This study evaluated, in the dog, the periodontal response to resin-modified glass-ionomer cement or amalgam restorations placed in surgical windows and left for 124 days. Plaque control was performed in half of the sites. Histologic analyses showed that sites restored with amalgam were consistently more inflamed than sites restored with resin-modified glass-ionomer. Plaque control was associated with less inflammation in both cases. Some sites restored with resin-modified glass-ionomer presented bone repair and a connective tissue lining. The inflammatory response of the periodontium to resin-modified glassionomer restorations is less pronounced than that associated with amalgam restorations.