Block-out resins are tinted, light-cured resins that were originally developed as a rubber dam substitute or for bleaching tray reservoirs, but the materials in this specific category are mainly used to protect the gingiva during power bleaching and when performing intraoral sandblasting. In addition, they can block-out gingival embrasures when taking final crown and bridge impressions to prevent the material from locking into them.
Unfortunately, many of these products give off heat when curing, with most producing enough heat to cause pain when they are applied over the gingival and polymerized. To test this potential problem, we applied each product designed for soft tissue application to the gingiva around the maxillary incisors in two volunteer research staff members. This application simulated the procedure we advocate prior to power bleaching. We then light-cured the products until the staff member signaled that the pain caused by polymerization heat generation was not tolerable. The amount of time it took each product to cause pain was recorded and noted below in each product's narrative.
NOTE: Even though the heat produced caused a painful response (described as penetrating deep into the tissue) in our test subjects, there was no visible gingival inflammation nor was there any negative sequelae once the light-curing was stopped. However, even when the patient is anesthetized, it seems prudent to apply these materials in as thin a layer as possible to keep the polymerization heat as low as possible.
Fortunately, this heat and pain response can be minimized or eliminated by not curing these resins more than a few seconds at a time.
These materials come in push-type syringes and are easy to apply directly from the syringe, not requiring any additional instruments for placement. However, they can be runny, so apply a small volume at a time and then cure for a few seconds. They are also very easy to remove.