The aim of this study will be to evaluate the effect of a double layer application of a universal adhesive system used as etch-and-rinse application mode in non-carious cervical lesions (NCCLs), on the 6- and 12-months clinical performance.

Materials & Methods: 144 restorations were randomly placed in 36 subjects (16 male and 20 female) according to the following groups (n=36): ER1 (one layer of Scotchbond Universal Plus adhesive applied as etch-and-rinse mode); ER2 (double layer of Scotchbond Universal Plus adhesive applied as etch-and-rinse mode); SEE1 (one layer of Scotchbond Universal Plus adhesive applied as selective enamel etching); SEE2 (double layer of Scotchbond Universal Plus adhesive applied as selective enamel etching). All groups were light-cured for 10s/1,000 mW/cm2 only after final layer. A resin composite will be placed by applying three increments and each one will be light cured for 20s/1,000 mW/cm2. The restorations will be finished immediately with fine diamond burs and polishers. The restorations will be evaluated at baseline and after 6- and 12-months by using the FDI criteria. The following outcomes will be evaluated: retention, marginal staining, marginal adaptation, post-operative sensitivity and recurrence of caries. The differences among the groups will be calculated using Friedman repeated measures analysis of variance rank (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 applying a double layer of Scotchbond Universal Plus adhesive applied as etch-and-rinse mode.

Experimental group 2: 35 non-carious cervical lesions (NCCL) will receive composite resin restorations applying a double layer of Scotchbond Universal Plus adhesive applied as selective enamel etching mode.

Control group 1: 35 non-carious cervical lesions (NCCL) will receive composite resin restorations applying one layer of Scotchbond Universal Plus adhesive applied as etch-and-rinse mode.

Control group 2: 35 non-carious cervical lesions (NCCL) will receive composite resin restorations applying one layer of Scotchbond Universal Plus adhesive applied as selective enamel etching mode.

LCNCs will be randomized to application mode and number of layers. All groups will be light-cured with a light-curing device (SmartLite Focus, Dentsply) with a light intensity of 900 mW/cm² for 10 seconds. Operators will restore the cervical area by applying three increments of resin (Filtek Supreme XT, 3M). Each increment will light cure for 20 s at 900 mW/cm2 (SmartLite Focus, Dentsply). Restorations will be finished immediately with fine and extra fine diamond burs and polished with polishing spirals.

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