Application of nanotechnology in pediatric dentistry

BACKGROUND: The aim of this work was to study and pro- duce a dental adhesive with antibacterial properties through the use of micro and nanometric fillers based on graphene. METHODS: Graphene is the name given to a flat monolayer of carbon atoms tightly packed into a two-dimensional (2D) honeycomb lattice, and is a basic building block for graphitic materials of all other dimensionalities. It is extremely durable and hard (100 times more than steel), transparent and flexible. In addition, it present, at room temperature, an electrical conductivity superior to any other sub- stance and in recent years he has shown raised interest also in the biomedical field. In the present study it was developed and produced an den- tin/enamel adhesive with antibacterial properties thanks to the introduction of the graphene nanoplatelets (GNP) used as filler, starting from a common commercial adhesive used in dentistry and its widely-known properties. The GNP have been made from expanded graphite (EG), which in turn was produced from graphite intercalation compounds via rapid evaporation of the intercalant at elevated temperatures. The GNP thus obtained, have been incorporated into the commercial adhesive with the technique of solution processing. Antibacterial tests were carried out treating our experimental adhesive with bacterial strains of Streptococcus mutans. The antimicrobic effects of the adhesive were analyzed at both zero time 0 and after aging (1 week). Furthermore, tests of resistance to microtensile were carried out. RESULTS: Tests have shown that GNP present toxicity on microorganisms, thanks to mechanic interaction by wrapping and trapping bacteria. Furthermore, they show also an antibiofilm effect causing fractures in the structure of the same biofilm. The produced material shows a high efficacy the first days of application in which the bacteria mortality was detected by 100% and then the stoppage of biofilm growth. After the aging of the material concordant results were obtained, with a slight decrease of bacteria mortality as the hours passed. The mechanical tests analysis, in order to study the binding strength in the adhesive by GNP introduction, has shown a value by 29,1 MPa, slightly inferior to the value shown by the corresponding commercial adhesive. The given testing value is anyway included within the average of values referred to dental adhesives currently on the market. CONCLUSIONS: The undertook study permitted to develop an enamel dentinal adhesive with innovative antimicrobic properties. The main component of such properties is GNP, which has shown also a high biocompatibility on both human and animal cells. By analyzing bacterial cells in suspension by the method of Colony Forming Units (CFU), it was observed that GNP not only have toxicity on single cells, but also an antibiofilm effect interfering with the vital cycle of the same, thus inhibiting its development. Mechanical tests have shown excellent characteristics of the experimental adhesive so much that it can be considered virtually competitive.