BRITISH DENTAL JOURNAL VOLUME NO - PDF document

BRITISH DENTAL JOURNALVOLUME 192 NO. 6 MARCH 23 2002 J. M. WhitworthA. W. G. Wallsand R. W. Wassell CROWNS ANDEXTRA-CORONALRESTORATIONS:1.Changing patterns and2.Materials considerations3.Pre-operative 4.Endodontic 5.Jaw registration and 6.Aesthetic control 7.Cores for teeth with 8.Preparations for full9.Provisional restorations 10.Impression materials and11.Try-in and cementation12.Porcelain veneers13.Resin bonded metal PRACTICE BRITISH DENTAL JOURNALVOLUME 192 NO. 6 MARCH 23 2002 encircles the tooth, extending 1–2mm ontofor moderately and severely broken down ante-Posts: a means of protecting teeth fromtooth provides reinforcement. In reality, the postaccommodate it may in fact weaken the toothtion at the terminus of the post channel (Fig. 10).pulp chamber and canal entrances (Fig. 11), thenshould be given to how it can provide retentionfor the core without weakening or stressing thenew systems continue to appear. but as in many other areas of dentistry, well-It is likely that many post systems will pro-Post lengthby extending the post apically, but also by pre-least 4–5mm of gutta percha should remain api-11,33 (a)(b)(c) Figure 10 a) Wide and tapered rootweakens the root further. Stresses little or no further loss of tissue Fig. 11 Canal entrances and pulpall amalgam core in a molar. similar way for anterior teeth (a)(b)(c)Additional post Fig. 12 a) Fractured and root-treated incisor to be restoredb) Rooftop preparationdamagingly removes allremaining coronal toothtissue, and may compromiseprotective ferrule. c) Conservative preparation ferrules PRACTICE BRITISH DENTAL JOURNALVOLUME 192 NO. 6 MARCH 23 2002 Post shapeposts, such as the Parapost (Fig. 13) are moreHowever, theTapered posts such as the PD system have aing stresses by tapered (including customisedfracture. However, such forces are not active ining a protective coronal ferrule cannot be over-systems, Torbjornet not, however, directed to posts involving activeIn summary, parallel-sided posts are preferredto tapered posts, but each case should be carefullywedge-like, tapered design.Popular commercial threaded posts include:Radix Anker (Fig. 15) Dentatus (Fig. 16) Kurer Anchor (Fig. 17) option. Increasingly, resin-bonding agents may Fig. 13 Parapost —parallel, serrated post (a)(b) Fig. 14 a) Stress concentration atthe base of a parallel post concentration with a chamfered tip Fig. 15: Radix Anker —parallel, self-tapping or pre-tapped post Fig. 16 Dentatus screw —tapered, self-tapping post Fig. 17 Kurer Anchor —parallel, canal is pre-tapped PRACTICE BRITISH DENTAL JOURNALVOLUME 192 NO. 6 MARCH 23 2002 the crown and coronal 2–3mm of the root canal.ate a ‘rooftop’ preparation (Fig.12a, b). Weak,complete the preparation coronally. required (Fig. 12c). This may either be cast, orcanal, leaving 4–5mm of filling material api-cally. An initial path is made with hot instru-mum speed achievable with the slow speedand shape the channel. Excessive dentineshould not be removed to accommodate snuglyImpressions may then be taken for the pro-unlikely to provide an hermetic coronal seal dur-Posterior teeth, which have lost one or bothconsidered necessary, it should usually be placedservative as a cast metal onlay, or three-quarter1–2mm onto sound tooth tissue to provide all-Adhesively retained plastic restorations can-splints. If there is no plan to crown a weakenedment is on probation, or for financial reasons,reduced in height by 3mm and overlaid withTeeth with little or no coronal tissue remaining (a)(b) Fig. 18 Cuspal protection and development of protective ferrules for posterior teeth with varying amounts of tissue loss: a) Simple metal onlay, b) Three-quarter crown, c) Full coverage crown Fig. 19 Cast post and core with a damaged incisor root PRACTICE BRITISH DENTAL JOURNALVOLUME 192 NO. 6 MARCH 23 2002 an effective ferrule. Alternatively, a convention-collar extending 1–2mm onto tooth tissue toAlternatively, self-curing composite can becore build-up, or advantage taken of the cohe-Posterior teeth which cannot be built up withent angles may be manufactured (Fig. 21).1.All teeth to be crowned should be carefully2.Teeth with healthy pulps should be prepared3.Root-treated teeth are at risk of fracture and1.Randlow K, Glanz P O. On cantilever loading of vital and nonvital teeth: an experimental clinical study. 271-277.2.Zach L. Pulp lability and repair: effect of restorativeOral Surg 111-121.3.Pashley D H. Clinical considerations of microleakage. 70-77.4.Cox C F, Subay R K, Suzuki S, Suzuki S H, Ostro E.Int J Periodont Rest Dent 241-251.5.Bergenholtz G. Iatrogenic injury to the pulp in dentalprocedures: aspects of pathogenesis, management and1991; 41: 99-110.6.Seltzer S, Bender I B. 7.Abou-Rass M. The stressed pulp condition: An endodontic-J Prosthet Dent8.Bergenholtz G, Nyman S. Endodontic complicationsJ Periodontol9.Felton D, Madison S, Kanoy E, Kantor M, Maryniuk G. Long (a)(b)(c)(d) Light post within the composite resin ‘reline’. Tooth margins prepared for thetakes advantage of the materials cohesive strength in thick section. Tooth margins prepared for the crown to provide a ferrule Fig. 21 a) Metal post and core for adecoronated posterior tooth. The palatal root a