Polymer networks in dentistry

Abstract

Polymer networks applied in clinical dentistry can be divided into two groups: (i) hard, solid two‐and threedimensional crosslinked structures formed during photo‐curing of dental polymeric filling compositions, and (ii) soft, hydrogel‐type of networks based on polymeric ionic complexes, used for the tightening of microchannels in teeth. The first group is based on crosslinked di‐ and trifunctional monomers, and on solid poly(acrylic acid) ‐ inorganic glasses (“glass ‐ ionomer cements”) This group has found wide clinical applications, in spite of many disadvantages such as susceptibility towards hydrolytic, mechanical. bio‐ and enzymatic degradations, and contents of toxic, allergenic and mutagenic components. The second group, the soft‐hydrogel type of networks, has been investigated and developed at our institute in order to tighten channels in teeth. The microchannels, with a diameter of 30–200Å in enamel and 1–3 μm in dentine, are filled with a loose, native bio‐hydrogel of protein origin. Hydrogels have the ability to swell in water of biological fluids present in the oral cavity, and can retain a significant fraction of fluid within the structure. Decreasing pH below 5.5 causes a slow dissolution of the hydroxyapatite crystals in the walls of the microchannels with a consequent widening of their lumens. Metabolites and toxins from microorganisms, which are always present in the oral cavity, can penetrate into these enlarged channels and cause inflammatory reactions in the underlying pulp tissue. In order to decrease fluid flow and inhibit penetration of microorganisms, but still allow diffusion of ions and water, we have developed and tested polymeric hydrogels based on poly(acrylic acid) and metal salts, and chitosan, which can be formed directly in the micro‐channels of dental hard tissues.

Molecular and Aggregate Structural, Thermal, Mechanical and Photophysical Properties of Long-Chain Amide Gelators Containing an α-Diketo Group in the Presence or Absence of a Tertiary Amine Group

“…Related to these observations, bimolecular photoinitiator systems comprised of an α-diketone and a tertiary amine have been used as dental restorative materials [17,18]. A mechanism involving a triplet exciplex has been suggested to be the reactive intermediate preceding an electron transfer [17,18], although no specific evidence for such a complex has been shown. Regardless, electron transfer from the tertiary nitrogen lone-pair to the α-dicarbonyl group is the most plausible mechanism for the initial step.…”