If a wooden tooth-stick (Siwak) is unavailable, what can a worshipper use to fulfill the Sunnah of cleansing the teeth?

Wudu: Completion Rules and Sunnahs Part 1

• Wiping with a wet cloth three times.
• Rubbing the teeth and gums with one's wet finger (al-Isba').
• Chewing a leaf of a fruitful tree.
• There is no substitute; the Sunnah is missed.