Hacham Ovadia Yosef, in his work Halichot Olam (vol. 7, p. 267), addresses several laws relevant to the obligation of Tebilat Kelim – immersing utensils purchased from a gentile (listen to audio recording for precise citation). He writes that a nutcracker does not, strictly speaking, require immersion. A nutcracker resembles scissors used to cut vegetables, which do not require immersion, and, in fact, a nutcracker is less of a candidate for Tebila because it comes in contact with only the shell, and not the edible food. Hacham Ovadia cites this ruling from the work Zibheh Sedek (by Rav Abdullah Somech, 1813-1889). However, he adds, since some authorities dispute this ruling, it is preferable to immerse nutcrackers without reciting a Beracha.
Dentures do not require immersion, even if they were manufactured and sold by a non-Jew.
If a Jew purchased utensils as merchandise which he intends to sell, he should not use them, even once, unless he first immerses them. There is a common misconception that one may use a new utensil once without immersing it. This is incorrect; a new utensil may not be used even once without immersion. Hacham Ovadia adds that if somebody purchased a utensil as merchandise and immersed it, he must inform the customer that the utensil has already been immersed, so that the customer will not recite a Beracha Le’batala (blessing in vain).
If a Jew gave pieces of metal, such as silver, to a gentile craftsman to make a utensil for him, the utensil does not require immersion. Since the material belonged to a Jew, the utensil does not have to be immersed, even though it was produced by a non-Jew.
Summary: Nutcrackers do not require immersion before use, though it is preferable to immerse them without a Beracha. Dentures do not require immersion. If a Jew purchased a utensil as merchandise which he intends to sell, he should not use it without immersion. If he immerses it, he must inform the customer that it has been immersed. If a Jew gave metal to a non-Jewish craftsman to make him a utensil, the utensil does not require immersion.
