Objective: This double-blind randomized clinical trial evaluates the influence of increased application time of a new etch-and-rinse two-step adhesive Single Link; (Angelus Dental Products Industry) applied in non-carious cervical lesions (NCCLs).

Methods: A total of 221 restorations were randomly placed in 35 patients assigned in four groups to two different etch-and-rinse two-step adhesive Peak® Universal Bond (P) (Ultradent Products Ind) and Single Link (SL) (Angelus Dental Products Industry). The adhesives systems were applied on the NCCLs follows: P1 - applied according to the manufacturer's; P2X - applied for the double time; SL1 and; SL2X. The resin composite Amelogen (Ultradent) was placed incrementally. The restorations were evaluated imediataly (baseline), 6 and 12 months, using the FDI and USPHS criteria. Statistical analyses were performed using appropriate tests (=0.05).

Methods:

Recruitment Patients were recruited as they seek for treatment in the clinics of Dentistry of the local university. No advertisement was made for participant recruitment. Patients were recruited in the order in which they reported for the screening session, thus forming a sample of convenience.

Eligibility criteria A total of 183 participants were examined by two calibrated dental students to check if they met the inclusion and exclusion criteria.

Sample size calculation The annual retention rate to one-step self-etch adhesives in NCCLs was reported to be 4.4% in a recent systematic review. Considering that this decline follow a linear trend, the overall retention rate of one-step self-etch adhesives will be approximately 78% after 5-year of clinical service. With an of 0.05, a power of 80%, and a two-sided test, the minimal sample size will be 41 restorations in each group in order to detect a difference of equivalence of 15% among the test groups.

Interventions A total of 221 restorations were randomly placed in 35 patients assigned in four groups to two different etch-and-rinse two-step adhesive Peak® Universal Bond (P) (Ultradent Products Ind) and Single Link (SL) (Angelus Dental Products Industry).

The adhesives systems were applied on the NCCLs follows: P1 - applied according to the manufacturer's; P2X - applied for the double time; SL1 and; SL2X. The resin composite Amelogen (Ultradent) was placed incrementally. The restorations were evaluated imediataly (baseline), 6 and 12 months, using the FDI and USPHS criteria. Statistical analyses were performed using appropriate tests (=0.05).

Inclusion Criteria:

Participants had to be in good general health, at least 18 years old, have an acceptable oral hygiene level, and present at least 20 teeth under occlusion, at least four NCCLs in four different teeth, these lesions had to be non-carious, non-retentive, deeper than 1 mm, and involve both the enamel and dentin of vital teeth without mobility. The cavo-surface margin could not involve more than 50% of enamel, and all lesions had cervical margins ending in dentin.

Exclusion Criteria:

Participants had not be in good general health, at less 18 years old, have not an acceptable oral hygiene level, and present at less 20 teeth under occlusion, at less four NCCLs in four different teeth, these lesions had not be non-carious, retentive and involve only enamel of vital teeth with mobility.

A staff member not involved in the research protocol performed the randomization process with computer-generated tables. Details of the allocated groups were recorded on cards contained in sequentially numbered, opaque, sealed envelopes. Opening the envelope only on the day of the restorative procedure guaranteed the concealment of the random sequence. The examiners were not involved with the restoration procedures and therefore blinded to the group assignment, performed the clinical evaluation. Patient were also blinded to group assignment in a double-blind randomized clinical trial design.