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Teeth; Fillings and Braces:
Natural teeth without fillings and the like: Teeth do not have to be cleaned or Kashered from the letter of the law. Nevertheless, the custom is that after finishing eating Chametz on Erev Pesach, one brushes his teeth, and cleans and wash them well with water prior to the start of the 5th hour on Erev Pesach, to make sure that no crumb of Chametz has remained in one’s teeth.
Teeth with fillings: Although there is much argument to be made that fillings do need not to be Kashered from Chametz, nevertheless, the Rabbinical directive given is to clean them out prior to the 5th hour on Erev Pesach, and then swish one’s mouth with the hottest temperature water from a Keli Sheiyni, that he can intake. It is best to not eat hot Chametz 24 hours prior to doing so. [Although this is a mere stringency and is not required.]
Braces: It is a Hiddur for one who wears braces to have the braces removed by a dentist before Pesach, and have them cleaned and Kashered. If this poses difficulty, then one is to clean them to the best of his ability, and follow the above-mentioned order for fillings.
Dentures: Dentures are preferably to be removed, cleaned and Kashered with Iruiy Keli Rishon before the 5th hour on Erev Pesach. If this is not possible, then one is to clean them to the best of his ability, and follow the above-mentioned order for fillings.
Toothpaste: It is customary to purchase Kosher for Pesach toothpaste. See Chapter 5 Halacha 4 in Q&A!
 See Yad Yitzchak 3:78; Darkei Teshuvah 89:11; Sdei Chemed 4:24; Minchas Yitzchak 8:37; Minchas Shlomo 2:46; Shevet Halevi 1:148; 4:74; Tzitz Eliezer 9:25; Mishneh Halachos 3:56; 4:68 and 93; Piskeiy Teshuvos 451:23; Nitei Gavriel 78
Background: The idea of Kashering teeth, fillings or dentures is not recorded in the Talmud or classical Poskim and was first dealt with amongst the more recent authorities. Aside for the status quo custom to not make an issue of this throughout the year regarding meat and milk, the Poskim suggest various explanations for why they do not pose a Halachic problem that require Kashering, such as 1) The material of the teeth, filling or dentures are smooth and do not absorb; 2) One never enters hot food in his mouth of a temperature that can transfer taste. Practically, while the Poskim agree that from the letter of the law no Kashering is required, regarding Pesach, it is proper to be stringent. [See Piskeiy Teshuvos ibid footnotes 107-110]
 Setimas Haposkim who all omit any obligation or reminder of cleaning the teeth prior to the 5th hour on Erev Pesach.
 Darkei Chaim Veshalom 568; See Poskim ibid
 As even by actual Chametz vessels waiting 24 hours prior to the 5th hour is a mere custom and is not required from the letter of the law.
 Nitei Gavriel 78:4
 Poskim ibid
 See Admur 451:54 regarding a grater that we suspect a Chametz crumb has been leftover, and it hence requires Libun Chamor
 Nitei Gavriel 78:3
It is best to buy new tablecloths for Pesach. Nevertheless, from the letter of the law, one may Kasher and use the tablecloths that he used during the year. The following is how they are Kashered: One is to wash them with hot water and laundry detergent.
 Admur 453:23-24; Piskeiy Teshuvos 451:42
 The reason: As it is very difficult to ascertain that not even one crumb of Chametz will remain stuck to the cloth. [Admur ibid regarding the sacks for flour]