Lava Z90 screen is a whole combo of display and touch screen both. It simply means that both parts are joined together and can't be detached.
Numerous consumers notify us that they only need to change the touch screen glass because their display is perfectly fine. Though, It is not possible as both parts are combined with each other.
The touch screen glass is closely attached to the display. Think it like, two very thin glasses are attached together and you want to separate them to replace one.
For this reason, If you have a broken Lava Z90 and looking for screen replacement then, buying a complete combo is the right way to go. The mechanic will take out the broken display unit and change it with a new one.