cosmetic dentistry_ beauty & science

CE article _ bioactive materials I _Glass ionomers and resin-modified glass ionomers Glass ionomer cements have long been used as a direct restorative material. Theirearlyformulationsmade the material difficult to han- dle, and the break down of the material made it an un- desirable solution in dental restoration. However, these materials, especially in to- day’s formulations and pre-encapsulated presen- tations,havemanypropertiesthatmakethemvery important in the restorative process. TheworkatcompaniessuchasSDINorthAmer- ica (Riva product line), GC America (Fuji product line) and VOCO (Iono product line) have continued to make great strides in improving these products foreasierandlonger-lastinguseofGICandRMGIC products. First, these materials are bioactive, and up until recently, they were the only materials with this property; that is they have the capacity to interact with living tissue or systems. Glass ionomers re- lease and recharge with ions from the oral cavity. This transfer of calcium phosphate, fluoride, strontiumandothermineralsintothetoothstruc- ture helps the dentition deal with the constant assault of the acidic nature of day-to-day in- gestion of food and beverages and encourages remineralization; and the incorporation of phos- phorous into the acid in today’s GICs creates polyvinylphosphonic acid.8 ThispropertyofGICsmakesthemamajoragent in the reduction of MMP formation, and thereby minimizing if not eliminating the collagen break- down commonly found in many resin-dentin bonding procedures.9 Second, they bond and ultimately form a union with the dentition by chemically fusing to the tooth. The com- bination of the polyacrylic acid and the calcium fluoro- aluminosilicateglasstypically found in GICs reacts with the tooth surface, which re- leases calcium and phos- phate ions that then combine into the surface layer of the GIC and forms an intermediate layer called the “interdiffusion zone.”10 No resin bonding agents are required due to thischemicalfusingtothetoothstructure.Thision release helps inhibit plaque formation and pro- vides an acid buffering capability that helps to create aneutralization effect intraorally. In addi- tion, these GICs have very good marginal integrity with better cavity-sealing properties, have better internal adaption and resistance to microleak- age over extended periods of time, have no free monomers, can be bulk filled and offer excellent biocompatibility.11 Another important consideration is that GICs are moisture-loving materials, which makes them very sensible for use in the intraoral cavity. The transfer of dentinal fluid from the tooth to the GIC essentially creates a “self-toughening mechanism of glass ionomer based materials… serves to deflect or blunt any cracks that attempt to propagate through the matrix [and]…plays an adjunctive role by obliterating porosities [which] delay the growth of inherent cracks in the GIC under loading.”4 The intermediate layer of the GIC provides flexibility during functional loading and acts as I 07cosmeticdentistry 1_2013 Fig. 4 Fig. 5 Fig. 6 Fig. 7