Restoring teeth following crown lengthening procedures David Assif, D.M.D.,* Raphael Pilo, D.M.D.,** and Barry Marshak, B.D.S.** The Maurice and Gabriella School of Dental Medicine, Sackler Faculty of Medicine, Tel-Aviv University, Tel Aviv, Israel Crown lengthening procedures are often necessary to successfully restore teeth that have been mutilated at or below the level of the bone crest. Forced eruption is preferred to surgical removal of supporting alveolar bone, since forced eruption preserves the biologic width, maintains esthetics, and at the same time exposes sound tooth structure for the placement of restorative margins. To properly construct a crown, the minimal distance from the alveolar crest to the coronal extent of sound tooth structure should be 4 mm. Before initiation of forced eruption, the restorability of the root after completion of the orthodontic phase must be considered. A technique is suggested to calculate the root-to-crown ratio that will be created after root extrusion with respect to the coronal level of sound tooth structure before treatment. (J PROSTHET DENT 1991;65:62-5.) I n order to support and retain a cast restoration, the clinical crown of the tooth must provide adequate bracing, retention, and resistance.l Sound tooth structure may be present only at or below the level of the bone crest. The presence of sufficient sound tooth material coronal to the bone crest is essential to satisfy the following criteria2: (1) the placement of the margins of the cast restoration on sound tooth structure; (2) preservation of the biologic width together with a healthy periodontium; (3) the abil- ity to make an impression of the prepared tooth; and (4) esthetics. Table I. Values of average crown height, root length, and root-to-crown ratio for maxillary and mandibular teeth Tooth Crown height Root length (mm)* (mm)* R/C Maxilla Central incisor Lateral incisor Canine First premolar Second premolar 10.5 13.0 1.24 9.0 13.0 1.44 10.0 17.0 1.70 8.5 15.0 1.76 8.5 14.0 1.65 These teeth usually have undergone endodontic therapy. The first step in the reconstruction is the construction of a post and core. The margins of the final restoration must embrace at least 2 mm of sound tooth structure apical to the inferior border of the core material, which usually re- quires a crown lengthening procedure. This procedure can be carried out by surgical or orthodontic techniques, or by a combination of the two.3 Mandible Central incisor Lateral incisor Canine First premolar Second premolar 9.0 12.5 1.39 9.5 14.0 1.47 11.0 15.0 1.36 8.5 14.0 1.65 8.0 14.5 1.81 *Data from Kraus BS, et al. Dental anatomy and occlusion. Baltimore: The Williams & Wilkins Co., 1980:5-115. SURGICALLY LENGTHENING CLINICAL CROWNS Lengthening the clinical crown by removing supporting alveolar bone to expose more sound tooth structure may be effective, but usually produces other problems.4 Some of these are: (1) it is difficult to perform an ostectomy on a single anterior tooth without creating an esthetic defor- mity; (2) following’removal of bony support, an inverse and unfavorable root-to-crown ratio (R/C) can be expected due to the resultant long clinical crown; (3) if the osseous sup- port of the tooth is questionable before surgery, additional removal of bone further decreasesthe R/C so that restora- tion becomes impractical; (4) removal of supporting bone from adjacent teeth to create a normal bony architecture may severely compromise these teeth; (5) should the ostectomy expose furcations, exceptional oral hygiene measures are needed to preserve the tooth; and (6) teeth that have short or concial roots may exhibit excessive mo- bility after surgery, and should the conditions for splinting of adjacent teeth not be favorable, alternative treatment is indicated. FORCED ERUPTION OF TEETH *Coordinator, Senior Clinical Lecturer, Department of Pros- thodontics. **Instructor, Department of Prosthodontics. 10/l/23149 Heithersay5 and Ingbe# suggested the use of forced eruption for treatment of teeth with sound tooth structure at or below the bone crest, and for isolated osseousdefects. The objectives include conservation of bone, preservation of biologic width, exposure of sound tooth structure for the placement of restorative margins, and maintenance of es- 62 JANUARY 1991 VOLUME 86 NUMBER 1