Dave Bonta starts with a humble tool, tin snips, and sees a mouth in it. The blades are like scissors with an overbite, and as they cut through metal they seem to chew up a text, like quotation marks swallowing words. What they leave behind is a ragged tear rather than a neat line. That image leads the speaker to a personal admission: he is buck-toothed himself, so he knows how hard a clean break, or a clean fit, can be.
From there the poem widens out. A perfectly straight bite is rare, the speaker says, whatever orthodontists suggest, and most people learn early to compensate, hiding or adjusting their flaws. The final image, the "tin grin," ties the snips to the human smile.
The mood is wry and good-humored, with a gentle fondness for imperfection. The speaker doesn't seem ashamed. He treats awkward teeth, and awkward cuts, as ordinary and even a little comic.