I hadn’t written earlier concerning the article "Clinical Performance of Bonded Amalgam Restorations at 42 Months" by Dr. William Browning and colleagues in May JADA because I had expected a flood of letters to the editor concerning its experimental design and results.
Surely everyone in practice knows that amalgam has very little "adhesion" to a set resin. If you doubt that, just try condensing amalgam onto the next composite you place. It virtually slides off. The authors alluded to this obvious fact when they referred to the "atypical" directions for Kerr concerning Optibond Plus Solo. The instructions call for condensing onto set resin (one coat) that has been light-cured.
That is, of course, because Kerr does not state that Optibond Plus Solo is to be used for amalgam bonding. They specifically state that it is for amalgam sealing only. The amalgam sealing refers only to sealing the dentinal tubules, not to significantly increasing the retention of the amalgam nor to supporting tooth structure.
You cannot make this claim for a light-cured resin that is fully set before condensation of the amalgam. To set the oxygen-inhibited layer in contact with the amalgam, one has to expose the Optibond Plus Solo to light again after placement of the amalgam; that is, light-curing after amalgam condensation. This could become a reality the day someone develops an amalgam that transmits light (unlikely).
This is not to say that amalgam bonding is impossible; quite the opposite. Thousands of dentists do so every day, utilizing the appropriate dual-curing material such as Resinomer (Bisco), Liner-F (Bisco), original OptiBond 3A and 3B (Kerr) or Amalgambond Plus (Parkell).
No one should advocate using OptiBond Solo Plus (Kerr) for amalgam bonding. It simply would be inappropriate to do so. The authors simply were studying the effects of sealing with a bonding agent (as one would have used Copalite more than a decade ago) as opposed to no sealer at all. The research was only capable of determining the presence of gross microleakage and no more.
Since there was no significant bond of the amalgam to the already set OptiBond Solo Plus, the two groups were virtually the same except for less dentinal permeability in the Opti-Bond group. It takes many years before one sees clinically obvious secondary caries with properly condensed amalgam restorations, especially with "ideal" preparations restored with Contour alloy. This is also an interesting sidenote as Kerr has always recommended their Tytin alloy for "bonding."
I have contacted the Kerr people, and they are aware of this. I understand they may also be responding with a letter to the editor.
Thank you for this opportunity to discuss this important issue. Without being sarcastic, if one were to place a dentin bonding agent in a preparation before placing IRM, does this make it a "bonded IRM"? I think not.
