Dental materials – what goes where? the current status of glass ionomer as a material for loadbearing restorations in posterior teeth

The demand for tooth-coloured restorations in posterior teeth is increasing worldwide,1 with the principal alternative to amalgam being considered to be resin composite. However, resin composite restorations in loadbearing situations in posterior teeth take longer to place than amalgam, with one study indicating that they take 2.5 times as long2 while, in another, they took only 35% longer, with the three composite steps of acid-etch, wash/dry, and light cure accounting for 86% of the mean time differences for the two materials.3 Since a dentist's time is the most expensive component in a restoration, resin composite restorations are more expensive than amalgam: patients have therefore sought cheaper alternatives. Accordingly, there is some evidence of dentists offering patients a glass ionomer material for restoration of posterior teeth.4 These materials may be placed in bulk, resulting in a saving in time when compared with the time-consuming incremental build-up required for posterior composite restorations. This, in turn, results in a restoration which is less expensive than the equivalent posterior composite. Such a technique has the advantage that the initial fee to the patient will be less than that for a composite (insofar as it could be considered that a glass ionomer restoration in a posterior tooth may be placed in a similar time as placing amalgam) and, even if the restoration later requires re-surfacing (vide infra), the fee to the patient will be spread over a number of years. However, the glass ionomer restoration in a loadbearing situation, while costing less to place initially, may not be cost-effective if its survival is less than an equivalent resin composite restoration.