Evaluation of Surface Treatment of CAD-CAM Composite

Protocols for the surface treatment of composite materials utilized in indirect posterior restorations are not consistent. The best treatment for the inlay surface remains to be determined. Objective: This study was designed to determine the best method for preparing the composite indirect material for luting. Methods: Sixty Paradigm™ (3M ESPE, St Paul MN) MZ100 CEREC® composite discs were prepared at 10mm diameter 2mm thick. Specimen were embedded in an acrylic resin and resurfaced with 600 grit paper under irrigation. Specimens were randomly assigned to one of six treatment groups: No treatment (NT), Silane (S), Aluminum oxide etching (AO), Aluminum oxide etching plus silane (AOS), Hydrofluoric acid etching (HF), and Hydrofluoric acid etching plus silane (HFS). Following surface treatment, each specimen was bonded with RelyX™ (3M) cement in a 2.38mm diameter column and light cured. Bond strengths were determined by subjecting each specimen to a shear force at a crosshead speed of 0.5mm utilizing an Instron 5566 (Canton, MA). Force at failure was recorded. Mean bond strengths (MPa+sd) were calculated and analyzed with an ANOVA statistic with a Scheffe post-hoc test. Results: The mean shear forces were HF: 99.5 (±33.4), HFS: 71.8 (±13.3), AO: 112.5 (±11.7), AOS: 118.9 (±15.5), NT: 74.8 (±20.0), S: 107.7 (±11.8). Significant differences were found across treatment groups with the exception of the HF treatment group. S, AO, or AOS treatments displayed higher shear forces as compared to the NT and HFS treatment groups (p<0.05). Conclusions: HF etch alone was very variable and should not be utilized. Acid etch plus silane treatment and roughened control groups (600 grit) were weaker than all treatments. Accordingly, such treatments should not be used to prepare milled composite surfaces. Silane, air abrasion, or air abrasion plus silane treatments are preferred techniques with low standard deviations and high bond strengths.