It has always amazed me that teeth have such a high failure rate when they contain 0 moving parts. There's also no biological or chemical processes that need to happen. They're literally just an inanimate object that you use for biting. How can they be so unreliable??
For starters, teeth are alive and the soft core (dentin) is in continuous regeneration like any live tissue.
Teeth are also not not moving. During chewing the jaw itself flexes quite a bit, and teeth don't have a rigid connection to the jaw (there is a gap between the root and the jaw filled with collagen fibers), and this flexible connection bears all forces a tooth is subjected to.
I'd also argue that correctly maintained teeth and periodontia are very reliable given their long life span.
The tooth-food or tooth-tooth interaction "counts" as a moving part - it gets friction, it gets all kinds of forces/stress applied, exactly as the interaction between moving parts in a mechanism.
