The polymerization of resin based products is inhibited by oxygen. We deal with this uncured ” Air or Oxygen Inhibited” resin layer everyday. It is the smeary outer coating on a bisacryl provisional that gunks up and ruins burs. This same smear layer remains inside the provisional matrix, and can result in reduced accuracy if they are reused. It is also the layer that can bond your bisacryl provisional to freshly prepared teeth if you have placed a composite the same appointment or followed the protocol of immediate dentin sealing. Lastly, if you follow a protocol of making your provisionals directly prior to the final impression, it is this layer that interferes with the set of some VPS impression materials.
Managing this air inhibited layer in the process of curing resin comes from using an oxygen barrier to prevent it’s formation. In other clinical situations, instead of preventing the formation of the air inhibited layer, we need to remove it. One simple chemical is the solution to this clinical dilemma, rubbing alcohol. When we fabricate provisional restorations we keep a small dappen dish or cup of rubbing alcohol available. Once the bisacryl is cured, prior to beginning the process of trimming and shaping it, we drop it into the rubbing alcohol. Let it sit for 30 seconds or so, and then we remove and wipe it with a 2 x 2 that is wet with rubbing alcohol as well. This technique will extend the life of your acrylic burs, and diamond disks, and make cleaning them easier at the end of a procedure. For the inside of a provisional matrix, dip a cotton tip applicator into rubbing alcohol and wipe down the inside surfaces.
In the situation where the smear layer is left behind on the teeth following a bonding procedure or the fabrication of a direct provisional, alcohol is still the answer. For this application I add rubbing alcohol to flour of pumice, and using a prophy cup clean all of the tooth surfaces to remove the uncured resin layer. I have in the past tried wiping the teeth off with a 2 x 2 or cotton tipped applicator wet with alcohol, but this is imprecise and difficult to cover all of the tooth surfaces adequately and can leave resin behind.