There are several differences between OEM and aftermarket screens, but I will only explain the touch. The reason that OEM Screens’ touch still functions when the top glass cracked, is because the digitizer(touch functionality) is adhered to the actual LCD and not the top glass. So as long as the LCD isn’t cracked, the digitizer shouldn’t be damaged either. On most aftermarket screens, the digitizer is adhered to the top glass. When this top glass breaks, typically the digitizer does too. Some after market screens have Incell technology. This means that the digitizer is adhered to the lcd and not the top glass(similar to OEM screens). So if just the top glass breaks then the touch should still work. As Minho pointed out, there are lots of different quality aftermarket parts. Here is a breakdown: OEM: topglass breaks, touch should still work Incell Aftermarket: Topglass breaks, touch should still work Most Aftermarket screens: Topglass breaks, touch should stop working.