A new compound found in molds helps increase the durability of dental fillings

Leading researchers from the Faculty of Dentistry, University of Hong Kong (HKU), Wuhan University (WHU) and Peking University Hospital in Shenzhen have found that a compound present in the molds helps to increase the durability of a dental filling.

In a journal article published inMaterials Today OrganicTitled “Improving Resin-Dentin Bond Durability Using a New Mold-Inspired Monomer,” they explain why this is a promising clinical finding for the future of dental filling treatments.

A dental filling is commonly used to restore tooth decay and broken teeth. Its durability is highly dependent on the longevity and stability of the bond between the compound (resin) and the hard tissue of the tooth (dentin). This is where mussels come into play.

A small shell very common in the marine environment, mussels offer unique wet adhesion properties that have long been of interest to the scientific community. Thus, the interaction between mold plates and substrates in humid environments has been widely studied to better understand potential clinical applications. The study found that a compound found in an adhesive protein of mussels could strengthen the resin-dentin bond.

Mussels must retain their grip in harsh marine environments including humidity, drastic changes in water temperature and pH value, sudden shocks, etc. These are similar to the daily activities that take place in the oral cavity. Our research aimed to understand the adhesive properties of mold compounds, which can improve the longevity and longevity of dental fillings. »

Professor Cynthia Kar Yung Yiu, Clinical Professor of Pediatric Dentistry, HKU

Other members include Dr. James Kit Hon Tsoi, Associate Professor of Dental Materials Science and Mr. Kang Li from HKU Faculty of Dentistry; Professor Cui Huang of WHU and researchers from Shenzhen Hospital of Peking University.

In a typical dental filling procedure, the dentist first removes the decayed tooth structure and fills the cavity with a tooth-colored restoration using a dental adhesive to bond the filling to the tooth structure . However, the durability of this bond can be affected by several factors, such as humidity inside the oral cavity and repeated mechanical stresses induced by chewing. Therefore, it remains a clinically significant challenge for the dentist as well as the patient as it leads to frequent replacement of dental fillings at additional costs.

The study revealed that the wet adhesive property of mussels is attributed to the amino acid Dopa they secrete. Based on the result, the team successfully applied N-(3,4-dihydroxyphenethy) methacrylamide (DMA), a compound derived from mussels, as a dental adhesive. The team then tested the durability of this resin-dentin interface against the new DMA bond.

The control group and those with distinct DMA concentrations underwent different tests, including thermocycling aging, a process where dental materials are exposed to varying temperatures. The international standard for testing dental adhesives requires specimens to be repeatedly held first in cold water at 5°C and then in hot water at 55°C for a large number of cycles. Results after further testing consistently show a decrease in bond strength.

The researchers then used the nanoleak assessment method in which an acid is added to measure the quality of the bond. The team used a silver nitrate solution to observe the nanoleak patterns.

In the resin-dentin interface, the thermocycling aging process caused cracks and fissures to form which further led to silver particles infiltrating and depositing along the bonded interface. The silver deposit therefore clearly reflected the waterlogged and destroyed areas along the interface. In the control group, silver particles were observed propagating along the resin-dentin interface and infiltrating inside the dentinal tubules after aging (nanoleak deposition increased from 36.57% at 50.41%). On the contrary, no obvious change could be detected for the groups treated with DMA (nanoleak deposition of about 20%). The team therefore deduced that DMA could strengthen the resin-dentin bond and its durability and would increase the longevity of a dental filling.

“This research found that DMA is effective in strengthening the resin-dentin bond and improving its durability. Cytotoxicity is also similar to resin monomers in traditional dental adhesives. It is believed that this compound may be commercialized in the future” , said Dr. Tsoi.