Tooth vitality will be confirmed with cold test (ethyl chloride) and registrated. Bleeding of the gingiva will be recorded using a periodontal probe. Local anesthesia will be applied to prevent pain and discomfort during cavity preparation. Tooth surface will be cleaned using a commercial non fluoride prophy paste (Cleanic, fluoride free, Kerr dental). The cavity preparations will be performed by removing old fillings or/and opening carious lesions using rounded and cylindric diamond burs (Komet). Round tungsten carbide burs (Komet) and hand instruments will be used to excavate carious dentine in both groups. For composite resin restoration, sound dentin verification will be based on probing and tactile sensation. No marginal bevel will be prepared and a horizontal platform (avoid apical shift) in approximal box will be made. Before placement of the materials, impressions will be taken to registrate cavity depth.

Restorations with EQUIA Forte (GC corp., Tokyo, Japan) will be placed according to the manufacturer recommendations. The site will be isolated with cotton rolls. A sectional metal matrix system and wedge will be placed. GC cavity conditioner (20% polyacrylic acid, GC) will be applied for 10 sec., rinsed and the cavity will be dried with a cotton pellet. EQUIA Forte (GC) will be prepared according to the manufacturer instructions, applied in bulk and compacted with a condenser. The self-curing restoration will be finished after hardening, approximately 2 minutes 30 seconds after the start of the capsule mixing, using Arkansas stones under water cooling. Occlusion and articulation will be checked by using two sided and coloured articulating paper (blue for occlusion and red for articulation) 20 microns thickness. EQUIA Forte restoration will be rinsed and gently dried. EQUIA Forte Coat (GC) will be applied to the surfaces using a micro-tip applicator. The coated surface will be light cured with D-light (GC) for 20 seconds. Patients will be instructed not to eat during one hour after the restoration placement.

For composite resin restoration, rubber-dam will be applied, and the same matrix system will be used. Enamel will be etched with 37% orthophosphoric acid (Ivoclar Vivadent, Schaan, Liechtenstein) for 10 sec., avoiding etching dentine as much as possible. The acid gel will be rinsed with air-water spray and the cavity will be carefully dried with a mild stream of air until the etched enamel appears white-frosted and dentin dull (avoiding to over-dry of dentine surface). The adhesive (Adhese 2, Ivoclar Vivadent) will be applied according to the manufacturer's instruction and light cured with D-light (GC, 1200 mW/cm2, slow mode) for 10 sec. The composite resin (Tetric EvoCeram, Ivoclar Vivadent) will be placed with an incremental technique (2 mm layers). Composite will be light-cured with D-light (20 sec) from the occlusal direction by placing the light tip as close as possible to the restoration. After removing of matrix, additional light curing will be performed from vestibular and palatal/lingual direction. Finishing will be performed using diamond burs. Restorations will be finished with fine diamond burs in high-speed hand-piece for gross finishing (Komet) followed by fine carbide burs in slow speed hand-piece for fine finishing (Komet). Occlusion and articulation will be checked by using two sided and coloured articulating paper (blue and red) 20 microns of thickness. Polishing will be performed using flexible polishing discs (Komet), rubber points (Compo system, Komet) with a diamond particle paste (1μm) (Gradia diapolisher). Fine polishing stripes will be used for proximal surface below the contact point.

One week after the placement of the restorations, baseline evaluation will be performed and follow-up evaluations will be done on yearly bases up to five years. Two experienced, blinded, calibrated examiners (e-calib) who will not perform clinical procedures will evaluate the restorations. Evaluation will be done by using loops (magnification x 2.5).

Impressions obtained before procedure, after cavity preparation, at baseline, three and five years will be directly scanned using 3D laser scanning device (GC Aadva Lab scan). After direct impression scanning, a gypsum cast (GC Fujirock EP OptiXscan) will be also made (baseline, three and five years). These models will be scanned for wear analysis with the GC Aadva software in order to compare two different evaluation methods.

At baseline and at every recall, four photos will be taken: one photo from the occlusal view, buccal view, oral view and direct view.