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Recently 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 that he'll first place silane and then dental primer followed by curing the primer layer before doing any sort of try-in. He then says that he will try in his veneers and feels that he can then rinse or clean the internal surface of the veneer without compromising that cure layer. He feels that this way it keeps the etched internal surface protected while going through the try in phase.
My argument is that firstly the cured primed layer is surely a fragile layer, (i.e., compromised by water, etc.) and secondly if one is rinsing and delaying placing the resin adhesive layer, (if one is placing multiple veneers at one sitting) that the bond strength must surely be weakened.
WHAT IS THE TRUE CHEMICAL ANSWER?????? >>
Both technique can provide adequate bond strength. However, by placing silane and then dental primer followed by curing the primer layer before trying in the veneers needs an extra step. It is important to re-etch the veneer with phosphoric etchant since saliva will compromise the bond strength enormously. Siliva 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. 2) That it removes all debre and provides a highly reactive surface which adheres better to all bonding procedures that will 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 the spray indicator can be used on the tooth and it is transferred to onto the veneer at try-in. This leaves an area on the tooth where the indicator was removed. This area would be adjusted. Once adjusted phosphoric acid etching is need to clean the spray indicator, tooth chips and saliva, from the veneer. Etching also increases the surface energy for bonding. Water is a major bearer to a 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.
Unfortunately, their are a lot of lecturers who are unknowing giving bad advise. Their is no substitute for understanding the science involved which would allow the clinician to make this and other decisions by him or her self. I which this science background were offered at more schools.
How do you handle cementation of a lucent porcelain veneer and crown in the same arch?
Since lucent veneers change color after cementation cement them first and temporary cement full crowns. After about 2-4 weeks the veneers will have undergone most of their change. At this time remove the crowns, stain to match the veneers and permanently cement. Using a 100% masking veneer with crowns allows cementation at the same appointment. However, esthetics may be difficult unless the veneer has considerable thickness.
I heard a prominent speaker on the west coast advocate not using a silane when bonding a porcelain veneer. Are silanes really necessary?
Silanes improve the consistency and stability of porcelain resin bonding. Although clinical success is possible without them they stabilize the porcelain resin bond, particularly in the presence of moisture. Since etching porcelain is not always consistant it is wise to routinely use them.
What is the major maintenance problem with porcelain veneers?
Generally, cement wash-out of margins in function and porcelain chipping at thin margins subjected to occlusal forces. Both are treated by rebonding composite resin to these interfaces.
How long do porcelain veneers last?
We really do not know. The laboratories and dentists in our study group programs have placed many thousands since 1984. The number of failures we know of is very small and all related to improperly adjusted occlusion. Our experience of a 99% success rate is much better than that reported by some investigators.
What is a fair fee for a porcelain veneer?
Porcelain veneers can be much more technique sensitive than crowns and offer a high benefit to the patient. Because of this a full coverage veneer should have a fee similar to a porcelain fused to metal crown. A veneer on a discolored tooth is more difficult and should have a higher fee (25%-50% more), while a partial veneer is generally easier than a crown and should have a lower fee (about 25% less since the lab fee is similar). Fees should reflect the time, skill, judgment, and maintenance necessary to provide this service. Lab fees are also at least comparable and frequently higher than for PFM crowns.
Do most insurance plans cover porcelain veneers? If not would crowns be indicated when veneers are not covered?
The first issue is who is diagnosing and treating the patient. Without direct access to the patient, no insurance carrier is competent to diagnose patient pathogy or recommend treatment.
What insurance carriers do is determine benefits and they may not cover newer and more progressive treatment planning. Discuss this with the patient.
Under no circumstances would I alter a treatment plan based on insurance benefits unless that treatment was also the recommended treatment for that patient's condition.
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