In vitro evaluation of shear bond strength of nanocomposites to dentin

In-vitro evaluation of the shear bond strength and fluoride release of a new bioactive dental composite material

BACKGROUND

The aim of this study was (1) to determine and compare the shear bond strength (SBS) of a bioactive composite "Activa Bioactive Restorative" with and without bonding agent and a nanocomposite "Filtek Z350 XT/Z350" and (2) to measure and compare the amount of fluoride release from a bioactive composite "Activa Bioactive Restorative" and a glass ionomer "Equia forte".

MATERIAL AND METHODS

Forty two dentin surfaces from freshly extracted human molars were prepared for shear bond strength testing. The specimens were randomly divided into three equal groups. The restorative materials were applied to all dentin surfaces according to the manufacturer's instructions, using a special jig (Ultradent) in the following manner : Group 1 (Activa Bioactive Restorative with adhesive), Group 2 (Activa Bioactive Restorative without adhesive) and Group 3 (Filtek Z350 XT/Z350). The bonded specimens were subjected to thermocycling in 5°C and 55°C water baths then tested for SBS in a universal testing machine (1 mm/minute). Kolmogorov-Smirnov and Levene tests were used to evaluate the distribution of the variable and the equality of variances respectively and a Student's T- test was applied to compare the mean strength between the groups. In the next test, thirty disc shaped specimens were fabricated using Activa BioActive restorative and Equia Forte; 15 specimens from each material. The specimens of each group were immersed separately in 5 ml of deionized water. Fluoride release was measured daily throughout 15 days using a fluoride-specific ion electrode and an ion-analyzer. Repeated measures analysis of variance with one within-subject factor (time) and one between-subject factor (Activa Bioactive / Equia Forte) was applied to compare the amount of released fluoride between groups and within time. It was followed by univariate analyses and Bonferroni multiple comparisons tests.

RESULTS

The mean shear bond strength of Activa Bioactive Restorative with adhesive was found to be 17.379 (± 8.5043) MPa and 19.443(± 8.3293) MPa for the Filtek Z350 XT/Z350 group. There was no significant difference between both groups. Regarding fluoride release, the amount of Fluoride released was significantly greater in the Equia Forte group compared to the Activa Bioactive group (-p-value<0.05). The mean amount of Fluoride has significantly decreased over time with Activa Bioactive group (-p-value<0.001); it showed the highest fluoride release during the first 24 hours post-setting. Also in the Equia Forte group, the mean amount of Fluoride release showed a progressive and significant decrease over time (-p-value<0.001), although the amount of Fluoride released was significantly greater in the Equia Forte group compared to the Activa Bioactive group (-p-value<0.05).

CONCLUSIONS

Activa Bioactive Restorative with adhesive and a nanocomposite showed similar bond strengths. Activa Bioactive Restorative doesn't have the self-adhesive property. The fluoride ion release profile of Activa was lower than that of the Equia Forte. Key words:Bioactive composite, nanocomposite, glass ionomer, fluoride release, shear bond strength, thermocycling.

Analysis of micro-shear bond strength of self-etch adhesive systems with dentine: An in vitro study

BACKGROUND

Success or failure of a composite restoration largely depends on its bonding to enamel/dentine. Several better adhesive systems have been developed during the last few years due to rapid advancement in the technology. Recent self-etched adhesives have fewer clinical steps and are less technique sensitive.

METHODS

Ninety extracted human permanent molars were collected, grounded and finished to prepare flat dentine-bonding surfaces on their occlusal surface. All specimens were divided into three groups (n = 30) on the basis of three adhesive systems Adper Easy Bond (AE), Beautibond (BB) and Xeno IV (XE). These adhesive systems were applied on prepared mid-dentine-bonding surface. A restorative resin was added with the help of a transparent tube of 2 mm height and 1.7 mm internal diameter and cured. Fifteen specimens in each group were loaded to failure in an Instron Universal Testing Machine after storage for 24 h at 37 °C to check micro-shear bond strength. Another fifteen specimens from each group were thermocycled 500 times at 5 °C and 55 °C with dwell time of 1 min in each bath followed by loading to failure. The data obtained was analyzed with SPSS version 21 at significance level of <05.

RESULTS

After 24 h, micro-shear bond strength of BB was higher (26.04 MPa) than XE (23.69 MPa) and AE (21.50 MPa). After thermocycling, micro-shear bond strength decreased significantly in BB (P = .001) and XE (P = .03).

CONCLUSION

The micro-shear bond strength of BB was highest among three groups, which decreased after thermocycling.