Sir, establishing the occlusal plane is a fundamental step for occlusal balance. The anterior occlusal plane plays a significant role in developing aesthetics, symmetry and harmony while rehabilitating a patient. In complete denture prosthodontics, the interpupillary line is almost always used as a reference plane to establish the anterior occlusal plane.1The maxillary anterior occlusal plane is established parallel to the interpupillary line with the Fox occlusal plane indicator and a ruler. An anterior occlusal cant of 4° results in a slanted smile which can be observed even by laypeople.2 This can influence the aesthetic and psychological outcome of the treatment. Furthermore, anterior occlusal cant may not be perceptible in the mounted casts or photographs but can be observed only in the patient's mouth in relation to the facial features.3 In our practice, in many patients the interpupillary line is not straight and cannot be relied upon as a reference plane such as in cases of vertical orbital dystopia.

Various causes of vertical orbital dystopia have been identified which include congenital (craniofaciocervical scoliosis complex, coronal craniosynostosis and facial clefting syndromes), trauma, torticollis, tumours, iatrogenic and idiopathic factors.4 Among these the congenital factor plays a crucial rule. Certain cases of strabismus, unilateral proptosis and ptosis can also add to the difficulty in establishing the parallelism. Studies are needed to identify and classify these conditions in cohorts. A study report supports the fact that only in 13% do subjects' incisal plane coincide with the interpupillary line.5 Establishing the anterior plane perpendicular to the facial midline and choosing a reference plane closer to the oral cavity would be more acceptable. A simple and reliable method or an instrument needs to be designed to establish the anterior plane without relying on the interpupillary line.