Why is cross-mounting so important? It is used in the laboratory to verify, replicate, or correct the horizontal plane. Cross-mounting is an important process used to verify the clinical scenario and make the final restorations with predictability. On a more complex case, it is a very helpful way to minimize errors in the esthetics and the functional outcome. The smallest case for which cross-mounting is effective is when restoring the maxillary central incisors, and continues to be a crucial step in the fabrication process through cases as extensive as a full-mouth rehabilitation. It is used to establish the following on of the maxillary anterior teeth:
- The horizontal plane;
- the midline angulation;
- the incisal length;
- the anterior/posterior position;
- their inclination, and
- the envelope of function.
The most important thing you can do to develop an acceptable esthetic outcome, is to establish harmony between horizon, the interpupillary line and the smile – especially a line between the commissures and the maxillary and mandibular occlusal planes.
- If a facebow transfer is taken of a patient's approved provisional restorations and subsequently mounted on the articulator, the clinical scenario is now able to be visualized in the laboratory.
- If there is a slight cant to the incisal plane of the maxillary provisional cast or a midline cant, this should be confirmed by the photographs taken of the patient's smile relative to a horizontal line behind the patient.
- If the facebow of the tooth preparations is made and the cast is not cross-mounted, it is not possible to confirm the facebow is correct relative to horizon. If photographs are taken of the facebow transfer relative to horizon, this could be used to confirm the mounting.
- If the cast of the provisionals is correctly mounted with the facebow transfer, then the mandibular cast can be mounted and the occlusion properly established.
Next week we will discuss the steps involved in cross-mounting. This should help you to understand why it is important to provide the correct sequencing of bite registrations for the lab.