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Medical Forum / General / Dentistry / April 2006cementing a PFM crown
Hi there, I am going to be cementing a PFM crown to a preped tooth. We have relyx at our dental school, which is a GIC. Would anyone advise etching the the prep to open up the dentinal tubules, so that the GIC can bond by micromechanical and chemical bonding, or is this theory a load of crap? What about having the fitting surface of the crown sandblasted, ultrasonic and dipped in HF solution, then using a silane coupling agent? This is a lot of messing about because I would then have to etch the tooth, use a dentine bonding agent and a chemical cured composite as a sandwich between the dentine bonding agent and silane coupling agent. And I guess this would have to be all done under rubber dam. Any thoughts/ advice appreciated. Its overkill. Glassionomers bond ionically to tooth structure. The reason we etch (that is, acid phosphorylate) tooth structure is that composites are Bis-GMA and therefore bond (polymerize) to like molecules but cannot interact with tooth structure. We etch (but do not over etch) to open up tubules so that the adhesive layer can penetrate and bond mechanically (not chemically). As for HF, un-uh. That is strictly for porcelain bonding. Please become knowledgeable with Silane that is coming into the market as of recent. Joel -- Joel34 but in theory opening up the dentinal tubules should allow for an increase in surface area hence a larger area for bonding. anyone do this? >but in theory opening up the dentinal tubules should allow for an >increase in surface area hence a larger area for bonding. > >anyone do this? Have done it when using Calibra. Are we talking all ceramic or porc/metal ? Porclain metal crown > Porclain metal crown If you are using a glass ionomer (or a resin-modified glass ionomer) cement, then no etching of tooth structure should be necessary. An all-resin type of cement, on the other hand, requires etching for any bonding to take place -- UNLESS you use a self-etching cement. Why not just ask your professors at the dental school? That's why you are paying the dental school so much money! They are supposed to be giving you an education regarding the different crown and bridge cements, their properties, their indications, and the details of proper preparation and use. - dentaldoc >Porclain metal crown Nothing wrong with using fuji 1, flecks, durelon, etc... Any instructions with the Rely- x? Silane is for bonding composite resins / cement to porcelain (eg cementing a veneer / Cerec) I doubt you need it with the Rely-x if it is a GI cement. (Do check it is GI - Rely-x also do a composite cement). In my humble experience, when cementing a crown, I remove the temporary, give the prep a clean, often with an ultra sonic scaler, blow it dry and stick the PFM crown on with GI cement with no further treatment to any of the surfaces prior to cementation. Seems to be fine. >>Porclain metal crown > > Nothing wrong with using fuji 1, flecks, durelon, etc... YUP ..... PFM .. porcelain fused to metal ..... is the correct terminology versus "ceramic crown" (no metal) or "veneers" which are a thin fingernail-like shell of porcelain bonded to the fronts of the teeth -- Joel34 You can etch prior to GIC for a modest increase in bonding strength - not sure if it's worth the trouble. You must etch with polyacrylic acid or not at all. If you use conentional etch you will fully expose the collagen fibres and you're going to lose bonding strength with the GIC (it's not like composite). George
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