Can rhinoplasty thin the frontal process of maxilla? My nose looks bigger due to that.

While rhinoplasty does not commonly alter the maxilla, changes in other areas of the nose may cause certain aspects of the nose to appear differently. The best way to determine the cause for your unhappiness with the appearance of your nose is to contact your rhinoplasty surgeon. Best of luck. 

Great question.  I don't think a rhinoplasty will affect the size of the maxilla bone or any of the other surrounding bones.  Sometimes changing one aspect of the nose may change the appearance of another aspect of the nose making it look bigger than it actually is.  I would discuss these issues with your plastic surgeon.  Sitting down with your plastic surgeon and reviewing your before and after photos may also be helpful.All the best,Dr. Remus Repta