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We know that a lot of Loricariidaes have odontodes on different places on the body - some more than others. And we know that males develops more odontodal growth than females.
And we know they are "calcified conical structures, which strongly resemble comb-like teeth" (from The Ancistrinae Internet Lecture)
But why and what do they use them for?
My thoughts:
Has it something to do with parental care? (maybe - but I don't think so)
Maybe it's something to do with males fighting other males? (asuming that odontodes somehow protect the body - maybe)
Defense against predators? (nahh - then females should have the same amount)
Only for show off and/or possible breeding purpose? (nahh - I don't think so)
What do you think?

Only for show off and/or possible breeding purpose? (nahh - I don't think so)

Why not? In some cases, they enlarge and regress following the breeding cycle.

ok - but what do they use them for in relation to breeding? Do the odontodes help the male to do something to the female?
I think there's a purpose for these...

Could be like the peacocks tail - only for show...the bigger the tail the more of a hinderance in the wild = only the fittest males are able to survive with big tails, therefore female sexual selection is for males with bigger tails... maybe

I'm inclined to agree with the peacock theory.

And it's the same reason humans have hair. How many people find a bald person more sexually attractive than a person with a full set of hair?

Has it something to do with parental care? (maybe - but I don't think so)
Maybe it's something to do with males fighting other males? (asuming that odontodes somehow protect the body - maybe)
Defense against predators? (nahh - then females should have the same amount)
Only for show off and/or possible breeding purpose? (nahh - I don't think so)

Just my thoughts... I believe it does have to do with parental care, protecting fighting males, defense against predators, as well as for showing off. They just might serve slightly different purposes amongst different genera.
In those spp. that develop relatively light odontodal growth like Sturisoma, Farlowella, and Rineloricaria, it might give a male a better weapon to use against rival males and predators. They may also signal to females, "Hey, I am a ready to spawn guy." Some loricariinae do get rather covered in odontodes and this may help them like it does the genera below.
In those spp that show heavy odontodal growth like small Panaque, the former Aphanotorulus, Peckoltia, etc note that they are all cave spawners. A spikey male can not only provide a better barrier between himself and the eggs from predators, he can also wedge those spikes into the nook and crannies of the rock or driftwood hollow and make himself almost impossible for even a strong a predator to pull out.
Spp. that do not spawn in stone or wood hollows rarely have much odontodal growth. Note odontodes are almost absent in the lip brooding loricariinae and the mud bank spawning spp like Hypostomus and Glyptopterichthys.
Just an observation.
-Shane

Ryan S and Shane, love the responses. How about another combination. Protection, fighting off other males, a show for females and,... [b]feeding the young[/b]?

Its been mentioned that fry kept with the parents grow at a much faster rate when compared to fry taken after the first few days. Since the odontodes increase the surface area of the male could the odontodes, especially those all over the body, be used as a surface for the production of food for the fry, whether directly(male produces food for the young) or indirectly(increased surface area for infusoria, bacteria etc)?

Just another opinion-
Alga

My thoughts from observation of big Panaque spp.
Both male and female have them to protect themselves.
All females I dissected in my field study had well developped
odontodes. There are no difference between sex on odontodes
development in adults during reproductive seasons, I think.
They use those protective spines to fight against each other
when they should.

Usually, bigger fish quickly win, but sometimes fight
persists among individuals that have likely equal body size
or potential of fighting skills. Then, fish
behaviour/strategy change...

If fish fight/compete and neither of them run away, fish
start attacking to opponent's eye balls by covering their
well developped muscular oral disc over them. Besides not
very visible in the water of their habitat, they have very
good eye (and it is true their eyes are sensitive).
How they avoid getting injured on their eyes?? Twisting
their body?? May not enough... If they extend odontodes
on their cheek (end of gill cover), they can protect their
eye balls from attacks of most angles. You will surprise
if you see how fish use their pectral/cheek odontodes for
attacking and protecting during the fight.
I think...odontodes on pectral fins are for fight, and those
on their cheeks are for protection or small fight.
Interesting topic anyway.