Short answer: Yes—during Biyasana (two meals a day), you may brush your teeth in the daytime. Do not brush after sunset.

Simple guidance

• When: Brush after sunrise, in daylight. Avoid brushing at night due to chovihar (no food/water/taste after sunset). ( jainknowledge.com)
• Water: Use boiled and filtered water for rinsing; do not swallow. ( jainknowledge.com)
• Paste/taste: To keep tapa pure, avoid flavored/sweet toothpaste. Prefer a neem datun or a plain, non-flavored tooth powder; keep it strictly for cleanliness, not taste.
• Care: Rinse minimally and spit carefully, observing ahimsa and cleanliness.

By tradition

• Shvetāmbara: Daytime brushing is fine; many avoid flavored paste on fasting days to prevent “rasa-sevan.” Night brushing is avoided due to chovihar. ( jainknowledge.com)
• Digambara: Same daytime rule; many prefer datun and avoid paste. Strictly no water use for such acts after sunset. ( jainknowledge.com)

Essence

• Biyasana = two meals before sunset; maintain saiyam by avoiding any taste or water-use at night. Brushing is a daytime, non-taste act done with boiled/filtered water. ( en.wikipedia.org, jainknowledge.com)

Related reading from JainKnowledge:

• Chovihar (why no eating/drinking after sunset):
• Water rules in chovihar (timing and boiled/filtered):