The toothbrush battle - I lost

I yelled at my 2-year old son today because he didn't want to brush his teeth.  He always wants to hold the brush himself because he likes to suck on the toothbrush so he can eat the toothpaste (it's baby toothpaste so there's no floride).  Usually, I would let him hold it, watch him swish it around his mouth, and then make funny faces at him so he would let me finish brushing his teeth.  This works most days. Today, I clearly had no patience for him.  When he tried to take the toothbrush from me, I yelled at him and hit him 3 times on his hand.  I have only ever hit him on the hand because I don't believe in spanking.  However, I felt bad after I hit him (3 times) because I knew I had hit him out of anger instead of discipline.  It's a fine line and I crossed it.  Later, just before he went to bed, I said sorry.  I don't know if he understands but I apologized anyway.