if they are growing inward, it means more pressure is on the outsides of his feet than the inside (the flare always grows where there is LESS pressure) and may not mean that he is toed in - it could just mean that he sort of walks on the outsides of his feet. That's not necessarily a bad thing - it's just how he goes. Draw an imaginary line (or use a pencil, lol) down the center of his hoof from the coronary band to the toe (don't look at the ankle while you do it - only the hoof - you want to get the very center of the hoof only regardless of the rest of the leg) and then stand back and look at the leg as a whole.
if the cannon bone/fetlock is straight and your pastern and hoof/pencil mark sort of turns in, then you can say he's officially toed in. If the leg, pastern and hoof(pencil line) all run pretty much straight, then he is just has hoof flares b/c he walks on the outsides of his feet more than the inside. If this is the case, then that's why you see it when he's due for a trim, but then goes away right after. Hopefully some of this helps? LOL!