Organic-Polyelectrolyte Adhesives

Prior to the use of the adhesives, the dentin surface is etched with a conditioning solution which is usually an aqueous acidic solution of citric acid-ferric chloride, phosphoric acid, or even polyacrylic acid [192]. These solutions tend to demineralize the dentin and expose the collagen (organic fibers in the dentin) [193], and thereby result in higher bond strengths. The effects of various pre-conditioning treatments on the bond strength of 4-META to dentin have been discussed [194]. 

The dentin-adhesive interface has been studied using a Raman microprobe technique [199], which shows the formation of resin-reinforced dentin and the penetration of resin into dentin substrate to a depth of 5-6 microns. Further study of the interface showed that only small molecules such as MMA, 4-MET (hydrolyzed 4-META) or oligomers infiltrated the dentin, and that all of the resin in the dentin originated from the monomer solution [200]. SEM and TEM studies of the ultrastructure of the resin-dentin interdiffusion zone showed a 2 micron zone with closely packed collagen fibrils running parallel to the interface [201]. 

The nature and type of initiation scheme plays an important role in the performance of the adhesive [194,202-204]. Stresses due to polymerization shrinkage lead to the creation of a gap between the adhesive and tooth material. In the case of bulk chemical initiation, shrinkage stresses tend to create gaps at all interfaces, drawing material inward isotropically. With a photoinitiation scheme, polymerization begins at the free surface and pulls the material away from the dentin towards the free surface [194]. Thus the gap is created at the 

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Polyelectrolyte-based dental cements or restorative materials include zinc polycarboxylates, glass ionomers, a variety of organic polyelectrolyte adhesives as well as alginate-based impression materials. Dental cements are primarily used as luting (cementing) agents for restorations or orthodontic bands, as thermal insulators under metallic restorations, and as sealents for root canals, pits and fissures. They are also sometimes used as temporary or permanent (anterior) restorations. For further introduction to dental materials the reader is referred to standard texts [122,123]. 

Another application for polyelectrolyte materials is in the forming plastics with unusual physical properties with regard to adhesion. The incorporation of small amounts of organic acid materials into polyolefin structures results in materials that have excellent adhesion to metals, paper, glass, and a variety... 

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