Please read the first 5 paragraphs of my post here (which explains how 'culpability' and 'harm' are assessed, and their effects upon sentencing):
http://www.theanswerbank.co.uk/Law/Question1350836.html
Given your previous convictions, that means that you should expect a sentence near to the upper limit of the relevant category.
So, if the judge is in a generous mood and assesses broken teeth and stitches as only 'low' harm and you didn't kick or headbutt the victim (or otherwise make 'culpbality' high by, for example, deliberately seeking him out for attack or by acting as part of a gang) there's an outside chance that your offence will be rated as 'Category 3', meaning that you could avoid a custodial sentence altogether.
However it'smore likely that 'harm' will be rated as 'high' (i.e. at the upper end of 'ABH'). If culpability was only low (e.g. no kicking, no headbutting, no weapon, an offence not related to the victim's race or sexuality, not seeking out the victim for attack or acting as part of a gang), then it would be 'Category 2' with a sentence of perhaps 9 months imprisonment.
If the court rated both 'culpability' and 'harm' as 'high, it's 'Category 1', with a likely sentence of around 2 years.
So, based upon the limited information available, I'd guess at 9 months if you only threw a punch or two but 2 years if you launched a sustained attack or (for example) kicked the victim in his face.