What is a butt joint margin?

Standard prescription is 1.0mm to 1.5mm of cervical reduction for monolithic zirconia and lithium disilicate butt joint preparations. Less than 1.0mm risks ceramic fracture at the margin during seating or function; more than 1.5mm is rarely needed and removes sound tooth structure unnecessarily. The 2023 Journal of Prosthetic Dentistry consensus on all-ceramic prep design treats 1.0mm as the working floor. Dani Dental's prep checklist flags any scan that shows under 1.0mm before the case enters CAD.

Generally no. Porcelain-fused-to-metal restorations use a chamfer or shoulder-with-bevel margin because the metal coping needs a defined seating stop and the porcelain layer needs a finish line that hides the metal collar. Butt joint geometry is specifically a monolithic ceramic design. If a case requires PFM, prescribe a chamfer at 0.5mm to 0.8mm cervical reduction instead. Mixing margin designs across a quadrant case creates fit and esthetic inconsistencies.

Undercuts at the cervical margin cannot be milled accurately and force the CAD technician to either digitally block out (which creates an open margin) or send the case back. At Dani Dental the technician on the case calls the practice within the same business day when a scan arrives with margin undercuts, so the rescan happens before the case loses three to five days in the queue. The alternative, a silent remake after seating, costs the dentist chair time and the patient a second appointment.