Tunnel or saucer-shaped restorations: a survival analysis

The aim of the present effectiveness trial was to compare the survival of restorations placed in saucer-shaped cavities to that of restorations placed in tunnel preparations. Ten operators placed a total of 85 tunnel and 97 saucer-shaped restorations. The dentinal part of the tunnel was restored by resin-modified glass ionomer cement. The remaining part of the tunnel was restored by composite resin using an adhesive technique. Composite resin was used to restore the saucer-shaped cavities. The restorations were assessed clinically and radiographically for up to 79 months, with a mean observation time of 28.8 months for tunnel, and 30.3 months for saucer-shaped restorations. The survival proportion of the tunnel restorations was 46%, and the survival proportion for the saucer-shaped restorations was 76%. A main reason for failure of the tunnel restorations was fracture of the marginal ridge (24% after 24 months). Caries development in relation to the restoration was significantly higher for tunnel restorations compared with saucer-shaped restorations (41 and 19%, respectively, after 24 months). There was no difference between the two types of restoration in marginal deterioration and caries progression in the neighboring tooth (40% after 24 months). Based on findings from the present study, it is suggested that saucer-shaped restorations should be preferred for tunnel restorations in small- and mid-sized cavities.