I have a tooth in the upper front of my mouth that needs dental work due to decay. A part of the tooth has changed color because of the decay. I would like to know if getting a gold cap or lining around the perimeter of the tooth in order to cover the decayed part and the new filling that the dentist will use permissible? Will it render Wudu invalid? Know that the gold would be visible from the front of the tooth.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

There is no harm in putting a golden cap or lining on this tooth as long as there is a need for it, Inshaa' Allaah. Most of the scholars stated that it is permissible for men or women to use gold to fasten the tooth or to replace it. The evidence about this is a sound Prophetic narration.  'Arfajah Ibn Sa'd had lost his nose in a pre-Islamic battle and he made a nose of silver which became smelly and rotten. So, the Prophet "Ordered him to have a nose made of gold." [Abu Daawood]. Al-Khattaabi commented on this narration saying: "In this narration we notice that it is permissible for men to use some gold in case of necessity to fasten the teeth and the like if there are no other alternatives." As regards filling teeth, there is no harm in it, as long as it does not include a forbidden matter, like something which is impure and the like. This filling material or gold does not affect the validity of ablution or the ritual bath. 

Allaah knows best.