Normally it isn’t necessary to have an anaesthetic for a Maryland bridge. However It's usually necessary for a conventional bridge, unless the tooth or teeth being used for the retainers have already had root canal treatment. The dentist will let you know before work starts whether you need an anaesthetic and, if you do, will anaesthetise the teeth before starting to work on them.
Bridges normally last for many years. It does depend on how you care for them. Consider the daily habits that affect your bridges, and you'll be able to extend their wear.
Normally because you have had a tooth extracted or had one knocked out, leaving you with a gap in your teeth. Obviously closing the space is important for cosmetic reasons, but your dentist also has good clinical reasons to fill in the space, too. Leaving the gap open often puts extra strain on the teeth either side. It can also affect your bite. The teeth on either side of the gap may come together into the space and alter the way that your teeth meet, which can cause further problems.