PDF: Tooth preparation for ceramic veneers: when less is more

Historically, preparations for ceramic veneers have varied from extremely aggressive to a minimal reduction or a lack of preparation.

The most modern classification takes into account the amount of enamel available and the amount of dentin exposed: 

Class I – without preparation or minimum preparation with the maintenance of approximately 95% of the enamel; 
Class II – minimally invasive preparation with a reduction of up to 0.5 mm and the maintenance of approximately 80% enamel; 
Class III – conservative preparation with tooth reduction between 0.5 to 1.0 mm and the maintenance of approximately 50% to 80% enamel; 
Class IV – conventional preparation with more than 50% enamel reduction.

Today, we are moving toward minimally invasive dentistry with the philosophy of less is more. Less tooth reduction means more adhesion and clinical longevity. In a longitudinal study with a 12-year follow-up, ceramic veneers cemented on enamel showed significantly higher clinical longevity than those cemented on dentin, with success rates of 98.7% and 68.1%, respectively. 

Deeper preparations with dentin exposure increase the risk of microleakage and adhesive fractures. Mechanical interlocking with enamel provides a more stable bonding than with dentin.

In addition, the flexural strength of the tooth/porcelain set may be affected because dentin provides a less rigid base for restoration placement than enamel does due to its much lower modulus of elasticity than porcelain. 

In recent years, laboratory techniques have evolved to produce ultrathin ceramic veneers, which has led to no-prep veneers becoming more popular. 

This type of treatment gives the false impression of greater technical ease because it dispenses with the manual skill necessary to prepare a tooth, does not require temporary restorations, and the impression may be performed without gingival retraction.

However, clinical experience has shown that at least enough reduction is required to obtain clear cervical and interproximal finish lines. 

This is important because it clearly indicates to the dental technician the boundaries of the veneer, avoids unwanted overcontour, and assures well-finished margins and a more natural transition between tooth and restoration. 

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