This “lip” can break off or abrade on the die during the fabrication process resulting in an open margin on the definitive restoration. This is a critical correction since it is not uncommon to accidently cut too far axially with the rounded diamond creating a “J” margin that leaves a “lip” of tooth structure at the outward extreme of the prepared margin. At this point, fine margin correction is accomplished with the rounded, tapered diamond bur using a plastic or cord packing instrument to protect the gingival tissues (Fig. If desired, the cords may be soaked in a hemostatic solution then dried with a 2X2 prior to placement. The excess at both lingual ends is trimmed, and the ends of the cord are tucked into the lingual gingival sulcus so that the ends butt against one another. First, a #00 cord is packed around each preparation margin starting from the lingual proximal to the facial aspect, then back through the remaining proximal area to the lingual aspect (Fig. This is the ideal location for dentin and enamel bonding procedures.ĮQUICREVICULAR AND INTRACREVICULAR IMPRESSIONS: THE TWO-CORD TECHNIQUEĪ two-cord impression technique is utilized to capture most master impressions for full coverage (circumcoronal) and facial veneer restorations with both intracrevicular and equicrevicular margins (at the free gingival margin). All ceramic restorations can often be placed at the free gingival margin, or in the case of “contact lens” porcelain veneers, slightly supragingival. Porcelain fused to metal crowns are often more esthetic with intracrevicular margin placement. With today’s aesthetic materials options, the restorative margin can be located supracrevicular (above the gingival tissues), equicrevicular (at the free gingival margin), or intracrevicular (in the gingival sulcus). Retraction techniques for master impressions will vary depending on restorative marginal placement. RESTORATIVE MARGIN PLACEMENT IS DICTATED BY THE RESTORATIVE MATERIAL CHOSEN Techniques will be described to aid the dentist in achieving this result. It is important for the dentist to have a critical eye and reject all but the “perfect” master impression. Remember in dental school hearing, “Let’s pour it up and see what we’ve got.” If you can’t see the margins in the impression, they won’t “magically” appear when the impression is poured. Without precision, the definitive restoration is doomed to clinical failure. Marginal detail and tooth structure apical to the restorative margin are both necessary elements of an acceptable master impression. We often think of this procedure as “basic”, but dental laboratories will many times report that “only 20-30% of the master impressions that they receive are clinically excellent!” Because of the nature of the oral environment, moisture control and crevicular bleeding are two things that can make even the most “simple” impression hard to make properly. The precision of the master impression is something that cannot be compromised. The excellence and marginal fit of the definitive laboratory restorations can only be as good as the master dies from which they are created. INTRODUCTION: MASTERFUL FINAL IMPRESSIONS
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