بسم الله الرحمن الرحيم
(Fatwa: 1349/1327/N=11/1434)
Shariah has allowed a man to enjoy all the parts of his wife except her back side. There is no evidence that enjoying any specific part except backside is prohibited. If any husband does mammary intercourse with his wife then it is allowed as per the Shariah, but there are some Fiqh scholars who prohibit this. (Shami, Vol. 3, p 371, published by: Maktaba Zakaria Deoband) Therefore, one should avoid it as long as one can and should enjoy it only in the time of need i.e. when the wife is experiencing her menses and the sexual desire of husband is highly aroused.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband