Recent Developments of New Components for Dental Adhesives and Composites

Abstract

The currently used commercial self‐etching enamel‐dentin adhesives and restoratives composites are mainly based on a mixture of various monofunctional and cross‐linking dimethacrylates. New developments of enamel‐dentin adhesives concern the improvement of technique insensitivity and storage stability. Improvements of restorative composites are focused on the reduction of the polymerisation shrinkage, as well as the improvement of wear resistance, biocompatibility, and processing properties. In the past five years, many research efforts have been carried out to develop new monomers and tailor‐made components for filling materials, such as fillers or initiators. New phosphonic acid ether acrylates and cross‐linking bis(acrylamide)s enable the preparation of self‐etching enamel‐dentin adhesives with improved storage stability. With free‐radically polymerisable cyclic monomers, such as bicyclic cyclopropyl acrylates or cyclic allyl sulfides, low‐shrinkage storage‐stable restorative composites could be prepared. In case of the cationic polymerisable cyclic monomers, like siloxane‐based cycloaliphatic epoxides, the lower curing rate, stronger exothermic effect and lower curing depth compared to dimethacrylate‐based composites presently prevent their dental application. Designed methacrylates with tailor‐made properties and sol‐gel polycondensates can also contribute to the improvement of the currently used restorative composites. Radical polymerisable dental materials are initiated by light curing and by redox initiator systems. Under acidic conditions amine containing initiator systems are deactivated by acid‐base reaction. Non amine‐based initiators have to be developed for acidic monomer containing dental materials. The use of discrete nano‐filler particles mainly concerns the reinforcement and, in some cases, the increase of X‐ray opacity of composite filling materials.magnified image

Use of NIR light and upconversion phosphors in light-curable polymers

“…Light-curing resins have been widely used in restorative dentistry for several decades [1]. These resins are acrylate based and can be polymerized by blue light.…”

Can CQ Be Completely Replaced by Alternative Initiators in Dental Adhesives?

“…By the acid-base reaction between the acidic monomers of self-etching adhesives and the amine coinitiators of the initiator system, the concentration of amine and thus that of the formed amine radical -which is responsible for the initiation of polymerization -will be reduced. These decreases will result in retarded or insufficient polymerization [9][10][11] .…”

“…In the same vein, the initiator CQ can be replaced by polymeric radical photoinitiators bearing the photosensitive CQ groups in the side chain 13) . Another promising way to overcome the use of amines as accelerators is found in Norrish Type I photoinitiator systems 14) . They are based on photochemical cleavage of aldehydes and ketones into two free radical intermediates, which initiate polymerization without the need for an additional amine.…”

“…They are based on photochemical cleavage of aldehydes and ketones into two free radical intermediates, which initiate polymerization without the need for an additional amine. Recent developments of Norrish Type I photoinitiator systems for dental materials include acyl phosphonates, acylphosphine oxides, bisacylphosphine oxides, and titanocenes 14) .…”

Polymerization shrinkage stress of composite resins and resin cements – What do we need to know?

“…72 Most conventional materials contain dimethacrylate monomers in their composition, with average molecular weight varying from around 500 g/mol (BisGMA: 512 g/mol; UDMA: 470 g/mol; BisEMA: 540 g/mol) to around 290 g/mol (TEGDMA: 286 g/mol, commonly used as a low viscosity diluent). Over the past 15 years, much effort has been dedicated to developing low-shrinking formulations, either by virtue of using a ring-opening polymerization mechanism (as is the case with the product containg epoxide-based silorane monomers) or by using monomers with higher molecular weight (as is the case for composites using dimer-acid dimethacrylates, or DX-511, a monomer developed by DuPont, both with Mw greater than 800 g/mol), or even pre-polymerized additives.…”