Upper second premolars – #13 and #4
The second premolars on each side of the upper jaw, just in front of the first molars.
Roots
Usually one (85% in a Saudi scan study). Depending on the study, roughly 10% to 30% have two.
Canals
Usually one at the tip of the root (80% in a Saudi scan study), but in a worldwide study about half had two canals for at least part of the root.
These are typical counts from scan studies. Teeth vary, and only an X-ray or scan shows what a particular tooth has.
When they come in
Usually at 10–12 years old, according to the ADA's eruption chart.
They replace the upper baby second molars, which fall out at 10–12 years.
They bite against the lower second premolars.
Sources
Alqedairi et al. 2018; Martins et al. 2024; American Dental Association 2012; Harris 2005. Full titles are on the About page.