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Bleaching (Lightening Natural Teeth)
Ceramo-Metal Bonded Restorations
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Lightening Natural Teeth
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Another dentist and I have been having a debate about a technique for bonding porcelain veneers. The other dentist claims that after receiving his veneers from the lab, he places silane and then dental primer and follows by curing the primer layer before doing any sort of try-in. He says that after doing a try-in, he can then rinse or clean the internal surface of the veneers without compromising that cure layer. He feels that his procedure protects the etched internal surface during the try-in phase. My argument is that 1) the cured primed layer is surely a fragile layer, (i.e., compromised by water, etc.) and 2) if one is rinsing and delaying placing the resin adhesive layer (placing multiple veneers at one sitting), that this surely weakens the bond strength. What is the true chemistry?
Both techniques can provide adequate bond strength. However, an extra step is needed in the technique that involves placing silane and then dental primer followed by curing the primer layer before trying in the veneers. Specifically, it is important to re-etch the veneer with phosphoric etchant since saliva will compromise the bond strength enormously. Saliva cannot be removed with water spray only. After etching with phosphoric acid the bond will be pretty good.
The advantage of HF etching just before cementing is twofold: 1) you can use a spray indicator to adjust the bite, and 2) it removes all debris and provides a highly reactive surface that allows better bonding in the procedures that follow. Unfortunately, surface energy is easily reduced by contact with any material and you would like to reserve that energy for the bonding process.
If the veneer is already etched, a spray indicator can be used on the tooth; it will be transferred to onto the veneer at try-in. The area on the tooth where the indicator was removed will then need adjustment. Once adjusted, phosphoric acid etching is needed to clean the spray indicator, tooth chips, and saliva from the veneer. Etching also increases the surface energy for bonding. Water is a major barrier to the hydrophilic resin bonding agents used today. In all cases, the veneer must be completely dry before proceeding with the bonding process. I use a warm air dryer.
I always have good results with zinc phosphate cement and glass ionomer cement seems like a lot of trouble. Why should I change?
Although zinc phosphate cement has a long and honored history, it also has a number of disadvantages. It is not adhesive and requires considerable mechanical retention. It does not inhibit caries and it is more soluble than most other cements. Clinical success is mainly because it is highly bacteriostatic.
If the tooth survives the initial acidity of zinc phosphate cement, long-term pulpal health will usually be good.
We feel the correct class of glass ionomer provides more favorable results since compressive and tensile strengths are higher, solubility is lower, adhesion is positive to tooth structure and most restorations, caries inhibition is good, and the material selected can match the pulpal needs of the tooth. Glass ionomer cements have been used successful for nearly 20 years and to date have no equal in terms of overall effectiveness.
When are metal–resin bonding procedures preferred over conventional cementation techniques?
As an alternative to bonding with conventional cement, metal–resin bonding is more technique-sensitive and has much less clinical history. Metal–resin bonding should be used where conventional cementation provides inadequate retention. Long-term clinical data is not yet available.
I pride myself on providing high-quality dentistry and want the very best for each patient. What cements would you recommend for optimum dental care?
Typically, you will need three: a polycarboxylate for sensitive teeth; a glass ionomer for slightly sensitive teeth where caries protection is important; and a resin cement for non-vital teeth, cementing custom-cast posts, and enamel–metal bonding of conservative partial-coverage units.
I work in a low-cost clinic and we are allowed to have only one cement for all purposes. Which would you recommend?
This is difficult since limiting cementation materials is not a good way to lower expenses. If retention and caries control is the main concern, choose a glass ionomer since it can be used in most situations.
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