The process of fabricating a denture usually begins with an initial dental impression of the maxillary and mandibular ridges. Standard impression materials are used during the process. The initial impression is used to create a simple stone model that represents the maxillary and mandibular arches of the patient's mouth. This is not a detailed impression at this stage. Once the initial impression is taken, the stone model is used to create a 'Custom Impression Tray' which is used to take a second and much more detailed and accurate impression of the patient's maxillary and mandibular ridges. Polyvinylsiloxane impression material is one of several very accurate impression materials used when the final impression is taken of the maxillary and mandibular ridges. A wax rim is fabricated to assist the dentist or denturist in establishing the vertical dimension of occlusion. After this, a bite registration is created to marry the position of one arch to the other.