Here's the verse from Sadachara Smriti of Shri Madhwacharya.
- All the above austerities hold good both for Gruhastas (married people) and Vanaprastas. Except Vaishvadeva, Baliharana and Dantadhamana – rest of the austerities should be performed by Brahmacharis also.
Vasishta Smriti has a long list of requirements in terms of physical hardship that a naishtika brahmachari should undertake. A few examples are as follows
आहूताध्यायी सर्वभैक्षं निवेद्य तदनुज्ञया भुञ्जीत | खट्टाशयन दन्तप्रक्शालनाभ्यन्जनवर्जः तिष्ठेत् अहनि रात्रावासीत ||
He should undertake studies at any time (that the guru orders); He should hand over all his bhiksha to his guru and eat only what the guru gives; He should never sleep on a cot; He should never brush his teeth with any special paste; He should never apply any oils or perfumes; He should always be seated, day and night, ready for studies
Now, is such a prohibition present in any other Smritis or Scriptures? Is the reason behind such a prohibition known? What can the modern Brahmachari do?
Is it more along the lines of brushing the teeth with luxuriois powders to enhance the scent which is fitting to a Grihasta and not to a Brahmachari, where only bare minimum is required. Also note Brahmachari cannot use perfume. So maybe brushing for hygiene is ok, but not to enhance mouth odour like with camphor and paan is prohibited?