The surgery through the belly button is the least safe and provides the least control for the final implant position. Additionally, the implant manufacters are beginning to VOID the warranties on the implants if they have been placed this way. A necklift is a very good operation alone and in conjunction with a facelift. These operations provide the most satisfactory long-term results. There are also indications for the using liposuction in the neck, either alone or in conjuction with a traditional necklift.
Breast augmentation is a permanent enlargement.
If you are asking how long do the implants last, then the answer is unknown. Nursing, mammograms and breast exams are all still posiible after breast augmentation. There is no causal link between silicone gel implants and autoimmune diseases in today's literature. Capsular contracture is a variable response to implants and multifactorial. Good surgical technique and massage avoid encapsulation.