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Bonding Porcelain Restorations
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Ceramic Etching Products: Hydrofluoric (HF) acid-based etchants etch ceramics well. Two commonly used products are Ceram-Etch (Gresco: 800-527-3250) and Ceramic Etching Gel (Austenal: 800-621-0176).

Posterior Bonded Restoration Luting Agents: Posterior resin luting agents should be autocured or dual-cured. Generally only a few shades are required, such as light or untinted, universal, and dark. Commonly used materials include: Varilink II (Vivadent), Nexus (Kerr), Duo-Cement (Coltene), Enforce (Caulk), and Lute-It (Jeneric Pentron). Many other good products are available.

How Porcelain Etchants Work: The porcelains and ceramics used in dentistry are heterogenous materials that contain a high-fusing filler in a low-fusing glass matrix. The low-fusing matrix is more soluble in acids, which allows for micromechanical porosities to occur when this matrix dissolves and leaves the roughness of the filler.

Determining the Proper Ceramic Etching Time: Porcelain can be under- or over-etched. Always make a test strip to determine the proper etching time before using a new ceramic etchant with a new porcelain. To do this, place a thin line of etchant gel at one end of a ceramic restoration. In 30 seconds, place a second line next to it. Keep adding lines at 30-second intervals until about eight lines have been placed. Thirty seconds after the last line is placed, rinse all of them. Now you have eight etching times that are 30 seconds apart. Examine the lines closely. The first lines are usually dull and then become white, then frosty. The frosty lines continue until the lines appear white and powdery. The dull lines are not etched enough since the surface does not scatter light. The first most frosty line (with the shortest etch time) is the correct etching time for that etchant/ceramic combination. The maximum light refraction or frosty appearance is the optimum etching depth. A longer etch time just dissolves the surface away but yields no more depth in microporosity. The powdery lines have so much matrix removed that the filler is contaminating the surface.
       Over-etched ceramics are weak, have lower bond strengths, and fit more loosely than properly etched porcelains. This test strip can be done by a laboratory if you and the lab use the same ceramic etchant (and you should).
       Porcelains and ceramics used in dentistry are heterogenous materials that contain a high-fusing filler in a low-fusing glass matrix. The lower fusing matrix is more soluble in acids, which allows for micromechanical porosities to occur when the matrix is dissolved and leaves the filler.

Silane Products: Silanes once came as two components that the dentist had to activate by mixing and then waiting 10 minutes before use. Others needed to be added with an etching solution. RelyX Ceramic Primer (3M), formerly Scotchbond Ceramic Primer, was the first preactivated silane primer. Most manufacturers now offer good preactivated silanes. These products are used by simply placing on a cleaned porcelain surface and drying off. Clearfil Porcelain Bond (Kuraray) is a three-part chemically activated primer with good adhesion. Porcelain Bonding & Repair Kit (KHS) is a unidose kit with HF acid and a silane. Many other good products are available.
       Silanes can go bad over time and precipitate out of solution to form a silicone barrier (such as the silicone used in impression materials), which can actually reduce the bond strength to porcelain. Bad silanes usually appear cloudy.

Silanes--What Do They Do?: Silanes reduce the surface tension of etched ceramics to allow easier penetration by a resin. Silane bonds to porcelain well and, once applied to the ceramic, can be cleaned with phosphoric acid, rinsed, and dried. The silane does not need to be reapplied. Reapplication is only necessary if the porcelain is adjusted or re-etched with hydrofluoric etching gel. Most silanes provide equal clinical success since the bond strength is achieved through the etched surface, not the silane. However, silanes are helpful to improve the adapation of resin to etched ceramic and reduce voids. Silanes can also be used to attach resin to porcelain without HF etching. Although the initial bond strength may be high, it deteriorates over time. Thus, ceramic materials that can be etched should be etched prior to resin bonding.

Silane Shelf Life: Silanes can go bad over time and precipitate out of solution to form a silicone barrier (such as the silicone used in impression materials), which can actually reduce the bond strength to porcelain. Bad silanes usually appear cloudy. After applying the silane, rinsing the ceramic with water will wash off any silicone layer since it can not attach to the surface. Most ceramic primers today are highly diluted to extend their life. However, if large amounts of the solvent (usually ethanol) evaporate, the higher concentration of silane will tend to precipitate out and the product should be discarded. It is important to keep the bottles well sealed.

Porcelain Veneer Luting Agent Materials: Variolink II (Vivadent) and Nexus (Kerr) come in three basic shades (universal, clear, and opaque). Calibra (Caulk) comes in two basic shades (translucent and light). All come with a low- and high-viscosity catalyst paste that can be mixed with the base paste to alter viscosity of the dual-cured mode. Compolute (ESPE) comes in capsules and in Vita shades. The most useful shades are untinted, clear, neutral, or translucent. These retain the original tooth shade and provide the best vitality. Many other luting agents are available. These are made by a few manufacturers and sold under a number of different brand names. This is common in dental materials. Among the products available are: Veneer Luting Agent (Bisco), Insure (Cosmedent), Recover (Teledyne Getz), and Mirage FLC (Chameleon). Many other good products are available from ceramic and composite manufacturers. A medium-viscosity milk-colored shade can be made by hand mixing a white color modifier with a heavy viscosity composite.

Porcelain Veneer Cementation: Porcelain veneers should always be cemented with composite. The increased stiffness of composite compared to other luting agents improves the support of the porcelain. With lucent veneers, a light-cured composite that will flow (usually 60-70% filled) works well. With masking veneers or posterior ceramics, a dual-cured composite is preferred. The major consideration in selecting a luting agent is the shade. Generally, only three shades are required when cementing veneers. Lucent, universal (A2-A3), and milk-white (opaque). Dark shades should rarely be used since they darken teeth (which few people want) and they reduce vitality.

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