Halacha requires a woman, before immersing in a Mikveh, to ensure that her body is free of Chatzitzot – foreign substances that prevent the water from coming in direct contact with her body. This requirement applies even in "Beit Ha'setarim," areas which in any event do not come in contact with the water, such as the inside of one's mouth. Thus, for example, the Talmud tells that Rabbi Yehuda Ha'nasi's housekeeper immersed in the Mikveh and then discovered a piece of meat wedged in between her teeth. Rabbi Yehuda ordered her to repeat the immersion, because the substance in her teeth constituted a Chatzitza and disqualified her immersion. Accordingly, a woman must thoroughly clean her teeth before immersing in a Mikveh.
Furthermore, Jewish women have adopted the custom to refrain from eating meat (including chicken) on the day before immersion, as meat can easily become wedged in between one's teeth. Even though a woman will thoroughly clean her teeth before immersing, she should nevertheless refrain from eating meat on the day before her immersion. This applies to chopped meat, as well. A woman may, however, eat meat in liquid form – such as soup with meat fat – on the day before immersion. She may eat fish, as well, as fish does not commonly become wedged in between one's teeth. (For related topic, see the Daily Halacha dated June 5, 2005 entitled “Does A Woman Have To Return To The Mikveh If There Was Food Unintentionally Stuck In Her Teeth”)
Chacham Ovadia Yosef, in his work Taharat Ha'bayit (vol. 3, p. 128), addresses the question of whether a woman may eat meat on the day before immersing in the interest of maintaining the privacy of her immersion. If a woman finds herself in a social setting where refraining from meat will clearly indicate to those present that she is immersing that evening, may she partake meat in keeping with the Halachic requirement to keep the information of one's immersion private?
Chacham Ovadia rules that if she can provide some compelling explanation for refusing to partake of meat, she should do so. Otherwise, if her refusal to eat meat will be clearly understood as an indication that she is to immerse that night, she may partake of meat. In such a case she must be particularly vigilant in cleaning her teeth in preparation for her immersion.
Do braces on one's teeth constitute a Chatzitza and disqualify a woman's immersion?
Chacham Ovadia Yosef (in Taharat Ha'bayit, vol. 3, p. 143) rules leniently and allows immersing while wearing braces, on the basis of a number of different factors: the braces are located inside the mouth, they cover only a minority of the area of one's mouth, the woman wants the braces to be in her mouth, and they are very difficult to remove. For all these reasons, the braces may be seen as part of the woman's mouth and therefore do not constitute a Chatzitza. Retainers, however, must be removed before immersion. Needless to say, a woman with braces must ensure to thoroughly clean the braces to remove all food particles that might have become attached to them.
Crowns and fillings on teeth may be worn during immersion. Even if they were placed in the tooth only temporarily, they are not considered a Chatzitza insofar as they are firmly fixed in place and cannot be easily removed.
Summary: A woman must thoroughly clean her teeth before immersing in a Mikveh, in order to remove any food particles that might be wedged in between her teeth. A woman should not eat meat or chicken on the day of immersion, except in situations where refraining from meat will make it obvious that she is to immerse that night. A retainer must be removed before immersion in a Mikveh, but one may immerse with braces, provided that they are thoroughly cleaned. One may immerse with fillings and crowns in one's teeth, even if they are temporary.
