When veneering maxillary posterior teeth for esthetic reasons such as widening the buccal corridor or making significant color changes, I recommend always overlapping the buccal cusp. The tooth preparation should extend into the lingual incline of the buccal cusp, reducing it a minimum of 1.0 mm in depth. The extent of the preparation down the incline towards the central groove is dependent on:
- The extent the buccal cusp is being altered.
- If there is an existing restoration on the occlusal surface of the tooth.
How far the preparation then extends down the incline is dependent on the alteration in cusp height – the greater the alteration in cusp height, the further the preparation extends down the lingual incline.
The reasons for this are that it creates a positive seat when the veneer is being bonded to the tooth, and to create a smoother transition from the tooth to the ceramic to accommodate the potential change in cusp height. If you do not accommodate the change in height during tooth preparation, the ceramic veneer would extend beyond the original cusp height and would be very prone to fracture from shearing associated with functional or parafunctional movement.
If there is an existing occlusal restoration, I remove it and incorporated that tooth reduction into the preparation design of the veneer. It then becomes what I call a veneerlay, veneering the buccal surface and onlaying the buccal cusp.