One of many articles that can be used to overcome skepticism that this route actually delivers (note that the 6-hour thing doesn't mean it disappears then, only that the body has cached it into estrone effectively by then).

Each of the hormones was readily absorbed via the buccal mucous membrane. Peak plasma concentrations of estradiol and progesterone were comparable to those found normally in young menstruating women.

The concentration-time area under the curve of estradiol after sublingual estradiol-HP beta CD was also significantly larger than after oral administration of either estradiol-HP beta CD or micronized estradiol, reflecting a larger estradiol bioavailability. The estradiol/estrone concentration ratio after sublingual estradiol-HP beta CD revealed a predominance of estradiol for the first 2 hours after the dose, followed by an estrone predominance. Both oral doses produced a predominant delivery of estrone to the systemic circulation.

Supports the efficacy of transbuccal delivery of estradiol

Supports the efficacy of transbuccal estradiol delivery