Posterior indirect adhesive restorations: updated indications and the Morphology Driven Preparation Technique

The aim of this article is to identify the indications for adhesively cemented restorations and to provide a correct step-by-step protocol for clinicians. New cavity preparation principles are based on morphological considerations in terms of geometry (maximum profile line and inclination of cusp lines), and structure (dentin concavity and enamel convexity). In this article, we discuss previous preparation concepts that were not designed purely for adhesive restorations and were therefore not conservative enough or suitable for adhesive procedures. The novel cavity shape consists of continuous inclined plane cavity margins (hollow chamfer or concave bevel) on axial walls, whenever they are coronal to the equatorial tooth line. A 1.2 mm-thick butt-joint preparation is performed in the interproximal box and on the axial walls when the margins are apical to the equatorial line. The occlusal surface is anatomically prepared, free of slots and angles. The author's suggestion is to avoid shoulder finish line preparation around cusps, occlusal slots, and pins, as they are less conservative, incompatible with adhesive procedures, and involve unnecessary dentin exposure. The clinical advantages of this new "anatomic" preparation design are 1) improving adhesion quality (optimizing the cutting of enamel prisms, and increasing the available enamel surface); 2) minimizing dentin exposure; 3) maximizing hard tissue preservation (the cavity being designed for cementation with reinforced composite resins, improvement of flow, and removal of excess material); 4) optimization of esthetic integration due to the inclined plane design, which permits a better blending at the transition area between tooth and restoration. These preparation principles may be effectively used for all adhesively cemented restorations, both according to traditional concepts (inlay, onlay, overlay) and new ones (additional overlay, occlusal-veneer, overlay-veneer, long-wrap overlay, adhesive crown). Thus, a balance between restoration and prosthodontics is created, which is characterized by a more conservative approach.