Ceramic veneers: the preparation is designed backwards, starting from the final shape

The veneer is the one prosthetic restoration where preparation is designed backwards: one does not reduce the tooth and then decide the shape, one decides the final shape and calculates from there how much to remove.

The mock-up is the instrument that makes this reasoning possible. The desired form is built in resin over the natural teeth, the patient assesses it, and only then is the preparation cut through that form.

The practical difference is substantial. Preparing on the natural tooth removes tissue without knowing how much will actually be needed; preparing through the mock-up removes only where the final volume requires it, and at some points nothing at all.

In cases with rotated or slightly retruded teeth this approach can reduce removal to zero on certain surfaces. The missing volume is added by the ceramic rather than carved from the tooth.

Minimum thickness depends on the material. Feldspathic ceramic layered on refractory can descend to 0.3 millimetres in areas of pure colour, while pressed lithium disilicate requires at least 0.5 to 0.6 millimetres to express its mechanical properties.

Disilicate is more forgiving at try-in and cementation, less fragile to handle, and has flexural strength around 400 MPa against 100 to 150 for feldspathic. Feldspathic remains unsurpassed aesthetically in the hands of a skilled ceramist.

What determines longevity, however, is something else, and it concerns where the margin ends. Bonding to enamel is predictable and stable over time; bonding to dentine is inferior and degrades over the years.

A veneer with margins entirely in enamel shows survival above 90 per cent at ten years. When the margin falls in dentine, figures decline and marginal leakage and discolouration appear.

This constraint governs the extent of preparation more than any aesthetic consideration. If reaching the contact point means leaving enamel, it is better to stop short and manage the colour transition differently.

Incisal reduction is the decision with the most consequences. The window design preserves the natural incisal edge but leaves a visible junction line; palatal wrap offers a superior aesthetic result and better strength, but requires more removal.

In patients with parafunction, palatal wrap is contraindicated: it exposes the ceramic to eccentric load precisely where it is thinnest, and is the commonest cause of fracture in this group.

Cementation requires rubber dam isolation and a purely light-cured resin cement, not dual-cure. Dual-cure cements contain tertiary amines that yellow over time, and at half a millimetre of thickness that shift is visible.

In summary: design the final shape before touching the tooth, stay in enamel even at some aesthetic cost, and choose the material according to who will fabricate it. A well-designed veneer lasts longer than its thickness would suggest.