Proper Handling Of Zirconia Restorations
by Richard Pavlak, CDT, MDT, FNGS
Proper handling of the zirconia substructure is very important to insure a long term favorable result. The reduction and contouring instruments that are utilized, as well as, how they are utilized, become a big part of the final result.
The instruments this author chose are from the Green State Zirconia Finishing kit. After the pre-sintered coping has been removed from the milled block, the inside edge of the margin is marked with a red pencil. The excess is reduced using the HE Silicone wheel # 501(Fig1). After preliminary reduction of the connector, final adjustments were made with the GS Contour 2 step instrument (Fig 2). The GS Contour instrument should be used under loupes or microscope, and at the very last adjustment point. The larger gray segment of the instrument quickly reduces the larger final mass of the connector. The ultra fine white tip then gently removes and smoothes any final excess material.
The 6 hand piece diamonds in the kit are excellent for refining the anatomy of full contour zirconium crowns prior to the final sintering. Before the restoration is put in the sintering oven, it is recommended that the coping be placed in a conventional porcelain oven. The coping is fired from 500c to 700c, and then held there for 5 minutes. No vacuum is used. This cleaning process helps to eliminate any contaminants acquired during the milling and finishing stages.
After the coping has been sintered and cooled, the fit is verified, and the final adjustments are made to reduce and perfect the marginal integrity. This step should be done under a microscope. Diacool diamond infused stones are used for this procedure (Fig 3).
The technician should always use minimal pressure and low RPM so as to prevent introducing micro fractures into the restoration.
The coping is now ready for the ceramic application. The fit is verified once again (Fig 4). A fluorescent liner material is used to create a natural fluorescent layer at the deepest level. The ceramic is mixed with glaze liquid so that the thin layer will shrink more when fired. This procedure provides an opportunity for the ceramist to mix in fluorescent stains that will characterize the gingival and occlusal areas. This layer is carefully dried under the furnace muffle until it is chalk white in appearance. The coping is now fired, under vacuum, to 50 degrees centigrade higher than the material’s normal temperature. This will insure a tenacious bond. The coping is now ready for the ceramic buildup. (Fig 5 ) The final firing of the crown should have a long cooling cycle to insure that the ceramic ends up in a state of compression.
Utilization of the proper contouring techniques and instruments, will afford the technician the opportunity for excellent long term results with zirconia restorations.