Coloured Computed Tomography (CT) scan in axial section through the head of a patient, showing impacted molar teeth. On either side of the nose, behind the nasal cavities, are the maxillary sinuses (black). At the base of each sinus is a molar tooth growing crooked and impacting on each sinus, which can cause infection. Also seen is a congested (blocked) left nostril (at upper centre right).