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Physical Properties and Toxic Potential of Dental Composites Containing a Triazole-monomer

Torbjørn Knarvang, Hilde M. Kopperud and Jan T. Samuelsen
Nordic Institute of Dental Materials, Oslo, Norway
tok@niom.no

INTRODUCTION
Resin-based restorative materials are widely used in dentistry. In general, the resin part of these materials consists of a mixture of methacrylate monomers that are polymerized in situ with a in a blue light initiated free-radical polymerization . The polymerization process never reaches completion, and unpolymerized monomer may be released after curing. The resin composition is a parameter influencing polymerization (degree of conversion; DC), material properties and toxic potential.

2-[3-(2H-Benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate (UV090) is a mono-methacrylate monomer used in several commercial materials such as contact lenses and as an UV-absorbant in in polymer industry. It has also been used in small amounts in resin-based filling materials. In this study we aim to characterize the physical properties and toxic potential of resin-based dental composites containing different amounts of the Triazole-monomer.

EXPERIMENTAL METHODS
Experimental dental composites containing 70 % inorganic filler, 12.5-15.0 % bisphenol A glycidyl methacrylate (BisGMA), 12.5-15.0 % triethylene glycol dimethacrylate (TEGDMA), 0-5 % Triazol-monomer and initiator components were prepared. The composites (2 mm thick) were cured for 20 seconds using blue light irradiation before the tests.

The degree of conversion (DC) was determined by FT-IR and ATR-method directly after irradiation and after 3 hrs. Flexural strength was determined according to ISO 40491 with a Lloyds LRX testing machine. Leakage of unreacted monomer was measured in extracts from cured specimens incubated for 24 h in ethanol/water (75/25 vol/vol) at 37 °C using gas- chromatography.

Fig 2. Leakage of unreacted TEGDMA and Triazol-monomer in a mixture of vol.75/25 etanol/water measured after 24h with gas-chromatography

The toxic potential of Triazole-monomer was determined by the MTT test (ISO 10993-52).

RESULTS AND DISCUSSON
Decreased flexural strength was observed as (figure 1). That caused by the formation of a less complete polymer network using the mono-methacrylate.

There were no differences in DC (78 % at 3 h) with different Triazole-monomer contents in the composites. This may be due to the relatively small amounts of the Triazole-monomer (0-5%) in the composites.

The MTT test yields a relative number of living cells showed a dose-dependent decrease of viability in the L929 cells. Both cell death and decreased cell growth may be the cause of this finding. HEMA a widely used monomer in dental composites showed the same level of toxcity as the Triazole-monomer( 200μM ) at 50 times higher concentration. Use of flow cytometeri indicated an accumulation in the G1-cell cycle phase Figure 3 Viability measured with MTT. Increasing amount of Triazole-monomer in test-solution reduced the cell viability

Fig 3. Viability measured with MTT. Increasing amount of Trizole- monomer in test-solution reduced the cell viability

CONCLUSION
•Addition of theTriazole-monomer to the resin reduced the flexural strength of the composite
•The Triazole-monomer is released from cured composites
•The Triazole-monomer has a toxic potential in vitro

In summary, this study showed that increased amounts of the Triazole-monomer negatively influenced the measured properties of the experimental composites.

REFERENCES
1. ISO 4049:2009 Dentistry – Polymer-based restorative materials. International Organization for Standardization, Geneva, 2009.
2. ISO 10993-5:2009 Biological evaluation of medical devices — Part 5: Tests for in vitro cytotoxicity. International Organization for Standardization, Geneva, 2009.
ACKNOWLEDGMENTS
The authors would like to thank Anne Wesmann and Hanne Wellendorf for excellent technical assistance.