Study design The ethical committee of Istanbul Medipol University approved this clinical study. Patients were given written informed consent to participate before treatment and agreed to a recall program at baseline 2 weeks, 6 months, and thereafter annually. All restorative procedures were carried out by one experienced dentist from the Department of Restorative Dentistry at Istanbul Medipol University.
Inclusion and exclusion criteria
Patients in need of removal of old large amalgam restorations or having extensive caries lesions were recruited for the study. Inclusion and exclusion criteria were as follows:
Adults of at least 18 years of age, with good oral hygiene, having an antagonist tooth in occlusion, being mentally in a good state to provide written consent to participate in the clinical study, and willing to attend the scheduled follow-up appointments. Exclusion criteria included the presence of teeth with severe periodontal problems, high caries risk, and bruxism.
Cavities were prepared according to common principles, which included an occlusal reduction of 1.5-2 mm with a wide isthmus and rounded occlusal-axial angles, and an axial wall of 1.5 mm in thickness. Where possible, the gingival margins were prepared entirely in enamel at the cemento-enamel junction, and cavities for overlays included both buccal and lingual/palatal cusps. Both cavity types (onlays and overlays) were prepared with rounded internal angles, with a divergence of 6-15° between the walls and margins with a 90° cave surface.
Full-arch impressions were made with a single impression/double mixing technique using polyether material (Impregum Penta H Duoso, 3M ESPE, Minn, USA) cavity preparations were provisionalized for 1 week with photo-polymerized provisional material (Clip, Voco, Cuxhaven, Germany). All onlays were definitively inserted within 1 week after impression. After the removal of provisional restorations, the teeth were thoroughly cleaned with a prophylaxis brush and pumice.
After adjustment when needed, the restorations were luted adhesively under a rubber dam, employing a total-etch system in group A. The prepared teeth were initially cleaned with pumice slurry and etched with 35% phosphoric acid gel (Ultra-etch, Ultradent, South Jordan, UT, USA). The dentin adhesive system (Syntac Classic, Ivoclar Vivadent, Liechtenstein) was then applied uniform and gently air thinned. The internal surface of the restorations was silanized (Monobond S, Ivoclar Vivadent), waited for its reaction for 60 s and the solvent was evaporated with oil-free compressed air. The onlays and overlays were luted adhesively with etch and rinse, dual cure resin cement (Variolink II, Ivoclar Vivadent). In Group B were luted using a self-adhesive resin cement (Relyx U200, 3M ESPE).
Excess resin cement was removed in all cases with an explorer, a brush, and dental floss interproximally. Each only surface was light-cured for 40 s with a polymerization light (Elipar Highlight, 3M Espe, Seefeld, Germany). After placement and removal of the rubber dam, static and dynamic occlusion was adjusted using fine grit diamond burs, then inlays were finished with disks and strips (Sof-Lex, 3M Dental Products, St. Paul, MN, USA).
