The aim of this study will be to evaluate the effect of prolonging solvent evaporation time on the 6- and 12-months clinical performance of two universal adhesive systems used as selective enamel etch (SEE).

Methods: 140 restorations will be randomly placed in 35 subjects according to the following groups: SUP5 (Scotchbond Universal Plus evaporated for 5 s); SUP25 (Scotchbond Universal Plus evaporated for 25 s); GBU5 (Gluma Bond Universal evaporated for 5 s); GBU25 (Gluma Bond Universal evaporated for 25 s). Resin composite will be placed incrementally and light-cured. The restorations will be evaluated at baseline, after a week, 6 and 12 months using the FDI and USPHS criteria. Statistical analyses will be performed using appropriate tests (α = 0.05).

This is a four-arm, double-blind, randomized controlled clinical trial. Experimental group 1: 35 non-carious cervical lesions (NCCL) will receive composite resin restorations using an alcohol- and water-based solvent universal adhesive (Scotchbond Universal Plus; 3M) in the selective enamel etching strategy with evaporation of solvent for 25 seconds. Experimental group 2: 35 non-carious cervical lesions (NCCL) will receive composite resin restorations using an acetone-based universal solvent adhesive (Gluma Universal Bond; Kulzer) in the selective enamel etching strategy with solvent evaporation for 25 seconds. Control group 1: 35 non-carious cervical lesions (NCCL) will receive composite resin restorations, using an alcohol- and water-based universal solvent adhesive (Scotchbond Universal Plus; 3M), in the selective enamel etching strategy, with evaporation of solvent for 5 seconds. Control group 2: 35 non-carious cervical lesions (NCCL) will receive composite resin restorations, using an acetone-based universal solvent adhesive (Gluma Universal Bond; Kulzer), in the strategy of selective enamel etching, with solvent evaporation for 5 seconds. LCNCs will be randomized to universal adhesive usage and flash-off time. All groups will be light-cured with a light-curing device (SmartLite Focus, Dentsply) with a light intensity of 855 mW/cm² for 20 seconds. Operators will restore the cervical area by applying three increments of resin (Opallis, FGM Prod. Odont.Ltda, Joinville, SC, Brazil). Each increment will light cure for 10 s at 1200 mW/cm2 (Radii Cal, SDI, Victoria, Australia). Restorations will be finished immediately with fine diamond burs (#3195F and #3195FF, KG Sorensen, Barueri, SP, Brazil) and polished with discs and polishing gums (Soflex, 3 M ESPE, St. Paul, MN, EE. UU.).

Inclusion Criteria:

• Patients older than 18 years.
• Presence of at least two Non-Carious Cervical Lesions in the dental arch with a need for restorative treatment.
• Acceptable level of oral hygiene according to the Simplified Oral Hygiene Index.
• At least 20 teeth in function.
• Non-Carious Cervical Lesions with a maximum of 50% of enamel margin.

Exclusion Criteria:

• Driving difficulties that prevent adequate oral hygiene.
• Periodontal disease.
• Active caries lesions on the teeth included in the research.
• Parafunctional habits.
• Active staples of removable partial dentures on the teeth included in the research and that these are not pillars of prostheses.

Two blinded, experienced, and calibrated dentists (who specialized in esthetic dentistry with more than 15 years of clinical practice), will perform the clinical evaluation. Patients will be also blinded to group assignment. An inter-examiner and inter-examiner agreement of at least 85% will be necessary before beginning the evaluation