This study will evaluate the performance of three different tooth-colored onlay materials in adult patients' posterior teeth. First, investigators will use a bulk-fill composite resin to raise the cavity margin above the gum line and below the contact point. Then each patient will receive three onlays made from different materials. Investigators will follow patients at 2 weeks, 6 months, 18 months, and 24 months to assess how well the onlays fit, function, and whether restorations cause sensitivity or new decay. The results will help dentists choose the most durable onlay restorations for deep-margin elevation cases.