Pekka Vallittu

Synthesis of antibacterial and radio-opaque dimethacrylate monomers and their potential application in dental resin

OBJECTIVE In this study, three dimethacrylate quaternary ammonium compounds N,N-bis[2-(3-(methacryloyloxy)propanamido)ethyl]-N-methyldodecyl ammonium iodide (QADMAI-12), N,N-bis[2-(3-(methacryloyloxy)propanamido)ethyl]-N-methylhexadecyl-ammonium iodide (QADMAI-16), and N,N-bis[2-(3-(methacryloyloxy)propanamido)ethyl]-N-methyloctadectyl ammonium iodide (QADMAI-18) were synthesized and proposed to be used as antibacterial and radio-opaque agents in dental resin. METHODS All QADMAIs were synthesized through a 2-steps reaction route, and their structures were confirmed by FT-IR and 1H NMR spectra. Antibacterial activities against Streptococcus mutans (S. mutans) of QADMAIs were measured by agar diffusion test. Each QADMAI was mixed with TEGDMA (50/50, w/w) and photoinitiation system (0.7 wt% of CQ and 0.7 wt% of DMAEMA) to form resin system. Degree of monomer conversion (DC) was determined by FT-IR analysis. The flexural strength (FS) and modulus (FM) of the polymer were measured using a three-point bending set up. Radiograph was taken to determine the radio-opacity of the polymer, and aluminum step-wedge (0.5-4 mm) was used as calibration standard. Surface charge density was measured using fluorescein binding. A single-species biofilm model with S. mutans as the tests organism was used to evaluate the antibacterial property of the polymer. Bis-GMA/TEGDMA resin system was used as control material in all of the tests. RESULTS FT-IR and 1H NMR spectra showed that the structures of QADMAIs were the same as designed. ANOVA analysis revealed that antibacterial activity of QADMAI decreased with the increasing of alkyl chain length (p<0.05). QADMAI containing polymers had higher DC (p<0.05) but lower FS and FM (p<0.05) than control polymer. Alkyl chain length had no influence on DC (p>0.05), but FS and FM of QADMAI-12 containing polymer were better than those of QADMAI-16 and QADMAI-18 containing polymers (p<0.05). QADMAI containing polymers had much better radio-opacity than control polymer (p<0.05), and the radio-opacity of polymer decreased with the increasing of alkyl chain length (p<0.05). All of QADMAIs containing polymers had higher surface charge density than control polymer (p<0.05), and surface charge densities of QADMAI-12 and QADMAI-16 containing polymers were nearly the same (p>0.05) which were higher than that of QADMAI-18 containing polymer (p<0.05). All of QADMAI containing polymers had good inhibitory effect on biofilm formation. SIGNIFICANCE QADMAIs had no miscibility problem with TEGDMA, and QADMAIs could endow dental resin with both antibacterial activity and radio-opacity. Formulation of QADMAI containing resin should be optimized in terms of mechanical stregth to satisfy the requirements of dental resin for clinical application.

Polymer Composites for Bone Reconstruction

The need for reconstructive surgery of bones is continuously increasing along with the ageing of the population as well as the increase of traumatologic injuries. In the United States, the number of bone grafts was 350,000 in 2001. Nowadays, over 500,000 bone graft procedures are performed annually, and approximately 2.2 million worldwide (Giannoudis et al., 2005). The estimated cost of these procedures approaches US

Dental and medical polymer composites and compositions

2.5 billion per year. Hence, the considerable demand for these replacement procedures cannot be met solely by using donor material. Therefore, superior synthetic orthopaedic materials and techniques should be available on the market for clinical practice. Adjustable porosity, bioactivity, identical biomechanics, as well as all the other tissue-friendly properties to bone are central for achieving a durable, bonding-like, interface between the synthetic material and bone (Aho et al., 2004). Actually, modern material technology would have all the know-how for preparing excellent synthetic orthopaedic materials. Autografts are still regarded as optimal reconstruction material, because of the lack of good enough synthetic materials. However, in orthopaedics, the demands for synthetic materials could be fulfilled by using composite structures. In fact, it is possible to mimic better the structures of living materials, like bone, cartilage or teeth using composite structures. Therefore, there is still a constant need to search for better synthetic bone substitute materials for tissue engineering (Chung et al., 2007).