It looks like you’re asking: “Can we brush (teeth) during upvaas/Paryushan/poshad?” Here is the simple Jain achar followed by most traditions:

• Daily (for śrāvaks/householders): Brushing is allowed. Do it carefully, preferably before sunrise, with boiled-and-cooled, filtered water. Spit out completely; avoid swallowing. Use a soft brush; keep himsā as minimal as possible.

• On upvaas/poshad/Paryushan days:

- Many Śvetāmbara and Digambara acharas advise brushing before sunrise with only water (no or minimal/unflavoured paste). This keeps saiyam and reduces needless rasa (taste) and himsā. - If you are observing Tivihaar (water allowed during day): morning brushing with filtered water is acceptable. - If you are observing Chauvihar (no food/water after sunset): don’t brush at night. Brush before sunset, or the next morning after sunrise when water use becomes permitted again. - For very strict fasts like Nirjala (no water even by day): avoid brushing until the fast allows water.

• Monastic rules are stricter; laypeople should follow their own guru/saṃgh’s instructions.

Small care tips to reduce himsā:

• Use only boiled-and-cooled, filtered water.
• Avoid strong/flavoured pastes on fast days; plain water is best.
• Do not keep the mouth open near a running tap; pour measured water from a lota/mug.
• Rinse thoroughly and spit carefully.

For short explanations of these vows and timings, see:

• Chovihar (no food/water after sunset)
• Upvaas with water-only pachchakkhan basics

If your local guru or sampradāy follows a different practice, please follow that specific achar.