Registration rims

The base of the registration block should normally be made of a rigid material.  Close adaptation of the base to the working cast is essential for stability in the mouth and accurate registration of jaw relations.

Registration rims are usually made of wax.  The upper block should measure approximately 22 mm in height from the deepest part of the sulcus adjacent to the midline fraenum.  The equivalent dimension of the lower block should measure approximately 19 mm anteriorly

Wax rims are positioned bucco-lingually in the same place as the lost teeth, according to the amount of resorption that has taken place.  The occlusal surface of the lower rim passes posteriorly from its anterior edge to a point 2/3 up the retromolar pads.  The upper rim should be created using an occlusal rim inclinator so that in the mouth it can easily be adjusted to be parallel to the alar-tragal line antero-posteriorly.

The registration rims are mounted on a semi-adjustable or average value articulator (according to clinical requirements), preferably using the split cast technique.  After noting the prescription for tooth arrangement, the maxillary anterior teeth are set up in accordance with the marked centre line, always conforming to the contour of the wax rim.

Unless the prescription says otherwise, or a neutral zone technique has been used, the mandibular posterior teeth are placed to conform to the buccal contour of the wax rim.  It is wise, particularly with flat lower ridges, to avoid the most posterior tooth being positioned over an inclined plane, and to achieve this, the last tooth should be at the posterior extremity of the horizontal part of the ridge.

The teeth are adjusted to allow balanced articulation in lateral and protrusive excursions.  Any part of the try-in base which was removed to facilitate registration is replaced unless this interferes with occlusal balance.