Effects of different storage media on dentin moisture, microhardness, and bond strength of resin composite

Background

In in vitro studies, it is desirable that the storage solutions in which dental samples kept between extraction and experiment should prevent dehydration and have antimicrobial properties. However, it should be taken into consideration that these solutions may have some effects that directly change test results on physical and mechanical properties of laboratory samples.

Aims

The aim of this in vitro study was to evaluate the effects of different storage media on dentin moisture, microhardness, and microshear bond strength of resin composite to dentin. Thirty non-carious human premolars were randomly divided into three groups: 1. 0.1% Thymol (T), 2. Distilled water (DW), 3. Dry storage (DS) (control) (n = 10). Dentin moisture was measured with a digital grain moisture meter. Dentin microhardness was measured with the Vickers test. The bond strength was measured with a microshear test.

Materials and Methods

Analysis of variance (ANOVA) followed by the Bonferroni test was used for statistical evaluation (p = 0.05).

Results

Dentin moisture of the experimental groups was statistically higher than that of the control group (p < 0.05). In addition, the dentin moisture of group DW was significantly higher than that of group T (p < 0.05). The mean microshear bond strength of resin composite to dentin was higher in group DW than in group T and group DS (p < 0.05), while there was no statistical difference between group T and group DS. The microhardness values of all groups were statistically similar.

Conclusions

Storage solutions used for disinfection and to prevent dehydration may have negative effects on dentin moisture and bond strength.

Effect of Surface Moisture on Bur-cut Dentin on Bonding of HEMA-free and HEMA-containing Universal Adhesives with or without Methacrylamide Monomer

PURPOSE

The effect of surface moisture on bur-cut dentin on the microtensile bond strength (μTBS) of universal adhesives with various contents of 2-hydroxyethyl methacrylate (HEMA) and methacrylamide monomers was evaluated.

MATERIALS AND METHODS

Flat mid-coronal dentin surfaces of human molars were exposed, and a standardized smear layer was prepared using a fine-grit diamond bur. The surfaces were either left wet or air dried for 10 s before bonding with Clearfil Universal Bond Quick (UBQ), experimental UBQ without an amide monomer (UBQexp), Scotchbond Universal (SBU), Prime&Bond Universal (PBU), or BeautiBond Universal (BBU). The specimens were built up with resin composite, sectioned into sticks and subjected to the μTBS test after 24 h or 10,000 thermal cycles. The μTBS data were analyzed using three-way ANOVA followed by pairwise comparisons with Bonferroni's correction (α = 0.05).

RESULTS

The level of dentin moisture did not significantly affect μTBS of UBQ and BBU (p > 0.05). HEMA-containing UBQ, UBQexp, and SBU exhibited higher μTBS to dry dentin, while HEMA-free PBU and BBU showed higher μTBS to wet dentin. Thermocycling significantly decreased the μTBS of UBQexp (p < 0.01) and BBU (p < 0.001) irrespective of dentin moisture level, while SBU was significantly affected only on dry dentin (p < 0.001). Thermocycling had no significant effect on UBQ and PBU containing methacrylamide monomers (p > 0.05).

CONCLUSION

Dry surfaces enabled obtaining optimal bonding for HEMA-containing adhesives to bur-cut dentin, while wet surfaces enabled optimal bonding for HEMA-free adhesives. Methacrylamide monomers could contribute to the improvement of the initial and long-term bonding performance of universal adhesives to bur-cut dentin.

[The results of computer simulation of the dentinal fluid hydrodynamics in the open crown dentinal tubule]

OBJECTIVE

To study the hydrodynamics of the dentinal fluid along the dentinal tubule in the event of its opening as a result of mechanical and acid treatment of the dental crown dentin. Material and methods: A licensed version of the ANSYS / FLOTRAN computer program was used, which is a software tool for solving various problems of hydrodynamics, including laminar and turbulent flow of an incompressible or compressible fluid.

RESULTS

The results of computer simulation showed that 1.5 ms after drying of the dentin tubule (length 6 mm) it is refilled with dentin fluid, which then begins to accumulate on the treated surface of the dental hard tissues. Reducing the length of the dentinal tubule as a result of the cavity preparation leads to an increase in the speed and mass of pulp fluid released through it.