okay this has annoyed me enough that i'm making this full post again
if you are exerting force down onto an object, then it is spread out along the contacting surface area. this is how a knife or a sword works — you are putting force down onto a long, thin line, and thus, all that force is focused down onto that long, thin line. if you have something like, say, a bat or a club, then you are putting that force down along the rounder and wider edge of that object, making it a blunt force object, yeah?
the same applies if you have multiple edges. for instance, this is how a bed of nails works. sure, if you step on a single nail, then all of your weight is pushing down onto that point. but, if you lay on many nails, maybe even fairly close together, then each one takes your weight equally, and they don't have that same ability to puncture the skin. you're putting the same force down onto multiple points, but even though there's space between the surface of each point, that force is getting divided between all of them like it's all just one surface.
this is pretty bad if we're talking about weapons. for example, if you put too many nails into a spiked bat, then you may as well have basically added none. it might inflict some scrapes and surface wounds, but you won't do any more damage than the bat itself would do.
here's a pretty good video for a demonstration, and you can see how, by spreading out that force exerted, you can even restrict your own ability to pierce.
(behold, an image that looks like someone being injured, but, by definition, is someone showing how uninjured they are)
the same applies for teeth.
if you have multiple rows of teeth, and you exert force down onto them to bite, that force is being spread out and divided over every point of every tooth.
this is not a very good setup if, say, you are a macropredator trying to eat large prey. you require teeth that can shear into and cut flesh, even break bone, and adding additional rows means that you no longer have a cutting edge through which to push through flesh or bone, but instead, many objects forming one larger surface to push through flesh or bone together, something which requires exponentially more force for much worse results, and is likely to instead end up breaking your own teeth.
think about knives for a moment. the reason a knife is good at cutting is because that force is being exerted down onto a very thin edge, making it hard to resist. knives get dull when they lose this thin edge, and have to have the thinness of that edge restored in order to regain cutting ability.
adding multiple points is, effectively, intentionally dulling this edge. to add a point of comparison, seeing multiple tooth rows in designs intended to have high bite force or ability to cut through flesh, is a lot like seeing overdesigned anime swords. animals have one, shearing edge to their teeth for the same reason that, on the surface, all real swords tend to look the same (with similar vast differences in the details).
"but!" you may say, "sharks have multiple rows of teeth! and they bite hard!"
which is where i point to how white sharks' (and other, similar macropredatory sharks') dentition actually works.
this is the lower jaw of a white shark. you can see that they do have multiple rows of teeth — but only the frontmost row is actually being used. you might see doubles, like in the front, but they occur when the shark is actively in the process of replacing that tooth with another (the same reason that humans might appear to have a double tooth, when a baby tooth is being lost and the adult replacement is coming up underneath). the other rows are pressed flat towards the back of the mouth, like a switchblade, ready to spring up and replace that outermost tooth.
although these sharks might have multiple rows of teeth, only one row is actually being used at any given time.
you can also see how this functions in another known bone-crusher, the spotted hyena. the teeth are very thick and massive, but each individual tooth still comes up to a point after the previous tooth's point, forming a singular shearing edge, the carnassial, that pushes down on bone in a singular, cutting edge.
so, what good are multiple rows of teeth? why do animals have them?
well, one, because they can operate more like barbed wire.
caecilians are one group of animals with well-developed multiple rows of teeth, and this is because they are primarily insectivores. they are very good at gripping onto soft bodied prey, much like barbed wire or burrs catching onto exposed flesh, and shredding it. these teeth would not survive contact with plentiful resistance, so mostly, they don't.
this is also why other species of sharks, like sand tiger sharks (or ragged tooth sharks), do have multiple rows of teeth — they are much more useful for holding onto slippery prey, like fish or cephalopods, and shredding flesh. these teeth are much thinner, so that they can fit more into the mouth, and each one has a longer profile than the nearly square frame of a white shark's tooth. they might not be hunting marine mammals, but this is quite handy as a generalist in the ocean.
alternatively, if multiple teeth are spreading out that force anyways and working as blunt force weapons, then you could lean into it. you could make your teeth massive and thick, to sustain such forces, but flatten them, and turn them into a crushing battery like these stingrays, better for cracking apart hard-shelled animals like crustaceans and mollusks. in our metaphor, this might be closer to a nutcracker, or a hydraulic press. not very useful at cutting flesh, but good at getting through objects that no one else can.
so, yes. please consider this at least a little, before i start thinking your cool monster design has teeth that don't work.
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