Innovative dental adhesive: When fillings last

Adhesive restorations are expected to function in a harsh oral environment. Several factors have been associated with the deterioration of the adhesive restorations,  including occlusal and (or) thermal stresses, chemical and various enzymatic attacks, compromising the integrity of the tooth restoration interface. Other contributory factors to the degradation process of this interfacial junction are secondary caries, exposure to water and bacterial biofilm formation. Enzymatic hydrolytic degradation of the collagen matrix by host derived enzymes, namely matrix (MMP’s) metalloproteinases and cysteine cathepsins are repeatedly held responsible for digesting the collagen fibrils exposed at the adhesive interface. The collagen degradation leads to uncoiling of the fibrils into gelatin and loss of the typical helical ultrastructure and fragmentation.

Conventional adhesive systems allow immediate bonding to tooth structure via polymerization without requiring aggressive cavity preparations. However, it does not prevent degradation of the adhesive interfaces, which may lead to secondary caries, hypersensitivity, pulpal inflammation and compromise the long term clinical success of adhesive restorations. Hence, the tooth and filling interface is always considered as an inherently weak link and a lot of research work has been conducted to improve and enhance this interface.

The present invention relates to a novel dental adhesive for restorative purpose. The innovative formulation has an antibacterial and crosslinking additive, a monomer adhesive and a photoinitiator material. The primary objective of this invention was to provide an adhesive composition for dental treatment that made up of a crosslinking additive comprising a quaternary ammonium compound (QAC) bonded with a riboflavin, a monomer adhesive, and a photoinitiator material. The research findings have shown positive results that this adhesive has potential to provide long term antimicrobial, anti-protease and collagen strengthening at the tooth restoration interface, enhancing the long term clinical outcomes of adhesive restorations.

The cross-linking additive has 1 % concentration of QAC, in which the quaternary ammonium compound and the cross-linking agent are having a ratio of 1:1. The quaternary ammonium compound used is dioctadecyldimethyl ammonium bromide, while the photoinitiator material comprises camphorquinone ethyl (4-dimethylamino) benzoate and diphenyliodonium hexafluorophosphate.

The formulation also incorporate riboflavin, which when activated by ultraviolet A (UVA) radiation, acts as a cross-linking agent. Various strategies for collagen crosslinking and disinfection have been devised by researchers which involve the use of either cross-linkers like genipin, chitosan, glutaraldehyde and grape seed extract and riboflavins. It is possible to increase the resistance of dentine collagen to endogenous proteases in addition to cross-linking proteoglycans such as glycosaminoglycans. Including a QARF (Quartenary Ammonium Riboflavin) compound at a concentration of 1% within the adhesive provides long-term antimicrobial effect and simultaneously cross-linking dentine matrix for clinicians to compare the results with any other modified adhesives or pre-treatments.

The formulation of this novel dentin adhesive modified with both antimicrobial and collagen crosslinking compounds resulted in unique combination of antimicrobial, anti-proteolytic effects, and collagen crosslinking effects. Photoinitiator has been incorporated to ensure adequate polymerisation of the adhesive. From research findings this innovative adhesive formulation is not cytotoxic to pulp stem cells and is biologically compatible and easy to use on human teeth. This novel adhesive formulation that has been modified, has anti-inflammatory properties that could be beneficial in inducing healing as well as regenerative responses. It seems promising that the bond strength values were comparable to the current commercially available bonding agents. This novel adhesive formulation has successfully obtained patent in Malaysia (MY-197766-A).

To summarize, this novel adhesive formulation has the following potential advantages:

• Provide a strong, immediate, and lasting bond to tooth structure.
• Seal the dental cavity and minimize leakage problems.
• Resist microbial or enzymatic degradation at the tooth restoration interface.
• Prevent post-operative sensitivity in patients.
• Reduce the risk of recurrent caries.
• Prevent staining in margins of cavities.

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