Going by owlbear illustrations in the Monster Manuals (or edition equivalent), most have serrated beaks.
clearly serrated: 1e, 2e compendum, 4e essentials, 5.0e, 5.5e
unclear, maybe serrated: 2e MM, 4e
single tomial tooth and notch: 3.Xe
probably no tomia: OD&D
OD&D Greyhawk Supplement - probably a normal owl's beak:
1e Monster Manual - a bunch of small serrations, like a goose:
2e Monstrous Compendium Vol. 1 - large, jagged, teeth-like serrations:
2e Monstrous Compendium Annual Vol. 3 - The Arctic Owlbear also has teeth-like serrations:
2e Monstrous Manual - the inside edges of the beak look a little jagged. I think it's supposed to be small serrations, but it's pretty subtle:
3.Xe Monster Manuals (both use the same illustration) - looks more like a falcon's beak with a single tomial tooth on each side and corresponsing mandibular notches, used for severing spines:
4e Monster Vault - like the 2e Monstrous Manual, it's subtle, but I think the underside of the top beak is intended to look serrated:
4e Essentials Monster Vault - serrations prominently displayed on the cover:
5.0e Monster Manual - serrated:
5.5e Monster Manual - definitely serrated: