There is an adage that states "a stitch in time saves nine." This line of thinking is quite applicable to the use of sports mouthguards. Once tooth damage has occurred it opens a cascading course of events that will have at least minor, and quite possibly fairly major, repercussions for the person throughout their lifetime.
Except in the most minor cases if a tooth has become damaged some type of tooth repair will need to be made. Having a small tooth-colored filling placed so to repair a relatively minor chip in a tooth might cost as little as $100 or so. More significant repair such as having root canal treatment performed and then a dental post and crown placed can cost anywhere from a few to several thousands of dollars. The higher end of this same price range could be expected to apply if a tooth is lost and is replaced with either a dental bridge or an implant.
This means that the cost to repair the damage caused by a sports injury can easily be in the range of 10 to 30 times the cost of a custom mouthguard. Of course this cost doesn't include what a person might wish they could have paid so never to have experienced the pain, suffering, and inconvenience associated with an accident. It also doesn't include an accounting of the amount of time the person will spend having the dental treatment performed.
Beyond the cost of the initial dental work you can expect that additional treatment will be needed in the future. Dental restorations cannot be expected to last a lifetime. This is especially true in those cases where the cosmetic appearance of the dental work is a major consideration. White fillings can be expected to stain and deteriorate over time. The gum line of teeth that have had dental crowns placed on them can recede as years pass and as a result compromise their cosmetic appearance. Beyond just replacement dental work, additional new dental treatment may be required. The nerve tissue inside any tooth that has received a hard blow can necrose (die), sometimes even years after the original traumatic event, and therefore necessitate root canal treatment. All of this adds up to the point that the oversight of not wearing a sports mouthguard can potentially end up costing a person tens of thousands of dollars in dental expenses over the course of their lifetime.
Mouthguards really don't need much in the way of care but here are some points that would be a good idea to keep in mind as you put your guard to use.
You should expect that as time goes by your mouthguard will show signs of wear and will need to be replaced. You may find that holes, rips, or tears have formed in the guard's plastic or that its fit has become slack. If you notice any of these changes you should simply realize that the effective life span of your sports mouthpiece is probably coming to an end. Even with a high-end dentist dispensed mouthguard it is usually not possible, practical, or cost effective to attempt a repair. You should simply have your mouth fitted for a new guard.