If you want to get the anticipated final restorative dimensions, keep your preparation guided.

Control of reduction with silicone guides :
In regards to veneer preparation, the depth of cut must be guided and controlled as it has a direct influence on the establishment of the desired ceramic veneer shade after cementation.
A diagnostic wax-up should be utilized as a reference for tooth reduction. Silicone guides, fabricated over the wax-up, provide simple and indispensable tools for control and in the reduction of enamel. 

Two guides should be fabricated: 
 a vertical guide (sectioned in the buccolingual direction) for reduction control in cervico-incisal direction.
 a horizontal guide for the mesiodistal reduction control. 


⛔️ With teeth darkened by endodontic treatments in which the labial surface is intact and the rehabilitation of which will maintain the natural morphology, the silicone guide may be fabricated directly within the mouth and prior to preparation (use the natural morphology as a guide).