> The BG29 chips will be available in 5 mm × 5 mm QFN and 2.6 mm × 2.8 mm WLCSP form factors
That "wireless oral health monitor" example is a concept from Lura Health[1] that integrates a marginally smaller BG27 (2.3mm x 2.6mm WLCSP)[2].
[2] https://www.silabs.com/applications/case-studies/small-bluet...
> and its power consumption is low enough that the device can last from six months to a year on a battery of the equivalent size
The average "width" of the first mandibular molar from this article[1] is 5.1-5.2mm. It sure would be interesting to see a CAD model of the design inside the module on the band. The graphics from the posted article vs. the first link above are also a bit different, making it even harder to infer much I think.