Tech Tip: We’re trimming differently to make retention 2x - 4x stronger

As you know, strong retention of aligners on the teeth is key to producing desired tooth movements and tracking of aligners.

In a recent study*, doctors from the University of Nevada compared the retentive strength of three trimming techniques:

Examples of aligner trimming techniques

  • A) a scalloped margin,
  • B) a straight cut at the gingival zenith, and
  • C) a straight cut at 2 mm above the gingival zenith.

The difference between the techniques was remarkable.

For clear aligners without attachments, the straight cut 2 mm from the margins was about twice as retentive as the scalloped cut. For clear aligners with attachments, the straight cut 2 mm from the margins was over four times as retentive as the scalloped cut!

Trimming the aligners differently had more of an impact than adding or removing engagers. Scalloping the aligners right at the margin is the technique employed by “the other guys.” Traditionally, we’ve loosely scalloped our aligners slightly over the gumline.

Based on these findings, we’ve decided to start trimming our aligners with a smoother contour and a larger overlap with the margins. This technique should improve the efficiency of the aligners and may reduce the need for engagers in some cases. We expect the new aligners to move teeth more effectively, especially when performing difficult movements like torquing.

Ideal trim area shown between alveolar crest and marginal gingiva

We also expect our aligners to be more comfortable than before, because there will be less risk of them impinging on the unattached marginal gingiva. The edge of the aligner will be concealed further under patients’ lips during everyday use, so this should also slightly improve the discreetness of the aligners.

You won’t see a difference right away, but we expect to start rolling out the change over the next few weeks. As always, we welcome your feedback.

*"The effect of gingival-margin design on the retention of thermoformed aligners" by Daniel P. Cowley, James Mah, and Brendan O'Toole in the Journal of Clinical Orthodontics: JCO 11/2012; 46(11):697-702. Illustration used with permission.

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