The one constant contraindication for a composite restoration is

The constant contraindication for using a composite restoration is the inability to properly isolate the operating area. Occlusal wear of composite is similar to that of amalgam. Extension onto the root surface may result in gap formation with composite but also results in initial leakage with amalgam, indicating that there is no ideal material for root-surface extended restorations. A high C-factor (Class I) can be largely overcome by using a liner under the composite, a filled adhesive, and incremental insertion of the composite.