Found in mussels’ adhesive protein, this biocompatible compound could be used as a dental adhesive to strengthen the bond between tooth tissues and the resin used for dental filling.
Dental fillings are widely used to “fill” an area of tooth removed due to decay and to repair cracked or broken teeth. The durability of these fillings depends on the longevity and stability of the bond between the compound (resin) and the hard tissues of the tooth (dentin). Now, researchers from the Faculty of Dentistry, the University of Hong Kong (HKU), Wuhan University (WHU), and the Peking University Shenzhen Hospital have discovered that a compound derived from mussels can boost the durability of dental filling by strengthening the resin-dentin bond, potentially advancing future developments of dental filling.
Generally, the first step of dental filling procedures involves the removal of the decayed tooth structure and filling the cavity with a tooth-coloured restoration with the help of a dental adhesive. As its name suggests, the dental adhesive serves to glue the filling to the tooth structure. However, the durability of this bond can be compromised by humidity inside the oral cavity and repeated mechanical stress caused by chewing, among many other factors. Consequently, patients need to frequently replace dental fillings, which come at extra costs.
In search of a solution, the researchers looked into mussels. The wet adhesive properties of mussels have long intrigued the scientific community as they could potentially be harnessed for valuable bio-applications like developing bio-adhesives. In particular, scientists have been investigating the interaction between mussel plaques and substrates under humid environments.
“Mussels need to maintain their adhesiveness under harsh marine environments, including humidity, drastic change of water temperature and pH value, sudden shocks and so on. These are similar to the daily activities that happen in the oral cavity. Our research aimed to understand the adhesive properties of the compounds from mussels, which may improve the durability and longevity of dental fillings,” explained Professor Cynthia Kar Yung Yiu, Clinical Professor in Paediatric Dentistry of HKU who led the research team.
Through their investigation, the researchers determined that the wet adhesive property of mussels is attributed to the amino acid Dopa secreted by these shellfish. These results led the team to apply N-(3,4-dihydroxyphenethyl)methacrylamide (DMA), a mussel-derived compound, as a dental adhesive. To assess the durability of this new DMA dental adhesive, the researchers compared the DMA bond with that of a normal resin-dentin interface.
A control group and those with distinct concentrations of DMA were subjected to a series of tests including thermocycling ageing, which involves exposing dental materials to varying temperatures. Following the international standard for testing dental adhesives, the researchers exposed the test specimens repeatedly in 5°C cold water and then in 55°C hot water for many cycles, which invariably decreased adhesive strength. Then, the team leveraged the nanoleakage evaluation method in which acid is added to measure the quality of the bond. The patterns of the nanoleakage were subsequently analysed using a silver nitrate solution.
The results of their experiment showed that the thermocycling ageing process caused cracks and fissures to form in the resin-detin surface. This enabled the silver particles to infiltrate and settle along the bonded interface, reflecting water-filled and destructed areas. In the control group, silver particles were found to spread along the resin-dentin interface and infiltrate inside the dentinal tubules after the ageing treatment. Nanoleakage deposition also increased from 36.57 per cent to 50.41 per cent. In contrast, the DMA-treated groups exhibited minimal change. Nanoleakage deposition remained constant at about 20 per cent for samples treated with 5mM of DMA. With these optimistic findings, the researchers concluded that DMA could be used to boost the strength and durability of the resin dentin bond and extend the longevity of a dental filling.
“This research discovered that DMA is effective in strengthening the resin-dentin bond and improves its durability. The cytotoxicity is also similar to the resin monomers in traditional dental adhesives. It is believed that this compound may be commercialised in the future,” stated Dr. Tsoi. [APBN]
Source: Li et al. (2021). Enhancing resin-dentin bond durability using a novel mussel-inspired monomer. Materials Today Bio, 12, 100174.