Alginate is forgiving right up until it isn't. Tears, voids, and distortion almost always trace back to one of four moments: the mix, the seat, the wait, or the pull.
The four moments
- The mix: measure water and powder as the manufacturer directs, and use the water temperature they specify. Cold water slows the set, warm water speeds it. A thin, runny mix tears; a dry, crumbly one doesn't flow into detail.
- The seat: load the tray evenly, seat posterior first, then roll forward, and hold it still. Any movement while it's gelling records as distortion.
- The wait: leave it in place past the point it feels set. Alginate keeps gaining tear strength for a minute or two after the surface firms up. Pulling early is the most common cause of a torn interproximal.
- The pull: break the seal at the periphery and remove with one quick snap along the long axis of the teeth. A slow, rocking removal stretches the material and it tears.
After it's out
Rinse, disinfect per your office protocol and the manufacturer's instructions, and pour it promptly. Alginate loses water in air (syneresis) and gains it in water (imbibition), and both change the dimensions. If you can't pour right away, wrap it in a damp paper towel in a sealed bag, and still pour it soon.