When treating patients, the objectives of restorative therapy must be clear. The first and most basic objective is preservation of the teeth. The attainment of this objective would be far less complex if it could be considered independent of restoration of function, comfort and esthetics, but such is not the case. The latter objectives usually require sophisticated restorative dentistry and often include restorations with intracrevicular margins. Although it is widely accepted that the best restorative margin is one that is placed coronal to marginal tissue, most restorations have margins in the gingival crevice, and permanent tissue damage is common. In attempting to reach his objective, the restorative dentist must remember the fundamental precept of the health professions, which is: Do no harm. Daily observation of the three physiologic dimensions permits the therapist to restore teeth with minimal injury to the periodontium.