Evaluating the clinical behavior of composite restorations in NCCLs when the surface is pre-conditioned using bioactive glass air-abrasion has not been reported in the dental literature. This double-blinded randomised clinical trial evaluated the effect of surface pre-conditioning with bioactive air-abrasion on the performance of composite restorations in NCCLs placed using etch&rinse and self-etch adhesive systems.

15 Patients with 100 teeth meeting the inclusion criteria were enrolled in this study. NCCLs characteristics were evaluated and recorded before the placement of restorations. The cavity dimensions in millimeters (height, width, and depth), the cavity geometry (labeled at >45°, 45° - 90°, 90° - 135°, and <135°), the degree of dentin sclerosis , the existence of attrition facets, and the existence of spontaneous sensitivity were measured and recorded in the patient's form. The preoperative sensitivity was also evaluated by applying air from a dental syringe placed 2 cm from the tooth surface for 10 seconds.

NCCLs meeting the inclusion criteria were randomly assigned into four experimental groups (n=25); A: air-abrasion + etch&rinse, B: air-abrasion + self-etch, C: etch&rinse and D: self-etch.

Prophylaxis was conducted using a rubber cup with pumice and water. The color of the composite was selected using VITA classical shade guide before applying local anesthesia with Lidocaine 2% with 1:100000 adrenaline. Retraction chord was inserted into the gingival sulcus with the aid of a blunt spatula without excessive pressure to the periodontium. Teeth were isolated with rubberdam. No preparation or beveling of cavosurface margins was performed to the NCCLs.

In air-abrasion groups, a clinical air-abrasion unit was used to pre-condition the NCCLs with bioactive glass 45S5 powder for 10 sec. The operating parameters were; air pressure, 20 psi; powder particles size, 20 µm; nozzle angle, 90◦; nozzle-lesion distance, 5 mm and the internal nozzle diameter, 900 µm

For the etch&rinse groups, enamel and dentine were etched using 37% Phosphoric acid for 30 sec and 15 sec respectively. NCCLs were rinsed thoroughly for 20 sec to remove the acid. Excess water was removed using a cotton pellet to leave a moist dentine surface. One coat of bonding adhesive was gently scrubbed on the entire enamel and dentin surface for 20 sec, air dried for 5 sec and light cured for 10 sec using LED curing light ( output >800mW/cm2).

In self-etch groups, the bonding adhesive was applied to enamel and dentine for 20 sec with agitation, gently air dried and light cured for 10 sec.

NCCLs were restored using FiltekTM Z250 XT resin composite, placed in 2 mm increments and light cured for 20 s per increment. Final contour was achieved with a fine diamond rotary instrument followed by finishing and polishing using Optrapol polishing kit .

Clinical evaluation was conducted by two trained and calibrated examiners. The examiners and patients were blinded to the group assignment, in accordance with the double-blinding randomized clinical trial design. Each restoration was evaluated at baseline (one week after restoration placement), 3 months and 6 months. This evaluation was conducted according to World Federation criteria (FDI)

Inclusion Criteria:

• Be at least 19 years old, be in good general and oral health and be available for follow-up visits
• NCCLs inclusion criteria are; at least 1 mm deep, involving enamel and dentin of vital teeth.

Exclusion Criteria:

• Chronic therapeutic drug history, rampant uncontrolled caries, periodontal disease, pregnancy or lactation, orthodontic appliance use, evidence of xerostomia, evidence of severe bruxing, clenching or TMD, and known sensitivity to acrylates or related materials.
• NCCLs exclusion criteria are; teeth with periapical pathology, symptoms of pulpal pathology, non-vital or previous root canal therapy, previous pulp capping and tooth hypersensitivity

Clinical evaluation of NCCLs restorations was conducted by two trained and calibrated examiners.The examiners and patients were blinded to the group assignment.