Polyacid-modified composite resins curing

G. Eliades, A. Kakaboura, G. Palaghias, Acid base reaction and fluoride release profiles in visible light-cured polyacid modified composite resin restorations. Dent. Mater. 14 (1998) 57-63. 

As mentioned, these materials seem to have found particular application in children s dentistry. The successive reformulations mean that they may have lost their original distinctive characteristic of having a small amount of acid-base reaction following post-cure moisture uptake. There is evidence that modem polyacid-modified composite resins primarily release fluoride as a result of the additional fluoride compound, as with fluoridated conventional composites, and that any acid-base reaction is so slight that it has little, if any, effect on the properties of the material. Overall, these materials do not duphcate the properties of either of the parent materials particularly well, and their current use in clinical dentistry is fairly limited [1]. 

As already mentioned, the distinctive property of polyacid-modified composite resins is that, once the polymerization reaction has occurred, the set material is able to take up traces of moisture. This activates the acidic character of the carboxylic functional monomer and triggers an acid-base reaction with the glass [1,2]. The water uptake behaviour of these materials has been studied in detail [15], along with the corresponding water desorption processes. Three commercial polyacid-modified composite resins were used in a study of water uptake and loss, and cured samples were prepared as small discs of size 6 mm diameter x 2 mm thickness. Water uptake was allowed to take place in a controlled humidity environment at 93% relative humidity. Following the initial water uptake, there was an intervening desorption cycle in which specimens were stored in a dry atmosphere over concentrated sulfuric acid. 

Polyacid-modified composite resins are favoured by many clinicians over conventional composites to repair primary teeth [50]. This is on account of their fluoride release [1,50]. To emphasize their application in primary teeth, certain brands have been specifically produced for this purpose and are highly coloured. For example, in America, there is a dual-cure compomer called MagicFil (Zenith Dental, Englewood, New Jersey) which is produced in four colours (pink, green, blue and yellow) with gutter inclusions, and a similar material, Twinky Star (Voco, Germany) is available in Europe [51]. 

N.S. Koupis, C.W. Vercruysse, L.A. Marks, L.C. Martens, R.M.H. Verbeeck, Curing depth of (polyacid-modified) composite resins determined by scraping and a penetrometer, Dent. Mater. 20 (2004) 908-914. 

Table 4.1 Variation in equilibrium water content (%) of polyacid-modified and conventional composites resin stored at 37°C (specimens cured for 40 s)...

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