Are there different types of self-etch bonding agents?

There are three types of self-etch bonding agents – 6^th-generation (Type I), 6^th-generation (Type II), and 7^th-generation. The 6^th-generation (Type I) bonding agents are applied in two layers – an acidic primer and then an adhesive. Examples are Clearfil PROTECT BOND (Kuraray America) and AdheSE (Ivoclar Vivadent). The 6^th-generation (Type II) primer and adhesive are mixed and then applied in one layer. An example is Xeno III (DENTSPLY Caulk). The 7^th-generation bonding agents are supplied pre-mixed. Examples are G-BOND (GC America), BOND FORCE (Tokuyama America) and Optibond All-in-One (Kerr Corporation).