Oral cavity is divided in two major arches and each of these arches are divided into 2 Quadrants each.                                                                                

The dental archs are divided into 4 Quadrants:

Maxillary Quadrants:       Right Maxillary Quadrant ( I ) 

                                                    Left Maxillary Quadrant  ( III )

Mandibular Quadrants:   Right Mandibular Quadrant ( II )

                                                    Left Mandibular Quadrant  ( IV )

Each Quadrant has 8 teeth- 3 anterior & 5 posterior teeth.

The Quadrants are divided by an Imaginary line which passes through the central Incissors of both the maxillary and mandibular arches