The effect of surface modifications on titanium to enable titanium–porcelain bonding

Objectives Titanium–ceramic restorations are currently used, despite the pending problem of titanium–ceramic bonding, which has only been partially solved. The surface treatment of the metal proposed by the manufacturer promotes lower bond strength between titanium and porcelain when compared to the conventional metal–ceramic systems. The objective of this study was to evaluate the influence of acid and caustic baths on the bonding characteristics of specific titanium porcelain bonded to cast commercially pure titanium (CP Ti). Methods Eighty strips of cast CP Ti were obtained in dimensions of 25 mm × 3 mm × 0.5 mm, and divided into eight groups (n = 10) which were subjected to surface treatment by immersion in one of the follow solutions—group HF: HF 10%; group NaOH + HF: NaOH 50%–CuSO4·5H2O 10% followed by HF 10%; group HCl: HCl 35%; group NaOH + HCl: NaOH 50%–CuSO4·5H2O 10% followed by HCl 35%; group HNO3: HNO3 35%–HF 5%; group NaOH + HNO3: NaOH 50%–CuSO4·5H2O 10% followed by HNO3 35%–HF 5%; control group: treated according to the manufacturerʹs instructions; NaOH + control group: treated according to the manufacturerʹs instructions followed by immersion in NaOH 50%–CuSO4·5H2O 10%. Low fusion porcelain (Vita Titankeramik) was applied to the center of one of the sides of each CP Ti sample with dimensions of 8 mm × 3 mm × 1 mm. All groups were submitted to a three-point flexure test. Scanning electron microscopy (SEM) photomicrographs were taken to characterize the failed surfaces at the titanium–porcelain interface. Anova and Tukeyʹs multiple comparison tests were used to analyze the data at a 5% probability level. Results All groups treated with NaOH 50%–CuSO4·5H2O 10% solution showed significant superior values when compared to groups treated exclusively with acid solution. There were no significant differences between HF (21.2 MPa) and HCl (23.4 MPa) groups; control (25.2 MPa), HCl (23.4 MPa) and HNO3 (26.6 MPa) groups; NaOH + HF (29.9 MPa) and NaOH + HCl (30.8 MPa) groups; NaOH + HNO3 (34.8 MPa) and NaOH + control (32.1 MPa) groups. SEM analysis indicated a combination of cohesive and adhesive fractures in NaOH + HNO3 and NaOH + control groups, while mainly adhesive fractures were found in the other groups. Significance Bond strength between porcelain and cast CP Ti can be increased by use of a caustic bath prior to porcelain firing.