Influence of silane type and application time on the bond strength to leucite reinforced ceramics

INTRODUCTION: All-ceramic restorations currently dominate the market of indirect restorative materials due to their biocompatibility, longevity and superior aesthetics [1]. Silica-based ceramics, such as leucite, carry the advantage of being receptive to surface treatments, making them bondable to tooth substrates [2]. However, a standardised application protocol regarding silane coupling agents is lacking. Such step is critical to ensure durability of the restoration placed in situ. Post-etch cleaning and silane application have been proven to increase bond strength, however, this step varies for each material [3]. The aim of this research was to assess the influence of different types of silane coupling agents and respective application times on the bond strength of the ceramic-resin interface. MATERIALS AND METHODS: Ten leucite reinforced glass ceramic blocks (IPS Empress CAD LT BL4/C 14) were divided into equal halves. Of the samples obtained, 6 were randomly divided into three groups according to the silane used: G1 BIS-Silane (Bisco, Schaumburg, IL, USA); G2 ESPE Sil Silane Coupling Agent (3 M ESPE AG, Seefeld, Germany); G3 Monobond Plus (Ivoclar-Vivadent, Schaan, Liechtenstein). Each was then divided into two subgroups, according to the surface conditioning time: T1 (1 min.) or T2 (5 min.). Each block was acid etched (HF 9.5% − 1 min), post-etching cleaned (OPA 37.5% − 1 min; ultrasonication − 2 min.) and silanized. Heat treatment was carried out at 100 °C (1 min.). Then a thin layer of Optibond FL (Kerr) adhesive was applied and each block was adhered to pre-heated resin at 55 °C. The samples were light cured for 40 s on each side (1200 mW/cm(2)). Samples were sectioned into microspecimens (1 ± 0.2 mm(2)) that were subjected to aging (10,000 thermocycles − 5 and 55 °C). The microspecimens were tested in tension at a crosshead speed of 0.5 mm/min, until they debonded. Data analysis was carried out by a two-way ANOVA, at a significance level of 5%. RESULTS: The group featuring BIS-Silane with longer application time (G1T2) presented a mean µTBS value (32.4 ± 19.6 MPa) significantly higher to all other groups (p < .001). Monobond Plus registered the lowest mean µTBS value (G3T1 − 18.5 ± 7.3 MPa) and (G3T2 − 17.3 ± 5.8 MPa). The type of silane coupling agent has shown to have a significant influence on the microtensile bond strength (p = .001; η(2)=0.16). DISCUSSION AND CONCLUSIONS: Some authors have previously suggested that silanization could benefit from longer application times, but seldom research has been found featuring this variation protocol [3,4]. Silanes require a hydrolysation process in order to establish chemical bonds. Two-bottle systems show the highest bond strength results and may benefit from longer application times. The addition of 10-MDP seems to have no significant advantage over traditional silane coupling agents.