Dental Tribune India Issue

impression (Figs. 8, 9 & 10). Technical procedure The most commonly used mate- rial for fabricating models is dentalstone,owingtoitscompat- ibility with all types of impres- sion materials, low expansion and high compressive strength. The use of Class IV dental stones thathaveavolumetricexpansion of approx. 0.08% is preferred, e.g. Tewerock and Tewestone (Kettenbach; Figs. 11 & 12). Careful pouring of the impres- sion using vacuum-mixed dental stone ensures precise reproduc- tion of all the details (Fig. 13). A precise, stable working model should be fabricated that can reproduce the anatomical fea- tures (occlusal surfaces, proxi- mal contact points). The gingival section was removed under a stereomicroscope to expose the preparation margin (Figs. 14 & 15). It is difficult to recreate the natural aesthetics with metal-bonded restorations, par- ticularly when there is little space available. Apart from the search for materials with im- proved aesthetic characteristics, development concentrates on new technologies, e.g. fabrica- tion with semi-finished products using the CAD/CAM technique, which eliminates certain work- ing stages that are normally completedmanually.Inthiscase, thepatientwastreatedwithazir- conia crown, which was ve- neered using low-fusing por- celain. Zirconia, with a flexural strength of 900 MPa and a frac- ture resistance of 9 MPa, has bet- ter mechanical properties than conventional porcelains without a metal core;14 zirconia is partly stabilised with yttrium, which further enhances its mechanical properties. In addition to aesthetics and fractureresistance,animportant requirement for the long-term success of a restoration is also a high degree of marginal adaptation (Fig. 16). The major- ity of researchers agree that marginalgapsof100µmareclin- ically acceptable with regard to the service life of a restora- tion.15,16,17 In our opinion, how- ever, the overall goal should be to attain a marginal adaptation in the region of 20 to 30 µm. Clinical finishing Cementation is the final stage of prosthetic treatment. It should be noted that while the luting cementdoesnotprovidetheden- tistwiththepossibilityofcorrect- ing inaccuracies in the restora- tion, it does contribute to clinical success.Thelutingcementinflu- ences the functional perform- ance of a prosthodontic restora- tion; should the wrong cement be selected or used incorrectly, it can have an adverse effect on the service life of the crown. A high mechanical compressive strength is one of the most important properties. As luting material is distri- buted in very thin layers, it must be capable of withstanding com- pressive loading in order to pre- vent fractures. We used glass io- nomer cement that has not only a high compressive strength, butalsotheadvantageoffluoride release. A comparative study of various cements established that the glass ionomer cement we used in this case produced the lowest film thickness of 20 µm.18 A follow-up examination was completed one week after per- manent cementation to check the integration of the prostho- dontic restoration into the tissue. The clinical procedure was completed with a further follow-up examination to check the occlusal relationship, which in most cases cannot be com- pleted satisfactorily when fitting the restoration, owing to stress to the patient. The correct use of a temporary restoration & an adequate morphological design of the permanent restoration contributed to good adaptation of the incisor tooth papilla, as was established at intervals of 30, 60 and 90 days (Fig. 17). Editorial note: A complete list of references is available from the publisher. DT Dentaltribune|July-September, 2010 Clinical 19 Dr Ugo Torquati Gritti and Giancarlo Riva are founder members of the international laboratory association “Dental Excellence-International Labora- tory Group”. They currently live andpracticedentistryinMilan,Italy. About the author Fig. 6: Apply a thin coating of Panasil adhesive to the impression tray and adhere to the drying time.—Fig. 7: Load the impression tray uniformly. Also load the palatal vault.—Fig. 8: Note the thickness of the material at the margins of the impression, which is an indication that there was not excessive horizontal displacement of the gingiva.—Fig. 9: Details of the impression: it is evident that the area above the preparation margin is extremely smooth and has been reproduced very accurately around the entire 360°.—Fig. 10: The one-step putty-wash impression enables intimate contact between the flowable and viscous material; the light material is used for optimally reproducing the details.—Fig. 11: The most commonly used materials for fabricating models are Class IV dental stones, owing to their compatibility with all types of impression materials.—Fig. 12: The impression material should not be sprayed with wetting agent before pouring. The low volumetric expansion of the model material ensures excellent volumetric reproduction of the tooth impression.—Fig. 13: Working model fabricated using high-strength dental stone; note the excellent reproduction of the preparation margin, which was produced with minimal horizontal and vertical displacement.—Fig. 14: Retention of the crown was achieved not only by the luting cement, but also by the convergence angle between the two opposing axial walls. According to current thought, this angle should be between 10 and 22°.—Fig. 15: The gingival section was removed under a stereomicroscope to expose the preparation margin. In this case, no spacer was required with the selected prosthodontic restoration, a zirconia crown; the cement gap required was determined using CAD.—Fig. 16: Finished zirconia crown, which was veneered using low-fusing porcelain. A follow-up examination was completed three weeks after cementation; note the gingival integration of the restoration emergence profile at the sulcus owing to the good marginal adaptation.—Fig. 17: The correct use of a temporary restoration and adequate morphological contour of the permanent restoration produce an optimally adapted incisal papilla.