Dental restorations - What do we mean by 'permanent'?
Dental restorations (fillings, crowns, bridges, implants etc) are often referred to as 'permanent' or 'temporary'. But what do these terms mean?
Temporary (dictionary definition : lasting, existing, serving, or effective for a time only) is easier to understand.
Temporary fillings/crowns are understood to be anything that is intended to be replaced by something else in the course of a treatment procedure. For example: In the vast majority of cases a crown is made in 2 treatment visits. During the first visit, all the necessary preparations are made to the tooth receiving the crown. Then all the necessary records are taken (impressions, bite records, colour records etc). The tooth then needs to be protected till the next visit. This is usually done with a temporary crown. The temporary crown is designed to be removed easily and quickly without damage to the underlying tooth at the next visit, unsually 1-2 weeks later.
'Permanent' has the connotation of something that lasts forever or at least a very long time.
In dentistry anything that can reasonably be expected to last 5 years or longer is understood to be 'permanent'. Dental materials are subjected to the same wear and tear as our natural teeth and gum structures. Furthermore there is never such a thing as an 'ideal' filling/crown/denture/etc. The very fact that there is a filling/crown/denture/etc present means that the most ideal object in that place (an intact tooth) is not there anymore. ALL dental restorations are, at best, necessarily compromise solutions to problems presented by a less than ideal oral health condition. They represent repair work and are placed because not doing anything would be even worse.
While most dental materials can be expected to perform well when placed properly under optimum conditions, cost and other considerations often cause materials to be placed in conditions that almost ensure that the restoration will fail before long.
An example of this is the very large filling. Most of the time, if a tooth has lost more than 50% of it's crown structure, it is best to place a crown. But crowns are more costly than fillings, so time and again, we find teeth that are more filling material than tooth substance. The can result in breakage, leakage, renewed tooth decay and further breakdown of the tooth structure.