This study investigated the early erosion of glass ionomer-cement that had been used to lute complete cast crowns. Restorations had margins ending on either enamel or cementum and had various sizes of marginal openings. These restorations were compared to those using a standard zinc phosphate cement. Results showed that leaving the band of excess cement, expressed during the seating of the crown, undisturbed for 10 minutes prevented significant erosion in a wet field. A resin coat was not necessary to provide further protection after removal of the band. Zinc phosphate cement also showed significant early erosion when exposed to moisture.