Baby's can be sensitive when teething. If they go off their food and you have reason to believe that they need something extra to fill them up as nurish them then there isn't a problem with them having an extra bottle. However continue to offer the food at each meal to encourage your little one and let them know that it is meal time and at meal times we eat food even if he doesn't want it and doesn't really eat any.
DS is full of cold & teething so generally feeling sorry for himself and off his food. Is it OK to give him an extra bottle? He was ebf until I went back to work a month ago and when I was bf'ing him, I wouldn't have had any qualms about giving him extra feeds or even just comfort feeding him. Logically, it makes sense that there's no difference now he's on formula but I do recall friends who have ff'd wondering about whether they're overfeeding their DC and the HV expressed surprise the other day that DS is on 4 bottles a day when he should only be on 3 even though he's still having the same amount of formula in a day as he's having less in each bottle. Its only now I've stopped bf'ing that I've realised it can actually be an advantage not knowing how much they've taken in a feed!