might be found in other variables of the bracket-cement-enamel system such as the elasticity of the materials.

The influence of environmental conditions on the material properties of setting glass-ionomer cements.

OBJECTIVES: Aim of this study was to investigate the influence of temperature on the setting time and compressive strength of two conventional glass-ionomer cements (GIC's) and to determine the influence of storage medium, oil or water and storage time. MATERIALS AND METHODS: Two conventional GIC's, Ketac Molar (3 M-ESPE Dental Products, Seefeld, Germany) and Fuji IX Fast (GC Corp., Tokyo, Japan) were used to perform flow property tests and compression tests. Flow property measurements were performed using a displacement rheometer at six different temperatures. From the results of the rheometer tests, the working times and setting times could be determined. The samples for the compressive tests were stored at four different temperatures and in two different media. Testing took place at five time intervals reaching from 1 h to 3 months. RESULTS: The results of rheometer tests showed that a temperature increase speeded up the setting reaction significantly. The compressive strength results showed a jump in time as a result of the higher curing temperature but no long-term strength effect was observed. Materials curing in oil reached a significantly higher compressive strength compared to storage in water and Fuji IX Fast is significantly stronger than Ketac Molar. SIGNIFICANCE: It was concluded that a temperature between 333 and 343 K almost sets conventional GIC's on command and improves the early compressive strength.